What do you hope to accomplish, Greg? I did some (admittedly half hearted) research on the subject when building my board and most of the info I found seemed to pertain to the dynamics of "surfing," not so much flatwater padlding. I have no real surfing experience, so that's all I'll say. Ultimately I installed a single fin box and have been using a 9" fin. It tracks really, really well. Maybe I'll experiment with something smaller, but I'm happy with the performance for now.

Did you find your board wanting in this regard with the two smaller fins? How are you using the board? These were the guiding questions that kept cropping up when I was looking for info. If you can answer them you may find your best path.

Good Luck,

Patrick

no need for a third fin on the kaholo.  the two skegs are meant for tracking the board straight.  If you feel you need more depth just lay up some cloth to make them deeper after you make the new one or make two new ones a bit deeper and maybe with more base or more depth and rake. 

The third fin on a thruster or tri fin surfboard is meant to hold in while making a hard turn.  it is also only a few inches from the tail.  Typically, the outside rail fin will almost break free of the water during a turn.  Also, the two side fins are canted and are not parallel because the board is always turning from one rail to the next and really never goes straight.  The side fins are foiled on the outside and flat on the inside, most are.  I paddle my Kaholos in a bit of tidal currents and wind and use the two skegs that came with it and find that they work fine.  I surf on all multiple finned boards.  From two to five fins.  Well placed fins will make the board accelerate with turns.  I think the only benefit from deeper wider skegs or a single fin on the Kaholo would make the board stay on course better with side winds or current.  They would also help when riding swells and small mushy waves - straight!  good luck with the new fins!

Patrick:

I'm going with a single fin as well.  How far off the transom did you set the rear of your fin box?  I'm thinking setting mine about 9 inches in.

Chris

Hi Chris,

I followed Dan Bright's lead on this one:

http://www.clcboats.com/forum/clcforum/thread/22340.html

Dan has the reinforcement block butted against the last bulkhead- I assume for stability- and this mostly defines the placement of the box. In retrospect, I think the assembly would be plenty strong without attaching to either transom or bulkhead, but  if you're putting in a long fin box you probably have just a few inches of play between the bulkhead and transom, regardless. I am far from an expert but I'd guess this doesn't matter much in my context. Unlike SurferBill, I'm using my board on flatwater and some pretty easygoing rivers so my performance requirements are pretty basic!

I deviated from Dan's plans in a few other- probably trivial- ways.

I used solid cedar for the "block," and atached this block only to the bulkhead, deck, and hull- I didn't extend it to the transom. I created a template and used a plunge router to create a snug fit with the fin box. I used only thichened epoxy to bed the fin box- no glass. When glassing the hull, I masked off the slot in the fin box and glassed over the whole thing. Before the glass had fully cured I cut through the glass with a razor blade to remove the masking tape.

Good luck!

Patrick

whatever you do, do not add a center fin if you keep the two skegs.  That would create too much drag.   Do one or the other.  I do not ride waves on my Kaholo, not worth it.  They dont work well for that purpose.  As far as placement for a single fin if you grind your skegs off, check on some of the racing sup boards, it looks like the fin is further up from the tail or transom than a surfboard would be.  The method of installation of a box above is fine.  Check out Woodogres box, I think his link is on this forum.  His box is sandwiched in foam and is probably placed well based on his experience with other boards and sailboards.  Also, check out how Grain Surfboards do their boxes.  You do not need to have the box between the bulkheads.  If you wanted it to go through a bulkhead that is fine.  You just glue in material on either side of the bulkhead and then rout through all the material to install the box.  It will be plenty strong and actually make the bulkhead affected even stronger.  good luck!

Great point SurferBill- especially the tip on WoodOgre's Kaholo build. Here's a link to the Swaylock's thread:

http://www.swaylocks.com/forums/wood_ogre-builds-14-ft-koa-kaholo-kook-box

This was realy inspirational to me when I was getting started, though being a newby I'm sure I only managed to apply a fraction of the tips mentioned. Guess I need to build another one!

When that build log ended WoodOgre was still trying out different fin setups on the Kaholo. I've seen his login on this site- WoodOgre, if you're reading, did you come to any conclusions about fin dimensions/placement for this board?

Thanks!

Patrick

Wood_Ogre here. Yes I did come to a conclusion on fins for flat water paddle boards. I did 22 different fin combinations. Low aspect fins track the best. High aspect turn the best. Reverse D with long bases stear with your feet never need to change paddle sides but increase drag ( no point in this fin as you get tired of paddling on one side after about 20 strokes. I made all my proto type fins except 2. A Jimmey Lewis 11 inch, (horrible fin ) and a 10" fat boy. The conclusion is for flatwater paddling you are going so slow that shape of fin doesn't make much difference. Surface area does. The more surface area the better it tracks. In the end I am useing a 10" fat boy because it has more surface area deep in the water and is midway in performance. Another fin I liked was a weber performer hatchet fin. In the end it turned out what look cool to me and I will continue useing the fat boy. As far as fin placement it doesn't matter a whole lot but I prefer way back on the board with the back tip of the fin about even with the back of the board. You want your board to track better just move your feet forward on the board. Now if you are building stand up surfboard fins are a total different thing as you are up on a plane and the faster you go the more important fin shape and placement become.

PS I have 2 kaholos, one for flatwater and one for windsurf fishing. The windsurf fishing has 2 side by side fat boys ( Bill Thrailkill set up ) which is bitchen because it creats a ventury between the fins so I can point real high while under sail pulling a fishing line. But it is a bitch for flat water paddling as it picks up leaves and twigs. If you want proven fins for your Kaholo the best are Larry Alison fins , he knows more about fins than God !