Porpoising Problem...

[fireman57]

I smell NautiJohn on the way. All kidding aside this will probably your best way to go if your setup is the best you can get right now.

 

[pilot4net]

Porpoising Problem...

I just purchased a 2005 Xpress H56 Bass Boat (18'3") with a 115 Hp Yamaha 4 Stroke on the back. The boat is great but I have a few questions. The boat gets on plane quickly but when approaching top speed and as I start trimming the motor up, the boat starts porpoising. I can get the motor trimmed up enough to squeeze 48-50 MPH out of her with two adults and and small teen in the boat with a full fuel tank (30 gallons). I don't think that is bad at all, but I know I could get better performance since with it trimmed where it won't porpoise, the area where the water is hitting the bottom of the boat is about even with the console or where I am sitting. I can trim it up some more, but that's when it starts acting up. I had a smaller boat before this one, namely a 16' with 25 Hp Johnson and put a hydrofoil fin on it to help with the hole shot and eliminate the porpoising. It worked great and helped drastically with both problems. I was wondering if a hydrofoil stabilizer fin would help me with my problem on this boat. I have read on here where most suggest the trim tabs, but I don't want to be drilling holes in my brand new boat when there may be some other way to solve my problem. If anyone could let me know what they think either from direct or indirect experience or what you have heard through this site. Thanks.

 

[xltier]

Re: Porpoising Problem...

the hydrofoil works great as u know but not as stable in the water as tabs.they can be a little tippy at times.hth

 

[tommays]

Re: Porpoising Problem...

i love my foil but i really dont think it would be a good pick for a stabilty problem at 50 mph<br /><br />its a good item on something like your old boat that doesent go that fast<br /><br />and you would still have to drill holes in your brand new motor to use one <br /><br /><br />tommays

 

[Jdeagro]

Re: Porpoising Problem...

The porpoising issue is a balance problem. I can understand that you do not want to drill holes in you new boat, especially when the dealer says that your boat does not need trim tabs. He is correct if you boil the performance down to the basics, "the boat floats". <br /><br />If you Spend the $25.00 for a hydrofoil you may stop the porpoising but i doubt the boat will run more than 45 MPH, and it will dive in hard turns and blow out the prop.<br /><br />If you do not want to dril holes in the boat, waite a few years until it is no longer new. Just kidding! I would not want to drill holes in my motor either.<br /><br />Mobster Tabs are the best investment you will ever make for this boat. I know as we make them.

 

[Dhadley]

Re: Porpoising Problem...

Hey John, check out the post in the E/J section about a handheld tach.

 

[MajBach]

Re: Porpoising Problem...

I have put 'Dol-phins' on three boats: 14 plain aluminum w/ 18hp, 17' DC with 90 hp 4 stroke and 25' Sea Ray Sundancer. The results were pretty much the same on all three boats but to a different degree. I went from 20 mph to 26 mph on the 14', planing speeds dropped 20% on the two larger boats, hole shot was unbelievably improved on the 17' and top speed was unaffected while it slowed top end by 2 mph on the Sea Ray. On the two smaller boats, porpoising ( a real problem as I was sooo stern heavy on both ) was eliminated. I don't understand why outboards aren't built with these things from the factory since the results seem so benefitial.<br />I wish I had the time and $$$ to try smart tabs, despite the claims from many here, they still have a 'snake oil' ring to them (although, I suppose some could say the same of the manner in which I just described a fin) and I just dont want to leave a bunch of holes in my transom.

 

[stevens]

Re: Porpoising Problem...

Yes, the Smart Tabs do seem too good to be true, but you'd be amazed at how well they actually work. I've only had mine for a few weeks now, and they have completely changed the way my boat behaves, at all speed levels. They were about twice the price over here, but still well worth the money.<br /><br />I was also hesitant about drilling holes in my nearly new boat (only 1 year old, and all 14 holes below the waterline). But, the instructions were fool-proof and I applied the sealant liberally. Get over it, you'll be glad you did.<br /><br />NautiJohn will probably elaborate on tabs vs. fins, and there is also an informative booklet on boat balance available from his website that you may care to look at. Good luck!

 

[Jdeagro]

Re: Porpoising Problem...

Let me go back a bit a discuss the Hydrofoils a little mote carefully. I don't want DHadley to get ticked at me. As most of you know he is a very knowledgeable man when it comes to boat performance. Not to mention a good guy.<br /><br />I do not debate the validity of hydrofoil technology. What I do have a problem with is the idea that anyone can take a $25.00 plastic wing, bolt it to the motor and achieve the performance they are led to expect without compromise. It is possible but it is a crap shoot. Why? Because it changes the running surface of the boat (the hull design). As Dale will tell you hydrofoils can be a very effective "tool" to improving boat performance. And "Tool" is the operative word. If the motor and we are now restricted to outboards, is at a running height that allows the hydrofoil to ride below or at water level when the boat is cruising, then it will induce other handling characteristics that most likely will not be good. Therefore the motor height needs to be adjusted correctly. This is not the trim but the actual mounting location of the motor. If the boat is an I/O drive then your stuck. <br /><br />When the hydrofoils run at or below water level they are in essence an extension of the hull. Therefore the hydrofoil changes the hull design. In this situation the additional lifting surface is centered on the hull and changes the lifting area toward the center of the boat (keel). At slower speeds the effect is less noticeable, but as the boat increases in speed the hydrofoil becomes more influential, because the boat rises up and rides on less hull surface. Between the reduction of the wetted surface (hull in the water) and the increased pressure on the hydrofoil (which is rigid) the boat will tend to rotate bow down. Trimming the motor will help compensate for the bow down attitude but this is not efficient since the prop is now fighting the hydrofoil. The typical loss of top speed on boats that achieve more than 40 mph is indicative of this, even though the speed loss is mistakenly attributed to "extra drag on the motor". It is more of an attitude issue. All of this can be avoided if the motor is raised to a point where the hydrofoil runs above water at cruising and higher speeds.<br /><br />If the hydrofoil runs at or below water the other handling issue are a bow down attitude in turns, and a exaggerated lean in turns unless the boat is slowed. The hydrofoil can act as a rudder in some cases. The loss of speed is also translated into a loss of efficiency (MPG.)<br /><br />Simply adding additional planing surface to a boat without the ability to adjust it is a gamble. <br /><br />Keep in mind that the motor manufacturers have seen and tested these devices many years ago, and if it were applicable to all boats they would have simply increased the size of the anti ventilation flange, especially on the heavier four stroke motors.<br /><br />Being able to "adjust" the hull design to suite the conditions maximizes hull efficiency and overall performance.

 

[pilot4net]

Re: Porpoising Problem...

Thanks NautiJohn and everyone else that replied to my inquiry. I appreciate all your inputs and will look at my options. In all honesty, do you think 48-50 mph, with a full tank of gas and three people in the boat, is a good top end speed for my set up?

 

[LubeDude]

Re: Porpoising Problem...

Id like to make a couple comments on this one.<br /><br /> I have the Mobster tabs on my 18' 150 Merc Bass Boat and they do what they are advertised to do. I can run over 60 MPH, but I have to say that an 18+' boat with a 115 is in my opinion just slightly underpowered. I know you do not want to hear that though. Even with the tabs, I can make my boat porpose by trimming too much without enough power. If its porposing, I can stop it by giving it more gas. It "IS a Balancing problem, there just isnt enough power to hold the bow up above 50 MPH.

 

[pilot4net]

Re: Porpoising Problem...

I hate to keep prying, but do you all think I may benefit from raising the motor one hole on the mounting bracket (no jack plate)? Right now there are two more holes that I can raise the motor with. I was just thinking that it would be quite a job since I am pretty sure that motor isn't very light. So my question for you all who are experts compared to me is, can raising the motor one or two notches (holes) help me? Thanks in advance for your responses.

 

[QC]

Re: Porpoising Problem...

My personal opinion is that raising the engine will potentially increase the porpoising. Speed sounds about right to me, but I think you should rearrange some stuff in the boat first. Put heavy toward the bow, and store light stuff aft. If you can get just a little bit of a balance shift going, then you should be able to trim out a little more without the porpoising; maybe gain you a coupla MPH. I would do that before I monkeyed with anything else. This way you know how much that will benefit you.<br /><br />The Smart Tabs are starting to grow on me, although I still swear by adjustable tabs like Bennett's. Remember, unless your hull is messed up, porpoising is usually a balance issue just like some others here have said. You will never see a hydrofoil on one of my boats. I would sell it first!

 

[stevens]

Re: Porpoising Problem...

No reason to remain sceptical to the Smart Tabs, Quietcat. They really do work well, and do so without you having to pay them any thought. Being an amateur boater, I have enough other things to concentrate on and look at, so I am thankful the Smart Tabs just sit there and do what they should.

 

[QC]

Re: Porpoising Problem...

Yeah Stevens, it is your report and another's recently that has started me thawing. I think you have hit it on the head. If you like to play with stuff, then go adjustable. If you are more comfortable sitting back and letting the thing do its thing then go SmartTabs.<br /><br />Cool! Something for everyone!

 

[LubeDude]

Re: Porpoising Problem...

I didnt address the foil in my last post. There is No way I would install a foil on this boat. It would, (or should), be out of the water when on plain anyway, so wouldnt have anything to do with the porposing issue. Raising the engine would help top speed, ( due to less drag), but you wont be able to trim the engine as much.<br /><br />Let us know what your present set up is. What prop are you running, and what is the relation of the bottom of your hull to the ventilation plate in inches?

 

[MajBach]

Re: Porpoising Problem...

John: NExt time you're in Peterborough ( or Toronto ), let me know. You can talk me into trying these things out in person.

 

[rwidman]

Re: Porpoising Problem...

I wish I had the time and $$$ to try smart tabs, despite the claims from many here, they still have a 'snake oil' ring to them

Considering that they are for a boat, Smart Tabs are pretty inexpensive. I don't know how anyone who couldn't afford the Smart Tabs could afford to own and operate a boat. <br /><br />I use to own an 18' Stingray bowrider and I installed Smart Tabs on it. They made a great improvement. It's not "snake oil", it's engineering.

 

[umblecumbuz]

Re: Porpoising Problem...

Stevens,<br /><br />If the pic by your name is your boat under power, and you've got tabs, then they work well - it's sitting exactly right!<br /><br />Here, we're solid with playboys during summer, and over 70% don't get the trim right - they're looking over the side mostly, just to try and see what they're gonna hit next.

 

[stevens]

Re: Porpoising Problem...

Stillfishing,<br /><br />No, that's not my boat exactly, nor my wife exactly - that picture came off the manufacturer website (ibizaboats.no). However, it is the exact same model boat, apparently equipped with some hydraulic tabs.<br /><br />I am happy to say that my own boat runs just like that now, with the new tabs. Before, it would only go level like that when it had almost no load on board, and only at high speeds. Otherwise it would be quite stern-heavy. The tabs fixed it though, and it feels like having a different boat.<br /><br />The summer weather is still deluding us though, and this entire week has been rainy and cold with no chance of going out at sea. Can't wait for some warmer weather. We should all be living in climates like Malta's!