DE23 laminating 4x 9mm?

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wildbriz
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DE23 laminating 4x 9mm?

Post by wildbriz »

Hi from Perth Australia, I'm building a DE23 but currently can't get hold of reasonably priced 12mm, 15mm or 18mm marine plywood. Is it OK to laminate three layers of 9mm BS1088? I can get hold of most thicknesses in BS6566 which has waterproof glue although I'd have to check for voids but this is for a transom so maybe not?
Thanks Richard

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Re: DE23 laminating 4x 9mm?

Post by OneWayTraffic »

Since plywood is laminated wood, then the strength will be equal or better if you do it yourself. However you will use more glue than you think to get a 1mm bondline in between layers, and you will need to use screws or a lot of weights to ensure you have glue exactly everywhere. Buying the thinner ply might not save as much as you think. At the end of the day the difference isn't a lot in the big scheme of things.

If it makes you feel better, voids in the transom are less critical than in the hull panels. Not ideal anywhere of course.

fallguy1000
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Re: DE23 laminating 4x 9mm?

Post by fallguy1000 »

In order to get a 1mm (ideal) bondline, you must use a 0.5mm vee trowel and bond each side of each laminate. It takes a lot of resin, but is doable. Best also done under vac at about 9" of Mercury. If you skimp on resin, make sure to at least neat coat the starved side or the joins will be poor. Make sure the resin is thickened enough so the vee lines don't collapse while you apply the resin. It needs to be pretty stiff. 9" Hg is a lot of pressure and about 4psi. So, for a transom say 20" high by 50" wide, 4000# which sounds like you ought to drive on it, but that would be too concentrated a load ftmp.

Shoot for 1- 2 psi with weights like cinder blocks on timbers. Yeah, that is about 1000#.
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TomW1
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Re: DE23 laminating 4x 9mm?

Post by TomW1 »

This is one you can do with a helper. One hint is to drill and position four dowels one in each corner to line up each transom piece as you position one on top of the other, this will keep you from sliding the glued pieces around on top of each other. Nest I would use a drill with torsion settings, so each screw is set to the same depth. Use only screws only long enough to go half way through the bottom piece. Set them every 6" for even pressure. Remove the screws and fill and cut the dowels even before the next sheet.

Well good luck you have a big transom to build. If you have any questions ask.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

fallguy1000
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Re: DE23 laminating 4x 9mm?

Post by fallguy1000 »

Pins are important. I use aluminum nails.
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Re: DE23 laminating 4x 9mm?

Post by OneWayTraffic »

If you don’t have a proper vacuum setup try those large storage bags with a valve for a house vacuum. You can cut one open so it covers the whole piece then duct tape it on a flat airtight surface. I should have done that with my transom. I used screws instead which was more work when all’s done.

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Re: DE23 laminating 4x 9mm?

Post by wildbriz »

Thank you for the tips on laminating the transom. I'll look into the vacuum baging suggestions, not sure my wet and dry vac will provide enough suction though.

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Re: DE23 laminating 4x 9mm?

Post by fallguy1000 »

wildbriz wrote: Fri Sep 03, 2021 6:27 am Thank you for the tips on laminating the transom. I'll look into the vacuum baging suggestions, not sure my wet and dry vac will provide enough suction though.
A big shop vac can pull enough, but it can be hard on them. You can test it by plugging the end. If the motor is cooled by incoming air; it'll likely overheat and either die or trip a breaker. You need a bag and some butyl to seal the bag to a flat surface.
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Re: DE23 laminating 4x 9mm?

Post by OneWayTraffic »

I would think that if the valve and seal all around is good you would be ok with a house vacuum. Switch off as soon as it starts to whine. It won't heat up in that short time. Different story if you are planning to use vacuum bagging for a layup. Absolutely experiment first.

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Re: DE23 laminating 4x 9mm?

Post by BarraMan »

I've held off replying to this thread until I had a bit of time to look up and DE23 - but here's my 2 cents worth.

I think vacuum bagging to laminate this transom is over-complicating things.

Cut out the layers that you want to laminate, prime them with epoxy, line them up dry and dowel them, apply a slurry of expoxy/woodflour (tomato sauce consistency) to both surfaces, put them together using the dowels to keep them aligned, tap them down ( I used a rubber hammer) then put some weights on them (I used 5L bottles of water from Woolies) until the epoxy has gone off.

The transom on my boat is of similar dimensions ie 2.45 M wide ( I did 5 x layers of 12 mm ply to get a 60 mm thick transom). My transom is solid as a rock and has had a 250 hp Yammie hanging off it for the past 5 yrs.

PS: I can give you the details of where to source high quality woodflour in Australia, for epoxy glue and fillets.

Cheers
Lee

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