Motor Performance Tips

[mudcatwilly]

I have a 1990 Suzuki 85 hp 2 stroke strapped to the back of my 16-foot, 1975 Lund trihull.  The motor runs well.  I was looking at some magazine ads for those hydrofoil stabilizers that bolt on just above the prop.  I guess they are supposed to increase your hole shot and eliminate porpoising (which my boat likes to do when too much weight is in the back).  Do these things work like they say they work and if so, what is the best one out there?

[NBR]

I have a 150 Merc on an 18' fiberglass. I added a plate by Cobra called "The Edge". This aluminum plate is just straight with a tipped down trailing edge. After adding my hole shot was much better.

With my rig I have found that porpoising is a function of the amount of trim out and throttle position. I can be running down the lake flat and if for some reason I reduce the throttle the boat will start to porpoise. The solution is either increase the throttle or reduce the trim out a bit.

[RollONTwo]

The Lund does not really have a pad does it? I assume NBR that your boat does correct? If so that is 2 different reason boats can porpoise. Once a boat lifts up on the pad and trim is fully extended slowing down can make the boat come off the pad so the boat will do that trying to get more lift. The first boat I owned was fiberglass but did not have a pad and it would porpoise bad but it was 15' with a 135hp Johnson on it. I put one of those hydrofoil things on it and it helped. I think what I am trying to say that with a pad speed and trim would be the major factors. Without a pad the Hydrofoil might just help.

[Way2slow]

Normally SS props provide a slightly better hole shot, and a little more top end but on your and a 85 hp motor, will you see a big difference? NO!!.   Unless you've just got an extra $400 bucks to spend and feel like you must spend it on a new SS prop, I think you can find better uses for your money.  There just will not be enough gain in performance to warrent it.

If you had a big V6 with buches of hp and torque, you would probably see a noticable gain, but the smaller midrange motors usually see a much less the benifit.   Now if drop down the small motors like the 25's and smaller, so many of them run such a sorry combo prop, a good SS on them make a pretty big difference.

[mudcatwilly]

My boat sometimes wants to porpoise at full throttle (about 30 mph), but that's only when I have other people in it.  I have an aluminum prop on there now, but I also have a second prop that I have never used that the guy gave me when I bought the boat.  That prop is much heavier and stiffer and has sort of a rubberized coating on it.  Does anyone know what that kind of prop is for?

[cart7t]

Porpoising is most commonly caused by hull design and weight distribution inside the boat.  In effect, it's a instability where the prop thrust is no longer capable of holding the bow up and the stern falls down into the water, the prop thrust then picks the stern back up and the process keeps repeating itself.  Those doelfin type devices to solve the problem but they can add drag at the upper end speeds.  4 blade props can help the problem on larger HP motors.  Before putting a fin on try redistributing the weight in the boat and see what happens.  If you're not having a holeshot problem that may all that's needed.  If not, those fins will solve your problem a lot cheaper than a SS prop.

[cart7t]

I also have a second prop that I have never used that the guy gave me when I bought the boat.  That prop is much heavier and stiffer and has sort of a rubberized coating on it.  Does anyone know what that kind of prop is for?

That's quite likely a SS prop that's teflon coated.