porposing

bigbass69df

Cadet
Joined
Sep 14, 2002
Messages
9
When I trim my motor up about 1/4 of the way the front end starts to porpose. I have a jack plate and was wondering if raising or lowering the motor would help this problem? Also if I need to raise it will it hurt my hole shot? If so will a bigger prop help that? thanks
 

Combee

Seaman Apprentice
Joined
Sep 11, 2002
Messages
42
Re: porposing

Bigbass,<br /><br />Trim tabs will solve your problem. Just a suggestion.<br /><br />Dan
 

superman

Petty Officer 2nd Class
Joined
Aug 23, 2002
Messages
133
Re: porposing

Your best performance should be with your cavitation plate at the same level or just below the bottom of the boat. You don't want to raise the motor to where it is higher than that. As for your prop, you want to prop your engine where your engine runs at rated rpm. Don't know what kind of motor you have but rpms probably should max at about 5000 to 5300.
 

MGuckin

Senior Chief Petty Officer
Joined
Jun 10, 2001
Messages
760
Re: porposing

Been following your other post also.<br />Are you sure about your rpm and max speed?<br />125 hp @ 5400 rpm on a loaded weight of about 2000 lbs. with a 17" pitch, should run around 43 mph?? <br />Don't make sense.<br />Forget about the cavitation plate and where it is.<br />For maximum performance you want as little of your boat and motor in the water as possible and still be able to handle hull without cavitation and porpoising, you do need to watch your water pressure as lifting it to high may miss the pickup.<br />Less drag and rev quicker.<br />If trimming your motor a 1/4" up is causing porpoising, your going to high or your jack plate is set a bit to high. Back it down a bit and try it again.<br />Could you maybe have a spun or damaged prop?
 

bigbass69df

Cadet
Joined
Sep 14, 2002
Messages
9
Re: porposing

Prop is new so that sgould rule that out. 43 mph would be great if I could get it there. But I did forget to mention 1 thing that may or may not effect, my motor has about a 24 inch shaft I think and my boat measures 22" from top of transom to bottom of boat. This is why I used a jack plate, to raise the motor up more. Could the weight of the engine being higher in the air cause my problem?
 

Skinnywater

Commander
Joined
Mar 7, 2002
Messages
2,065
Re: porposing

Because of the setback a jackplate has, it's possible to raise the motor a few inches higher then a boat/motor without one.<br /><br />As water leaves the back of the hull it gets cleaner and less turbulent the further back it gets. It also rises in height in relation to the trailing edge of the hull.<br /><br />Both this and the porposing is hull design characteristics.<br /><br />Combee's suggestion of trim tabs is also correct as the tabs modify those characteristics.<br /><br />The height, holeshot, performance, handling can only be answered with experimentation.<br />Take some tools to the lake and find your boats own "sweetspot".<br /><br />When raising your motor into the upper limits of your experimentation range be sure your motors cooling system stays submurged at speeds. MG's post mentions this also.<br /><br />Keep in mind what may be an ideal setting during one set of operating conditions may not be in another. Find the compromise.
 

rdmoore

Cadet
Joined
Jun 9, 2003
Messages
14
Re: porposing

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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