why is my wilson so slow?

[oojamaflip]

i have recently purchased a 20 ft wilson flyer 70 hp yamaha but the gps tells me 14.6 kts
according to all sources should get 28kts
engine seems to purr.
am confused this is such a general question but does anyone have any suggestions
that may remotely start my investigations

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[duncan]

weight / drag / prop

assuming the hull is clean (if not polished bright) then it won't account for that much differential. If it's covered in a fine layer of barnacles then thats your problem.

the flyers often had a lot of added gear put on - much of it heavy. Check it on you local weighbridge and see what you have after substracting the trailer weight. I seem stories of people adding foam which then got saturated and weighed a ton as well.

Finally prop - at the speed you are getting the hull is fully planning so you are not underpowered per se. What engine revs are you getting flat out and what prop do you have on it?

Finally 28knots from a 70 on this seems a little ambisious but I would certainly expect mid 20's when clean and light with the right prop.

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[Dave_Snelson]

Don't know what a Wilson is?? However...the test is to find out what the maximum revs are for that engine, my guess is 5750-6000rpm. Next, run it on the water with the throttle wide open. Does it under rev, i.e. won't achieve max revs? If so, check throttle linkages and look down the venturis to see if the butterflies are opening fully - horizontal to air flow. If not, then adjust. If they do open fully, maybe then you are over-propped and the pitch is too coarse. Get a prop with reduced pitch.

Does it easily over rev, i.e. when you open it up, does it rev into the red? If so, then it is under-propped. Get a prop with a more coarse pitch. The aim of the game is to have the engine at top revs with WOT (Wide Open Throttle).

What about trim? Assuming it has power trim / tilt you can adjust the trim of the motor whilst going along, to raise and lower the angle of the bow. You should raise it in small increments (trim out) until the boat starts to "Porpoise" (bow bobs up and down like a traditional cartoon motorboat). Then lower the trim (trim in) until this effect ceases and the boat runs even.

My guess at propellor pitch would be around 15" - but dont take my word for it.

All the above assumes that the boat is in fine condition and clean underneath.

Let us know how you get on.

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