How fast does it need to be to go 10 miles an hour in the water?

Question

i'm going to make a small boat, and i want to know haw fast the prop has to spin (rps) in order to go about 10 - 20 miles and hour, the boat is about 12 feet lenght 2-3 feet width

Answer 1

Need more info!  

Need to know the propeller's  specs....  input them into the formula... and zoom, zoom...

Depending on the country where you live, there may be different coefficients in use. All coefficients used here, are based on the publications of the NACA, which defined the following coefficients:

Thrust                 ==     C_T = T / (rho*n^2*D^4)

Power                ==     C_P = P / (rho*n^3*D^5)

Advance Ratio  ==     v/nD = v/(n*D)

Efficiency           ==     eta = v/(n*D) * C_T / C_P

{ Where  

           v= velocity m/s;

           D =diameter m;

           n =revolutions per second 1/s density of air kg/m³;

           P =power W;

           T =thrust N

}

  

A cinch!  

No really follow the link below...  They acctually know what all this means!  :)

Answer 2

Depends on how large the prop is.. and what pitch it's at. The drag  (hull design) of the boat is also a factor so getting an accurate answer without that info is going to be difficult. Typically a 2-stroke engine will produce about 12,000 RPMs... I'm sure that a 9.9 HP will push a light 12' boat nicely along at 10+ MPH.

Answer 3

Everybody has elements of a correct answer.

>>>Also depends on wind and windage(wind resistance)of the hull.

>>>also depends on amount of chop or waves...a little chop helps the hull break hydraulic surface adhesion....too much chop can slow it down from impacts of oncoming waves.

Answer 4

this will depend on the pitch of the prop, the drag of the hull, and the efficiency of the prop.  Then you will need an appropriate HP.   Goto an outboard motor salesman, someone educated, not just a mouth.  He should be able to match hp, rpm, hull size & shape and props until you have a fair idea of what you need.  Allow for adverse weather.

Answer 5

A prop with a 10" pitch at a 10% slip ratio would have to rotate 19.45 rps to go 10 mph.

Answer 6

Depends on the drag on the hull, pitch of the prop, # of blades on the prop and other factors.

Answer 7

it depends on the weather. Weather or not it goes that fast.