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Sunday, September 13, 2009

Convert from Glas-on Keels to a Quad with Keel Twin options

This Jeff Bushman Twin was sent to me from Hawaii to convert to Proboxes. The rider of this board do not want to change the postions of Jeff's Keels but wanted to expand the use of the board to a Quad option. This thread will take you through the process of the change.
First thing I did was remove the Glas-on Fins and mark how far in Jeff had his fins from the rail, as show in the pic below. The back marking should read 1-1/2" not 1-1/4", oops!
I then prepared the tail section of the board with a tail patch. I prefer 6oz or 7-1/2 oz glass for this stage, because your bottom lamination is the most important part of supporting a Fin System from failing.
After the lamination is completed, trim and hotcoat the tail patch for installs.
Now place your boxes for a visual and make your markings on the Hotcoat. This board the tailing edge of the Keel Fins were 7-1/4" from the tail, which put the back of the ProBox 8" from the tail. These measurements put the same Keel Fin template with a ProBox base back to Jeff's orginal placements, 1-1/2" off the rail with 2-3/8" toe to flat inside of the front of the box.
Now that we have set the first set of ProBoxes, this will dictate where the next set of boxes are placed. My choice from all the conversions I have done were to add the next set of boxes to the front of the existing set. What people forget here is, that we have a adjustable Fin System so if the ProBoxes seem alittle far forward we adjust the fins back in the box. If more adjustment is needed then we can custom make the Fin Tab of the ProBox fin to be further forward allowing more adjustment further back. Most Older Fixed Fin Systems won't allow this to be possible, which then the board builder will have to compromise this position and hope the board works. Having the boxes to far back and shifting the Fin Tab on the fin base back which allows you to push the leading edge of the fin further forward will work against you. This causes the leading edge of the fin to flex in creating drag.
Once I find where my front set of ProBoxes are placed, I will set my toe. In this case the toe of the front boxes will be dictated by Jeff's original toe set by his keels from the rear boxes. To find the toe of the front set of boxes, mark in from the rail to the flat of the inside of the box at it's rear. In this case 1-1/2" off the rail to the flat and 3/4" forward of the rear boxes. Then toe in the front box until your flat side is running parallel to the flat side of the rear set of boxes.

After all your markings are done, lay down heat treated tape. I use 1-1/2" tape. This will act as a guide in sanding and creates a good bond with our install jigs with the spray glue. DO NOT over lap the tape!! This tape build up will throw your box install off in depth. Lay the tape side to side.
After your jigs are set and the hole is routered. Spike a few shallow holes around the inside of your routed hole half way up. This helps create a fiberglass flange concept when you resin or epoxy is poured.
Cut your glass with a template for ease of cutting multiple layers of glass at a time.

Center your glass over the hole and push 2 layers in like the pic below. Then press the glass outward inside and you are ready to pour.Now do your install of ProBoxes per our instructions on our website
Make sure to prep boxes properly before installing.

When your install is done and jigs are pulled then you can deflash your boxes with this deflashing jig by Greenlight at
Now enjoy your new Quad Keel combo with no compromising (-:
Top pic is this Bushman with Glas-ons. Bottom Pic is after with ProBoxes in same placement as Jeff started with Glas-ons.
Now from Twin to Quad mode.
Here's the happy owner of this Bushman Board.



  1. Larry,

    This is just what I needed and probably others as well. The directions plus the pictures are a great combo. This gives me the confidence to go and do this as well. Thanks.


  2. Hey Larry,

    What is the advantage of putting the large fin path covering the whole back area of the board as oposed to small 'rectangular' ones under each box? I would have though the later method would be lighter?


  3. Hi andrew, Doing the tail with one patch is easier and cleaner looking. Individual patches are hard to get a even blend to the existing bottom lamination. Weight issue is very little if you work the resin into the glass and not float the glass in resin. Hope this answers your question, Thanks for asking. Mahalo, Larry

  4. Dude i love this board, i would love you to give me a bit of an advice, i have a twin fin from the 80s it has rainbow fins and i would love to turn this board into a quad
    Could you please give me some advice, Do you think is possible to turn this board into a quad.
    the dimensions of my twin are the following
    Nose 13 5/8
    centre 20 1/4
    tail 15 5/8
    thickness 2 3/4
    Tail V through the front all the way to the tail
    Do you think the dimension or placement of you fins will be good enough for mine too, could you please email me your dimensions for a point of reference, thanks
    Also I am planning to take the rainbow fin boxes out, or do you think they could lie next to the new fcs plugs
    thanks and beautiful board mate
    kind regards,

  5. Larry,
    I noticed on the Keel Quad the Keel fins are the rear fins and the smaller fins are the front fins, (Twinzer setup)?
    What would be the affect if the Keel fins are the front fins and the smaller fins are the rear fins?
    I want to try the best Quad setup. What would you recommend?