spin fin placement?

[Rex R]

I'm thinking of adding a couple of spin fins to help my boat track down the straights. any thoughts on where they should be mounted(aside from on the transom, that much I can figure) such as one prop radius from center? thanks

[BoatDoc]

i'm not sure if adding a spin fin is going to do much good rex. removing part of the inner most strakes may help...kinda like what you asked me before but i never answered because i'm a lazy bum :D i think we may need to have another look at the turn fin that's already on the boat. is it perpendicular to the bottom of the hull? also, IMHO, i think it may help to move it to the transom instead of the side of the hull. hopefully we can get some folks to the pond this weekend...there is testing to be done! maybe, just maybe, we'll go even faster than last sunday :cool:

[Rex R]

lets see I've; removed 3(and a bit)" of the inner strakes, added 3 oz of birdshot(to move the cg), still have trim tabs to do... be nice if I can get it to complete a high speed pass :). otoh I see that other folks have tried it before(on another forum) and given up on it. well if we can't get it to work mayhap I'll get one of them 'el lobo 2's' that some folks like.
edit
turn fin angle perpendicular, check. yeah I hear that drobie has a new boat to play with :)

[BoatDoc]

yeah...dougie has his new toy. wish i could afford one at the moment. maybe if i sell a small pile of props i can afford one! i still have to cut up a 52mm for the viper before sunday. doug's killing me and i need to catch up. it was nice to see his dark horse go on my prop though...i think i can make it even faster. we'll get some more work done on your boat next time we meet up.

[Fluid]

Spin fins are used for....avoiding spining in the turns. :rolleyes: Many monos will not corner at all without spin fins, but their effect on straight-ahead performance is usually marginal. They are mounted on the transom right at the chine line - perpendicular to the hull bottom, not straight up and down parallel to the rudder.

A non-straight tracking problem is usually associated with prop torque on a surface drive boat. This is countered by using a very very sharp prop, dialing in some rudder trim, or twisting the strut to the left a few degrees. I usually prefer the latter. ;)

[Rex R]

well since the problem seems to manifest itself at the end of the straight (with chine walking reported,prior to a spin out) before I start turning... I'm thinking that I'm getting to much hull lift(prop riding)*. thanks for the info
*course it could be that I'm simply asking too much of the hull :)