Ocean Engineering 104 (2015) 219-237
E L S E V I E R
C o n t é n t s lists available at ScienceDirect
Ocean Engineering
j o u r n a l t i o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / o c e a n e n g
A novel full scale laboratory for yacht engineering research
F. Fossati'''* 1. Bayati^ F. Orlandini^ S. Muggiasca", A. Vandone^ G. Mainetti^ R. Sala^
C. Bertorello^, E. Begovic''
' Department of Mechanical Engineering, Politecnico di Milano, Italy
Department of Industrial Engineering, Marine Section, Universita degli Studi di Napoii Federico II, Italy
CrossMark
A R T I C L E I N F O
Article liistory:
Received 16 December 2014 Accepted 7 M a y 2015 Available online 4 June 2015 Keywords:
Yacht engineering Full scale tests Dynamic VPP Sail sliapes Sail pressures Sail forces A B S T R A C T T h i s p a p e r p r e s e n t s a n o v e r v i e w o f t h e Lecco I n n o v a t i o n H u b p r o j e c t a n d i n p a r t i c u l a r t o t h e S a i l i n g Y a c h t Lab p r o j e c t a 10 m l e n g t h s a i l i n g y a c h t w h i c h a i m s t o b e a f u l l scale m e a s u r e m e n t d e v i c e i n t h e s a i l i n g y a c h t r e s e a r c h field. A d e s c r i p t i o n o f s c i e n t i f i c f r a m e w o r k , m e a s u r e m e n t c a p a b i l i t i e s as w e l l as o f t h e p r i n c i p a l d e s i g n , b u i l d i n g p r o c e s s , p r o j e c t m a n a g e m e n t a n d c o m m i s s i o n i n g is p r o v i d e d w i t h s o m e e x a m p l e s o f p r e l i m i n a r y c o l l e c t e d d a t a o b t a i n e d d u r i n g t h e first sea t r i a l s . F i n a l l y a n o v e r v i e w o f t h e o n g o i n g p r o j e c t tasks a n d f u t u r e p r o j e c t d e v e l o p m e n t s is p r o v i d e d i n c l u d i n g p o t e n t i a l r e s e a r c h a n d k n o w l e d g e a c h i e v e m e n t s f o r s a i l i n g y a c h t r e s e a r c h field. © 2 0 1 5 E l s e v i e r L t d . A l l r i g h t s r e s e r v e d . 1. I n t r o d u c t i o n
This p a p e r presents a n o v e r v i e w o f t h e Lecco I n n o v a t i o n H u b p r o j e c t a n d i n p a r d c u l a r o f t h e Sailing Yacht Lab p r o j e c t a 10 m l e n g t h s a i l i n g y a c h t w h i c h a i m s t o be a f u l l scale m e a s u r e m e n t device i n t h e s a i l i n g y a c h t f e s e a r c h f i e l d .
Lecco I n n o v a d o n H u b (LIH) is a d e d i c a t e d n a u t i c a l research a n d t r a i n i n g c e n t e r at t h e Lecco Campus o f t h e Politecnico d i M i l a n o u n i v e r s i t y a i m i n g t o encourage t h e t r a n s f e r o f t e c h n o l o g y t o a n d f r o m t h e n a u t i c a l a n d r e l a t e d sectors.
Lecco I n n o v a t i o n H u b consists o f t w o basic e n t i t i e s :
• The S a i l i n g Yacht Lab (SYL), a 10 m l e n g t h s a i l i n g y a c h t f i t t e d w i t h i n s t r u m e n t s f o r a c q u i r i n g data o n t h e b e h a v i o r a l variables o f t h e b o a t a n d h e r c o m p o n e n t s a t f u l l scale t o s u p p o r t a s c i e n t i f i c a p p r o a c h t o design a n d research a c t i v i t i e s r e l a t e d t o s a i l i n g y a c h t design a n d p e r f o r m a n c e
• The S.Ma.R.T (Sustainable M a r i n e Research a n d T e c h n o l o g y ) l a b o r a t o r y is d e s i g n e d to s u p p o r t n a u t i c a l i n d u s t r y i n m e e t i n g t h e i n c r e a s i n g p r e s s i n g d e m a n d s f o r i n n o v a t i o n a n d s u s t a i n -a b i l i t y . Specific lines o f rese-arch -are t h e -an-alysis -a n d - assess-m e n t o f t h e e n t i r e l i f e cycle (LCA) o f n a u t i c a l p r o d u c t s , d e s i g n f o r d i s a s s e m b l i n g , e x p e r i m e n t a t i o n w i t h n e w m a t e r i a l s f o r c o n s t r u c t i o n a n d fitting out, e r g o n o m i c s , s a f e t y a n d c o m f o r t o n b o a r d , i n t e r i o r l i g h t i n g a n d t h e i m p r o v e m e n t o f t h e q u a l i t y o f air. * Corresponding author.
E-mail address: fabio.fossati{5>polimi.it (F. Fossati).
http://dx.doi.Org/10.1016/j.oceaneng.2015.05.005 0029-8018/6) 2015 Elsevier Ltd. A l l rights reserved.
I n a d d i t i o n t o these, t h e r e are t h e research i n f r a s t r u c t u r e s p r e s e n t i n o t h e r sites o f t h e P o l i t e c n i c o d i M i l a n o , such as t h e W i n d T u n n e l - Europe's largest - at t h e M i l a n Bovisa c a m p u s (Fossati, 2 0 0 6 ) . A i m o f t h i s p a p e r is t o p r o v i d e a n o v e r v i e w o f t h e S a i l i n g Yacht Lab p r o j e c t : a b r i e f s u m m a r y o f t h e o r i g i n a n d early e v o l u t i o n o f t h e vessel's d e s i g n w i l l be g i v e n , a l o n g w i t h a d e s c r i p t i o n o f p r i n c i p a l d e s i g n a n d p e r f o r m a n c e c r i t e r i a . Design, b u i l d i n g process, p r o j e c t m a n a g e m e n t a n d c o m m i s -s i o n i n g w i l l be d e -s c r i b e d i n t h e f o l l o w i n g ; t h e m e a -s u r e m e n t c a p a b i l i t i e s a n d data a c q u i s i t i o n p r o c e d u r e w i l l be d e s c r i b e d i n details. The p r o j e c t is s t i l l i n progress; i n o r d e r t o p u t i n t o p e r s p e c t i v e r e s e a r c h t h e c a p a b i l i t i e s p r o v i d e d b y t h i s n e w available t o o l s o m e e x a m p l e s o f p r e l i m i n a r y collected data o b t a i n e d d u r i n g t h e first sea t r i a l s are repeated a n d discussed.
F i n a l l y an o v e r v i e w o f t h e o n g o i n g p r o j e c t tasks a n d f u t u r e p r o j e c t d e v e l o p m e n t s is p r o v i d e d i n c l u d i n g p o t e n t i a l research a n d i m o w l e d g e a c h i e v e m e n t s f o r s a i l i n g y a c h t research field. 2. F u l l scale t e s t i n g The a b i l i t y t o p r e d i c t t h e m a x i m u m p o t e n t i a l p e r f o r m a n c e o f a r a c i n g s a i l b o a t is a s t r o n g asset y e t d e m a n d i n g v e r i f i c a t i o n o f b o t h e x p e r i m e n t a l results a n d n u m e r i c a l d e r i v e d data. First m e t h o d i c a l approaches f o r c a l c u l a t i n g y a c h t p e r f o r m a n c e c a m e n o t b e f o r e t h e T h i r t i e s as d e m o n s t r a t e d b y t h e GIMCRACK
Fig. 2. Load cells arrangement.
Fig. 3. Load c e l l - f r a m e connection detail.
case w h e n O l i n Stephens a n d t h e D a v i d s o n L a b o r a t o r y at Stevens I n s t i t u t e d e v e l o p e d a f u l l e x p e r i m e n t a l p r o g r a m c o m b i n i n g f u l l scale s a i l i n g t e s t i n g a n d t a n k tests o n scale m o d e l w i t h t h e i n t e n t i o n o f d e t e r m i n i n g sail c o e f f i c i e n t s a n d p r e d i c t i n g p e r f o r -m a n c e o f s a i l i n g vessels.
The e s t i m a t i o n o f a sailboat's p o t e n t i a l speed based o n its d e s i g n alone began i n the 1930s w i t h sea t r i a l s o f GIMCRACK a 3 4 ' -6" LOA, 2 3 ' L W L l o w - f r e e b o a r d day-sailer designed b y S p a r k m a n a n d Stephens.
Since 1936 w h e n G i m c r a c k s a i l i n g p e r f o r m a n c e s w e r e m e a -sured at f u l l scale, t h e m o s t o f such tests have b e e n p e r f o r m e d i n t h e f r a m e o f A m e r i c a ' s Cup boats t e c h n i c a l d e v e l o p m e n t a i m e d at c o m p a r a t i v e analysis.
Fig. 5. Safety rod concept.
O l i n Stephens and the Davidson Laboratory at Stevens Institute successfully used Gimcrack to correlate scale m o d e l results w i t h f u l l -scale sailing testing, d e r i v i n g the l o n g i t u d i n a l d r i v i n g force, aero-d y n a m i c siaero-de force anaero-d heeling m o m e n t . The c o r r e l a t i o n constants b e t w e e n m o d e l and full-scale performances d e r i v e d b y these studies became k n o w n as the Gimcrack Coefficients (Davidson, 1936). The Gimcrack Coefficients w e r e t h e first k n o w n c o m p a r i s o n o f this type, p r o v i n g to be a significant b r e a k t h r o u g h i n t h e science o f sailing y a c h t p e r f o r m a n c e p r e d i c t i o n .
The s c i e n t i f i c data c u r r e n t l y available t o designers a n d builders was d e r i v e d f r o m studies based o n n u m e r i c a l o r e x p e r i m e n t a l data g e n e r a l l y o b t a i n e d f r o m scale m o d e l s , p r o t o t y p e s o r m a t e r i a l samples analyzed i n a r t i f i c i a l e n v i r o n m e n t s , s u c h as w i n d tunnels, t o w i n g t a n k s or t e s t benches.
W i t h p a r t i c u l a r r e f e r e n c e t o sail a e r o d y n a m i c s , t h e m e t h o d s c u r r e n t l y used t o a t t e m p t t o characterize a sail p l a n are tests either i n w i n d t u n n e l s o n scale m o d e l s o r o n f u l l size boats a n d t h e use of c o m p u t a t i o n a l f l u i d d y n a m i c s .
A t present n u m e r i c a l m e t h o d s p r o v i d e sound results f o r u p w i n d a n d close r e a c h i n g sailing b u t are s t i l l u n d e r d e v e l o p m e n t f o r d o w n w i n d sail design. T h i s is because t h e n u m e r i c a l techniques d e v e l o p e d f o r t h e aeronautical sector can be a p p l i e d t o sails used f o r u p w i n d s a i l i n g because these behave l i k e t h i n a i r f o i l s affected o n l y t o a l i m i t e d flow separation, w h i l e i t is m u c h m o r e c o m p l e x to solve t h e flow p a t t e r n t h a t develops a r o u n d a spinnaker or gen-n a k e r w h e r e the s i g gen-n i f i c a gen-n t a m o u gen-n t o f c u r v a t u r e leads t o large areas o f flow separation. I n a d d i t i o n d o w n w i n d sail aerodynamics is actually a f f e c t e d b y the aeroelastic m e c h a n i s m : the " f l y i n g " shape o f a n o f f w i n d sail u n d e r real sailing c o n d i t i o n s is d e t e r m i n e d b y the pressure d i s t r i b u t i o n a c t i n g u p o n t h e sail, w h i c h are n o t d e p e n d i n g o n l y o n w i n d s t r e n g t h and d i r e c t i o n b u t also f r o m s t r u c t u r a l p r o -perties a n d sails t r i m controls a c t i n g u p o n t h e edges a n d corners o f t h e sail as w e l l as o n forces a p p l i e d to t h e r i g a n d sail. A l l o f these factors c o n t r i b u t e t o t h e v i r t u a l l y i n f i n i t e n u m b e r o f flying shapes over t h e range t h a t a p a r t i c u l a r sail can achieve u n d e r actual sailing c o n d i t i o n s a n d d i f f e r e n t l y f r o m t h e u p w i n d sails t h i s is p a r t i c u l a r l y
F. Fossati et al. / Ocean Engineering 104 (2015) 219-237 221
:
Huil geometry fitting
- maximization (moment of inertia)
- rigging elements attached to structural
nodes or beams
FEM static analysis
3D CAD model updating
Geometrical improvements
Check geometric updates:
- space fitness (crew, instruments...)
- consisteiicj' of rigging elements position
Fig. 6. Frame design worl<flow.
Fig. 7. Frame f i n i t e element discretization.
Fig. 8. Frame final design.
t r u e f o r d o w n w i n d sails, as spinnakers, gennakers a n d MPS because o f t l i e l i g l i t w e i g h t o f t h e c o n s t r u c t i o n materials a n d t h e i r r e l a t i v e l y u n c o n s t r a i n e d n a t u r e (Ranzenbach a n d Kleene, 2 0 0 2 ; Graf a n d M u l l e r , 2 0 0 9 ; Renzch a n d Graf, 2013).
The i n s u f f i c i e n t reliability o f n u m e r i c a l tools a n d a b e t t e r u n d e r -s t a n d i n g o f the general r e l a t i o n b e t w e e n m o d e l te-st-s, n u m e r i c a l simulations (e.g. CFD m e t h o d s ) a n d f u l l scale data have encouraged the a m b i t i o n o f collecting data at full-scale, i n real sailing conditions. A direct measurement system o f actual sail forces and m o m e n t s i n sailing conditions was initially developed b y M i l g r a m et al. (1993): this system was based o n a 35 f o o t boat containing an internal f r a m e
Fig. 9. Frame manufacturing.
connected t o the h u l l b y means o f load cells. The h i g h effectiveness and potential o f the sailing d y n a m o m e t e r have been d e f i n i t e l y d e m o -nstrated by the m o r e recent experiences o f F u j i n and DYNA projects developed at Kanazawa Institute o f Technology (Masuyama and Fukasawa, 1997) and Beriin T U (Hochldrch and Brandt, 1999).
I n p a r t i c u l a r t h e w o r k achieved b y M a s u y a m a ( 2 0 1 3 ) w i t h F u j i n boat w a s m a i n l y a i m e d at i n v e s t i g a t i n g t h e u p w i n d sail a e r o d y -namics i n steady state c o n d i t i o n s a n d the o b t a i n e d results w e r e c o m p a r e d w i t h t h e n u m e r i c a l calculations u s i n g t h e m e a s u r e d sail
222 F. Fossati et al. / Ocean Engineering 104 (2015) 219-237
Fig. 10. Calibration tests.
Fig. 11. Inclined calibration load cases.
shapes as i n p u t data. T h e n t h e a e r o d y n a m i c f o r c e v a r i a t i o n d u r i n g tacl<ing w a s m e a s u r e d a n d a n e w m a n e u v e r s i m u l a t i o n m o d e l w a s p r o p o s e d . O n the o t h e r side DYNA p r o j e c t deals e x t e n s i v e l y also w i t h h y d r o d y n a m i c s aspects i n t e r m s o f i n t e r a c t i o n h u l l k e e l -r u d d e -r a i m e d at appendages o p t i m i z a t i o n . A n o t h e r i n t e r e s t i n g e x p e n e n c e i n v o l v i n g f u l l scale t e s t i n g is g i v e n i n H e n t i n e n a n d H o l m ( 1 9 9 4 ) w h e r e a p r o j e c t f o c u s e d o n t h e a c t u a l loads a c t i n g o n a s a i l i n g y a c h t such as s l a m m i n g , r u d d e r , c h a i n p l a t e a n d g r o u n d i n g loads f r o m t h e keel is r e p o r t e d . A n " h a l f t o n n e r " (a r a c i n g y a c h t a b o u t 3 9 ' LOA) w a s b u i l t w i t h t h e star-b o a r d side o f s a n d w i c h c o n s t r u c t i o n a n d t h e p o r t side o f single s k i n c o n s t r u c t i o n w i t h t w o l o n g i t u d i n a l stringers i n a d d i t i o n to t h e b o t t o m s t r u c t u r e a n d e q u i p p e d w i t h pressure a n d s t r a i n gauges. Statistical data w e r e g a t h e r e d d u r i n g 2 7 0 0 n a u t i c a l m i l e s o f s a i l i n g
Fig. 12. Sketch o f the calibration tests.
Fig. 13. Dynamometer accuracy over the xy plane.
; F i g . 14. Dynamometer accuracy over the xz plane.
d u r i n g w h i c h 3 0 0 h w a s t h e m e a s u r i n g time g i v i n g n e w a n d v a l u -able i n f o r m a t i o n .
Due t o t h e l i m i t e d c r a f t d i m e n s i o n s , a series o f t h e I n t e r n a -tional M o t h class f u l l scale t o w tests have b e e n r e c e n t l y p e r f o r m e d (Zseleczlcy a n d Beaver, 2 0 0 9 ) t o characterize s o m e o f t h e m a j o r
F. Fossati et ai / Ocean Engineering 104 (2015) 219-237 223 10 9 8 7 6' 5 4 3 2
Fig. 15. Dynamometer accuracy over the y z plane.
200 300 AW 500 600 700 SOO 900 1000 1 100 External l o a d [N]
Fig. 16. Lateral force Fy accuracy as f u n c t i o n o f applied load along y axis.
Fig. 17. W e i g h t i n g o f the f r a m e and experimental d e f i n i t i o n o f the center o f mass.
p a r a m e t e r s i m p a c t i n g ttie p e r f o r m a n c e o f a f o i l i n g IVIoth p r o v i d i n g a s o u n d t e c h n i c a l basis f o r f u r t h e r p e r f o r m a n c e i m p r o v e m e n t s o f these boats.
Fig. 18. Sailing Yacht Lab project workflow'.
W i t h reference t o the experimental v a l i d a t i o n o f aero-elastic m o d e l i n Augier et al. (2011), the f u l l scale testing activities p e r f o r m e d o n a J80 sailboat are described: a dedicated i n s t r u m e n t a t i o n is developed t o measure the loads at slirouds a n d at tension points o f t h e sails, t h e yacht m o t i o n , t h e sails f l y i n g shape and t h e navigation data p r o v i d i n g u s e f u l data f o r the validation o f the f l u i d - s t r u c t u r e i n t e r a c t i o n m o d e l described i n Augier et al. (2012).
A t present, t h e pressure d i s t r i b u t i o n m e a s u r e m e n t s o n t h e surface o f f u l l scale sails are u n d e r i n v e s t i g a t i o n b y several research g r o u p s : t h i s i n f a c t represents the k e y p o i n t f o r the role o f f u l l scale tests as a b r i d g e b e t w e e n m o d e l tests and n u m e r i c a l m e t h o d s .
I n Lozej et al. (2012), Viola and Flay (2012), Graves et al. ( 2 0 0 8 ) a n d P u d d u et al. ( 2 0 0 6 ) several pressure measurements are r e p o r t e d ; t h e c o m p a r i s o n w i t h measured data b y w i n d t u n n e l tests shows v e r y i n t e r e s t i n g differences i n t h e pressure d i s t r i b u t i o n b e t w e e n f u l l scale a n d m o d e l scale. Pressure measurements are also c o m b i n e d w i t h sail shape measurements at full-scale a i m i n g t o evaluate t h e forces and a t t e m p t i n g interesting investigations into steady a n d unsteady sail aerodynamics (Le Pelley et al., 2012).
W i t h i n t h i s f r a m e t h e a m b i t i o n o f t h e S a i l i n g Yacht Lab is t o a l l o w pressure a n d sail shape m e a s u r e m e n t s i n a d d i t i o n t o t h e forces m e a s u r e m e n t s p r o v i d i n g m o r e precise i n f o r m a t i o n d u e t o t h e d y n a m o m e t e r i n c l u d i n g b o a t d y n a m i c s . F u r t h e r m o r e s o m e e v o l u t i o n w i t h r e f e r e n c e t o t h e pressure a n d sail shapes m e a s u r e -m e n t s syste-ms c a i j be p r o v i d e d .
3. T h e s a i l i n g y a c h t lab d y n a m o m e t e r s y s t e m
The Sailing Yacht Lab (Fig. 1) w a s designed to operate as a d y n a m o m e t r i c balance and was strongly inspired a n d encouraged b y the previous experiences developed at M I T ( M i l g r a m et al., 1993), a t Kanazawa Institute o f Technology (Masuyama a n d Fukasawa, 1997) and Beriin T U (Hochldrch and Brandt, 1999).
The h e a r t o f t h e s y s t e m is a 5 0 8 3 a l u m i n u m a l l o y f r a m e i n s i d e t h e h u l l t h a t a l l o w s t h e e n t i r e rig a n d sail p l a n t o be c o n n e c t e d t o a set o f l o a d cells t o m e a s u r e t h e overall forces a n d m o m e n t s t r a n s m i t t e d b y sails a n d r i g to the h u l l .
Fig. 2 s h o w s t h e g e n e r a l a r r a n g e m e n t o f t h e s i x l o a d cells w h i c h k e e p t h e f r a m e i n isostatic c o n s t r a i n e d c o n f i g u r a t i o n w i t h respect to t h e h u l l .
224 F. Fossati et al. / Ocean Engineering 104 (2015) 219-237
Fig. 20. H u l ! Shell preparation.
W i t h respect t o t h e s h o w n reference s y s t e m , t h e 6 l o a d cells are set as f o l l o w s : one l o a d cell a l o n g x d i r e c t i o n (FX), t w o a l o n g y d i r e c d o n ( F Y l , FY2) a n d t h r e e along z d i r e c d o n ( F Z l , FZ2, FZ3). The idea b e h i n d t h e choice o f t h e i r p o s i t i o n is t o be as near as possible
Fig. 21. H u l l - f r a m e c o n c e p t .
t o t h e h i g h e s t loads a l o n g t h e respective d i r e c t i o n s , so t h a t e.g. FX cell is p l a c e d near t h e m a s t - s t e p c o n n e c t i n g t h e h u l l to t h e central p a r t o f t h e f r a m e . I n a d d i t i o n a n i m p o r t a n t c r i t e r i o n o f the p o s i t i o n i n g o f t h e cells w a s t h e i r accessibility d u r i n g m a i n t e n a n c e o p e r a t i o n ; M a x i m u m loads o f t h e a d o p t e d cells are r e s p e c t i v e l y 20 k N f o r t h e FX, F Y l , FY2, FZ3 a n d 50 k N f o r the F Z l a n d FZ2.
E Fossati et al. / Ocean Engineering W4 (20t5) 219-237
The c o n n e c t i o n o f t h e l o a d cells t o t h e f r a m e a n d to t h e h u l l fixes any possible axial m i s a l i g n m e n t a l l o w i n g each m o n o - a x i a l l o a d cell t o measure n o d i f f e r e n t forces t h a n t h e axial ones (Fig. 3 ) .
A n a d d i t i o n a l s y s t e m w h i c h is able to I<eep t h e c o n n e c t i o n b e t w e e n t h e f r a m e a n d t h e h u l l has b e e n designed a n d m a n u f a c -t u r e d . This is a safe-ty s y s -t e m based o n passive safe-ty rods' -t h a -t keep t h e f r a m e a n d t h e y a c h t rigging a r o u n d the n o m i n a l p o s i t i o n i n case o f any accidental l o a d cell f a i l u r e or m e r e l y i n case o f n o m e a s u r e - s a i l i n g c o n d i t i o n as w e l l as w h e n t h e sailboat is i n the harbor. As r e p o r t e d i n Fig. 4 the safety rods can be classified as one a l o n g X d i r e c t i o n (SX), f o u r a l o n g Y d i r e c t i o n (SYl, SY2, SY3, SY4) a n d f o u r a l o n g Z d i r e c t i o n ( S Z l , SZ2, SZ3, SZ4).
The safety rods are m a d e o f screw bars c o n n e c t e d t o t h e p l y w o o d bulkheads b y m e a n s o f C shaped flanges w i t h w h i c h large screwed disks come i n c o n t a c t i n case o f load cells failures (Fig. 5). These disks can be also screwed t i g h t l y t o t h e C shaped flanges i n t h e n o - m e a s u r e s a i l i n g c o n d i t i o n ( o r m o o r e d ) i n o r d e r to p r e v e n t t h e load cells f r o m any u n p r e d i c t e d b u m p s .
3.1. Frame structural design
A f t e r a p r e l i m i n a r y assessment o f design loads a n d o f r i g g i n g e l e m e n t s p o s i t i o n o n t h e deck, to d e f i n e t h e final f r a m e c o n f i g -u r a t i o n a m -u l t i - o b j e c t i v e i t e r a t i v e design process has b e e n per-f o r m e d b y means o per-f s t r u c t u r a l analysis ( F i n i t e E l e m e n t IVIethod) a n d a 3 D CAD t o o l . This process deals w i t h g e o m e t r i c a l constraints as w e l l as w i t h t h e m a x i m i z a t i o n o f t h e s t r u c t u r a l resistance, as r e p o r t e d i n Fig. 6.
The f r a m e was r e q u i r e d t o fit t h e h u l l space as m u c h as possible i n o r d e r t o increase t h e o v e r a l l m o m e n t o f i n e r t i a o f t h e s t r u c t u r e . Nevertheless, g e o m e t r i c a l issues w e r e also taken i n t o account, such as t h e d e f i n i t i o n o f t h e e l e m e n t s c o n n e c t i n g t h e r i g t o t h e f r a m e i n correspondence t o nodes o r m a i n beams. The finite e l e m e n t s t r u c t u r a l analysis leads t o g e o m e t r i c a l m o d i f i c a t i o n s t h a t have t o be addressed w i t h i n t h e CAD t o o l , t h a t i n t u r n r e q u i r e f u r t h e r s t r u c t u r a l v e r i f i c a t i o n s as w e l l as c h e c k i n g t h e consistency o f t h e n e w p o s i t i o n s o f t h e a t t a c h i n g p o i n t s o f t h e r i g g i n g a n d space fitness f o r c r e w a n d i n s t r u m e n t a t i o n s .
The F E M t o o l a d o p t e d i n t h i s w o r k is FEMAP/MSC NASTRAN a n d Fig. 7 shows t h e r e l e v a n t a d o p t e d FE m o d e l .
The choice o f t h e m a t e r i a l f o r t h e f r a m e s t r u c t u r e relies o n m e e t i n g c r i t e r i a such as c o r r o s i o n resistance, greatest stiffness, l o w e s t w e i g h t , easy c o n n e c t i o n a m o n g t h e e l e m e n t s a n d e c o n o m -ical a f f o r d a b i l i t y . F r o m a s t r u c t u r a l p o i n t o f v i e w t h e c o m p a r i s o n b e t w e e n d i f f e r e n t materials was c a r r i e d o u t by c o n s i d e r i n g a specific parameter, Ejy, w h i c h is t h e elastic m o d u l u s - u n i t w e i g h t r a t i o , r e p r e s e n t i n g t h e r e q u i r e m e n t o f m a x i m u m s t i f f n e s s a n d l o w e s t w e i g h t s i m u l t a n e o u s l y . Stainless steel and titanium have b e e n discarded f o r w e i g h t a n d cost, respectively. C a r b o n fiber tubes have also been considered, b u t d i s c a r d e d f o r t h e highest cost a n d f o r t h e d i f f i c u l t i e s i n c o n n e c t i n g t h e l o a d cells t o t h e f r a m e .
The 5 0 0 0 a l u m i n u m - m a n g a n e s e a l l o y series was d e t e c t e d as t h e m o s t c o m p a t i b l e m a t e r i a l w i t h respect t o t h e r e q u i r e m e n t s : i n p a r t i c u l a r t h e 5083 series w a s c h o s e n f o r t h e m a i n s t r u c t u r a l c o m p o n e n t s o f t h e f r a m e , w h e r e a s 5 0 8 6 f o r t h e plates w e l d e d to t h e f r a m e w h o s e task is c o n n e c t i n g t h e r i g g i n g and t h e h u l l to t h e f r a m e itself. Fig. 8 shows a p i c t u r e o f t h e final f r a m e design a n d Fig. 9 a m a n u f a c t u r i n g i n t e r m e d i a t e step.
C o n c e r n i n g t h e m a n u f a c t u r i n g process, t h e w e l d e d c o n n e c t i o n b e t w e e n t h e various b e a m s was m a d e possible b y c u t t i n g t h e b e a m s ' e x t r e m i t i e s b y m e a n s o f CNC tools. T h e n t h e beams w e r e M I G w e l d e d and t h e w h o l e f r a m e w a s t h e r m o - t r e a t e d t o r e l a x a n y l o c a l stress due t o t h e w e l d i n g process. For m o r e details o n t h e f r a m e s t r u c t u r a l design readers can r e f e r to ( R e p o r t D e p t . M e c h a n i c s , 2012)
225
3.2. Dynamometer calibration
The goal o f t h e c a l i b r a t i o n procedure is to d e f i n e a " c a l i b r a t i o n m a t r i x " C:
Cl
.2
Cl.3
Cl,4 Cl,5 Cl,6
C2,l C 2 , 2 C 2 , 2 C 2 , 2 C 2 , 2 C 2 , 2 C3,2 C3,3 C3,4 C3.5 C3,6c =
C4.2C4.3
CA,4 Q,5C4,6
C5.2 C5.3 €5.4 C5,5 C5,6 C6,l C 6 , 2 C6,3 C 6, 4 C6,5Ce.e
(1) t h a t correlates t h e m e a s u r e m e n t s o f t h e 6 l o a d cells S: Sj=
[Sx Syx Sy2S21
Sz2S23]
^ (2) w i t h t h e forces a n d m o m e n t s F r e f e r r e d t o t h e b o d y axes o f t h e b o a t a n d r e d u c e d t o c e n t e r o f mass o f t h e w h o l e y a c h t : F^=[F,FyF,M,MylVl,Y (3) The d e f i n i t i o n o f the e l e m e n t s o f t h e m a t r i x C is c a r r i e d o u t b y means o f a m i m i m i z a t i o n process i n t h e u n k n o w n s Cy as a s o l u t i o n o f t h e o v e r - d e t e r m i n e d p r o b l e m over a set o f e x p e r i m e n t a l m e a s u r e m e n t s S c o u p l e d w i t h t h e c o r r e s p o n d i n g set o f k n o w n loads f .Fig. 22. Hull internal structures.
226 f- Fossati et al, / Ocean Engineering W4 (2015) 219-237
Fig. 24. Sketch of the keel internal structures.
For t h e c a U b r a t i o n tests t h e b o a t w a s set ashore a n d loads w e r e appHed b y means o f a c a l i b r a t i o n rig w h i c h a l l o w s f o r k n o w n l o a d a p p l i c a t i o n as s h o w n i n Fig. 10. M o r e t h a n one h u n d r e d l o a d i n g c o n d i t i o n s w e r e a p p l i e d t o t h e d y n a m o m e t e r u p t o 1 k N u s i n g w a t e r t a n k s h u n g t o a r o p e . Also i n c l i n e d tests w e r e p e r f o r m e d (Fig. 11), so t h a t m u l t i d i r e c t i o n a l loads w e r e a p p l i e d , d u e t o t h e b o a t i n c l i n a t i o n , as w e l l as t o t h e generic d i r e c t i o n o f t h e loads t h e m s e l v e s
For each l o a d i n g c o n d i t i o n t h e d i r e c t i o n o f t h e a p p l i e d load a c t i n g l i n e w i t h respect t o t h e y a c h t b o d y reference f r a m e m u s t be detected. To t h i s a i m t h e p o s i t i o n o f t h e m a r k e r s M l a n d M 2 o n t h e r o p e w a s m e a s u r e d b y a laser t o t a l s t a t i o n a n d t h e p o s i t i o n o f a set o f m a r k e r f i x e d o n t h e deck w a s m e a s u r e d t o o .
M o r e specifically, w i t h reference t o Fig. 12, t h e m a r k e r P c o i n c i d e s w i t h t h e p o i n t t h a t e v e r y i t e m p o s i t i o n o f t h e y a c h t is r e f e r r e d to, a n d t h e m a r k e r s 0 , X a n d Y d e f i n e t h e t r i m o f t h e y a c h t - f l x e d r e f e r e n c e f r a m e w i t h respect t o t h e l a s e r - f i x e d refer-ence f r a m e a l l o w i n g f o r t h e e v a l u a t i o n o f t h e r o t a t i o n m a t r i x b e t w e e n t h e laser s t a t i o n fixed ( a b s o l u t e ) r e f e r e n c e f r a m e a n d y a c h t - f l x e d r e f e r e n c e f r a m e . The d e f i n i t i o n o f t h e e l e m e n t s o f t h e m a t r i x C is c a r r i e d o u t b y m e a n s o f a m i m i m i z a t i o n process i n t h e u n k n o w n s C,;,- as a s o l u t i o n o f t h e o v e r - d e t e r m i n e d p r o b l e m o v e r a set o f t h e e x p e r i m e n t a l m e a s u r e m e n t s S c o u p l e d w i t h t h e c o r r e s p o n d i n g set o f a p p l i e d k n o w n loads F.
For the sake o f completeness, i n Figs. 1 3 - 1 5 , t h e results o f t h e c a l i b r a t i o n process are r e p o r t e d . A f t e r h a v i n g d e f i n e d e, a n d ^ j , r e s p e c t i v e l y as t h e p e r c e n t a g e e r r o r ( n o m i n a l f o r c e a p p l i e d vs. f o r c e m e a s u r e d ) a n d t h e d i r e c t i o n cosine o f t h e a p p l i e d load, w i t h r e s p e c t to t h e axis i , t h e o v e r a l l p e r c e n t a g e e r r o r can be w r i t t e n as:
s = V ' t e - Q ' + ( e y f y ) ' + ( e z ' f z ) ' (4)
Figs. 1 3 - 1 5 s h o w , as f u n c t i o n o f t h e d i r e c t i o n cosines, t h e m a g n i t u d e o f t h e o v e r a l l percentage e r r o r e, c o l o r e d a c c o r d i n g l y . These g r a p h s m u s t be i n t e r p r e t e d as f o l l o w s : dots o n t h e circle o f
r a d i u s 1 are associated w i t h l o a d cases w h e r e t h e d i r e c t i o n o f t h e f o r c e has n o , o r s m a l l , c o m p o n e n t a l o n g t h e r e m a i n d e r axis, w h i c h is n o t d e p i c t e d i n t h a t figure (i.e. z i n Fig. 13, y i n Fig. 14 a n d x i n Fig. 15), w h e r e a s , m o v i n g r a d i a l l y t o t h e c e n t e r o f t h e disc, t h e t h i r d c o m p o n e n t increases to the l i m i t o f t h e c e n t e r o f t h e circle, w h e r e t h e d i r e c t i o n o f t h e load is c o m p l e t e l y a l o n g t h e t h i r d d i r e c t i o n . A c c o r d i n g l y , i n Figs. 1 3 - 1 5 , t w o l i g h t a n d d a r k b l u e a r r o w s i n d i c a t e a c o u p l e o f sample l o a d cases, t h a t can be r e c o g n i z e d i n each figure, s h o w i n g t h e same e r r o r s b y d i f f e r e n t v i e w s : m o r e s p e c i f i c a l l y , t h e y are r e l a t e d t o a c o u p l e o f d i f f e r e n t cases i n w h i c h t h e f r a m e w a s l o a d e d basic ally a l o n g v e r t i c a l (z) d i r e c t i o n . For t h e sake o f completeness, i n Fig. 16 t h e errors, as f u n c t i o n o f d i f f e r e n t l o a d levels, are r e p o r t e d (i.e. p u r e loads a l o n g
y d i r e c t i o n ) . Fig. 16 s h o w s a n e v i d e n t t r e n d o f decreasing e r r o r as
t h e e x t e r n a l l o a d increases, p r i m a r i l y due t o a b e t t e r s i g n a l o v e r noise r a t i o . Also, w i t h regards to Fig. 16, t h e o v e r a l l p e r c e n t a g e e r r o r r e p o r t e d t u r n s o u t t o be t h e e r r o r a l o n g t h e r e l a t e d axis ( y ) only, a c c o r d i n g t o Eq. ( 4 ) , because o f t h e d i r e c t i o n cosines o t h e r t h a n can be n e g l e c t e d .
As can be seen o b t a i n e d errors are i n c l u d e d i n t h e [ 2 - 9 % ] r a n g e a n d i n a n y case less t h a n 10% w h i c h s h o u l d p r o v i d e a n a d e q u a t e p e r f o r m a n c e o f t h e d y n a m o m e t e r .
I t is also i m p o r t a n t t o notice t h a t t h e errors d e p i c t e d i n Figs. 13¬ 15 suggest t h a t there is n o t any specific p r e f e r e n t i a l d i r e c t i o n i n w h i c h errors are, o n a n average, h i g h e r t h a n t h e others, so t h a t t h e d y n a m o m e t e r is n o t less accurate a l o n g a specific d i r e c t i o n . The o r i g i n o f the errors h e r e i n r e p o r t e d can be associated t o t h e u n c e r t a i n t y r e l a t e d to t h e elements c o m p o s i n g t h e m e a s u r e m e n t c h a i n o f t h e c a l i b r a t i o n process, such as t h e l o a d cells, t h é A D C converter, t h e r e f e r e n c e load cell, w h i c h has been used f o r t u n i n g t h e s e n s i t i v i t y o f each m o n o a x i a l cell, t h e m e a s u r e m e n t o f t h e d i r e c t i o n o f the a p p l i e d l o a d d u r i n g t h e c a l i b r a t i o n a n d t h e t r i m o f t h e boat, as w e l l as a possible m i s a l i g n m e n t a m o n g t h e l o a d cells d u e t o t h e m o u n t i n g process. Being unavailable any reference f o r t h e e v a l u a t i o n o f t h e u n c e r t a i n t i e s o f such a device, a m e t r o l o g i c a l q u a n t i f i c a t i o n o f t h e e x t e n d e d u n c e r t a i n t y requires a t h o r o u g h
F. Fossati et al. / Ocean Engineering 104 (2015) 219-237
Fig. 26. Frame-Huil assembly procedure.
Fig. 27. Electric motor.
Fig. 25. Keel manufacturing.
e x p l a n a t i o n , w h i c h is b e y o n d the scope o f t h i s paper, also d u e to t h e f a c t t h a t t h e flnal s y s t e m o u t p u t (i.e. sail a e r o d y n a m i c c o e f f i c i e n t s ) is also a f f e c t e d b y a w i d e r c h a i n o f uncertainties, w i t h respect to t h e
p r e v i o u s l y m e n t i o n e d one. Fig. 28. P o l i M i students and researchers at w o r k .
3.3. Force signals processing: frame weight and inertia correction
To d e t e r m i n e t h e sail forces i t is necessary t o d i s t i n g u i s h b e t w e e n t h e forces o n t h e d y n a m o m e t e r , d u e to t h e w e i g h t o f t h e f r a m e and rigging, as w e l l as t h e i n e r t i a l forces, a n d those d u e to t h e sail a e r o d y n a m i c s only. Based o n t h e i n f o r m a t i o n a b o u t t h e p i t c h , h e e l angle a n d t h e y a c h t angular accelerations, g a t h e r e d f r o m p r o p e r sensors, as e x p l a i n e d i n Section 5, as w e l l as t h e k n o w l e d g e
o f t h e i n e r t i a l p r o p e r t i e s o f t h e f r a m e a n d r i g g i n g c o m p o n e n t s , i t is possible t o s u b t r a c t t h e w e i g h t and i n e r t i a l forces f r o m t h e m e a -surements, i n o r d e r t o o b t a i n t h e a e r o d y n a m i c forces o n l y . To t h i s end, a l l t h e spare c o m p o n e n t s s i n g u l a r l y , f r a m e i n c l u d e d (Fig. 17), w e r e w e i g h t e d , t h e n p r e c i s e l y p o s i t i o n e d w i t h i n a CAD e n v i r o n m e n t , i n o r d e r to reach a q u i t e h i g h l e v e l o f accuracy i n t h e d e f i n i t i o n o f t h e o v e r a l l center o f mass, as w e l l as t h e t e n s o r o f i n e r t i a .
228 F. Fossati et al. / Ocean Engineering 104 (2015) 219-237
4. T h e s a i l i n g l a b d e s i g n a n d c o n s t r u c t i o n
4.1. Concept design
The S a i l i n g Yaclit Lab p r o j e c t was e n t i r e l y d e v e l o p e d a n d
m a n a g e d b y a t e a m o f researchers i n t h e M e c h a n i c s D e p a r t m e n t o f t h e P o l i t e c n i c o d i M i l a n o .
I n Fig. 18 the d e s i g n m o d u l i f o r LIH S a i l i n g Yacht Lab d e s i g n are r e p o r t e d . Some o f t h e m are w i t h i n s t a n d a r d y a c h t design p r o c e -d u r e w h i l e 2, 6 a n -d 10 are p e c u l i a r o f t h e b o a t m i s s i o n p r o f i l e . M a i n d i m e n s i o n s have been d e f i n e d i n coherence t o t h e 9.99 m LOA l i m i t g i v e n b y I t a l i a n r e g u l a t i o n t h a t i n t h i s case does n o t r e q u i r e a n y n a v i g a t i o n d o c u m e n t .
H u l l f o r m a n d m a i n characteristics m u s t p r o v i d e adequate s a i l i n g p e r f o r m a n c e as w e l l as a f a i r b e h a v i o r i n t e r m o f f o r m s t a b i l i t y a n d seakeeping. The choice t o use lines f r o m C o m e t 35 p r o d u c e d b y COMAR YACHTS (Fig. 19) is r e l a t e d also to GRP bare h u l l s h e l l a v a i l a b i l i t y (Fig. 2 0 ) ; n e v e r t h e l e s s t h e p r o j e c t has n o t s u f f e r e d a n y c o n s t r a i n d u e t o t h e use o f a n e x i s t i n g boat.
Q u i t e d i f f e r e n t has been t h e a p p r o a c h t o s t r u c t u r a l design. This is d e e p l y i n f l u e n c e d b y b o a t p e c u l i a r tasks a n d by t h e l i g h t a l l o y f r a m e , s h a p e d t o fit rig a n d rigging g e o m e t r i e s .
P l a t i n g s t i f f e n e r s , b o t h transversal a n d l o n g i t u d i n a l have been c o m p l e t e l y redesigned a c c o r d i n g t o t h e i d e n t i f i e d l o a d cells p o s i t i o n s (Figs. 21 a n d 2 2 ) .
Deck l i n e s have also b e e n c u s t o m designed. This is due t o t h e s t r o n g i n t e r a c t i o n s o f deck lines w i t h t h e l i g h t a l l o y f r a m e a n d t o t h e necessity o f a v e r y large o p e n c o c k p i t . Obviously, t h e deck l a y o u t o f a p r o d u c t i o n boat was v e r y f a r f r o m t h a t . Deck, c o c k p i t a n d d o g h o u s e have b e e n l a m i n a t e d i n a single piece o f GRP s a n d w i c h u s i n g a o n e - o f f p l y w o o d m o l d (Fig. 2 3 ) .
A n i n t e r n a l case w i t h t r a p e z o i d a l l o n g i t u d i n a l a n d transversal sections has been used f o r ballast k e e l a t t a c h m e n t . This s o l u t i o n is m o s t e f f e c t i v e w h e n keel section is v e r y t h i n and, m o s t i m p o r t a n t f o r t h i s boat, i t a l l o w s a 2 0 0 m m k e e l l o n g i t u d i n a l s h i f t i n case o f d i f f e r e n t sail p l a n t o be tested (Fig. 24),
T h e b a l l a s t k e e l consists i n a w i n g w i t h c o n s t a n t NACA 65 s e c t i o n a n d a cast lead ballast (Fig. 2 5 ) . The k e e l s t r u c t u r e is m a d e by a d o u b l e C w e l d e d AISI 316 b e a m w i t h 10 m m t h i c k w a l l s , w h i l e CMC m a c h i n e d h i g h d e n s i t y p o l y u r e t h a n e f o a m p r o v i d e s t h e right shape a c c o r d i n g t o t h e chosen p r o f i l e . A 2 m m t h i c k s k i n o f glass/ e p o x y is used to g e t adequate surface hardness.
The ballast lead has been cast i n closed m o l d m a d e f r o m a CNC shaped w o o d m o d e l . This a l l o w e d a p e r f e c t shape a n d surface o f t h e lead t o r p e d o w i t h o u t any m a n u a l f a i r i n g . The transversal sections o f t h e ballast lead are designed to give l o w e s t possible CG p o s i t i o n .
Fig. 29. Deck assembly.
The use o f t h e i n t e r n a l case f o r t h e keel fixing a l l o w s a v e i y easy m o u n t i n g w i t h j u s t t w o b o l t s a n d a self a l i g n i n g m o u n t i n g . The keel m o m e n t w i l l be t r a n s f e r r e d t o t h e h u l l s t r u c t u r e t h r o u g h teak wedges b o l t e d t o the stainless steel b e a m u p p e r part.
Once the l i g h t alloy f r a m e was m a n u f a c t u r e d i t was directly assembled w i t h i n the h u l l p r o v i d i n g load cell alignments w i t h the relative h u l l shnctures (Fig. 26). The last peculiar design feaUire o f this project is related to the internal waters w h e r e the boat w i l l be used, The Sailing Yacht Lab is a sustainable, n o n - i n v a s i v e p r o j e c t t h a t is c o m p a t i b l e w i t h t h e ecosystems i n w h i c h t h e b o a t w i l l operate. A zero e m i s s i o n electric a u x i l i a r y p r o p u l s i o n has been designed u s i n g s t a n d a r d p r o d u c t i o n e l e m e n t s , to a l l o w t h r e e h o u r s range at five k n o t s c r u i s i n g speed i n c a l m w a t e r (Fig, 27).
The Sailing Yacht Lab w i l l also be a t e s t i n g g r o u n d f o r the f u r t h e r d e v e l o p m e n t o f e l e c t r i c a l p r o p u l s i o n i n t h e n a u t i c a l sector, especially as concerns t h e storage o f electrical e n e r g y a n d t h e use of r e n e w a b l e sources.
4.2. Building process
The c o n s t r u c t i o n has b e e n e n t i r e l y c a r r i e d o n b y t h e D e p a r t -m e n t o f M e c h a n i c s s t a f f (Fig. 2 8 ) w i t h i n Lecco I n n o v a t i o n H u b f a c i l i t i e s (Fig. 2 9 ) . One o f f c o n s t r u c t i o n is v e r y c o m m o n i n y a c h t -ing. T h e m o s t o f large r a c i n g yachts are b u i l t t h i s w a y . I n t h i s case t h e m o s t i m p o r t a n t - a n d d i f f i c u l t - task o f t h e b u i l d i n g t e a m has been t o assure t h e p e r f e c t a l i g n m e n t o f the c i n e m a t i c c h a i n c o n t a i n i n g the l o a d cells to t h e d e s i g n e d d i r e c t i o n s .
To t h i s a i m t h e GRP h u l l s h e l l has b e e n b o l t e d t o a d e d i c a t e d cradle, (Fig. 3 0 ) t o get a p e r m a n e n t reference d u r i n g t h e w h o l e
Fig. 30. H u l l supporting structure design.
F. Fossati et al / Ocean Engineering W4 (2015) 219-237 229 Table 1
Yacht construction main steps.
Purchasing/prebuilding Check points
Hull shell purchasing Cradle construction Hull aligned Deck mold Deck lamination Deck completed Cutting f r a m e components CNC Frame w e l d i n g
Frame geometry check
Frame completed
Engine-sail drive coupling Engine installation
Engine installed
Hull transversal f r a m i n g Load cells fittings
Frame-cells-structure alignment check
Hull longitudinal stiffeners Hull transversal f r a m i n g
Frame m o u n t i n g - cell alignment check
Deck custom hardware Accommodation Battery installation
Preliminary deck check - deck removed
Hw/Sw installation
Genoa boat show
Load cells system p r e l i m i n a r y check w i t h boat upright and heeled
Deck m o u n t i n g Outside decoration External/internal details
Hull and deck completed
Rudder shaft/rudder blade Keel structure/feel fairing Ballast model/ballast cast
Rudder and keel set
Rig and Sails set up Ready to sail
c o n s t r u c t i o n . The f r a m e g e o m e t r y a n d mass p r o p e r t i e s have b e e n c o n t r o l l e d b e f o r e m o u n t i n g i t as w e l l as t h e l o a d cell a l i g n m e n t s w i t h t h e relative h u l l s t r u c t u r e s (Fig. 31). I n t h e f o l l o w i n g Table 1 t h e m o s t i m p o r t a n t p r e f a b r i c a t e d e l e m e n t s a n d t h e c o n s i d e r e d check p o i n t s are r e p o r t e d .
4.3. Project management and commissioning
W h e n b u i l d i n g p r o t o t y p e o r e x p e r i m e n t a l c r a f t t h e p r o j e c t m a n a g e m e n t is a c r i t i c a l f a c t o r a n d i t is v e r y m u c h i n f l u e n c i n g t o get t h e e x p e c t e d r e s u l t i n t e r m s o f q u a l i t y , d m e a n d b u d g e t .
The o p d o n s f o r a successful a n d e f f e c t i v e b u i l d i n g process are basically t w o . The m o s t c o m m o n is t o i d e n t i f y a m a i n c o n t r a c t o r t h a t w i l l take care a n d r e s p o n s i b i l i t y o f t h e w h o l e b u i l d i n g process a l t h o u g h a l l o w i n g e x t e m a l c o n t r i b u t e s f o r specific y a c h t features. The second is to m a n a g e several contractors one f o r each y a c h t f e a t u r e a n d merge these c o n t r i b u t e s t o g e t h e r t o get t h e f i n a l result.
A l t h o u g h m o r e rislcy a n d c o m p l e x t h i s last o n e is m o r e f l e x i b l e to d e s i g n changes a n d has b e e n c o n s i d e r e d p r e f e r a b l e f o r t h i s p r o j e c t w h e r e a l m o s t n o r e f e r e n c e w a s available, I t is e v i d e n t t h a t i n t h i s case t h e i n f l u e n c e a n d r e s p o n s i b i l i t y o f t h e p r o j e c t m a n a g e r are m o s t i m p o r t a n t a n d he m u s t have s p e c i f i c e x p e r i e n c e a n d skill. The general p o l i c y o f b u i l d i n g process o f SYL has b e e n to manage separately the d i f f e r e n t subcontractors a n d to merge t h e m a c c o r d -i n g t o -i d e n t -i f -i e d steps -i n w h -i c h p a r t -i a l results c o u l d be checked. This a p p r o a c h is v e r y s o u n d w h e n t h e q u a l i t y o f t h e results is t h e p r i m a r y target b u t generally h a r d l y c o m p l i e s w i t h sharp deadlines.
Fig. 32. D e c k - f r a m e - h u l l p r e l i m i n a r y alignments.
Finally SYL as any p r o t o t y p e or e x p e r i m e n t a l c r a f t can never b e e n considered c o m p l e t e d , b u t o n l y ready f o r t h e n e x t scheduled task. Furthermore, t h e acquisition system needs periodical t u n i n g a n d setting. For these reasons a dedicated logistic has been p r o v i d e d . It allows any t y p e o f p r e p a r a t i o n a n d set u p to be done ashore, adequately s u p p o r t e d .
230 F. Fossati et al. / Ocean Engineering 104 (2015) 219-237 Scanning range in m ( f t ) 9 0 (295.20) 6 0 (196.85) M o t o r - r e r h i c e r u n i t Laser scanner - 9 0 (-295.20) - 6 0 - 3 0 O (-196.85)(-98.43) 3 0 6 0 9 0 1 2 0 (98.43) (196.85) (295.20) (393.7) Scanning range in m (ft)
I I Scanning range max. 8 0 m ( 2 6 2 . 4 7 f t )
•
Scanning range f o r objects up to 1 0 % remission 2 6 m ( 8 5 . 3 f t )Fig. 33. Flying shape detection system: scanning range.
Fig. 34. Flying shape detection system.
5. E x p e r i m e n t a l a p p a r a t u s
In t h e f o l l o w i n g t h e S a i l i n g Yacht Lab m e a s u r e m e n t set u p a n d
d a t a c o l l e c d o n s y s t e m a r c h i t e c t u r e w i l l be b r i e f l y d e s c r i b e d .
5.3. Force measurements
Force measurements are carried o u t b y means o f sfrain gages based mono-axial FIBM S9M load cells. Tlie c o n d i t i o n i n g system is given by a Burster 9235 m o d u l e f o r each load cell, i m p l e m e n t i n g a full-bridge 6 - w i r e c o n d i t i o n i n g configuration. The protection class o f the load cells and conditioning modules are respectively 1P40 and 1P68, that could be considered adequate f o r this k i n d o f application. Tlie load cells are also highly accurate and h i g h l y stable w i t h respect lateral force.
1^ A x i s o f r o t a t i o n
-Fig. 35. The TOF flying shape detection system.
Load cells signals are c o n v e r t e d f r o m a n a l o g t o d i g i t a l b y m e a n s o f N a t i o n a l I n s t r u m e n t s t e c h n o l o g y t h r o u g h a 9 1 7 8 - 9 2 0 5 chassis-a n chassis-a l o g i n p u t m o d u l e .
5.2. Yacht trim and motion measurements
A 3DiVI-GX3-35 GPS-aided i n e r t i a l n a v i g a t i o n s y s t e m c o n s i s t i n g o f a n A t t i t u d e a n d H e a d i n g Reference U n i t (AHRS) a n d a Global p o s i t i o n i n g System (GPS) receiver is used t o m e a s u r e t h e y a c h t a t t i t u d e a n d boat d y n a m i c s . The sensors used are gyroscopes, accelerometers a n d m a g n e t o m e t e r s and are arranged o n the t h r e e p r i m a r y axes to acquire angular rate, acceleration a n d t h e local m a g n e t i c field respectively. The system can c o m m u n i c a t e t o t h e h o s t v i a USB p r o v i d i n g p o s i t i o n v e l o c i t y a n d a t t i t u d e e s t i m a t i o n i n d i g i t a l f o r m a t a c c o r d i n g to a specific Data C o m m u n i c a t i o n Protocol. The heel and t i i m angles are also measured using a GEMAC 2 3 5 5 4 analog inclination sensor t h a t is analog-to-digital converted along w i t h the load cells signals b y means o f t h e same converter. This sensor provides i n f o r m a t i o n o f the r o t a t i o n along t w o perpendicular planes, that t u m o u t to be p i t c h a n d roll. The inclination sensor is installed j u s t beside the inertial navigation system i n order to compare analog vs. digital signals o f t h e same quantities (Euler angles):
5.3. Navigation data
A classical n a v i g a t i o n e q u i p m e n t is also i n s t a l l e d p r o v i d i n g w i n d speed a n d d i r e c t i o n , b o a t speed, d e p t h as w e l l as t h e y a c h t course b y m e a n s o f a d i f f e r e n t i a l GPS receiver. The n a v i g a t i o n s y s t e m s u p p o r t t h e NIVIEA 2 0 0 0 a n d can c o m m u n i c a t e t o t h e h o s t v i a N M E A 183 s t a n d a r d p r o t o c o l 5.4. Wind measurement I n a d d i t i o n t o t h e m a s t t o p a n e m o m e t e r an u l t r a s o n i c 3 D a n e m o m e t e r is m o u n t e d o n t h e t o p o f a n a d d i t i o n a l m a s t w h i c h is set o n t h e y a c h t b o w a n d w h i c h keeps t h e v e r t i c a l p o s i t i o n i r r e s p e c t i v e o f t h e boat heel. U s i n g t h i s d e v i c e t h e a d d i t i o n a l a n e m o m e t r i c m e a s u r e is p e r f o r m e d i n t h e c o r r e s p o n d i n g s a i l p l a n g e o m e t r i c c e n t e r o f e f f o r t h e i g h t a n d t h e 3 w i n d speed c o m p o n e n t s are p r o v i d e d b y m e a n s o f a f i a l o g signals.
5.5. Sail flying shape measurements
The Lecco I n n o v a t i o n H u b Sailing Yacht Lab is fitted w i t h t h e "LIH TOF F l y i n g Shape D e t e c t i o n System"^ (Patent P o l i t e c n i c o d i
F. Fossati et al. / Ocean Engineering 104 (2015) 219-237 231
Comandi Grafico 30 • Manuals
Ricostruzione tdcilmensionale (Scannér TOF)
SM Contit) VISft Serial ref
% C0f,13 ~ T Motor Config
ïncodErRatio (ccunt/rev) !;| 2000.0Ö DriveRatic (mm/rev) r^j i.00
PosLimit t (mm) '. :'• 1000.000 PosLimit - (mm) I ,.j 1000.000 MotorType J _ | ' 5 M 2 3 ~
Cartella salvataggic ^ C:\Uter5\user\Desttcp
Porta Mome File
'-17999
Trigger ricevuto
iP Scanner 169,254.10,127
Veiccita [few's] Accelerazione [re'.'/si]
— — Angoic [ Ruota motore Scansiona Angolo di EcansioneCI ';i8ci Autoscala asse Z Saiva Dati
Risposta inviata a dient
Errore Trigger statui code source [01 HP Webcam HD 2300 Errore V.'ebcam 3
Fig. 36. TOF acquisition system snapshot.
M i l a n o , h t t p : / / w v v w . r i c e r c a . p o l i n i i . i t / i n d e x . p h p ? i d = 5 0 4 1 ) w h i c h p r o v i d e s t h e 3 D sail g e o m e t r y i n actual s a i l i n g c o n d i d o n s (Fig. 3 2 ) .
This s y s t e m relies o n T i m e Of Flight (TOF) t e c h n o l o g y and, i n particular, a laser scanner was selected t o ensure h i g h m e a s u r e m e n t accuracy a n d speed. The scanner e m i t s a laser pulse i n a c e r t a i n d i r e c t i o n , a n d estimates the target distance by e v a l u a t i n g t h e t i m e the pulse takes to r e t u m to the sensor. The device is e q u i p p e d b y a n i n t e r n a l m i r r o r t h a t deflects t h e laser pulse t r i g g e r i n g t h e acquisi-t i o n w i acquisi-t h r e g u l a r angular sacquisi-tep o f m i n i m u m 0.167° o r m a x i m u m 1°. Its o p e r a t i n g range goes f r o m 0.5 m to 8 0 m c o v e r i n g a n angular section o f 1 9 0 ° f r o m - 5 ° to 1 8 5 ° (Fig. 3 3 ) .
M o r e o v e r , t h e 5-echo t e c h n o l o g y can be e n a b l e d e n s u r i n g t h e r e l i a b i l i t y o f t h e m e a s u r e m e n t s even i n o u t d o o r b a d w e a t h e r c o n d i r i o n s s u c h as r a i n , f o g a n d dust.
T h e selected TOF device p r o v i d e s i n f o r m a d o n a b o u t t h e m e a -sured p o i n t s i n t e r m s o f polar c o o r d i n a t e s : f o r each d e t e c t e d p o i n t a r a d i u s r a n d a n angle a are p r o v i d e d w i t h reference to t h e o r i g i n o f t h e c o o r d i n a t e s s y s t e m l o c a t e d o n t h e i n t e r n a l m i r r o r r o t a t i o n a l axis (Fig. 3 4 ) .
D u e t o its i n t r i n s i c characteristics, t h e laser scanner is able t o m e a s u r e o n l y p o i n t s l y i n g i n t h e s a m e p l a n e w h i l e i n t h i s p a r t i c u l a r a p p l i c a t i o n t h e e n t i r e sail surfaces has to be m e a s u r e d (Fig. 3 5 ) .
To o v e r c o m e t h e p r o b l e m , a d e d i c a t e d h a n d l i n g u n i t based o n a brushless m o t o r a n d a n epicyclical gear has b e e n d e v e l o p e d t o enable t h e c o n t r o l l e d r o t a t i o n o f t h e m e a s u r e m e n t device a r o u n d a n axis p e r p e n d i c u l a r t o t h e TOF m i r r o r r o t a t i o n a l axis. A p r o x -i m -i t o r -is used t o -i d e n t -i f y the -i n -i t -i a l s c a n n -i n g p o s -i t -i o n f o r each data a c q u i s i t i o n .
A n i n house s o f t w a r e has b e e n d e v e l o p e d a l l o w i n g f o r t h e h a n d l i n g u n i t c o n t r o l strategy. T h r o u g h t h e r e a l i z e d user i n t e r f a c e (Fig. 3 6 ) i t is possible t o : c o n t r o l t h e brushless m o t o r v i a serial p o r t
( s e t t i n g v e l o c i t y a n d acceleration), e s t a b l i s h t h e c o n n e c t i o n t o t h e laser scanner a n d acquire data f r o m i t v i a E t h e r n e t p o r t u s i n g TCP/ IP p r o t o c o l , set t h e s c a n n i n g p a r a m e t e r s , such as s t a r t i n g angle a n d angle t o be scanned, receive a n d e x t e r n a l t r i g g e r to a u t o -m a t i c a l l y r u n t h e s c a n n i n g ( u s e f u l f o r s y n c h r o n o u s a c q u i s i t i o n o f d i f f e r e n t devices c o n t r o l l e d b y a c o m m o n u n i t c o n t r o l ) . M e a s u r e d data are saved o n t o a p e r s o n a l c o m p u t e r h a r d d i s k .
U s i n g t h e ' T O F F l y i n g Shape D e t e c t i o n System" t h e sail shape 3 D g e o m e t r y i n t e r m s o f p o i n t c l o u d w h e r e t h e 3 D c o o r d i n a t e s i n a n a b s o l u t e f r a m e is m e a s u r e d f o r each i n d i v i d u a l p o i n t a n d t h e f u l l 3 D c o o r d i n a t e s o f each i n d i v i d u a l p o i n t b e l o n g i n g t o t h e sail surface are s t o r e d f o r IGES f i l e c r e a t i o n .
I n a d d i t i o n , a real t i m e analysis o n a l i m i t e d n u m b e r o f sail surface sections can be p e r f o r m e d p r o v i d i n g s e c t i o n camber, d r a f t , e n t r y , exit, f r o n t , back a n d t w i s t r e l a t i v e t o y a c h t c e n t e r l i n e .
These values aj:e o u t p u t t o file a n d d i s p l a y e d o n t h e s y s t e m i n t e r f a c e a l l o w i n g t h e e v a l u a t i o n i n r e a l t i m e o f b o a t p e r f o r m a n c e as a f u n c t i o n o f t h e sail t r i m m i n g p a r a m e t e r s .
M o r e details o n t h e L I H TOF F l y i n g Shape D e t e c t i o n S y s t e m can be f o u n d i n Fossati et a l . (2015).
5.6. Sail pressure measurement
A n i m p o r t a n t feature o f the p r o j e c t is t h e availability o f systems f o r m e a s u r i n g the loads acting o n t h e sails at f u l l scale. The possibility o f k n o w i n g the effective pressure d i s t r i b u t i o n over t h e sail p l a n is o f great interest f o r t h e aerodynamic and sUructural design o f sails, and also f o r the selection a n d o p t i m a l use o f materials a n d p r o d u c t i o n techniques. Integral measurements alone m a y n o t be s u f f i c i e n t f o r a n u n d e r s t a n d i n g o f h o w t o use a sail p l a n i f i t is n o t possible to d e t e r m i n e the c o m p l e x interactions t h e y provoke. O n t h e Sailing Yacht Lab, the pressure d i s t r i b u t i o n o n t h e sails is carried o u t b y
232 F. Fossati et al. / Ocean Engineering 104 (2015) 219-237 0.5 ni 0.5 i-n • - T J 1 m O 5 ni
83 % 6 taps
7538
taps
62 % 8 t_aps
50 % 8 taps
82 % 8 taps
1.2 01 1 n i62 % 8 taps
37 % 16 taps
(optional)
2 5 % 16 taps
4 3 % 16 taps n
(optional)
25 % 16 taps
IFig. 37. Mainsail and j i b pressure taps layout.
means o f MEMS sensors (an excellent c o m p r o m i s e b e t w e e n size, p e r f o r m a n c e , costs and operational c o n d i t i o n s ) a n d dedicated pres-sure pads w h i c h have b e e n designed a n d p r o d u c e d a i m i n g t o p r o v i d e the d i f f e r e n t i a l measurement b e t w e e n t h e sail l e e w a r d a n d w i n d w a r d side.
The pressure pads are single p o i n t m e a s u r e m e n t spots w h i c h can be i n d i v i d u a l l y placed o n t h e sail a n d c o n n e c t e d t o t h e pressure scanner b o x w i t h s m a l l t u b i n g fixed i n a c u s t o m b u i l d sleeve o n t h e sail.
W i t h r e f e r e n c e t o t h e SYL sail i n v e n t o r y Figs. 3 7 a n d 3 8 s h o w t h e sail pressure m e a s u r e m e n t s sections a n d t h e r e l e v a n t n u m b e r o f pressure taps. I n Figs 37 a n d 38 t h e pressure scanner boxes p o s i t i o n s are s h o w n w i t h reference t o each sail. Table 2 s h o w s t h e pressure scanner s p e c i f i c a t i o n s (Fig. 3 9 ) .
A t the m o i n e n t this paper is going t o press the pressure measure-m e n t systemeasure-m is under testing i n the Politecnico d i M i l a n o W i n d T u n n e l using the yacht scaled m o d e l described i n Fossati, (2006).
5.7. Data recording equipment: real time and synctironization
The data r e c o r d i n g s y s t e m relies o n a m a i n s o f t w a r e , d e v e l o p e d i n c # a n d I n t e m p o r a ® p r o g r a m m i n g e n v i r o n m e n t s , w i t h the a i m o f a c q u i r i n g signals/data as w e l l as m a n a g i n g , t r i g g e r i n g a n d s y n c h r o n i z i n g o t h e r m e a s u r i n g systems as r e p o r t e d i n t h e Fig. 4 0 .
M o r e specifically, a g r a p h i c a l user i n t e r f a c e (GUI) is d e v e l o p e d i n c # a n d c o u p l e d w i t h I n t e m p o r a ® , w h i c h is d e d i c a t e d t o t h e s y n c h r o n i z a t i o n o f d i f f e r e n t t y p e o f signals ( A n a l o g vs. D i g i t a l ) a n d d i f f e r e n t l y s a m p l e d signals (i.e. Load Cells vs. N M E A ) . D u r i n g t h e n a v i g a t i o n , t h e user ( a n d the c r e w ) is able t o w a t c h at e v e r y single signal t h a t is r u n n i n g i n real t i m e , b y means o f t h e above m e n -tioned m a i n GUI (Fig. 4 1 ) .
Then, w h e n e v e r the user decides to start to save a n e w time history, the acquisition system m u s t be enabled a n d user can also decide w h e t h e r to t r i g g e r the other separate a c q u i s i t i o n systems (i.e. Sail Shape), also i n d i f f e r e n t a n d m u l t i p l e m o m e n t s o f t h e time history. A " t x t " file is t h e n stored w i t h t h e time h i s t o r y o f each device, collected by columns, a n d " l o g " file, c o n t a i n i n g various i n f o r m a t i o n (e.g. t c p / i p c o m m u n i c a t i o n success o f t h e t r i g g e r i n g c o m m a n d s ) , is consistently filled d u r i n g the e x p e r i m e n t a l session.
6. S o m e e x a m p l e s o f g a t h e r e d d a t a
I n the f o l l o w i n g s o m e examples o f m e a s u r e m e n t s collected d u r i n g one o f t h e first t r i a l sessions are r e p o r t e d (Fig. 4 2 ) . T r i a l tests have been c a r r i e d o u t o f f s h o r e Colico M a r i n a i n t h e n o r t h o f C o m o Lake w h e r e SYL is based, i n s o u t h e r l y w i n d a n d q u i t e flat w a t e r .
R e p o r t e d data are r e l e v a n t t o a close h a u l e d s a i l i n g course w i t h j u s t t h e m a i n s a i l h o i s t e d a n d t o a "stable" t i m e w i n d o w o f a b o u t
F. Fossati et al. / Ocean Engineering 704 (2015) 219-237 233 7 0 s e x t r a c t e d f r o m a 4 m i n data a c q u i s i t i o n p e r i o d . A d e t a i l e d
discussion o f the results r e p o r t e d i n t h e f o l l o w i n g is b e y o n d t h e a i m o f t h i s paper, w h i c h aims at g i v i n g an o v e r v i e w o f t h e f i n a l i z a d o n o f t h i s m u l t i d i s c i p l i n a r y p r o j e c t .
Fig. 4 3 shows t h e m e a s u r e d t r u e h e a d i n g angle a n d Fig. 4 4 shows t h e c o r r e s p o n d i n g a p p a r e n t w i n d angle a n d a p p a r e n t w i n d speed. Fig. 45 shows t h e c o r r e s p o n d e n t b o a t speed m e a s u r e d b y means o f t h e b o a t l o g i n c o m p a r i s o n w i t h t h e speed over g r o u n d m e a s u r e d b y t h e GPS (Fig. 4 6 ) .
Fig. 4 5 shows t h e r u d d e r angle a n d t h e b o a t p i t c h a n d r o l l nneasurements. I n Fig. 47 t h e m e a s u r e d a e r o d y n a m i c forces a n d m o m e n t s r e f e r r e d to t h e b o d y axes o f the boat are r e p o r t e d w h i l e Fig. 4 8 shows the v e r t i c a l a n d l o n g i t u d i n a l m e a s u r e d p o s i t i o n s o f
7 5 % 16 taps
50 % 16 taps
2 5 % 16 taps
t h e a e r o d y n a m i c c e n t e r o f e f f o r t c o m p a r e d w i t h t h e g e o m e t n c e s t i m a t e d values.
As far as the sail f l y i n g shape measurements are concerned. Fig. 49 shows an example o f the p o i n t clouds (respectively o f the mainsail and the j i b ) directly measured o n board by means o f LIH TOF Flying Shape Detection System and Fig. 50 shows the 3 D surface obtained after the segmentation and surface f i t t i n g procedures.
Finally Fig. 51 s h o w s a n d e x a m p l e o f t h e c o m p a r i s o n b e t w e e n t h e r e c o n s t r u c t e d 3 D sail shapes s u p e r i m p o s e d t o t h e SYL CAD m o d e l and t h e c o r r e s p o n d e n t j i b p i c t u r e t a k e n o n b o a r d i n t h e same c o n d i t i o n s (Fig. 52).
Fig. 39. Pressure tap.
Load Cells
Ultrasonic Anemometer
Inclination Sensor
Sail Pressure System
Analog D A C
-Digital
C#/Intempora
Main SW
A n a l o g T i ' i g g e r / S y i i c TCP/IP TCP/IPInertial Navigation System
NMEA-GPS
Sails Shape System
Fig. 38. Gennaker pressure taps layout. Fig. 40. Dynamometer/sail shape acquisition software flowchart.
Table 2
Pressure scanner specifications and i n Fig. 39 a picture of the pressure pad Is reported.
Parameter Z16 Unit Comment
FS pressure range + 1000 Pa 2000 Pa dynamic range
Number o f pressure sensors 16 Differential pressure sensors, b o t h sides of each sensor membrane routed to an individual tap
Measurement resolution 0.1 Pa
Static accuracy after zeroing 0.5 %FS Includes the combined errors o f non-linearity, hysteresis and repeatability
Total thermal error 0.05 %¥src Zero and span relative to 25 °C
Sampling rate 1-20 Hz Per channel
Input voltage 5 - 1 2 v Supplied over CAN cable
Stand by current 10 mA Sleep mode
Operation current 40 mA Scanning mode
Communication CAN interference 1 Mbit/s - Daisy chain topology
Calibrated temperature range 5 - 4 0 °C Optional - 3 0 to 60 °C
Size 65 X 50 X 5 m m L x W x H
234 F. Fossati et al. / Ocean Engineering 104 (2015) 219-237 : D I H A M O M Ë T R O | mE\.'.0\ I M C L I N O i R U D D E R : A C C ; V E L _ A N G ' | E U L E R ! G P ' S , N M E A R e a l T i m e S t r e a m i n g
PW
- \ — I — 1 — \ - - 1- 1 - I I I I l l l ax ax ay az 37.0 37.5 Tempo [s]NOME SESSIONE Eo!ina2| PATH SAVE SIZE (byle) ACO'REFRESH F I L E S A V E DOlinal M Fx O Fy1 O Fy2 O F z l O FzZ O Fz3 O TinleSlömp - Inlenipora SHUT-DOWN TRIGGER FORUE A 2 Z E R A P R O G R E S S I V I j
STATUS TRIGGER SMALL ST.i.TUS TRIGGER BIG
RISPOSTA TRIGGER SMALL RISPOSTA TRIGGER EIG
Fig. 41. Dynamometer/sail shape acquisition software snapshot.
Fig. 42. Experimental session.
7. P e r s p e c t i v e of t h e p o t e n t i a l of s a i l i n g y a c h t l a b p r o j e c t
Despite t h e i n c r e a s i n g a m o u n t o f research i n y a c h t e n g i n e e r i n g f i e l d , i n a u t h o r s ' o p i n i o n t h e r e is s d l l a real n e e d f o r researchers to g e t t o g e t h e r t o debate t h e issues a b o u t sail a e r o d y n a m i c s . In p a r t i c u l a r t h e c o r r e l a t i o n b e t w e e n scale m o d e l tests a n d CFD s i m u l a t i o n s w i t h a c t u a l s a i l i n g p e r f o r m a n c e r e m a i n s a n i n t e r e s t -i n g t o p -i c . U n t -i l n o w t h e r e are f e w f u l l scale tests f o r t h e assess-m e n t o f h y d r o d y n a assess-m i c forces o f s a i l i n g boats.
As m e n t i o n e d i n the i n t r o d u c t i o n the p r o c e d u r e used f o r t h e G i m c r a c k p r o j e c t w a s based o n f u l l scale tests, w h e r e a p p a r e n t w i n d speed a n d d i r e c t i o n as w e l l as b o a t speed w e r e m e a s u r e d , a n d scale m o d e l tests w h e r e d r i v i n g force, h e e l i n g f o r c e a n d t h e r a t i o b e t w e e n h e e l e d and u p r i g h t resistance w e r e m e a s u r e d . W i t h
240 — 'niu> Hrmliiiu
l:iO 1-1(1
m
IGO 170 180 190T i u u - [s]
Fig. 43. True heading of a sample t i m e history.
t h e d a t a f r o m m o d e l tests i t w a s possible t o calculate t h e set o f sail c o e f f i c i e n t s i n t e r m s as a f u n c t i o n o f t h e h e e l angle alone.
W h i l e G i m c r a c k was sailed " b y an e x p e r i e n c e d h e l m s m a n a n d m e a s u r e m e n t w e r e r e c o r d e d w h e n i t w a s j u d g e d t h a t t h e b o a t was :sailing a t o p t i m u m speed m a d e g o o d t o w i n d w a r d " , Sailing Yacht Lab f u l l scale p e r f o r m a n c e s can be i d e n t i f i e d a n d r e c o r d e d i n q u i t e s u p e r i o r w a y . The s a i l i n g d y n a m o m e t e r a l l o w s t h e d i r e c t e v a l u a t i o n o f d r i v i n g a n d h e e l i n g forces a n d t h e assessment o f t h e r e s u l t i n g c o e f f i c i e n t s so t h a t n o e x t r a p o l a t i o n f r o m t a n k test is necessary.
E Fossati et al. / Ocean Engineering 104 (2015) 219-237 235 11 42 40 38 30 130 l ü . ü
as
ac
9.4 9.2 'J.D 140150
10.1 ISO l l J I l •^
<-Wind .spu'i l 1.3Ü 140 1.51) 1011 170 180Fig. 44. W i n d angle and w i n d speed o f a sample time history.
2um
i-'jno g I I I U U 1.1 1 3 U 11(1 150 IfiO 170 1811 IDOÜl) 5000 . i . O I -50(11) ^ . -UKiOO -1.5()()0 1.30 140 150 ICO 17U 18(1 T i m e [.-;]Fig. 47. Aerodynamic forces a n d moments o f a sample time history. iü(! 2.4 2.2 2.0
1.8
1.0 SpeedSpeerl over grimiid
|:i(l 110 150 100 170 180 Tinu' (hi
Fig. 45. True speed and speed over ground o f a sample t i m e history.
Rudder 130 5 I — -10 140 1.50 ICO 170 I S O
190
Pitch Hull - l. i : 130 140 150 ICO 170 180 190 Fig. 46. Rudder angle, pitch and roll o f a sample t i m e history.T h e r e s u l t i n g c o e f f i c i e n t s c o u l d be used f o r s i m i l a r h u l l f o r m s a n d sail g e o m e t r i e s a n d w i l l h i g h l i g h t possible m o d e l s h i p c o r r e -l a t i o n . T h i s -last presents p e c u -l i a r aspects w h e n d e a -l i n g w i t h s a i l i n g yachts a n d f u r t h e r c o n t n b u t e s based o n g e o s i m h u l l s could led t o w i d e l y a p p l i c a b l e results.
A n e x p e r i m e n t a l p r o g r a m based o n t w o scale m o d e l s (i.e. 1/4-1/8 scale r a t i o ) o f the SYL h u l l f o r m a n d o n t h e f u l l scale
( I — COE,, — COE,
Geometrie COE.^
— Geoiuelrie COE. 1:30 140 150 160 170 ISO 100 T i m e h ]Fig. 48. Measured centers of e f f o r t vs. geometric centers o f effort, o f a sample t i m e history.
