hydrofoil worked

[scottykrug]

For those of you worried about installing a foil and whether it will work, we just did, and in our case it worked. We installed a combination hydrofoil/trolling plate that we got from Cabelas. I can't remember the name, but is the only combo listed. In short, it worked better than expected.

We swapped out our 75hp Force with a used 115 Merc. There was a large weight difference which caused the boat to porpoise and made the hole shot very slow and almost, well, funny with the nose shooting straight up in the air. We tried to redistribute weight towards the front, but we could not overcome the extra weight and extra hp. We already had a whale tail, and suspect it may have worked well by itself, but we also wanted a trolling plate (even at idle, the 115 pushed just a little too fast). The Cabelas product offered the best of both worlds in one package. The fin/plate feels somewhat flimsy being plastic, but so far, it has worked well. I did order extra pins for the locking device (the plate locks down with a brass pin which shears when you forget to raise the plate and punch the power).

I know after reading many posts that others favor use of tabs, but for the money, this option worked out perfect in our situation. For the record, since people might ask, we installed it on a 96 Larson Flyer 166 (16') with a 97 Merc 115 elpto. We now have (again) full trim range use but have to work on speed. The boat tops out at 33 mph and around 4800 rpm with a 17" (pitch) prop. Suspect it may be a linkage issue- I don't think I am getting full range on the throttle. The boat will get me to the fish and that is good enough for now. I can fiddle with the speed later.

scooter

 

[NBE]

Re: hydrofoil worked

Well, I suppose if you shoot at a target 500 times you are bound to hit it at least once.

Glad it worked out for you.

 

[scottykrug]

Re: hydrofoil worked

As long as I hit the bullseye on the first shot, I'm happy.

 

[NBE]

Re: hydrofoil worked

Good, no wasted ammo (or money) that way. What I said up above meant that if you poll 500 people who have tried or used a hydrofoil you'd be lucky to find one who was really satisfied.

Looks like you did hit the bullseye the first try. Again, glad it worked out for you.

 

[tmcalavy]

Re: hydrofoil worked

Now I don't feel so alone...according to NBE's logic. I, too, put a hydrofoil on my 15 foot aluminum boat with 18 hp Johnson. Love it. Really gets on plane fast, runs faster and turns better. That's two of us...now where are the 498 dissatisfied customers?

 

[cobra 3.0]

Re: hydrofoil worked

The key is to be able to height adjust your motor height to adjust the height of the anti-cavitation plate in relation to the bottom of your boat. Otherwise, it will slow down your boat by a few mph.

 

[tommays]

Re: hydrofoil worked

In the dark ages before there were smart tabs foils were widely used

And before everybody started copying the orginal doel fin with a BIGGER is BETTER one there really were not that many problems and many happy people



Tommays

 

[scottykrug]

Re: hydrofoil worked

The key is to be able to height adjust your motor height to adjust the height of the anti-cavitation plate in relation to the bottom of your boat. Otherwise, it will slow down your boat by a few mph.

We had the boat shop swap out the motors for us and when we tried the first test run with dismal results, my first question was to the plate height relative the bottom of the hull. There was a slight difference and there were still holes on the engine mount that would allow the motor to be lowered into a better position. The tech said that the plate was in tolerance and the reason that height was chosen was better draft and a little faster speed. Speed is not as important as controlability for me. I knew that the foil would reduce the speed slightly due to induced drag. I might try dropping the engine one more hole to lower the AC plate next summer when I have more time to tinker. Like a test pilot, some of this stuff is hit or miss and I only started this post to add encouragement to others who were in the dark regarding the issue. I did not know that the failure rate for this product was so high, guess a few of us were lucky.

"every now and then the sun shines on the south end of a northbound dog"d

Thank you for the replies- it is good to see both sides and get an "experienced" opinion, that is why I love these sites.
Scooter

 

[Rancherlee]

Re: hydrofoil worked

I susupect an issues with your motor or boat. A 115hp on the back of a 16.5' boat should have NO issues getting on plain in a hurry unless you have a lead reinforced fiberglass hull. you should have been getting 33mph out of the Force 75hp on your boat and north of 40mph with the 115hp. If your having issues with the nose pointed in the air while plaining and porpoiseing I suspect the engine isn't being trimmed in all the way which will cause both issues. Either the trim pin is too far out or the power trim is malfuntioning causing it not to come in all the way. I loved my hydrofoil on my engine, UNTIL I learned on this site how to set up the engine on the transom. Once I learned how to tweak my setup I removed my hydrofoil and picked up 2mph on the topend, better fuel economy, AND all the issues I thought the fin solved dissapeared also.

 

[scottykrug]

Re: hydrofoil worked

That was my thought too- the 115 should blast this boat out of the water. The trim was in the full retracted- down- position, verified by visual inspection. When I tried to go the other direction with the trim, the prop quickly cavitated and lost thrust. This was all prior to the installation of the foil. After installation, planing is fast with the trim fully down. A small adjustment is required to get the nose up just a little bit and pop up the speed. Right now top speed is about 34-35 indicated (I forgot to bring the GPS for verification). I still don't think I am getting full power, but will verify that later with a trick I read from another post. I agree that the fin does cost me some in speed and economy and would love to not have to use it. I am always open to other ideas. Just for the record, the anticavitation plate is within an inch of the hull bottom and is perfectly parallel to it when full down on the trim.

scooter

 

[cobra 3.0]

Re: hydrofoil worked

Bringing the motor up an inch would probably gain you a few mph.

 

[cobra 3.0]

Re: hydrofoil worked

Bringing the motor up an inch would probably gain you a few mph.

Also, just noticed 4800 rpm is quite low. You should be aiming for the top end of your recommended rpm range. Prop troubles...maybe? Check out the prop section for fellas with a similar set up. How's the engine's compression?

 

[Texasmark]

Re: hydrofoil worked

You just said something that answers part of your nose high problem. You said that tucked all the way in, the cav (vent) plate is parallel to the bottom.

Not the right answer. The engine should tuck in from perpindicular rougly 15 degrees for best hole shot. No wonder you snauze is in the air.

Take a look at the slant of the prop on a "full inboard" boat (Ski Natique, Correct Craft ski boats to name a couple you have probably seen) and that is about the angle that full tuck should position your engine.

I agree on something keeping you from WOT. That boat should be easily in the 40's with a 17 and rpm's should be up around 6000 at least.

I had a 115 tower on a 17' ranger with a 13 ( ) x 19 Merc SS prop and ran 40's easily and my WOT rpms, trimmed out to the loose speed point, were a consistent 6000.

HTH

Mark

 

[scottykrug]

Re: hydrofoil worked

Cobra-
Regarding raising the motor, it is already about 3/4" (cav plate) above the hull bottom. I was always under the impression that the plate had to be at the same level as the hull bottom to get adequate water flow on the prop, but the mech said it was at the best height.

I agree the rpms are low and will tinker with it. Secifically a few tricks that I have read on this page:

1- check that the remote is not bottoming out before the throttle linkage on the carbs

2- squeeze the primer bulb and look for a surge of power indicating a dying fuel pump

last but not least, verify that the tach is accurate. I think it is right on based on the speed that I am seeing, but I guess that both gages could be wrong.

Texasmark-

you are right, I had never thought of the drives on the inbd boats, but figured the prop angle had something to do with thrust vectors (location of prop- under vs behind the boat). The engine is fully bottomed out in the engine mount, and I cannot imagine that the transom is at some wierd angle causing an issue. I will also examine this more closely and try to accurately measure the angle. I can borrow a fancy angle finder from my friendly neighbor/helicopter tech rep.