What Prop on my Merry Fisher 625

[bigboy]

I wondered if you could help me i thinking of putting a s/steel prop on Merry Fisher 625 with a Suzuki 115 the standard prop on it is 8 x 14 x 19 but different people recommend different sizes etc so you help would be appreciated, also where’s the best place to get on and will I see an improvement.

[michael1923]

I have done quite a bit of research into this.
It is very complicated. As i see it you have two options,
1) Go on to Merc prop selector and fill in the info as needed and that will point you towards the correct prop.
2) In my opinion the one to do, Get a Mechanics multimeter, the type that fit on the spark plugs HT lead and will give you the revs of the engine. Now you need to take the boat out for a spin and record you revs at WOT (full throttle) You engine should have a guide of what this figure should be.
Now if yours is running different you need to work out by how much.
Each 200rpm out is 1 degree pitch.
If it is too low then you need to go down in pitch and if too high up the pitch.

For example if the engine is reving at 5100 and should be 5500, you might have a 17" pitch, you need a 19".

I hope this helps.
Best thing to do is type in google correct prop or something, as if your prop has a rake prop this will adjust he figure of pitch by 1 degree, and i believe a stainless prop does too.

Mike

[squidlips]

nearly right mike


to increase the revs from 5100 with a 19"pitch prop to 5500 you need a 17"pitch

decreasing the pitch or diameter increases the revs

[michael1923]

Oh yeah, what a plonker!!!!!!!! ignore the example

[Dave.S]

Try this site for a prop calculator www.castlemarine.co.uk/pitch.htm

Just download the program and then enter the details.

The critical thing is weight, this must include all your fuel, people and fishing gear as you would go out fishing.

Like most things the more accurate information you enter the better the result.

Dave