Mercury 420 Ocean Runner - First outing

[harrison]

Tellum, 27knots ain’t too shabby.

Doubt you have a problem, as sounds like it’s just bouncing off the rev limiter. If sucking air in and ventilating then you’d hear a rapid rise in revs coupled with a dramatic loss of forward motion. Similar to a slipping clutch in a car.

Trimming in or out may help eeking out a knot or two. We tend to trim in to maximise hole shot. When planing keep trimming out until prop just starts to slip (ventilate), then trim back in slightly. This should give max straight line speed. You will most likely then need to trim in to avoid ventilation in powering through turns.

If you find your easily hitting the rev limiter when typically loaded then you could consider upping the prop pitch. Typical rule of thumb is each 1” increase in pitch will reduce revs by around 150/200rpm. The increase in top speed will be at the expense of slower hole shot... it’s all a compromise. Also important not to overprop to the extent motor cannot reach its recommended max rev range at wot.

Personally, if you’re getting 27 knots before hitting the limiter I’d leave well alone until fully run in.

[sonny1]

well , this seems to me to be a problem common to tohatsu, i have had mine checked out by barnet marine and rather galling to be told that as everything checked out there wasnt a problem but if i wind mine right up the warning light/buzzer activates and it bugs me. iwas thinking of maybe putting a heavier prop on, stainless steel but i need to experiment a bit before i spend that sort of money although i do like the look of them and it would be a lot more durable. any thoughts anyone. my mate had a tohatsu 20 and his did the same. i asked another dealer and he thought it might be a faulty oil pressure switch

[harrison]

Well, we run slightly under propped on the rib as propped for towing. We get good hole shot and a more than reasonable top speed...it’s all a balance/compromise. Out solo the motor can easily bounce of the limiter, which is not a major problem. Just don’t push the bim bim lever right to the floor.

At our sort of horsepower I’m not tempted to go for a stainless prop. Yeah slight performance advantage and look cool, but expensive and high risk of even more expensive gearbox damage if I hit summat.

[Tellum]

That makes sence Harrison ,thanks.
I will put a few more hours on her before I think about doing anything regarding the prop. I am more then happy to be able to do 25 knots I will have to live with not pushing that lever all the way up.
Although when I have the wife and daughter in the boat i wouldn't think it would be an issue.

[sonny1]

a couple of fair points there ian ,particularly "possible damage if you hit something" it really is annoying though.