Porpoising Problem

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Krahammer
Southern Airboat Member
Posts: 98
Joined: Fri May 06, 2016 11:18 am
Location: Jupiter, FL

Porpoising Problem

Postby Krahammer » Wed Jan 10, 2018 1:30 pm

My boat is a 2009 GTO, 14 foot, open welded aluminum hull. 3/8 Polymer on Bottom, 1/4 inch poly on sides, up 6". 450 HP MAS 383 Stroker, with Sensenich 3 Blade Super Wide H Prop. WOT is 5200 RPM. Has never porpoised before, in any conditions. Sunday, took a ride in Everglades Conservation Area 3A North, which meant a good bit of semi-dry running. I ran for a few hours, off and on, running a total of about 40 miles, running from camp to camp. No porpoise problems until after I left the last camp and started heading back to the ramp, about 7 miles away. Although the engine was developing full power, the boat felt sluggish, like it was dragging something. At 4000 RPM, the boat began to porpoise in only an inch or two of water. I could only get it to stop by reducing back to 3200 RPM. Back at the ramp, put the boat on the trailer and looked at the bottom. There are no tears in the polymer. No loose screws. Can't find any loose polymer. No missing pieces of polymer. The engine mounts and bolts are solid, are all of the rigging and connectors. Does anyone have any ideas of what I should be looking for as a cause of the sudden porpoise problem? Suggestions appreciated!

SHOOTER250
Southern Airboat Member
Posts: 59
Joined: Tue Sep 17, 2013 6:23 pm
Location: BROWARD

Re: Porpoising Problem

Postby SHOOTER250 » Wed Jan 10, 2018 2:03 pm

Make sure the lip sticking out past the transom
On the bottem is not bent up from running up
Up in the yards to park. I did the same thing in
the same place just bend it down even or just
a little lower and try it .A very little goes a long way make very small adjustments and test it

Krahammer
Southern Airboat Member
Posts: 98
Joined: Fri May 06, 2016 11:18 am
Location: Jupiter, FL

Re: Porpoising Problem

Postby Krahammer » Wed Jan 10, 2018 4:38 pm

Thanks, Shooter. I had not checked that.

Gary S
Site Supporter - I
Site Supporter - I
Posts: 1495
Joined: Wed Mar 03, 2010 3:30 pm
Location: Redlands

Re: Porpoising Problem

Postby Gary S » Fri Jan 12, 2018 6:10 am

You sure there are no rips under the bunks?

Krahammer
Southern Airboat Member
Posts: 98
Joined: Fri May 06, 2016 11:18 am
Location: Jupiter, FL

Re: Porpoising Problem

Postby Krahammer » Fri Jan 12, 2018 6:17 pm

I have thought of that. Going to lift it off the bunks and make sure before I do anything else. Thanks!

Krahammer
Southern Airboat Member
Posts: 98
Joined: Fri May 06, 2016 11:18 am
Location: Jupiter, FL

Re: Porpoising Problem

Postby Krahammer » Sun Jan 21, 2018 10:57 pm

Found the problem. When I left the last ramp, jumped a small hill. Apparently landed on a lump of marl or a rock. Caused a saucer size indentation between two stringers just in front of the transom. The indentation was less than 3/16". Removed the transom bracket so we had room to swing a three pound hammer. Used a block of wood against hull and hit it about 5 times. Made it flat again. Problem solved.

loudmouse
Southern Airboat Member
Posts: 479
Joined: Tue Jan 22, 2013 3:20 pm
Location: Ocala Fl

Re: Porpoising Problem

Postby loudmouse » Mon Jan 22, 2018 6:45 am

That was going to be my suggestion to look for, a dent near the transom. Glad you got it back running right.
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

Krahammer
Southern Airboat Member
Posts: 98
Joined: Fri May 06, 2016 11:18 am
Location: Jupiter, FL

Re: Porpoising Problem

Postby Krahammer » Mon Jan 22, 2018 3:43 pm

Thanks for the suggestions!


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