Advice on prop sizing

[Bobc]

Is there anyone on here that can help with this please?

I currently have a 19x14 fixed 3-blade, and wondered how a 21x12 2-blade folder is likely to compare with it power-wise.

I'm kind-of assuming that the 2" bigger diameter with the slightly lower pitch will produce a similar result?

 

[Concerto]

You are best to ask several propeller suppliers as they will give an honest answer, personal opinions from the forum are only worth the paper they are written on (or computer screen).

 

[Moonbeam]

I'd echo Concertos advice...

But at the risk of anything else written here being worthless screen space, I'll outline our experience of changing prop. We had a fixed two blade 15 x 13 which felt under powered. After speaking to a few companies (who will want to know which boat and engine you have as well as the kind of motoring you do) we changed to a two blade 16 x 12 Flexofold. We ending up buying the Flexofold from Darglow Engineering (no connection etc) who were very helpful with their advice and machine matched the new prop to fit our shaft bore/keyway/taper etc.

Even the wife agreed, it was the best money we spent on our boat (and we had already spent a fair bit on upholstery!!) The new prop has given us a knot of extra speed/grunt under power and 1/2 knot faster sailing. We'd do it again if we changed boat.

 

[Bobc]

Thanks for that info Telstarr. The prop I'm looking at is a flexofold (a 2nd hand one). From your experience is appears that the shallower pitch combined with the bigger diameter worked for you, so I might take a punt on it if I can get it at the right price.

Any other feedback welcomed.

 

[RichardS]

There is, I believe, a general understanding that an inch off the pitch approximately equates to an inch on the diameter and vice versa.

Richard

 

[Tranona]

Thanks for that info Telstarr. The prop I'm looking at is a flexofold (a 2nd hand one). From your experience is appears that the shallower pitch combined with the bigger diameter worked for you, so I might take a punt on it if I can get it at the right price.

Any other feedback welcomed.

Give Chris at Darglow a call. He is the UK Flexofold agent and the guru on sizing props. He will almost certainly have your boat on his database and know what works and what does not.

In my experience of Flexofold the best size is not necessarily the same as the fixed. My 33 came with a 16*13, but the Flexofold is 16*11 and is spot on - as Chris said it would be!

 

[Moonbeam]

Thanks for that info Telstarr. The prop I'm looking at is a flexofold (a 2nd hand one). From your experience is appears that the shallower pitch combined with the bigger diameter worked for you, so I might take a punt on it if I can get it at the right price. .

Agree with Tranona about giving Darglow a call. I'm sure they would be happy to advise even though you are looking at buying second hand. If the second hand Flexofold needs machining to fit your shaft/saildrive, then they are the ones to go to.

Interestingly, I got a quote for the new prop direct from Flexofold in Denmark, and also via Darglow here in the UK. Darglow were only £30 more expensive, but it turned out to be a huge saving getting it from Darglow because Flexofold in Denmark were going to send me an 'of the shelf' prop that their records indicated would fit our shaft bore/taper etc. That would have turned out to be the wrong fit. Instead we sent Darglow our old prop and they machined the new one to the exact fit which was quite different to what we would have been sent direct from Denmark.