Matt Lang wrote:
On the water we opened the throttle all the way and then turned the
ignition to change the timing, it made a difference but resulted in
the low top speed..

I will get the boat to the dealer but would like to know whats up with
the boat beforehand ..

How fast (roughly) is such a 18.5 boat with 125 HP supposed to go ?

Matt



Matt,

With about a 2:1 gear ratio give-or-take (I think these were 28:14 gear
sets) and a 17" cupped prop, you should be able to get 38-39 MPH at 5000
rpm on most any planing hull. With the Merc 125, and a good/lighter
hull, 42-43 MPH @ 5000 rpm is reasonable with a 19" prop.

I've seen Lake X test results, with the 90 hp 6 cyl on a lightweight
(Offshore 17 DSC) boat produce a best top speed of 50.1 MPH on radar
with a Merc 3 blade 23" stainless prop, and only turning 4400 rpm (two
on board - about 8 ft. ASL). They tried every reasonable prop in
inventory, this one produced top speed... kind of a weird power band.
Also, the mod-tri-hull starts to entrap air at 47-48, and it starts to
chine-walk, so this prop is just getting the boat fast enough for a
little lift hence the speed. It's kind of squirrelly to control at this
point too.

It was (still is) a great all around ski/sport boat with a cupped 17" on
it, it gets up into its designed full-throttle range nicely at its home
here at 1729 ft ASL, at about 41-42 MPH.

Rob