Rear of pontoon submerged at WOT

[BlackToothONeil]

I have a 1991 16' Crest pontoon. The boat originally came with a 35hp Force motor which was basically junk when I got the boat. I now have a rebuilt 79' Johnson 85hp which is a couple hundred pounds heavier than the Force and consequently the boat sets 2" or so lower in the rear. To address the larger motor and weight I unbolted and moved the transom forward 7" as well as welding on additional bracing as the transom was only rated for 50 hp. I also relocated the fuel to the middle of the boat with a permanent tank and got rid of the two orange tanks setting on the rear platforms. Lastly I rearranged the furniture while re-carpeting and now the bench seat is along the side instead of in the rear. The problem is at WOT the rear of the pontoons become completely submerged causing a significant drag. I still have one of the fastest pontoons on the lake, but I would like it to ride somewhat level under power. Anyone have any ideas? I have considered a hydrofoil stabilizer to create some lift on the motor.... Maybe after this season I will weld on some full length strakes to try to get some plane effect. Any suggestions would be greatly appreciated.

 

[lncoop]

Re: Rear of pontoon submerged at WOT

Holy smokes that's a lot of juice on a little 16' barge. Not sure if there's anything you can do to completely counter the effects of being so overpowered. At some point all the modifications will just result in the whole thing sitting lower in the water. Someone might have an idea though. Good luck and welcome to iboats.

 

[EGlideRider]

Re: Rear of pontoon submerged at WOT

Don't know if anything can be done but you may try experimenting with the trim. I would first try more down trim. You may have to add spacers to the motor holes.

 

[OldePharte]

Re: Rear of pontoon submerged at WOT

My guess is that ya done overloaded it with the 85hp motor.

That said, ya most likely need to add a middle tube. Ya can find tubes with a motor mount and transfer the fuel tank to the middle tube. (for example, my 'toon has a 56 gallon internal tank). Find a tube maybe an inch or two bigger in diameter than the ones ya got.

Until ya solve the weight issue, I see little value in adding lifting strakes.

 

[lncoop]

Re: Rear of pontoon submerged at WOT

I still have one of the fastest pontoons on the lake

I bet! Probably one of the coolest too. Definitely one of the most modified, huh? If it's convenient throw up some pics.

 

[5150abf]

Re: Rear of pontoon submerged at WOT

Look into a Water Glide, sounds like exactly what you need.

16' of tube isn't alot of floatation, I imagine they are 23'' tubes also, you may just be stuck with what you have.

Careful with chines, hydrodynamics are a funny thing, what you are sure will work doesn't and things you don't give a chance work really well.

I am at Bennington and getting a chine combo to work right can be alot of trial and error but if you like to tinker and can weld why not, I am a welder myself and it is a REALLY nice thing to know how to do.

 

[mgjtkt]

Re: Rear of pontoon submerged at WOT

How about adding an aluminum "skin" to the underside of the deck. If you're sitting that low, water hitting the deck bracing may be dragging the rear down. Just a suggestion.

 

[jusfloatin]

Re: Rear of pontoon submerged at WOT

How about adding an aluminum "skin" to the underside of the deck. If you're sitting that low, water hitting the deck bracing may be dragging the rear down. Just a suggestion.

I would also suggest that.

If the cost is a concern you could try that with some 1/4" plywood this way if it did you would have a great pattern to work from.

Let us know.

 

[stevetedder]

Re: Rear of pontoon submerged at WOT

How about adding an aluminum "skin" to the underside of the deck. If you're sitting that low, water hitting the deck bracing may be dragging the rear down. Just a suggestion.

Im not trying to steal your thunder here but my problem really seems to be on par with this one.
How much effect can water hitting the bracing really have? Ive noticed it seems to be happening on my 24 ftr and I have a hard time getting it on plane. When I am in motion (someone else driving) I look under the deck from the top and see a lot of water being thrown on top of the toons from the fins on side of the transom. Think adding an aluminum skin to the back section of the bottom would help me as well or would a hydrofoil be more effective ? (its not actually in the water Im just looking for it to sit a little higher on the stern)

 

[flycaster]

Re: Rear of pontoon submerged at WOT

I have a 1991 16' Crest pontoon. The boat originally came with a 35hp Force motor which was basically junk when I got the boat. I now have a rebuilt 79' Johnson 85hp which is a couple hundred pounds heavier than the Force and consequently the boat sets 2" or so lower in the rear. To address the larger motor and weight I unbolted and moved the transom forward 7" as well as welding on additional bracing as the transom was only rated for 50 hp. I also relocated the fuel to the middle of the boat with a permanent tank and got rid of the two orange tanks setting on the rear platforms. Lastly I rearranged the furniture while re-carpeting and now the bench seat is along the side instead of in the rear. The problem is at WOT the rear of the pontoons become completely submerged causing a significant drag. I still have one of the fastest pontoons on the lake, but I would like it to ride somewhat level under power. Anyone have any ideas? I have considered a hydrofoil stabilizer to create some lift on the motor.... Maybe after this season I will weld on some full length strakes to try to get some plane effect. Any suggestions would be greatly appreciated.

I would suggest that you check the "TOONS" for water. It sounds like when you take off there must be some water in the toons which goes to the back causing more weight in the rear.

 

[sumcat1]

Re: Rear of pontoon submerged at WOT

Check out Nauticus trim tabs. They work great on boats with a hull. Since you can weld you may be able to adapt them. John at Nauticus may be able to help.

 

[gmc1962]

Re: Rear of pontoon submerged at WOT

I was chat with a guy last week that has lfting strakes on his twin tubed boat. He was out with a crew of guys fishing and the bow took a dive on him. The lifting strakes actually pulled him down once the nose started diving.....Be careful with a twin tube and lifting strakes, and for heavens sake load your boats properly!!! P.S. Skinning the underside of your boat helps more than you would think. That Water Glide says they give 700# of floatation....that would help.