next »

[Marco]

Snipped from my New Members post:
My idea is this build an inverse rocker table, lay down a glued up 1/8" redwood (now luan ply) panel, wetted out 3.2 oz, sheet of 1" EPS, wetted out 3.2 oz. , sheet of 1" EPS, wetted out 3.2 oz., glued up 1/8" redwood panel. breather around the edges, bag and vac.
Then once that has cured, cut out the template, and glue on higher density foam rails, shape and wrap rails in CF tape. Then glass the whole shebang with 6 oz. (now 4 oz. )

This will be a 6'6" retro fish rocker and bottom but with more of a spoon template (I hate pointy things) and twin keels.


So I went and priced my supplies yesterday.
Home Depot:

  4' x 8' sheet of 1/8" Luan Ply ( I know, I know, environmental disaster)
  $9.89
         After seeing the doorskin fish, I have to try it.

  2 ea. 4' x 8' x 1"  1.5# EPS
  $18.96

DMC in La Mesa
  7 yds of 3.2oz four harness satin glass (Inside)
  $56.00

  5 yds of 4oz plain weave (Outside)
  $22.95


J. Greer & Associates
(AeroMarine 300/21 Epoxy)
  ~$40.00 (out of my own stock)


Total: $147.80 USD

If I do Carbon/Kevlar rails instead of foam/wood I have to add  ~$50
   (4" Carbon/Kevlar Tape is available from US Composites)


I'm going to start this up after I clean out the workshop. (It's still a mess from my last project)

I'll keep you all posted on the build.

[RoyStewart]

 So it's going to finish at around 2 and a quarter inches thick ?

 We have done 6 foot fish at that thickness, kind of chunky but nice, volume about 30 litres at 21 wide, very little flex ( but a nice resonance  ) 

 No doubt a compsand build will give significant flex at 2.25" thick.

.

[Marco]

Roy,
I thought about the flex issue, thinking that the parallel profile would tend to have more flex than a foiled profile.
I'm going to do some tests with the rail to see how tunable this is.
I'm thinking grain orientation changes at different points in the rail may adjust things here and there.
Really just experimenting at this point.

Thanks, looking forward to your input.

[RoyStewart]

Yes the parallel profile definitely does have more flex than a tapered profile.

.

[paul cannon]

is luan ply a rainforest timber??
i know teaks an no no

maybe plantation veneers and plys wood be better

fir perhaps and or cedar

[Marco]

've heard back from the bamboo supplier.

The 4' x 8' sheets of 1/8" flat grain is $76 USD per sheet.   
They also have an unadvertised two-ply veneer (1/21" or 1.2mm) he's getting me the price on that.
 
Also, they stopped carrying the sheet because they were getting too many returns as it is very brittle.
They had 4 sheets left at the local warehouse and I got a chance to look/touch it.
It's very nice but as he said, very brittle. i.e. you can split the strips apart very easily by hand.
The 1/8" is also quite heavy @ 16# per sheet. If I figure the rough numbers correctly that would bring the skins for a 6'6" fish out to 12# just for the skin.
I talked with Bob Mitzven this morning @ Tourmaline. He had his Western Red Cedar chambered fish (5' 10" I think). He says it's 14#, which felt about right.
Not much advantage to the 1/8" bamboo skinned compsand weight wise.


So, I have some questions for the group. How thin can the skins be before they become just decoration?
I'm thinking standard veneer thickness (1/42" or 0.6mm) has no structural benefits, and would just be a hassle to repair in the event of damage.
Wouldn't we get the same benefit as wood skin from a layer of Hexcel 7715 (7.3 oz warp glass)?
http://www.fiberglasswarehouse.com/fiberglass_cloth.asp

[Kit Sidwell]

Wouldn't we get the same benefit as wood skin from a layer of Hexcel 7715 (7.3 oz warp glass)?

Yes you would - in that you wouldn't get much benefit!
The thicker the skins core (wood), the greater the properties of the sandwich. The idea is to save weight by having a light weight sandwich core, while still providing the appropriate amount of stiffness you require.
Its a balancing act.
You could use a heavy wood, but you wouldn't save any weight.
You can use a super light weight engineered foam, and save heaps of weight.
Wood adds spring and is damage tolerant, looks nice.
Foam is the ultimate for lightness.
So a 1/32 thick piece of wood is still a sandwich core, but if you doubled the thickness, you'll get many times more stiffness with while only increasing the weigh by (less than) double.

[point]

Luan Fish feedback-

So the board ended up at 10.5lbs and stiff.  I mean real stiff.  In the water it doesn't feel that heavy so maybe it will be a good bumpy/windy day board.  It surfs great but looking back now the board would have been about 6 to 6.5 with balsa skins, which is a pretty big difference.