Prop for Hysucat 6.5 + Evinrude 225 h.o.

[Fabian]

Hello!

Maybe you have some idea for a good prop for my Hysucat 6.5 with a single Evinrude 225 h.o. Etec.
At the moment a standard stainless 14 1/2 x 21 is mounted. The Etec easily spins it to 5800rmp and 60mph.

First, I think there should be even more speed to squeeze out of this setup?!
The 60mph were done with 3 persons on board and with approx. 150l of fuel. Prop has some small dents/scars at the moment.

Problem:
Hitting the 60mph, the boat feels like falling down from the foils, hitting the water for a short moment and then rising up again on the foils. Speed is not decreasing much while this up and down, but it’s annoying.
The engine is only trimmed up a few degrees, 14 or so, that gives the best speed.

I think the prop touches the surface and looses grip for a second, so that the boat goes up and down. Might this be possible?

If so, what props would you suggest to be the right for my boat? Something like an powertech VMS for more surface operation or simply an Evinrude Raker?
Or are there real surface piercing props that fit the Etec?
Should I increase pitch and/or diameter?

Many questions, I know

Thank you!

Kind regards
Fabian

[paintman]

This suggests that the WOT throttle range is 5400-6000 rpm. Is that correct?
http://www.evinrude.com/en-US/e-tec-...ecs.html#tab=7

[Fabian]

Not exactly….
Mine is an Evinrude Etec G1.
Your link shows the G2 specs.

Mine should rev 5600-5800 at WOT.
It pushes the 5800 easily with the actual prop.

[paintman]

Helps to have all the info

When you say it pushes 5800 easily with that prop, is that it or does it rev past that & if so what does it actually top out at?

[Pikey Dave]

60mph is a fair old lick, most conventional RIBs would be into chine walking territory at that point. I’m not familiar with the handling of the Hysucat, but if it’s porpoising, maybe it’s approaching its flipping point.
What sort of speeds is that hull designed for? How does it handle at sensible speeds? If you’re just looking for all out speed, is it the right boat for the job?

[neil.mccrirrick]

I agree at that speed could easily be aerodynamics. Certainly cars need a down thrust at a certain point.

[Fabian]

Hi!

It pushes to 5800 and passes them to almost 5900 with 3 persons on board.
So if I’m alone, I‘ll over rev.

In the specs the strongest Hysu 6.5 has Twin 70hp and does 50 mph.
Mine is (supposed to be) a prototype for up to 250hp.
(The ID plate says so…)
But I think Hysucat didn‘t reinforce the transom very well. I hat to built tie bars to avoid the transom cracking.

The fastest ride was at 63mph (GPS) with 3 persons and choppy water. The Hysucat doesn’t even care for the waves. It‘s like on rails, feels very save at WOT, disregarding the annoying up and down.

It acts a bit aggressive in cornering (normal for a cat I think) and is most sensible in trim. 14deg, 2deg up or down and the boat tends to nosedive or stall. (That‘s ok for me, you just have to know….)

I heard of people pushing the Hysucat to 100mph with twin 250hp, but I don’t know if this is very plausible.

My aim would have been 75mph and I think the hull can do this. That‘s why I‘m asking for props.
I‘m also curious about, how much mph are lost through the scars and dents in the actual prop.

Regards
Fabian