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Core Sound 20 Hull #102


wkisting

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I think you are over worrying. If the boards aren't quarter sawn then you rip the 3/4 stringer and turn it sideways. No big deal. And cut around any knots. You'll use plenty of short pieces here and there that can come from between the knots. If most of what they have looks good, just get what you need. You MIGHT have to buy an extra board, but again, that's no biggy. the only place I really get choosy ( REALLY Choosy) is when I'm building the masts using Birdsmouth And that's only a few boards, so just select from what you get.

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Thanks Charlie... I've decided I'll just go back tomorrow with a plate of home-baked brownies (courtesy of my wife) and tell them, "If your guy 'happens' to pick out a few exceptionally straight boards with vertical grain, that would be a very pleasant surprise."  :)  But yes, I am probably over-worrying, and I appreciate you and Ray putting me at ease.

About the masts... do you recommend birdsmouth or aluminum spars? Is the birdsmouth method really labor-intensive? (I do have a table saw and router, so tooling is not a problem.) Can the birdsmouth spars be made with Douglas Fir or does it need to be Sitka Spruce? (I might have trouble finding the latter around here, based on my recent experiences.)

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Laura and I cut the staves, and cut the mouths in the staves for both masts on the CS 20 in less than 1 hour, all on the table saw- I don't use a router- too slow.. Glue up takes 30 minutes or so. Planing and sanding round, maybe half a day or a tad more. So maybe a full days work for both masts.

I like aluminum bottom parts with tapered birdsmouth tops. Hard to taper the aluminum tubing ;D

I cut a  tenon on the lower part of the birdsmouth to insert into the tubing. DON'T forget to allow for that when you measure and cut your staves. I like a full foot of bury. I also make round wooden inserts to go into the bottom of the masts. When doing a tabernacle I extend that "doubler" above the pivot pin. On masts that stand in steps, such as mizzens, I extend it about 3 inches over the partners. Gets some beef right where the max strain is, with very little added weight. Somewhere recently ( on here) I posted pics of the base doublers, the tenons and the parts of the mast. But if you can't find them, let me know and I'll email you pics of the whole thing.

Oh and doug fir is just fine. Ive built 10 or 12 spars now using Birdsmouth and always have used fir. Except for one double paddle shaft where I used "whitewood" cause it was really light. ;D Paddle came in at 31 ozs.

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Well, the brownies worked... went back down for Fir today and gave them the brownies. The guy softened up immediately, and though I didn't ask again about quarter-sawn, I noticed that the fellow who helped me load was selecting nice flat boards, many with vertical grain, while setting others aside. So, I got a nice pile of clear Fir today, with plenty of good pieces to use for the keel, king plank, etc.

Now I have a garage filled with all of the necessary materials to build a CS20 (except the paint, masts, rigging, and gunwales, which can all come much later). I just have to get the rain to let up so I can start building!

I'm going to post a building log on my kayaking website at: www.roguepaddler.com/coresound20.htm, but of course I'll post updates here too as I get underway. At some point, I'll also write up a materials list (on the website above) with the name and numbers of suppliers so that others in the GA area can benefit from my (tedious) experience of tracking down suppliers.

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Got the side panels and bottom panels rough cut. Scarfed them all on the table saw, then epoxied the bottom panels together. Hoping to do the sides later today.

For scarfing, I built a jig that holds the panels at exactly an 82-degree angle (8 degrees off of true vertical). I clamp the sheet to the jig and run it along the table saw fence into the blade... makes a nice scarf as long as the sheet is FLAT against the jig. For warped sheets I just clamped a sacrificial piece over the "real" piece to hold it flat to the jig then ran the saw through the whole lot. Came out nice. Of course, it means you have to balance an 8' tall sheet of plywood vertically on the table saw, but as long as it's not windy, it's fairly easy to do... didn't even need any additional support up high since the sheet is almost perfectly vertical. The 2' wide 1/4" thick Okoume sheets were easy and I could run the whole operation alone... the 3' wide 3/8" thick Meranti were much heavier so I had to get a helping hand from Anna on those.

Scarf ratio ends up at about 8:1, so cuts in 1/4" ply end up 2" wide, and cuts in 3/8" ply end up 3" wide (or slightly less).

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Here's a question for CS20 builders...

The plan sheet shows that the bottom hull panels are made up of 3/8" plywood 165 inches long and 1/4" plywood 72 inches long. That adds up to a total of 237 inches. HOWEVER, if you look at the 210-inch mark, it shows that the curve on the front of the hull panel ends at a tip located "27 1/4" inches forward from the 210-inch mark (which would make the total length 237 1/4 inches... i.e., an extra 1/4 inch).

So... are the bottom panels 237 OR 237 1/4 inches long? The math doesn't work out, so one of the two measurements must be in error (I think).

For now, I've played it safe and cut to the 237 1/4 mark... I can always cut off the 1/4" later if it proves superfluous. But I'd be interested to know if others have the same error on their sheets.

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I don't remember ever noticing that.  The main thing happening in that area is the shaping of the forefoot.  I think that the panels are 237", and that the 27 1/4 inches is there only to locate the station from which further 6" stations (substations?) are located for shaping the forefoot.  This could be tested experimentally: since that 1/4" difference is in the last 3" (or 3 1/4) of the forefoot, the line should be noticeably kinked if you cut the panel to 237 1/4" and measure those substations from the 210" station.  Good luck!

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Actually, Jeff, my plan sheet measures the 6" curve markers from the 210-inch line, not the tip... the tip just appears to float an extra 1/4" past the "master line" that marks the end of the panel... I left it at 237 1/4 and the curve looks fair to me, but there's very little difference in curvature if I were to cut it down to 237 instead. Baffling, but probably not significant as long as I fair the curve into the side panels carefully.

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Hi Ray,

We're in the 70s here yesterday and today. The days haven't dipped below 55 all week, but the nights still get cool into the 40s. I'm in heaven. Back in Iowa, we didn't see this kind of weather until mid- to late-April. But down here in GA, it's been hitting the high-50s (sometimes mid- to high-60s) several times per week all winter long!

This is the right place to build a boat, I guess.  :)

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Glued the inwales on today and finished stitching the sides.

How does one "level" the boat? I saw on the plans that the bow should be 10 5/8" higher than the gunwale at the transom, but it would be helpful to know how much vertical rise there is supposed to be from the lower chine at the Temporary Station to the lower chine at the transom (so I can adjust my cradle). Anyone know? Or can you recommend any good "leveling" tricks?

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I'm building a totally different boat Wes, but I used the LWL. It's on all the bulkheads, the temp, and the transom. I have a laser level. That helped alot. Shoot a level beam down the middle and measure from there as a reference. Bring the centers, also marked on all, on line. Should have perfect shaped boat. Good luck, and have fun.

Norm

post-955-129497666814_thumb.jpg

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I remember I had the same problem when I built my 20. This was the first 20 and  it so happened that Graham landed a big powerboat job at the same time so details for the twenty were slow in coming. I decided that since I would probably spend more time sitting inside the boat than anything else I knew I wanted the plane of the seats to be be nice and level. Using strings and working with existing stringers I defined the seats to my liking. Then using the top of the seat plane for reference I worked back to check and level the rest of the boat. It took me two  or three hours but at the end I had the seat tops as flat as a pool table with strings and temporary battens defining all major surfaces. The rest of the boat followed suit. And you know what- everything pretty much checked out. Within 1/4" at most. Don't bet on your glued-in stringers to be perfect. No two ever come out the same. Do your best but don't sweat the small stuff. Let your eye be the final judge. If she doesn't float exactly on her designed water line you can always help the trim with some loose ballast. Unless you screw it up big time she will come out just fine. The nightmare about her floating like the Titanic in the movie poster is not going to happen. And trust the plans. PeterP

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About leveling the boat...

I ended up buying a 25' long piece of 1/2" diameter aquarium tubing (clear vinyl type of tubing). I taped one end to the side at the transom and one to the bow at the tip, then let it sag to the ground in the middle. Filled the tube with water slowly to establish a level mark. Then adjusted the boat (and occasionally added or removed small amounts of water) until the water line at each end of the tube was dead even with the transom top, and exactly 10 5/8" lower than the bow tip. Seems to be a pretty reliable way (and cheap!) to level a boat, so thought I would pass it along.

Oh, and I started filleting seams today, but for some reason all of the seams behind the aft bulkhead sagged. I don't know why... all the others (up the sides) came out fine, and I mixed them all the same. Any secrets on ensuring fillets won't sag? I'm using fumed silica in large quantities and mixing to peanut butter consistency. That should be correct, right?

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Was the runny fillets done with the bottom half of the mix? Sometimes in a confined container and thickening the epoxy, on the top half of the mix gets mixed thicker than on the bottom of the container. Pull your blend from the bottom and scrape the mixing stick along the inside of your containers clearing it and then then begin to mix again. This may be the cause of the runnier glue.

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I ended up buying a 25' long piece of 1/2" diameter aquarium tubing (clear vinyl type of tubing). I taped one end to the side at the transom and one to the bow at the tip, then let it sag to the ground in the middle. Filled the tube with water slowly to establish a level mark. Then adjusted the boat (and occasionally added or removed small amounts of water) until the water line at each end of the tube was dead even with the transom top, and exactly 10 5/8" lower than the bow tip. Seems to be a pretty reliable way (and cheap!) to level a boat, so thought I would pass it along.

The standard technique for a loooong time before laser levels were available. It's amazing that gravity works so reliably ;D

Peter HK

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Oyster, I think you were right... I tried mixing in larger containers today, and no problems with sag... must've been failing to get the Silica mixed in on the lower part because it was always the end of a batch (the bottom of the container) that sagged. Thanks! (Also, I think we were being too conservative with the silica in some batches. Today, I mixed in extra to get it noticeably thicker.)

How important is it that the fillets extend 3/4" onto each panel? That's what Graham specs in the plans, but it seems like a very large fillet. Mine currently extend about 1/2" onto each surface, and I'm sure they'll accept fiberglass tape nicely. But if they need to be larger, I can go back over and build mine up once they start to firm.

Wes

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How important is it that the fillets extend 3/4" onto each panel? That's what Graham specs in the plans, but it seems like a very large fillet. Mine currently extend about 1/2" onto each surface, and I'm sure they'll accept fiberglass tape nicely. But if they need to be larger, I can go back over and build mine up once they start to firm.

Cold weather today means I can't add fiberglass tape before the fillets cure. Do I just rough them up with 80-grit tomorrow? Or how to ensure a good bond?

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