Prop for Mariner (Tohatsu) 30

[gibbo500]

Hi guys,

On succesfully upgrading my Marathon 25 to 30 by changing carb gasket and timing, i fitted a tiny tach to see what RPM i was getting.

On a 4m inflatable with a 9.99 x 13 prop the max i could get at WOT was 4700 rpm, so below the recommended 5150-5850. I couldn't identify top speed as i didn't have GPS, but will have one next trip out.

From reading other posts on the subject, i need to increase the pitch size?

So bearing in mind i dont want a stainless steel prop(due to where i use the boat), what size would you fit as a starting point and can i expect any speed increase over the current prop and is it worth doing?

Many thanks in advance.

[uncle al]

Gibbo give me ring in the morning you should have my phone number.
uncle al

[outboardtech]

hello UNCLE AL . YOUR joke was great at the UPDATE .

[gibbo500]

Originally Posted by outboardtech

hello UNCLE AL . YOUR joke was great at the UPDATE .

That wouldn't be the Pinnochio one, would it?

[uncle al]

i just cant stand cheeky kids

[Ian Sharlot]

Originally Posted by uncle al

i just cant stand cheeky kids

Wecome to ribnet uncle al have I gone and missed one of those mother-in-law again, must have done the model update on the wrong day.

[gibbo500]

Fitted new prop and now getting 5870-5900 max RPM. Very happy with the performance but do i need to be concerned this is slightly over the recommended max of 5850?

Advice really appreciated.

[codprawn]

There is this remarkable new invention called a throttle - if you turn it a fraction it won't over rev.........

[gibbo500]

Originally Posted by codprawn

There is this remarkable new invention called a throttle - if you turn it a fraction it won't over rev.........

Thanks Codprawn,

I just wondered why others were concerned about an engine over revving (didn't think this was good)? So no need to worry then, just use the throttle carefully.

Cheers

[codprawn]

The reason being the prop should get you to spot on peak revs for maximum efficiency but you are so close and if you are happy with it it's not worth messing around.

[yoyo]

You could always adjust the throttle stop a little, stops you going all the way. Its just a screw and nut under the hood.

[outboardtech]

Becareful GIBB bud you dont blow that powerhead up . TO ME THAT engine is DEFINETLY REVVVVVVVVVVVVING too HIGH for that model . I have seen these powerheads and have got one NOW blown up after 43 hrs being over propped and I promise you a two stroke engine as we all KNOW are high revvvvving engines but being run like that you are asking for probs . It would be interesting to know what your top speed is with it revving that high? that my opinion if it was mine i would be propping to run @ 5300 max to be on the safe side . chow

[yorfuoj]

Your prop is definitely too long with 13" pitch, you should decrease to 11, with this one you should rev WOT above 5500 without risk.
Over-revving : no risk, all the engines have a rev limiter !