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.

foils

finally something tangible! part 1 of the conversion is the new main foil. i figured it would be simpler to start with that and then build the boat around it. i can also get the centreboard case and the deck going when i get off my ass. i've pretty much bought all the materials.

heres the process:

The foil is longer than the last one, and the strut tapers. the hydrofoil is a higher lift section with a larger flap, as i found by doing this that the lift/drag ratio was generally better in that configuration because of the reduced area needed for takeoff. Top speed may suffer, we'll see. Also maxed out the span as much as i thought i could structurally with standard modulus carbon and wet layup (span is 1050mm). The flap is designed so that the deflection at the tips is limited to 5 or so degrees, and hopefully that should decrease induced drag when the flap is fully deflected up or down without affecting lift too much. I found that even though the tips twist down slightly, it is difficult to keep the lift distribution fairly elliptical when the flap is allowed to operate through its full range at the tip.

anyway, will lay up some bits when i get time. might have to wait till the new year.

whisper

Just did some cunning measuring on the whisper boat. Looked to me like the mast was a bit forward and so was the foil. and the wings. I was thinking the same thing so i thought id check the actual numbers, out of interest of course!

I think im going to have the mast at like 850 and the foil at 1500. Keeps about the same proportion, with a bit more bow sticking out, but then ill have a gantry too. Ill have to move the wings forward because they're connected to the bloody sidestays. what an awesome idea to get rid of them! Also the rake adjustment on the fly is a step forward, with the spherical mast bearing. And come to think of it, I like that a ply and glass hull can be 6kg and $700.

Cant wait to see how this boat goes in Perth.

Half-meanie!

Finished architecture on Monday, just sobered up with no intention of even trying to remember what happened yesterday and the day before. back to the blog! And before you ask, no. my sailing and my boat, sail, and attitude toward training are the main things that are slowing me down at the moment, not the blog. its not like im shaving the last couple of percent off my top speed or anything anyway.

speaking of shaving, i shaved more than 10kg off my boat this morning. this is what I had in mind thew whole time:

http://www.youtube.com/watch?v=A9AvhDm7rI8

So the hull was 19kg. ha your all laughing but i dont have any money. Now the glass shell is just over 8kg, and ill chuck a flat carbon deck on it and a couple of new bulkheads which might take it up to something like 13 or 14. Seriously the foredeck was about 4kg, the mast base was 4kg. and the deck was wrecked. The skin is not in great condition with a bit of osmosis and whatever, but it'll have to do for now. It looks overbuilt anyway, so thats a bit of a plus.

This is definitely the way to build boats though! well so far its been more like destroying one but its pretty much the most fun you can have. especially when you're trying to take your mind off a cracker hangover. There are so many good second hand boats out there that are a bit too big nowdays, getting an old prowler and doing this might even work out cheaper than building from scratch. and you'd get good foils, a rig etc. and you can use your own ideas.

So the Flashheart idea looks to be out the window. Boat 2 (yes im optimistically thinking about a year ahead) might be a big mod of a light, pre-preg well built boat. So much less work. Time on the water mate!

Also, obviously I didnt sell the boat. It is still for sale, though I probably might want to hold off until the mods are done and Ive completed at least 1 race!

Alright, gotta go get drunk again. more later.

n

CNC

so heres what ive been doing lately.

http://www.youtube.com/watch?v=LKyu_ECy8rg

designed it in rhino, built it from the cheapest bits I could find, and very suprisingly it seems to work! Got a kit with the electronics and everything from http://www.oceancontrols.com.au/ to power it. Its cutting area should (i say should because i havent actually tested this) be around 1210 X 2440 X 300mm. So a whole moth mould will still be in a couple of bits, but it will cut out a whole set of foil moulds from one bit of MDF. cant see why it wont cut solid fibreglass or solid carbon in the future either. We're thinking of using it to do some ply stuf for joinery and that kind of thing as well, and of course the last couple of models i have to do for my architecture degree.

anyway im theoretically set up to be a moth home-builder now. you seem to need one of these things if youre going to even have a chance at building a good boat these days, foils etc, so we'll see what happens. heres an image of my test file in wood. Below it is the toolpath.

As always the rhino file for the machine is available if anyone wants it to inform their own design. im not going to go so far as to recommend it just yet!

for sale

ive decided its time to sell the moth to get some cash together for the new boat. 

also i probably wont get much time to sail it while building the new one, its about as fast as it will ever be anyway, and tinkering with an old boat distracts you from doing work on a new boat.

so if anyone is interested, it comes with:

• home built foils that have had 30 or so sails and plenty of crashes, with no structural repairs, still in good condition except maybe the main flap hinge but i think ill fix that before selling the boat 
  
• adjustable wand that still needs some tweaking, but fundamentally works well
  
• lowriding centreboard and rudder that still fit (rudder needs gudgeons)
  
• road trailer, built for the boat, ok condition, painted not galv.
  
• ka sail, standard bladerider one, been used about 20 times total. still in good condition
  
• burville mast (bladerider) with the top section repaired, but going fine and sail sets exactly as before, used 10 times, so like new.
  
• alloy boom, near new ropes and blocks

generally the hull, wings and traps are starting to get a bit tired, the boat leaks a bit etc. and its by no means pretty. at this point i might as well admit that it could use a coat of paint.

that said its been my faithful steed over the last 3 years, ive learnt stacks sailing this boat and though not that compeditive at any point, its been a great introduction to moths for me. the hull is a bit heavy and thus bulletproof, and thats been a pretty important thing. the boat has finally progressed past the point of breaking something every time you go sailing, so everything is strong enough now by a long process of trial and error. With the current setup, although you cant go upwind at the same angles as well.. sabots.. you can still match the slower skiffs around the course, losing on the upwinds and gaining on the downwinds. also it takes off with my 75 kilos in like 8 knots, not 6 or 5 like good boats with light people. mainly due to the extra weight and the increased drag from the square foils.

so its a bit of a sad day, anyway ive put $4500 on it, thats gotta be about the cheapest foiling moth with flaps and wands and stuf. ever. for that price its a good toy or a relatively cheap first moth to learn foiling on and get on the water. you can work out pretty well from my old posts whats there and its condition, so otherwise make me an offer. remember im a starving, barely employed uni student.

wingtips

Ok so i have been slack. I still dont even have a mould for the new hull or even a block or foam. absolutely no progress there. the 3d file is router-ready but thats about it. Had a few projects that took over and now that theyre done im back at uni and so progress i fear will be slow. 

anyway ive been still tinkering with the blue boat - broke the gantry and it was off the water for a while and now its fixed back up again, a truly crap repair job later. one of the things i did was redistribute some area between the foils, just for the sake of an experiment. so i cut 100mm off the rudder span and added that to the centreboard, in the form of these wingtips. 

 Everyone i talk to says "wingtips are tricky, you need to do 3d analysis and work out the nature of the vortex at the design speeds etc." Anyway i pretty much ignored the advice of everone who knew what they were talking about and just designed some in rhino that looked good, cut them out, took a mould etc. I think they came up pretty good, the foil sections are pretty accurate at least. and they seem to work too, subject to a bit more testing, two things have happened; the boat launches much better and at lower speeds, and the hum that i used to have is gone. also there is no noticeable loss in stability from a smaller rudder (550 span i think) and it all feels smoother, and the boat want to go straighter. i could be kidding myself about that last bit. foiling manoeuvres were easier. also i have a new wand which i reckon is my best one so far, with a paddle about 200mm from a very flexy tip. If i do anything else i may want to extend the flap onto the wingtip, i dont seem to have quite as much response.

anyway heres a pic of my wingtip, if anyone wants one for their old and shit square foil let me know and ill make you a pair of blanks, im keen for another opinion. chord is like 115mm or so.

done

So the aussie flasheart design is done... sort of. feel free to email me if you would like the rhino file. note the bridle attachment point. i think its cool. wand mechnism: grearing is adjustable by a thumb screw. the front bung goes in above the pushrod exit point, under the cover.I thought of a neat way of adjusting the rake of the centreboard too, which is basically a stevo top rudder gudgeon for the centreboard, that the retainer pin goes through. a thumb screw at the front of the centreboard, just above the deck, pushes a rod back and forth inside the top of the foil and the pin goes through that. the rod would be like 50mm long and is held in there pretty well so the hole in the carbon can be elongated. it means your centreboard case needs to taper slightly, but the range of adjustment is no more than 1 or 2 degrees to accommodate all wind conditions.. just a thought. i think ill be doing that if i build another foil.

also had a glamour sail in 12-15 kts and pretty flat water at RQ, took my iphone with recently updated gps software and for the first time i could download my track. the data was pretty noisy, but i used excel to average it out and im pretty sure i hit about 20.5kts, my best average over 100m was 18.1. i was doing about 12.5 - 13 upwind, but not pointing very high at all. I might try again one day with a real gps. it really didnt feel that fast, and i think the boat has gone faster so ill keep pushing it.

^ i entered the seabreeze.com.au competition. i couldnt help myslef, the prize is pretty amazing. i reckon the dude with his hair on fire is a definite winner but.

fixed the mast, sort of. have been sailing without using too much vang or cunningham, and because it has two sleeves in it now its pretty much the stiffest topmast ever. so i dont really get a good leach anymore and hence the no pointing. im getting a new one.. just as soon as i go to work, earn some money and get paid, subtract bills and living expenses. i think i logged 6 hours this week so im not looking good.

finacial situation doesnt look good for a speedy build either, i might have to find a sponsor. though i am in brisbane, going to uni full time, its all a bit hard. anyway at least that gives me time to go over in my head the procedures and simplify it right down.

anyway thats about all, best of luck everyone at the nationals, hope you dont break anything, forget what hole it was in etc, hope your knots all stay tied up, and that the breeze is between 8 and 20kts the whole time and that the chop is less than 2 foot!