Sponson building.

[Terry Keeley]

Have to build a new left sponson for my 40 boat due to a mishap last summer and thought I'd pass along a method Mike Hallam showed me some 35 years ago.

Block squared up and boom tube mounts drilled, I like 5lb Kledgecell (now Divincell H80), I make the width so it's easy later to measure and sand in the dihedral (see below). Divincell is available from Mark Bullard and Andy Brown.




Templates can be made of G10 fiberglass, plexiglass etc. Attack angle of 3* works well, I like a long flat planning surface (no "belly").



Mount the templates to the sides with double sided carpet tape, the fiber type seems to work best.



Cut off the excess with a bandsaw, hacksaw, knife, hot wire etc.



Sand to the templates.



Raise the outside back template to sand in the dihedral you want, I like 3*. The distance to move up is tan (dihedral angle) x the sponson width, these are 3.5" wide so tan 3* x 3.5 = 5/32".



By blending the dihedral into the front tips it handles heat racing water better I think.






I've used CA but find the skins can bubble so epoxy it is, I use West 105/206. I weigh each part and for small amounts 5g of resin & 1g of hardener works great.



The rear cap is the first to be glued in place. I use 1/32" all around except 1/64" for the bottom and outside.

 

[Jerry Dunlap]

Love WOF
JD

 

[Grimracer]

Keep it coming TK...

 

[David Murany]

Terry set the table at the 3 degrees and cut it on the first cut. Saves a step

 

[longballlumber]

Love this stuff! Thanks for sharing!

 

[Grimracer]

I have to wonder how urethane adhesives would work on this. I use them on foam core wings and the like.. (the old Villian S1 used urethane)

When I designed the Pea-Shooter I did a full laser cut wood sponson/parts.. VERY untraditional.. But.. so far.. I like that best.

CAN NOT get the tubes in wrong.. and with the design have full control of the epoxy to glue them in.. (some day I will have to show some of that)

Grim

 

[Terry Keeley]

Terry set the table at the 3 degrees and cut it on the first cut. Saves a step

You mean the attack angle?

 

[Grimracer]

I think he was thinking deadrise.. Me.. I like progressive dead rise.. so a saw cut wont get it.. (one could wire cut that however)

 

[David Murany]

You mean the attack angle?

The dihedral angle. We typically glue on the inside piece of wood after it's cut out an basically use it as a template. Then cut everything to it on the bandsaw.

 

[Mark Poole ModVP]

I like your scale set up. Solid sponsons are strong.

 

[Ron Jefferson]

So Terry, just to clarify. You fully shape the sponson foam before you start to skin it?

 

[Terry Keeley]

So Terry, just to clarify. You fully shape the sponson foam before you start to skin it?

Yup, except for the outside.

1/64" bottom.

 

[Terry Keeley]

I make the tubes with a stop in the middle and a hole for a 4-40 SHCS, glue an insert into the carbon booms and fasten them from the outside. In the past I've just used brass tubing with brass stop soldered in or you could probably glue a stop in place.

To get the chine angles I just take the side profile templates and use them to sand the foam to shape.

 

[Zimmerman]

I've been using Kledgecel for about 40 years and was told by the Mfr that you SHOULD NOT hot wire it as it gives off cyanide gas. Don't know about Divinicel as I still have a large quantity of the other left.

 

[LibertyFrancis]

I've been using Kledgecel for about 40 years and was told by the Mfr that you SHOULD NOT hot wire it as it gives off cyanide gas.

Is that bad? Asking for a friend....

 

[Zimmerman]

It doesn't take much to kill you.

 

[Terry Keeley]

West G5 and 64th ply for the outsides, a little blemish fixed with West 410 and wala:

 

[RaceMechaniX]

Terry, what tool are you using to get such a clean boom tube hole in the angled sponson side? I assume you are drilling through from the inboard side, but then how are you preventing blowout on the outboard side?

 

[Terry Keeley]

Terry, what tool are you using to get such a clean boom tube hole in the angled sponson side? I assume you are drilling through from the inboard side, but then how are you preventing blowout on the outboard side?

They're called "flat drills", I got the OSG brand. Not cheap but I was making a lot of SAW sponsons and it was worth my time. I drill in from both ends to leave a 1/8" stop in the middle.

An end mill didn't make a good hole and boring on the lathe was tedious. As mentioned I usta solder a brass plug into K&S tubing but that's tricky and I had one come loose once.

Tubes are sanded to the angle with the foam.

 

[dr gary turner]

They're called "flat drills", I got the OSG brand. Not cheap but I was making a lot of SAW sponsons and it was worth my time. I drill in from both ends to leave a 1/8" stop in the middle.

An end mill didn't make a good hole and boring on the lathe was tedious. As mentioned I usta solder in a brass plug into K&S tubing but that's tricky and I had one come loose once.

Tubes are sanded to the angle with the foam.

My friend Terry’s building technique is excellent and ver similar to the way I build sponsons and tubes.

I would like to add how I do the pegs in sponsons.

If you ever tried to remove a fence post from the ground, if you start wiggling it back and forth before long you can pull it right out of the ground IE sponson pegs pulling out.

So several years ago I decided to drill all the way through the sponson. Put a carbon fiber tube in the hole in the sponsonand then I run a CF tube or rod that extends all the way through the peg tube through the outer plate.

Thus the boom tube is locked into the sponson by the inner and outer plates of the sponson.

Carbonfibertubeshop has excellent CF tubes and you can get sanded tubes so they easily slide into each other.