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Old 12 April 2012, 10:25   #1
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Country: UK - England
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Fins/Hydrofoils, do they work?

I want to fit a Piranha hydrofoil kit to my anti-cav plate but have not found much on the 'tinterweb' about success or failure of said hydrofoil.
Anybody use one?
It's going on a Tohatsu 50hp on my 5.2m deep V.
These things are supposed to give upto 30% fuel savings, get you up faster (ooer) and up for less revs.
For the 38 it costs for one of these, it seems a bit of a good (and cheap) idea to me.
Any input gratefully recieved.
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Old 12 April 2012, 11:12   #2
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"up to 30% less fuel" translates to you might notice lol

I had one years ago. It did help lower the planing speed by lifting the stern a bit. Top speed was about the same. I don't think it did anything for fuel consumption because I still ran the boat WOT all the time
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Old 12 April 2012, 11:35   #3
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I've had most success with underpowered boats, planing earlier and at lower RPM, still as the capt says, you run it at WOT you-ll save no fuel at all.
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Old 12 April 2012, 14:33   #4
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hi amityslave
im in the same position has you when it comes to hydro foils, i have brought the doel finn ones, the two piece ones, i have not fitted them yet due to fitting instructions and lack of support from manufacture. i have read positive things on the net about getting on the plane faster and can improve turning,would be nice to speak to some one that has fitted them on the site and get there feed back, but doesn't seem to be many on the site
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Old 12 April 2012, 15:22   #5
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I have !

I have a 4m Avon with a heavy 50hp 4stroke ( as in my pic on ther left), that while fine once on the plane was not so fine in the transition ...very bow high .....

I fitted them (doelfins) easily in less than an hour & they transformed my boat. Nice gentle small bow lift when getting going , planes within the local 10knt limits .

I lost a knot or two of top speed, but I dont do that very often so its fine.

I have power trim which makes them very affective , not sure I'd want them without, or on a tiller steered boat.

It was never under powered, just stern heavy ....

I'm glad I did it . ( though drilling the holes is always unpleasant) . Fitting really is line them up with the back of the anti cav plate, mark the holes , drill them ( which may need the prop off) slide them back on and bolt in place.

I recall eplainin it to someone on here with the same boat at the time who I think may have fitted them (Lakelandterrier maybe ? ) so a PM to him may shed more light on his views.

A search on here should uncover some posts about them I have made ( and others) - search Doelfins

Pete
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Old 12 April 2012, 16:39   #6
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Hi have some doel fins fitted to my 25hp mariner on back of honwave 4 mtr sib, it does seem to get on plane at lower speeds , as peter m said can make tiller steer a bit of hard work in certain conds, not sure if it helps my fuel ecconomy as usually wot most of time. Easy to fit , just have to be brave with the drill.

Trevor
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Old 12 April 2012, 16:52   #7
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I had them on my 4.5m Valiant, I couldn't work out if it was better with or without them - they were there as the engine was on the heavy side and it was stern heavy so the fins helped it onto the plane without the bow pointing at the sky.

It was better at low speed and onto the plane with them but once on the plane I guess you need to be trimmed perfectly else they'll cause a heap of drag.

If they did live unto the manufactures figures then wouldn't the outboard makers have cottoned on and redesigned their legs?
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Old 12 April 2012, 16:53   #8
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Investigate hydraulic planing/trim tabs that fit to transom. Work a treat on my SR4. Planing is immediate, stability great, loss of 'flightyness' when on WOT which can be translated as previously mentioned "stability". They are adjustable which is a big pro over the DOELFINS.
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Old 13 April 2012, 03:28   #9
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Well thanks everyone for the input! to be honest it's all pretty much what I expected.
The drag problem if not trimmed just right might be the only disadvantage but I like the idea of a lower bow on take off. I did take the 30% savings bit with a large pinch of salt, WOT always rules out anything sensible!
On ballance, getting on the plane a bit earlier might give up a few extra MPG.
I'll keep a note on how it works out and update in the next couple of months.
The boat, motor, trailer etc. etc. was second hand and all came in under 6k so spending on hydraulic trim tabs is not really an option on this boat but will seriously consider it on my new one.
Thanks all

Quote:
Originally Posted by amityslave View Post
I want to fit a Piranha hydrofoil kit to my anti-cav plate but have not found much on the 'tinterweb' about success or failure of said hydrofoil.
Anybody use one?
It's going on a Tohatsu 50hp on my 5.2m deep V.
These things are supposed to give upto 30% fuel savings, get you up faster (ooer) and up for less revs.
For the 38 it costs for one of these, it seems a bit of a good (and cheap) idea to me.
Any input gratefully recieved.
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Old 13 April 2012, 03:34   #10
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Sorry chum, the "hydraulic" bit just means that they have a pair of shocks acting on them, the adjustment is manual. They cost under a 100 a pair.
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