Re-profiling a bronze propeller

[Nigel-in-Oxford]

Just swapped out my old yanmar and installed a new beta. But cannot rev more than 1500 rpm.
The boat yard suggested having the prop re-profiled it needs about 3" of the pitch.
Is that amount of profiling possible and if so any one know of a firm that will do it?

 

[PaulMcC]

No idea but I can recommend a company called steel developments for all things prop related. (They specialise in steel props as you might expect from the name but do bronze as well.)

PS - Just a satisfied customer

 

[mtb]

what size prop have you got fitted ?

cheers
mick

 

[robmcg]

Give T Norris a ring, they repitched our prop a few years back.
020 8560 3453

http://www.tnorrismarine.co.uk/

Rob

 

[Tranona]

Just swapped out my old yanmar and installed a new beta. But cannot rev more than 1500 rpm.
The boat yard suggested having the prop re-profiled it needs about 3" of the pitch.
Is that amount of profiling possible and if so any one know of a firm that will do it?

Adding 3" of pitch will do exactly the opposite of what you want to do. Typically each inch of pitch adds about 250-300 rpm. So you want a finer pitch or a smaller diameter to bring your revs up. Whoever installed your Beta should have worked out the size of prop required for your combination of boat/engine/reduction gear. You can get a good estimate of what is required by feeding your boat's data into the Propcalc programme on www.castlemarine.co.uk You will almost certainly need a new propeller so get a quote from a prop supplier such as Norris or Sillette giving them the same data. Alternatively ask Beta for a recommendation.

Running your engine on load at 1500 rpm will not do it any good and not give you the speed you require.

 

[Nigel-in-Oxford]

Thanks for the feed back. I will give Norris a ring. The boat is still in the water but the prop was always wrong. It was the wrong hand for the yanmar (correct for the beta) so I ran in reverse for the last year. The pitch was way too much for the 10hp yanmar, I was hoping it would be ok for the 20hp beta, but not so. A previous owner must have replaced the original prop with one they found laying around in the yard.

 

[Spyro]

Adding 3" of pitch will do exactly the opposite of what you want to do. Typically each inch of pitch adds about 250-300 rpm. So you want a finer pitch or a smaller diameter to bring your revs up. Whoever installed your Beta should have worked out the size of prop required for your combination of boat/engine/reduction gear. You can get a good estimate of what is required by feeding your boat's data into the Propcalc programme on www.castlemarine.co.uk You will almost certainly need a new propeller so get a quote from a prop supplier such as Norris or Sillette giving them the same data. Alternatively ask Beta for a recommendation.

Running your engine on load at 1500 rpm will not do it any good and not give you the speed you require.

Does he mean 3 inches off the pitch?

 

[bignick]

Adding 3" of pitch will do exactly the opposite of what you want to do. Typically each inch of pitch adds about 250-300 rpm. So you want a finer pitch or a smaller diameter to bring your revs up. Whoever installed your Beta should have worked out the size of prop required for your combination of boat/engine/reduction gear. You can get a good estimate of what is required by feeding your boat's data into the Propcalc programme on www.castlemarine.co.uk You will almost certainly need a new propeller so get a quote from a prop supplier such as Norris or Sillette giving them the same data. Alternatively ask Beta for a recommendation.

Running your engine on load at 1500 rpm will not do it any good and not give you the speed you require.

I think he means 3" off the pitch, which will do exactly as you suggest and increase the rpm to somewhere in the right range.
3" does sound a lot to repitch an existing prop though 1 - 1.5" max is more normal for an operation like that I believe, in which case a new prop will be required. It would be a shame to hamper a nice new engine, and possibly coke it all up due to labouring at too low rpm.
Nick

 

[NormanS]

I think he means 3" off the pitch, which will do exactly as you suggest and increase the rpm to somewhere in the right range.
3" does sound a lot to repitch an existing prop though 1 - 1.5" max is more normal for an operation like that I believe, in which case a new prop will be required. It would be a shame to hamper a nice new engine, and possibly coke it all up due to labouring at too low rpm.
Nick

The confusion is something of a pedant's delight. A demonstration of how the meaning of something is totally destroyed when the OP used "of", when he actually meant "off".

 

[Tranona]

Thanks for the feed back. I will give Norris a ring. The boat is still in the water but the prop was always wrong. It was the wrong hand for the yanmar (correct for the beta) so I ran in reverse for the last year. The pitch was way too much for the 10hp yanmar, I was hoping it would be ok for the 20hp beta, but not so. A previous owner must have replaced the original prop with one they found laying around in the yard.

Sorry I misunderstood. 3" less pitch may not be possible with the prop you have. For motoring peerformance best to aim for the largest diameter possible in the space you have, but that is constrained by tip clearance - min of 15% of prop diameter and to an extent the reduction ratio of the gearbox which determines the shaft speed. With a 2:1 reduction you would be looking at a 13 or 14" prop, but with a 2.6:1 you could go up to 15" diameter.