bad porpoising help!

[johntimothyellen]

hi i just bought a 1989 procraft 1660 ski-fish it has an 88 johnson with a 13 3/8x 19 prop. it has a hard time coming out of the hole and when it does right away it start porpoising (about 3000-4000 rpms) i tryed different trims but nothing helps. i have no idea what i should do. should i us a smaller prop? any help would be very much appreciated thx
john.

 

[Laser87]

Re: bad porpoising help!

If you have power trim, put the motor all the way down, then after the boat has planed off you can trim out to a balanced ride. If the trim is manual with the pin, place it in the lowest and see how it does. In the lowest position the bow will be down in the water and handling will be effected.

If you have a tachometer you have the right prop if you are running at the maximum operating range with a light load and one person in the boat.

 

[Texasmark]

Re: bad porpoising help!

Your rig should perform nicely as set up. Porposing is caused by the angle of the engine to the hull not matching the hull to water interface for a given speed. Sometimes the boat has problems which can cause it.

Since you said that you tried different trim positions a couple of things come to mind. If manual trim, you didn't tuck the engine in far enough to get the bow down for a given speed which will also cause sluggish hole shots. If power trim, you still could have a tilt pin or problem with your trim unit that will cause the problem.

If your engine mid section is parallel to the tilt of the transom (tucked in all the way) I'd say that most boats will not porpoise at any speed unless it has hull damage as listed below.

Speed affects porpoising and for a given trim angle/load/hull/etc. there is an equilibrium speed where above you are stable and below you will porpoise.

Porpoising is usually caused by too much weight aft or the engine pushed out too far "trimmed out") for a given speed. A hooked hull can cause it (damaged sitting on a trailer full of water as an example), or water absorption in the stern of the boat....flotation saturated sort of thing.

Look around and get back if you have more information specific to your rig which may help in solving the problem.

HTH

Mark