Porpoising with new prop

[wed]

I was checking out my new prop, trimming for best speed and found that it causes the toon to porpois. The old prop never gave even a hint of porpoising. The old prop was a Solas Myth 13.25 X 17 aluminum and was good for 39MPH @ 6000 RPM. The new prop is a Turning Point Hustler high preformance aluminum 13.25 X 17.

The new prop seems to cause a lot more bow rise on acceleration from stop and also seems to reach plane a little easier/faster. The problem occurs when approaching max RPM. The boat really likes to run level and as I trim down the front of the toon with RPM around 5600 and increasing the bow begins to bounce up and down. It gets increasingly worse (scary!) until I either pull back on the throttle or trim the front up. If I trim the bow down a little slower it does not go into gyrations and I was able to trim to about 5800 rpm (38MPH). I doesn't appear to do this with more than one person on board. Also around 33 mph it seems looser on the water, sort of skating along. I have seen regular boats do some strange things but I did not figure a pontoon would act this way will only 90 HP. Mid range cruise is geat and the boat works better in the turns with this prop.

Can anyone help with this? yes, I know one solution would be to just not run it wide open but what is the fun in that?

[lakerunner]

Why are you trimmimg down so much? The less log contacting water seems to me would be the fastest where trim down would cause the nose to plow

[Durante]

a 21' pontoon with a 90hp doing 38mph... thats smoking
Im running a 225 on a 26' tritoon and with the prop the dealer put on I was having a hard time breaking 40. I have the boat in for its 10 hr service now and swaping the prop up 2 inches in diameter, more cup with the same pitch. The are also altering (with manufatures blessing) the back end of the center tube to allow for more water to hit the prop, because I can not trim my motor up, so I am running my boat trimmed down and its plowing the water.

[wed]

Lakerunner...You are correct, if I trim down jost a little too much it will plow and speed drops off a lot. I just go by the tach and GPS and have found that it has best RPM/speed when almost level in the water, I am pretty sure the bow is a little higher than the stern but it seems level from inside the boat. If the bow is up a little too much I am trading speed for bow lift and it slows down.

Durante ... This is pretty typical of this model boat. There are several members of this forum with the same or better performance.... and the manufacturer stopped offering the performance pontoon option this year.

What I am trying to figure out is why it wants to porpoise with the T.P. prop .... it never did this with the old prop. I bent the old prop, had it repaired, and have it back in the shop for adjustment. I would still be running the Solas prop if I had not damaged it. Is it possible that I need to adjust the motor height with the new prop?

[WaltF]

Youre just trimming out too much for that prop apparently.
Just back it in abit and that should stop..

[HandymanHerb]

New prop might have more cup to it, that would lift the front more, just don't fight it and trim for speed.

[Bmac]

Sounds like the TP prop has more stern lift,which could be a good thing here. This would make it feel loose,and loose some leverage against the bow. Try dropping the motor 1" and test again.

[GXPWeasel]

Just by what you're saying, and by looking at your sig picture... my guess as to why you loose speed slightly above level, is because your lifting strakes don't go all the way to the back of the toon. When the toon is level, you are hitting 100% of the strakes, but once you trim the nose up a bit, you are losing some of the strake, or putting more weight on the rear portion of the toon that doesn't have the strake, i.e. losing speed. I agree that the TP prop may just have more cup, and therefore more lift.

[wed]

Thanks for the input everyone

Talked to Turning Point yesterday about the porpoising problem. It was the first call they had taken about this problem happening to a toon with this small (HP) of a motor on it. Discussed the high performance logs, trim procedure and a few other issues. The tech guy said the rake of the TP prop was much more agressive than the Solas prop that had been on it as it is designed for higher performance boats (they made the recommendation to me) to make them jump up on plane. This prop does get on plane quicker. Also has more cup as some of you suggested which I am sure plays into this. His focus was more on the rake causing the bow to rise on accelleration and in general the whole boat ride a little higher when on plane. He suggested raising the motor 1 inch if possible and if that is not possible move a little weight to the front of the boat.

In any case it seems the fulcrum point of the boat has changed due to the prop design. The prop is a little longer than the Solas which might affect trim sensitivity and overall stability. After thinking about what he said I think Bmac recognized the problem and maybe has a better description of what is actually going on even though there is disagreement as to which direction to adjustmet should go.

I will not be able go to the toon for several weeks (bummer!) to look at the motor mount so could any of you Tracker guys tell me if there is a height adjustment on your OB setup. If there are any other thoughts or suggestions I would really like to hear them. I will follow up if I can find a solution. Thanks again!