Prop resizing

[Roy Smith]

I have a 23" Yamaha pro plus S/S prop and whilst its good when we are i/4 tank and two people it just wont pull the rev on a cruise
the engine should rev to 6250 but we find it hard to get 5500 rpm
full tank and 4 people
My question is, as any one had there prop resized and are happy with it
i think i need to take it down to 21" as the cleaver (i think thats the right term )
is much larger than the standard prop
How much should it cost etc.

[Chris]

Originally Posted by Roy Smith

I have a 23" Yamaha pro plus S/S prop and whilst its good when we are i/4 tank and two people it just wont pull the rev on a cruise
the engine should rev to 6250 but we find it hard to get 5500 rpm
full tank and 4 people
My question is, as any one had there prop resized and are happy with it
i think i need to take it down to 21" as the cleaver (i think thats the right term )
is much larger than the standard prop
How much should it cost etc.

Roy,

I have tried two prop specialists Steel Developments (rude, unhelpful and overpriced)

And propeller solutions http://www.propellersolutions.co.uk

Prop solutions were very helpful and did an excellent job on a repair that I had done.

You can reduce pitch and the price would be around £60 to have it done however I think the most you can change by is about 1". That would probably give you about another 100-150 RPM.

I imagine your Scorpion was probably rigged at the factory so I would have thought that the engine height will be correct as if it is too low this could also be costing you some top speed and RPM. Not sure what the best height is for a Yamaha / Scorpion, I imagine you would want the anti ventilation plate a couple of inches above the bottom of the transom.

Chris

[Roy Smith]

Thanks Chris
bit of a dark art this prop stuff
I surpose for £60 its worth ago
but i wonder if i should try to lend a prop at 21" and see if make all that much differance

[Cookee]

I think you would be hard pushed to get 750rpm out of a repitch - try and borrow a 21, it will give you better acceleration and come out close to your aim. It is worth talking to some other owners and the factory to determine which prop would be best first, as they have very different characteristics.

[Chris]

Roy the Specs on this engine suggest its top RPM is 6000.....

http://www.yamaha-motor.com/outboard...s/1/specs.aspx

With a full tank of fuel and 4 up thats a fairly heavily laden boat so I reckon you should be aiming to get to the 5800 RPM mark when fully laden so that as your fuel level drops and perhaps you run with only two people you RPMs will then increase upto 6000RPM.

So you are really looking to gain about 300 RPM to get you to the sweet spot. You could probably get close to this with a repitch although getting a 21" would probably be spot on. There are quite a few on ebay from sellers in the US but you are still looking at £3-400. You could always sell you current prop on ebay and get a couple of hundred back on it.

Chris

[Chris]

Just found this thread on a US site. It confirms my thoughts above.

Aim for 5800 RPM.

http://www.thehulltruth.com/boating-...-f250-wot.html

[Cookee]

A repitch would work for you then, and if you want to change over to a 21, then try a few different ones if you can you won't believe the difference!