Is my Engine set too deep?

[two stroke mick]

I am still tring to get the prop just right on my rib. A Valiant Dr 490 and a 60 Etec.

I am running a 13*20 prop. When the engine is trimmed in the prop will not achieve the desired WOT 5800-6000 RPM. When the engine is well trimmed out (more tilt than trim) I can achive 5800 and the boat does 30 kn.

The cavation plate is currently 10mm (circa 1/2 inch) below the planing pad. This is the recommended height according to the Valliant Documents.

I suspect that the engine is set too low.

Your thoughts on this problem please
TSM

[martini]

Is that 13" diameter x 20" pitch? If so sounds too big, I would have thought 17" pitch would be nearer the mark. Hopefully someone with a similar set up will come along and tell you their top speed to give you a better idea of what you should be achieving

[Hightower]

The pitch of the prop does look too big.

However if you want to experiment with the height of the outboard, well that should be just a case of lifting it to a different set of holes in the bracket assuming that you still have some adjustment left. Otherwise you're looking at drilling a new set of holes in the transom.

If you decide to lift the outboard go for a 1" lift at a time and see what difference it has on the WOT and handling.

[two stroke mick]

I also have a 13 * 17 prop but the engine revs to 6300-6400 RPM (max WOT is stated at 6000)

[Erin]

Take care reading rpm off a tacho. They are notorious for being innacurate. If you can, it would be better to rig up a dedicated digital test tacho for the purpose of testing.

[outboardtech]

DROP to a 17 , That PROP is way too big

[Hightower]

Some tachos have the facility to be set to different models of engines so that it may be used to cover an entire range.

It might well be set up inaccurately, so might be worth considering checking it.