Doel fins ... ye or ne ..

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Volusian

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Hi ...

Im thinking of fitting a pair of Doel Fins onto my Mariner 60 / Wilson flyer combo but would like some upto date feedback on the pros and cons of fitting these. There seems to be a division amongst articles ive read and people ive spoken too as to their benefits. Some say they can greatly weaken the outboard leg where the drill points are ...

anyone fitted these then regretted it ?
 
I have fitted them on two large outboards and two 4.3ltr inboards and have no regrets. They get you on the plane easier, make it more steady when just on the plane and allow it to plane at a lower speed which is more efficient.

If you fit them properly (i.e drill 8mm hole not 10mm hole twice) then you will have no problems.

A cheap option for a big improvement

Paul
 
They help you plane at lower speed, so if that would be a benefit to you then give them a go. If you fit them it's important to ensure the cavitation plate is at the right height, if it's too deep then the boat will plough at higher speeds.
 
Nick_H said:
They help you plane at lower speed, so if that would be a benefit to you then give them a go. If you fit them it's important to ensure the cavitation plate is at the right height, if it's too deep then the boat will plough at higher speeds.
Click to expand...

what are the cavitation plate depth guidelines for outboards .. or how deep is too deep ?

thanks .. :)
 
Volusian said:
what are the cavitation plate depth guidelines for outboards .. or how deep is too deep ?

thanks .. :)
Click to expand...

The cavitation plate on your outboard should align with the lowest part of your hull at the blunt end!
You will probably find on Your Wilson Flier that this is the case.
When the eng was fitted on Your boat it should have been located on the transom so the Cav plate is 'level' with lowest part of your keel aft.

This is difficult to explain in 'writing', maybe a cleverer Forumite than me will post a piccie please!

Anyway.
A Standard, for want of a better word. shaft outboard should align and sit at the proper depth for Your boat.

Most large or high power outboards are 'standard' or 'long' same thing really.
There are applications for 'short' leg outboards of the larger type but rare.

After all that drivel.
Where the 'v' at the back of the boat is underneath, that is where the cav plate should be level with.
Bleedin H, I,m off now:eek:
Confused?
You probably are now:)
 
All good advice above.....but just tuppence worth....for marginal powered, heavy a*sed sterndrives 21 to 25 feet, I have found the Stingray Hydrofoil excellent.
The lifting 'wing' is just aft of the cav plate.
 
Volusian said:
Hi ...

Im thinking of fitting a pair of Doel Fins onto my Mariner 60 / Wilson flyer combo but would like some upto date feedback on the pros and cons of fitting these. There seems to be a division amongst articles ive read and people ive spoken too as to their benefits. Some say they can greatly weaken the outboard leg where the drill points are ...

anyone fitted these then regretted it ?
Click to expand...

I once fitted them onto a 25hp outboard that was on an Orkney Strikeliner. Took them off after a season.

Pros :- planed more easily and stayed on plane at lower speed than previously.
Cons :- increased tendency to broach in following sea. Greater area at the stern for wave
action to lift up and deflect.
 
Volusian said:
what are the cavitation plate depth guidelines for outboards .. or how deep is too deep ?

thanks .. :)
Click to expand...

Most outboards specify the cav plate should be between 0 and 50mm lower than the keel, but if you fit it 50mm lower, then at high speed the doel fins lift the ar5e end of the boat higher, and as a result the front of the boat starts to plough. It's obviously more noticeable on small rib tenders, than on bigger boats.

As Kawasaki says, best to fit the outboard so the cav plate is exactly level with the keel. This is easily done just using a straight edge along the keel to see how much lower it is at the moment, then you know how much to lift the outboard by, if at all.
 
Sorry for delay but did a post last night but must have hit the wrong button.


"Mr Mercury/Mariner" says in the service manual: " best transom height for engines is to locate engine's anti-cavitation plate at the boat bottom. Boats with heavy keels will require lower settings to avoid propeller cavitation. Engines installed higher on transom may experience higher boat speed but will increase possibility of cavitation. The effect of higher tramson setting on boat speed is slight below 25 mph. Engines installed at lower-than-recommended height have increased pulling power but will have a lower top speed and fuel use per mile will increase because of more lower unit drag.........."

more or less, same as already been said.



You will find that some speedboats with "standard" props can have the o/b set up a wee bit higher than inline with bottom of hull but it can all be a bit of trial & error.
 
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I have had the same Doel fins on four boats now with mixed results.
1) Old 16ft Glastron with trihedral hull and 50hp outboard. Big improvement all round.
2) 20 ft Searay with 185hp Mercruiser outdrive. Improved on the plane time but frightening tendancy to fall onto its chine at speed. Took the fins back off.
3) 25ft Searay Sports cruiser with 260hp mercruiser outdrive. Same as nuber 2) above.
4) Now fitted on 21ft Bayliner with 135hp outdrive. Works well making boat better to plane and more 'planted' at speed. No issues so left on.

My impression was that may be the higher powered motors were lifting the boat to far out of the water with the fins, so the boat just fell over on its side. Very frighteneing.

No harm in trying to see what happens, the holes are easy enough to fill and paint over if you change your mind!
 
dpb said:
I have had the same Doel fins on four boats now with mixed results.
1) Old 16ft Glastron with trihedral hull and 50hp outboard. Big improvement all round.
2) 20 ft Searay with 185hp Mercruiser outdrive. Improved on the plane time but frightening tendancy to fall onto its chine at speed. Took the fins back off.
3) 25ft Searay Sports cruiser with 260hp mercruiser outdrive. Same as nuber 2) above.
4) Now fitted on 21ft Bayliner with 135hp outdrive. Works well making boat better to plane and more 'planted' at speed. No issues so left on.

My impression was that may be the higher powered motors were lifting the boat to far out of the water with the fins, so the boat just fell over on its side. Very frighteneing.

No harm in trying to see what happens, the holes are easy enough to fill and paint over if you change your mind!
Click to expand...



We don't use this brand of foil (Doel-fin), but I have noticed on a particular brand of deep vee hull (Whittley) even with the brand we do use, there is a tendency to lay on the chine in the first few seconds of achieving a planing attitude.

This is only when the leg is trimmed hard in, after climbing out of the hole. As soon as the leg is trimmed out slightly, the boat levels up.
 
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