Sunday, January 23, 2011

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.



15 comments:

Cookie said...

2 degrees relative to what? I've never run more than 0.5 degrees relative to the waterline.

Teknologika said...

Nick,

I have to say that the build quality of your home built foils is, bar none, the best I home builts have seen.

Bruce

nick flutter said...

Cookie,
yeah 2 degrees to the waterline. it seems to work better but im not completely sure at this stage. maybe because my foil is small at 0.90m2.

Bruce,
cheers! pity the rest of the boat was a bit crap. it seems you cant do these thing by halves. looking forward to seeing your new steed when it comes out of the shed!

n

Niki Liebscher said...

Hi Nick,

do not realy understand the last layer carbon with grashite powder. How do you build this? Thanks for some more info!

Niki

Noodle said...

We don't go so technical on the virtual Moth, but we do sail it. Check the pictures here noodleqt.blogspot.com

Karl said...

The optimal angle of attack varies with the 2d foil section and probably with the hinge geometry. So I'm not sure it is meaningful to compare the angles from boats with different
mainfoil designs...

Cool hinge; maybe make a sliding plate for the underside like the Toronto boys.

nick flutter said...

Niki,
the graphite powder was an idea my carbon suppliers had to create a nice fine pnihole free surface for the foil. its basically that black stuff that you put in locks, but SP sells it in large quantities. The first layer of laminate is bagged into the mould with resin that you pre-mix with quite a bit of grahite, to thicken it up. it doesnt go clumpy like with microballoons or soemthing, because the particles are so fine. i just got the quantity so that it looked about right, then put it in the vacuum bag with peel ply on it and no bleeder, to keep some excess resin in there and eliminate the pin holes.

karl, the next foil will definitely have a flappy bit on the bottom or top or something. ill probably use the carbon/sikaflex composite for the flappy bit too somehow. see how it goes.

You're right about the angle of attack being dependent on some of the specifics of the foil. im tending toward a smaller foil at higher AOA, where others have gone the other way. not sure which is better.

nick flutter said...

re reading that its not very clear. - the fist layer of carbon that gets bagged into the mould is:

-200g carbon
-resin and graphite powder in approximately equal parts by weight, so that the carbon is just submerged in resin mixture
-peel ply

n

Niki Liebscher said...

Hi Nick,
I bought 1 box of industrial 99% pure graphite. Mixed it up with resin and put it on a test layer of carbon. So I got a sheet of carbon with this graphite mixture. One with 50/50 in weight and one with about 10/90. The 10/90 was broken and the 50/50 got cracs after bending! The 50/50 had a very nice facing from the foam! But I did not use any peel ply at all - not shure this will make any big differences? Did you use the graphite mixture for the hole last layer? Thanks again! Niki

nick flutter said...

Niki,

those fractions both worked for me.
i can think of two things. what radius did you bend the carbon around before it cracked / broke? my hinge only bends around about a 40 or 50mm radius, so it would definitely break if i bent it around say a 20mm radius. Also, because I used the vacuum bag, the carbon sheet was very thin, with no significant layer of resin on each side. that may also affect it. Of course my hinge would break if i bent it on a very sharp angle. the sikaflex layer on the back prevents that, so does the geometry of the foil. with a 10mm gap and 10 or 15 degrees of flap deflection, the smallest radius you will get it probably 50mm.
if that doesnt work and it is still too brittle then maybe the resin is too stiff? i dont know.
nick

Karl said...

Guys the resin properties have a huge impact on laminate performance. If you look at the recommended cure schedules including temp ramps, total cure time and max temp you can induce either higher strength with lower flexural modulus or the other way around. So take a good look at the manufacturer data for cured properties. I use ProSet which gives a very large range of properties for any given resin/hardener combination. This is probably not as true for room temp resins, but most will benefit from some post cure when it comes to toughness.

nick flutter said...

Karl, definitely! I've not done much experimentation at all with different resins / hardeners / mixes. just got a working combination straight up and stuck with it. here's the data sheet for the resin i've been using:

http://www.kirkside.com.au/Uploads/Images/aralditekitk3600.pdf

might have to copy paste. basically after a post cure at 80 deg. the resin has a flexual modulus of 4800M/mm2 and a tensile strength of 70N/mm2. pretty stiff and strong by normal standards so its not like i used floppy resin. The post cure more than doubles both numbers compared to a room temp cure. There is obviously room to play with resins but my philosopy was to use something stiff and thin, and find the best radius for that particular laminate.

Karl said...

yes Nick I was only referring to Niki's comment on the resin fracturing. Your thoughts on the radius and using Sika backing seem spot-on.

K

Andrew said...

nick

I'm looking at doing trim tab C Board for the Int 14 that obviously requires symetric flap movement around the ection center line. I want to use a version of the Off Yer rocker foil sliding cover over the gap in the core that is required to allow the +/- 7 deg flap range. Steve Killing (c class hydrofoil designer) used kevlar at +/- 45 deg for the hinge section. Why did you feel you needed the stiffness of carbon to accomodate the rigidity of the flap hinge along the span?

I note that your hinge detail calls for varying gaps in the Sikaflex along the span to stop the flap from S bending. Is this because of the foil deflection under load or the base foil geometry not supporting a straight line hinge? My concern with the 14 centerboard is the lateral deflection of the centreboard is in the opposing direction to the flap articulation. My guess is that if the flap is made flexible enough then the restraint that the central hinge provides will dominate and allow the flap to deform and follow the opposing curvature of the main structural element. Have moths any learnings on this effect that I should be aware of?

nick flutter said...

andrew,

yeah, forget about my carbon hinge and the thin-fat sikaflex, none of that applies to a symmetrical board, because you want the pivot point of the flap to be on the centerline of the board. have a look at the section of my foil and you'll see what i mean.

the hinge will be your issue because of the defleciton. I'd start by measuring the defleciton under sailing loads somehow, and that will inform what you decide to do about the hinge. it may have to be quite rubbery, or you may just need to make a super-stiff board.

the cover strips like on the C class and many other foils previous and since are pretty easy to do. just make sure you cast in a bit of an indent to accept whatever carbon/kevlar/plastic tape you choose to put over the slot. make sure your cover strip curves inward, so that it presses against the flap on both sides. that way when its deflected the cover wont stick out straight and leave a big gap.

step 1 - measure the deflection of your board and see if you have an issue with the geometry.