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Board Build #2

Forum for hydrofoil builders.


DartBoard
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Posts: 61
Joined: Sun Nov 27, 2016 11:57 am
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Local Beach: Longreef in Sydney, NSW
Favorite Beaches: Longreef, Yorkeys Knob
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Gear: RPMs, Switch, Homemade TT, Homemade Foils
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Board Build #2

Postby DartBoard » Sat Oct 07, 2017 9:36 am

The windy season is just starting up in Sydney and after much longer than expected I finally finished my next board (bought the foil this time).

Specs are

115cm x 43cm
50mm rocker (basically bugger all because with such a short board there is no point trying to recover a nose dive, just have to avoid them)
50mm XPS foam core
1 x 460gm double biases glass top and bottom
1 x 300gm basalt biaxial top and bottom
wrapped rails
2 x 4mm marine ply stringers running the full length of the board and 2 x 40mm sub strings
2x 12 inch Chinook mast tracks for mounting the foil
Top coat of white flowcoat
Board weight with grip deck 3.3kg. this is a massive 1.5 kg lighter than last effort!! 6.5kg with foil.


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Here's some construction shots:
I made a foam cutter and used a power supply salvaged from an old PC. 15-20W was the power through the Nichrome wire. Made for a very easy job of it but a bit rougher than hoped. On the bow for the wire cutter I used a bed spring to keep tension. However it wasn't strong enough and allowed the wire to gain and loose tension which translated to uneven cutting action. Next time I'll use twisted wire or string to avoid the stretching.

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The two 4mm stringers I used on both sides of the foam block as guides to the wire cutting. The tail is 50mm thick and the nose about 20mm thick so 30mm rocker without trying. Then I cut the core into 3 and used polyurethane glue to bend the core and glue the stringers in place. This added about another 20mm rocker. Just wanted enough rocker to push through chop when the board is on the water. I'm not so worried about relying on the rocker for recovering from a touch down as I mostly manage to avoid touching down these days. Also, with a really short board I think it would take a load of rocker to be of any use for this so I decided to keep the rocker limited and make the build easier.

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I used 2 straight edges and hot wire cutter to shave the rails way down
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Mast tracks were a very tight fit which was perfect. Eventually qcell'd everything and on the back of the mast tracks I put tasmanian oak wood blocks to connect it through to the top layers of laminate.

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I had to do the top laminate and lower laminate seperately and wrapped the rails. The double biased wrapped around better than I thought but not as good a twill. Something that worked well when I was putting under the vacuum was to stop just as the bag started to suck down and pull the bag around the edges, making big pleats on the opposite side of the board to the laminate. This consolidated the rails and deck with limited amount of sanding needed afterwards.

Another lesson learned was to buy good vacuum bag material. This was nylon vac bag material which I sealed with blu-tac (like you use for hanging posters) as it was much cheaper than tacky tape. I bought a knock off version of blu-tac from the Reject Shop and $4 for enough to seal the whole bag. I made the bag about 20cm longer than needed. This meant that after the vacuuming, rather than throw the bag away I just sliced off the blu-tac( or tacky tape) and there was enough bag left to be able to use it again. I managed to use bag 4 times ( the last time to press the deck grip down) and it never sprung a leak plus the seal was great. Even my dodgy old vac set up would hold about 24 inHg for 30mins before the pump kicked in. Saved so much waste and frustration trying to find pin holes.

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After doing the laminating I did a bit of sanding but not too much. The nose of the deck only had 1 layer of 450gm double bias as I only partly covered the board in the basalt (bottom 2/3) so I didn't want to break through. There were a couple of major divits that filled in with qcell and then a light sand over. To cover over the remaining sins I did a top coat of flowcoat.

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I'd never worked with flowcoat before so googled around on it. Flowcoat is polyester gelcoat with wax in styrene in it to create a airtight cover over the gelcoat so it will cure completely (otherwise it stay tacky). Big lesson learned. Old catalyst does not work. I later found out 6 months is about as long as you can trust it and its good to keep in in the fridge as its very temperature sensitive. I had catalyst that was about 1 1/2 years old and it did not kick. So 20 hours later the flowcoat was a liquid as when I put it on. So i had to wipe it off, acetone wipe down, 200 grit sanding. Then I invested $2.99 in new catalyst and redid it. Flowcoat went off in about 10 mins. I put a super thick coat on and its self leveling properties cover over all manner of problems with the surface finish and it ended up looking pretty good.

The reason I was okay with using flowcoat is that with the stringers and basalt there will be zero flex in the board so there won't be an issue of the different stiffnessess of polyester and epoxy causing it to shear off. I read around a lot on whether the polyester resin will stick to the epoxy and there were some very credible sites where they had done a very good job of creating and testing flowcoat on epoxy and found the bond strength as good as polyester on polyester and no delamination after some cycling of it. I've also used Bondo ( car body filler which is just polyester resin with chopped glass fibres ) on previous foil wing as filler directly on the epoxy and after a year of use no separation so I'm quietly confident it will be okay.

Tomorrows forcast looking good so hoping to test it out along with the aliexpress foil ( they had sold out by the time I order so I ended up getting one with some decoration that ummmmmmmm will have to go).
Last edited by DartBoard on Tue Oct 10, 2017 8:42 am, edited 4 times in total.

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rynhardt
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Re: Board Build #2

Postby rynhardt » Sat Oct 07, 2017 12:46 pm

Nice job! Hope it goes as well as it looks! :thumb:

max
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Re: Board Build #2

Postby max » Sat Oct 07, 2017 2:12 pm

awesome write-up and build Matt :D

my 118cm has about 6cm nose lift . . . wish it had a bit more but most accidental touch downs are fine, just the drops from near full height are generally not recoverable. I started a build with a lot more rocker but found that once I had the air gybes, I could not find the incentive to finish it.

Am impressed by the weight, both of the board and overall with the foil. Hope it goes as well as it looks. Am keen to hear your thoughts on the foil.

BWD
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Re: Board Build #2

Postby BWD » Sat Oct 07, 2017 3:05 pm

If you managed an xps core with anything containing styrene over it and didn't have a meltdown I'm impressed. Result looks good!
If you want a less stretchy hot wire you can just use a guitar string.

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Rufusz
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Re: Board Build #2

Postby Rufusz » Sat Oct 07, 2017 4:00 pm

Nice build please report back how it holds up! Why did you use basalt glass? Just for the looks or any added strength, stiffness, etc?

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Re: Board Build #2

Postby TomW » Sat Oct 07, 2017 9:22 pm

Pretty good build man!

DartBoard
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Re: Board Build #2

Postby DartBoard » Sat Oct 07, 2017 9:54 pm

BWD wrote:
Sat Oct 07, 2017 3:05 pm
If you managed an xps core with anything containing styrene over it and didn't have a meltdown I'm impressed.
The flowcoat was over the fully cured epoxy which also had any pin holes filled in so it never came in contact with the foam. I did drip some on a piece of foam cut off and she melted instantly.

DartBoard
Medium Poster
Posts: 61
Joined: Sun Nov 27, 2016 11:57 am
Kiting since: 10
Local Beach: Longreef in Sydney, NSW
Favorite Beaches: Longreef, Yorkeys Knob
Style: Surf Foil
Gear: RPMs, Switch, Homemade TT, Homemade Foils
Brand Affiliation: None

Re: Board Build #2

Postby DartBoard » Sat Oct 07, 2017 10:06 pm

Rufusz wrote:
Sat Oct 07, 2017 4:00 pm
Nice build please report back how it holds up! Why did you use basalt glass? Just for the looks or any added strength, stiffness, etc?
I'm not sure it was absolutely necessary but I'm so used to building much heavier, stronger structures that a single layer just seemed a bit light on and I want this to be the last build for a while as I'm about to get busy at work.

Double bias glass has fibres at 45/45 which I believe halves the strength along the 0/90 axes. The basalt runs 0/90 so thought it would help strengthen it. Also, I want to avoid heal dents in the deck which I see on epoxy surfboards all the time so wanted an extra layer. I also prefer to do lay ups with the same laminate schedule on the top and bottom. I'm not sure if this is absolutely true but my spider senses tell me that if you have an asymmetric laminate schedule the neural axis moves away from face where there is less laminate so chance of that laminate failing gets a double hit. Finally, I would have used carbon if I had some but I bought basalt a while back and made a couple of twin tips with it. Its about 2/3 of the strength of carbon and was much cheaper to buy. Unfortunately it doesnt really look very good. The cloth itself has a fantastic copper/bronze metallic sheen to it but when you put the resin on it just looks brown. And not even a high performance brown, just a sensible speed in an urban area brown.

DartBoard
Medium Poster
Posts: 61
Joined: Sun Nov 27, 2016 11:57 am
Kiting since: 10
Local Beach: Longreef in Sydney, NSW
Favorite Beaches: Longreef, Yorkeys Knob
Style: Surf Foil
Gear: RPMs, Switch, Homemade TT, Homemade Foils
Brand Affiliation: None

Re: Board Build #2

Postby DartBoard » Sun Oct 08, 2017 8:57 am

Very happy to report that I got out in 10-15knots on 10m switch element 5 today and had a great 2 hours on the water with it. Very happy overall.
Board - not much to say about a board except that worker just like a board should and is a significant improvement over my last one. The lighter weight and extra buoyancy made it noticeably easier to manage in the water and body drag with. Nice solid platform to stand on and did a 6/10 job of recovering from touch downs. If the board was flat and the nose went under it did not recover. If the nose when under and I was leaning the mast over the curve of the nose on the corners was enough to get it to recover. Overall very happy with finished product.

The foil also turned out to be very good. Much more stable on the waves and chop. My own made one needed to be very actively balanced when I road over the waves but the chinese foil road through them without the need to re-balance. Straight up on the plane plus the stall angle was large ( I only manage to get it to stall in the very deep lulls when i actively tried to breach the foil). Low end was excellent. Not problems staying on the plane through very slow turns. I had no problems kiting straight down the face of the 1-2 ft waves. On my old one it would stall on the waves unless I pumped it or carve away from the direction of the wave travel. A few times I kited at the kite and stayed on the foil with just a couple of pumps after the kite lines had gone slack.

I can vouch for it being solid because first dive of the kite I got up on the plane and ran it straight into a reef. I chipped the clear coat and some of the dress carbon on the outside but did not put any dings in the underlying core material whatever it may be. Trucks upwind as you'd expect. I was able to lean it really aggressively ( the rail touching the water and kite only about 3-4 meters off the water and it remained really stable and had a great locked in feel. Hard to say what the top end speed would be like as it wasn't really cranking. Its a smooth stable ride and without a speedometer I find it very hard to guesstimate the speed. Its a 600cm^2 wing so its unlikely to be super racey.

Two things I don't like about the foil: high pitch and torsional stiffness. It had two distinct sounds emanating from it. Reasonably high pitch. Annoying ( although I tuned out it it easily and it went away when I powered up and edged hard) and always a concern that it will attract large toothed fish. I've heard that this can be caused by having too fine a trailing edge on the mast. KFA foil maker says that when he has this issue he squares off the trailing edge. With two separate notes coming at me, and if the trailing edge theory is right, it will be the trailing edge of the stabilizer. Unfortunately I'll will need to experiment.

The torsional stiffness is similar to that of my own build glass and wood one. Understandably the mast is much thinner than my old one so its not surprising but I didn't feel comfortable doing hard cut backs on it as I could feel the delay in the foil responding and that made me concerned about cracking the mast. It just meant I had to carve harder in the turns and drive it more like a surfboard rather than pivot it like I used to. Small issue to address but I now understand why solid is appealing. The overall rigidity is okay and I actually think it might have absorbed some of the turbulence under waves (that's when I could feel it flex and wobble a bit - its a mushy dis-embodied feel at the board).

Subject to the ringing ( which several production ones I've ride have) I'm very very happy with it.

BUT the greatest thing of all on this test day was not the feel of new foil board slicing and singing away under my feet it was the fact that I just kited with 3 whales !!! 2 adults and a calf. Tail slapping which the calf seemed to be trying to imitate and hanging around. The popped up about 100m away from me and I hung around for about 15 mins, tail slapping and bumping into each other. These are freaking big animals BIG ANIMALS. This was a serious bucket list thing for me. I just freakin kited with a family of whales!!!!@! HOLY CRAP!!! It must have been the new foil. I am sure of that now!!!! :)

max
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Re: Board Build #2

Postby max » Sun Oct 08, 2017 9:41 am

DartBoard wrote:
Sun Oct 08, 2017 8:57 am
Very happy to report that I got out … Very happy overall :thumb: …. I just freakin kited with a family of whales!!!!@! HOLY CRAP!!! It must have been the new foil. I am sure of that now!!!! :)

:thumb:


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