Turn fin

[JohnsonM50]

A question about an old time boat and new hanlding tech... Ive got a Hal Kelly Airborn, it has a 31.8 OMC on a Bass foot. Im thinking of trying a chicken wing to flat turn it. Origionally and according to design this had the lower chine squared 1/4 inch for the last 3 ft or so. I heard that could cause a flip so I planed it to a slightly rounded chine, [a noticable improvement.]
Ifff I go and do it, is there a proportional location guidline ? What do I expect from adjustments front to rear? How do I determine depth and should it be angled inward? The boat weighs 460lbs [me in], the length is 11ft 8in, the bottom is flat, 38in wide and it has a bottom fin now that is not very predictable. The boat climbs off the initial grab then will do a twisting porpoise that gets bigger each time :eek: . Ive leaned to goose it around a turn amid this all:cool:. Just need some insight from real racers :confused:. Maybe I need more area on the type fin I have [D] or to move it back a little. The boat is in show your boat page 5 [from beginning]. I moved the fin back about 5 in since then.

[Joe Silvestri 36-S]

My CSR measures 11'8" when measured square off the bottom and has a 38" bottom. I have my side fin mouted 36" forward to the center of the fin bracket, measured from the aft end of the bottom. My fin is 5" wide and hangs roughly 4-1/2" to 5" below the bottom when measured off of the flat pad. BE SURE the fin bracket is perfectly square with the transom and I run my fins perfectly vertical. If the fin bracket is not perfectly square with the transom you will be in trouble. The fin may dig and go right pitching you out doing so. I've seen it happen, not pretty. Some guys will run their fins a little cambered in to suck the left side of the boat down while turning so they do not have to lean over as much but I do not do so. I figure I can lean over myself and adjust the ride of the boat with my body weight. I've run CSR for quite a few years with many different boats and this set-up has always worked for me. Be aware that once you put a side fin on your boat you can not turn right at least not much and very gently while at full speed, no different than a hydro. If you mount your side fin correctly the boat will handle better and turn very well for you. The other thing you may want to do is add a trailing fin to the transom on the left side. Mount a little fin about a 1-1/1" wide about a 1" deep at the left edge of the bottom. This will help the boat track and not skid through the turns. Some guys do not like to do this as they feel it slows them down but it adds a lot of control to the boat. I've always felt that I had to be in total control of the boat if I was going to make it around the track to win. I hope this helps. Attached are pics of the two CSR's I've built and raced. The first boat is now owned by Tom Enyon and the second boat is my current CSR.

[Tim Weber]

Joe,

38" is wiiiiide for a Sorenson. Do you mean 38" including the shingle before you go into the non trip?

Tim

[Joe Silvestri 36-S]

No, my bottoms are 38" wide at the pad. My CSR's have a tall outside cockpit side like a Sorenson but they are my own design.

[Tim Chance]

I have a 13-6 Krier Runabout and I run a 250 c.c. Pro motor and a 49.7 OMC Mod motor on it. The back of the fin is 4' from and square with the transom. It is 4" wide and sticks 4" below the bottom of the boat; 3/16" thick. The bracket is billet aluminum, custom made by Brian Matheson. The trailing fin sticks 2" below the bottom of the boat and is in a hydro sponson fin bracket as far to the left as I could put it.

The first time I tested the side fin I almost tore the whole thing off the boat. The plywood of the chine wasn't strong enough to take the stress. So I cut a hole in the side of the boat and cut a 1" board to fit between the stringers and frames. I screwed and glued this in place. Then I cut another 1" board that fit between the frames and on top of the new piece and also on top of the inner stringer and butted the outside stringer. I glued, screwed and bolted this in place. I also took two pieces of angle iron and bolted to the frames and flat to my new stiffeners. Then I patched the hole. Hopefully you can get access from inside the cockpit.

About your forward/back position of the center fin. I have found that if the fin is too far forward the boat will tend to spin out. Too far back and the boat doesn't want to turn at all. I don't have any experience but I would think it would be the same situation with a side fin. Hope this helps - Tim

[JohnsonM50]

Thanks Joe and Tim, Its good to know that questions like these get answered this well. I could imagine a chicken wing veering the boat right if the leading edge was off to the left a little..yikes or being too far forward and spinning.. I was spun once from a surprise wake, at least I was still mostly in the boat.
Beefing up the area, I would definitly need to do. If go with a wing Im off to a good and reasonably safe start. The trailing fin with a hydro bracket sounds good.. easy to do, adjustable / changeable. Im thinking about getting a D size bottom fin 1st and the trail fin. Nice runnabouts Joe, Its amazing to see CSRs charge the 1st turn.

[Joe Silvestri 36-S]

Your welcome. If you have any other questions that I may be able to answer, ask away. As far as beefing up the inside chine, definitely do that! I built my CSR's with the side fin in mind and beefed the chine up while building. Good luck and have fun with your project.