Building sponsons with CA part 2

Here's the second part of the building sponsons with divinycell/Airex and CA glue pics I published a few years ago at the old International Waters gallery.

Missed part 1?

Do note that these build pics are ment to show the principle of building it with CA glue and give you ideas to do it yourself. The actual design of these sponsons are the ones I did in 2006 that are the ones that are included for the first Freebie PDF drawing I published a year ago. Today I would not make them this way personally (see the Freebie .21 V1.09). At that time we thought it was needed with non-trip chamfered cuts etc. But we have now found out they arent needed so the over all width of the sponons can be made narrower = the same as the width of the running surface. The narrower design of the sponsons makes it kind of not needed with the anti-chine cut also but thats up to you.

Some tools I use. I have tested ZAP green and Great Planes Pro CA medium together with GP pro kicker. It works great with Divinycell H60 & H80 (and Airex C70.55/C70.75). If building bigger sponsons then 21 size maybe you should use a slow setting one though - or if you work sloooowly... ;-)

The outside angled chine-cut is made - glue the plywood in place. I used 1 mm plywood here. Trim it down after it has set. I would recommend only to final trim its edges down WHEN your done... If you trim the plywood edges down after each step all the time, you're very likely to sand through the plywood as you will affectively sand the same spot several times... Only sand down the edges that you need to do for the step you will do "now" if you know what I mean. If, not - think about it for a while and it will sink in... ;)

2 mm thick lite-plywood is used for the top (3-ply version). I have used 3 mm also, one can have the top edges even smoother and even more radius then... (Updated: use normal 1.5 mm airplane birch plywood instead - it will be lighter and stiffer!)

The rear step plywood strip is glued in place. The one to the right is trimmed down to the same angle as the foam (2.5 deg). Also the rear step is sanded down to the same angle as the sponson ride surface = 2.5 deg - that is of course done before the plywood strip is glued in place...

Trim the 0.8 mm plywood down to the same level as the bottom. Leave the sides a little wide...

Here the lite-plywood is trimmed down. But as mentioned here above use normal 1.5 mm airplane birch plywood for the top instead. It's lighter and makes the sponsons more rigid.

The rear step bottom skin is glued on - 0.8 mm plywood is used.

Trim and guide lines.

Trim lines shown. The one on the foam is a glue guide at this point though for the bottom skin. The side line is parallel to the ride surface. The two lines meet at the front...

The bottom skin is glued in place supported with the cut away foam. 0.8 mm plywood is used.

Ready to be skinned with plywood.

For that final good "fit", when almost ready with the sanding, use light pressure on your bar sander so the foam and plywood are sanded perfectly level - then there wont be much of an visible air gap... if any.

The chamfered outer plywood is glued in place (1.2 mm) and trimmed.

The leading- and trailing edges band-sawed away and sanded smooth. I use 10x10 mm hardwood for the rear tip and 10x15 mm for the front.

20 mm wide 1.5 mm thick riding surface plywood glued in place - they're 130 mm long. Front and rear hardwood blocks glued in place (with CA).

When CA gluing hardwood - one needs to hold the parts in place way longer... Don't use kicker to begin with either - press together for a couple of minutes and then use kicker (updated: you could actually use a little "dust coat" of kicker on the wood). Then the glue has time to soak in the hard wood better.

They're almost done. Will drill the holes for the 8 mm carbon tube rods later plus also the 6 mm holes for the fin mounts.

The final sponson. Its just sanded "roughly" smooth - the final sanding will be done just before epoxy prepping and paint.

The trailing edge of the bottom is sanded at an angle to the front.

Close up.

Sanded smooth to blend in with the bottom... Keep the edges sharp!

Close up on trailing edge.

Leave all bottom riding surface edges sharp!

Front part sanded somewhat smooth. The 20 mm wide bottom plywood chamfered smooth so it blends in with the bottom.

Front hardwood nose piece sanded smooth. I like my leading edges to have big radius...

The rear trailing edge sanded smooth, first in a table top band sander, then by hand with GP bar sanders.

Side chine-cut sanded somewhat smooth. This is the final uploaded picture for now... The left sponson at this point weights 64 g and the right weights 70 g. The right hand one uses a thicker inside... Its not super light for sure - I just wanted to test how heavy a pair would be - I cant build them heavier then this... ;)