Hydrofoil Advice

[hl&s]

My boat wants to porpoise much more than I think it should. Even in smooth water I have to constantly adjust speed/trim to smooth the ride. Was thinking about installing a hydrofoil but I've read good and bad about them. My concern would be the stress they put on the lower unit mounting area. I've seen pics of broken ar cracked lower units caused by them.

My boat is 16' with 88hp. Would appreciate advice from anyone that has experience with this.

Thanks

 

[bigbux]

I have had a dolfin on my last two boats.The first was on a 15 ft smoker craft with a 40 hp chrysler, had the boat five years and no problems.The second is a 20 stratos with a 200 hp johnson, also has no problems.I highly recommend a hydrofoil.

 

[flip1up]

There are some that dont require any holes to be drilled.

 

[Guest]

I have had experience with them on 2 boats and they are not worth the plastic they are made of. One boat had a porposing problem that the hydrofoil did not solve and the other had a planing problem that the hydrofoil did not solve.
To put it like my boat mechanic said, who by the way has been working on boats for over 30 years, if outboards needed a hydrofoil they would come from the factory with one on them.
Your porposing is coming from motor height on the transom and or prop.

Cheez

 

[DHaun]

I have one on my boat - details here:

http://www.chattanoogafishingforum.com/forums/thread-view.asp?tid=330

 

[G-MAN]

DHaun - 5/23/2007 1:31 PM

I have one on my boat - details here:

http://www.chattanoogafishingforum.com/forums/thread-view.asp?tid=330

Great Advise!

 

[hl&s]

Thanks everyone for the info. That's a very informative post DHaun, describes my boats condition to the T. I like the idea of no holes and the part actually strengthening the plate. If It cost a couple of MPH I'm not much on going over 40 anyway. I think a custom fit hydrofoil made of good material may be worth investing in.

I'm an auto mechanic by trade and I have never supported additional add-ons as I feel it is best to correct the problem than to cover it up. I'm also ignorant about such boat problems and their cures. According to my OMC repair manual my engine height is good. My prop is going to a local shop for some TLC although nothing serious is wrong with it, just a few small knicks. I've also been told porpoising is more common with smaller boats like mine so I don't see anyway around trying one.

Thanks again to all who take the time to share their individual experiences and knowledge.

 

[flip1up]

I put one on a 16 foot bumble bee with a 88 special on it. It helped a whole lot with keeping the bow down on take off and planing out was alot quicker. On the other hand I bought a 20 footer with a 200 hp on it that had one on it. I took it off and nothing changed at all, dont know why it was on that boat. I recon they will help some boats and are not any help at all on others. Probably like said above, they may help boats that have heavy motors on the back or light bows.

 

[fisherpal2k]

I have had two different boats with them on it. It seems to work to some extent but most of the problems stem from the way the boat is loaded. Some boats like to have all the weight in the back and some need more weight to the front. I moved some of my heavier tackle around and found the sweet spot and it worked out great..

 

[Liveliner]

How many RPM does your engine turn at WOT? What is the recommended maximum RPM for your engine. You should make sure you are correct here first.

Sounds to me that you have too much pitch in your prop, Your engine is a knotch or two too low on the transom or you may need a new set of spark plugs. Any or all of the above is most likely the root of your problem. The extra fin kit may help but not resolve your problem. If I were you I would get the engine performing close to correct first then add the Hydro-foil. It will sure make you feel better about your fuel gauge.

 

[hl&s]

My engine turns 5000 at wide open throttle. Spec is 4800 to 5400. CV plate is 1 1/2" above bottom of transom. Spark plugs are new. Engine performance is smooth. A talk with a local prop shop owner I deal with pretty well eliminated the prop as the cause. He even recommended the stabilizer in my boat/motor combination and to move all weight I could forward. I don't know what else to try !!

Thanks

 

[flip1up]

No doubt that weight distribution will help on some boats. I have a 18 1/2 foot G3 with a pretty heavy 115 four stroke. The bow is light. It was porpoising pretty bad. I added quite a bit of weight in the front compartments. This helped it out a whole lot with just me in the boat. But when I have 2 people in it the porpoising returns and is pretty bad. I'm sure a jack plate is what I need. It needs set back and raised alot. I understand that a good starting place on motor height is the prop shaft even with the bottom of the hull. Of course you will have to adjust from there, making sure you have the right amount of water pressure to cool the engine.

 

[Liveliner]

Thanks hl&s. If your boat turns 5000 with only you in the boat it could stand to be loosened up a bit. Your prop guy should know that. If you are loaded with a partner that would be about right. I am assuming that you have power trim. At WOT at 5000 RPMs do you have balanced steering. (Same pull or resistance turning Port/Starboard)?
I still think that if you could get 5400 RPMs at Balanced steering and at the point where you are running your max speed, then your boat would be near perfect. Four Hundred RPMs at top end does not seem to be that much, However in mid-range you are really loading up drag on your engine. That drag in mid range is holdind your boat back and restricting it from getting up on plane. It keeps falling off plane hence the porpoise. If your prop friend will loan you a prop with the same pitch but with slightly less cup, I would be willing to bet that it would spin a little bit better and pop your boat up on plane. Just be very carefull and watch your RPMs. Don't over rev.

Like Flip said, a jack plate would help if you wanted to spend the $$$. But I think that a little prop tuning and the Hydra-foil will fix you right up.

A hydra-foil will do different things to different setups on boats. Generally it will lower your top RPMs and drop about 2 MPH. On boats that are running loose and easy to blow out it will be a great improvement. It will hold the foot down in the water curve helping it bite better. A setup like that can actually run faster at WOT. The Hydro-foil helps hold the boat down in turns and under throttle. However, it will do the opposite when you back off throttle. It will just keep on plane and not settle down into the water like you are used to. You can hit the dock if you are not cautious.

I hope you get your setup figured out.

 

[Liveliner]

Also FYI.. I once had a 158 Vision with a 75 HP Suzuki engine. That setup is simular to what you have in size and power. It would porpoise. And even worse with two people in the rear seats. I even had a 5" jack plate that hepled a little. I traded the engine for a 100 V4 Suzuki. The extra power at mid range solved all the problems. I was running a "worked" 22 p OMC Raker prop and that boat would run 60 MPH with just me in it.

 

[hl&s]

Thanks for your input LL. You have a good knowledge of the situation.

The boat was fully loaded. Full tank,3 batteries,gear, full livewell,and 2 adults. It planes, it just takes a little longer. It's the porpoising that was much worse.

When alone and loaded the boat handles much better. Good holeshot and porpoising is controlled by trim. (I do have PT)

I would prefer to fix the problem with a new prop. Unfortunately, I can't just borrow one to try out. Since I'm trying to get the best improvement for the least bucks, I'm still leaning toward the "no drill holes required" hydrofoil. If I'm not happy with it I can sell it and recover most of my expense.

Thanks!

 

[Liveliner]

emoThumbsup

When you take off just take your time trimming out your motor. Watch your speedometer and you can learn how to get to plane with minimul hopping.. When your nose dropps trim 2 seconds on, 2 off and so on. You can what off and on trim speed works for you. If you trim out too fast it will lift the nose making it harder on your engine to get you on plane. With the nose down you can start to feel hull drag. At that time you can feel relief. Get familiar with that hull drag feel and you can run your boat up and out of the hole much better and reduce the porpoising.

 

[hl&s]

I get the picture !emoBigsmile