Tuesday, January 29, 2013

Deck and fairings

With the foam moulds finished for the main hull components, it was time to do the layups and pull parts off. I did the smallest part, the foredeck first to test the process using a few odd-shaped bits of carbon and some 3mm Nomex inside the curved section.  It was a bit of a half-assed job and when it came out, it was a little bit heavier than I'd hoped - just under 500g - but in the end I decided it was god enough to use. I did the deck and fairings next, one at a time as the vacuum pump was sounding a bit sick and I didn't want to loose them all at once. Meanwhile I made an effort to track down someone who sold vacuum pump oil. 

The fairings were simple to lay up except for the sail track that picks up the lower skin of the tramp. That ended up being a 9mm ID tube that I glued into the monolithic carbon part, and then reinforced a bit more on the inside and cut the groove at the end. 

The foredeck fresh out of the mould

The deck was the last thing to do, and I laid it up with 200g cloth on 6mm foam with some local reinforcing. On Andrew's (CG) advice I used a bit of 75g glass between the foam and the top skin of carbon to trap some extra resin there and ensure a solid bond, as I had some delanination there with my last deck. I carefully cut the recesses for the wingbar sockets out of the foam, not realising they were the wrong way around, an went ahead with the layup and the bag. It all sucked down very well when the vac pump finally choked and died. I think some oil leaked through the shaft seal and into the motor, and started burning on some hot part. I turned off the valve to seal the bag and just waited to see if it was all going to go to waste. Amazingly, the bag and foam mould were completely sealed, and it held a reasonable vacuum until cured. I ended up with a bit more resin in there than I hoped, but the part was usable. If I did it again I could probably save 50-100g, so a bit like the foredeck, I figure I can live with it.

I went to the cleverly named vacuum pump place 'absolute vacuum' and sorted out some new oil, took the pump apart and cleaned it out, and miraculously it now works like new. It turns out when you let it suck resin and whatever else into the rotor, it stops working. I now have a proper gauge, but am still waiting on a couple of valves and a new 'catch pot' for all the unwanted bits, and then I'll have confidence in the pump again.

the deck gallantly holding a vacuum
Laying up the carbon tube for the sail track. The mandrel was a bit of clear hose
fed over an old yacht sidestay. Because the hose getts thinner when you stretch it,
you can just pull it out.  It worked really well.
The back of the sail track, showing the bit of reinforcing on the inside.

Anyway those four major parts are now ticked off. The deck weighed in at 1.6kg with the fibreglass rods glued into the sides, the fairings / sail tracks ended up being a bit under 1.4kg for the pair. That's a bit of a weight penalty, but it's a trade off - add a bit of weight, subtract a bit of drag. It's hard to know where to go on things like that, but I'm committed to the design so im going with it. I can always cut them off again if the boat's slow. 

The last image is of the four parts post-curing on the roof. It was easily 50 degrees up there so I thought why bother with the oven!

Wednesday, January 23, 2013

Part 2 - tooling up

I was thinking of calling this port 'tooling around' because that probably best sums up what I've been doing for the last month. No-one cares about that though, instead Im going to run through the process for creating all the moulds needed for the new build.

Because I still have access to the CNC router - its now being housed by my mates at Street&Garden Furniture Co. - it was pretty straightforward to send every part, big or small, to it and create a set of female moulds. Detailed things were made in ply or MDF, and the large simple shapes were cut from 'Isoboard' EPS insulation foam, recommended by the guys at CG. I designed the boat and made the 3D model so that everything would be able to be done this way, and it was super quick to pull parts out, create the toolpath and press print. I set up a new dust extraction system to deal with the polystyrene dust, and it works really well. didn't miss a drop.

Here's a photo of the setup, and another after a weekend's of successful routing.

The bigger parts took an hour or two to cut, the smaller ones obviously were quicker. I had a couple of small issues cutting the foam where it melted etc, but that's boring so I won't go into it. Thick parts were made in layers 75mm thick, and then guled together with epoxy later. The rough-ish surface (3mm step) sanded back easily and I then sealed it with some epoxy and colloidal silica bog. Then another quick sand, another layer of thinner epoxy/silica, carefully applied with a credit card, and you're done! The moulds all held a good vacuum with no problems, important because you can't envelope bag it as it compresses the foam, and the surface quality was generally within range of 'high build'. It's gotta be the quickest way to make large composite parts.

The MDF/ply bits are now pretty straight forward. I've learnt that it's better to cut them with a much finer stepover (1.2mm or so) so that you almost don't need to sand them. It takes a bit longer on the machine, but saves you lots of stuffing around later. Then one coat of resin and a sand and they're good to go. The foil strut mould was the last thing I did, and turned out the best.

Saturday, January 19, 2013

The build - part 1

Just reporting that construction is well under way on the new boat. After reading Phil's post the other day about how the moth blogs are drying up, I thought I might as well have a crack at keeping this one a little bit up to date. Uncharacteristically for me, the build is well ahead of the blog, so this and the next few posts are going to be something of a retrospective about the various stages of the construction that began in December last year. I've tried out a few interesting methods that I'd like to share, that have really sped up the process and allowed for a bit of extra complexity.

So, this is what it's going to look like:

The design is based on the shapes I was playing with in the last post and prior. The design development/evaluation did progress to a better CFD package (thankfully), and the results looked promising enough to invest some time in building. You have to draw the line somewhere right? There was certainly still room for improvement but CFD runs take so much time that I got sick of trying new things and decided to aim for some real world testing. More fun. Notable features: wing shaped tramps blended into the hull for super sweet aero, forward mast and foil position, centre 'console' to consolidate all the messy lines and reduce drag, aero gantry and probably some other things that I'm not talking about just yet. The rig, mainfoil horizontal, complete rudder and adjustable wand are all spares that didn't go with 'Half Meanie'.

As usual my composite products and consumables have come from CG composites, Tubes are from CST, and the tramps will be built by Yancy and Pete Williamson at Doyle Mooloolaba. Thanks to all those guys, I appreciate their patience and technical know-how. The hull shell was built by Doink, and mate once I got all that furry shit out it looks great, cheers! Very light and stiff in pre-preg from John Gilmore's Alpha mould. All the little fiddly bits will be 3D printed from Shapeways where required -easier and cheaper than machining. Sometimes.

Current status: All the large parts are done, internal structure is half-in and the wings are about to go together. Here's a photo taken a couple of weeks ago of the whole deal held together with sticky tape. Target finished hull weight is less than 10kg.