Materials Comparison - Construction Techniques

[Mick J]

I know most people on here have tried many different constuction techniques in the pursuit of lightness and rigidity, myself included. I thought I would throw this one out there to see if others might share their experiences.

Whilst working on a new build I decided to explore other options a little further and make some very rudimentary comparisons on materials used. Why, cause I was waiting for epoxy to dry and had an idea. I was more than suprised by the result. Now, I have not undertaken any testing on sheer strengths etc, this was a weight saving comparison only.

I made up 3x different pieces, all uniform to each other 3" x 2" (1/8" thick) and came up with the following weights.

1x 6ply @ 12 grams

1x Divinycell H80 core skinned with 1/32", Finnish 3ply both sides @ 8 grams

1x Divinycell H80 core skined with 200gsm (5.7oz) carbon fibre twill that was Vacuum Bagged @ 5 grams

I know none of the above stuff is new to us, just thought the topic might engage some constructive discussion on material choices and construction techniques.

Penny for your thoughts

Johno

 

[Archie Stanton]

I know most people on here have tried many different constuction techniques in the pursuit of lightness and rigidity, myself included. I thought I would throw this one out there to see if others might share their experiences.

Whilst working on a new build I decided to explore other options a little further and make some very rudimentary comparisons on materials used. Why, cause I was waiting for epoxy to dry and had an idea. I was more than suprised by the result. Now, I have not undertaken any testing on sheer strengths etc, this was a weight saving comparison only.

I made up 3x different pieces, all uniform to each other 3" x 2" (1/8" thick) and came up with the following weights.

1x 6ply @ 12 grams

1x Divinycell H80 core skinned with 1/32", Finnish 3ply both sides @ 8 grams

1x Divinycell H80 core skined with 200gsm (5.7oz) carbon fibre twill that was Vacuum Bagged @ 5 grams

I know none of the above stuff is new to us, just thought the topic might engage some constructive discussion on material choices and construction techniques.

Penny for your thoughts

Johno

Great post Johno

I can't really give you any theory's on the topic. I can say that strength/vs. weight could be a topic all to itself. I do have some additional data to throw in the mix:

on the same exact structure using the same gluing procedure:

1) Solid 1/16" G10 at 520 grams....strong as mama's will

2) Ply of 1/32" birch ply and 1/32" G10 2 coats on the Plywood before crating the ply with vacuum at 402 grams even...still very strong (77% of the weight of solid g10)

3) 1/16"" Birch ply with 2 coats of West Systems epoxy prior to assembly 310 grams it's rigid and still suitably strong but slightly fragile (60% of the weight of the solid G10)

4) 1/32" Balsa wood/ 1/32" Plywood ply both coated with West systems prior to making the ply with vacuum....twisting the structure I notice the epoxy is the limiting strength. getting lighter at 265 grams (51% of the weight of solid G10)

5) 1/16" Balsa...epoxy coated...................not tried ....but is a candidate for a SAW tub

KB

 

[Mick J]

Thanks Kev appreciate your input,

I am hoping the "gurus" out there will chime in with some input and their experiences in due course.

Could prove to be a good discussion point, much like your "where do we go from here" post.

I see divinycell cored, carbon covered rigger sides and bulkheads in my future. Should make for a light set up no matter what size I opt for. Too many ideas, not enough hours in the day to make it happen.

Johno

 

[TomMoorehouse]

Where is a good place to get Divinycell H80? It would be cool if someone sold sheets of the cf divinycell at a fair price.

Id like to hear more about different foams to use. What other foams have people tried?

I keep searching for a plastic wood substitute. Ive used expanded pvc and G10 successfully to build a boat but it is not any lighter and difficult to get good glue joints.

 

[Mick J]

Where is a good place to get Divinycell H80? It would be cool if someone sold sheets of the cf divinycell at a fair price.

Id like to hear more about different foams to use. What other foams have people tried?

I keep searching for a plastic wood substitute. Ive used expanded pvc and G10 successfully to build a boat but it is not any lighter and difficult to get good glue joints.

Tom, I got roughly 9 full sheets left (enough to keep me building till I reach the grave). I bought 10x sheets a while ago for a good price.

I'd be more than happy to mail some across the big pond if you like...............just say the word mate.

Johno

 

[Charles Perdue]

Thanks Kev appreciate your input,

I am hoping the "gurus" out there will chime in with some input and their experiences in due course.

Could prove to be a good discussion point, much like your "where do we go from here" post.

I see divinycell cored, carbon covered rigger sides and bulkheads in my future. Should make for a light set up no matter what size I opt for. Too many ideas, not enough hours in the day to make it happen.

Johno

Use a shape for the sides other than just flat, parallel surfaces. This is a very flimsy shape.

Triangulated sides, thicker at the bottom and narrower at the top to form a triangle. A very rigid shape with almost no weight added.

The greater the torsional rigidity, the more consistent the boat handles and turns.

This was the shape used on the original BOSS boats.

Charles

 

[Terry Keeley]

I can tell you from personal experience that a tub made of this stuff is very light, strong and rigid:

http://www.braider.com/?a=57

 

[Albert Araujo]

OK Guys,

I will share with you all the method I use to build my riggers. It results in the strongest hull and the weight is as light as any light wood kit.

I start by building the tub with 1/16 sides and 1/32 ply bottom. Trans and front 1/8 ply. I then cut out two sides that are about 3/16 shorter in front and back, made from 1/4" end grain balsa with .010 carbon both sides. Now I cut out two pieces of 5 oz kevlar cloth. The kevlar must fill the bottom, sides, transom and front. I snip two slits on the transom and front to fold over in the corners. once I have all the kevlar cut to size along with the carbon balsa sides I get ready to laminate using West System Epoxy resin.

I now wet the entire inside of the flimsy hull and lay up the cloth. make sure to fold the corners over the transom. Once the kevlar cloth has been saturated with resin I install a 3/16 plywood doublers on the inside of the transom and the front bulkhead. I clamp these two pieces to the flimsy frame. The resin comes out from all sides and compresses the kevlar between the two pieces of wood. I now set the two balsa carbon sides inside the hull making sure they seat well all around. You will need two 3X3 aluminum angels about 48" long. You set the angels on the sides and use them to clamp the carbon and kevlar. The aluminum is what aligns the whole boat up. It makes the sides perfectly straight and also makes them perpendicular to the bottom. I set a clamp up at about every 2" and clamp the crap out of the whole thing. Make sure to push the carbon balsa down into the corners so that the kevlar is pushed tight into the corners. Once all is clamped in place I start to clean up all the excess resin that has come out from the sides. I then proceed to pull as much resin from the bottom till I can't get any more out. I use paper towels to dry the resin as much as I can. Once you have cleaned all the resin you can remove two clamps at a time to clean the carbon sides with thinner. re install the clamps and move on to the next few clamps. Once the process is complete you have a great looking tub that is virtually unbreakable and light weight. You will never loose a bottom or get any cracks on the tub AT ALL. I have had these boats plow through others and always finish the heat. I was nick named Kevlar Killer.

 

[RickGlover]

Hey guys how about this? Currently building a feather lite JAE 45 will complete this weekend. I milled 1\4 Spanish Cedar for the sides and 1\16 for the bottom and deck. I have West system, color, and will be applying clear coat. I am now at about 18 oz on the tub. I hope to be around 3.5lbs to 4 lbs on completion. Spanish cedar is a dense lite wood. We use it for high end exterior grill hut cabinets. It was available and free. I used solid 1\4 soft Maple on the sides of my tub on my 67 Jae. It has held up well. Ran it into the bank at 70 mph only broke the boom tubes and my sponsons a little. Thankfully we have alot of weeds along the edge of the pond.

 

[Paul Traufler]

I would think the CF route will make a stronger/lighter boat, however much can be said for low cost, easy to work with and simple also! All the materials have some good points and some bad, the trick is to find the best material for this use. I'm sure a 45 size boat COULD get in the 3.5 lb range, I think at this weight and heat racing you would find this not to be the most durable either. A few more oz of structure can really make the boat bullet proof. It is all about choices.