Open Water Efficiency

[stalin]

I have optimised the propeller as follows:

Propeller Diameter = 1.1
P/D = 0.75
Pitch = 0.8250
AE/A0 = 1.0328
RPM = 689.43
open water eff = 0.42
cav.number = 0.2857

Vessel particulars:

LWL = 21 M
dISP = 117T

Engine is 1x400 hp @1800 rpm, with gear ratio 2.59. Max diameter of the propeller is 1.1m, according the stern shape. Can anybody confirm that the open water efficiency is reasonable for this size of vessel.

Thanks in advance.

[bmsyachts]

Hi Stalin,

What is the design speed of the boat at which the prop is to be selected?

[conceptia]

also the number of blades...

[stalin]

Sorry for late reply. No.of Blades are 4 & design speed of the vessel is 10 knots.

[conceptia]

hey stalin, the effieciency value is ok. But you can improve it if you want to. I feel the main problem is the space constraint for accomodating propeller, right? In that case, you can ahead wid dis. But also listen what Daiquiri, Leo and others has to say about it.

[bit]

Pitch too high?
D = 1100 mm
P = 711 mm
Ae / Ao = 0.7
z = 4
w = 0.1344
Eta0 = 0.466
T = 31.11 kN
Pe = 195.7 hp
Pb = 415.3 hp
No. Cav. = 0.271
Cavit. = 4.91%
My opinion ...

[bmsyachts]

Your selection is most likely correct, but in terms of efficiency not close to "optimized".

The potential open water efficiency could be as high as 76% but with a much lower prop RPM and much larger diameter (in fact, huge!) Twin screws ease the situation but still very slow RPM and large diameter props to enjoy full potential prop efficiency.

So it's a balancing act with compromises in efficiency (fuel consumption) fighting prop size and space constraints and first cost.

[bit]

Ok.
Is D = 1100mm : stop.
Better not be
Bye