Prop Calculations - How accurate?

[WayneS]

Having just upgraded our engine, our next task is to re-prop the boat.

I want to go for a folding prop but am loathe to shed out a whole lot of bucks only to find out that it is not the right one...

An option we have considered is to fit a 2/3 blade fixed and once we are happy with that, convert to folding.

A couple of anomalies that we have,

1. moved up from a 12hp to a 20 hp engine
2. hydraulic drive with 2:1 reduction
3. because of hydraulics we cannot run the engine at more than 3000rpm.
4. Orig setup was wrongly prop'd with a gori 15/11 folding.

Have had a number of people quote and they all seem to come out with the same prop specs.

13x9 3-blade fixed
14x9 2 blade fixed
14x9.5 gori folding
14x8 radice folding

Has anyone got any additional advice for me?
Are there prop dealers out there who will do folders on a sale or return?

cheers

Wayne




<hr width=100% size=1>

 

[steve_cronin]

With so many variables in hull shape, keel design, pitching motion, etc my guesstimation is that to get within +- 15% is the best you will do. That is why Bruntons are so efficient.

Steve Cronin

<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[charles_reed]

Don't know of anyone who lets out folding props on a SOR basis.

However you could fit a fixed prop to check out the calcs, any folding prop is going to be the same od and pitch. Try Lake Engg to see if Les has any 2nd hand props of about the right pitch for sale, he'll probably take it back off you if you buy the final replacement from him.

<hr width=100% size=1>

 

[omega2]

give Paul Williams a ring on 01234 378814, Clements engineering, St Neots Beds. he is primarily a power boat prop man but may be able to assist, if he does he will be spot on.

<hr width=100% size=1>J HAMER