How long is your board?

[roland_trim]

I plan to cut the foam for a new CB, hopefully tomorrow evening. Before starting work on my 3m long board I thought I'd check to see what the rest of the class are using.

If possible an indication of if the measurements are the wet or total length or even photos would be handy.

(PS Old board is fine and dandy even after both Hopsons and I used it to cut a hole in the botom of Bala, it's just that I promised to build Laurence one for Amber Dragon so thought I'd make two rather than one)

[ghislain_devouthon]

Mine is about 1m45 outside of the hull.

It is 23 cm chord at the top decreasing from the 2/3rd till 10 cm.

About 3 cm thickness tapered.

[roland_trim]

OK very behind schedule due to mammoth Hayfever year.

Have cut the foam into usable pieces. The initial bits arrived 6 inches thick, using a hotwire fomr 3D models, a desk top from the skip, my router as a counterweight, the ironing board to keep it all off the floor and Will's old trainset transformer to supply juice to the wire I now have a good selection of 2 inch slices. For further  hot wiring at that length I think a transformer with a bit more juice is neeed - maybe a car battery and a thiristor.

Yes ross there is some for you there too.

Tonight we bog two bits together of foam together (board is to be longer than 1.2m)  and measure Amber and Slippy's CB sections so we can make some boards that fit.

Any ideas how to transfer the patten onto the foam. Options for experiment currently are;

• Punch through little holes with a pin and draw on the lines
• Digitally project onto the board from laptop and trace
• Spray mount printed pattern to foam

[Will_Lee]

Go Roland!

Good slicing technique!

I think spraymount - especially if you have a big printer.

Both Kevin and Paul have talked to me about conformal surface ideas - but perhaps that is best saved til next time.

 

[Phil Alderson]

What about a template at each end and hotwire the profile across.

[Tim Noyce]

We tried that with poor results at foil club a couple of years back. Not sure if the hotwiring process has improved enough since then for it to be a viable option!

[neal_gibson]

foam pah

what you want you need is one good old solid oak dinner table, a belt sander, couple bottles of wine and a not steady hand

chop table into sensible sizes belt sand so it loks foil shaped then wrap with carbon  bobs ya uncle indestrucble

[phil_kirk]

I would ask mum and dad before chopping up their oak dining table.  They might notice if it went missing.  I don't think they would appreciate the offer to replace the table with a carbon/foam light weight one built overnight in the other half of the house.

Use foam for boats and leave the table in one peice in my opinion.

[roland_trim]

Both Kevin and Paul have talked to me about conformal surface ideas - but perhaps that is best saved til next time.

The conformal surface idea confuses me. If I understand it correctly I'd need to wire a correct Wedge and then route from there.
Hot wiring 700mm of foam felt a bit like as long as I wanted the wire to be. for the conformal surface to work I think I'd need a 1.7m long wire - that needs a thicker wire and alot more juice than I currently have. If I'm being thick here please yell.

[Will_Lee]

The conformal surface idea is an alternative to routing along a line to make the contour router cuts.

You get a wood or mylar or whatever thin sheet and shape it so it marks the contour, but 60mm outside it. You alter your router with some kind of ring attachment so you push up againts the edge and you cut the line in the right place.

The jigs are reusable, and as long as you position each one correctly then the only tricky bit is getting the router to the right depth.

[matt_burrows]

If you are interested I've just embarqued on a rudder and tfoil assembly looking for the simplest light construction. Plan is to use profiles from Profili 2 to route the basic shape in 1mm steps out of two sheets of 10mm core cell foam. These placed back to back should make a rough naca 12 section. when they are on the routing table (sheet of melamine!)  I'll laminate the contoured surface with one layer of 200gm carbon. this should stop the relatively unstable core cell foam warping or snapping. Stick them togethor back to back then fair in to a smooth naca section with glass bubbles or P38 then overwrap another sheet of carbon. I recon that the intermediate fairing is a far easier way of getting the correct section than any of your hotwire or router fence tom-foolery  - and hopefully the fairing mix won't add too much weight.
I'll let you know how I get on.

By the way Will - to get accurate router depths you need a Trend router setting tool. More accurate than any other depth guage I've used.

Cheers Matt   

[Will_Lee]

Thanks for that!

[Will_Lee]

Looking at their website, I now understand the router bush thing that Kevin and Paul have been talking about.

Hmmmm revision time.

www.uk-trend.com

[Phil Alderson]

I have one of those depth tools and it is good, however I get approx 2mm of end float on the router and it tends to drift during longer runs.

I have used the guide collar when doing kitchen worktops and a few other jobs you can get good results but the collar must be fixed to the side you want to leave uncut so you would have to pin the templates with dowels to the centre of the  foam.

Matt, I think your plan would be quite heavy, as you would have foam/carbon/filler/carbon/filler. You have to fair the outer surface once you have the carbon on to smooth out the different layers so you might as well get close with the core and do your final shape after the carbon.

[matt_burrows]

Phil,
I've a mind to press on as planned. I'll weigh the board when its complete and post it here. Would be interested for a comparison with pre-faired core boards.
For me time is the most important factor after fairness. I've got a whole boat to build and it'll go on for years if I don't compromise here and there
Cheers anyway
Matt