Porpoising boat

[dtg]

I went out for the first time in my 14' open V aluminum boat powered by a 15hp Johnson. I was in it by myself and couldn't get it to plane without porpoising like a bucking bronco. My initial reaction is with no weight in the front, this is what is causing it. Do any of you think this might be the case?

It does have a long shaft, but I dont think that this boat really needed one, but that's what came with the deal. Could this also be a possiblilty?

[waterfoul]

On my little aluminum I always had to put my gear forward if I was alone. Tackle box, anchor, and I even lengthened the fuel line and moved the tank to the front half of the boat. This helped a LOT. Gas is about 6.5 lbs a gallon... a 5 gallon tank weighs 38 lbs or so... move it forward if you can.

[dtg]

I think the next time I got out I'll put one of my 75# bags of sand that I keep in the back of my truck in the winter time, in the middle of the boat and see if that helps.

[Rodbuster]

I think you may have your motor trimed too far up.. Move the adjustment pin down one or two holes and see if that helps? I know on my 19' if I trim the motor to high it will porpuse like you are describing.. I'm sure the weight in the front will help also.. I hope this solves the problem ??

Steve

[dtg]

This weekend I will have time to tinker around with it. I think I've only got one more hole to go, I moved it down one hole Wed. night and it was a little better when I leaned as far forward as I could possiblely go without letting go of the tiller. I couldn't crank the throttle all the way, because the porpoising got really bad. I think I'll start with adding some weight to the middle of the boat and then move the motor down to the last hole.

Thanks for the advise

[FYRE926]

If the weight distribution & motor reposition don't help, try fabricating a pair of wings to rivet one to each the side...it might plane out & leave just the lower end in the water...imagine the speed you could get with no drag from the bottom of the boat!

[waterfoul]

You can actually buy small "trim tabs" for these types of boats. I think I've seen them at West Marine in Grand Rapids... and there is a new West Marine in Grand Haven now.


Or you can order them from Overtons I believe.

Being a long shaft motor, I don't wonder if the thrust vector is just way off... move it to the lowest trim hole and see what happens (as was suggested above). If your transom allows, maybe you could replace the wood that the motor clamps onto... make it taller and thus putting the prop closer to the bottom of the boat (this is called the X-dimension)... it may plane right off with the motor up on the transom, thus creating a higher X-dimension.

[coverdog]

Where is the cavitation plate on the motor in relation to the bottom of the boat? It should be nearly even. If not within a inch or so and more like 5 inches off you have the wrong length shaft and will never get it to operate correctly.

[dtg]

The transom is 21" and the motor is a long shaft, so everything is ok there. I think I've finally figured this out. With a passenger the boat planed, but didn't quite feel like it was going as smooth as it could, plus I had water spraying over the transom. I did some searching on the net and came to the conclusion that a) I need to adjust the motor down to the last pin and b)slide a piece of wood uner the mount to raise the motor up an inch

I read the water coming over the transom is from the cavitation plate not being even with the bottom of the boat and by raising the motor up to 7/8" will correct this problem. I will have to wait until the weekend to test this idea out. I hope it works out.

[lawnboy]

As in your other thread, I have the same boat motor setup. One thing that I did was move the gas tank and battery up to the front. Along with the anchor toolbox and so on.

By the way, the battery is a deep cycle and it’s hooked up to a fish finder that I charge every second or third time out.

[thedude]

you may want to look into a "whale tail"
similar to the tabs that everyone is talking about, its just a big cavitation plate that looks like a fin. it will help you boat plane no matter what your weight dist. is, especially on non-planing hulls like yours.