S.P. Holes in Marine Propeller Blades

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3.S.R.A. Translation

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"S.P. Holes in Marine Propeller Blades.'t

-).

T. OkiGa Ko'oe Chemical industries.

P. Takikawa Superior Maritime Court.

Nautical Society of Japan. 16 (1961) p.47 (Dee)

:t is conon kroíledge that, in a single-screw steam ssel, when engines are stopped and the vessel moves ahead under her own way, steerage i lost to a great extent. ..Lfl

recent years this is beccing rore noticea'ole due to the struction o± very large vessels with proportionally

cverfui enzìnes.

s shown in Pig.1if.:propeilers are stcoed while he

shifl is.

-:.cer way, a scrc:- crag current

ica'ted 'oy the arrows, buiids

out the shipts stern and on

rear surfaces of the proreller -.ces. This oncses and there-_ore weakens tne current o: water

ìo;;ing towards the stern hetv.een

'olades of the idling rope1ler.

-.aref ore, even if full rudder is

applied to alter course in these conditions, the variaion

. Water pressure on each side of the rudder, which occurs

-.e the propeller is rotating u:-er power, does not take

-?;e to such a great extent and nanoeuverability is greatly

T

Pig.1.

Stern, Propeller

and Hull

S.' :' '

F-4 «

(7)

_2_

-t is common mracice to manoeuvre a ship while the propeller

s idling when entering or leaving port (it is most common .hile entering) and the reducing cf steerage at such tines

ees ship handling very tricky and is a most undesirable :hencmenon when it comes to ships of larger tonnage, where the condition is even more marked. It is therefore essential

hat every practical step should be taken to test any method which shows possibilities of reducing this condition.

The efficiency of forward movement is high about the

tips of the blades and is lower about the centre of the thst shaft while at the root df the blade, efficiency is extremely

ow.

:t s generally acceted;-that the uroDellers -thrust power

operates in the outer 70v/o of the area Of rotation while in

the centre 30% of the rotation circle thrust power is virtually

nil.

Thus, in order tO improve steerage to some degree, if two rows of holes (H in Pig.2) are made from the base of the blì to a suitable position along the blade (within the limits of

manufacturing

ossibility), the flow

blades combines with the flow of water through the boles, and us încrease the Dresure on the faces of the rudder -to gve increased steerage efficiency.

In such a case, if such holes are drilled in the blades

simply -to improve the water flow, it will be found that the

water pressure in the section of these boles will impede

rotation of he propeller thus reducing force of propulsion.

This calls for

It is feasible that if Fig.2.

Suitable manufacturing processes are carried out,

aking into account the

ano.

L-a o

)--configuration of the holes and their section, and the relationship between the angle of the blade faces and the axis of thrust, these factors can bring about an improvement

in nropulsion efficiency.

2

ectio1 o± Right Eanded Blafe.

In r. 3., L indicates :tìae Dropulsion force of the blade

and the tronulsion force lost due to the rovision of the

holes is indicated by

1a and

Toreover, in consideration of the section o± the holes and the Section (S) of the secondary blade' formed by the

fabrcaton o:

process is carried out ma:ing use of the relative angle between te face of the blade and the axis of thrust, the propulsion

force exerted

_{by Hxa}

That the propulsion force of the en-tire blade te greater than when holes are not applied, is shown in the

ollowing formula.

.13

'

xa ' -a

If the variation between left and right is X

then:-and propulsion force is increased by the value cf X.

That is to say that, by provision of holes and secondary

::olades _{in the propeller blades, not only is steerag-e}

efficiency increased, but there is also a resulting

4

it is conditional that the thickness and width of such

ropeiler blades 'ce in accordance with the existing Ship

Test Regulations. At resent a test nroDeller, with S.?.

rìo.es 1nserao

ifl

On completion, it is intended that the propeller 'ce put to

immed iats test. It is regrettable that, to date, no figures

from such tests are available.

A point which must come _{Fig. 3}

under consideration when Section of base of Right Handed

blades of this design are Biade

to 'ce incorporated into ships under construc-tion

4- 4

ia e re o

inserting holes into the

base o± Drceller blades will be to weaken the blade overall. Further there is the pósslbility

of damage to the blade, due to increase in ionisation _processes in sea water resulting from the intricacy of construction at

the blade base.

With reference to blade strength, it would be relatively simple to increase the thickness of blades to the limits demanded by the regulations, or again to obtain suitable material from the recent marked progress in metal alloy

development, which will meet the strength standards required

by the regulations. Research is also in hand, where an

insulating membrane is fitted over propeller blade surfaces

to nreven-t ionisation acivitv. There should be no nroblem

ln adapting these research methods to practical application at a moderate cost. H .L7. I" -r-

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