please help: how to stop porpoisng

[rg33]

the bass boat I have is stated in my signature. cannot seem to stop porpoising. started with the motor trimmed fully down and raised it in steps occording to the trim guage. no good. started with the cavatation plate in line with the stern bottom, the same. comes up on plane in a timely manner, then it starts. please help

 

[swist]

Re: please help: how to stop porpoisng

The boat is stern heavy. Try moving some weight forward.

 

[rg33]

Re: please help: how to stop porpoisng

I have three batteries and a 25 gallon tank in the rear. would moving two of the batteries help? trim tabs, stabilizer?

 

[shep70057]

Re: please help: how to stop porpoisng

You can play with sand bags to see if it helps your problem. Start out with two or three sand bags in the front to see if it helps. Then decide whether or not to relocate your batteries. If you have a front livewell, you can also fill it up to see if the weight up front helps out.

 

[rg33]

Re: please help: how to stop porpoisng

I have no front livewell, but the sandbag trick sounds interesting.

 

[Mark42]

Re: please help: how to stop porpoisng

My boat was porpoising at top speed (29mph). I was trimmed the motor all the way in and that helped quite a bit. I was going to add Smart Tabs but decided to wait until after I installed 14 gal tank in the bow. That made all the difference. Surprisingly the boat doesn not porpoise even with half or less tank of fuel. I think it is not only because of the weight added to the bow, but because the two 6 gallon tanks are no longer in the stern. So moving any weight from stern to stem might give a similar improvement.

 

[bigbrownbuku]

Re: please help: how to stop porpoisng

you could try a "doel fin" on your av plate to add some stern lift. it does sound like poor weight distribution though.

 

[dragrace2000]

Re: please help: how to stop porpoisng

Check your transom....a weak transom will cause the motor to flex causing a porpoise effect

 

[Mercury140-I6]

Re: please help: how to stop porpoisng

Mark42:<br /><br />Where did you find a 12 gallon bow fuel tank????? <br /><br />A friend and myself have looked all over the web for one, but haven't found one.<br /><br />Any help would be appreciated<br /><br />Craig

 

[rg33]

Re: please help: how to stop porpoisng

Originally posted by blownsilly:<br /> Check your transom....a weak transom will cause the motor to flex causing a porpoise effect

What are the signs of this that can be found while the boat is in the garage?

 

[dragrace2000]

Re: please help: how to stop porpoisng

Put the motor fully up with the travel lock in place.... reef up and down on the prop and have someone watch your transom for flex if there is any movement at all then your transom needs to be replaced.... some people temporarily fix with an aluminum plate but this does not last.

 

[dragrace2000]

Re: please help: how to stop porpoisng

Just adding one more thing.......another one is that if you have side rollers on your trailer...these could be denting the hull and causing an irregular form in the hull (just a thought).

 

[rg33]

Re: please help: how to stop porpoisng

Thanks, I will do that today. I have a drive on trailer with flat bunks.

 

[Mark42]

Re: please help: how to stop porpoisng

Originally posted by Mercury140-I6:<br /> Mark42:<br /><br />Where did you find a 12 gallon bow fuel tank????? <br /><br />A friend and myself have looked all over the web for one, but haven't found one.<br /><br />Any help would be appreciated<br /><br />Craig

You may be thinking of the triangle shaped tanks? I put in a regular 14 gallon rectangle/cube shaped tank available from most suppliers. This one is a Moeller

<br /><br />If you want to see the whole "permanent fuel tank" project, click here<br /><br /><br />EDIT:<br /><br />BTW I tried a fin to eliminate the porpoising but it didn't help much. In fact, adjusting the trim pin to full in and removing the fin made the boat run better than with the fin.

 

[rg33]

Re: please help: how to stop porpoisng

Tried to flex the transom and could not. I will try to move weight forward to see if that helps. No comments on trim/smart tabs or hydrofins?

 

[Mark42]

Re: please help: how to stop porpoisng

Try everything you can to get the boat to ride as best as you can get it before buying solutions like trim tabs. Even if you can't get rid of all the porpoising, if you can eliminate most of it and still want trim tabs, the tabs will perform much better than if you throw them on a boat that has not been "fine tuned" first.<br /><br />I tried a hydro fin as stated above. I'll be putting in on e-bay soon.<br /><br />Have there been any modifications done to the boat since new? Like more seats, live tanks, etc? These sort of changes can affect the boat.

 

[rg33]

Re: please help: how to stop porpoisng

No changes from stock. bought from original owner and received purchase receipts. Got me wondering thou, as if porpoisng. is a recent development. Boat sat up for 2004.

 

[Mark42]

Re: please help: how to stop porpoisng

Check the bottom of the boat for a condition called a "hook". That is where the hull is out of straight. Usually attributed to sitting on a roller trailer or bad bunks for a long period of time. Causes the fiberglass to deform. The deformity in the hull shape can cause porpoising. I haven't see a hook but read about them numerous times on iboats.<br /><br />Don't discount that the boat may have always porpoised. The previous owner may have never run it fast enough to notice. But then again, maybe he did. Can you contact the previous owner and ask?

 

[LubeDude]

Re: please help: how to stop porpoisng

rg33:<br /><br />I have that exact same boat, (except it has a merc), Same thing, I have no Porposing problems.<br /><br />Is it just possible that you dont understand performance boats?<br /><br />First, if you are not at WOT, you will porpose if you trim much at all, you didnt mention how much throttle you were using when the porposing occures. At WOT, with a four or five blade prop, I can max out the trim and not porpose. I now have Smart tabs on the boat, but there was no porposing before I installed them. Do youself a favor and get a set, they are awesome. I can plane between 10-15 MPH, and the ride is fabulose.

 

[rg33]

Re: please help: how to stop porpoisng

Porposing starts just as the boat comes up on plane, about 20 mph, 4000 rpms with the trim fully down. Have not buried the throttle to the stop, but not far from it. I tried to trim it up to stop the bouncing, but no help. I have a 3 blade 23 pitch prop and the next time I go out, planning to go to a 3 blade, 19 pitch cupped Hustler prop. This is my firsr performance boat, previously having a 14 foot, 25hp tiller boat. You may treat me as uninformed on the subject and any help is appreciated.