Here's another set of pics and some info that I published a few years back in the gallery section of International Waters forum. The original link is to the right marked as "Kep's 21 build tips #2" or you could just klick here.
As mentioned the pics and texts where done a few years back. The actual design of the sponsons in the pics is pretty similar to the ones in the original Kep's Freebie PDF drawings.
Today I would not build them exactly like this with chine-angles and non-trip angles etc but I hope you find the info and pics somewhat inspiring at least!?
Building is fun! :)
Also read my earlier blog about the glue test.
Couldn't live without them, Great Planes bar sanders - I use almost exclusively 80 grit paper.
Sponson templates made from 1.5 mm plywood. The drawing is glued on with spray cement. Be very careful when cutting them out. Cut them on the inside of the outline. I make my boat drawings in Illustrator.
Template with 1 mm holes for making a punch hole to the plywood sponson insides.
A set of inside parts for 4 pairs of sponsons. Its way easier and faster to do more then one set at a time. The plywood is hold together with pieces of carpet tape.
Divinycell H60 closed cell PVC foam core material. In this case for building a pair of .21 size sponsons. Works very well with normal CA glue if "right" technique is used. When I have tested - CA glue makes a superior glue joint when skinned with plywood vs epoxy glue - on Divinycell H series that is...
4 left and 4 right inside plywood parts after they are "broken" apart. R = 2.5 mm & L = 1.5 mm.
2.5 & 1.5 mm thick.
Another view of the plywood insides. Ready to be CA glued to the foam core.
Use the inside sponson template and make a rough outline on the Divinycell foam. Vacuum the foam or blow the excessive dust away... Spray kicker on the plywood, then spread CA glue on the drawn line all the way around, then fill it in in a zig-zag "pattern" between the lines. Apply the "pre-kicked" plywood (kicker side down!) to the Divinycell. Then turn it upside down and push down. It helps if you have a flat surface of course and some plastic wrap or similar so you wont glue you sponsons to the table...
The CA glue has set.
Maybe I have used too much CA glue... Speaking of glue - I have only tested Great Planes Pro CA medium and slow + ZAP green + slow. They all work the same - no difference what I have seen. The slow/thicker one just isn't needed for how I work. If you're slow working or uncertain how well you will do, try out the slow curing ones. Make sure to add kicker to the plywood part (no glue added there).
After cutting the upper part away in the band saw, use the bar sander to smooth the top surface. Not important at this stage to make it perfect. Use the top view template and make a line for the outside cut.
Before you take it to the band saw again. Sand the outside and keep it at 90 degree measured from the bottom that is 90 degrees from the inside... Right!? When working in the band saw, check that it saws in 90 deg (adjust the baseboard of the saw). Pay attention to making the band saw cut as close as possible to he line and be smooth. The outside back-support wont need any sanding - it will support the ply good anyways...
I make an simple matching line with a pen on the foam. Its way easier to make it right as one doesn't have sooo much time as with epoxy...
After the band saw. Only 2 of these parts is used. The outside and bottom parts are used for support when gluing those plywood parts to the foam core.
The outside is here ready to have its plywood glued in place.
After the band saw. The outside is sanded smooth - the other parts are not sanded yet.
Ready to be glued. The guide line is on the inside of the plywood also - it just makes it easier. Kicker on plywood and CA glue on foam - press it together for about 60 sec. Use a little extra kicker if needed. Use a table fan to remove the glue and kicker odor...! BTW, use some throw-away vinyl protective gloves also.
The CA has set. The cut away foam part is used as back-support. Only hand/body pressure is used. No weights etc.
On this set of sponsons I used 1 mm plywood on the outside. When measured its 1.2 mm though. On the thick side I guess, 0.8 mm isn't a problem.
After the CA glue has set. The plywood isn't trimmed yet...
The top part is sanded smooth and in 90 deg to the inside. This is the guide lines for an chine-cut.
Short depth of field here - oops. The "curved" part here gives itself... Viewed dead on (from the front or back) its completely flat.
Bad picture... Just a view of the angled chine-cut before the plywood is glued. This "version" is perfectly straight and parallel to the inside. One can do them different or not at all... Its all up to you.
Stay tuned for part 2 within a few days...