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Old 28 June 2018, 19:15   #1
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Country: UK - England
Town: Derby, UK
Boat name: Seafire
Make: Almarine
Length: 3m +
Engine: 50hp Yamaha (short)
Join Date: Jun 2017
Posts: 17
Performance Prop Selection

Been working on a slightly daft project for a while and finally ready to start trying to fine tune it.

The boat is a 1970's seafire, 10'6 Deep V Hull, 16" transom with a 50hp yamaha 3cyl with power trim.

Naturally I'm wanting to get it to go as fast as possible, I've always had 50mph in my mind as a nice target...

What sort of propeller should I be looking at for this setup? It currently has a 17" stock yamaha 3 blade on there and it runs well with that, mid 40's (mph) around 5700 rpm, so a little room for manoeuvre.

I've looked at chopper style props but get confused when they go on about boats needing bow lift and this and the other..

In layman's terms, which types of prop would anyone recommend trying on this for the best top speed with reasonable holeshot, it will also be used at sea and for playing around etc..

The engine height is currently setup with the cavitation plate on line with the bottom...

Please see attached images for idea of hull type etc..

Cheers,
Jack



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Old 29 June 2018, 02:09   #2
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Country: UK - Scotland
Town: north ayrshire
Boat name: charlie girl
Make: reiver 3.8/regal3760
Length: 10m +
Engine: 40hp 2st 2x6lp 315
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My first start would be to jack the engine up the transom a little to reduce drag.
1.5-2" is usually doable. See what that does to your rpm and go from there
Just watch out for the water pickup holes staying in the water
Most high performance props like to run high.
Roflhat on the forum often has props for sale as he's always messing with his zapcat he may be able to give some advice on setup etc too
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Old 06 July 2018, 03:13   #3
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Country: UK - Scotland
Town: Isle of Lewis
Boat name: Macleod Special
Make: Ceasar Thundercat
Length: 4m +
Engine: Yamaha 70ces
Join Date: Jul 2010
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RIBase
As Ken said you want to lift the engine up a bit from there, especially if you go for a bigger prop.
For a 50hp an 18p chopper or cleaver will work well on your setup. Depening on your boat weight I'd say 55-60mph should be achievable. You could possibly go to 20p but you'll lose a lot of acceleration.

In theory a chopper will lift the bow and a cleaver will lift the stern, in practice it's hard to notice any difference between the two. At 50 knots on a thundercat the setup and trim is identical for the 2 prop styles.

If you're going to be messing about with engine heights and setup etc. it may be worth getting a jacking plate, either manual or hydraulic
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