LM 18 with Tunnel Build - Texas

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joe2700
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Re: LM 18 with Tunnel Build - Texas

Post by joe2700 »

pee wee wrote: Sat Jan 15, 2022 10:05 am Did you neat coat both pieces with epoxy before spreading the Gel Magic?
FYI you don't need to do that for gel magic. From the TDS:
NOTE: GelMagic may be used directly on new wood without pre-coating with an epoxy coating or sealer. If substrates are
pre-coated, sand any cured material in the bonding area prior to using GelMagic.



pee wee
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Re: LM 18 with Tunnel Build - Texas

Post by pee wee »

joe2700 wrote: Sat Jan 15, 2022 10:43 pm
pee wee wrote: Sat Jan 15, 2022 10:05 am Did you neat coat both pieces with epoxy before spreading the Gel Magic?
FYI you don't need to do that for gel magic. From the TDS:
NOTE: GelMagic may be used directly on new wood without pre-coating with an epoxy coating or sealer. If substrates are
pre-coated, sand any cured material in the bonding area prior to using GelMagic.
I learned something today, thanks!

Here's a discussion on gluing up transom pieces that may help. By the way, Cracker Larry was an expert builder who we all benefited tremendously from.
viewtopic.php?t=60364&start=20

You will notice that Larry likes to glue all the panels up at once, like you mentioned (but aren't you glad you didn't mess up all the panels in one go?). I find the search features of the forum to be a bit difficult to use, but there is a lot of information here if you can dig it out.

As to the differing ply thickness on what you bought at the hardware store, it should be okay for a flat panel like the transom, but isn't great for bent panels.
Hank

TomW1
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Re: LM 18 with Tunnel Build - Texas

Post by TomW1 »

Grant are the number of layers in your new Okume the same as the ones you got in your CNC kit, and can you show us the Okume label so we can make sure it is good for you.

Now for applying the Gel Coat the best way is a toothed trowel going in opposite directions on each board. Here is one sold in the store here but you can buy similar ones at any hardware or home depot/lowes tile section. https://www.boatbuildercentral.com/prod ... st-system/ Use the tall teeth. Do not worry to much about time Gel Magic has a 30 minute work time till it gels at 77F. The other thing is to make sure your weight is evenly distributed.

Well good luck to you.

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: LM 18 with Tunnel Build - Texas

Post by fallguy1000 »

Glueup.

Precoat the join with epoxy 2oz per yard both sides. Allow it to gel for one hour. Then make thickened epoxy.

Use 1/16" vee trowel.

Trowel both sides of the bond.

It takes a lot of thickened epoxy. A lot.

Use about 2.2 times the volume of epoxy for the amount of fumed silica. Sorry no data on wood flour; guessing close-ish. The stuff is ready when it won't sag or flow. After you get it stiff enough; lay it out flat on a board and it won't gel too fast.

It takes a long time to apply, but don't worry about direction; just get it all coated. Do not do it in hot sun or hot weather. 70F is your friend.

The perfect bond dimension is 40 microns or one millimeter.

The ideal bond pressure is about 4 psi which is basically unattainable with weights. But 2 psi is plenty. Avoid unbalanced weights. Use timbers or wide boards to disburse loads. Concrete blocks or water jugs or other heavy weights.

A 1.5 foot by 6 foot glueup is 9 square feet or 1300 square inches; 2 psi is 2600 pounds, but avoid driving a car on it. That will point load and squeeze out the resin.

You won't get to 2600 pounds, but you need a LOT of weight. A 1/16 vee both sides is 1/8" and 3mm and you are trying to push it down to 1mm.
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viewtopic.php?f=12&t=62495

GrantL
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Re: LM 18 with Tunnel Build - Texas

Post by GrantL »

Thanks everyone for the input. Had family in town last weekend so got delayed on my next plan to re-glue the transom.

Fallguy - thanks for your detailed input on gluing. I am using Gel Magic epoxy but assuming the procedure (minus mixing of silica) is about the same. Just so I understand, you are saying about 1 mm on each bonding surface is a good way to measure the proper amount of glue to apply?

Do prefer to use weights on flat ground or combination of weights and clamps on elevated surface to let cure?

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Re: LM 18 with Tunnel Build - Texas

Post by VT_Jeff »

You don't need to precoat with gel.magic. per their doc. Do your own research but that's my understanding. If you do precoat, make sure it's compatible(silvertip).
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fallguy1000
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Re: LM 18 with Tunnel Build - Texas

Post by fallguy1000 »

Find the flattest surface you can find.

1mm final is the ideal bond

This is achievable with 1/16" vee trowel each side and a lot of pressure from vac bag or weights. You will want several hundred pounds balanced on timbers.

Both sides get resin. If you are using gel magic; you may not have enough to do both sides. It takes a lot of resin. A lot for proper bonding. You should be prepared to run out of gel magic and be ready to mix homemade with either silica or wood flour (No sawdust!).. about 2.2 to 1 (fillers to mixed epoxy)
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viewtopic.php?f=12&t=62495

GrantL
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Re: LM 18 with Tunnel Build - Texas

Post by GrantL »

Thanks everyone for the continued insight and advice! Ended up re-cutting and re-gluing the transom as instructed and it was night and day better. The one item that made the most difference was a v-notched trowel. I used a 1/8'' but 1 /16'' should work as well. Having the glue spread on evenly really does make a huge difference in ensure there are no gaps in the bond.

I also spent some time glueing the stringers up. used same method of laying a thin pre-layer of epoxy and sanding down. Then went back over with gel magic on both bonding surfaces using a 1/8 v-trowel. slapped the pieces together and used clamps at various intervals to hold together while it set. I was curious as i feel i needed more clamps than what i used. I only had good glue ooze out of the seam in the areas where the clamps were applied. Some other areas, you could tell weren't squeezed together as tought, however i know the epoxy bonded between teh two pieces, there is just a couple slight/tiny gaps in between the pieces along the edge of the stringers. Assuming that is ok? was thinking of mixing up some thin epoxy and laying/pouring in a coat over the seam of the two pieces along the entire edge, to hopefully fill in any tiny gaps and seal the seam from any possible moisture intrusion.

I spent some time looking at how others clamped the stringers and i would say i was about average (slightly below) on the number of clamps/spacing used. Any more thoughts on this before i move on to framing everything up?
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fallguy1000
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Re: LM 18 with Tunnel Build - Texas

Post by fallguy1000 »

The best way to clamp is flat surface; lotsa weight. Local clamps will result in less than flat surfaces as clamp pressures are not even...

Not enough c clamps? You can use a board woth any warpage in the middle and to the work and use fewer clamps,

But clamps and a flat surface are needed.

When I use 1/8" trowel; I one side the bond and neat coat the other side.

Timbers and weights or vac are my preferreds. My vac pumps need repair or a kit now.
My boat build is here -------->

viewtopic.php?f=12&t=62495

GrantL
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Re: LM 18 with Tunnel Build - Texas

Post by GrantL »

Here are some pics of the gaps I was discussing. Do you think those are ok or if I poured some epoxy into the gaps to seal?

If this is something I need to re-do, I’m totally fine with it as I already re-cut and glued transom hahha. But at same time if that gap is maneagable for the stringers then I’ll leave it. Any advice is appreciated!
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