power estimation

[sobo]

hi there

I got a question to ask regarding my project. i need to determine speed of a boat where the total resistance and the type of engine used are known. This boat is using the outboard engine which the detail as in the link below

http://www.mercurymarine.com/engines...51.72120954655

For your information, the only detail that i have currently is the RPM of the engine that they used during voyage. i need to find the speed of that boat at that particular RPM.

Once i obtain the effective power of that boat, i can determine the require speed in the maxsurf software.

my question is,
1) how can i obtain the effective power when i don't even know the efficiency of the shaft,brake,etc..?
2) as stated in the engine specification, the horsepower is 50. Does that mean 50 hp is engine power?or brake power?

I do hope anyone can help me with this kind of problem. Thank you.
will appreciate your kindness

[terhohalme]

In estimations, you can use 50 % of installed power as an effective power.

[sobo]

thanks for d answer..
can you help me to confirm that the installed power is 50 hp based on the link below?

http://www.mercurymarine.com/engines...51.72120954655

i am not sure whether i am doing it correctly or not.
thank you

[sobo]

and 1 more thing
from the equation P = R x V
effective power means the maximum speed that the boat can run for that specific power right?

how can i determine the speed that they used at certain RPM of the engine which is specified?

[terhohalme]

Effective power is what is needed to tow the boat at specific speed. Resistance will also chance by speed. How do you know the total resistance? Savitsky?

For the Power/RPM you need the engine curves.

Somehow your thinking is too complicated for me and my English...

[gonzo]

Outboards are rated at propeller HP. You don't need to do any calculations for transmission loss, etc.

[sobo]

thanks for the info sir
really appreciate your help..

thank you

[Booker]

Originally Posted by gonzo

Outboards are rated at propeller HP. You don't need to do any calculations for transmission loss, etc.

I'm interested in the reference you have for this statement.

Thanks,

MPB

[sobo]

Thanks for your advise.really appreciate it.