I'm in the planning stage of a power box to tuttle box conversion for my JP 2012 109 Supersport Pro ("Have router, will travel.").


I am thinking of positioning the fin box 1cm forward from the original power box location. What are member's thoughts on this ?

Nb/ I run exclusively non-offsetted weed fins. I won't be running pointers, freeride fins or deltas in this board.

Thanks for any advice

I'd go 3 cm.
Watch the router grabbing
Tip , about 8 cm on either side of the centreline , about 50 cm long , build up a strip of layers of masking tape until above the V of the board. ( between 5 and 10 layers ) . It lets the router slide nicely and makes a square neat job .

3cm !. Wow. That's a lot. Ok. I'll try that.

I have not formed up the board yet. I'm going to copy this guy's method using wood as form work to stop the router going "ZZZZZZZZippp !!" and me going "$@%& !!"



Thanks for the tip about the tape.

I like the idea of a plywood template. It seems like a good idea.

I have always copied the boardlady's advice and laminated a layer of divinycell around the finbox. I am not sure if it actually makes a difference, but its the way I have done it.

I think the idea is that the divinycell is easier to stick to the plastic finbox and then the divinycell is easy to stick to the foam or the epoxy and filler.

Thinking about it now I think it would require more thickened epoxy to fill in the voids around the finbox, but it is much easier to do when the finbox is not in the board.

Yes, I remember reading that quite a few years ago now. I'll relook at her advice. Thanks.

How far forward depends on where the fin centre of lift is, the longer the fin @ 45 the further back. I think imax uses big fins in choppy water, so his 3cm is justified. My fins are no longer than 28cms, and I'd go 1cm further forward.

Usually the tuttle box is long enough to go right through the board, this allows it to be tied into the deck, making it super firm. If you hit the fin hard enough it can rip the back of the board off before moving the box.
Divnycell isn't needed for strength in that case, but helps as a water proofing agent between box and core.

Because the original box is probably surrounded by Divinycell, I would rout a tight hole for the new box to slide into . No need for extra Divinycell. Rough up the box with corse sand paper .I use Chinook boxes ,$ 45 from Surfsail Australia . Although they won't take the extra deep Tuttle bases . As Decrepit suggests, go through the top of the deck . Your going to need a long router bit . I start with the router bit as far as I can go and then use a long wood drill in the router and plunge down through the board and out the other side . The type of drill with the square edges and the little point in the middle . Not a spade drill .This is scary but works good . Finishing with a file from the top . This is where tight is good . Trim the excess of the box to match the deck . Don't worry about countersinking the screw holes , unless it's already in the box , it's a big hassle and a weak point . Just use longer screws . Stuff foam into the voids of the box and screw holes . Half a dozen layers of 4oz glass over the top will be plenty .( I always overkill ) . Sand fill and paint .
On the bottom ,( this is what I do , some may not ) , I would also lam over the box . Resin in the box level with the bottom of the board . Fill the box opening with jammed in foam . Using a medium file , file the box level down and the board a couple cm around the box fairing out . A sanding block can be used , a file is more accurate . About 1 mm deep over the box but not going all the way through the glass / carbon , except close to the box .. Using a straight edge ,( ruler ) , check your depths .Two layers of 4 Oz glass over the box . Sand and bog flat . Carefully drill and file away the glass over the box opening . Do this before painting so you can see where the hole is . This will make sure the box is as solid as an ox . Again , probably overkill.
ps ; always do fixes with the vent screw open .
This is how I do it . There are probably many different ways of doing this .

Thanks Imax and decrepit. Really good advice. I have a bit of planning to do

Imax, is this the bits you are referring to ?


The fin sizes for this board will be 28-33cm.

Yes , that kind of drill . Half inch , 12.7 mm ,straight shank to go straight into the router collet . Check what size your router is . Get one 30 mm longer than the thickness of your board . You can gently go sideways with these kinds of drills . Bloody noisy though . Plunge cut most of the hole and gently finish going sideways.
Mine is blunt and still works good .

The routing complete. Now drill bit jobbie. Suppose I am going have to use some divinycell for the forward part of the fin box (where the foam is exposed) ?

Looking good
When all the way through , for that front bit , I'd roughly pick out the soft foam with a screwdriver , about 1 cm wider than the fin box . Dam up with some foam and fill with 90 kg pour foam and re rout . This is how I install fin boxes , strap plugs and mast boxes . IF you don't want to buy pour foam , for that little bit I think it would be OK to use foam in a can from Bunnings .$8 . It does leave bubble holes but for that bit would be fine . Pour foam is expensive and goes off .
Keep the pics coming.
Did u get a chinook box ?

Nice talking with you tonight imax. Thanks for your tips.

So, tomorrow it will be punching those four holes through the board to see where I need to cut out from the top of board (as you recommended). I'm thinking of using an abra file (without the handle) to do the cutting. I should be able to slip it though one of the holes.

BTW: this is my router.


This is my box:

www.surfsailaustralia.com.au/product/chinook-tuttle-fin-box

You would hope the fin box was put in the best place in the board, like wise you would hope the fin(even weed fins) were designed to work in a box that was put in the right place so why move it

Ben, This board has never been great at pointing, even when I used to use freeride fins. Most of my fins are weedies now. The weed fins make this board slightly worse to point. So, I am moving the box fwd a smidge to compensate for weed fin's aft centre-of-effort (if that is the right term to use ?). If I was still running freeride or pointers, I would not be changing the box position.

Nb/ This is a trash board anyway. I've owned it 10 years from brand new. I've had a lot of fun with it. It owes me nothing if I balls it up. I thought about buying another non-performance "go anywhere" board, but then I thought it would be cheaper and more fun to tinker with my existing.

Select to expand quote

jn1 said..
Ben, This board has never been great at pointing, even when I used to use freeride fins. Most of my fins are weedies now. The weed fins make this board slightly worse to point. So, I am moving the box fwd a smidge to compensate for weed fin's aft centre-of-effort (if that is the right term to use ?). If I was still running freeride or pointers, I would not be changing the box position.

Nb/ This is a trash board anyway. I've owned it 10 years from brand new. I've had a lot of fun with it. It owes me nothing if I balls it up. I thought about buying another non-performance "go anywhere" board, but then I thought it would be cheaper and more fun to tinker with my existing.

I had a JP FSW which was about 98L I think. I started using weedfins exclusively and did something similar to what you are contemplating/doing. I used a powerbox though, but I moved it forward by half a fin box.

It certainly made the board behave differently. The same as you are trying to do, it moves the centre of effort of the fin back to where it should be (forward) with pointer fins. It made it feel much more like it did with a pointer.

I am not sure if I threw the board away or kept it somewhere. I think if I did it again I wouldn't move it as far forward as I did, but it sounds like you are not moving it very far forward either.

I had a board with a tuttle in it that also feels too far back when using weedfins in it. It felt like you would go from riding it fine to spinning out as the COE of the fin felt so far back.

Thanks FN. Good assurance I am going down the right path. My offset is 1cm (as suggested by decrepit).

From yesterday's session, here is a pic just before I routed. The router did not sit on the wood form. It was beside it. The wood kept it where it needed to cut.


And today's progress. Having a chat with imax the previous night regarding the tooling I had at hand, he suggested a plan of attack. So, I am following his guidance.

So I drill out four holes using a very long drill bit at each corner of my routed cut as a cut guide on the top of the board. I don't own a level or a drilling guide. It was all eyeballed. But imax said, if I stuff it up, then it's not a problem.

Flip board over, and remove foot pad and mark out where to cut.


Dremel shell. Unfortunately board specs and Werner's lovely signature must go.

Nb/ In future, I probably won't bother about milling the box out with a router. I'll just cut the box out. The router made airborne some very nasty materials that caused me to itch for 24hrs. It's like a glass rash. The box grinds to a white powder, and the router bit sparks sometimes when I milling the box with it. I think this white powder is the culprit.

Cut slots out for hack saw blade.

Cutting.

Finished off with an abra file to cut through the box - as it's 1cm offset (where I could not get the hacksaw into).

The result for today. Cheese cake anybody ?

Then it got windy. So I packed my car and went sailing (not using this board obviously ! ).

Next: The first part of fabrication using some expanding form. Watch this space.

So far so good.

Looking shmik, How does the box fit , nice tight , and square ?

boardhead: Thanks

Imax: It's an "interference fit", so will put the board in the oven and the fin box in the freezer. (hey, just kidding ). So will have to file the hole out for the box to fit. I'll see if I can get out there tonight and do a bit of work on it. I'll do that next I think. Dinner first though.

Yes, nice n tighty Imax

Not glued yet. Checking for size/fitment.

Imax: Did you say box should be 1mm recessed ?


Checking box is orthogonal. Looks pretty good. (yes, checked both sides due to the rocker)

This is the top.

I ran a string line down the centre of board to make sure the box is aligned. Looks ok.


So, the next thing now is to pick out the foam area fwd of the box, then form it up with a small polystyrene block, and then fill that void with expanding foam.

Then I prepare the box for glueing: cut the aft/top side of it down with a hacksaw, and then cover the bottom with a layer of 4oz, and plug the holes.

Glue in the box flush with the bottom of the board . When dry , with a rough file , file the box and surrounding area down one millimeter. Faring out to nothing , ( 1 cm around the box ) . This is easy because of the v in the board .Don't go through the glass \ carbon . Sand off all the bog and paint in that area . Fill the box with styrene foam and sand flat . Fill any holes around the box with resin . Sand flat again . I'd go 2 layers of 4 Oz glass squeegeed flat with minimal resin over the box area . Sand the area flat . You will remove some glass that isn't recessed . Paint layer of resin . Sand flat . Bog . Paint .

Do the same with the top with 5 layers of 4 Oz glass . Remove paint and bog but don't worry about recessing .
You can leave the top proud a couple mm and blend in after the box is glued .

ps: rough sand the box . Mix resin with filler to mayonnaise thickness . Using an icy pole stick , or similar , cover the inside of the board hole and all over the box and in the grooves . This is messy , so use gloves and mask off a big area . Make sure box doesn't move while drying . I use masking tape on the top of the board ,which will be upside down , to stop the box sliding down . Don't go anywhere for the next hour while gelling . Make sure it doesn't move .

Select to expand quote

jn1 said..
Then I prepare the box for glueing: cut the aft/top side of it down with a hacksaw, ....

That doesn't sound right, you cannot cut the top of the box itself...?
It sure sticks up a lot, on the upper side of the board, is that a deep tuttle box or a regular TT-box?

Edit: Sorry, I think I understand now, just check that the top of the box can be cut down enough without cutting into the part where the fin-head stops.

Select to expand quote

SurferKris said..

jn1 said..
Then I prepare the box for glueing: cut the aft/top side of it down with a hacksaw, ....

That doesn't sound right, you cannot cut the top of the box itself...?
It sure sticks up a lot, on the upper side of the board, is that a deep tuttle box or a regular TT-box?

The chinook boxes are made long to chop to correct size to mount like this . The actual hole where the fin goes is sealed off inside .

Yes, thanks, I understand that now. :)
I guess most boards are thick enough too enable the fitting of a regular TT box, and simply cutting off the intentional sacrifice material.
So it is only for the deep tuttle heads that the board thickness could be an issue.

Thanks for the tips Imax . Next bit is the gluing, and working with the bottom of the board. Summary (see if I have got this right):

- shape top of fin box to roughly conform with deck
- rough up outside of fin box (so it sticks better to the resin)
- hard pack inside of box with polystyrene (to stop any resin going in it)
- the gluing (butter method, mayonnaise thickness: resin + talcum powder, check level, don't leave job until resin goes plastic)
- resin injections in the fin box grooves (where required)
- shallow chamfer the fin box and area of board around box like this:


- Put 2 layers of 4oz glass in this chamfered area. Board ladies method: boardlady.com/fiberglass101.htm
- make sanding tool (Glue 80 grain sandpaper to a wood length), and use tool to sand around box. Make glassed area flush with board.

I'll probably wait for the weekend to do most of this work.

That's removing way too much. Keep the file flat, not inwards. The V in the board will naturally fair out.



Close up of the area that needs to be removed. Showing the cross section of paint, bog, carbon, divinycell and then carbon that makes up the lamination. Just remove the paint and bog. You want to leave the Carbon there. Doing that should drop the box down about 1 mm. That leaves some room for the 2 layers of glass.



Run a ruler along the board V to make sure the box is 1mm down. After glassing, your sanding board will remove excess glass that is not covering the box and in the faired-out part.

Thanks Imax. I'm clear what to do now (I'm a picture man ! ).

Pics from tonight.

Set the fin box flush with bottom of board, then roughly conformed top of box with deck, but still protruding out. Angle grinder worked a treat.

Roughed up outside of box with a chisel.

Nearly forgot to do this: Dig out 1cm of polystyrene and replace with 90kg pouring foam, which acts as a substitute for divnycell.

But I am going to use this stuff instead of 90kg pouring foam.

Form it up at the bottom of board.

Spray in from the top of board:

First, a compatibility check. Looks good. No reaction (I think ?).

The result, and the first fabrication step for my board.

I only used a bit of foam, and the instructions on the expanding foam can said this stuff can be cleaned off with acetone. So, I cleaned up the straw and spraying mechanism with acetone, so I can reuse the can at a future date. Wow, this expanding foam does not like acetone at all ! . It turns the expanding foam into instant clear liquid !

In the future, I'd avoid spray/canned foam. Lots of voids inside which compromise strength and require more filler material/bog. Plus, the density is hit or miss depending on how much room it had to expand. What you used is low density foam from what I can tell, meant to fill bigger voids (such as shown on the can) which compounds the problem.

And, I'd suggest using masking tape next time instead of duct tape. Duct tape can leave residue which clogs sanding paper and inhibits epoxy adhesion. Duct tape is good for ducts but not so good for board and sail repair.

Select to expand quote

Paducah said..
In the future, I'd avoid spray/canned foam. Lots of voids inside which compromise strength and require more filler material/bog. Plus, the density is hit or miss depending on how much room it had to expand. What you used is low density foam from what I can tell, meant to fill bigger voids (such as shown on the can) which compounds the problem.

And, I'd suggest using masking tape next time instead of duct tape. Duct tape can leave residue which clogs sanding paper and inhibits epoxy adhesion. Duct tape is good for ducts but not so good for board and sail repair.

Righty-o Paducah. Thanks for the tips . And what you said about the voids played out too. This is all a good learning experience.



When I had a chat to Imax, he explained that expanding foam is inferior to pouring foam, but because I don't run big fins and the expense/storage life of it, the expanding foam would be an adequate substitute for my application.

When I pulled the 100MPH tape off, the expanding foam was not cured. So, will have to wait a bit before starting work.

That foam should have hardened by now . It looks a bit strange . Did u shake the can well ? That's a big hole that doesn't look like it's foamed properly .If it hasn't hardened by tomorrow , dig out the soft part and do it again . It could be OK where u needed the foam . I wouldn't worry about it too much . Just fill any holes with bog .

Hi Imax. I followed the instructions on the can last night. The only thing I didn't do (that it instructed) was spray down the surface with water.

I think this may be an operator error on my part. I remember you telling me this is going to make a mess. I didn't make a mess. I think I didn't give it enough courage. I'll have look tomorrow after it's cured. Worst case scenario, I scrap it out and try a different product.

Meanwhile, I'm checking out this Australian made product. The same co that makes Flex2's potting epoxy.