Re: porpoising real bad need help
 

I bought my boat used with one installed. Should I remove it? Why do people install them?

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Re: porpoising real bad need help
 

I"m not sure it warrants the punishment that mikeyt suggests but many of us feel these hydrofoils don't provide the value the manufacturers claim. I'm not a Fluids Engineer so take my opinion with a grain of salt. My experience is most people install a hydrofoil to get better performance from their boat. If you think about how the hydrofoil works it doesn't make sense that it would improve performance. Quite the opposite, the hydrofoil exaggerates the effect of trimming the motor. If the motor is trimmed all the way down the hydrofoil increases the pressure on the bow of the boat and vice versa in the trim up position.
The problem is that while the hydrofoil provides increased lift on the bow as the motor is trimmed up, it has the inverse effect on the stern and pushes the stern down as it grabs water. The nose up position is what causes the porpoising. Trim tabs on the other hand provide lift on the stern of the boat and allow the motor to more naturally effect the attitude of the hull which allows for better handling and performance. Most boats are stern heavy and are designed to run on the back 1/3rd of the hull at speed. The challenge is we don't pull skiers or do most of our boating at full speed. Trim tabs allow the hull to ride in a similar attitude at slower speeds. They also help with getting on plane quicker due to the increased lift on the stern.
The other concern I have about hydrofoils is the increased pressure it applies to the anti-cavitation plate and the trim rams. This can cause issues over time.

Re: porpoising real bad need help
 

I know some guys who are genius with the tools to look at fluid mechanics. I actually spoke with one of them about this sort of thing a couple years ago when i got mine and he would agree.

In fact he would probably say if you fix the hull you don't need much on the outdrive but a propeller. A dynamic hull would be more effective than a dynamic drive, more like an inboard.

I'm surprised Mariah didn't put something like the smart tabs on the hull from the factory with them offering so much improvement for a low cost.

Re: porpoising real bad need help
 

Tell me how you really feel about whale tails, Mikey.....


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Re: porpoising real bad need help
 

I have a 94 Shabah Z206 that had the same problem. I went with the less expensive "plastic" smart tabs (vs steel) and they helped a ton. I'd recommend them as the others have. Good luck.

Re: porpoising real bad need help
 

I like the term composite better than "plastic". Plastic sounds kinda cheap:)

Re: porpoising real bad need help
 

Keep in mind that there is more adjustment capability on the SS tabs rather then the composite ones. Also, they stick out less but are wider.

Re: porpoising real bad need help
 

May be fixing to piss y'all off but my personal opinion is;
Trim tabs are solely for leveling boats due to either, lopsided loading or, steep deadrise hulls, inherently unstable. The absolute best situation for "the perfect plane" is, as little contact with the water as possible. Sticking trim tabs in the water flow is added drag. Remember, the ONLY purpose of the outdrives "trim" is to get as much boat (front) out of the water. And you want as much boat (drag) out of the water to make a more efficient plane.
Every boat I've ever owned, albeit they were all big bass boats, used trim up till either cavitation, prop out of water OR till you started porpoising.
You have to first understand why porpoising happens. When you trim up too much, the engine has enough power to lift the bow up but doesn't have the power to keep the bow up at that position. As the bow falls, the too high trim setting is now exaggerated and the motor snaps the bow up even higher. There is no problem here.
There are really only two ways to PROPERLY fix this.
Either, put a higher horsepower engine that can support the higher trim OR, quite simply, trim it down just enough to stop the galloping. What I'm saying is; if it's galloping, it's the boat and motors way saying "Too much". Ease off the trim just a little at a time till you find that split second between "too much" and "what the engine and hull can SUSTAIN."
There is no recommended trim height. The trim gauge is not meant to show you where your trim should be. Trim is set by the feel of the seat of your britches, by the sound of the engine (you can hear when your prop is biting and when it's just making bubbles) and by your speed.
Driving the nose back down with trim tabs, at the expense of mph, is counter productive because what they are doing is REVERSING the effect out the motor being too high, from the first place.
Try this game. Trim down, note your speed at exactly 3000 rpm. GPS is the best for this. Now, keeping the rpm at 3000, start bringing the nose up in short lifts. Watch your speed go up and notivce you'll have to ease off the throttle after every trim up. Keep lifting it in short burst till it starts galloping. What you'll find is your fastest speed was well before porpoising started. If you add trim tabs and use them for , untrimming of the engine(???), you WILL LOSE SPEED AND HULL EFFICIENCY.
Flame away boys!! I can take it.

Re: porpoising real bad need help
 

The tabs on my boat were added solely for minimizing the idle speed steering wander. The tabs eliminated that and I am happy because that was a real deal breaker for me. I lost no top speed, 55 mph before and 55 mph after. I do have them set to the lowest angle available.

Re: porpoising real bad need help
 

Same here GaryDoug. I have the port side all the way up and the starboard down just enough to level it. I've monkeyed with them to see if I could get any more top end but the more I lowered, the more top end I lost.