The Shipyard ( Dry Dock ): Builds & Questions > Pleasure boats, Sports, Race, Power and Leisure Boats:

Turn Fins?

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john54:
Hi All
Can anybody advise on the ideal (if poss) position for turn fins (a pic will do) Shes a hor 25 from astec running a surface drive 3000k.v.
She slides on turns at speed makeing for a lot of prop slip {:-{ have been told 90 degrees from deadrise angle ?
Cheers

andyn:
Parellel to the sides of the boat, with the fins themselves as close to the sides of the boat as possible, without overhangin the bracket.

Andy :-))

ids987:
Sorry Andy, gonna have to disagree with you on the angle - especially if it's a Deep-Vee design. I'd go with 90 degrees to the deadrise. At that angle, normally, the end of the turn fin should be just above the keel line (when the hull is flat horizontally). That way, it is clear (or nearly clear) of the water when the boat is going flat out in a straight line, and enters the water when you turn - and the boat leans. As the boat leans, the turn fin will rotate towards a vertical position. If the turn fin starts off vertical, it will rotate underneath the boat.

Ian

john54:
So when she is fully on the plane the fins should be just in or just touching the water and when she starts to bank over in the turn the fin should dig in and help her track round?
My main concern is that she might trip over herself and Flip over :(( Being She Is Not Fitted with a flood chamber This Might Be Putting It Mildly a Bit of a Nuisance!

ids987:
In the great world of theory, the turn fin doesn't touch the water when you're going straight ahead. The idea being (as you pretty much said) that it digs in as you turn, and acts as a pivot (the boat basically pivots around the turn fin).
In my minds eye, I would have thought that; if the turn fin is at 90 degrees to the dead rise - and therefore shouldn't go beyond the vertical, the forces acting on the turn fin should try and push the boat level as you straighten the rudder. To look at it another way, as you start to turn, and the turn fin starts to touch the water, the lift created by the turn fin touching the water will try to level the transom, as well as pushing the nose down.
Not sure whether this helps - mostly for consideration and comments.........

Ian

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