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.

entry level CFD

CFD has been - and probably still is - the realm of people who know what they're doing. However recently Autodesk released a little bit of software called Vasari, which is really a software preview of some of the things that might be available in future versions of Revit. The 'wind tunnel' in Vasari is admittedly a bit crude compared to other things on the market, so you have to take the results with a grain of salt, but it does seem to give a reasonable impression of what goes on.

The thing I have been initially trying to test for ís whether the hull tramps in any particular configuration acts as sail, or otherwise increases the efficiency of the sail. This could probably come about in a couple of ways:

• The wing tramps act as an end plate, and reduce the size of the vortex coming off / wrapping around the boom
• The leeward tramp generates lift in a downward and to windward direction when the boat is heeled strongly to windward, acting as not very productive sail
• A fixed foredeck fairing of whatever size could generate lift as long as the AOA is reduced somehow so it doesn't stall, or it is a very high stall angle section
• A fixed fairing might fill the gap between the deck and the boom and increase the end plate effect, even if it is stalled.
• The underwater profile of the hull generates lift

There has been mention on Facebook that there might be some legality issues with fixed aerodynamic fairings attached to the hull. I couldn't immediately see where aerodynamic fairings of this sort were ruled out, but please if you want to comment do so, I want to open up the discussion.

a couple of screen vids showing the airflow over different tramps, all other things remaining equal:

An early hypothesis is that the vortex trailing off the tramp actually seems to counteract the one from the bottom of the sail slightly. When you have a full tramp, that vortex seems to work better than with a small tramp. Just an early theory though.

gh

For those who aren't all over it yet, grasshopper is a plugin for Rhino that allows you to build 3d models parametrically. You can choose to model the normal way and just let grasshopper calculate the surfaces, or draw every component from scratch in grasshopper. By using number sliders for certain dimensions, you can create fully adjustable 3d models that you can easily change and optimize after finishing the model.

In my experience this type of modelling is normally used to make things like this:

But that said, I know people use tools like Catia and Generative Components in all sorts of industrial and product design fields. So parametric models are probably being used to make boats. In fact, I'd say that if you are trying to design a boat and not using a generative 3d model, then you're doing it tough.

Here's a screen vid of one of first forays into moth design using grasshopper - the parametric wing: Apologies for the daggy commentary and vigorous cursor gestures!

back on the horse

Its been about 10 months since the worlds. A pretty good amount of time to rest, digest new information, work on other things etc etc. But, the itch to go sailing is back and I now have a Doink-built Alpha shell (thanks mate!) sitting in the garage waiting to get turned into a new boat.

So, the plan was to start with the most outrageous contraption possible, and gradually change it into something that sort of worked. I'm not sure about that plan anymore, due to day to day time constraints and the pressures of modern life and whatever else. So, I've decided to go with something more conventional. Evolutionary rather than revolutionary, and maybe then try and put a wing on it.

But, it seems like a waste to just chuck ideas away, so I decided to post some things I've been thinking about on here, maybe generate a bit of discussion and possibly inspire someone else to take it a step or two further. They might trickle in, but here's the first one.

The canting foil.
After an initial thought experiment and then some basic 2d cad "calculations," I decided that this would probably be worth a try. But a discussing it with Nick and Markla, we came to the conclusion that it was going to be a lot of work and structural compromise for no a huge gain. Markla did a few proper numbers to illustrate this point. Anyway, I'm still not completely discouraged and it will just go on the back burner I think!

The system I arrived at to make this work is as follows: The foil cants side to side about a bearing mounted at deck level. Very important to have the bearing on the deck, as you seem to get absolutely no advantage over a fixed foil with it at the keel. The bearing needs to be pretty snug, so there are replaceable nylon inserts inside the carbon tube. The centreboard case is supported from the top, but a sliding 'car' that runs along a bit of aluminium bike rim acts as a third point in case you hit a sand bank. I was initially thinking of using a stainless lead screw to control the cant, but decided there was too much machining involved, so I went for an 8:1 purchase system running through laminated-in thimbles. The purchase would need a serious amount of pre-tension in the form of a big bungee to compensate for the changes in line length between 'centred' and 'canted'. Even so, you would never achieve the stiffness from the foil that you get from a fixed centreboard case. That's probably the biggest trade-off. Another issue is that you're left with a large hole in the bottom of the boat, which is among other things a structural problem. This is overcome by some longditudinal bulkheads that tie the fore and aft bearings into the chines and act as beams to stop the hull from snapping. A laterally sliding carbon plate, flexible in one direction only, sits around the base of the foil and fits into a specially moulded carbon groove at the front and back of the hole (not modeled, quite difficult to draw actually) and a small fixed venturi drains it.

In the end, the foil can cant through about 15 degrees comfortably, which is all you would need. From a sailing point of view, i envisaged that the controls would be quite lightly loaded and accurately adjustable. You would probably just centre it in the tacks and when sailing downwind. its an upwind device really.

interview

Finally got around to watching my interview from the worlds. Knowing full well that i'm a pretty rough looking bloke I was putting off watching at it in the name of self esteem, but now I've seen it and i think the worlds media team really did a great job so i thought I should share it. The particular 'some guy' mentioned I think was Bill Olsen (with probably the nicest paint in the fleet) - don't think we'd met at that stage.

cheers

Belmont

thanks very much to Thierry Martinez for the shot. www.thmartinez.com

Without going into too much detail, I had a great time at Belmont. It was especially good to meet so many moth people for the first time. Thanks to John Harris and Clive Watts for helping me get set up with a rig that worked, and cheers to the guys like Andrew Stevo, Bruce Gault, Bill Olsen and Al Goddard who generally hung around the repair shed and were really generous with their advice and bits of carbon. It was also cool to meet Dave Lister and check out some of his genius carbon work on the 'monstro' and likewise Luka with the scalpel and John Ilett with his latest prowler. All three are lovely looking boats with great ideas and top blokes behind them.

So anyway I didnt do very well on paper - 34th in the silver fleet and I think over the regatta i had as many DNFs and i had places. In one race i did manage a 15th in silver, which I was quite happy about in breeze. Also i logged a new top speed on the speed puck of 27.2 knots. I was really pleased, but I heard later that the fast guys average that on a downwind, so again i need to find another gear.

The boat performed reasonably. I cant say I had it right on its game because I was stuffing around with the foil angle of attack the whole regatta, and never quite got it right. I noticed after the first day's racing that my boat was sailing around with the flap fully down, which cant be fast. The refinement process was complicated when I snapped the strut in one very windy race, after the gudgeons on the gantry came apart and the rudder parted company. I could say I was a victim of the weed clumps, but the reality is that I needed a carbon spar in the strut. On Bruce's advice I hollowed it all out and glued a stack of carbon rods in the break, then scarfed the laminate back over it and she's probably stronger and stiffer now than before.

for reference, A good angle of attack for my main foil design is 2.0 - 2.5 degrees from what I have seen and what people suggest.

I got more DNFs for other stupid things - my vang strop came undone at one point and I had to sail in to fix it. The sail got chafed on the concrete and wore through the webbing strap at the top, causing it to fall down the mast and I lost 3 races I think. Angus had a similar issue and we were both at the sailmakers on the same day. Probably the dumbest was when I went out after racing was cancelled in a gusty 25 - 30knots, and blew up the vang, causing the sidestay to get overloaded and rip the front wingbar off the boat. the rescue was a bit difficult and I felt a bit bad for going out and causing drama when I should have stayed on shore. the wingbar will be sleeved together in good time, but after that I called it a regatta. It was actually pretty fun sitting in the club on the last day watching the racing. probably the best spectator sailing ive ever seen - and ive watched a lot of match and team racing!

So as a way of capping off this post, heres a diagram of something I was keeping a bit secret. Its my integrated hinge concept. It has never worked in the past, but I fixed it I think. It survived the nationals and worlds anyway. The trick is to make the centre 70mm or so a standard sikaflex hinge like a bladerider, and then have a couple of narrow points, about 5mm wide (section a) along the span to stop the hinge going 's shaped'. section b shows the normal 10mm gap to allow the carbon surface to bend around a decent radius. A few people mentioned that it might work better if the seamless surface was on the bottom, which is fine, as long as you keep the hinge dead straight so it wont bind up.

foil progress

finally had some racing this week. I've been waiting to see if there was some video that I could scavenge from the pretty decent Sail Brisbane media coverage, but despite having a camera gaffa-taped to my boat I don't feature anywhere except for some brief moments. Always a bit apprehensive watching videos of yourself - its hard to know whether you're going to look like an uncoordinated fool or not. i reckon a bit of column A and a bit of B.

Aside, the foils are going well and both the boat and my technique are improving. Had a top speed of 22.7 in a predominately light to moderate-air and choppy regatta. Still that's the fastest the boat has gone, although I reckon there's a lot left in it. I never really felt like i had it wound up. Anyway hopefully with a new rig and some tweaks here and there I should get away without too much embarrassment at Belmont.

Still cant get the height control perfect through the chop, although i was pleased to see everyone else having occasional problems as well! People keep telling my that my boat goes up and down more than the others, and I'm not entirely sure what to put this down to. Sure the waves are a factor, by why do the affect me more than others? I'm putting a kink and my wand to try and space it further forward of the foil and we'll see what that does. I know the bowsprit is an option but i quite like the bow as it is. Also a lower profile boom will allow the mast to come back further while still giving me enough space to get through the tacks. more rake may help.

I put limiters on the flap down and flap up because I found that too much movement was causing a bit of cavitation around the flap that I could actually hear from on the boat. I suggest to anyone looking at building the foils that they do this too. Mainly down- 15 degrees is too much deflection. I'm not sure what its set at now, but email me if you're interested and ill measure it.

Also worthy of note, the ride height lever was really helping my takeoff. I worked out that i can neutralise the flap, reach off and get the boat speed and apparent wind up then gradually pull the ride height on, and the boat takes off much more easily than it otherwise would have. at the risk of losing what may be a slight edge, i reckon the same technique will work with a dial on your mach 2, prowler assassin or whatever you happen to bring to the potentially marginal foiling conditions at the worlds.

a couple of photos courtesy of the AYF media people, (http://www.saildownunder.org.au/) who by the way were tops.

So, reckon I should try and paint the boat before the worlds or is it fine as it is? I'm tending toward no, but I could be swayed. I think the rust stains particularly add charm.

simple harmonic motion

so no results from the foil testing as yet because i cracked the bottom rudder gudgeon before the first race. sometimes when you say 'that probably wont be strong enough' its a bad idea to convince yourself that it will be. anyway its glued back together and tomorrow it will be beefed up and i should make it on the water later in the week.

The reason I loaded up the rudder and snapped the gudgeon was because of the annoying downwind motion the boat exhibits through our short chop. I drew a diagram to help myself understand what was going on- my theory is that the wave motion is wildly changing the angle of attack on the foil as it goes through the water. This can be up to around + - 5 degrees or more, depending on the boat speed and ride height. The boat tries to follow the wave- up the back and down the face - but there is a bit of lag because of Newton. The flap also complicates things a bit because it is reacting to the lag and not the wave.

The calcs suggest the best thing to do is go faster. The more waves per minute you go through, the less time F=ma has to crash the boat. But the faster you go, the greater the lift from that extra AOA and F becomes a bit more significant. also, there will be a sort of no go zone, where dead square is ok, beam reach is ok, and somewhere in between the effective wavelength gets in a problematic range and causes this kind of crap behavior. Probably people who can sail will be saying 'duh' but this has been hurting me for ages!

I still don't get why 2 boats with very similar setups will respond differently to this. Ncik said its all in the shock chord...

PDF here

more tinkering less sailing

I think the 'hours tinkering to hours sailing ratio' this year is about 278:6. Not doing my boat-handling any good at all. I've been thinking i should really just outsource the sailing part and focus all my energy on stuffing around in the shed. Anyway although I'm still not landing most of my maneuvers, my work with CNC and carbon is getting better and I've been busy applying the stuf I learnt building the moth to other products.

Anyway here are a few pics of my (almost) finished set of foils. They've been out a few times now and i think they could be on the pace. not that I can judge, of course, because no-one ever comes sailing with me! Thats probably my fault for having the boat in bits every time theres a race on and going out mainly on Tuesday mornings.. mm. The 3D model of the foils is available for download permanently on the right hand side of the page. Ill get back on here with an actual review when I've had a chance to line up against someone.

The top of this has become a bit of a mess. It functions, without any reference to form whatsoever. I like it.

I also chucked a set of spreaders together. So far they work. And they weighed in 300g lighter than my old ones.

Finally, has anyone got a carbon boom they want to sell? My alloy boom is nearly dead, (ugh, corrosion) and probably adds about a kilo or more onto the boat! Luka mentioned there may be Mach 2 owners who have upgraded to CST HM gear and have no use for their flexy Mach 2 boom. Anyway I reckon even the worst carbon boom will vastly improve my boat, so please let me know if you know of anything.

Right, now for some sailing.

first sail

fist go in a moth for quite a while! needless to say i was a pro and not rusty at all... anyway there wasn't too much skill required, it was just a quick check of the boat to make sure everything was going together well. It was 8-10 knots so perfect for a first go.

almost everything worked and didn't break. even though i hardly sanded the foil and there were pin-holes all through it, the boat lifted off pretty early. you could feel the skin friction so with a bit of bog and paint i reckon it will go well. much, much better already than the last foil. about half the weight too. the second attempt at the horizontal came out lighter again. the sikaflex hinge let go though. i hit the bottom once, and i think the tip got ripped off a bit and after that it started to separate. does anyone know exactly which Sikaflex you're supposed to use? i just used whatever one i had that was open. i might try a hidden hinge system of some sort, even if it means i have to make a new flap.

the 'dial' thing works well. i was a bit skeptical but the lever and rope that i have going is really effective in controlling the ride height. basically the wand pivot fitting is upside down so everything is in tension, and then the lever just slightly adjusts the length of the rope between the wand and bell crank. i have a slight problem with rope stretch/spring, but i think that will improve with use and you can compensate for it with the system.

the wand pivot is strong and declared good. basically its a Harken ball-bearing sheave stolen from an old block glassed into the hull. i modified it a bit so by tensioning the bolt you control the friction/slop on the sheave and hopefully find the happy medium. very direct, straight and very low friction under load.

the AOA adjuster on the centreboard works well except as it it you cant adjust it when the board's in the boat, because of the centreboard case prongs. bit of crap management but ill sort that out. eventually i think it will have a dial too or some other way of moving it on the water.

the weird kingpost i made seems fine but not yet tested in breeze. the cleat attachments are interesting and they seem to work. i did that because i couldn't fit them on otherwise, without buying new cleats. and the small stainless ones were like $80 each. the vang retainer is good as well - i got the angles right so the vang doesn't tighten up as you ease sheet, like it used to. wave peircing bow also a tick - i have the same freeboard as the assassin but heaps more volume because the old girl is a lot fatter, so the boat sits higher in the water and sails quite well lowriding. the water sheds well off the peaked foredeck. i reckon a proper wave piercer with no compression strut is definitely on the cards at some stage. i think it has legs. i dont actually mind the fatter hull when i think about it, because it will keep the freeboard down and thats less windage. i think i could cut another 50mm off the freeboard and 50mm off the rocker of this boat.

the gantry is shit but hasnt broken yet. the product of a vacuum bag that got a hole in it. i chucked it on anyway, but i think ill do something different. i really like the assassin gantry, might do something like that.

the flat wingbars also work. in fact the boat is noticeably easier to sail as a lowrider, really nice to sail as a foiler and much cooler looking. the little wings are good - i cant imagine they need to be bigger, actually could be smaller again.

the rudder is the final thing. i designed one already for Sam Schneider's SR71 foiler. it looks about right, at some point ill scale it back down and pull some moulds off it. i'll make the rudder foil available for download from the blog too at some point.

so im going overseas now, so the boat will be mothballed for a while. but its all set up for some serious tuning when i get back! really pleased i got it sailing before i left.

this is a good way to do the moulds if you're going to cnc it. helps to keep everything straight because the MDF is so crap with heat. that said, id minimise the use of MDF because it shrunk fairly considerably in the oven. no big deal as long as you let the foil cure before you heat it, as i did because i accidentally didn't turn the oven on! the first time round i used chip board glued to MDF, so the mould surface was still in the MDF but the whole thing had a 18mm chip board backing, and that didn't shrink as much.

below is a comparison of my foil and the assassin foil. area is pretty similar.

hull

Finally the hull is faired and undercoated. wings are re-built, new foil is curing. tramps are re-done. lots of fiddly jobs but the boat is looking a lot closer to hitting the water. Im optimistic as always - we'll see if we can go for a sail this weekend. its not getting a top coat because i cant be bothered fairing the hull right now. done enough sanding lately.

I think the renovation has shaved about 7.5 or 8 kilos off the boat - hull down to 12.5 or so, lost 0.5kg from the wings too at least. anyway it looks strong enough, looks good enough. hope it works.

files

having actually bought some web space the other day, i can now host big files! here are a few rhino files that i've promised in the past:

CNC Machine

Aussie Flasheart

Main Foil

Half-meanie

ill get back to you on the progress of the boat! briefly, the hull is done aside from bog, sand paint, wingbar joints to go (they suck!), gantry is done but needs a bake, foil is not CNC-d yet and I still have to afford the materials for it.

new foil

I re-designed the foil with a bigger bulb, so that the socket could be 25mm deep. The bulb looks a bit fat, but in theory it should work. I wish I could use CFD to sort this out propperly, but bloody ANSYS are too on top of their licensing.

anyway that can get cut out tomorrow, if anyone has any comments about the shape please let me know before then!

deck goes on tonight hopefully. making pretty good ground, a good 1/3rd of the list is ticked off.

finished!

well, practically. i stuck the wingbars on with string.

stood back and admired my work. (you'll notice that i stuck them on once before, made holes in the hull, then decided they were too far forward and moved them back. not like me to be that conservative, but i realised that i got my numbers wrong, upon measuring a Mach 2, and i probably should have put the centreboard case about 85mm further forward. im happy with how its sitting now. mast step is 985 from the bow, front of centreboard is 1585.) anyway, standing there planning how i was going to paint it, i realised there were still a few jobs to do. made a list.

The list nearly fitted on the foil alignment template, so thats a good sign. i reckon if i tick a few of these jobs off each day i should be done in like 3 or 4 weeks. start work in a week.

bits

Foils and deck done. the laminates came up really nice. the araldite 3600 resin that Ive been using becomes so high modulus when you bake it (80 - 100 deg) that you'd almost say its prepreg. Foil came out at 1.8 kg and the deck at about the same, with a further 250 grams for the bulkheads. so the vacuum did the trick. The only problem is that the socket in the foil looks a bit too shallow, (by like 10mm, massively too shallow!) so if thats the case i might re-do just the horizontal with a much bigger bulb, and cut the tab on the strut a bit longer. Will try and make what ive got work first. I put 2 tubes down the strut this time, in case i want to do a swept horizontal with a split flap at some point. I really should have put some high build primer down in the mould first, as Andrew at CG composites suggested, because im going to have to go over everything with some black bog to patch up all the tiny holes in the weave that the vacuum leaves behind.

Anyway lots to do, tomorrow the bulkheads go in and I need to make some little angles so that the deck can stick to something. I really have no idea how people would normally stick a deck on a moth. If anyone has a suggestion let me know! also the gantry mould is ready for the CNC machine to cut out. opted for a box gantry over tubes because then I could avoid buying tube, and use the materials I have already that are leftover from the deck. quite like the design of it though so it should be fine. function over form!

ps. if anyone would like some free moth bits, i have some now redundant lowriding foils, need some care admittedly, some moulds for a NACA 66014 strut and an old repaired carbon strut that is about 1.3m long. and my old gantry.