Porpoising problem

[Dembe]

Hello everyone,,

I have a 2004 19 foot Skeeter with a Yamaha 150 4 stroke and I have a lot of trouble with porpoising. I can get it to run smoothly as long as I have it trimmed up on the pad and I run at 4000 rpm or higher. Once I drop below 4000, it starts porpoising. I can trim it down and it doesn't stop. Once it is completely trimmed down, it is better, but not entirely gone. Doesn't matter if the water is rough or smooth. If it drops below 4000, it's going to porpoise regardless of where the trim is. I can't move weight forward, batteries, etc., because there is nowhere to put it. The boat uses 4 batteries and has a 32 gallon tank. I've even let the gas get down to a quarter of a tank to eliminate fuel weight and it didn't help at all. I've thought about getting a fin to mount on the cavitation plate. Any ideas would be greatly appreciated.

 

[Scott Danforth]

welcome aboard

move the batteries forward (there is always a way) or move the cooler of beer up front. you have too much weight in the back 1/3 of the boat

at higher RPM's you are probably loosing prop bite which is why you are not porpoising at higher RPM's

 

[Texasmark]

Usually thrust angle and amount determines the attitude of the hull to the water and there is a critical point whereby thrust has to be increased, or the angle reduced to keep the hull from oscillating.

My simple minded thoughts are that you have something in your setup that prevents you from experiencing the angle reduction part of the equation, below 4k RPM.

Could be improper set-back, engine height, or wrong prop. The setback and engine height are said (by experts on here...check archives) to be 1-1 ½ inch of engine height increase per 6" of setback. Since most pad boats (of which I am aware) have 4-6" of setback in the hull, you are automatically at the above dimension when you start. Adding a 6" additional setback with a jack plate would give you another 1-1 ½ inch of height requirement.

You may be too high up on the transom......course any lowering amounts to drag and since that obviously hurts your top end you have to decide which it is that you prefer.

Rake is the bow lift part of your prop and it could be that you have too much. Sounds silly but your problem is that you can't drop the bow-thrust angle as thrust is reduced and too much rake could do that. Or you are sitting too high on the transom for your amount of setback.

Food for thought, proven theory-not necessarily, trial and error thing.

 

[Dembe]

Hello everyone,,

I have a 2004 19 foot Skeeter with a Yamaha 150 4 stroke and I have a lot of trouble with porpoising. I can get it to run smoothly as long as I have it trimmed up on the pad and I run at 4000 rpm or higher. Once I drop below 4000, it starts porpoising. I can trim it down reverse image search email checker and it doesn't stop. Once it is completely trimmed down, it is better, but not entirely gone. Doesn't matter if the water is rough or smooth. If it drops below 4000, it's going to porpoise regardless of where the trim is. I can't move weight forward, batteries, etc., because there is nowhere to put it. The boat uses 4 batteries and has a 32 gallon tank. I've even let the gas get down to a quarter of a tank to eliminate fuel weight and it didn't help at all. I've thought about getting a fin to mount on the cavitation plate. Any ideas would be greatly appreciated.

Thank you for ur help....

 

[ezmac]

Had the same problem with a 2005 Century 17ft center console. the boat would be fine on calm water but any chop at all it would start to porpoise. Even with my partner up front it would start to act up. 15 gal gas tank under the deck in front of the console so there was no moving that. Tried experminting with the trim but no success. Had to drop off plane to get it to stop. Three batteries in the center console and a 90 Yamaha 2 stroke hung on the back. Instead of trying to move anything forward I bought some automatic trim tabs from Bennett and problem solved. Did not effect my top speed that I noticed. No lines or wires to run. Easy to install and not very expensive. If all else fails, I would give it a try.

 

[GA_Boater]

The OP is a spammer.

Closed.