Material test

Hi,
I did a test with the chosen carbonfiber and foamcore and it's no bad at all ! The unidirectional fiber (see previous post) is composed of three layer, two unidir at 45° sewn together covered with a last layer at 45° lightly glued (or just pressed). As this last layer comes free easily it's got to be on top for wetting with epoxy. This weave seems to take more time to suck up enough epoxy to glue well to the foam afterwords, so one must take care it's wet enough on both sides. The good news is it definitly leaves no pinholes and assures a watertight surface.

Mouldwise : the mould is nearly finished since to long ... I needs quite some more craftmanship as I expected. Initialy the female mould is out of wood, glassfiber plates and polyester putty. The putty shrinkes when hardening and is very hard to carve or sand. I now use plaster which expands (slightly) with drying and is softer. I'm looking for a hard wax for the ultimate smoothening, but it must stand the curing at 60°C...

That's it for now, best winds.

Pinholes and thermofoam

Hi,

I'm back at work, slow but steady. Latest news, I changed carbon form twill to unidirectionl ; it's two layers of unidir at +/- 45° sewn together. It avoids the pinhole problem. Remember the youtube vid where there put an extra layer of kevlar to assure water tightness. The reseller said it'll be a bit more difficult to use though.

I also ordered Airex R63 thermoforamable foam, it seems to be the best solution, but I'll tell you as soon as I get it and do a test.

I'll do the curing at 60° myself, so I bought polystyrene boards to build the oven, that'll need testing too !

On  more point : if you choose to do this, don't copy me and skip the male mould to build a female mould from scrap. It's so much harder to carve concave shapes and to make it slick...

Spring's already near, but I'll be sailing on my 470 in stead of a moth for a while more.

thank's for reading.

who want's a sandwich ?

Spent some time at work this week-end, the first half hull mold is well on it's way and I did my first sandwich test with the rohacell and glassfiber just to pick-up the trick. I definitly need some more practice... and different foam. I did a little review to compare as you can see.

I didn't find an other way to answer the posts, so I'll do it here. I intend to build foils too as that's he most interesting part, but I've got a lot to learn till then...

Next steps : sandwich sample test 2 ; order new foam (maybe 2 different) and some carbone fiber ; finish first hull mold.

See ya.

Thanks !

Hey ! Thanks for your posts, all very useful advice that I'm studying now. Really honoured to be part of the moth community, might win my wings soon ! My working pace is maybe a bit slower as some of you as I haven't planned any vacation for this (thicking about it though). It might just take some time before I start thinking of the foils for example... aber wäre eine gute Idee.

I would like to thank all my former colleages of Firbourg for contributing to my boat project. It is definitly very usefull ! I just bought my first load of stuff from the local composite retailer and hell it's expensive.
On this week's skedule there's finishing the frame of the hull mold and doing a first test of a flat sandwich plate (with a leftover of glass fiber). I chose to copy the half hull method of the amercans on youtube (see previous link).
The test foam I bought is 5mm Rohacell 51, but it much too stiff, not at all what I expected. I'll try Soteco next, it only comes in 6mm thickness, but that'll do. It's supposed to be more flexible and it's also available partly sliced (pic) for really sharp curves.

I can heat the workshop up to 15-20°C as long as it doesn't freeze outside, hope that'll do for the fast epoxy I bought (15min working time). I also took a slower one with 90 minutes working time, thtat will definitly need curing ; I might need to do a test at the car body shop next door which has a 60°C oven.
Well I'll try and get some pics for next week to make this look a bit better. Thank's for reading !

Still there, still playing...

Hi there,

THAT was a long time ago ... I started playing with CFD and must admit it's quite some work, but fun ! After fiddling with 3D, I am now playing with XFOIL, to compare some foil shapes.

I put up a little excel sheet to transform the xfoil variables into somthing standard. I also read on the net that the Ncrit variable should be put to around 3 to have a water behaviour of the turbulence. If you have any other advice, I'm interested of coarse.

Meanwhile, I'm nearly done installing a little room where I hope I'll be playing around with epoxy soon. We saw a very usefull Youtube vid http://www.youtube.com/watch?v=mROBlWIu8q4 of the beaver hull bluiding and it opened my eyes a bit. I'll have to build a team too and we'll probably just copy all the rest... One thing I didn't understand is why they put a layer of aramid under the nomex ; you know ?

Stay tuned, post a comment, happy christmas.

Simulating ...

Hi there,

I'm working at simulations of the structure to fully understand the stresses it undergoes and be able to build it as light as possible. This is going to take some more time 'cause it isn't easy to simulate laminates and apply realistic pressure loads.

I'm also planing to do some CFD on the foils measured in this paper (don't miss it if you're on the same path as me ...) :

http://www.moth-sailing.org/download/CSYSPaperFeb09.pdf

I don't really know how to build the foils yet and that is an important point, so if you've got ideas or good references to share, please do !

Voilà, see ya.