hull speed power calc

[nautical]

i tried this program

http://www.castlemarine.co.uk/pitch.htm

its giving me bogus results

[RANCHI OTTO]

Displacement at fully loaded ?
Length waterline?
Breadth at waterline?
Max. propeller diameter that you can install (20% clearance btw. prop's tip and hull)

[nautical]

120 tons
30 m
7.6 m
cant fit a big one maybe .5 -.6 m

[Çemberci]

Dear
What type of vessel are you building?
Do you have a plan ?
oktay Çemberci

[nautical]

Its a wooden 30 m cruiser. yes I do have a plan and not for building yet. I hope it will be built oneday.

[RANCHI OTTO]

I've quickly checked the power for the 14 knots speed.

I would suggest 1200 bhp abt.

The propeller diameter is too small, with 30m length vessel the max. diameter would have a diameter of 1.5 m abt.

[Çemberci]

Dear
If you send me your plan -
hull data
engine data
I would calculate hull speed
oktay@cembercidenizcilik.com
oktay cemberci

[RANCHI OTTO]

I've designed fast patrol boat having 26.5m length and prop. diameter of 1400mm with 10° shaft inclination.
The diameter depends on the choosen rpm of the propeller.
Check the resistance before to choose the engines power.

[nautical]

I have done the analysis and acording to this I selected the this engine

http://www.volvo.com/volvopenta/glob...nboard/d9-500/

[RANCHI OTTO]

Is this?

[nautical]

yes these are the details . Dont you think two of these engines would do the job. This is what I asked in the DiselEngine room. When I used one of the spread sheets here it gave me very bogus answer. IT said i will need 2400hp to get a speed of 14 knots.. and i think its way too much

[RANCHI OTTO]

For so heavy vessel, it would be better to reach the speed of 14 knots at 80% of maximum power.

So doing the engines will never be overloaded even with strong fouling or in rough sea.

[nautical]

80 percent of maximum rating of the engine 300 KW 2 of them will give 600 KW

I need 500 kW even if I add a seamargin of 15 percent it will be 588 KW

and an Overall Propulsive coefficient when I did the resistance analysis is taken as 0.6 ( you said .575)

[RANCHI OTTO]

I start with a power of 2 x 600 bhp for reach 14 knots.
Then 600/0.8 = 750 hp (552 kw)

This engine has not enough power, but this is only my opinion.
With such superstructure you has to install a bow thruster and at low speed you will have a lost in power.

[nautical]

ok i get it.. so you are saying you will take 600 instead of 400 hp each ok now i get you .. sorry for the previous comment