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How to stop porpuising?

Old 02-14-2019, 06:43 PM
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Default How to stop porpuising?

Hello, I just bought an aluminum boat. What is a good way for it to sop porpoising? (bow going up and down on a flat day) any suggestions? should i get a hydrofoil? TIA
Old 02-14-2019, 06:44 PM
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Do you porpoise on purpose?
Old 02-14-2019, 06:52 PM
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I called that one out of the park. Touchè BT.
Old 02-14-2019, 06:55 PM
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Originally Posted by obear View Post
Hello, I just bought an aluminum boat. What is a good way for it to sop porpoising? (bow going up and down on a flat day) any suggestions? should i get a hydrofoil? TIA
Before you can stop porpoising you have to find out why it's doing it in the first place. Usually too much weight aft. Some props can help, what size boat and what engine?
Old 02-14-2019, 06:57 PM
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What boat, year, engine? Any other heavier equipment on the boat (e.g., trolling motor, extra batteries)? At all speeds or in a certain range?
Old 02-14-2019, 06:57 PM
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There may be a "Hook" in the bottom of the boat. Sight and take a long straight edge to check. Trim Tabs (active) or a Permatrim (in my opinion the best of foils) may well help. Just trimming the motor correctly, moving helms person / passengers or getting more weight in the bow may also help.

Tell us about the aluminum boat. Brand, model, type size, age etc.
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Old 02-14-2019, 06:58 PM
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It is from too light a front end. Any slight rise will cause the oscillation to start and get progressively worse.

Check that the outboard isn't set with excessive trim setting... basically there is usually a pin/bar that sets the angle of the outboard away from the transom in the down position.

If all else fails... get some weight of some kind up in the nose to help. But you should be able to get the motor adjusted down to accomplish the smooth ride.
Old 02-14-2019, 07:03 PM
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Originally Posted by Flybull View Post
It is from too light a front end. Any slight rise will cause the oscillation to start and get progressively worse.

Check that the outboard isn't set with excessive trim setting... basically there is usually a pin/bar that sets the angle of the outboard away from the transom in the down position.

If all else fails... get some weight of some kind up in the nose to help. But you should be able to get the motor adjusted down to accomplish the smooth ride.
As said above, I would start with motor trim. But without more information like everyone has stated no way to know.
Old 02-14-2019, 07:15 PM
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sorry I should have clarified. It is a G3 1652 SC w/ a 50 yamaha. i have the gas tank, and two batteries in the back plus me. i mainly keep the motor trimmed down. rarely touch the trim. with just me on the boat, it will porpoise up and down. almost no weight upfront as i dont have any ideas to keep bow down. planes off no problem.
Old 02-14-2019, 07:18 PM
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Just gotta get the trim right
Old 02-14-2019, 07:21 PM
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Originally Posted by BillTex View Post
Do you porpoise on purpose?
Yep, kids love it
Old 02-14-2019, 07:26 PM
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Motor height can make one porpoise. Check to see if its to low.
Old 02-14-2019, 08:04 PM
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Why do the majority of guys load there boats ass heavy ???? the hull need to be balanced properly !! I promise you a well balanced hull rides better goes faster , Is easier to drive and handles like a dream !
And yes hook in the bottom is another of the many problems that get the ups and downs going down and up !
Motor trim and motor set up height is all very important stuff !
So make a list and gradually work through it one thing at a time ! the old saying change ONE thing and upsets 3 other things applies !
Old 02-14-2019, 08:05 PM
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Get some weight in the bow. The trim angle isn't the critical factor in this scenario. Your center of gravity is way too far aft. Whatever you put. inn the bow needs to be secured properly as it's going to be a rough ride up there. Portable fuel tank is probably the easiest thing to relocate, but if we're talking 6 - 9 gallons it probably isn't enough weight, especially when you consider the weight will drop as you ru out your fuel. Batteries will take a pounding up there too. Find a fat friend to take along.
Old 02-14-2019, 08:26 PM
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i will bring a fat friend and strap him to the bow! thanks THT! 🤠🤠
Old 02-14-2019, 08:33 PM
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Moving the gas tank forward in a small boat will take care of it a lot of times. Relocating the batteries will help too.
Old 02-14-2019, 11:07 PM
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You need to look at this methodically, don't do 10 things at once, motor height is the very first thing to get right because it can cause your problem, and a dozen other issues as well, once that is sorted, the trim angle needs to be right, does it have power trim? hull geometry needs to be checked, as mentioned, a straight edge will work, weight is simple, but motor height is first job, has it always done this?
Old 02-15-2019, 02:39 AM
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I know a couple of people who have fitted the Nauticus tabs to tiller steer 17ft open boats and they recommend them. I think they are only a couple of hundred to buy.
Old 02-15-2019, 03:00 AM
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Move weight forward and/or trim the engine down (in).
Old 02-15-2019, 05:21 AM
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Hook will push the bow down, not up. Rocker is the opposite of hook and puts the bow up and causes porpoising.

Last edited by Fiberglass1 Inc; 02-16-2019 at 08:03 AM.
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