Author Topic: Hollow foil board construction method  (Read 3846 times)

PonoBill

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Re: Hollow foil board construction method
« Reply #15 on: December 17, 2022, 10:55:53 PM »
Good choice of video, I watch all the Dark Aero videos. Those guys are amazing. There are three YouTube videos I watch religiously: Dark Aero, Easy Composites, and Welding Tips and Tricks. That wing structure is astonishing. Rigid enough to handle the flight characteristics of a high-performance aircraft and serve as a huge gas tank as well. The only thing I find a little odd is that the leading edge is formed as part of the support structure. I would have thought they would make the structure boxed and added the leading edge as non-structural.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

clay

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Re: Hollow foil board construction method
« Reply #16 on: December 18, 2022, 08:42:53 AM »
Technically speaking blanks are already "hollow" as in 90 something percent air.  The Mike's Lab guys are using light density foam, like 1lb, for sub 10 pound SUP foil boards. 

I have been playing around with lighter density, to me this seems easier (cheaper and faster) than hollow or chambered.
Aloha, I welcome and appreciate all responses of positivity and good feeling.

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surfcowboy

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Re: Hollow foil board construction method
« Reply #17 on: December 18, 2022, 09:24:23 AM »
Clay's on track. But I'll add that a blank made of pieces might be best. Central piece of 1.5lb and the nose and rails from ultralight or chamber them. Strong, light, minimal extra work.

Also I'll add that PeterJ and the SF crew's method of microballoon filler with no hot coating is the way. Far less resin, far less weight.

tarquin

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Re: Hollow foil board construction method
« Reply #18 on: December 18, 2022, 09:42:27 AM »
Spend money on good products. Spread tow carbon, the right epoxy and maybe some innegra. A wet out table.
 As others have said I don't think you can easily make a hollow board lighter than an EPS core without spending quite a bit of money and experimenting.

jondrums

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Re: Hollow foil board construction method
« Reply #19 on: December 18, 2022, 11:52:22 AM »
Thanks for all the great comments.  I'm running a bunch of different math on this, and I agree with so much of the points people are making - this type of construction is really best for high ratio of volume to surface area. 

Looking at the numbers - nomex honeycomb core is really incredible stuff - 3lb/ft3 but holy crap is it expensive.  And yes, it would have to be done in a mold with prepreg.

check this out:
https://www.catsailingnews.com/2020/04/windfoil-tech-patrik-air-inside-the-carbon-nomex-hollow-board.html
https://www.youtube.com/watch?v=7ihSg_9s7Qw

Looks like a great way to make a $10k+ board that might be a little lighter

SUPeter

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Re: Hollow foil board construction method
« Reply #20 on: December 22, 2022, 06:20:18 AM »
I agree with Surfcowboy. Foam is lightweight in comparison to laminate. I've been making "hollow' boards for some time now and am satisfied with the results. Any density foam will do as long as you use divinicell/carbon in the standing/kneeling areas.  Basically, I hotwire cut the board in 3 longitudinal sections( left,right and center), after 90% of shaping is done. Using a hot wire gouge to remove matching chambers of foam along entire length of board in each of these 3 sections.  Chambers are approximately 4-6" wide, leaving about 1" of foam on both hull and deck.  Columns between chambers are approx. 1.5" thick. All should be done being careful not to cut chambers into foil box area as well as leaving a bit more deck thickness in standing area, say 2".  After chambers are completed, I use a hot steel rod to open communications between adjacent chambers. There is only one communication hole between chambers on left and right sides, at the tail. In essence, the foam along the stringer line is solid except for that one hole at tail. Hope that makes sense. I then insert 2 Gortex vents in the very nose, a left and a right, into the forwardmost chambers. When completed, I can then blow air into the left vent which travels down the complete left side of board to tail, crosses over to right side of board, and travels all the way up the right side of board to second vent in nose. This allows me to dry the board out completely should I get a leak. Total weight savings when removed foam blocks are measured, 1.5 lbs.(8' x 20" Barricuda style downwind board). When using a hot wire gouge or hot steel rod to make cuts or hole, you are simultaneously sealing those portions of foam by melting its surface. should water ever enter the chambers, it is far less likely to soak into the foam.  Skinned with 1 layer of 4 oz Innegra, 1 layer of 4 oz fiberglass. Vacuum Bagged. Carbon cloth under where necessary (standing area, foil boxes forward). This technique has reduced the nose/swing weight quite effectively. Is it a stupid amount of extra work for 1.5 lbs.? Maybe, but not for me.

PonoBill

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Re: Hollow foil board construction method
« Reply #21 on: December 22, 2022, 07:51:37 AM »
The Dave Brewer balsa board sitting over my head (hanging on my wall) is chambered. That board has never been wet and probably never will be. Expensive for a board but as art goes, it's cheap, and it is definitely pure art though a lot of the artwork is inside and invisible.

Some art is also inspirational. In my wall hanger, a lot more weight was removed since the medium was Balsa, and the chambering is longitudinal like SUPeter's method. Dave cut the rough-shaped board along its long axis, though the cuts were along the stringers rather than in line with the tracks. If I were building a Kalama-syle board I'd chamber the nose, tail, and any other non-weight-bearing areas. I'd do Dave Daum's trick of using door skins for the stringer, maybe two skins for the track reinforcement dropping to one skin in the nose and tail, or maybe light plywood or honeycomb all along the board with cutouts to match the chambers. The chambers in the balsa board are rectangular with corner filets and were cut with a router, but the shape and the cutting method should suit the core material and be strong enough for bagging. The chambers are blind for the outer two sections but run all the way through the center section. Add stringers to reinforce the tracks and the standing area of the deck and glue it back together. 1 1/2 pounds is worth the effort if you're doing it for yourself. That's probably about 25 percent of the foam weight and 20 percent of the total weight. More importantly, the weight is removed from the nose, where any weight gets slung around at the end of a long lever and is therefore more critical to performance.
« Last Edit: December 22, 2022, 08:31:21 AM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Beasho

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Re: Hollow foil board construction method
« Reply #22 on: December 22, 2022, 05:53:15 PM »
I had called JonDrums to talk about some other ideas when he posted this.

I have worked up some ratios on the weight of foam vs. lamination.  Here are my assumptions and resulting matrix. 
  • Foam Density 1.6 lbs per foot cubed
  • Lamination = Carbon Single Layer 6 oz per square yard
  • Carbon to Resin Ratio: Layed up on plastic and placed on blank 60% Carbon : 40% Resin
  • No weight for TRACKS nor Stringer or beefing up the deck area - NAKED Blank Only
  • Shape of Board is Downwind 7' 6" x 24" x 6" for example

Using Volume of a Rectangular BLOCK vs Final board shape (~ 52% reduced) and then estimating the Surface Area:

--> 120 Liter Board would weigh 8.2 lbs with 1.6 lbs foam

Add ~ 2 or 3 lbs for the installation of TRACKS and deck reinforcement.
« Last Edit: December 22, 2022, 06:08:29 PM by Beasho »

Beasho

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Re: Hollow foil board construction method
« Reply #23 on: December 22, 2022, 06:03:21 PM »
Different FOAM Densities would result in the following weights.  Blank and Lamination only.

This shows the influence on foam weight to final board weight.

Do these look roughly accurate?
« Last Edit: December 22, 2022, 06:09:09 PM by Beasho »

jondrums

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Re: Hollow foil board construction method
« Reply #24 on: December 22, 2022, 06:58:01 PM »
I haven't personally seen a 120L board that is sub 10lbs - but those are all more like surfboard shapes with a lot of surface area.   I agree with your math though, its similar to what I was calculating.

My conclusion is that the only way to really win on this is to build it with pre-preg (30/70 resin cloth) and nomex honeycomb - one shot in a two piece female mold  =  $$$.  It'll be bombproof but niggling issues like how to get the boxes installed really well will really make it a nightmare.  I'm super impressed by those formula windsurf boards I linked up above.  Seems like they nailed the process.

surfcowboy

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Re: Hollow foil board construction method
« Reply #25 on: December 22, 2022, 08:04:15 PM »
I love the ideas here and the desire to innovate.

Meanwhile I'm on board #9 and have a 8.8lb 4'9" wing board with 6oz carbon and 6oz glass, boxes and a handle.

It's not done but I'm doing Peter's barely filled microballoon method so I think I'll be good.

It cost under $200 in new parts since I used all my leftovers. Y'all boys need to go to the garage and get sticky and dusty. It'll all work out.

If you wanted to get crazy I'd follow Peter's crazy carbon tow reinforcement path. Shape the bottom and rails on a blank like a canoe, leave the top off. Lam a top on a thin sheet of eps. Cut out all the foam from the bottom "canoe" and then put in the carbon tow superstructure. Glue the top on and ride.

You're welcome. But thank Peter, he paved that road.

Dwight (DW)

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Re: Hollow foil board construction method
« Reply #26 on: December 23, 2022, 04:05:41 AM »
Different FOAM Densities would result in the following weights.  Blank and Lamination only.

This shows the influence on foam weight to final board weight.

Do these look roughly accurate?

Did you use true weights for EPS?  EPS always comes in right at the legal minimum. See this chart. https://carpenter.com/wp-content/uploads/2022/04/TypicalPropertiesC578.pdf

So 1.5# actually weighs 1.35#
1.25 is 1.15. This is the ideal EPS for wing, when you can find it. The factories donít make much of it. Low demand.   
1.0 weighs 0.85#
« Last Edit: December 23, 2022, 04:10:38 AM by Dwight (DW) »

PonoBill

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Re: Hollow foil board construction method
« Reply #27 on: December 24, 2022, 09:29:28 AM »
If you wanted to get crazy I'd follow Peter's crazy carbon tow reinforcement path. Shape the bottom and rails on a blank like a canoe, leave the top off. Lam a top on a thin sheet of eps. Cut out all the foam from the bottom "canoe" and then put in the carbon tow superstructure. Glue the top on and ride.

You're welcome. But thank Peter, he paved that road.

Yes, that's a very clever approach to Kalama-style canoe boards. It's really the weird design that sparks all this innovation. For a common surfboard shape it wouldn't be practical. I'd jump in and get all sticky and dusty, but the last thing I need is another project.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

surfcowboy

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Re: Hollow foil board construction method
« Reply #28 on: December 24, 2022, 12:21:40 PM »
. I'd jump in and get all sticky and dusty, but the last thing I need is another project.

That comment was pure Pono bait to see if you'd do it. 😆 Hope someone does.

I'm literally in a cold sweet trying to not start a DW SUP right now. Gonna do a tow boogie if I can stay away from the foam and carbon for a minute.

 


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