Guidelines for creating single fin box in Kaholo

I'm searching for a clear, step-by-step process on the best way (strong and light) to create the internal support that will house a 10" single fin box in the Kaholo 14'.

I have read and viewed any number of articles, links and photos regarding the installation of a single fin box in a Kaholo 14' but can't seem to track down specifics for a "go to" plan.

What does seem clear to me is that the 10" single fin box I plan to install should be 8" from the tail, meaning that I can take advantage of the number 11 bulkhead.

How much support material (foam?, ply?, other?) is required and what recommendations can builders who have made successful installs give to me and others wishing to go the single fin route?

As always, I appreciate the feedback and insight all you folks in here offer!

Cheers.

Dan 


16 replies:

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RE: Guidelines for creating single fin box in Kaholo

G'Day Dan.

I did mine on Friday.  I had Intended to making a routing jig but ended up using a forstner bit to remove bulk of material and chisels to get the final fit.

 I glued a block of paulownia eiher side of he rear frame. WRC would be good and probably more availible in you neck of the woods. Balsa can be used as well. I have seen foam used on the web somewhere but the builder also included a ply frame around the foam.

When gluing in the box you will need to ensure that it is aligned. I did this by fitting the fin in the box and marking some reference points on the fin and the sides of the hull. A small error at the box can translate to a big error with a large fin. I have a pic or two that I will upload when I get to a pc.

Cheers

RE: Guidelines for creating single fin box in Kaholo

Craig,

Good to read from you as always. Thanks for the tips. I would love to see pics of the fin box reinforcement you built for inside the hull. Sounds too. like I should get the actual "fin box strip" and fin to help visualize what I need to do.

When its all said and done I think what I'm suppoesed to have created is:

a reinforced box made of okume ply and fill it with foam, all materials level to where the deck will set. I should mark the placement of the foam box by drilling precise holes that extend through the bottom of the hull. These holes I'll use to cut the hole/slot that the fin box strip will be glued into with epoxy. The actual gluing of the fin box strip happens after glassing and varnish the board.

What might I have missed or need to change?  

RE: Guidelines for creating single fin box in Kaholo

G'day Dan,

I like to look at other peoples build diaries but I'm afraid I'm a bit slack when it comes to taking pics myself. However, i did take a few of the fin box I installed. Sorry, no pics of internal block and I attached deck this morning.

i glued paulownia blocks either side of the rear frame. The blocks were about 40mm wide and 50mm deep.

The box location was marked out on the hull in pencil.

the hull glassed but no fill coat

Rather than use a plunge router and jig, I decided to remove waste with forstner bit and chisels. A spade/paddle bit will do.

[IMG]http://i124.photobucket.com/albums/p23/CraigMel/Kaholo/221220121091_zps33e811bc.jpg[/IMG]

The fin box was fitted flush and fixed in to place . I marked reference points on the fin and hull so that I could get square and glued in to place. I used polyurethane glue along the bottom to fix it. When I apply fill coat, I will push some expoxy down the sides of the box. thickened epoxy would be the standard procedure but I am playing around with different adhesives on this project

[IMG]http://i124.photobucket.com/albums/p23/CraigMel/Kaholo/221220121095_zps961268c9.jpg[/IMG]

[IMG]http://i124.photobucket.com/albums/p23/CraigMel/Kaholo/221220121096_zps83815df5.jpg[/IMG]

 

I have seen the method that you describe ie foam filled frame to deck level and that will work as well. Might even be a bit lighter. I don't have the high density EPS foam so that method wasn't an option for me.

there is a SUP thread in the bluheron kayafoundary forum at the moment. The OP has just posted pics of his kaholo which he modified by narrowing the beam. He used balsa for his fin box and the front of his deck.

Off to work to trim off the deck. Another advantage of polyurethane, 4 hours to fully cure.

hope the pics provide a bit more info for you.

cheers, Craig

 

 

RE: Guidelines for creating single fin box in Kaholo

[IMG]http://i124.photobucket.com/albums/p23/CraigMel/Kaholo/221220121096_zps83815df5.jpg[/IMG]

RE: Guidelines for creating single fin box in Kaholo

RE: Guidelines for creating single fin box in Kaholo

http://s124.beta.photobucket.com/user/CraigMel/media/221220121096_zps62792003.jpg.html

RE: Guidelines for creating single fin box in Kaholo

Removing waste

Removing waste

 

Inplace and glued

Fin in place

 

Reference points for setting up

RE: Guidelines for creating single fin box in Kaholo

Thanks Craig! And Happy Holidays. The pics are helpful and I will check out the blueheron thread you mentioned. The deck might go on this weekend if I can get this box build fashioned. I'll keep ya posted.

Cheers!

Dan

RE: Guidelines for creating single fin box in Kaholo

On page 4 or 5 you see how I made the inside boxes for a side by side fin box. After this was insalled and the skins wer installed I drilled a pilot hole into the boxes then routed them out with a pattern bit. these boxs were 1/4 inch wider , deeper, and longer. Then the fin boxs were resined into these boxes. Some where in this thread there should be pics of doing the same thing with a mast track box that shows how the fin box is held in place while the resin is filled around it. Just go through the pics and you might find something useful or interesting.     http://www2.swaylocks.com/forums/wood_ogre-builds-14-ft-koa-kaholo-kook-box

RE: Guidelines for creating single fin box in Kaholo

Page 5 inside fin box support

 page 9 inside fin box supports before skin installed

page 10 Mast box being installed

On the mast box the inside support goes all the way to the bottom of the board. On the fin boxs it is glued to the bottom skin and to the frame.

I have over 1500 miles on this Kaholo now and have tried 30 fin combinations. My conclusion on fins is long base fin keels ,large reverse D and large C fins give good tracking, any fin works OK for paddleing although surfboar fins dont track nearly as well as long base keels . More fin surface area = better tracking.So for paddling any fin will work. For windsurfing when the board is up on a plane deep fins with a lot of surface area are a must, the fins then are everything and it took a lot of effort to find what would work on a board this big. So I went with what works with for the wind surfing and it works good too for paddling. Hope you find something usefull here. I am very impressed with the Kaholo board. When it is sitting on the water it looks so gracefull. No outher board even comes close. I get endless comments on this board.

RE: Guidelines for creating single fin box in Kaholo

Thanks Wood Ogre for the links and tips. I really apreciate it. I am thrilled with how this project is coming together and having built a Pygmy kayak years ago I can taste the fruits of this current labor already. I'm less than two weeks into the process and once I get the fin box reinforcement and box thing figured out I can attach the deck and continue on my way!

One of my gigs is working for a kayak and SUP outfitter in Sarasota, Florida. I'm around Bark, BIC and Hobie boards and have put in many, many miles as well on a variety of boards. As I build the Kaholo I can sense it's glide, it's ease and response that it'll have on the water. Her lines just feel and look sleak; you know she wants to move.

Great to read that after so much time on your Kaholo you have such high praises for her. I can hardly wait!

Cheers! 

RE: Guidelines for creating single fin box in Kaholo

Hi, I built two of the original Koholo 14's a few years back.  Just used the parallel keels though. 

 A box set up for a single fin should be set in solid wood.  If you use foam around the box it will weaken over time and water will get in.  Especially if you use the board in the shallows.  The nice thing with the keels is that they are shallow draft.  Not sure any of the Koholos will turn much better with a single fin.  But I have not tried any.

 I built a Grain Root longboard last year.  A good fin box comes with little tabs on the sides so it sits perfectly level on the bottom.  No need to use a fin and try to eye it up with tape.  More important to get the box to sit perfectly on the tabs and tape it down when setting, i used toothpicks to make sure it didnt move side to side in the play.  The tabs also insure correct depth.  and also, since there is no center stringer, critical to have it lined up perfect, obviously.  I used a jig and router since my friend has the set ups from building surfboards for 40 years.  He helped.  But, you can use bits and chisels to make the bed for the box.  just make sure it is not too wide. I would not think that it is necessary to install the wood from deck to bottom.  would not add that much weight though and would be super strong.

Good luck!

RE: Guidelines for creating single fin box in Kaholo

SurferBill , There is no foam surrounding the fin box in my board. The foam was used to hold the shape of the wood box which the fin box goes into. The foam holds everything together in allighnment untill the epoxy fillets have dried, keeps everything square and plumb. Aftere the skin is put on the box is routed out and all the foam with it and the fin box is installed in the wood box and wood box filled with resin. No the fin box does not need to extend from deck to bottom on the fin. But on the mast box it does need to go from top to bottom. There is a lot of stress on the mast box. Craig your fin is an excellent fin and the location dead on.  My fins are two fatboys side by side and are for ocean fishing with a windsurfing rig. I wounder if anyone even knows the function of side by sides or even what they are ?

RE: Guidelines for creating single fin box in Kaholo

Fully agree with the use of wood instead of foam and can't see any need to add a block from hull to deck for normal use. Wood ogre was/is using his for windsurfing so I expect there would be a much higher load placed on his  fin/s. Hence the ply frame form top to bottom. Its my understanding that on commercial EPS SUPs they use a denser EPS foam in the fin box area.

I do however, believe that it is a good practice to have a system to check alignment and not rely on the hull alone to be spot on. When I fit my fin box flush and checked for square, the fin (10"hatchet) was out a few mm at he top.  Some may say thats not much and it can't be seen by eye but its an easy fix and its just good practice to check all measurements.

Summary, at th very least you should check and measure your fin box with fin in before committing to glue. If its all good or you aren't that particular with measurements then glue it up. If its out a bit, fix it.

Cheers

 

 

RE: Guidelines for creating single fin box in Kaholo

So, the deed is done (almost?) and I'm pretty happy with the results. Plan on attaching the deck Monday the 31st.

I created a 12"x3.6"x1.5" block out of 6 balsa sheets, epoxied together. This "balsa block" is sandwiched in between 2 custom made okume sheets. The okume sheets butt against the number 11 bulkhead and run all the way to fit into and follow the angle of the tailblock. This also gave me a little under deck framing for a leash plug/vent.

The balsa gives me ample material to cut out a 10.5"x 1"x1" slot for the Bahne box a few steps from now.

I made it so that  the entire sandwich is flush with the deck. I see from other posts that it is not necessary to run the reinforecement all the way to the deck but...

*****Perhaps I should drill out some the block???????????? while I have the chance? From what I'm reading it certainy wouldn't compromise the strength of the fin box. Hmmmmmm. Suggestions?

The entire "sandwich" was still extremely light, perhaps not much more weight than the fins included in the kit. 

At the moment the hull and deck (with the underside glassed and ready to go on tomorrow) is coming in at 29 lbs.

Cheers!

Dan

 

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