Hydrofoil/Whale Tail Good or Bad

EZDuzIt

Seaman
Joined
Aug 29, 2021
Messages
57
My 76 Apollo tri hull came with a hydrofoil when I bought it. I've seen quite a few videos that they're garbage and actually hinder performance and top speed. What are your thoughts? After watching so many videos saying they're a scam and do more harm than good I'm about to take it off and see if I notice a difference. What say y'all? Cheers.
 

briangcc

Commander
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Jul 10, 2012
Messages
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They were all the rage back in the 80's/90's. Some people still swear by them - usually on smaller/underpowered boats.

I've personally never run one...the thought of drilling into the leg just doesn't sit well with me.

Your mileage may vary and it may very well work for your particular setup. Only way to know is to remove it and test to see what the results are. Most have left them off but as I mentioned, some do swear by them.
 

Chris1956

Supreme Mariner
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Mar 25, 2004
Messages
27,840
They are supposed to help the boat plane. They often drag at planning speed.

Tri-hull boats plane pretty easily, compared to Vee hulls. What length boat and HP engine?
 

EZDuzIt

Seaman
Joined
Aug 29, 2021
Messages
57
They are supposed to help the boat plane. They often drag at planning speed.

Tri-hull boats plane pretty easily, compared to Vee hulls. What length boat and HP engine?
17' bow rider tri hull with a sweet running old Mercruiser 165 (GM 250 straight six).
 

flashback

Captain
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Jun 28, 2002
Messages
3,963
I am one who Swore at them and still do. If they really did something, the Engine manufacturers would be equipping their motors with AV Plates that size and shape
Not necessarily, engine designers don't design for a specific hull. I'm not a fan but suspect they have an advantage in some applications.
 

airshot

Vice Admiral
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Jul 22, 2008
Messages
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Normally the weight in the boat is not properly distributed so the fins are a cheap substitute for a poorly balanced boat. In most cases moving the loads can make a boat get up on plane much quicker but many folks just refuse to experiment. In some cases, I have had no choice, such as a small skiff with just me in it. Moved everything possible forward but me and the motor was to stearn heavy. However I did not use one of those poorly designed contraptions. As a machinist/ toolmaker, I just made a small fin from SS sheet metal, much smaller and performed very effieciently. There are times when a larger fin can actually help, but a much more practical and efficient fin can easily be made.
 

Scott06

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Apr 20, 2014
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I will play the other side of the fence. I had decent results from a whale tail on my 17 ft 3.0 l powered boat. Definitely improved holeshot and stern lift and only cost like $35-40 (plastic two piece) back in the day. Did cost some top end Mph.

i suspect your boat like mine may have been under powered And i think they got adoptance for holeshot improvment.

problem i ultimately had is my cav plate cracked where the two holes were drilled… might have hit something but i think more likely the cav plate can handle the stress of the wing.
repaired my cav plate and then started running 4 blade props for my holeshot needs, neverran the cav plate and the 4 blade at same time …
 

Drivewayboater2

Petty Officer 1st Class
Joined
Aug 21, 2019
Messages
334
I’ve got one… 1993 16ft bayliner classic with a force 70 hanging on the back… made a big difference in getting up on plane. Didn’t impact overall top speed.
 

QBhoy

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Mar 10, 2016
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8,342
Care to elaborate? I'm interested to see everybody's experience. After seeing what I have I may take it off and see for myself.
They can damage or even break clean off, the AV plate they attach to. They may have their place on a boat that just has the plain wrong power in it on it…but other than that, just shocking things. Decades of R&D see merc and similar do withiut them. Who is anyone to argue with them ?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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I have brought in many boats to get broken AV plates welded
 

harringtondav

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May 26, 2018
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My opinion: Band aid for under powered, or poorly designed boats, waterlogged boats, etc. If you're stuck with one of these, try one. If it helps, keep it. If not, pitch it. ...less expensive than anticavitation plate repair.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
13,446
They also exaggerate trimming of the engine in, which can be dangerous as it can cause the Bow to be forced too low, and then acting as a Pivot Point when the engine is pivoted to steer, when on plane. Many boats have went out of control when operated in this configuration
 
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airshot

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Jul 22, 2008
Messages
5,080
They also exaggerate trimming of the engine in, which can be dangerous as it can cause the Bow to be forced too low, and then acting as a Pivot Point when the engine is pivoted to steer, when on plane. Many boats have went out of control when operated in this configuration
I could see that happening with some of those big monstrocities, I guess bigger must mean better to some. On the few ocassions I have ever needed something like that, I find smaller plates are far superior to the big monsters!!!
 

achris

More fish than mountain goat
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May 19, 2004
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27,468
Wow, lots of opinions here, but nobody touched on what they actually do and how a boat/engine has to be set up properly to take full advantage and not create a dangerous situation.... So, let's dive into 'Hydrofoils 101'. :)

First thing is that a 'foil generates lift while it's in the water and being moved forward. I think that's pretty obvious and well understood. And the faster it is moved, the greater the lift.

It's the high lift at high speed that causes the AV plate to get broken. It's also this lift that causes the boat to take on a 'bow steer' effect, which can be VERY dangerous at high speed.

So, why the 'foil in the first place if it creates SO many problems? Well, most foils don't carry the right instructions on the packaging, and if they do, it's in really really small print... And what does that print say?

"This hydrofoil is designed to be fitted to engines with a minimum increase in installation height of at least 1" above normal."

Why is that important? Because with the increased height, the foil will come out of the water once the boat is planing! And once out of the water it no longer exerts force on the engine/boat. It's no longer generating lift, putting excess pressure on the AV plate or generating bow steer.

Hydrofoils have there place, but it's not on most boats, unless they are specifically set up for one to be installed. The reason it's not on the packaging is because the sales would be far less! And when has safety ever been considered (by a corporation) higher than that sweet sweet profit?

I hope this clears up hydrofoils for everybody...

Chris.......
 
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jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
13,446

...
And when has safety ever been considered (by a corporation) higher than that sweet sweet profit?

...

Chris.......

Many workers have died because of that Ideology. I would like to see management, executives, and owners placed in Prison, for what it is. Premeditated Murder
 
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