balsa tub construction questions?

[TomMoorehouse]

I am trying to learn more about balsa tub construction. You guys that are doing this.....

do you really find it significantly lighter than 1/8" light ply?

Do you cover both sides with 1/64" ply or only one?

do you use 1/8 or 1/4" balsa?

Do you recommend CA or epoxy to attach the tub top and bottoms?

is it a particular grade of balsa that works best?

any other tips for this?

thanks

tom

 

[Grimracer]

Mister T

Let me start with this.

My E Ninja is built using balsa sides and ply top and bottom. The balsa sides give me plenty of gluing area and at a reduced weight of Light Ply.

I then cover the balsa with .56oz per sq.yard glass cloth and west systems. the trick to light weight/strength is the application of the cloth. Note: leave the spray glue on the shelf. You will not need it to tack the cloth in place. Besides as the epoxy works through the cloth the spray glue is no longer effective anyway. Next, using a playing card work epoxy over the cloth and squeegee off all the epoxy you can. Leave no build up. All the build up does is float the glass and therefore the glass is not touching the wood. You want the glass touching the wood.

After the epoxy sets remove the excess glass with some sandpaper and your ready for paint.. in my case auto clear.

I see others use ply over balsa. This is good also as it provides great strength over just light ply.

Grim

 

[crowebar]

I build the boat out of 1/8th Balsa then cover it all in 1/64th ply. ONLY on the 6/8 cell boats. The bigger ones get thicker Balsa.

Building with Balsa is about as easy as it gets, Sheeting with 1/64th is very easy too. I just trace the the pannel, cut it with scissors and CA it on. Then, CA and suspect edges that didn't get enough glue the first time. Finally, block sand the edges and finish with Minwax Polycrylic. I have no idea if it's fuel proof. My guess is it's not.

the top deck and cowl are almost all 1/64th ply, just a little balsa framework underneath.

Not sure which method is better overall, but I haven't had any problems with the Balsa/Ply boats. Maybe the epoxy would be better for fuel boats?

Dick

 

[chunkt]

Tom,

My experience with the two methods have both been good. I built a 3.5 31" mono out of balsa (ply transome and keel) and covered it with glass. TOO LIGHT I think the balsa was confused & thought I built a plane ;D

I aways make sure to use ply doublers everywhere that a structural piece passes through balsa (both sides of the balsa). As to type of balsa I prefer medium balsa for boats. The darker the color the harder (denser) the wood.

chunk t

 

[Hammerhead]

Have any of you electric guys tried the balsa that is pre laminated with carbon. That stuff looks light and tough. I'm interested in building a SAW electric some day. Keep up the good information.

Hammer

 

[Paul]

Hello Tom,

I'll toss my .02 in here as well. I used to do it like Grimm but had an unfortunate experiance with a tub splitting down the side when a battery came loose in a dump. The only way I build them now is with 3/32" balsa and a 1/32nd ply skin. I cut my ply skins first (with sissors) and glue them to a sheet of 3/32nd balsa then trim around the ply with the Exacto. The top and bottom are 1/32nd ply only. I do run a strip of 1/8th square balsa around the tub sides for a doubler. Here's a pic for you of one I'm building now. Very strong for what it is.

http://www.skullcaps.com/boats/tub1.jpg

Paul.

 

[Hammerhead]

Hey! That is the same way we construct the sponsons on the HH.12.

VERY EASY and bullet proof.

Has anyone ever though of making a vacuum molded ABS rigger? I think they would be light cheap, and easy to replace if you smash them up.

Hammer

 

[Dennis Whitt]

This is so funny.I just came in from the shop.I was out building my P/Q rigger.

From a purely electric perspective I have tried many different materials.

My first attempts were to build a balsa tub and seal it with super thin ca rubbed on with my finger.What a mess!

I then tried sanding sealer.Nice finish but too brittle.

Then I tried bass instead of balsa still too brittle.

Balsa with half ounce cloth?Pretty sturdy,mostly ding reistant,But not very strong and the tub still has too much flex.

Carbon fiber sandwiched balsa,Very stiff but hates to be cut with any thing other than a carbide saw blade.compresses too eazily when installing hardwear,And To heavy.

My absolute fave was balsa ply coated with zip finishing epoxy.

But tonight I built a PQ Rigger tub. The bottom and top are 1/32nd ply with the inside corners glassed. The rest is 3/16th balsa and sheated it with 1/64th skin and holey cow is this thing strong,light, rigid.The edges are super sharp and with just a light sanding I went strait to two coats of rustoleum crystal clear.the hull looks like it was hand waxed,and it only weighs 6.8 ounces!

Thanks again my old friend Dick.As always you were right on!!! I will try to put up a pic tomorow.

 

[TomMoorehouse]

hummmm lots of good ideas.....

thanks everyone!

but for sure the balsa/64th or glass is lighter than light ply huh?

 

[Paul]

Hello Guys,

Hammer, Randy at BBY is working on an ABS rigger in a couple different sizes. No where near as cheap as wood though.

Tom, I really don't like light ply because the stuff is #1 too porous, #2 not as strong, #3 never straight enough. In a side by side comparison of straight 1/8" balsa and the way I build them now the weight was barely any different and I can drive nails with the tub.

Paul.

 

[Grimracer]

Tom

Here are some numbers that i took.

The parts were 1.5"sq

.125" balsa 0.6grams

.062" AC ply 2.5grams

.093" AC ply 2.5grams

.125" light ply 1.5grams

.125" AC ply 3.1grams

Hope this helps

Grim

 

[Eric Perez]

I normally do 1/8 and 3/32 med-balsa with 1/64 ply with epoxy. Switced over to CA and the results are just increadible. Builds fast as lightning and is supper strong. And that's without the final epoxy top-coat.

Paul, thanks for the tip on cutting the ply first and then using it to cut the balsa -This basically cuts out the middle man.

All things considered you can build a rigger in a couple of hours with this method if you have everything down on paper first...

I use plastic folders (Impact) from Wal-Mart at a little over a $1.00 each to make templates with. Print out the CAD plans on the inkjet tape together the longer parts. Use 3M on the paper and I stick it to the thin plastic folder material. Cut it out, and presto a perfect template for boat parts. This technique really compliments the 1/32 1/64 ply balsa construction very well. I had my tub together in less than an hour!