Polymer changed my boat. Help

A general, non-powerplant specific, discussion on airboat technology, ie., hulls, rigging, polymer, etc..
RickMc
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Polymer changed my boat. Help

Postby RickMc » Mon Feb 06, 2017 9:22 am

Hello I just put 5/16 UHMW on my boat and went for a ride. The boat use to ride nose high and hop until I lower the trim tab. Now at higher speed it pushes the nose down hard no longer hops and doesn't need the trim tab at all. I expected some changes but not the other end of the spectrum. The boat is a 12 ft fiberglass hull with a 0320. what adjustments should I make to reach a happy medium? Thanks Rick
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Deano
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Re: Polymer changed my boat. Help

Postby Deano » Mon Feb 06, 2017 9:32 am

Raise the rear of the engine a little bit. Fender washers used as spacers work very well. If the polymer was the only change, I would expect that one or two will make the difference you are after.

The angle of thrust should be parallel to the water.
If the bow plows, it (the rear of the engine) needs raised.
If the bow porpoises, it (the rear of the engine) needs lowered.
As you add them, if it starts porpoising that's to much of a good thing, take one back out.

Fender washers are typically a small enough adjustment to dial it in where it needs to be.

Realistically there are many variables, but that is the first one to pursue in this case,
and with any luck will resolve that issue.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
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snookstalker
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Re: Polymer changed my boat. Help

Postby snookstalker » Mon Feb 06, 2017 10:21 am

Slide the boat off the trailer a foot or so and check to see that the last row of bolts didn't cause the trailing edge of the polymer to bend down a bit as the bolts were tightened. Had this happen before. It was just a very small amount, but it made my boat ride on the nose. A slight shave with a belt sander to the very trailing edge took care of it.
Hope this helps, Dan

RickMc
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Re: Polymer changed my boat. Help

Postby RickMc » Mon Feb 06, 2017 10:50 am

Thanks Deano. That's what I was going to try. If I remember right my motor is 3 washers down from level trying to kill the hop last year. Never thought I would have this problem
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Deano
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Re: Polymer changed my boat. Help

Postby Deano » Mon Feb 06, 2017 4:04 pm

It is quite possible that it isn't that you have a problem,
but rather that you have minimized the one you used to have. :)

If you did any work on the bottom and then added the poly, it may well be straighter than it was before.
If so, you would likely need to undo some of the prior adjustments that were made.

I will add that Dan brings up a legitimate possibility that shouldn't be overlooked.
If the furthest aft row of fasteners have the polymer pinched to far forward, he may be right.

Putting a straight edge on the aft most two or three feet, should show if that is a concern or not.
If you find a gap there, a little time with the belt sander or the like, could save you a bunch of grief.

If it is straight and flush, adding a washer or two would seem to be in order.
Ultimately, anything that eliminates the need for a trim tab is a wonderful thing.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan


SWAMPHUNTER45
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Re: Polymer changed my boat. Help

Postby SWAMPHUNTER45 » Mon Feb 06, 2017 4:52 pm

Some fiberglass boats have a lip at the transom area that the builder designed into the hull. When you add poly it exasperates this and forces the nose down. A old fabricator in my area suggests in that situation a hull jack about 18-24 inches from transom with slight downward pressure.

Just be careful a nose heavy boat will swap ends quickly.

RickMc
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Re: Polymer changed my boat. Help

Postby RickMc » Mon Feb 06, 2017 9:19 pm

Today I added 3washers to the rear motor mount. Prior to the polymer I repaired a cracked/worn aria at the transom. I was pretty carful not to add to much to the bottom and make a bulge. I did leave the polymer about 1/4 past the transom to help protect from further damage. After looking at it today it does have the slightest turn down in part of the rear. 1/16 maybe on about a foot in the center. Could that be more effective than the trim tab that goes an inch or so below the bottom? I am not going to get to test test ride till Wednesday. Thanks for the input guys. Anyone going to be down by the Nav A Gator Thursday.
Rick
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SWAMPHUNTER45
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Re: Polymer changed my boat. Help

Postby SWAMPHUNTER45 » Tue Feb 07, 2017 6:32 am

That poly runs the entire length of the beam and has a huge impact on how the boat will respond. The trick for boats that hop is to run the poly 1/2 inch past the transom and wedge it to force the nose down. I doubt washers will fix the issue that poly creates a lot of down force.

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Deano
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Re: Polymer changed my boat. Help

Postby Deano » Tue Feb 07, 2017 9:46 am

Using washers to adjust the angle of thrust is only assured to make a positive improvement when (and after) the bottom of the hull is straight, flat and true. This includes any polymer that may be present. This should be considered a final adjustment after the bottom is straight. Never meant to imply otherwise.

Wedging the polymer at the transom may be a trick to avoiding a trim tab, but is no substitute for correcting a bottom that is not straight and flat, nor will it allow for the same hull tuning results.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

One Eyed Gator
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Re: Polymer changed my boat. Help

Postby One Eyed Gator » Wed Feb 08, 2017 7:30 am

I had a fiberglass hull that was older, it would only bow in the water on plane you could watch the bottom flex up as you got on top off the water. It sat flat on a concrete floor. When I put new poly on it force the nose down. As hull bowed up it forced poly lip at transom. I put a (3) hull jacks in and it helped. Boat ran better than it ever had.

Was just my situation and something to think about.

RickMc
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Re: Polymer changed my boat. Help

Postby RickMc » Wed Feb 08, 2017 4:38 pm

I have 3 hull jacks. One is about 8 in. from the transom one at 3 1/2 ft. one about 7 ft. I added a few turns of tension to the center and rear when I had it out on Sunday. It seemed to help a little. I just slid the boat back off the trailer and put a straight edge on it and the polymer does have a turn down at the last row of bolts.Most of it is 1/8 th or so but some spots are a little more. So this is probably my problem. My next problem is that I'm about1200 miles from home and tools. Anyone near Anna Marie island with a belt sander I can use ? We are going down to the Nav A Gator tomorrow to eat and ride a little. I'll see them if the three washers added help at all. Thanks for the tips Rick
The glass is always half full....til I get a hold of it

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Junker
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Re: Polymer changed my boat. Help

Postby Junker » Wed Feb 08, 2017 6:06 pm

A quick trip to "horrible" freight would probably get you a one time use belt sander for $35
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RickMc
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Re: Polymer changed my boat. Help

Postby RickMc » Wed Feb 08, 2017 6:42 pm

That crossed my mind. I'll have to see how my day goes tomorrow. I'm not vacationing alone so it's not all about the boat. Worst case we are heading to Ft Lauderdale to see my brother in law Saturday. He has one and we are planning to go riding in the glades. Hopefully we can get it worked out then. Thanks Rick
The glass is always half full....til I get a hold of it

RickMc
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Re: Polymer changed my boat. Help

Postby RickMc » Sun Feb 12, 2017 8:52 am

I got a sander and removed the the turn down at the back of the poly. We took it out at the Loxahatchee boat ramp for a quick rip late yesterday It made a big difference and It rode much better. It's still really loose in the rear and slides sideways a lot in turns. It still probably still needs a little more tweaking I think if I load anything in the front it would be right back on the nose. Thanks for the tips and tricks guys Rick
The glass is always half full....til I get a hold of it

Dixiedog60
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Re: Polymer changed my boat. Help

Postby Dixiedog60 » Mon Feb 13, 2017 8:25 am

A short ride on asphault works wonders sometime. dont let it get too hot though!
Freedom is Abridged by Silent Encroachment.---James Madison

Teal fun
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Re: Polymer changed my boat. Help

Postby Teal fun » Thu Feb 16, 2017 6:04 am

leave it alone. When it gets broke in you'll be back to normal


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