Design of the KNRM Lifeboat NH 1816. Part 1 and 2

Date 2014 Author Keuning, J.A.

Address Delft University of Technology

Ship Hydromechanics and Structures Laboratory

Mekelweg 2, 2628 CD Delft

Delft U n i v e r s i t y of T e c l i n o l o g y

TUDelft

Design of the KNRM Lifeboat NH 1816.

Part 1 and 2

by

J.A. Keuning

Report No. 1 9 1 0 - P 2014

Page / o f 1/1

Bezoek ook onze website:

www.swzonline.nl

Inhoudsopgave

19

Design of the KNRM Lifeboat NH 1816

The Royal Netherlands Sea Rescue Institution (KNRM) exploits a fleet of life-boats around the North Sea coast of the Netherlands. The majority of this fleet consists of RIBs. The largest vessels are from

the so-called "Arie Visser" class with a length of around 18.5 metres and a maximum speed of 35 knots. These are all weather boats and fully self-righting. As this vessel type still had room for improvement, the KNRM set o u t t o create a new and better lifeboat, the NH 1816.

26

Duitse binnenvaart steekt de grens over

voorspudpalen

De Europese binnenvaart heeft nog steeds gebrek aan voldoende ligplaatsen langs de rivieren en vaarwegen. Daarom gaan steeds meer schipper-ondernemers over tot het plaatsen van een spudpaal in het voor- en achterschip.

28

Finding a Fair Energy Efficiency Index

for General Cargo Ships

IMO's key instrument of reducing ships' COjOmissions Is the Energy Efficiency Design Index (EEDI).This index, mandatory for new ships or ships that underwent a major conversion, is calculated dividing emissions by the benefit to society, expressed as transport capacity times vessel speed. It became clear, however, that some general cargo ships had difficulty meeting the new requirements.

Verder in dit nummer

2

Nieuws

24

Vinden van een n i c h e

-4

Maritieme markt

markt voor Nederlandse

6

M a a n d maritiem

34

A r c t i s c h e operaties

12

Voor u gelezen

34

Kotterrederijen omarmen

13

Expositie " L u c h t f o t o g r a f i e

36

pulstechniek

van de KNRM in a c t i e "

36

Simulating the Installation

14

Branciie zet alles op

of China's Largest FPSG

18

Maritime Technology

41

Nieuwe uitgaven

18

The Future Is in the W a t e r

42

M a r s Report

- Offshore Energy

44

Verenigingsnieuws

Omslag: De nieuwe reddingboot van de KNRM is het resultaat van intensieve samenwerking tussen KNRM, werf en onderzoeksinstituten (foto Flying Focus}.

(Integraal) Samenwerken

In dit nummer van SWZ treft u zoals gebruike-lijk een verscheidenheid aan onderwerpen aan. Graag vestig ik de aandacht op drie arti-kelen die ogenschijnlijk weinig met elkaar te maken hebben: een interview met Peter Zoe-teman, directeur van Netherlands Maritime Technology (voorheen Scheepsbouw Neder-land) op pagina 14, op pagina 19 de overwe-gingen en onderzoeken die hebben geresul-teerd in een nieuw ontwerp van een reddings-boot voor de KNRM, de NH 1816, en de evalu-atie van de Energy Efficiency Design Index (EEDI) voor kleine vrachtschepen op pagina 28. Deze artikelen beschrijven aspecten die alleen mogelijk zijn door samenwerking, en hoewel strikt genomen niet alles valt onder de noemer Integraal Samenwerken als toegelicht in SWZ Maritime van september vorig jaar, is het wel in de geest van dit clusterproject. Samenwerking tussen werven en toeleveran-ciers ligt voor de hand en is gunstig voor de sector als geheel, zeker in de pre-competitie-ve fase van nieuwe ontwikkelingen en bij het verdedigen van belangen van de Nederlandse maritieme sector bij de EU en de IMG, maar er zijn bij het verkrijgen en uitvoeren van op-drachten vaak ook tegenstrijdige belangen: werven en toeleveranciers concurreren on-derling en toeleveranciers zijn niet gebonden aan Nederlandse werven. Een uitdaging dus voor directeur Zoeteman.

Het ontwerp van de NH 1816 van de KNRM laat duidelijk zien dat deze ontwikkeling alleen mo-gelijk is door intensieve samenwerking tussen de reder/gebruiker en een onderzoeksinsti-tuut, waarbij bovendien wordt voortgebouwd op eerder onderzoek naar de optimale boeg voor snelle schepen in zware zeegang. Ook dat onderzoek was een toonbeeld van samen-werking tussen werf en onderzoeksinstituut. Het artikel over de EEDI laat zien dat dankzij intensieve samenwerking tussen onderzoe-kers, ontwerpers en een brancheorganisatie ongewenste effecten van potentiële regelgeving voor kleine vrachtsche-pen konden worden verklaard. Met gefundeerde argumenten werd bij de IMG aanpassing van de regelgeving bewerkstelligd. De conclusie: (integraal) samen-werken loont.

Hotze Boonstra, hoofdredacteur

(swz.rotterdam@planet.nl)

Design ofthe KNRM Lifeboat

NH 1816(1)

The Royal Netherlands Sea Rescue Institution (KNRM) exploits a fleet of lifeboats

around the North Sea coast of the Netherlands. The majority of this fleet consists of

RIBs. The largest vessels are from the so-called "Arie Visser" class with a length

of around 18.5 metres and a maximum speed of 35 knots. These are all weather

boats and fully self-righting. As this vessel type still had room for improvement, the

KNRM set out to create a new and better lifeboat, the NH 1816.

In the design of high speed ships, the hydrodynamics always play an important role. The aim to reach high speeds at reasonable cost calls for optimal calm water performance. Providing the capability to maintain this high speed and operability (and safety) in a seaway often calls for ingenious hydrodynamic approaches.

Lifeboats are a special design case because they need to be safe and acceptably comfortable in the "average" working conditions, in which most of their duties are carried out, but also be safe and op-erable in the most extreme conditions that can be met in their oper-ational areas.

The operational area forthe KNRM is the Dutch coastal area and the southern part o f t h e North Sea. This is a notoriously dangerous

This article has been divided into two parts. This is the first part. The second part will be published in an SWZ Maritime issue to come.

area due to the presence of many estuaries, shoals, associated strong tidal currents and the fact that usually, in the most severe conditions (that is, gales and storms from the west through north-west to the north), the Dutch coast is a lee shore. This calls for good operability in a wide range of operational conditions and a large fluctuation in ship sizes and types to be assisted or rescued. Typical design characteristics o f t h e present Arie Visser class boats are: maximum speed up to 35 knots, overall length around 19 metres, oc-cupancy of six crew, twin engines with water jets, full 180 degrees self-righting capability, good seakeeping capabilities, high speed to be maintained in head seas, and excellent manoeuvring behaviour in all conditions, that is, head, beam and following waves with (breaking) waves of 10 metres high.

Two decades ago, the emphasis for lifeboats was not so much on crew accommodation and comfort but on survivability. The present Arie Visser class designs, which were designed by the office of W. de Vries Lentsch are typical examples of that philosophy. A photo-graph of one of these boats is presented in figure 1 together with some main particulars in table 1.

The KNRM developed the NH 1816 to meet new demands on comfort and crew composition (picture Flying Focus). Jaargang 135 • mei 2014 19

S c h e e p s o n t w e r p

D e s i g n a t i o n S y m b o l U n i t

Arie V i s s e r D e s i g n - [-]

Overall length Loa [m] 18.8

Overall breadth Boa [m] 6.1

Draft T [m] 1.07

Weight W [ton] 28

Longitudinal centre of gravity LcG [m] 6.12

Wetted area with zero speed S [niA2] 60.9

Metacentre height GM [m] 1.77

Table 1. Main particulars ofthe Arie Visser class.

The operational achievements of these boats met the KNRM's re-quirements to a certain level and the crews were generally satisfied with the performance of these boats and certainly fully confident in their safety. However, from a series of full scale experiments con-ducted by the Shiphydromechanics Department of the Delft Univer-sity of Technology (DUT) over the years, it became evident that higher achievements with respect to seakeeping behaviour could be possible.

New demands on comfort and crew composition led the KNRM to initialise a large project in 2009 for the conceptual development, de-sign, engineering and finally construction of a new Search and Res-cue lifeboat for the North Sea, capable of meeting the new require-ments in the ten-twenty years to come. In addition, every way to im-prove on their operability in a seaway would have to be investigated.

W i s h List

To start the process, an intensive questionnaire has been sent around amongst the coxswains and crews of all Search and Rescue boats, including the KNRM'stechnical and supporting staff to ac-quire more knowledge aboutthe possible shortcomings o f t h e exist-ing fleet and the wish list for the future design. In short, the most im-portant design objectives f o r t h e new designs became:

• length around 20 metres over all; • no greater draftthan 1.10 metres; • maximum attainable speed of 35 knots; • range at full speed of circa 600 miles;

• crew of six, seated in the wheelhouse (maximum suggested ca-pacity of rescued persons on board circa 1201);

Figure I. The Arie Visser class.

• two engines with water jets in two separate engine rooms; • noise levels in the wheelhouse not above 70 dBa (present 92

dBal);

• fully self-righting over 180 degrees of heel;

• improved seakeeping performance in head and bow quartering waves with higher sustainable speed;

• at least a similar performance to the existing boats in large and steep stern quartering and following waves (that is, broaching and bow diving), preferably with increased course keeping capa-bilities at high speed; and

• good manoeuvrability at both low and high speeds, also in large waves.

With these design objectives now available, a design team was composed consisting o f t h e Hydrodynamics Department ofthe OUT, the High Speed Craft (HSC) Department of Damen Shipyards and the designers ofthe existing boats, De Vries Lentsch Design Office. This team, with the assistance o f t h e KNRM, took up the task to design the new boat. Recent developments in the hull form design of fast ships were introduced and considered in combination with fixed and moveable appendages. New calculations and experimental techniques were used to be able to predict and compare the hydro-dynamic behaviour of the various design variations.

The Designs

The principal decision aboutthe design procedure w a s t e make at least two full design alternatives to the existing Arie Visser and to compare these alternatives in their behaviour in both calm water and waves. In this way, the Arie Visser, of which very much full scale data obtained during many tests at sea were available, served as the "benchmark" for the evaluation o f t h e merits or shortcomings o f t h e other designs.

A design objective was to investigate the possible application of the Enlarged Ship Concept (ESC) and the Axe Bow Concept (ABC) in the new design. The application o f t h e ABC has been proven very suc-cessful for improving the operability in a seaway with fast patrol boats and Fast Crew Suppliers over the last decade, but these were generally bigger ships (35-55 metres Loa) and the Search and Res-cue boats o f t h e KNRM must be capable of dealing with rougher conditions such as breaking waves.

The development o f t h e ESC and ABC have been adequately de-scribed in various earlier publications by the author, amongst others Ref [1] and [2]. The ESC and ABC development were based on the observation made during numerous full scale measurements on-board fast patrol boats thatthe speed reduction sailing in waves (and so loss of operability) was for 85 per cent voluntary, that is, ap-plied by the crew. In addition, it was shown from these results that this voluntary speed reduction was primarily provoked by the occur-rence of rarely occurring events, for instance in vertical accelera-tions (high slamming) irrespective o f t h e significant (or "average") value of the vertical accelerations. Yet in the design evaluations made for comparing fast ships' designs, these significant values were often used as the basis of the operability limiting criteria.

Scheepsontwerp

To illustrate this, figure 2 is presented. Here, in the distribution ofthe peaks in a time trace of vertical accelerations measured on board a fast ship is presented. On the horizontal axis, the percentage ofthe total peaks in that particular time trace of the vertical acceleration that exceeds a certain value (on the vertical axis) is given. What really counts now for a good operability of the ship in a sea-way is the right hand corner of this distribution, in other words, the (large) magnitude o f t h e rarely occurring events. These should be lowered as much as possible and in that respect, the "black" boat behaves significantly better than the " r e d " boat, even though at the "significant" level (at roughly thirteen per cent probability of ex-ceedance) the black boat is somewhat worse.

Along these lines of thought, the ESC and ABC have been developed and with the aid o f t h e developed mathematical model, a hull shape could be "designed" that meets these requirements.

Combining E S C and A B C in a Lifeboat

The ESC aims at lengthening the hull substantially (25 or 50 per cent) without any change in the craft's functionality, speed and beam. This turned outto have a significant effect on the operability in a seaway (35 to 65 per cent better) without a major effect on the building cost (+3 to -1-6 per cent). As a benchmark, the StanPatrol 2600 from Damen Shipyards was used and the plans o f t h e Enlarged Concepts are shown in figure 3.

The results of this study are also summarised in figure 3, in which the length, building costs, operational costs, transport efficiency and operability on the North Sea are compared with the base boat as benchmark (that is, 100 per cent).

From this, the benefits o f t h e ESC became obvious. Since in particu-lar atthe fore ship void space is being created, extra space became available to shape the bow sections in such a way that slamming can be reduced to a minimum. This led to the ABC, in which a very deep fore foot with sections without flair combined with an in-creased sheer forwards and a downwards sloping centreline were

Vertical acceleration levels

100

50 2 0 10 5 2 1 .5 .2 .1

Probability of Exceedance [%]

Figure 2. Typical distribution plot for vertical accelerations.

Figure 3. The Base Boat and the ESC as used in Ref [2] and the comparison of operability, et cetera.

introduced. A t y p i c a l lines plan ofthe ABC is presented in figure 4. From experience gained over the last decade with ships built ac-cording to the ESC and ABC, the positive effect of lengthening the ship, increasing the Length to Beam (L/B) ratio and the Length Dis-placement Ratio (L/A"') combined with significantly increasing the deadrise o f t h e bow sections and reducing the bow flair on seakeep-ing performance has been shown. So it was decided to apply these new insights in two respective steps in the new design and to inves-tigate the effects on performance. The full shape of the Axe Bow, in other words, with the downward slope in the forward contour, could not be applied for the SAR design, because these boats often oper-ate at very shallow areas (and even go aground) and so the draft re-striction was very stringent. The increase in the freeboard height forward and the reduction in bow flare, howevBr, could be applied. The main dimensions o f t h e new design f o r t h e KNRM were more or less stipulated by the set of design objectives, so the most impor-tant considerations were the hull shape and in particular the bow

Scheepsontwerp

Figure 4. Typical iiuii siiape of an ABC.

shape of the new designs. From the existing design, it was l<nown that the relatively full bow sections introduced violent motions and high vertical accelerations in head and bow quartering waves, which usually led to a significant voluntary speed reduction by the crew in anything above 2.0 metres significant wave height. On the other hand, this full bow shape combined with a significant "tube" guaranteed sufficient reserve buoyancy to prevent bow diving in high and steep following waves.

Concept 1 and 2

So two alternatives to the base boat, the Arie Visser, arose: Concept 1 (C 1), with a sharper bow and deeper fore foot, but only modified modestly (this design was therefore nicknamed Evolution), and Con-cept 2 (C 2), with the Axe Bow philosophy applied, but without the negative contour forward (nicknamed Revolution). Both the C 1 and C 2 design had an increased length (ESC) to improve their L/B and L/A"l Another important consideration was the application of a "tube", so typical f o r t h e RIB concept. A careful weighing o f t h e pros and cons was carried out. Every now and then, structural problems with the tubes arose, in particular with respect to wear and tear, but also with respect to the connection to the rigid structure. Fora SAR boat coming alongside other vessels, often the advantage of having a

fender all around is clear. However, from a hydrodynamical point of view, the benefit of a tube is not so obvious. The blunt intersection between the underside of the tube and the hull may generate high impulsive hydrodynamic forces when the ship is performing large relative motions at high speed in waves. Furthermore, from a point of view of wave excited forces, the influence is actually disadvanta-geous, in particular atthe bow. The influence on the static stability of the tube at larger angles of heel (and pitch) is obvious, but it is not necessary to derive the desired GZ curves through the use of the tube and the reserve buoyancy can also be generated in other ways. Therefore, it was decided to minimise the size and volume of the tube as much as possible and to do so particularly in the for-ward third part ofthe hull. The tube was replaced by a so called "D fender" rigidly attached to a bulwark. This created considerable gain in deck area, which made a wider wheelhouse possible. The reserve buoyancy was created (as is the design practice in the ABC) through significantly increasing the freeboard forward. The weight distribution of the ship and the transverse moment of in-ertia of the water plane area and beam were chosen carefully to achieve a minimum value o f t h e static GM value of at least 1.75 me-tres at zero speed. On the other end, it should not be too large to prevent violent roll motions in waves.

An important aspect for the safety of life boats is the Ultimate Stabil-ity, that is, the stability at extreme values of heeling angle and their capability to recover from a full 180 degrees capsize. In first in-stance, this is driven by the boat's position ofthe centre of gravity and the shape and volume of the superstructure. Strict criteria are not available forthe values for GZ at 180 degrees of heel, but care

Figure 5. Stability curves over 180 degrees ofthe various designs. Figure 6. lines plan and rendenng ofC I.

Scheepsontwerp

-

-

Overall length Loa [m] 20.45 Overall length Loa [m] 21

Overall breadth Boa [m] 6.25 Overall breadth Boa [m] 6.35

Draft T [m] 1.14 Draft T [m] 1.17

Weight W [ton] 38.7 Weight W [ton] 39.9

Longitudinal centre of gravity LcG [m] 6.66 Longitudinal centre of gravity LcG [m] 6.891

Wetted area with zero speed S [m'^2] 72.73 Wetted area with zero speed S [m'^2] 78.57

Metacentre height GM [m] 1.82 Metacentre height GM [ml 1.46

Main dimensions of tiie two concepts.

should be taken to make these not too large because the motion (the re-righting roll motion) can become very violent. Over the years, the Arie Visser survived various 180 degrees knock downs in severe waves, so here GZ values were considered to be appropriate and taken as the ones for the others to meet. The initial stability of C 2 was considered too low and has been increased in the development ofthe final design, that is Concept 3 (C 3, not presented here). Various modifications to the designs were carried out during the

proc-ess using hydrostatic calculations, resistance calculations and mo-tions prediction analyses by using the non-linear time domain motion prediction programme Fastship as described in Reference [1] and [2]. All these considerations (and of course many more) led to the final development of the lines plans o f t h e new designs C 1 and C 2 re-spectively. The lines plans and a rendering o f t h e two designs are presented in the figures 6 and 7. The main dimensions are present-ed In table 2.

The construction material of the boats is aluminium alloy f o r t h e hulls and GRP f o r t h e wheelhouse. The increase in the overall weight that becomes apparent from the comparison of the above values with those o f t h e Arie Visser, as presented in table 1, can be largely attributed to the considerable amount of sound insulation that had to be applied in the new designs to reduce the noise levels to the desired level, which in its turn led to higher resistance, heavi-er engines, biggheavi-er watheavi-er jets and more fuel. This is the well-known downwards spiral!

References

1. Keuning, J.A., Pinkster, J . , Toxopeus, S. (2001). "The effect of bow shape on the sea keeping performance of a fast mono-hull", 11th FAST Conference, Southampton, UK.

2. Keuning, J.A. (2006). "Grinding the Bow", International Ship-building Progress ISP Volume 53, Number 4, IDS Press, ISSN: 0020-868X.

3. Ooms, J. & Keuning J.A. (1997). "Comparative full scale trials of two fast rescue vessels". International Conference SURV 4, Gothenburg, Sweden.

4. FAST Project. "Seakeeping Model tests for two patrol ves-sels", Marin 19112-1-SMB, Wageningen, Netherlands.

A c k n o w l e d g e m e n t

The author wishes to thank Damen Shipyards for its willingness to allow publication of part of the data and results of this project. Figure 7. Lines pian and rendering o f C 2

Bezoek ook onze website:

www.swzonline.nl

Inhoudsopgave

Kennisdelta: online maritieme kennis

vinden en delen

Nederland beschikt over een zeer complete maritieme cluster met unieke kennis en ervaring. Deze kennis wordt onder meer ontwikkeld door bedrijven, onder-zoeksinstellingen en universiteiten en is vaak ook voor een breder publiek be-schikbaar. Toch is deze kennis en informatie vaak lastig en/of verspreid toegan-kelijk. Daarom hebben diverse maritieme kennispartners besloten Kennisdelta op te richten.

16

Special Marine Engineering

For "complex specials", the design ofthe com-plex, often mission related systems dictates what the ultimate operational effectiveness will be. So system engineering and systems inte-gration take centre stage and marine engineer-ing becomes the drivengineer-ing force o f t h e design. But what is driving marine engineering? This special hopes to answer this question and will give some examples of innovative engineering.

42

Design of the KNRM Lifeboat NH 1816 (2)

The Royal Netherlands Sea Rescue Institution (KNRM) exploits a fleet of lifeboats around the North Sea coast ofthe Netherlands. The majority of this

fleet consists of RIBs. The largest vessels are from the so-called "Arie Visser" class with a length of around 18.5 metres and a maximum speed of 35 knots. These are all weather boats and fully self-righting. As this vessel type still had room for improvement, the . KNRM set outto create a new and better

lifeboat, the NH 1816.

Verder in dit nummer

2

Nieuws

4

IVlaritieme markt

6

Maand maritiem

13

Voor u gelezen

16

W h a t Is Driving M a r i n e

Engineering?

17

Fuels and Emissions

20

Diesel and Gas Engines

24

Auxiliary Systems

26

Propulsion and Electric

Power Generation

Systems

29

CNG-hybride v o o r t s t u w i n g

voor veerboot naar Texel

Jaargang 135 e juni 2014

34

Showers for Exhaust

Gases

36

Designing DC Grid

Systems in Compliance

w i t h Solas and Class

48

Digitale k w a l i t e i t s c o n t r o l e

met de t a b l e t

51

Nieuwe uitgaven

52

Mars Report

54

V e r e n i g i n g s n i e u w s

Omslag: De Hr.Ms. Holland is een Ocean Patrol Vessel metiiybride voortstuwing {foto Damen Sclielde Naval Shipbuilding).

Ontwikkelingen in

scheepsinstallaties

lets meer dan een jaar geleden, in februari 2013, besteedden we in ons blad aandacht aan elektrische installaties en automatisering aan boord van schepen. In het huidige num-mer nemen we scheepsinstallaties nogmaals onder de loep. Behalve dat er op dat gebied interessante technische ontwikkelingen zijn, is er ook maatschappelijk gezien aandacht voor het effect van scheepvaart op de vervui-ling van lucht in kustgebieden. Al in 2007 ver-scheen een rapport van de Wereldgezond-heidsorganisatie (WHO) waarin werd becijferd dat langdurige blootstelling aan fijnstof en stikstofoxiden (NO^) ten gevolge van scheep-vaart een grote belasting op de gezondheid van kustbewoners is. Volgens dat rapport zou-den hierdoor wereldwijd per jaar 60.000 pre-mature sterfgevallen door hart- en longziek-ten te betreuren zijn. In IMO-verband wordt dan ook gewerkt aan strenge milieuwetgeving in dichtbevolkte kustwateren (EGAs) en ver-mindering van uitstoot, waarbij nieuwe sche-pen moeten voldoen aan de Energy Efficiency Design Index (EEDI). Daarnaast is besparing op brandstofkosten, door verbetering van het voortstuwingsrendement of door de toepas-sing van bijvoorbeeld LNG, bij de huidige hoge olieprijzen voor reders van essentieel belang voor hun bedrijfsvoering. Alle reden dus een special over deze onderwerpen op te zetten. De redactie is zeer verheugd dat de staf van de sectie Maritieme Werktuigkunde van de TU Delft bereid was een aantal aspecten van scheepsinstallaties toe te lichten. De aanpak is iets fundamenteler van aard dan we nor-maal gesproken in ons blad gewend zijn; de teksten zouden niet misstaan in een college-dictaat, maar dat maakt het er niet minder in-teressant om, in tegendeel.

Uiteraard besteden we ook aandacht aan en-kele praktische toepassingen. Het betreft de ervaring met scrubbers om zwaveluitstootte minimaliseren, de toepassing en distributie van gelijkstroom in plaats van w i s s e l -stroom en het ontwerp van een hy-bride voortstuwingssysteem voor de nieuwe veerboot tussen Den Helder en Texel. En ook in komen-de nummers van SWZ wordt onge-twijfeld meer aandacht aan scheepsinstallaties besteed.

Hotze Boonstra, tioofdredacteur

Eventually, the NH WIS was based on the Concept 3 design (picture Flying Focus).

The Royal Netherlands Sea Rescue Institution (KNRM) exploits a fleet of lifeboats around the

North Sea coast of the Netherlands. The majority of this fleet consists of RIBs. The largest vessels

are from the so-called "Arie Visser" class with a length of around 18.5 metres and a maximum

speed of 35 knots. These are all weather boats and fully self-righting. As this vessel type still had

room for improvement, the KNRM set out to create a new and better lifeboat, the NH 1816.

This article has been divided into two parts. This is the second part. The first part was published in SWZ Maritime's May issue and discussed the creation of two concepts and how they differ from the benchmark, the existing KNRM lifeboat of the Arie Visser class. This second part continues with the evaluations of the designs.

In first instance, the evaluation o f t h e designs has been carried out on a number of different aspects, that is, the (ultimate) stability, the calm water performance, the behaviour in head waves under more or less "usual" working conditions and the behaviour in large fol-lowing and stern quartering waves with an emphasis on a possible tendency towards broaching. The principal aim o f t h e evaluation w a s t e discover if the new designs could yield a significant

Lex Keuning is universitair lioor'ddocent iivdromeclianica bij de opleiding Maritieme Techniek aan deTU Delft.

provement in seakeeping performance under "usual" conditions without losing any performance in large following and stern quar-tering waves. The Arie Visser design was incorporated in all results to serve as the benchmark.

To determine ifthe designs were indeed an improvement, experiments have been carried out. All experiments have been carried out with 1:10 scale models ofthe three designs. This scale has been chosen to suit the capabilities ofthe various experimental facilities used forthe experiments. A part ofthe tests has been carried out in the large tow-ing tank ofthe Ship Hydromechanics Laboratory of the Delft Universi-ty. The tests carried out in Delft were: the calm water resistance tests and the seakeeping tests in head and following waves. The experi-ments in stern quartering waves have been carried out in the Ship motions and Manoeuvring Basin (SMB) of Marin in Wageningen. During the Delft tests, the models were connected to the towing carriage in such a way thatthey were free to heave and pitch, but restrained in all other modes of motion. Therefore, these tests were carried out with constant forward speed.

During the tests in the SMB, completely free sailing models were used with an on board measurement system for all motions. These models were equipped with engines and water jets and autopilots. The inputs f o r t h e autopilots were the yaw, the yaw velocity and the cross track error (sway).

The maximum wave height attainable during the tests both in Delft and in Wageningen was about 4.0 metres at full scale. This was considered not high enough for testing the models in the more ex-treme conditions.

Calm W a t e r R e s i s t a n c e

The resuhs for calm water resistance o f t h e three models are psented in figure 9, as function of the forward speed. From these re-sults it can be seen thatthe Arie Visser comes out oft the water more than Concept 1, and Concept 1 in its turn comes more out off the water than Concept 2. A similar trend can be observed with the running trim. This is in line with expectations, because the Arie Visser's hull is designed to generate more hydrodynamic lift than that of Concept 1, and the hull of Concept 2 is designed to yield the lowest lift.

Overthe entire speed range, the Arie Visser's resistance is consid-erably lowerthan o f t h e othertwo. This can largely be attributed to the considerable difference in displacement and the difference in generated hydrodynamic lift, particularly at the fore part o f t h e ship. The difference between Concept 1 and 2 is dependent on the speed range: below 27 knots Concept 1 performs better than Concept 2. Above that speed, this trend is reversed.

From these results, ft can be concluded, as is generally known of course, that from a calm water resistance point of view, reducing the weight remains important (considering the results for Arie Viss-er) and that over a large speed range. Concept 2 performs better than Concept 1, except f o r t h e highest speed range.

The running trim angle o f t h e Arie Visser and Concept 1 are uncom-fortably high in the hump region. This may in real life even be

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vated by the addition o f t h e trimming effects caused by the water jets, which were not present during the resistance tests. From full scale measurements with the Arie Visser, these trim angles are confirmed. The negative influence of a large running trim on the mo-tions is known, but for the sake of comparison no trim tabs were added to the other designs as well, because the Arie Visser does not have them. In the selected final design ofthe new boat, an ad-justable trim tabs or "interceptor" atthe transom has been added to control the trim angle over a wide range of speeds.

P e r f o r m a n c e in Head W a v e s

During the design process, various motion assessments were per-formed using the Fastship code. Based on these computational re-sults. Concept 2 outperforms the two other models significantly where the vertical accelerations atthe bow and in the wheelhouse are concerned. Nevertheless, it was still decided to carry out these tests with the three models in irregular head waves in order to be able to verify those findings.

For these tests, to limit the amount of experimental work, a selec-tion of three environmental condiselec-tions with corresponding average forward speeds has been made. These combinations of wave cli-mate and speed were known to be more or less realistic for the Arie Visser from full scale measurements.

In particular, the wave Condition 2 is close to an environmental con-dition which is quite often met atthe North Sea by the Search and Rescue boats o f t h e KNRM during their operations.

The need was felt to check on the validity ofthe Fastship simula-tions, because these simulations were extensively used in the

de-sign stage. As a typical result of this validation, the vertical acceler-ations at the bow in wave Condition 2 (both measured and simulated) forthe Arie Visser and Concept 2 are presented in figure 10. The results are plotted as peaks and troughs distributions on an ad-justed horizontal scale, which would yield a straight line for a

Ray-leigh distributed signal. The deviation ofthe actual plot from a straight line is therefore a measure o f t h e non-linear behaviour of the system output signal under consideration because the incoming

figure 9. Calm water resistance results ofthe Arie Visser, Concept I and Concept 2. Jaargang 135 «juni 2014 43

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Figure 10. Az_Bow measured (ieftl and caicuiated (rigtit) for the Arie Visser and Concept 2.

surface waves (the input) are supposed to be Rayleigh distributed. The purple lines in these figures depict the distribution o f t h e peaks o f t h e upward accelerations and the green line the distribution of the peaks (troughs) o f t h e downward accelerations as found in the time trace of the signal under consideration. This is the case with all these kinds of distribution plots presented in the present paper. As can be seen from these distributions, the similarity between the measurements and simulations is satisfactory although the absolute values may differ to some extent. In all cases, however, the trends in the differences in behaviour between the various designs are identical.

Reducing High P e a k s in V e r t i c a l A c c e l e r a t i o n s

It is known from real life experience and full scale measurements that most speed reductions on board fast ships in head and bow quartering waves (and hence the loss of full operability) are volun-tary and imposed by the crew. The driving factor in this speed re-duction is the occurrence of high peaks in the vertical accelerations irrespective the average or significant magnitude otthe accelera-tions atthe time. Minimising these high peaks with a low(er) chance of occurrence, in other words, in the right hand corner of the distri-bution plots, is of prime importance for optimising operability. Therefore,the emphasis in the comparison o f t h e three designs is in that region o f t h e distributions.

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Figure ii. Az_CoG and Az_Bow for the Arie Visser

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F/gure )3. Az^CoG and Az_Bow for Concept2.

To show the differences in behaviour in that respect between the three designs in the figures 11,12 and 13, distributions o f t h e verti-cal accelerations in the CoG (close to the wheelhouse) and atthe

bow (atten per cent of Loa aft o f t h e stem) are presented. The re-sults f o r t h e other conditions showed a similartendency. From all these results it became obvious that Concept 2 outperforms the oth-er two designs to a large degree.

Behaviour in Following W a v e s

To check on the possible tendency to bow diving and compare the designs on this aspect, tests in high following waves were car-ried out in Delft. The conditions were chosen such that two situa-tions occured: one in which the ship was slowly overtaken by the wave and one in which the ship was slowly overtaking the wave. These tests were carried out with a constant forward speed. The speed during the tests was chosen at 18 and 25 knots respec-tively. The waves generated were a so called "bi-chromatic wave train". By generating two regular waves with a small difference in frequency, the amplitude o f t h e resulting wave is slowly varying in time overthe test run.

The capabilities o f t h e wave generator to generate the maximum wave height possible, determined the selected frequencies. The maximum wave height encountered was roughly 4.0 metres at full

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tigme 14. Results of stern quartering waves tests in Marin's SMB; Test 6 Arie Visser, Test 14 Concept I and Test 22 Concept 2.

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Figure 15. ne Arie Visser (ieftl and Concept! (NH I8i6l in an extreme tiead wave.

scale, this being the maximum capability of the wave generator at this scale and this wave length. The wave length was between 75 and 90 metres at full scale.

In the actual realisation of the waves, care was taken t h a t t h e high-est wave would indeed be met during the runs. This procedure elim-inated the otherwise inevitable necessity of carrying out an extreme large number of runs to gain sufficient statistically worthy informa-tion when carrying out the tests in a real spectrum due to the very low frequency of encounter between the ship and the waves. Care was taken again that all models were tested in exactly the same wave realisations. So for the sake of comparison, these test proce-dures proved very feasible and useful.

Presentation o f t h e results of these tests is rather cumbersome, be-cause sensible statistical elaboration o f t h e signals is not possible due to the limited amount of fluctuations and tests carried out. The most important output is the video taken from all runs. On these vid-eos, it is evidentthat not one o f t h e models had anytendency to bow diving.

Free Sailing Models in Stern Quartering W a v e s

Additional tests have been carried out with free "sailing" models in the SMB of Marin at Wageningen. Forthese tests, Marin had devel-oped a new measurement set-up allowingthe models to broach without being restrained by the measurement set-up. This implied that there was no connection between the model and the towing carriage, which followed the model through the tank. The models were under control of an autopilot and the motions were measured using an inertia measurement system. During these tests, the worst possible environmental conditions, which could be realised in this specific facility, with respect to the possibility of broaching were also sought.

This meant significant wave heights up to 3.5 metres, peak periods Tp of the Jonswap spectrum of 7.0 seconds and a forward speed (average) around 20 knots. The wave incidence angles were 0 de-grees (following) and 45 dede-grees (stern quartering) respectively. In each condition, at least fifteen different runs have been made, for all models in exactly the same part ofthe spectrum realisation. For these free sailing tests, the models Concept 1 and Concept 2 were equipped with two skegs aft to increase their directional stability.

Forthe Arie Visser design, these were not applied because all ex-cept one of the existing Arie Visser boats sail without them and for the benchmark role, it was considered sensible to keep as close to real life experience as possible.

Atypical result is presented in figure 14 in which the distribution of the roll and yaw motion are presented for the tests with 045 degrees wave incidence (stern quartering). It should be noted thatthe number of variations in these combined runs is still rather limited due to the low frequency of encounter between model and waves. As can be seen from these results, the Arie Visser rolls up to 10 de-grees and Concept 1 slightly more. The Concept 2 model rolls consid-erably more, up to 18 degrees. A similar difference can be seen for yaw. These differences are attributed to the difference in transverse stability: the GM values of the Concept 2 model were some twenty per cent lowerthan those ofthe other models. Through the coupling between roll and yaw, this contributes to the increased yaw motions. The achieved GM value for Concept3 was actually below the de-sign criteria set a t t h e beginning o f t h e project, but it proved difficult to achieve in the design process. In the development of Concept 3 (the final design) this has been corrected through amongst others the introduction of a GRP wheelhouse. The positive effect on the course stability o f t h e skegs atthe aft ship explains the difference in yaw between Arie Visser and Concept 1.

The maximum values of both roll and yaw are still relatively small considering the severe conditions the models were sailing in and it should be noted that from the visual observations and the videos, nothing like a broach was observed during any of these tests. The only model that actually came close to a broach twice was the Arie Visser, but unfortunately, this happened during a breakdown ofthe on board measurement system, so these are not included in the results.

A Third N e w Design

Based on these results and the requirements of the coxswains of the KNRM, a slightly different design was developed along the lines of Concept 2. Originally, the coxswains wanted a larger ship then the Arie Visser, but laterthat changed. Because most of their mis-sions nowadays were involving yachts, the coxswains wanted in

References

1. Keuning, J.A., Pinkster, J., Toxopeus, S. (2001). "The effect of bow shape on the sea keeping performance of a fast mono-hull", 11th FAST Conference, Southampton, UK.

2. Keuning, J.A. (2006). "Grinding the Bow", International Ship-building Progress ISP Volume 53, Number 4, IDS Press, ISSN: 0020-868X.

3. Ooms, J. & Keuning J.A. (1997). "Comparative full scale trials of two fast rescue vessels". International Conference SURV 4, Gothenburg, Sweden.

4. FAST Project. "Seakeeping Model tests for two patrol ves-sels", Marin 19112-1-SMB, Wageningen, Netherlands.

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the end not a longer, but a boat of a similar size o f t h e Arie Visser. Therefore, the new design. Concept 3, was slightly smaller, that Is, 1.5 metres, was considerably lighter, twenty per cent less weight made possible by the introduction of a GRP superstructure, it has smaller and lighter engines and carries less fuel. This became pos-sible through a change in the design specifications aimed at reduc-ing the weight. Originally, the high speed and the long range called for heavy engines and tons of fuel. By reducing the overall weight, smaller and lighter engines became possible consuming less fuel. In addition, the desired range was reduced.

All these changes resulted in a 9 tons smaller displacement and a similar GM value compared to the Arie Visser class. This new de-sign was called Concept 3 and most o f t h e tests as carried out pre-viously were with this design. These results showed improved val-ues in all motions and behaviours when compared to Concept 2. So for the final tests, this became the desired model and all further tests and comparisons were hnally made between the Arie Visser and Concepts.

T e s t s in More Extreme W a v e s

Next in the design process, a series of tests were carried out in the Delft towing tank in more extreme waves. The aim of these tests was to compare the behaviour of the Arie Visser and Concept 3 in head waves for bow submergence and in following waves for broaching. Hereto a special waves train was generated in the towing tank which resulted in a very short series of extreme breaking waves at one particular place in the towing tank and at one particular instant. Using this method, it was possible to generate extreme wave heights up to 8 metres at full scale. The models were remotely controlled and fully free sailing and the crux o f t h e experiments w a s t e be with the models at speed atthe right time atthe right place in the tank. When successful, this resulted in an extreme situation for the de-signs. These tests were carried out a considerable number of times to account for errors in the timing. During the tests, motions and ac-celerations were measured and video recordings were made. Of some of these tests, video "stills" are presented in the figures 15 and 16, which show the Arie Visser and Concepts (the later NH 1816) in head waves and following waves respectively. The tests in head waves showed that northe Arie Visser, nor Concept 3 ever dug its bow into the waves. In addition, the combined heave and pitch motion at the bow were considerably more modest with Con-cept 3 than for the Arie Visser. Furthermore, the surge motions were considerably less. This improved behaviour of Concept 3 was cer-tainly true f o r t h e vertical accelerations atthe bow. It is also worth noting that in eighty per cent of the tests in following waves, the Arie Visser made a broach while Concept 3 never broached.

Figure 16. Tiie Arie Visser and Concept 3 in a foilowing breaking wave.

derto make this design as course stable as possible in the following waves condition at high speed and as manoeuvrable as possible in the head wave condition, the skegs at the aft ship were made re-tractable. The coxswain can decide to have them fully retracted, half way down orfully lowered depending on the conditions. In combina-tion with the controllable interceptors atthe transom (control of run-ning trim), this yields extensive control on the boat's manoeuvring characteristics. So turning circles and computer controlled zig-zag tests were performed with the Arie Visser and Concept 3. With the Concepts design, these tests were repeated with skegs up and down and with various positions ofthe interceptors atthe transom, resulting in a range of running trim angles between 2 and 5 degrees. The results of these tests indeed showed that Concepts has a far better manoeuvrability (skegs up and interceptor down) than the Arie Visser and on the other hand, is much more course stable than the Arie Visser with the skegs down.

C o n c l u s i o n s

The result of this project is that a rather sensible and feasible meth-od has been found to analyse and compare the performance of rela-tively small and fast ships in average and more extreme conditions. It is obvious from the results that the Concept 3 design is the best for application as Search and Rescue boat, because this hull shape has a much better performance in head and bow quartering seas without losing any performance in following and stern quartering seas. The new design Concept 3 has been found superiorto the Arie Visser and Concept 1 and 2 in all aspects.

Now that the prototype has been built and delivered to the owners, full scale tests are envisaged in the near future to validate the re-sults. These tests will be focussed on the motions in waves and the manoeuvrability, as in the design process, and will be conducted as "side by side" measurements with the NH 1816 and the Arie Visser.

Manoeuvring

Finally, a series of manoeuvring tests were carried out with the self sailing models ofthe ArieVisser and Concepts. These were aimed at comparing the manoeuvrability o f t h e designs. This was of inter-est for Concepts (the eventual NH 1816) in particular, because, in

or-Acl<nowledgement

The author wishes to thank Damen Shipyards for its willingness to allow publication of part o f t h e data and results of this project.