Messages

1

The Shape Shack / Re: Maximum Displacement Hull Speed

« on: March 30, 2023, 09:50:55 AM »

There is a ton of interesting content in this thread for a design newb like me (thank you to the contributors). 

One thing that I'm trying to better understand is how to compare hard chines vs a more rounded hull on a pintail downwind board.  I generally understand the pintail, but more designs have very hard chines in the rear portion of the hull leading into the pintail (Baracuda, FFB Dagger, Sultan, Axis, Etc...).  There are some exceptions with more rounded features (Dale Chapman and Sunova), but they are not the norm.

Wouldn't the harder chines create eddys and drag?  wouldn't softer chines allow for better water release and perhaps less wetted area?

Please help a newb understand the hull design philosophy!  Thanks again.

Just the reverse-  water likes to stay attached to curved surfaces as it flows. Not only is water moving longitudinally along the length of the board but, it is also moving laterally as the board slaps down onto the waters surface as we pump and hop. These hard chines allow this lateral moving water to relaease .  When hulls are curved, the water will ride up along that curved hull trying very hard to stay attached to the hull.  All this added water weight is detrimental to an easy and clean separation of hull from water. I hope this helps.

2

The Shape Shack / Re: Maximum Displacement Hull Speed

« on: March 22, 2023, 08:35:40 AM »

Planing could happen during touchdown, though it's more like a skipping rock than a planing hull, and it's worth remembering that skipped rocks flip over with each touch. It's too dynamic a situation to even guess what's going on, though SurfGTP coupled to a few supercomputers could collect enough data and crunch it to model it.

Ok - I was like "what?" -- I had thought it had to be spun horizontally - and the gyroeffect would not go well with flipping over - but I also checked Google, got lost in the weeds/watched some fun videos including one about converting a clay-pigeon thrower into a "skipper" (of exact same discs, not actual rocks) - there are even some things on not-so-flat rocks and their skipping physics but I can't find anything about flipping?

You'd need to be a lifelong geek and present-day geezer to find the right reference. When I was a kid there was a challenge in Scientific American Magazine to explain the odd pattern that skipping rocks leave in the water. I chucked a few hundred rocks in the Charles River trying to figure it out. Close observation shows that there's a long skip, then a very short one, then a long one...etc., etc. Some guy painted a skipping disc with stripes that showed rotation, and different stripes to differentiate top from bottom, then ran a high-speed camera to record the skips. Turns out that when the stone hits the water it creates a depression that has a definite bow wave pushed up by the stone's forward velocity. The skipped stone "trips" on the bow wave and flips over, taking a short hop, then because of its rotational momentum on the second landing flips higher for the next hop. Lather, rinse, repeat. There was an exhibit showing the experiment in the Boston Museum of Science for quite a few years, which is also where I learned that water molecules in a wave don't move forward, they move mostly up and down in an epicycle.

I can remember a Scientific American article from the late 50s when I was about ten years old, but I have no idea where I put the .6mm extruder hot end that I set down "someplace handy" when I was swapping it in. I've cleaned the entire garage looking for it.

Yes, water molecules in a wave generally move up and down, but if those waves are created by wind, the uppermost water molecules travel slightly forward with each circular motion.  This makes catching a wind blown swell a little easier than catching the wake off a passing lobster boat.

3

The Shape Shack / Re: Maximum Displacement Hull Speed

« on: March 14, 2023, 07:02:50 AM »

I'm not an engineer but does nothing take into account the apparent weight of the supposed displacement/planing  hull and just how much water that hull is actually displacing once the foil begins to apply a considerable amount of lift.  When the foil lifts 90% of the board and rider weight, could not the very features designed for planing then become more advantageous versus the displacement portions of the same hull. Having spent considerable time doing flatwater pop-ups, the hopping/slapping phase, just before lift off, consists only of the very flat bottom of board temporarily touching the water's surface .  If the apparent weight of this board is only a fraction of its actual weight(from foil lift), could not planing occur during each, ever accelerating, touch down? just wondering.

4

The Shape Shack / Re: Maximum Displacement Hull Speed

« on: March 13, 2023, 02:23:31 PM »

All these boards take advantage of their partial planing hulls, if even only for brief moments. The more powerful the paddler, the longer and more frequent these brief moments of planing become, making displacement hull rules and regulations unworkable.

5

The Shape Shack / Re: Maximum Displacement Hull Speed

« on: March 13, 2023, 12:05:14 PM »

Interesting topic!  It seems to me that there is a hell of a lot more going on here than just dealing with maximum hull speeds. The shape of these boards and the way they are being propelled takes advantage of hull speed, foil induced speed and lift, and planing performance.  Greater hull speed is definitely tops when it comes to getting a board to fly. The additional speed and lift of the foil when pumping gives boards with pronounced bevels (ie. Barracuda rails) produces a narrower width as the board rises. Hence, even greater hull speed. Getting the board to completely leave the water (if only for a split second) , narrows the board a little more and then takes advantage of its planing performance. Hence the very flat bottom and hard release edges for most of its length.  For a flatwater pop up, All this happens in the span of maybe 30-60 ft. So all aspects of board speed become necessary, even planing.

6

Foil SUP / Re: Compressed air tank for filling wing during downwinder foil SUP

« on: March 01, 2023, 09:30:25 AM »

Thanks all!  I have a paintball/small SCUBA tank with regulator coming in. Is Carbon Fiber so it should be light enough.  Also have enough adapters from my son's paintball days to rig it up. No need to fill it to 4500 psi. I'm sure I'll get 2-3 fills easily even with filling it to 3500 psi. This could make for some interesting downwinders. 

7

Foil SUP / Re: Compressed air tank for filling wing during downwinder foil SUP

« on: February 28, 2023, 10:06:59 AM »

Yes, thank you! Just watched it! That’s what it m looking for. I message James Casey to get some pics, but I’m sure I could piece something together. Just wanted to know what size bottle would work. The video shows it well! Thanks again!

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Foil SUP / Re: Compressed air tank for filling wing during downwinder foil SUP

« on: February 28, 2023, 08:54:44 AM »

Thanks, I'll start searching YouTube.

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Foil SUP / Compressed air tank for filling wing during downwinder foil SUP

« on: February 28, 2023, 04:05:39 AM »

Anybody have any beta on what is needed and how to fill a wing during a Downwinder SUP foil run. Conditions in Maine change often while downwinder foiling. On longer excursions, I thought bringing a lightweight carbon fiber canister of compressed air to fill a wing when those conditions change or my fatigue prevents me from paddling up onto foil. Basically a bailout when the miles get long. I would carry the wing and canister on my back while DW SUP foiling and only inflate my wing if needed. Just a thought, since other iterations of this have already occurred.
Thanks in advance. Paint ball tanks seem to be ideal. I have a high pressure pump(4000 psi) already.

10

Foil SUP / Re: Axis Downwind Boards - inverse relationship of length/volume and width

« on: February 20, 2023, 06:17:47 AM »

narrower boards have less edge leverage when small waves and bumps are encountered.  Wider boards have greater edge leverage, making them roll more.  The stabilizing influence of the mast and foil have a proportionately greater effect with narrower boards versus wider boards.  These narrow boards are far more stable than they would at first appear.  longer water lines also increase stability. 

11

Classifieds / Re: Duotone Slicks - 7m 5.5m 4.5m with carbon boom

« on: February 20, 2023, 06:02:08 AM »

I'll PM you

12

Classifieds / Re: Naish Matador LT 3M and 5m $350 per

« on: February 09, 2023, 10:20:27 AM »

PM sent.  I hope it goes through. 

13

The Shape Shack / Re: Ultralight Board Designs

« on: January 27, 2023, 09:33:38 AM »

Spraying on a clear sealer coat of Rustoleum spray paint(can) was my final option on my last DW board. Prior to that just the very runny microballoon coat during some drastically falling temps, all sanded off. No leaks so far.

14

Foil SUP / Re: Weight Matters

« on: January 25, 2023, 08:20:56 AM »

In some interview with Dave Kalama I remember him commenting on DW boards that were too light were more pitch sensitive, especially when dropping down the bigger steeper bumps.  In some ways, I find that to be true.  While playing with mast positions on my DW board, Having the mast far forward (less nose swing weight) the board becomes a bit more challenging to control, though easier to pump.  Having the mast more rearward, control becomes much easier.  I, myself, prefer to make boards as lightweight as possible. Again, compromise is always the sweet spot.

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Prone Foiling, Surf foiling, Pump Foiling / Re: Swim Missiles

« on: January 17, 2023, 06:41:42 AM »

That board looks amazing.!   8 lbs!  holy shit, that's light!