Vacum Bagging

Hey SD hoping someone like you can save me some time on sways by giving me some links on vacum bagging and composite building. That is going to be my winter project. Love the look of new the IS and maybe that will be my inspiration for my first comp sand

Thanks Kona

Hey Kona,

Get Mark from Lakewakes input also, he's doing some bagging.

The heart of my system is the pump. I use the full system from ACP Composites in Livermore. Those folks are just down the freeway from me, so it's easy for me to get goodies from them.

There pump has a reservoir, which reduces pump cycling and also catches any excess resin that might get pulled out of the bag, as well as, an adjustable vacuum switch. The switch allows you to adjust the amount of vacuum from about 3 inches up to 20. The system isn't real accurate and the switch limits are WIDE at about 3 full inches, but for our purposes it's more than adequate.


ACP Composite's website:

http://www.acp-composites.com/acp-vbs.htm

The system I use:

I also use most of my consumables from those folks:

Vacuum bag, quik lock seals and perforated peel ply. They also offer breather, but I have found cheap walmart or costco paper towels are just a good and 1/3 the price.

I almost never use a normal peel ply/release film, instead just using the bag itself, OR I use a perforated release to allow any excess resin to get pulled out.

Thanks SD

The single best video that was ever available was Tom Sullivan's vacuum bagging, but I haven't seen it anywhere. There are folks that have copies and I think sell it...It'd guess technically they are boot-legged. This thread at Sway's has reference to a video available by trtldes, here

Also, the RC airplane sites are heavy with vacuum bagging details for wings. I'd do a google search for that also.

Hope that helps! Be sure to post up your experiences.

kona,
love the bagging on getting the laps to hold down , i use breather on top and bottom , i use mylar on the surface i just lammed with release film over it then breather, with perforated on the bottom then more breather. i use 3 lb, eps and right now having trouble getting the right vacuum setting so the finish will stay smooth and not wavy. imo its worth the $$

Jeff,
check this out on bagging
http://www.youtube.com/watch?v=w9Iy3Y5h7Ww
http://www.youtube.com/watch?v=CW7SjABe8Lc (part 1)
http://www.youtube.com/watch?v=MBMZ6DnATRg (part 2)
http://www.youtube.com/watch?v=xsgBUMUpCi4 (part 3)

Hey Mark,

Thanks! I have been following that WMD for a bit. I've only made it through the first two vids, though. That Cerritos college puts on a ton of great workshops each year.

Those boards do look good, don't they? Although I've sworn I will NEVER do business with Warvel!!!!

I'm not fully sold on the bamboo laminate. I'm getting the feeling that Greg L. and Warvel are doing a ton of hype over a slimplistic build tech. The bamboo laminate, at 1/40", doesn't seem to impart anything other than a separation between the fiberglass layers...well of 1/40" of an inch

In my experience, a seperation of less than 1/8" doesn't seem to affect stiffness noticeably, nor prevent heel dents in the underlying foam after a bit.

I don't know, we'll see how that tech catches on.

Are you going to try one?

i dont think it would be cost effective for me. looks real good and i would try this for cosmetic reasons , still trying to keep board manufacturing to 5 hours each board

For stock shapes - the molding is the way to go. I'd bet that labor hours can be reduced to just about 2 hours per board...they literally pop out of the mold finished.

Of course, the mold construction probably takes 100 hours

I am itching to finish up my mold, just to see how the process would work.

So SD what weights d cell do you use for the rails and the top and bottom? and what glassing schedule do you use?

I typically use H80 for everything - skin and rails. 1/2 d-cell on the rails and 1/8" skins. The core is .75 pound geofoam eps12 (when I can find it!) or 1 pound eps from just about anywhere.

On that flamed surftech knockoff, the lam schedule was, from top down:

4 oz deck
2 oz sandwich deck
2 oz sandwich bottom
2 oz bottom

On the one I am building now, I have also add a layer of 2 oz in the high traffic areas, plus I upped the resin in the deck sandwich layer.

On the flame board, all of the resin/glass ratio was 1:1 - so I had something like 10 oz of resin TOTAL for all the lamination, then I think 8 oz for the hoatcoat, I'd have to check my production notes to be sure.

On this current build, I have 2 oz of resin for the bottom skin and 2 oz glass, and 8 oz of resin and two layers of 2 oz glass total weight is just short of 4 oz of glass.

Thanks SD
Do you bag your deck and bottom lam or just the sandwich ? or after the vac bag is it just a regular lamination?

Kona

I bag all of the laminations. I know that the "experts" say that they can get a hand lamination down to a 1:1 resin:fabric ratio, but I sure can't! Bagging the external is a pain, but after you done a few it's not too hard. The biggest issue is wrinkles.

The way I do it, is to wet out my fabric and smooth it on the deck. Then I drape a section of perferated peel ply over the wet laminate. Finally I lay up some breather over the peel ply. With all of that flat, I pull the breather over the rails and tape it in several locations.

Slide that whole mess into a bag and as it is pulling a vacuum, I gather up the excess bagging material on the side OPPOSITE the side I am bagging. I use some clothespins to hold the excess while the pump is working. I also work the wrinkles out and pull out and loose parts of the bag along the rails. Easy!

Actually, it's not quite as hard as I've described it, but it takes a few tries to get it wired.

Ok SD Thanks for all the great info, but more ??????????
What do you use for bags and what do I need a special releasing agent?

No problem Kona, I enjoy seeing folks learn this technique - hopefully you'll learn new things and share with me, too!

I use a 36" bagging tube that is made of nylon. My major source of consumable supplies is ACP Composites just down the freeway in Livermore. Their website is http://www.acp-composites.com

The tubes are sealed on two sides and I use their quick-lock seals to seal up both ends of the tube. At 36" I can slide my board AND a rocker bed into the tube which allows me to also bag flat pieces of EPS into a desired rocker.
Picture of the seal and tube:



Nylon and polyethelene won't stick to epoxy, so you don't need any special release agent or film while you are building the blank itself, that is to say before the final external lamination.

For the final lamination, which would be BEFORE a hotcoat, I like to use a perforated peel ply. The peel plies are typically made from nylon or have a teflon coating so they won't stick to your cured resin, either. I like to extract any excess resin at this stage and so the perforations allow this excess resin to bleed through to the breather where it is absorbed.

Awesome thanks again SD I think I will start to amass what I need now and get ready to build and bag. I am sure there will be more ?'s on the way ?
I found a medical pump capable of 30 hg for $59 what do you think?

That's a serious pump. In our compsand builds, 7-8 inches is enough to conform skins to a low density EPS core. 12 to 15 inches will deform 1 pound EPS pretty significantly (read: crush to a crispy pizza crust thickness ).

The pressure isn't as significant as the CFM rating. My little pump takes forever to evacuate a bag, something with a higher CFM rating would move the air out quicker, and would be welcomed.

20 inches is adequate and the HIGHEST CFM you can find. Don't forget your vacuum switch...I prefer that my pump cycle on and off, rather than run continuously - saving the motor. An adjustable vacuum switch is worth the investment.

What it looks like bagging the deck lamination

Jeff i try to not handle the bag that much in fear of getting holes in it and running the pump , its a bitch when that happens and when i bring it inside cause its too cold in the garage to put a heating blanket over it to warm it up , the running pump makes me want to pull my hair out of my head

I found these guys yesterday the complete DIY shop
http://www.veneersupplies.com/vacuum_press.php

Thanks for for the info SD. Thanks for the input Mark any more info would be helpfull.

Sd have uever used balsa or bamboo. In the vids you linked to it looks like Greg lams the bamboo before putting it on the board ???

wow, great site Kona
Jeff , would you use the PSA backing plys and maybe try one of their bags that may not leak.???

Kona! WTH?! are you being a smartass? I thought you were a friend!!!! Just busting your chops buddy. I hate e.balsa, I did a balsa compsand last year that almost killed me. The wood is gorgeous, but such a PITA to work with. The build thread, I beleive is here

Long story short, my original order of foam got lost in Oakland, the place I ordered the e.Balsa from burned down before they shipped my order...if it COULD go wrong, it did with that build.

Picture before final lamination:

I see that Greg L is lam'ing before attaching the skins. Bert Burger of Sunnova is the father of that concept. He basically creates a stock skin, by infusing the deck balsa with a layer of glass top and bottom. His epoxy is thinned to allow penetration through the balsa and he basically cooks it in an autoclave device.

The theory is that the deck of the board carries all the weight and so needs to be super light, but super stiff.

Inland's use this concept also. They place an aussie pine laminate, which I believe is somewhere between .3 and .6 mm on the top and bottom of the core, then infuse it.

There is a pretty significant history of this sort of construction. The really thin laminate, when it is infused, is super strong, light and "twangy". But timber is different than bamboo which is grass. Also, a bagged fiberglass layer is significantly different than the infused timber as done by IS and Sunnova.

I saw yesterday that Greg L has a huge vested interest in his Timber Flex technology. He alluded to "teasing" folks with his Timberflex 1.0 technology giving that awy for free and that there is already a TF 2.0 and 3.0 but that he intends to SELL that tech. He has been talking down all of the other tech, sort of indicating that the ONLY tech that is useful is the TF. Which really turned me off to what he was trying to say.

Hey Mark...have you seen the prices on those bags? There are some in the $200 range! What I found is that there is some stretch with each pull and they don't recover...they aren't quite as permamnet as they claim them to be. For pressing wood laminates around a surface I think that's probably ok, but when we do external lam's we need that stretch to get rid of the wrinkles. Those bags are only good for 1 or 2 pulls, and then they lose their stretch, IMO.

As I noted above, I'm not a big fan of those wood laminates unless you can infuse them. They look cool, but unless they are going to enhance performance I'm really not interested. Josh Dowling out of Australia is using Pawolina skin laminates that are absolutely gorgeous:

http:\www.joshdowlingshape.com

Jeff , do you have any info on infusion pocess and supplies??

Hey Mark,

Airtech is probably the leading supplier of bagging and infusion products. They have a small site www.resininfusion.com It's mostly
just to sell product.

Gurit has a simple presentation, but it gives a good overview:

http://www.composites.com/seminar/presentations/09%20Gurit-SP%20Resin%20Infusion.pdf

Fiberglast has the most in-depth discussion available for free:

http://www.fibreglast.com/documents/361.pdf

In a nut shell, infusion is vacuum bagging, but rather than placing your laminate stack in the bag wet, it's dry. You arrange the layers,
pull a vacuum and then when you are satisfied, there is a tube from the bag leading to a valve that leads to a resin bucket. Open the valve and the vacuum draws the resin up from the bucket to saturate your laminate. Besides eliminating some VOC's it can allow precise
metering of resin and fabric ratios...or like Sunnova you can completely saturate what is basically a substrate.

The one thing to remember for our purposes is that infusion takes a HUGE amount of vacuum. Resins aren't thin like water, so drawing them up a tube against gravity takes some HG's...typically large enough to crush low density EPS.

Hope that helps!

Ok SD I am convinced that the cpa thing is just a front. Secretly you are EX NASA composites/ guy with ties to all sorts of top secret info. Did you invebt velcro .hehehehe
great work. I was thinking of bamboo for purely looks.

I think i may try this process , i saw some on utube and seems to give you a better product right out of the bag in less time . I thought that IS uses a 1 lb. core on their boards. I dont mind spending $ on tools as long as it saves me time, that no one seems to have anymore of. What type of epoxy to use off just thin with 91% alky

Yeah that's me - Ex-NASA composites engineer - shhhhhhhhhhhhhhhhhh

IS uses a mold, different process. The mold itself limits the forces on the part. I honestly don't know what density foam IS uses. I've heard folks indicate that it's white beaded, so I would presume it's EPS. Cobra blows their own foam and they use a ton of 1 pound or less in their NSP and Surftech construction, so I would assume that is what they use in the IS construction.

Infusion, by and of itself, doesn't offer a better finsihed product. It allows you more time to arrange your laminate stack...but a slow setting epoxy would afford that also. If you can't get a good external lam with a bag using slow hardener, infusion isn't going to help that.

The setup and cost of infusion drastically adds to the final cost of production. For surfboards, without a mold, I wouldn't think you'd want to be looking for a finished board out of the bag. Molding can afford that, but what you attempt to achieve with infusion is a rather dry laminate ready for a hotcoat.

Excess resin doesn't distribute evenly with infusion, as you'd want with a finished product, it gets pulled to the exit port(s) creating a pool in that area. OR is absorbed into the breather.

To get a glossy finish on a board, you want a resin rich wet layup and then something like mylar pressed on to that...the key being resin rich, which is typically only available with a wet layup. Look in the RC airplane forums they do a ton of bagged wings and do artwork on mylar then bag that over the wing skin - gives a glossy finish AND transfers the artwork.

The IS boards are seriously labor intensive. They layup the mold, but after that the boards are painted and polished. Hands down best finish of any wakesurf on the market, but also probably the most labor intensive construction too.

Molding can give you finished results. You apply your finish to the mold surface (paint or gelcoat like with boats) and then mold the laminates and core. All that's left is elimination of the flashing...if you look closely at some of the skimmers on the market, they just trim flush and don't make much effort to polish the flash/part line.

My 2 cents

Sorry Mark I didn't see your question about resin...there are infusion specific resins. Airtech (site listed above) offers things like Infusion tech LM 100A - the viscosity is such that it aids in being drawn up the tube.

Thinning with a solvent drastically effects the final structural integrity of the epoxy. Epoxy is a medium soft pastic, thinning it tends to make it a super soft plastic. Polyester is a soft plastic to start with thinned it's just junk.

HEAT will thin epoxy without affecting structural integrity and I do believe that many of the infusion resins work in that way.

Is it time to do a molding project? I'm going to have to dig out my supplies and see if I can do one.

Damb , well if i can lam both sides at one time and get a dry finish then i wont mind the hot coat. I just dont know if the epoxy that is to be used will not turn yellow after time in the sun.??

Yeah, most epoxy has that natural amber color and without a UV additive will turn yellow. I'm not aware of any of the infusion resins that come with a UV inhibitor - there may be some.

I would think you could do 100% of the external lam in a bag. You'll still have a flashing issue at the bottom of the rail, but it should clean up ok.

Try this:

1) Wet deck lam, lap bottom
2) Wet bottom lam, lap top
3) Wet deck lam second layer, lap bottom
4) Cover deck and bottom with wide mylar sheet (trimmed beforehand)
5) Tape the mylar to prevent moving.
6) Slide the mess into a FRESH bag
7) Flatten the excess bag onto the sides by the rail
8) Pull a vac and smooth wrinkles as you go.

I would think that process should net you an almost finished product out of the bag...the trick will be the rails/laps.

when using the mylar i have gotton a wavy surface ( like pressure dents) after removal of the mylar , some boards came out straight and others were wavy or with pressure dents . i know my cores are straight because of cnc hotwire process. i wonder if its a vac. psi issue . using 12/15 " psi

tent set up

Yeah, it's too much vac - back it down to 5-7 (if your pump will mange that low)...the wavy will disappear. You just want to keep the laminate pressed up against the foam. 12-15 is about 6 or so PSI - what is that over the board 4,000 pounds?

so 10 " of psi will be ok then , i bought the ACP PUMP set up . i just spoke with Jimmy at green room in N.C. about making me some resin that will flow for a VIP system and he said i can come up to see him lam some boards , he will be at the surf expo in jan, and so will Debra and myself.

my bad i thought it said back it down 5-7 . use 5-7 psi on the process

Jeff , i have not had a problem with mylar moving after installed on lam after wetout ,it sticks to the epoxy like glue.

Yeah once the mylar is on the wetted surface it's pretty good...what I always have trouble with is when I stick it in the bag, I'll hang an edge or something and rip a lap free...if I tape it, just to be sure, it stays while I wrestle it into the bag.

Keep us posted on what you see in Jimmy's shop. That would be awesome.

You're using 3 pound? I would think anything 10 HG or below will NOT squish your foam, and give you a good lam. You can do a quick test. Get a sandwich bag - one of those with a resealable closure. Punch a hole for your connector and toss a scrap of your foam in there. Set you vac switch for 10 HG and see what happens. The easiest way to test the crush point for any foam is to set it for 7, then every hour check it for deformation and increased 1 HG.

great stuff guys soaking it up

(Message edited by konaking on December 10, 2008)

Jeff
see pic above, this is how i set up my bag as a tent , tape bottom to table and run string for top like a old school tent with open sides , your product just slips right in with no mess on your clothes or forearms

Mark we need bigger pics. Thats just being a kid a setting a blanket up as a tent. Ha ha

Mark - cool idea! Thanks for sharing it.

sorry about the small pic , grabbed it off of myspace , and kona i have some xtrak traction-longbow for sale on my site just google lakewakes. Jeff i will adjust the psi to finish all 5 boards this weekend i ran out of bags and bought some fast resin to speed things up

what about fin box install? I am assuming you route th em in after bagging

I've done them both ways. I was talking with Mike Daniels of Coil about installing the small C-5's for a canard installation and they do all of their boxes in the bag. I've found grinding the lip flush before pushing it into foam and laminating in the bag is helpful, but really only necessary if you are using a rocker table without cutout for the box lips.

If your shape isn't dependent on a rocker table, you can lam with the bag just like you would do by hand.

I will have to cut out the mylar for fin boxes to stick out so no air gets trapped under the mylar

Jeff ,
coil seems to have a great concept on their stringerless shapes , DO they just VB or do they VIP, I wonder what their lam sched. is ? and if they try to get a dry finish after lam then put a thin hot coat to smooth in the voids. i would think they use no more than 1.5 lb. of eps

Hey Mark,

The folks at Coil are pretty secretive of their process. There is a thread over at Sway's that has some interesting details, but it also tends to cause as many questions as it answers:

http://www.swaylocks.com/forum/gforum.cgi?post=342296;search_string=coil%20infusion;#342296

Some highlights that can lead to an educated guess.

Mike responds to Silly by saying:

Hey silly,

If you're only doing one layer on a cored skin exterior laminate, bagging or infusion isn't going to give you much benefit. We're doing
multiple layers of different ''weaves'' and the benefit is substantial.

Our finished weights come out almost exactly the same, we just have different ways of getting there. As I've said before, there's lots of ways to build a surfboard, they're all fun...


Mike


In that same thread, further down, Mike makes this statement:

On weight -- we can do mid 3's (no fins) straight outta the bag, but the finish is different from anything you've ever seen. A finish layer gets 'em nice and smooth and more importantly tunes the edges.

Combine that statement with this - again further into the thread:

The boards are bright white because of a lack of excess resin in the lamination, there is no pigment involved. What you're seeing is the EPS blank, which is very white. Check the volume # on your friend's board (between the fins) and I can compare that board's bouyancy to yours.

Mike makes reference to the volume of the board being critical. In a few pictures of the boards there are notations of the volume being recorded on the boards. Many of the shaping programs available will give that metric, I think that Matt S demonstrated that on one of his boards and the demo of AKU? Can't remember now.

This quote from Mike, is representative:

Yours is .65 cubic feet, so that should be about right (you said your friend's was a little big for you). The volume measuring really becomes valuable once we establish a frame of reference.

On the Coil website, there is a picture of Kirk, with a blank to the left with the telltale pukas being ripped out after rough shaping which would indicated to me, it's 1 pound or less, EPS

Their website indicates that the fiber/resin ratio is 2x to 3x that of a PUPE board. Polyester is weaker than Epoxy and typically ratios are 2:1 Polyester to Fiberglass.

So the ratio would then be 2:3 to 1:1 if those were accurate. It's not unheard of in the aerospace composites industry to get to 40:60 or 2:3 resin:fabric.

That would certainly produce a dry laminate and the bright white look described above.

Trying to back into the laminate schedule, Mike indicated that the finished board out of the bag was 3.5 pounds, I am presuming that is BEFORE a finish coat, so it's just the board, boxes and lamination. Assuming the boxes weigh in at 4 oz and the 1 pound blank is around 12 or so ounces, the lamination would be:

Total weight 3.5 x 16 = 56
Less Boxes -4
Less Blank weight -12

Resin and fabric weigh 40 oz.

If we go with the super light resin 2:3 ratio that would give the fabric content as:

(40 oz / (2 + 3 resin + fabric) ) x 3 just fabric content = 24 oz of fabric. If the laminate was balanced, you could have 3 layers of 4 oz top and bottom, assuming that you'd need 1 square yard to cover a typical board per layer. Alternatively 2 layers of 6 oz. I almost wonder if it is 4 layers of 4 oz top and 2 layers of 4 oz bottom, all of the layers laid up on a bias in some fashion.

NOW, there is some speculation that they are using a sleeve/sock and if that is the case, it's balance top and bottom double 6 or triple 4.

So...anyway...that's my educated guess.

Forgot the VIP or Bag question...I don't believe they are infused. 1 pound foam sucks resin like a sponge and I don't believe you could seal it effectively enough to prevent intrusion of resin into the core on that first layer of fabric using infusion. It would also detract from the amount of fabric available. I believe they are carefully metering the resin and fabric ratio on a wetout table, then bagging, no doubt with a perf-ply and bleeder.

I had to post two pictures of that carbon/spectra prototype:

Jeff, About time you woke up. Coil must use 60" wide fabric to make the bias. What board worked better for you the surftech or the compsand??. I can get my hotwire guy to cut out 1 lb. core with 3 lb. rails that would fit perfect together and use carbon like you for the stringers. I hate the pukas

Hey Mark, I had to post this first:

There is an interesting dialog over at Sway's regarding compsands. You need to have sort of an understanding of the players involved, in
particular OTAY is presumed by many to be Randy French. He is outwardly supportive of Surftech, it's processes and is exceptionally knowledgable. His online persona is also exceptionally toxic.


Paul Cannon of Compsand.com

re. the new stuff, its all gunna get out eventually


OTAY (presumed by many to be Randy French, one time owner of Surftech)

The new stuff isn't getting out any faster than it did 30 years ago. If you keep on making nice boards like that quad fish pu/rr
(new saying alert by OTAY....Polyurethane foam and Resin Research epoxy= PURR) there is no reason to change. The shape is the jewel. The construction method adds durability and alleged performance. But looking at the pros this season in Hawaii are mostly on PUPE's. Whaddup with that???


Greg Loehr of Resin Research and long time shaper

Pretty simple here. Flex has to do with a combination of materials and geometry of shape. You use stiffer materials you balance that with a change in the geometry. Simple as that. In the late 80's we wanted to make the boards thinner so performance was enhanced. We made the boards thinner and they began to break. So we changed the geometry (crown decks) so we could leave more thickness at the stringer and the crown also stiffened the shape (a curved piece of fiberglass is stiffer than a flat piece). This geometry allowed a crappy tech (pupe) to hold the boards together well enough that we could continue selling this sh(expletive deleted).

So now we have compsand, whether it's TL2 or FW or TF or ....... We have an oppritunity to enhance the boards ride because this tech will allow us to concentrate on the shapes that are superior without breaking down. The way to increase the flex is to change the geometry. How? Flatter decks and thinner boards. No one in compsand has picked up on this yet. It's not like we didn't try these shapes back in the late 80's early 90's. They rode better. But when you have team guys breaking 50 boards a year you have to make some compromises and I did and in the end so did everyone else.

The crown deck was a compomise. It DID NOT enhance the ride. It was put in there to hold the things together ... PERIOD! So WTF are we making compsands for that have the same shape as a poopee??? Think about it. If compsand is to really make it into mainstream we need to go where they can't. The reason the pro's are riding poopee shapes is because we're not making the most of our tech. If shape is still the deal and we don't conceptualize something better then we deserve to fail.

Of all of the shapes/constrution we've messed with, the surftech is the highest performing. It doesn't have all the features built in to the board that James' TWP board has, but generates the same speed and air, and is two pounds lighter. I think fully shaped and it will be the best performing.

Balsa compsands...I hate wood...it would take some playing with the wood's thickness to make it work, I do believe. Wood is pretty stiff, e.balsa sucks water like a super dry sponge and getting all of that worked out would surely drive me insane.

I like foam though. So take that into consideration, I am an admitted hater of wood.

If you look at some of the board we use behind the boat - P5, now defunct Walzer, Calibrated, Triple X skimmers, ALL of the IS's...those boards are flat as a pancake deck and bottom.

The original Calibrated's didn't even have any rail work - just right angles.

I can remember a brief conversation with Jerry Price of Shred Stixx - he has a ton of shaping knowledge and he was reflecting on the fact that boards like the P5 have no real volume to them.

I wonder what a 1" thick composite sandwich rides like behind the boat? Flat deck, concave bottom, 3 pounds with fins and traction and still rugged.

and can you ride a board that light , my 4.8 quads weight is 5 lb. less fins, i know the prototype 2 will be lighter cause of a thruster set up and VBing. I saw the Vid of the Coil board being stepped on then sprung back as foot is removed. I would like to try a Coil build at 1.5 lb. with 3 lb. fin box supports at 1" thick with 4oz.sglass 4x3

I've done a little testing of the structure and it's doable. The surftech flame board we built was 4lb 3oz with fins AND traction, 3 something naked. I believe it's doable.

Sounds like a cool build! Post up what you learn.

Sorry no pics , to get air bubbles out of epoxy i use and old jar with screw on top , then drill hole in top to install fitting then hook up Vpump and vac down to at least 18" and see the bubbles go away , let vac for about 5 min.. I use green room epoxy and doing this for the hotcoat gives you a smooth glass like finish without bubbles or fisheyes.

Cool - so you vacuum the resin to remove the bubbles from the mixing process. When you spread the resin on for a hoat coat, there is no re-introduction of bubbles? That's a cool idea. Also, are you cleaning up the jar of the residual resin by using acetone or something?
Thanks for sharing that.

no bubbles in hot coat with GR epoxy , and no i get as much of the epoxy out of the jar and clean the threads and lid with a paper towel. any left over epoxy gets hard by the next application.

Kona,
i like to use a equal mix of fast and slow hardener to get 45 min. of work time , so you can take your time to get things right . after you get it in the bag and all ready then cover it with a heated blanket on HI and another heavy blanket and in 2 hours after you have bagged you can remove it and start to hot coat of lam the other side.