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Core Sound 20 mk 2, Hull #2


Tom the rower

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The joint was not starved.  This was a tear in the wood at the finger joints.  I am gut sure that the number of times I moved the 20ft bottom piece before unfolding was probably the culpret.  No worries... I will take it apart, fix the joint and do the unfold process again.  This will afford me the opportunity to get some video and photos of the unfold process, since it happens so quickly.

 

I wasn't sure if I could avoid the taking it apart and re-unfolding, but I guess it is the right thing to do.

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Hello Tom,

 

I think B+B are waiting to see if you have any problems with this hull before selling the plans...  I hate to ask you this but can you step up the pace alittle..  Do you live in Jaxsonville Fl?  If so do you need some help?  Can you post some pics, especially the joint that failed...

 

Thanks, Otto

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Tom,

 

24 hours in Florida is cured enough or most jobs but not completely cured. What I was concerned about was trying to figure out why the joint failed, was it a bad mix?

 

After 24 hours in your climate you can scrape at the glue to see how hard it is. It should be fairly hard, if it is still soft or gummy the mix could be bad.

 

Otto,

 

B&B is certainly not waiting to see if it works before before releasing the Mk2. I know that it works because I put hull #1 together with Chick and it went together very well not to mention that it is the same basic Mk1 hull. There are a lot of internal components as well as the house and deck parts that I like to get feedback on with a new boat so that each kit will get even better.

 

We have been very busy but I have leapfrogged to the CS20 Mk3 which I hope to build test in a month. Still the same hull and water ballast but with a raised deck instead of the house. I think that the cabin works better and I have changed the cockpit ergonomics to impove rowing.

 

I think that the raised deck looks good but as in all art forms people will love it or hate it.

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Hello Graham,

 

Our last e-mails were about waiting for the second boat to be built before selling plans...I do have a set of plans from you for the CS 20. Before I build it I would prefer the water ballest version. Raised decks even sounds better to me.

As far as my comment to Tom, I would offer building assistance if he so desired. Back when Dawn Patrol was ready to be removed from the house I offered to assist also. I do not want to be in a position that I built "A" when I could have built "B".. I like all your designs.

 

Thanks, Otto

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  • 4 weeks later...

Just pulled the folded hull apart to fix the torn wood.  That was tough.  Naturally, the tear tore even more.  I now have the stbd bottom and side layed out flat on the back deck.  Ended up coming apart, so I guess I will go get some really thick woven fiberglass, say a good 8 inches overlap on either side of what will now be a butt joint, as the cool finger joint is now gone.  Spent some time with the newly acquired mirka arbonet sand paper stuff to clean up the joint in preparation for the butt joint.  It won't be 70 degrees here till 2-3 pm today.  Dangit.   The boat looked so cool after the folding/unfolding process.  Everything lined up perfect, except that tear.  I was tempted to try a fix while it was still stitched together, but I thought I better take it apart and do it right. 

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  • 2 weeks later...

Otto, yes I live I Jacksonville,Fl and yes I could use some help.  Having just  pulled apart a Core sound 20 that looked like a boat to repair a tear (completely my fault), I could use someone who is excited.  I live on the water and usually just go out sailing instead of working.  I made a special boat building shed with all kinds of lights just for this boat. I am ready to re-wire the boat and re-unfold it.  I would guess that you live nearby.  Let me know.  Right next to the boat build is my last project, a wood fired pizza oven.  Come over and let us eat pizza and drink beer and talk of boat building.

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  • 1 month later...

You can see here that I don't quite have the sides attached just right to the bottoms. Kind of gappy.  Maybe moving the bulkhead around a little.  Ideas???   Sorry to be so slow about this build.

Hi Tom,

Good to see you're past the earlier tearing problem - "good on ya mate" as they say in places where it's summertime.

 

Looks like there are no joints done yet (bottom panels to each other, or bottom panels to side panels), so if that's true, here's some thoughts based on your pix.

 

((EDIT -- Tom, looking at your pics again, I may have been naming the bulkheads incorrectly -- in my text below, when I say "temp" bulkhead I am referring to the bulkhead that has the two slots in it, sorry if I'm confused/ing )))

 

There's two areas that look in need of adjusting: the shape near the temp bulkhead and maybe the bottom shape near the forward bulkhead...

 

First: the starboard hull panel forward looks to be rather concave (pushed in from the outside) while the fwd bulkhead looks to be needing a convex shape in the hull panels in the  forward bulkhead area. If that's true (looks/photos can be deceiving), inducing that shape needs to get figured out. Even though the bottom will eventually be nearly flat at the temp bulkhead, it might help to add a little (1/2") shim in the middle between the temp bulkhd and the bottom panel to start inducing the plywood to reverse it's shape from concave to more convex (again, as viewed from the outside) as you work your way forward. May also be helppful to (temporarily) add shims to the cradle-side to help (shims at the keel and chine areas) , try to get the bottom panel at least 'flat' up forward then when you try to force the forward bulkhead into place you wont be fighting it as much.

 

Second: looking at the gap between the temp bulkhead and the bottom panels (assuming with a kit, that bulkhead is correct shape) - clearly the bottom panels are too V-eed - the angle needs to be shallower by quite a bit. Cannot see what the cradle looks like underneath that area but that has to be the correct angle too. It looks like once you get the bottom flatter in that area the bottom will also become wider and the gap between the port side panel and the bottom panel will probably disappear.

 

Go nice and slow and easy don't force things too much, make sure there's someplace for to ply to go to whenever your trying to force in one area.

 

Keep posting pics they help a lot is seeing what's happening as you go along.

 

Cheers,

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Thanks... that is good advice.  I used as cradle supports pretty much exact copies of 3 different bulkheads (I took a bulkhead and traced it onto plywood and cut it out and used the opposite piece as the support).  One thing I haven't done yet is level it out.  It appears that the front of the boat is way too high as compared to the back of the boat, so that front support will probably need to be lowered.  I can take some more detailed pictures.

 

Tom

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Thanks... that is good advice.  I used as cradle supports pretty much exact copies of 3 different bulkheads (I took a bulkhead and traced it onto plywood and cut it out and used the opposite piece as the support).  One thing I haven't done yet is level it out.  It appears that the front of the boat is way too high as compared to the back of the boat, so that front support will probably need to be lowered.  I can take some more detailed pictures. Tom

Jeez, I hope somewhere in the plans there's info on what the keel profile measures from a baseline or waterline - you do need to have that cradle set up proper so that you can get the panels properly aligned while stitching and before gluing. If not, you should contact Graham as I doubt he omitted it, but it may be hard to find among all the plans sheets you have.
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Tom-

I struggled at this point as well. I think it is a question of assuring all the foundations (bulkheads, cradle) are correct, and if they are coaxing it in one wire at a time with as Tom says help from some wedges. At this stage I added both the temporary and front bulkhead, per graham's advice. Make sure your temporary bulkhead is in the right place ....it looks closer to me as to where the forward bulkhead goes and might belong aft of its current position. Then get both of them in and the "skin" can be pushed and prodded in place.

I'll check back soon but gotta run right now.

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On the prototype of the mark 2, Graham had it set on a saw horse forward on the keel, almost where it turns up at the bow, and the stern blocked up at the transom corners on another saw horse. There was no support anywhere else underneath during the build until the hull was wired and taped, and all of the transverse and longitudinal bulkheads were installed. We did have to run a couple of screws up into the temporary bulkhead to pull it in tight until the keelson was installed.That is when I took the boat from his shop home to finish. At that point, I built a simple cradle with transverse supports cut to fit the hull at about the aft bulkhead and up at the bulkhead (aprox.) between the cabin "footwell" and the head.

 

All of the panels fit perfectly without much effort, except we had to double up some of the wire ties in the bow area. Get everything close with the ties loose, and then work back and forth tightening them a little at a time until everything is snug.

 

If you go to my (and "designers---he started it) building thread, I think you will see some pictures of the wired hull sitting on the saw horses.

Here it is. Check pictures on page 1: http://messing-about.com/forums/topic/8080-cs20-mk2/?hl=%20core%20%20sound%20%2020%20%20mk%20%20by%20%20designer

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SNIPThere was no support anywhere else underneath during the build until the hull was wired and taped, and all of the transverse and longitudinal bulkheads were installed. We did have to run a couple of screws up into the temporary bulkhead to pull it in tight until the keelson was installed.SNIPAll of the panels fit perfectly without much effort, except we had to double up some of the wire ties in the bow area. Get everything close with the ties loose, and then work back and forth tightening them a little at a time until everything is snug.

Thank you Chick!Tom,I can see that I need to retract most of my previous post, especially concerning the emphasis on the cradle for assisting in aligning panels to shape the hull.As Chick so very correctly suggests, when the panels are truly perfect (and CNC cut is the only way to get there) then the stitch and glue process should be self-aligning - and in fact trying to align to another reference like the cradle (which couldn't couldn't be as precisely constructed) would in fact create additional constraints on the panels that are likely to work against you not for you.Thank you Chick, for reminding at least this old timer how much our old methods (and habits) have to be tested against mew methods such as building with CNC cut panels. I envy your experience.One caution which might apply in your unique situation. Since you had to do a repair to the joining of some of the panel scarfs, it is possible the one or more of you panels is not as precisely shaped now as was originally intended.
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Not so much experience as Graham doing such a great job designing a process that works so well. It also helps to have him there explaining what to do! When things don't seem to be lining up just right, he would "push a little here, tweek a bit there, and "poof", like magic, all would slide into place! But even without his presence, all will work out with a little fiddling.

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When we put the mk 3 together we did use a cradle. The new layout dictated no temporary frame so I made a cradle with a center support like a temp frame under the boat instead of inside the boat. I set up the camera to video the event to help future builders. I was disappointed with the video quality but was pleased to see that the timer said that it took 11 minutes to open the hull out, get the bottom attached to the cradle and wired back to about about 1/3 from the bow on each side. It took another 4 hours for Doug to wire the sides back to the stern and put in the transom an bulkheads like the picture in the mk3 string. It was every bit as fair as the mk 2, maybe better.

 

I found it awkward to get the temp frame in place without getting a gap in the keel line because the hull is trying to close up but you are forcing it apart and pushing down on the frame which in turn puts a down force at the keel line promoting a gap. I use to lay on the ground pushing the bottom back up to close up the keel gap and trying to get screws from the bottom into the frame without missing. This time I placed a pair of lead weights on the chine edge of the bottom over the frame and it was all over. This way the keel line is pressing down on the middle frame so that when the the lead weights were added it tightened the keel line instead opening it. 

 

I tested this method a couple of weeks ago at the boat building class on a CS15 and it worked so well I was sure that it would work on the mk3.

 

I have never posted a video but as soon as I learn how I will post it.

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Well, now I am a little mixed up. Should I remove my supports from under the boat?  I guess I have to admit that they are somewhat randomly placed, kind of . I don't think I am aware of exactly how far back from the nose of the boat goes bulkhead number 1 and so on. and since the 3 supports mimic the bulkheads, and I just kind of stuck them up under the boat and screwed them into the frame before unfolding the boat, maybe that is part of the problem. Maybe  they are off by a foot or more.

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