Porpoising

Outboard designs up to 14'

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BlueRidgeBoater
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Porpoising

Postby BlueRidgeBoater » Tue May 12, 2015 6:51 am

I finished my 14' Power Skiff and launched it last weekend with a 15hp 4-stroke. Perhaps not unexpectedly, it has horrible bow rise with only one rider and bad porpoising. (When it was just me in the boat, and at low speeds, but brother in law nicknamed the boat the SS Viagra). I've got the motor trimmed in. I put two 30 lb weights in the front, and that helped, but I still can't go more than mid throttle on a smooth lake without being like Flipper. I hate to have to add a bunch of extra weight to improve ride quality because of the room it will take up (but will if I need to). I ordered some Smart Tabs to install hoping that will help. Has anyone used these? If so, what is your reaction to the product?

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chugalug
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Re: Porpoising

Postby chugalug » Tue May 12, 2015 7:05 am

:D Haven't used those.used to have a plastic whale-tail on motor .really liked those. made the motor kinda ugly and was a pain to hand clear weeds but seemed to help putting boat on plane faster and at a slower speed
Working on regular-sized Bo-Jest


"If it's not crooked,It's not mine

BlueRidgeBoater
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Location: Blue Ridge, GA

Re: Porpoising

Postby BlueRidgeBoater » Tue May 12, 2015 8:53 am

I looked at the whale tails, but the only ones I saw that would fit a 15 hp motor bolt through the cavitation plate and that would void my warranty with Suzuki. I've also heard that trim tabs do a better job of adding lateral stability.

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fergal butler
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Re: Porpoising

Postby fergal butler » Tue May 12, 2015 10:33 am

I made up some trim tabs for my boat and they worked a treat and stopped the porpoising :D I never did like the idea of drilling holes in an outboard to fit fins I feel if they were that good then outboards would come with them :)

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Soloboat
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Location: Orange CA

Re: Porpoising

Postby Soloboat » Tue May 12, 2015 11:32 am

Maybe the motor is trimmed in too far. Once you are on plane trim motor out until it starts to cavitate then trim back in to the sweet spot.
) Champagne dreams and wishes are possible on a beer budget. Just build the boat.
Nice curves are easy on the eyes.
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gdcarpenter
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Re: Porpoising

Postby gdcarpenter » Tue May 12, 2015 1:52 pm

Before spending $$$ you might try placing some shims between the engine and the transom to effectively trim the engine in a bit more. I believe this has done been done by one or more builders on this forum.
This is my first, last and only boat build.

http://www.gdzipbuild.blogspot.com

BlueRidgeBoater
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Location: Blue Ridge, GA

Re: Porpoising

Postby BlueRidgeBoater » Tue May 12, 2015 4:14 pm

I'm confused on the issue of trim. If I'm reading the posts right, Soloboat you are saying I need to trim out, and gdcarpenter you are saying I need to trim in more. My instinct is that I need to trim in more because I don't have porpoising when someone sits in the front of the boat, so it seems to me I need to get the bow down more. A guy at Boater's World told me the other day, though, that I need to trim up to put more pressure on the stern. Having heard it both ways, I'm a bit confused. I guess I will experiment with more trim, but I think I did that already and still had bad porpoising. I'll probably install the trim tabs anyway since they are on the way and lots of people say it helps with porpoising. Looks like an easy install also.

BlueRidgeBoater
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Re: Porpoising

Postby BlueRidgeBoater » Tue May 12, 2015 4:16 pm

Fergal Butler: Sweet looking ride. Maybe down the road I'll try something that ambitious.

Soloboat
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Location: Orange CA

Re: Porpoising

Postby Soloboat » Tue May 12, 2015 4:42 pm

There are several youtube videos on how to trim properly Give a look, experiment before getting too drastic :) After 3 years I am still fine tuning my boat and honing my skills. The day I launched my boat was only the second time I was at the controls of a power boat.
) Champagne dreams and wishes are possible on a beer budget. Just build the boat.
Nice curves are easy on the eyes.
Go sell crazy somewhere else we're all stocked up here."As Good As It Gets" Jack Nicholson.

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Bill Edmundson
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Re: Porpoising

Postby Bill Edmundson » Tue May 12, 2015 5:34 pm

The first thing is to take a straight edge and make sure the bottom is flat the last several frames.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

BlueRidgeBoater
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Location: Blue Ridge, GA

Re: Porpoising

Postby BlueRidgeBoater » Tue May 12, 2015 5:46 pm

I'm pretty sure it's flat, but will check it.

gdcarpenter
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Re: Porpoising

Postby gdcarpenter » Wed May 13, 2015 6:19 pm

My apologies, must have had a 'senior moment' - yes you need to trim the bottom of the engine out to help it 'push' the bow down. If you have a standard tilt pin move it rearward a hole or two and experiment.
This is my first, last and only boat build.

http://www.gdzipbuild.blogspot.com

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chugalug
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Re: Porpoising

Postby chugalug » Wed May 13, 2015 7:00 pm

:D Actually, if you don't have weight in front, you should trim motor in .We had that problem at the resort-Dad had gotten a 4-stroke Tohotsu 25 ,A lot of weight for rear of 16 ft. lund with a single person. was a dog until we extended the fuel hose and put fuel tank up front and put lower pitch prop on.Now runs fine.When I had my 50 Johnson I even raised motor up 3/4 inch-made a lot of spray on back ,however gained 3 or 4 mph.
Working on regular-sized Bo-Jest


"If it's not crooked,It's not mine

cusoak
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Re: Porpoising

Postby cusoak » Thu May 14, 2015 5:03 am

Not sure how much your boat weights, but if you are in the back using a tiller handle, you weight and the motor weight might be enough that that 15 hp wont get the boat up on plane.
Does it get up on plane.
Jeff

BlueRidgeBoater
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Location: Blue Ridge, GA

Re: Porpoising

Postby BlueRidgeBoater » Thu May 14, 2015 5:52 am

The boat doesn't have any trouble getting on plane, it's just that without a fair amount of weight in the front when the engine is more than 1/2 throttle it porpoises badly. I got some Smart Tab SX tabs in the mail yesterday. Going to install them and see if that helps. If not, I'll probably get 50-100 lbs of lead weight and put it up front.


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