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Discussion Starter · #1 ·
First trip out since fitting the doel fins on Saturday (to a Mariner 60hp 2 str bigfoot). Conditions rough chop
Here are what I remember of the claims on the box:
15 minutes to fit - yes this is true

Better top speed - Not yesterday, if anything about 1 knot down but I will be interested to try in calm conditions

Better fuel consumption between 20 and 50% better, average 30%. - Difficlut to tell but subjectively I don't think there was any difference mainly because I was having to run the same revs to get the same speed and I would assume that the only way it's going to save fuel is if I could get the same speed at lower revs

Smoother ride (less porpoising) - I think this is true but not dramatically so

'Power steering effect' - didn't notice one

Planing earlier - no noticeable effect but my boat and engine with just me on board and no doel fins, comes on to the plane about 10-12mph and about 3000rpm which is pretty good anyway I guess.

...... and here are a couple of other observations. It certainly feels nice when it's in the sweet spot but it is much more sensitive to trim changes - obvious when you think about the design. When you have got the trim wrong there seems to be a noticeable slowing of the boat and an increase in noise - perhaps the plastic doel fins are vibrating if their angle of attack is too large. I also felt a slightly alarming tendency to roll more when barreling along at 45 degrees to the waves.

I'll post another report when I've been out a couple more times.
By the way it was indeed possible to fit them while the boat was on the water - and I never dropped a nut or washer !
PS the other point to bear in mind is that they might foul your auxiliary - see other post
 

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Discussion Starter · #3 ·
Spent an hour skimmimg around with the doel fins tonight, in fairly calm water. Top speed I could get was 25 knots - I think that's about 1 knot down on top speed without the doel.
Contrary to what I said earlier, it doesn't look like I can get on the plane unless I go for about 4000rpm and it does so at about 12 mph. I'm fairly sure it was better without the Doel fins
Cruising at 21 knots the ride was steadier but not dramatically so. and it was easier to control porpoising at 23 or 24 knots, which without the doel fins could only be done by winding in the engine quite a bit - with a consequent loss of speed.
So I think in this one claim Doel does what it says on the tin.
But the worrying thing tonight was that to attain my preferred 20 knot cruise I had to set the revs to 4400. This is at least 300 rpm more than I used to use, so I cannot see how fuel economy is going to be improved.
 
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