Doelfin Hydrofoil

LURCHER · 21 March 2003, 18:10

Does anyone have experience or comment on these devices (Doelfin Hydrofoil).
I run a 115 Evinrude Ficht on a Ribcraft 5.85

Dirk Diggler · 21 March 2003, 18:42

Although they look hideous, by all accounts they do work on the majority of installations.

Manos · 21 March 2003, 18:55

I fitted a set on a 5 mtr GEMINI with a 75 bhp Mariner (boat weight with engine but no fuel 550 kgs) the overall performance improved, acceleration, and also top speed.
It also had better consumption (but it was marginal).
For some reason skiers would come out of the water quicker and the boat was hardly lifting its bow when it was accelerating (with 17" and even a 19" pitch aluminium props).

jwalker · 21 March 2003, 19:39

They work well to prevent the boat pitching. Without them, you can often get a situation, going into waves, where trimming in forces the bow to drop into the trough more than you would like. Fins totally remove this. They perform as a stabiliser because they work both when they are pulled up through the water and when they are forced deeper in the water. I wouldn't be without mine.
I can't say they ever noticeably improved fuel consumption or particularly improved the time to plane. They do work very well to improve leteral stability on a twin engine setup.
Don't pay a fortune for the Doel. Buy the cheaper ones. They are equally good.
Oh yes, they make a nice big step for getting into your boat, at the stern, when launching. Or when you are overboard!
JW.

Nigel · 21 March 2003, 19:41

I've fitted Doelfins to three different RIB/engine combinations. In each case the boat got on the plane at a much lower speed - particularly useful in Portsmouth harbour with a 10 knot speed limit - and didn't seem to have to work so hard to 'get over the hump'. Without the foil, the combinations felt very back heavy in comparison. I also have the impression it helps the prop grip in tight turns.

You've got to be brave to drill those holes in a new engine though!

Nigel

"There is nothing - absolutely nothing - half so much worth doing as simply messing about in boats."

Windchill · 21 March 2003, 22:18

I put them on my 5.5m Humber Extreme/115 Johnson. They allow slower speed planing, but, more importantly from my point of view, give better handling/reponse to trim in short sharp seas.

I have'nt actually submarined (famous last words) since fitting them!

LURCHER · 22 March 2003, 08:55

Thanks everyone .I,m off to buy some now !

Manos · 22 March 2003, 09:41

Can any body advise please if I can use the fins on my 200 VMax?? or is it a rediculous idea??

Charles · 22 March 2003, 11:21

Ridiculous idea, methinks.......

Manos · 22 March 2003, 11:29

I thought as much Charles but I just wanted a second opinion.
Cheers Mate

Brian · 22 March 2003, 12:56

Still nobody has answered my question on these devices.

If they are that good (and certainly everyone seems to agree that they are), why don't the engine manufacturers either build them in, offer them as a model variant or offer the fins as an "extra" when yoou buy the engine?

Charles · 22 March 2003, 14:19

Hmmm, good question Brian. I used them on two of my ribs and they did exactly as it said on the box:
Gets you on the plane quicker.
Positive steering at low speeds.
Assists in maintaining planing at low speeds, and so on.
I suppose it is like anything extra, spoilers on a car to keep force you down (on to the road) at higher speeds etc. If your boat is set-up properly there should be no need for these things, that said, it can certainly enhance performance, BUT does take some speed off your top end due to additional drag.
I do not think Cyanide would benefit from having them

crazyhorse · 22 March 2003, 16:41

Well I was in the yacht club today for my usual lunchtime drink of coffee,discussing nautical matters as usual,When in walked a fellow ribster,who withought any provercation said ,you know I fitted them fins things and they work just great.

So why do they work so well as I am sure like Brian I am thinking if they work on a outboard then why not on a leg.So here is the maybe but dont know thought for today?
Do they opperate like a set of trim tabs ?.
I think they must as they are in a better position than tabs.I dont want to bring the tab question back and it is only a sugestion,but we know they seem to work,So could this be the reason?

If I am correct with this assumption then the larger the boat mybe the larger the fins,It may put extra loads on the trim and tilt motor,as the surfice area is greater?

This is a guestimate only and not a fact.If there is somebody who can tell us exactly why they work so well ,then great.

I am going with Bennet tabs at present but it might be possible maybe to just have some big foils on our single leg that will do the same instead providing our trim and tilt motor doesnt burn out?

Its only a suggestion at this stage So please dont anybody feel offended or upset about it.

Jonny Fuller · 22 March 2003, 20:13

With foils on a single drive instead of tabs, you would get stern lift, but not the benefit of being able to "level" the boat lateraly in a beam sea/wind, which is the main advantage of tabs on a boat like "your's to be".

P.S. like the name says, they are a "foil" or wing section, and get thier lift from this form, not like a tab which is less efficient.

wavelength · 22 March 2003, 20:14

We have had fins on two boats. Our little 4m searider with a 50hp 2 stroke had in its previous life been used by divers carrying heavy loads and came with fins fitted. Now the fins were fine on that but the boat was on the max power allowable and came up onto the plane like a rocket anyway. We also put some on a 15ft fast fishing boat which was a bit underpowered with a 40 two stroke. On that model boat with a manual tilt engine the o/b has to be out one pin past the centre hole to lift the bow with its cuddy or it would handle like a pig. The fins on that boat may have stiffened it up a bit in turns, taking some of the heeling out of it, but they weren't a success otherwise. With the o/b at that degree of tilt I think they occasionally acted like submarine diving planes and gave some strange effects and enough disturbance at times to ventilate the prop. Personally if the boat works without them I would not fit a pair again cos they didn't do the fishing boat any favours.
Why do they work? Theory is I suppose if you look at the leading edge they are an aeofoil shape so they should act as a wing and give lift.
Dave (it was lovely at sea today!) M

crazyhorse · 22 March 2003, 20:47

Well thanks Doods,

Seem good for small boats who want lift,but no good for squaring up to a beam sea,side on.

So i will stay as I was, and not try and reinvent the wheel,

Thanks Wavelength and Mr best behaviour JF

Yes it was a nice sea today of Blackpool W we just bought a 2.6 Maxon sib with a 2hp volvo penta air cooled so whatch out,I may be out there sooner than expected.

Jonny Fuller · 22 March 2003, 21:24

Quote:

Originally posted by crazyhorse
Well Thanks W and Mr best behaviour JF

?????????????????

Cookee · 25 March 2003, 11:53

I had some on a 14' Fletcher with a 70 hp Suzuki and it did what it said on the box as well - very much an all round improvement. Used the boat mainly for skiing and no idea what it did to the top speed but it was fast enough!

Read something recently about them upsetting a RIB or 2 but I think they are perfect for boats that maybe a bit underpowered or slow to plane.

Manos - I don't think your 200 hp is underpowered!

Brian - I think they will lower the top speed of a boat - will not suit or be needed on every hull - and may even affect some boats badly!

Trim tabs only work when needed unless they are lowered too much - therefore they will not affect the performance so much as they are not creating so much drag.

Manos · 25 March 2003, 12:25

Quote:

Originally posted by Cookee
Manos - I don't think your 200 hp is underpowered!

You are absolutely right!!
I just thought I may get a bit more out of it tha's all.
Any way will not use it for 200.

Cookee · 25 March 2003, 18:34

Manos - 2 reasons I can think of - Firstly the extra drag of something not designed to work with that size of engine and speeds, and you'd probably rip it off the cavitation plate if it wasn't bonded on in some way, which in turn would most likely do more damage - shall I go on?