Boat propellors

[jridgeback]

Can someone explain the markings on the propellor on my outboard motor. They are 10 3/4 X 13 5/8. I guess that they are to do with how far it will travel, or how fast, but I'd be grateful for any help

Thanks.

[xrayspecs]

They sound like imperial measurements possibly to do with the thread size and the blade circumference.

[Clanad]

If it were a fixed pitch propeller on a small airplane the first number would be the length and the second would be the pitch... the distance the prop would move with no slippage, in one revolution. Not having a boat, like some people, I don't suppose there is any correlation...

[sddsddean]

Should be the diameter and pitch and as mentioned, looks like its in inches. Try measuring it to check dia. The pitch is the distance the prop would travel in one 360 degree revoulution, which is not so easy to check!

[stanleyman]

I've got several boats ** and marine outboard mechanic certificates from Mercury, Mercruiser, Yamaha and Suzuki etc. This is indeed the diameter and pitch measurements. At a guess I'd say this was around a 40 to 60 hp motor on a planing boat.

The diameter for a given power is larger for a slower heavier boat within the limits of the outboard. This would also have a smaller pitch for the gearing to keep the revs within the powerband. A faster planing boat can have a much larger pitch or higher gearing but it is important to not be too large as it will be difficult to lift the boat onto the plane where power is limited.

[jridgeback]

Thanks all.

Stanleyman, I now understand - I think !!