Laying core on a flared or carolina bow

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#1

just do not see how can a foam core sheet be adapted to the double curvature surface of a flared bow boat mould, for resin infusion, not even using double cut on both sides of the core, and if the core is completely cut it would still have quite widely open gaps that will saturate with resin, if the core has some spring back tendency then there will be a tendency to leave voids that would be filled with resin when infused, so IMO the core should lay perfectly adapted to the shape underneath it when everything is laid down dry, something I just dont´t see happening.

Adapting it heating the core sheets in an oven and then adapting them while still hot is the only way I have found searching the web, but it seems to be a quite cumbersome job, is it there a clear guranteed way how is this done?

The bow section of our mould has a quite severe compound surface, and if we dont find a solution we might be forced to avoid coring the bow area …

#2

Using scrim cloth foam is fairly simple on these kind of curves. Not in large sheets, but in strips (30cm wide or so)

Another option is the use of Soric, which is 3D formable (limited, but better than foams)

#3

hi Jigger. Use the same principle that you used to plank the bow of the plug with sheets of MDF. The “planks” of grid scored foam can be wider than the MDF planks. And they could run vertically. You could cut them on the CNC Router.

#4

Thanks Herman, ASB, I was thinking of doing it with strips as you suggest but much I am afraid that the strips would have to be narrower than 30 cm, maybe even just 10 cm if they are to lay relatively flat on the curved surface and without too big gaps in between the strips, on the other hand soric may not have the necessary thickness (and several layers may be needed) and it might become a heavy solution if the material gets soaked in resin. Still it seems to me the most doable way, since glueing a lot of narrow vertical strips of foam core with just a bit of spray adhesive does not sound very good to me, the result may end up being messy, I will make some tests with both ways and see

#5

Jigger,

What about using strips of double cut foam, around 200-300mm wide, run vertically?

I use a single part, moisture cure, foaming polyurethane adhesive from a calking gun, to glue the edges of foam sheets together before infusing so that there is no chance of racetracking between the foam edges. I hold them in place whilst this glue cures (3 hours) using staples from a staple gun. If you use raptor composite staples you can leave them in permanently - otherwise you can pull them out before laying the laminate stack over it after about an hour in warm conditions.

Use a little spray tack - i like the airtech stuff, works great - and hold the strips down with it at the same time onto the tool side laminate. - It has surprisingly good holding power.

You might have to experiment with the width of the strips so not too much force is required to hold it down.

At the end of the day, a solid laminate might be easier and cheaper as the core material is expensive anyway. Youd have to look at a stiffening structure like a grid or stringers to keep it nice and stiff which adds more complexity and work later tho, also depends on what other structure your putting inside the boat up there. With alot of compound curvature, you may not need much in the way of stiffening either - youd have to test your layup schedule and see what stuffness you get, adjust the stiffeners accordingly to reduce the unsupported panel size.

BTW - how did the spreadsheet go for you? Works great doesnt it :slight_smile:

#6

CoreCork conforms well. Not many people know about it. Google it.

#7

Hi JIGGER, i wish i could get my molds to have that shine, what products/process are you using and lastly what release system

thanks

#8

Hi Goper, nice to hear from you again,:slight_smile: I will do as you say in regards to vertical strips, but stapling the foam will not be doable as the core will be inside the mould and has to lay dry and well adapted before infusing, but if we use single cut core ( on only one side but to the bottom of it) with a mesh, we believe it will not have any spring effect then.

Since our bow área is quite curved, we are worried about the foam leaving too many open gaps and this, might make for a heavy panel, neglecting the benefits of the sándwich construction.

On the other hand Lantor apparently makes some nice drapable materials that at the price of some extra weight ( wich might not be so much, if the absortion of resin of foams cores is considered), can be used in between layers of reinforcement to improve thickness and thus rigidity, those could be used and by the use of three layers of 6mm you will get the equivalent of a 18 mm core.

Since will son be making sveral tests and experimenting with those materials I will see what we do.

The problem is, that the laying of the reinforcements and core dry inside the mould before infusioón has to look and be nice and tidy for a quality product and I ahve my doubts about how nice will the core lay in the compound curved surfaces of our mould …

#9

HI Hansaullo, thanks for your advise, it could certainly be an option, but cork is a natural material, and in our área boats are kept at the sea for their entire life, and boaters tend to favor full composites construction, despite very likely being very suitable for the job.

I have seen a few pics in the net, (not many though) of the foams adapted but only in boats with bows flatter than ours, so I hope to solve it with narrower vertical strips, but the gaps of our cores will be quite open …and this I do not like …

#10

Hi Double, we used quite a few self made sanding tools, some made with eva foam some with harder 20 mm neoprene rubber sheet and some with thin Woods, we worked the surafces in four sanding directions with several down grading sand papers and wet sounded in this same manner up to grade 2000 this for the plug using duratec as sprayable sanding layers, then we sanded the moullds interior with 1500 (3M trizact sanding discs) and with 2000 and 3000 and then polish with 3M polishing compounds for fiberglass.

For the releases we use Zyvax products more precisely Zyvax#4 with their sealer, so far very easy and predictable products.

#11

Hi Jigger,thanks for the feedback, where i’m @ the finest paper they have is 2000 and i use the following 3M products [Perfect-It™ Rubbing Compound and Perfect-It Foam Polishing Pad Glaze], maybe i need to sanding in the 4 direction and see how it goes.

#12

The trick is to apply a coating which is thick enough, start with a coarse grit, to get things fair (in 4 directions), then work your way up the grit ladder (not skipping a grit). Use control powder, to see if you sanded enough (and not too much, great psyche helper).

#13

Hi Herman, what do you mean by control powder?

#14

I believe he is talking about a show coat. Basically you spray on, or apply in some cases a powder or paint. Then you sand until you cannot see the color anymore. 3M makes a carbon powder you rub on. Some people just use a cheap paint, or color dye.

#15

+1

I’m sure in the next few years cork will be used a lot more. It’s starting to get used in a lot of kayaks etc. Water doesn’t worry it as it does not soak it up. Also has a fantastic adhesion and does not de-lam like foams.
The cork it self doesn’t take up resin , but the little holes and voids create cylinders of resin joining the skins together for a near perfect bond from top to bottom of laminate.

Sorry for the hyjack :o

Tim

#16

In the automotive restoration business we refer to it in any form as a Guide-coat. Its removed with the next round of sanding to pinpoint any larger last grit marks before moving to the next finer grit.

#17

http://www.slimmerschuren.nl/flexicat-tools/mirka-schuurblokken/controlepoeder.html

Above a link to a guide coat.

#18

Hi all ! My experience comes from boat building by vacuum, not infusión. There was two ways to try it: a) using two or three layers of thin enough foam, which may be a mess by infusión. b) to make a puzzle as much accurate as posible in order to avoid big gaps. The secret is keeping the parts joined together by mean of staples or similar methods. Composite staples can be left on the laminate.

I don`t know a faster and simpler solution, sorry.

Keep an eye on gaps, owed to exotherms. Also remind to drill the foam each 100 mm aprox in order to let the air exit and avoid air pockets between foam and substrate.

#19

Hi, in regards to guide coats,I bough one wich looked the same as the product that Herman pointed out and I could not see any advantage to using it, it helped nothing, but maybe waht happened is that by the time we wanted to test it our plug was extremely fair already so the guide coat could show nothing, no highs or depths …, we tried to test it on a plug we made of a scaled down versión of our boat, some might enjoy taking a look to it:

#20

And back to the flared bow and laying the core stuff … we already ordered a box of 20 mm thick M80 Corecell CS and some Lantor products to test (more precisely Soric LRC, Soric XF and Soric TF plus some Lantor´s Finishmat D7760), I have to say that have been attended very politely by Mr Laurens Janssen at Lantor headquarters in Holland, we will then see if we manage to make the Corecell lay beautifully or not, I beleive that due to the very curved surfaces in our design the laying will not end up beautifully but messy instead, and that the unavoidable opened gaps in the precut core will absorb a lot of resin making then the theoric lighness of the Corecell core of 80 kilograms / cubic meter vanish and ending up with a much heavier core layer, wich may then get closer to the impregnated density (or specific weight)of the Lantor´s core materials wich in the case of Soric LRC is of 450 kg/cubic meter.

If that where the case, something we will know after our tests, we will then prefer to use Lantor´s core products instead of Corecell due to Lantor´s products being drapable and thus much easier to get good results with than with the undrapable and difficult to adapt nature of Corecell, we will post the results here for everyone to see …

If we finally end up with the intention of using Lantor´s core products, then there will be another reason to worry: does Lantor core products have the Shear strenght necessary to avoid delaminations?? we know Corecell certainly does and is even a bit elastic ensuring that delaminations due to shear forces will not occur but does for example the impregated Soric LRC have the same shear strenght ??? we do not know, maybe Herman as a Lantors representative in Holland can chime in and shed some light …