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Boat porpoising


sneak_e_pete

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Hi all, got the new boat out yesterday. Although it was really nice to have her in the water, she was porpoising like crazy once I got over 3,000 rpm. Although there were some small rollers, I should've been able to open it up.

 

Not sure what to do. It was trimmed down all the way. For reference, its a Smokercraft Promag with a 140hp.

 

Thanks in advance.

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Yep that's what thought also I had to do it with my 14'er years ago put the gas tank battery up front and it settled down

 

I also added a extension to my throttle out of PVC pipe do I could sit one seat forward it made for some harder turns but worked

Edited by Mike P.
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Did you try getting on plane and then backing off the throttle? That helped when I was playing with my boat weight...

 

Were you by yourself in the boat...? A second person might be all the weight you need...

 

Is there a bow livewell by any chance??? If so you could fill it for weight...

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Bring a buddy who doesn't mind being ballast and have him move around the boat to see if it makes it better or worse. There is a cure for this also involving shimming the motor but that is something that the dealer can help you with if it is needed.

 

 

Art

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If it is really all the way down. Then you have problems I think you need 15deg shims. Between your motor and transom your engine may may be too low. Post photo

Change prop or trim tabs

 

dang I hate autocomplete on phones

Edited by Terry
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My guess would be two possible causes without knowing all the symptoms...

Motor too low. Raise the motor mounts so the cavitation plate is at or slightly above water level when cruising.

Boat is too wide for its length and/or aft heavy. Make it longer with a jack plate or trim tabs.

 

A jack plate may be the right solution as it would address both issues but its not a cheap addition for a 'maybe this will work'

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Thanks. I don't have a pic right now, but there is a transom picture on page 2 under the post "New Boat (pics). Kinda sucks. Just wanted to get out there and use it.

It will get sorted out, I had some issues with mine that make yours look enviable! My motor was mounted to low and I experienced some porpoising but worst of all, they had the hydraulic steering set up backwards. Turn left, go right. Made it fun for trolling and docking.

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Try adjusting your trim when you have planes out.

 

X2, you got 2 forces fighting each other, the hull wants to break free with speed and run on top of the water while the trim down all the way is forcing it to plough, leave it down when you hit the throttle or else you are going to stick the bow straight up, once you are past the point of the bow rising start trimming out, if it is anything like mine, 18 foot Sylvan with a V4 you will feel the steering ease up and not be heavy and the rpm increase slightly. If anyone is stern heavy it is me with a centre console, everything is at the back , fuel, batterys, 9.9 kicker, riggers, nothing at the front but a very large Igloo cooler and some life jackets. You will find you are on the trim a lot depending on speed and water conditions, just remember at displacement speed down is best and trim out as speed increases.

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Does it has the 24v i-pilot on the front? If not, might be a great opportunityto get one! 2 12v deep cycle batteries will do the trick of adding weight to the front.

Edited by Rob C
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Has the 24 volt ipilot. I always thought that trimming up when on plane would make it bounce even more?!

 

 

Yep, thats correct.

 

trip up = bow up, trim down = bow down.

 

If your porposing, trimmed down all the way, you need to lift motor, shim the motor, or put some weight up front.

 

When you say there was a roll on the water....were you on lake O? I have a hard time running wide open in a roll without bouncing all over the place. A chop is a different story, she will cut thru it, but a roll feels like I'm porpoising.

 

I'd take it for another ride on a better day to get a proper feel for it.

 

If you have a livewell up front, fill it up.

 

Are your batteries for the TM up front?

 

S.

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I was on Erie10kmh winds, but the waves were rollers. Tm batteries are located under the console windshield on either side. I will test it out some more, but to me, I should've been able to go over 3,500 rpm w/ out bouncing like crazy.

 

Would trim tabs help?

 

I emailed the dealer to see what they have to say.

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