hydrofoil

[sonny1]

with fingers crossed and hopefully better times ahead i was thinking of my new boat and things to do . i came across a post on youtube about hydrofoils and so im asking for everyones thoughts . are they a bonus ?. is there a downside? or maybe a definite upside. i hear a lot about cavitation and ventilation although i dont understand either and the youtuber claimed that a hydrofoil would get rid of these problems, i dont know ,although i would have thought if it was a blanket solution to these problems they would be fitted as standard. my boat hasnt been out yet so i know nothing about what to expect . its just that with time on my hands its a job i would get done if it was a benefit to the days ahead ...... thoughts please

[Martin]

Having spoent many many hours reseraching this for my old honwave sib, I came to the conclusion that the only thing offering anything like what i required was the stingray junior... (Junior is too small for your rib)
Everyone told me i was mad, everyone told me it wouldn't do anything.... Everyone was wrong !
It stopped the bow rise no end, The hole shot was amazing, Handling was so much better and planing at very slow speeds was a bonus too...
At the opposite end of the argument, Having put the same outboard with the hydrofoil fitted to it on my FRIB, It made zero difference

If you do go down this route, i'd be tempted to look at the Stingray "No Drill" Hydrofoils...

Martin

[sonny1]

thanks @Martin . very good news. tell me , when you put the foil on the frib were there any negatives? . with regard to the actual hydrofoil i was looking at the"stingray xr111 jr 25-70" (no drill) . have a look please and let me know your thoughts. thanks . as i havent had the boat out yet i will have no yardstick for a comparison but if you think there is a possible benefit and unlikely to be a negative i will get one . anyone else got a thought on this . the motor is a mercury 60

[sonny1]

No dramatic difference so to speak on the frib, possibly a drop in top end speed.
Certainly no enhancements on the frib either, but when you have 20hp on a small and light hard hull like a frib, sod all will calm it other than a lighter hand on the throttle.....

One would hope that you could trim your way out of problems on a rib, I'd personallyt be absolutely gutted if i'd spent all that money on a boat to find i've now got to start solving problems....

Martin.

[warder54]

Try your setup without first. I used a Stingray junior on my Mariner 15 2 stroke, fitted to my Honwave 380 ie, worked like a dream - just like Martin found (slight drop in top speed due to extra drag but only noticeable if measuring speed). Put the same motor on my F-Rib 360 - no benefit, a horses for courses situation. I now have a Tohatsu 20 efi and feel no need to fit one. Both boats had the outboard trimmed in 2nd hole out from transom, which gave best performance with or without a "fin"

[Martin]

Both boats had the outboard trimmed in 2nd hole out from transom, which gave best performance with or without a "fin"

And both mine were trimmed to first hole for best performance..
Goes to show variation.

I agree with Warder, Deffo try it before adding anything..

Martin

[harrison]

Blimey @sonny1 is cabin fever setting in.

If it ain’t broke, don’t fix it.

Unless BMC have right royally fooked up installing your motor then 99.9% certain it will not benefit from a hydrofoil. In fact don’t even consider fitting one until you know how the boat performs out of the box.

Want to know the difference between ventilation/cavitation. Well here goes, boring but hey ho;

Propeller Ventilation

Propeller ventilation is caused by air from the surface or exhaust gases being drawn into the rotating propeller blades. This results in the propeller slipping more than usual due to the reduced water load on the blades. The obvious symptoms of this are a sudden increase in engine RPM as well as a possible loss of speed. This commonly occurs when trying to turn the boat at high planing speeds or if the outboard is mounted or trimmed out too high.

Ventilation can also occur when following another boat too closely. The small bubbles in the water created by the leading boat can cause ventilation of the propeller of the following boat, with a subsequent loss of speed. This is why you rarely see high speed race boats following directly in the line of the leading boats, even if they are far enough back to be out of the spray and wake.

Propeller Cavitation

Propeller cavitation is less obvious and far less common than ventilation, but can be far more damaging. When the propeller blade passes through the water at an increasing speed, the pressure that holds the water to the sides of the blades is lowered. If the water is sufficiently warm, and depending on the speed/power of the boat, formation of water vapour (boiling by pressure drop) can occur on the aft face/leading edge of blades. These bubbles that are produced then immediately collapse, releasing energy that can cause vibration and a cavitation burn on the propeller blades. This is one of the great advantages of stainless steel propellers. Due to their superior strength they can withstand cavitation damage better than aluminium and can also be produced with thinner blades to reduce the occurrence of cavitation.

[warder54]

Oops, just noticed your later post, and mention of a Merc 60. I do have the no drill fin on my Yam 60 efi fitted to my Smartwave 480, no negatives there, quicker on the plane, holds on plane at lower speeds = slight improvement on fuel economy. 1st run out with it fitted, I did notice that I never needed to be trimmed all the way in for a decent hole shot.

[bun]

just bought a 9.8 tohatsu 4stroke has one already fitted i see that its on the forth pin up ,dont think thats right im going to start at the no1 and go up wards till i get it right mine is on a v floor 330 so expecting better performance to be better on a tidal out going tide with side undercurrents . the 6hp managed it but its not what i need for the FORTH or the east coast of Scotland think it also make me think i safer with the 9.8
anyidea what the tilt pin should be at guys be gratful if some one with the knowledge could help thanks Bun