What is porpoising?

Hillfisher

Cadet
Joined
Nov 30, 2002
Messages
20
Is porpoising when the bow bounces up and down? What causes this and how do you fix it? <><
 

digimortal777

Petty Officer 1st Class
Joined
Jun 25, 2002
Messages
214
Re: What is porpoising?

waves cause it lolo<br /><br />it could be from the motor being trimmed out too much try trimming it in and see how she goes , also push come weight farwards
 

Jack Shellac

Lieutenant Commander
Joined
Aug 7, 2002
Messages
1,661
Re: What is porpoising?

Yes, it's when the bow lifts and falls in a rhythmic pattern. The motor is not providing enough thrust to keep the bow up continuosly. It can be solved by re-distributing weight, trim tabs, or changing props. Some people even wind up going to a 4 blade prop to solve the problem because of boat design, etc. when it can't be solved any other way. Some of the other guys may have a more technical explanation.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: What is porpoising?

Most porpoising is caused by the engine being trimmed too far out or the boat being stern-heavy.<br /><br />Good luck. :)
 

RJS

Petty Officer 1st Class
Joined
Mar 14, 2002
Messages
211
Re: What is porpoising?

I think Euro-transom also have a tendency to poroise
 

Zac

Cadet
Joined
May 23, 2002
Messages
19
Re: What is porpoising?

You can buy a hydrofoil stabalizer at a boat store for about 40bucks and it will work wonders!<br />I installed one on my boat and it never porpoised again and it gets up on plane alot faster and it also helps handling a ton!<br />Zac
 

Hillfisher

Cadet
Joined
Nov 30, 2002
Messages
20
Re: What is porpoising?

Thanks for the response. I know I can get temporary relief by trimming the motor down but I still get it at what I consider normal trim. Just put on a lower pitch prop but haven't had a chance to use it yet. Maybe that will solve my problem. I thought that the motor might be mounted too high and was considering lowering it a hole or two.
 

Fly Rod

Commander
Joined
Oct 31, 2002
Messages
2,622
Re: What is porpoising?

They had showed this on one of them bass fishing programs the other day and demostrated it. They showed it on calm water. power tilt should be all the way down when starting out and graudually tilt motor up and if she starts to porpoise trim the boat down to where she stops the porpoising. They didn't mention anything about the prop.The boat that they used was one of them over poweredddd bass boats. <br /><br /> :) ;) Happy boating!!! :cool: ;)
 

Hawaiian

Petty Officer 2nd Class
Joined
Feb 4, 2003
Messages
111
Re: What is porpoising?

Hillfisher, where is the anti-ventilation plate in relation to the bottom of the hull? Is it level or 1 or 2 inches above the hull when trimmed all the way in? Don't lower the motor until you get a good reference point. Does prop cavitate?
 

Hillfisher

Cadet
Joined
Nov 30, 2002
Messages
20
Re: What is porpoising?

The plate is about 3 or 4 inches above the bottom of the hull. I have a new prop that I haven't tried yet but the old one did not cavitate (if that means break loose and spin without gripping)
 

Neptune

Cadet
Joined
Oct 29, 2002
Messages
15
Re: What is porpoising?

Hi Hillfisher.<br /><br />It seems to me you would be experiencing prop cavitation at a setting of 3-4" above the bottom of the hull; this sounds too high for most boats. Do you have the correct shaft length for your hull? You might need to lower your engine on its mounts to get proper hull performance.<br /><br />Hi everyone else. Been gone awhile but glad to be back 'on board' no pun:)
 

rdmoore

Cadet
Joined
Jun 9, 2003
Messages
14
Re: What is 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.
 
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