Outboard engine fins

[C08]

Thinking of fitting a Whale Tail or Doel Fin to my 20HP outboard to reduce the boat stern squatting so much. The Whale Tail looks to have more area then Doel Fins and similar plastic fins and so may be more effective on the other hand would this perhaps put more stress on the cavitation plate than it is designed for and cause damage?
I would be interested to hear of any experience with outboard fins where there has been damage to the cavitation plate, as a result of fitting finns.

 

[maverickofpoole]

I doubt you would damage the cavitation plate but you will change the ride of the boat completely. I fitted Doel fins when I had a Hardy 17 fisherman the net effect was the boats top end was reduced by 2+ knots the boat didn't like to roll as much but just didn't feel right so after persevering for a few trips I removed them. Yes I was back to rolling a little more but that was expected and felt normal (to me).

If your stern is squatting could you not trim the engine in more? or maybe move some weight to the front of the boat?

Another option that I have heard good reports from some of our club members is smart tabs. These are fitted to the boat rather than the engine more like proper trim tabs Google them for more info.

Out of interest what boat do you have?

Martin

 

[C08]

Hi martin
The boat is a 27ft Catamaran-the stern squatting(about 8") is not really correctable for me by shifting weight forward as then when sailing the boat would be bow down. Do you mean the boat was pitching less as I do not understand how the fins could make the boat roll less? Interesting that your top speedwas reduced as that is contrary to what the makers claim, however I am only looking at about 7k max.

 

[whisper]

I've had both on small (14-16ft) dinghies. Were both good at doing what I wanted - easier plane and at lower revs.
Very slight improvement in fuel consumption.
HOWEVER I took them off after a couple of months because in a following sea the handling was horrible.

 

[Rum_Pirate]

I have had a set of Doel fins on a Yamaha 75hp outboard.
On a Suntrip 18

and a Calypso Marine 23


Excellent product. Got up on the plane very quick and cruise at lower revs.

I have had a set of Doel fins on a pair of Mercury 90hp outboards (carp engines).
On a Mako 22 Got up on the plane very quick and cruise at lower revs.
After a few years the fin on one side (can't remember which) of each engine developed a small 'tear'.

Currently have a pair of Yamaha 85hp outboards on a Mako 22.

Thinking about the doel fins.

 

[Scillyboy]

I had fins on a Mariner 75 when I bought the boat - very good for getting on the plane, but as the lift was all in the centre, there was quite a bit of directional instability. I replaced them with hydraulic tabs, and stability and fuel consumption are improved in my case - something to do with the angle of the prop when trimmed bow down on my particular installation. No damage to the anti-cavitation plate - I'm just left with four smallish holes.
Mine would have been available free if I hadn't dropped one in the water together with the bolts and my 10mm socket, when stupidly taking them off on the pontoon.....