Need advice to eliminate porpoising

bertherr

Petty Officer 3rd Class
Joined
Jun 10, 2001
Messages
84
My 1978 Ebbtide Dyna-Trak 160 SS will porpoise at any planing speed with the power trim all the way down or anywhere else. Should I try a one of those fins on the anti-cavitation plate or trim tabs? It has a 85hp Johnson. How do you determine which holes to put the rod in that stops the motor from going down? Thanks, Bert :D
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Need advice to eliminate porpoising

Hi, Bert.<br /><br />Porpoising is caused by too much weight astern, too much pitch in the prop or too much trim-out.<br /><br />Sometimes a hydrofoil helps, provided the rigging is correct. It moves the center of contact aft.<br /><br />Sometimes a wedge between engine and transom will help by providing less natural out-trim.<br /><br />Sometimes a shorter pitch prop doesn't run out of thrust when the bow rises.<br /><br />Good luck. :)
 

bertherr

Petty Officer 3rd Class
Joined
Jun 10, 2001
Messages
84
Re: Need advice to eliminate porpoising

Thanks. Would a "shorter" pitch be a higher or lower number? I have a 19" now. I think the weight problem may be the root cause. The outboard engine, two batteries, 18 gallons of fuel, and the driver all towards the rear. I can not change these so I am looking for something to combat this situation. Thanks, Bert
 

Mikedg

Petty Officer 2nd Class
Joined
Sep 3, 2002
Messages
131
Re: Need advice to eliminate porpoising

I would look into installing tabs. To keep it simple and at a reasonable cost you might look into Smart Tabs. They are self adjusting and don't require a pump. I've been looking at them to install on my dinghy. Check them out here http://www.nauticusinc.com/index_1024.html
 

Gold Bear

Petty Officer 1st Class
Joined
Sep 26, 2001
Messages
224
Re: Need advice to eliminate porpoising

bertherr <br /><br />I have the same boat with a 115 Merc.<br /><br />The guy I bought it from fabricated a stainless steel wedge that he fit between the engine and transom. At the top end the wedge is 1-1/2" thick, and it tapers down to nothing at the bottom. This wedge increased the rake angle of the transom.<br /><br />Tilt your engine all the way down (put the pin in the lowest hole) then site down the cavitation plate to see if the engine is still tilted up in relation to the keel. If it is you may need to do the same thing the previous owner of my boat did.<br /><br />I have a Sting Ray on my engine and it jumps right up on a plane. However, I do experience some porposing at about 45 miles per hour. If I continue to accelerate it gets past that when the bow lifts. I have considered moving my trolling motor battery up to the bow to help this minor problem.<br /><br />Good Luck,<br /><br />Gold Bear ;)
 

bertherr

Petty Officer 3rd Class
Joined
Jun 10, 2001
Messages
84
Re: Need advice to eliminate porpoising

Thanks everybody. Gold Bear, please go to the fishing forum and see my posting about charging the trolling motor. Do you have this switch that I mention? I just purchased the boat and do not know how this system works. My boat is green on green. bertherr98@yahoo.com Thanks, Bert :D
 

rdmoore

Cadet
Joined
Jun 9, 2003
Messages
14
Re: Need advice to eliminate porpoising

True Story. A few years back , I was looking for a smaller boat than my<br />Four Winns cuddy, mainly for taking the family out on small lakes for water<br />skiing and tubing. After looking around a bit, I purchased a Stingray 180<br />RX bowrider. It seemed to meet our space and performance needs and seemed<br />like a real value for it's cost. And it was, except for one glaring fault.<br />At anything less that W.O.T and speeds below 35-40, it would porpoise<br />horribly unless you kept the trim fully down. Because you had to drive with<br />bow always plowing the water, instead of planing as it was designed to,<br />cornering was very unpredictable, gas mileage suffered and handling in<br />general was poor. It got to be so bad, my wife refused to drive it when I<br />wanted to ski. Having owned many other boats that you could trim at any<br />speed (once on plane), I knew this was not correct and tried to work with<br />first my dealer, then Stingray the company, to get this corrected. To make<br />a long story short, lets just say they both were an absolute joke. All I<br />had to show for months of effort of trying to go through the proper<br />channels, was countless unanswered phone calls and e-mails, wasted trips to<br />the dealer, money wasted on another prop, a lot of frustration and the<br />first hand knowledge (after trying other 18 & 19 foot Stingrays out) is<br />that they all porpoise just as badly! Many other disgruntled owners had<br />also contacted me with this same issue, after I started asking for help on<br />various boating forums. But just as I was convinced this is a flaw in the<br />design and was putting the boat up for sale, I learned of the smart tabs<br />from Nauticus. I contacted the company, who was very helpful and promised<br />they would completely fix my porpoising problem. After all I had gone<br />through with the shallow answers and promises from my dealer and Stingray,<br />I was extremely skeptical, but I went ahead and ordered a set, figuring it<br />was a lot cheaper than buying another boat. Got them a few days later and<br />installed them in about an hour.<br />Let's just say the results were far beyond my highest hopes. There is<br />absolutely no more porpoising. None whatsoever, no matter what speed or<br />trim the motor is at. Additional benefits are that the thing planes almost<br />instantly, it virtually doesn't even lift the bow at all! You feel like<br />you're in a car, not a boat when you take off! Because of this the hole<br />shot improvement is amazing. Heavy slalom skiers I could not pull out of<br />the water previously, now are no problem. Gas mileage is improved and the<br />thing corners predictably and rides much better. I even called the owner of<br />the company and thanked him personally. That was 2 years ago, and I can<br />truly say I am now 100% satisfied with this same boat I was so disgusted<br />with before the smart tabs installation, and can't even imagining using it<br />without the smart tabs. I hear so much about boaters looking for<br />performance improvements with expensive engine and prop modifications, <br />or complicated hydraulic or electric trim tabs, <br />when they could just add a set of these and get better performance<br />improvements (except top speed, that was not affected) at a fraction of the<br />cost. Several of my boating friend have installed them after they heard of<br />my success, with similar positive results. So go ahead and give them a try,<br />you won't regret it. Feel free to e-mail me if you have any questions.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Need advice to eliminate porpoising

Thanks for the testimonial, RDM. <br /><br />This is the kind of info members really want.<br /><br />I have had good results controlling porpoising with a SE Sport 300 hydrofoil, but my porpoising wasn't nearly as bad as yours and my results, while good, weren't as spectacular.<br /><br />My only advantage was that I spent a lot less.<br /><br />Thanks again for your contribution. :)
 

suzukidave

Petty Officer 1st Class
Joined
Jul 1, 2000
Messages
387
Re: Need advice to eliminate porpoising

RDM, good testimonial. I also tried smart tabs with amazing results on a 16' deep v fishboat with a 55. No more porpoising, much less pounding, and turning without speed loss like I was on rails, I also picked up overall speed too. They are great.
 

rdmoore

Cadet
Joined
Jun 9, 2003
Messages
14
Re: Need advice to eliminate porpoising

Glad to be helpful. I'm just trying to stop others going through the frustration I had, when there was such a easy fix available. Randy M
 
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