keel fin foils and placement

[kfitz +]

Howdy, I've been making plywood boards for awhile,(1/2" ply) and would like to try some keel fins (single and double foils). But, I'm not sure about placement and line up, can you run them straight and/or with some toe-in? anyone making these have any tips on when to use dbl. foils or single foils? the internet is loaded with fish and twin fin surfboard ideas, but I would like some suggestions from the crew here. thanks...first post.

[SJB]

I asked a similar question of Rod sometime back....his response:

"My personal experience was moving from a single large fin to a three-fin setup. I've been riding the basic Austin template for about 20 yrs with some fine tuning of the rocker and rails over the years, in addition to some minor width and thickness changes. Regardless, my fin progression has been from larger 6 to 8 inch fins down to 4 to 5 inch fins. The side bites have always been around 2" and I generally favor not having very much toe-in. 
Placement of the center fin will vary depending upon hollowness and size of the waves. Small hollow waves will probably find the fin more aft than on larger but more sloped waves. The rails of the board do a decent job of holding into the face but there are times that there is simply no substitute for a fin(s), especially on turns and carves."

Taking that advice....on my Austin I tried and liked twin fin set up at 3 inch each. Then I tried three fin set up with center fin at 3 inch and sidebites each at 2 inch. Darn if I did not like that also. Both set ups seem to turn fine but the three fin seems to give more straight down the line stability. I found the 2 inch side bites as follows.

FCS 2 inch sidebites.
http://www.turbotunnel.com/product.asp?productid=165177

[kfitz +]

Hey, thanks, I am going to try the twin keel set up and you gave me very useful info . I was thinking 4 to 5 inch double foil with just a minute amount of toe in, but traditional set- ups seem to be straight, close to the rail, way back and fairly wide base...hmmmm...
I might make up a few templates and and see if one "feels" just right. Knowing me I'll want to make up several boards with different set- ups and drive myself crazy..... Not really,just an excuse to dig deeper! thanks again for your input.

[rodndtube]

My recommendation would be to focus on the fin box placement... then you can experiment with a range of fin sizes, shapes, foils and flex characteristics. Is the subject board a half-inch ply? How wide, long, plan shape? Maybe you won't be using a fin box after all although it is still possible.

[kfitz +]

Hi rodndtube, OOps! previous post was incorrect as to widths should read 20" to 20 5/8" SORRY, The boards will be 1/2" ply, I'm going to try and slot the fin bases in and also slot two horizontal inserts(lateral support?) (w/glue or epoxy) deck and bottom sanded flush, want to try to affix without Glassing(weight) boards are
in the 43-47 inch range and are tombstone shaped(tweaked noses and rear shapes, thinned nose to slight hull to flat and single concave(rear third), rolled with slight bevel at the last 6" out rear of board. 20" to 20 5/8" wide point carry through to slight tapering or very subtle curve to the end ,horizontal (straight)bottom or slight elipse curvature . this is still a work in progress,and want to get an idea how close to the rails the fins should be and how far to the rear.......its a lot for my plate, but I love the mechanics and the challenge. thanks again guys