Building foam core hulls with Female frame Jig

In regards to building with Divinicell core within a female frame jig (rounded chinned hull designs), would it not be possible to score through up to 70% of the thickness longitudinally … Instead of cutting the foam in narrow strips and routing all the edges with the subsequent loss of material.

Similar to what was done on some of the panels of the hard chine F12 Kiwi design, but with much more precision… (in the raw foam, not foam that has already has been glassed) using a fence and narrow blade in a circular saw where you can regulate the exact depth and width of the cut rather than just free handing it with a 4" grinder. One could also make similar cuts on the horizontal plane at the bow (although the cuts might not need to be as deep)where a compound curve is encountered. The spacing of the cuts could be tailored to the particular hull shape, instead of either going with the strip/rout method or to the factory cut contour panels with the scrim backing, which would be too flexible when used within a female jig frame.

Would it not offer a savings of both time and material?…H 80 Divinicell isn’t cheap @ $100.00 US a sheet, and over the course of 14’+ cat you could end up with 2/3 rds-to a full 4’X 8’ sheet of foam on the floor in the form of dust. Depending of course on the width of the strips cut, the width of the saw cut, and the amount of loss when you rout the male and female radius on the edges. My 12” table saw takes 3/16” of material per pass, loose another 3/16” from the routing process on the concave side (1/2 the 3/8” radius) I would loose 3/8” of material for each cut. For sake of argument say the strips are 2" in width...you would lose about 8" of width out of a 48" out of every sheet...or get 20 strips instead of 24 strips per sheet. In the course of 6 sheets you would lose a complete sheet to just cuts and routing.

Based on using 3/8”X 4' X 8' plain Divinicell sheets and ripping it into strips and doing the cove routing method. H-80 Divinicell 3/8" thick, each sheet is $100 US at this point in time...and that is 1/2 of the list retail price.

I am referring to the build method they used for the LR2/LR3 which is quite ingenious, but can’t resist the possibility of tweaking it to make a more efficient use of materials

Has this been tried with cat hulls in a female frame jig? I have used this technique before when vacuum bagging a 6mm Divinicell deck over EPS core on sailboards. I put relief cuts parallel to the rail where the core was too stiff to follow the rail curve. The vacuum could not exert enough pressure to pull down the Divinicell tight to the EPS core (due to the small radius on boxy rails) without the relief cuts.

You are describing the "Kelsall Swiftbuild System", later revamped to "Kelsall Infusion Swiftbuild System" I think. Look up Derek Kelsall and his building ideas. The system works, but at a small scale I dont think it matter that much. Better to use a tested method and get the boat out of the shop. That from a person two years into a boatbuilding project..

Thanks Rolf
I see a few similarities, but also quite a few differences...what I want to do is much closer to what was done on the LR2 & LR3
1) Make up the hull in "naked" foam first in a female open frame wood jig.
2) Glass the inner skin while nested in female jig.
3) Join both left and right halves (they did top and bottom)
4) Glass the outer skin.
5) Fair and finish.

In essence I want to use a very similar method to John Lindahl but without cutting a couple hundred strips and routing the edges of them if possible. After visiting the “Kelsall Swiftbuild System” website it seems their build system is quite different in approach to both John’s method and what to what I am proposing.

Kelsall glass the panel before cutting the "darts", and he dont use a mould. Otherwise the idea seems pretty similar.

For a small boat I would not bother. Cost of material lost in cutting when using a proven technique is a really small percentage of the whole project. Payoff is that the technique is proven so you know what you get. If your proposed method fails, you have lost a lot of materials. You will probably also have to do some testing to verify before comitting which is also lost materials.

I think you should go for it even if I argue against. It sounds like you want to try this so you will probably not be at ease before you have tried it.

The amount of material "lost" when cutting strips and doing the cove and beading is minimal. What is gained is the ability to accurately build to the female frame. You can minimize waste and speed the build process by cutting strips in different widths dependent on the hull curves. I had three different widths on the LR2 and two widths on the LR3. I would be very hesitant to use flat sheet darting due to the compound curves in the hull shape.

Rolf & John
I appreciate your input. After considering your comments... viewed in relation to the over all project costs of materials and labor... $100 for an extra sheet of divinicell might be considered a bargain.

John...I understand each individual hull will call for differnt strip widths, but just as a point of reference, what were the three widths you were able to use to achieve a fair hull on the LR2/LR3 without getting a "knuckle" effect at the joints.

Best regards,
Bob

Details of building at: http://groups.yahoo.com/group/LR2ACATS/
I cut foam strips 1"to 2" wide, depending on the hull shape. Determining factor was that I did not want any more than 1/16" gap between the foam and a frame. That 1/16" was for one layer of 5.8 oz. carbon, fairing bog, and paint. It also made fairing the outside of hull easy with minimal sanding on the bead-cove joint to get the hull fair.

If you're so concerned with loss of material just use a very thin Blade on the table saw, wood and alu discs are bet. 2-3.5mm thick, however there are special discs with thickness from 0.5-1.5mm. Foam doesn't need lots of torque to be cut unlike Al or wood, it doesn't squeeze the disc like wood does, you can also make a jig and cut it with a utility knife, that is what 0.3mm ?

regards

Florin
My table saw is 12" with a 64 tooth carbide tip blade...it's a beast...your trying to pry my wallet open again to buy a plywood blade with little "set"LOL...12" blades are not the $6- $10 a pop price of a 8" circular saw blade.

I have cut plenty of divinicell (up to 1-1/2" H130) with carbide tooth blades without problem but would be a little concerned about a saw blade with too little set...the slightest pause in forward progression thru the saw might melt the foams surface...as it has a fairly low heat distortion temperature.
3/8" = 9.52mm

John
Thanks for the info on strip width...I have been following you on the Yahoo LR2ACAT group for quite a while...I combed thru all your build information there, but didn't pick up the 1/16" gap criteria. Excellent piece of information.

Regards,
Bob

12" is not cheap indeed, don't know the price for it - but there are some smaller diameter solid carbide discs used in metalworking and model making, will try to find a price. If you have plenty of speed you can go smaller on the diameter. Not trying to open your wallet, just exploring alternatives.
Something like this:
http://cgi.ebay.com/80x0-8x22-SOLID...main_0?hash=item27ac4291fb#ht_500wt_1100

http://cgi.ebay.com/Solid-Carbide-S...main_0?hash=item439aafd80f#ht_500wt_1100

Another thing: if you're worried about melting and you have an air compressor - just set up a jig where a nozzle sprays air directly on the blade at the cutting tip - works great, cnc-ers cool their tools that way while milling Alu and steel.
regards

Isvflorin
I appreciate your help but something is getting lost in the conversion from inches to mm...LOL The first item on your list is 3-1/8 in diameter or 80mm and the second item is 2-3/4" Diameter or 70mm. My saw takes a 12" diameter blade which is 304.8 mm

I might have an old fine tooth plywood saw blade laying around some where...I just threw out a stack of old blades after holding on to them for over 10 years...isn't that always the case...LOL

Interesting note about using the air compressor to cool the blade...here in Florida we are having insane humidity, even with an elaborate water filter separator on my compressor it would almost be like "misting" the blade rather than blowing air on it...

I am a building contractor without a project going on at the moment so I was trying to make good use of down time with tools I already have at hand.

As long as the tool can tolerate moisture water don't worry about it, you can even water cool it as long as the tool has drainage, then just let the foam dry for a while. It is closed cell won't absorb water, just a tiny bit in the cells that get smashed, but easy to dry out. Also foam manufacturers recommend storing the foam after any kind of processing for a while, or at least not glass it immediately after cutting, even the non outgassing foams do outgass a tiny fraction from smashed cells due to cutting, heating or storing the foam for a while takes care of this issue. Same thing goes to sanding it - don't glass immediately after sanding, from what I've read corecell is one of the most stable regarding outgassing - being advertised as non outgassing foam (the SAN one), but PVC's do have some outgassing going on from processing like cutting and sanding. Baltek has very specific info for their Airex foam and issues with processing&outgassing - the C70 Airex.

If you will be cutting a LOT of foam I think the best approach would be to build a dedicated tool for it with very thin blade and indeed smaller diam. Long bed to accomodate sheet, solide fence, fingerboard, a jig to keep pressure on the foam to keep it on the table - and cooling of the blade - but only for lots of cuts of course. A smaller diameter disc will require lots of rpms but not much power for foam, ideal motor for this will be an RC motor running on 24V , they have speed controllers, at 24V you will get about 25-40000rpm from common rc motors, plenty of amperage and torque for cutting just foam.
This is just ideeas, don't get me wrong, it is always best to manage with the tools at hand. But if I had to (for example) cut foam for a 30' trimaran I would have a dedicated tool for foam cutting. Cutting foam with a 12" blade tungsten carbide teeth is like carrying groceries with a 40ton truck IMHO.
Anyway best of luck with your project and don't be shy on posting pics.

regards

Ok - so I haven't read this whole thread but is there a reason for not using the vertical foam strip method?

Forget about the heat gun stuff- just make a heat box with a fan heater ($20) or heat lamps and some ply.
Slide foam in for 2 or 3 mins pull out and bend into place then pull out the next bit of foam.
Lots of Farrier Tri builders use this method with great success.
If this is no good - have I missed something?

Regards,
Phill

I used 9mm Corecell and screwed 3 sheets together to rip to width. Blade was an old thin kerf B&D Piranha. Put an 8' fence on my radial arm saw. Foam was 8' long on LR2 and 4' long on LR3. 4 footers were much easier to handle and store and install. No heat issues when ripping.

Picture of my reverse engineering...LOL

I originally intended to make a full female mold but liked the one off/strip method better for my application... so a change of course.

Since I already shaped the full sized plug I just took 3mm ply templates @ 12" on Center off of one side and then transferring them to 1/2" and 3/4" ply (using up whatever scraps I have which are suitable) for the actual female jig frames.

I spaced my frames 6" apart. The reason was so that when you start squeeging resin out of the inner skin of carbon you don't push the foam out of shape. To get a good laminate you need to put some pressure on the squeege. Even though the bead and cove joints are glued together the foam is still very pliable prior to adding the inner skin. You should be looking for a 50-50 weight ratio of carbon to resin.

John
Thanks for the tips…
My project is a F14 hull 4.3m long (14’-1 5/16”). I would have loved to use carbon for the inner and outer skin but because of budgetary restraints I have purchased Kevlar for the inner skin and S2 glass for the outer skin. My hope is to have it similar to weight to an A cat hull but have it able to take a bit more off/on the water punishment. As I said in the above post I had originally intended to do a full female mold as I prefer to Vacuum bag Kevlar over traditional hand lay up, hopefully I won’t have too high a resin to fiber ratio…I remember from past use that Kevlar has a tendency to “float” when it’s not bagged down.

I did pick up on the fact on the LR2/LR3 site that you spaced your frames on 6” centers, and I was concerned about spacing them 12” on center… but then I saw that Racer-X’s blog where he was using your build method but spaced his out to 14”on center with what he said was no ill effect.

I hear what you are saying about squeegeing out the inner skin with too little support…but correct me if I am wrong…the foam will deform when pressure is applied but it will spring back to shape when the squeegee pressure is released. My idea would be to wet it out from the back (foam) and the front…use moderate squeegee pressure to insure complete wet out and then go back and using a light touch, squeegee any wrinkles out that might have been created by the foam deflecting under the initial squeegee pressure.

Unfortunately, I don’t have the luxury of having the frames cut by CNC…each one was scribed, cut and fitted painstakingly by hand with 3mm ply and then transferred over to 1/2'” and/or ¾” ply for the actual frame… which was also cut, sanded and checked for fit to insure accuracy. I just finished the creation of all the actual jig frame/stations yesterday and while I have anticipated adding a few extra frames at the bow where the curve is the most sensitive “if it proves necessary”, I was hoping not to have to go threw the whole process with an additional 28 individual pieces. It’s like being a kid in school and all week you think you are going to get out at noon time on Friday…as you sit there anticipating it for the last moments your teacher tells you at 11:45am that you are going to have to stay the whole day…LOL

Whether or not the fact that my hulls will be split on the centerline, rather than a top and bottom half, may diminish the effect (easier access to all areas of the laminate) or exacerbate it (less curve in the part being glassed) would not be revealed until I get to that point in the process.

Thank you again for your insight and your generosity in sharing your experience.

Best Regards,
Bob

Latest photos of the female jig progress. Original plug in the background.

Phill if it were a larger hull without so many small radiuses I would have considered the vertical foam strip method...it seems that for the shape I am trying to reproduce in a female jig, the longitudinal strip method would give me a fairer hull especially since I have my frames 12" on center and there are no horizontal battens.

Best regards,
Bob

I have just started cutting Corecell foam and polystyrene trial foam for foils with a 0.0012 inch 7-stranded stainless steel wire hotwire system. The resulting kerf is really thin.
Why use a saw?

dacarls
I don't know about corecell...I will be using divinicell...used to do this stuff for a living and spent a lot of time interacting with the factory reps, the big honchos from Europe. They came over for technical support in regard to a large scale project we were doing using their product.

They told us to not use hot wire techniques as the resulting fumes were very toxic. If I had a powerful enough blower system I might give it a chance...it sure would make the material loss a moot point. However I get a headache just thinking back on the one time I did try it in the past...it doesn't cut fast like EPS and the smoke it nauseating...even with a dual cartridge respirator on...and that was just 6 mm H80.

Hard at work today putting the backing on the frame Jig...here is some more pictures....

(Reposted from the F-14 Forum)...To take advantage of the most recent design trends I did a total revamp of my F14 design.
Including:
1) Broadening the hull from 9-1/2" to 14" wide
2) Completely changed the section shape
3) Add slightly more rocker profile

Almost finished with rebuilding the jig...here is the Starboard side Jig roughly completed…


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A little bit of progress...bulkheads on hull # 1 fitted almost ready to glass in place.

I want to a blind bond the two hull half's together without cutting the deck out. So not only did I build up a flange around the entire hull perimeter but also on both sides of each bulkhead which are to be spliced down the center line. This might be common knowledge or maybe not...thought I would share as it seems to be one method to get a decent bond. Those bulkheads are already glassed with 5 layers of 2.3 oz glass even though only the two layers of 2”, 7oz tape shows.



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From the stern looking forward.



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I like what you are doing there. I'm trying to figure out how to build the frames / jig for my AMA's. I'd like to take a firsthand look at it since you just up in Fort Pierce about an hour from my house. Could that be arranged?

Let me know next time you are heading up this way....

Seeker-
How's the build going? Thanks for the updates.

Nacra5.8NA1386...things have come to a screeching halt for the time being...wife's job at the space center vaporized and the construction industry is on its back like a "sprayed roach" so all my time is directed in other more essential areas...but I will get back to the F14 as soon as possible...its always nice to have something to look forward to....thanks for asking.

Best Regards,
Robert

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