Unknown Issues

[crispycritter1]

May of 2016 I purchased a 2003 Sanpan 25' pontoon boat w/ yamaha115 hp motor (620 hours). I had the motor serviced prior to placing in water and was told all is good. Since May I have taken the boat out over 15 times. I like to putt around but every once in a while I like to go WOT. Unfortunately, when at full throttle I'm at about 6600 - 6800 rpm' and speed is a sad 18 mph. I would think I would get up to at least 28 - 30 mph but not a chance. And this is when its only me in the boat in late evening with water surface like a sheet of glass. Looking for guidance going forward on what is the first thing I should check out and so on. Thank you for your time. See less

 

[CV16]

What's the max rpm for your motor?

 

[gm280]

crispycritter1, first of all, :welcome: to iboats. Glad you could join us...

The MPH you stated is with a GPS or gauge? And if a marine speedometer, you can't go by that as true MPH. Secondly, the engine RPMs you specified are way over revved. If I remember correctly, that engine is suppose to peak out at less then 6000 RPMs. But you can check that in the shop manual for the exact range. I would first use a GPS to get the speed and make sure your tach is reading correct as well. Second, is your engine setting in the water correctly? The anti-cavitation plate should be at water level on plane. If it is too high or too low, your performance will suffer, but so can your cooling system. Post a few pictures of your setup for us to see.

I will say this, my neighbor had a pontoon boat with a Mercury 25 HP on his. And we GPS the speed at WOT to be 11 MPH. So yours certain should move faster the 18 MPH. JMHO

 

[harleyman1975]

6600-6800 is wound way too tight!

 

[Scott Danforth]

welcome aboard.

first, with pontoons, the depth of the prop is a large factor with properly setting up the motor. too shallow and the prop ventilates, too deep and the lower plows and the prop doesn't run efficient. This is also very much load and weight distribution dependent.

second, pontoons take a lot of HP to get them to plane out to get you to 30mph. displacement speed is displacement speed until you get enough hp to get the hull to plane. with most pontoons you can put a 20hp on them or 100hp on them and the speed is the same (just the level of fuel consumption and noise generated increases)

your boat isnt a tri-toon with lifting strakes so the amount of hp to get it to plane is going to be fairly high.

I know Godfrey has a boat owners club, have you checked with other Sanpan owners to compare notes?

I agree, 6600 rpm is a bit high....

 

[Sea Rider]

Yams usually revs at 5-6K rpm, can compensate high revving going for a less prop pitch or adding more passengers accordingly if liking running wot on flat glass water cond.

Happy Boating

 

[Sea Rider]

Yams usually revs at 5-6K rpm, can compensate high revving going for a less prop pitch or adding more passengers accordingly if liking running wot on flat glass water

Oops, was the other way, a larger prop pitch to lover wot revs, Surely a senior moment LOL!!

Happy Boating