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Core Sound 17 #221


Randy C.

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I've been looking at boat plans on the internet for 6-7 months. I owned a boat for 25 years(they all had a key). I don't know what made me decide on a sailboat, just thought it might be fun, and maybe because you can boat all day for free. I finally decided on the Core Sound 17. After talking to Carla and her assuring me I could do it, I ordered the plans Wednesday 4/16/08. Received them the next Monday. Looked the plans over about a dozen times and decided to give it a try. Called Graham this Tuesday 4/22 to ask a couple of questions about plywood and to order the epoxy and tape. After I hung up I called and put in my order at Homestead plywood in Ohio, should be here early next week. I bought some real nice Hemlock fir today for the mast and framing(I hope it's the right kind).

I've been reading this forum for a couple of weeks. I've learned a lot, but I'm sure I will have some questions as I go along. I plan on taking pictures as I build. If I can figure out how to load them,( I'm surprised I was able to get signed up on this), I will. Let the fun begin!!!

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  Welcome abord Randy!

  As you've probably seen in the last few weeks there are plenty of helpful people here and we're always eager to see progress photos.  You'll have a good time building and if you're like me you'll have an even better time sailing.  I like all kinds of boats but I really like a core sound :)

  Keep us updated on your progress and feel free to ask any questiond you might have.

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Received my plywood today. It seems the trucking company didn't like the nice shipping crate that Homestead plywood sent my plywood in. They took it apart and layed it flat on the pallet with one metal band around it. As luck would have it, all four sheets of 1/4" Okoume I ordered were damaged, the rest were O.K.  It's being taken care of.

Tonight I started cutting out the bulkheads. I got the aft bulkhead cut and trimmed to layout line, and started laying out the foreward bulkhead. Also, I've read on this forum somewhere about doing a scarf joint, but can't remember where. I think it said the joint should be 8 times the thickness of the plywood, 2" for 1/4" ply, is that right? How much pressure do you need to put on the joint when glueing, and do the sheets have a tendency to shift?

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Hi Randy,

If you are doing a scarf joint 8:1 is a recommended minimum.  We are building five Spindrift 10s and have most of the scarfs done and they worked out well.  When gluing (with epoxy resin) we layed down a flat piece of 2 x 10, put some poly on it so the epoxy wouldn't stick to the 2 x 10, applied glue to both scarf edges, aligned them on the poly then tacked them down at each end with a one-inch finishing nail.  We did a couple of joints at the same time by stacking them one on top of the other then piled up a couple of rows of bricks on a board to weight the whole thing down. I like the scarf joint as it is smooth and barely needs fairing.

Bruce 

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I'm about ready to glue up my scarf joints. My problem is, I've never used epoxy. When do I use the fast set and when do I use the medium set? I would think I should be able to use fast set on the scarf joints, right? When just coating the plywood fast should be OK? What about doing the fillets, medium set?? Does anything cleanup wet epoxy, or is it even an option?

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I use slow hardener on everything. Of course we don't often get much really cold weather here.

I would most definitely want slow (or medium) on fillets because I want to get the tape on while the fillet is still wet.

Rubbing alcohol or lacquer thinner on a paper towel will clean up uncured epoxy- so will vinegar. I use the alcohol or lacquer thinner when cleaning on the boat and vinegar for cleaning tools.

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I'm about ready to glue up my scarf joints. My problem is, I've never used epoxy. When do I use the fast set and when do I use the medium set? I would think I should be able to use fast set on the scarf joints, right? When just coating the plywood fast should be OK? What about doing the fillets, medium set?? Does anything cleanup wet epoxy, or is it even an option?

The fast, medium and slow options are often considered as to end use....what project you are doing and how fast do you want it to cure, but I always consider how long it's going to take me to do it. Depending on how much you mix up, any quantity larger than about 50 ml (about half a cup) had better be used fast or the fast stuff will heat up and go off on you in the cup. At higher temps, you can feel it start heating up in as little as 5 minutes or so. Anytime the temp you are working in is much over 60 degrees, you don't have much time to work with large batches. At temps of 80 plus, even the slow stuff doesn't give you much time to work with large batches. Get it mixed and get it out of the pot, or use several small batches.

For your scarfs, you would mix up straight epoxy, and coat both sides with the mixed and unthickened stuff to let it soak as far into the end grain as possible. Then with what's left, add your cabosil or wood flour or whatever your thickening agent is, then apply a thin layer of that to one or both sides, then fit the pieces together. For most scarfs, that whole process is going to take me about 5 to 10 minutes. Depending on temp, I'd use slow cure hardener for that to give myself enough time. Less than 60 degrees and I'd mix in a dash of fast to get it moving later on. If it's 60 now, but going to warm up to 80 later, skip the fast.  It only takes a couple cups of goop going off on you in the cup to give you a feel for how much time you have to work with.

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Pinoypiper, Charlie, and Howard,

Thanks. It sounds like maybe I should send my fast set back to Graham and exchange for medium or slow set as it should stay above 60. I said it should stay above 60, this is Nebraska, anything is possble. Or, I'd better learn to mix small and work fast!!

How long do joints need to set? Overnight, 24 hours? When doing the fillet, do I wet the wood before adding the thickened epoxy?

Hope I'm not asking too many questions, I just don't want to goof anything up. I'm going to mix a little up and get a feel for the epoxy before I actually do my first joint.

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Don't worry about the questions- that's the purpose of this place ;)

On the fillets, Sometimes I do, sometimes I don't- depends on how major it is, and how I feel. If I don't, I mix the filleting blend slightly wetter, and let the wood absorb some resin. Otherwise the fillet gets too dry. Probably best to brush in a wet out coat first, actually. Then, as soon as the fillet is run, I lay the tape onto the wet epoxy dry brush it into place and let it absorb a bit of resin. THEN I go back and ad whatever more I feel is needed, trying to keep it JUST wet, without running. Too much resin can "float" the glass and give you a weak spot.

How long to let a scarf join cure? Depends on temps and epoxies. 2-1 mixes take longer in cooler weather than 5-1 mixes. In temps below 60, I've had 2-1 mixes ( such as B and B sells) takes 3 days to achieve a workable cure, where WEST with it's 5-1 is fine in 24 hours.

When the temps are like they are in my shop in the summer time- hitting 102 or higher, you learn to work fast even with slow cure hardener ;D Yesterday I was taping some hulls and it was over 90 in the shop, even with both doors open and a breeze blowing through- metal building.

But I HAVE glassed the hull of a 22 footer by myself in temps over 100. Just mix small batches and keep rolling- hit the head BEFOR you start, and un plug the phone  ;D

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Randy,

When I was a beginner, I was totally helped by a small little booklet published by System Three resins.  Check with them to see if they still have it.  It was very helpful with the questions you are asking.

Also, the Gougeon Brothers have a big book which includes just about everything you would need on epoxy, etc.  It is called: The "Gougeon Brothers on Boat Construction".  Maybe your library would have it.

Dale

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Dale,

Thanks, I'll check on the reading material.

Charlie,

I decided to mix some epoxy and glue a couple of scrap pieces together(scarf joint). I used fast set to see just how much time I'd have. I tried to be sure the pumps were primed before counting. I thought that I stirred the mix as good as I could. I wetted the pieces. I added thickener to make the mix like very runny frosting. I put the "frosting" on and clamped the pieces together. That was at 6:30PM. It was only 60 in the garage. It's now 10:30PM and I just went out and checked the leftover mix. It's just getting firm. Does that seem right? It seems like the fast set would setup faster than that, doesn't it. Maybe just not warm enough. I'll check it in the morning, hopefully it'll be set. I don't think I did anything wrong.

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Randy,

  Devlin's Boat Building is a great how to source as well. Probably also available at the library. And FWIW the epoxy I use says it takes 72 hours to completely cure, I left my scarfs for the entire 72 hours before moving. Took me a week to scarf three panels together but I'm thrilled with the results. Have fun.

Norm

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Norman,

Thanks, I'll check it out.

I went out this morning to check my 2 sample glue-ups. It's only 43 in my garage, 37 outside,(The crabgrass hasn't even sprouted yet this year, it's been a very cool spring here in Nebraska). The joints are a little soft, but they are setting up. I could start to pull apart, but only with a lot of force. I put the clamps back on and will check this evening. I was afraid I did something wrong, but I think it's just not warm enough for a fast set. I didn't try the sample scarf joint, I'll wait until the other joint is completely dry before trying it. Normally, I use Titebond for my projects, which sets in 30 minutes, so I'm not used to it taking so long. I'm OK with it taking a little time as long as I know it's going to work.

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Randy- can't tell you how long fast takes in those temps. I've never used it,, other than WEST System fast.

I can tell you that slow in 43 degrees will take up to 3 days to reach a cure. WEST will do it more quickly, but will still take 24 to 30 hours.

I'd sure not rush things with the scarfs. In those temps I'd leave the joints alone for at LEAST 24 hours.

You can find other parts of the boat to be laying out or cutting out while you wait. That's one of the things we have to learn when building for bucks- how to schedule work time  so you have stuff to do while something else is curing. Gets easier as the boat gets further along though.

You CAN speed things up by making tents to contain warmth and using some lights, like quartz work lights to warm the wood joint and surrounding wood. It also helps a LOT to keep the epoxy at about 70 degrees- you can keep it in a box with a light bulb, or bring it inside.

I won't insult your intelligence by explaining the steps you should take to avoid fire if you warm the wood;D

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You can download the System 3 Epoxy book from their website. A really good reference.

When I started working with epoxy, I used West System, as it was all that was available locally. Quart cans for the resin, those little cans for the hardener. Can't remember how many times I got part of a squirt as the pumps misfired or started to run dry. Part of a squirt means your mix is no longer accurate. You can chuck it or guess how much more you need. Bottom line is I don't trust pumps to get my mix ratio right. Get it wrong and you will have a bad mix that won't cure right.

So now I measure everything. I might use pumps to get it out of the jug, but it's still measured in calibrated cups. I have several sizes of cheap plastic cups from Walmart. You set one inside another, then pour a measured quantity of liquid (water) into the inside cup. You mark that level on the outside cup. If using 2:1 epoxy, then measure in half that amount and add it to the first quantity. Now mark that. You now have a calibrated cup in a 2:1 ratio. You don't use the calibrated cup except as a measure. Always put a clean, unmarked cup inside the calibrated measure cup. Into the clean, unmarked mix cup, dump in resin to the first mark, add hardener to the 2nd mark and start mixing.

I have little medicine cups I can mix up as little as 7.5 ml all the way up to gallon sized plastic buckets. My main sizes are 5:2.5 ml; 10:5 ml; 20:10 ml; 40:20 ml; 60:30 ml; and 100:50 ml. Rarely do I mix more than that unless I'm glassing over a large area and can pour it out of the cup and spread with a squeegy.

Next, latest, greatest trick is to settle on a fillet mix (amount of epoxy and amount of filler) so you can mix them up fast and accurate, then when mixed, dump the goop into a small zip lock sandwich bag and seal it up. Snip a corner and start squeezing. Works like a frosting bag to work it into the joint you are trying to fillet. Drag a mixing stick or some other rounded edge over it and you are done.

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