Prop on Yamaha 30hp behind my RIB

[Vintec]

Well at the beginning of this summer I had my 30hp 2 stroke 3 cilinder yamaha behind my SIB. The boat was a bit overpowered, the standard prop was damaged, and I had an stainless steel prop with it in the size 10x10. The standard prop was 9 7/8 x 11 1/4.
With the stainless steel prop my engine was reving like creazy (to much) behind my SIB. So I bought an original yamaha prop in the size 9 7/8 x 12. Just to go a little bigger then the standard prop.

I still use this new prop behind my new RIB, which ofcourse is a lot heavier then my SIB. But the hull is far more stiff and better lined, so no energy get's wasted like with the SIB on hi speeds. Hope I said this correct.....

My question now is, how do I know whether this prop 9 7/8 x 12 is also a good choice behind my RIB? The RIB has a total weight of aprox 200 kg and the engine is about 60 kg. Then with fuel, gear and myself with co-driver in the boat a total weight of about 440 kg.
I don't have an RPM meter, so have no idea what rev's the engine is doing, it's all by feeling and sound for me.
The combination now has a topspeed of 27 knots. This is done after testing for the best trimsetting of the engine, since I don't have powertrim on this engine.

Added one pic of the combination with the best view of the prop that I have at the moment.

Any information would be more than welcome!

Vincent

[Searider]

Hi Vincent,

I reckon if you're getting 27 knots you are probably about right with your propeller.

Our 4m Searider with the same 30hp yamaha as you have does about 26 knots (only tested by running alongside another boat with GPS - so a bit approximate) with an a 9 7/8 x 12F alloy prop.

I don't have a rev counter either but the engine sounds OK and acceleration is good so I think my prop is about right.

I hope this helps.

[Locozodiac]

Originally Posted by Searider

Hi Vincent,

I reckon if you're getting 27 knots you are probably about right with your propeller.

Our 4m Searider with the same 30hp yamaha as you have does about 26 knots (only tested by running alongside another boat with GPS - so a bit approximate) with an a 9 7/8 x 12F alloy prop.

I don't have a rev counter either but the engine sounds OK and acceleration is good so I think my prop is about right.

I hope this helps.

Go for the top/max rpm engine/boat for oustanding performance, buy Tiny Tach, a must have issue.

Happy Boating

[Vintec]

I think you are right.
It looks like, since we both have the same prop and same sort topspeed, that it's a good combination engine/prop/rib, but I'm still not sure.

That Tiny Tach system sure looks like a very good option to know for sure.