Got a honda 90 with a laserII stainless prop (dont know spec) on a zodiac pro open 550. At best i can get 30kn on the gps, flat out in dead calm and with the wind behind, and with c5000 rpm; which is all it seems to rev to flat out
The engine has always been serviced by Honda and has done less than 200hrs.
I'm not technical so is there any way I can check this is all it should do? Is this what I should expect?
30 knots sounds about right for the size of craft and engine set up, however 5,000 rpm max sounds a bit low, going on the latest model it specifies max revs at 5,800 rpm.
But on saying that, with the wind behind you in a flat sea it should have a bit more speed than 30 knots, the pro open 550 is not the heaviest of 5.5 metre ribs so 35-38 knots should be attainable with a 90 on the back in good conditions, although the Honda is not exactly the lightest 90 around, a 90 Yamaha for instance will give you better response and top end. I think the problem lies in the 800 rpm's that you seem to be lacking in if the tacho is reading correct that is? which means that it is probably a miss matched prop.
at first glance youre overpropped - but on second glance what are you doing with the trim? On flat water and on the plane trim up with the limiting factors being either (a) the prop sucks air, ventilates, and the motor over-revs or (b) the boat becomes unstable in which case trim down a bit.
in which case trim down a bit.
