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Rdubs

Dumbest butterfly opening question, ever. (Spindrift 10N)

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Hi all,

I bought the plans for a Spindrift 10 Nesting to serve as a tender / knockabout for a 33' sailboat.  Reading through the plans, it says to fiberglass the front/bow of the side and bottom pieces, then wait for it to harden.  Once it is hard, open up the butterfly like in the video.  I think it says to glass/epoxy both sides of where the two pieces come together at the bow.  My question is, if the glass/epoxy has hardened, won't unfolding it crack and break the joint all to heck?  I don't understand why where these two pieces come together it isn't just stitched together prior to unfolding, since having it stitched would allow it flexibility.  Glassing the joint would seem to want to lock it in.  I am clearly missing something.

 

Thanks.

'Dubs

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Hi Dubs - Welcome to the forum.

I have not built a Spindrift but I think the unfolding process is the same as the CS17.  The port side panel is glassed to the port bottom panel at the bow to make an area that is flat.  The same is done to the starboard side and bottom panels to make a mirror image of the port side.  Once that epoxy is cured the port side is stitched (but not glued yet) to the starboard side at the bow.  Don't use any epoxy on the joint at the centerline of the boat until the panels are folded out.

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I just re-read your question and I think I missed the point in my earlier post.  If you look at this photo that I stole from the B and B website you can see how the joint between the side and the bottom of the boat sort of fades out at the bow.  That's the result of the tape joint.

 

post-234-0-88136100-1462856990_thumb.jpg

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Please watch these videos. They make the process very clear.

 

S10 unfolding video by Michael Niemi:

They actually didn't install the "anti cracking" blocks just behind the glass joint at the boat but they still didn't seem to have any problems. 

 

 

CS-20 Mk3 unfolding video. There is more involved and it's larger but basically the exact same. 

 

 

 

 

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Dubs,

 

There have been over 1000 Spindrifts built so far not to mention more than half that number of Core Sounds which adds up to a lot of experience. The main point of the concept is that it uses the length of the boat for leverage to fold the boat. If you turned the construction around and wired the boat from back to front, you could not apply enough force at the very front of the bow to bring it all together in the nice bow shape that we want.

 

We did not develop this concept at the first try. It came from a lot of trial and error. With boats as short as the S10, there have been some failures in the bottom when folding. For insurance I recommend putting a hot wet towel on the bottom forward 2 feet inside and out for half an hour before folding. We were having a high incidence of bottom failures in my boat building class at the Community college but it almost never happened at my shop. We realized that it usually took a month or two for the students to scarf, mark out and cut the hull panels, make the transom, bulkheads and join the panels etc. The ply was in an air conditioned low humidity environment which reduced the moisture content making it stiff. Our shop is in the humidity capitol of the world and the hulls folded easily. We now soak the bottom panels on Spindrifts and the problem has pretty much gone away.

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I just re-read your question and I think I missed the point in my earlier post.  If you look at this photo that I stole from the B and B website you can see how the joint between the side and the bottom of the boat sort of fades out at the bow.  That's the result of the tape joint.

 

Ken - thanks very much for that photo, it explains what I was missing.  I thought there would be a definite angle where the side and bottom meet, but it's clear that up at the bow because of the curves the union of those piece should be flat, and only about a foot after that do the sides and bottom really start to come into their own.  It makes perfect sense now.  Hat tip.

 

Alan thanks for the videos, I watched the first one a few times before posting but now that I know what to look for thanks to Ken it stands out.  The second video also shows the same feature, thanks.

 

Designer!  Honored for your comments.  Thanks much for the tips, that is a great idea.  I thought about trying to set up a humidifier or something to help add a little flexibility but your idea sounds better.

 

I will let you all know how it goes.  Thanks again!

'Dubs

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Good luck 'Dubs-

 

I recommend the "anti-crack" blocks.  Better safe than sorry.  I know on my 17 they definitely helped, although I did the unfolding on my own.

 

Take care-

 

JP

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I recommend the "anti-crack" blocks.  Better safe than sorry.  I know on my 17 they definitely helped, although I did the unfolding on my own.

 

I cracked the "weld" folding my 9N.  I recommend them (blocks)  too.  The weld is at the transition from chine to lack of chine as you approach the bow.  It is under a ton of load and is responsible for a nice smooth transition from the hard corner to none at all.  I find the beauty of these hulls depends a lot on a fair transition.  This is a detail you want to do well.

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JP, Hirilonde - Sorry, not following what you are talking about re: anti-crack blocks.  What do they do, and have you come across a picture of them?  Are they something you clamp to that glassed meeting section at the bow to provide extra support during unfolding?

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Exactly- right at the end of the glassed section- if you look at the picture above (the second video) you can see them.  I used two 2.5 by 2.5 blocks, 1/2 in ply I think screwed to each other right through the hull.

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Hi gents,

Have another question, not relating to the fold.  What is the best way to scarf the 4' plywood halves onto the two 8' sheets in order to make the length needed for the 10' boat?  I'm thinking there are three options:

1) Just do a simple end-to-end join, but then you'd need some fiberglass across the seam to give it strength

2) Join it at an angle (I think I would need like a 2" mating surface on the angle), and

3) Lap it via cutting off one veneer face on one piece, then on the other piece remove the veneer plus the core

 

Any thoughts?  The main cutting tools I have are a table saw (hard to work with big plywood sheets on), saber saw and a hand saw.  

 

Thanks

Dubs

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Hi Dubs

I'll just point out that scarfing plywood is not the same as joining plywood see https://en.wikipedia.org/wiki/Scarf_joint

Butt joints with plywood or fibreglass can be done but are not pretty

Scarfing as per the above article is elegant and strong

Your option 3 will require glassing as well.

There is also finger jointing in its variations but not so easy without accurate cutting equipment.

 

A scarf is a lovely technique to learn.

 

Cheers

Peter HK 

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Rdubs,

 

An additional technique I use that hasn't been mentioned elsewhere for the butterfly joint is something I learned in engineering materials class. After the pieces are joined with fiberglass, drill a 1/4" hole at the very point of the V between the two sheets being joined. This eliminates the sharp point of the V which is where any cracks would start. Now the stresses are spread out over the circumference of the hole and less likely to start a crack. The hole is a convenient place for the screw joining the two backing blocks discussed above. And it's easy to fill later when glassing the seam.

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Hi Dubs

I'll just point out that scarfing plywood is not the same as joining plywood see https://en.wikipedia.org/wiki/Scarf_joint

Butt joints with plywood or fibreglass can be done but are not pretty

Scarfing as per the above article is elegant and strong

Your option 3 will require glassing as well.

There is also finger jointing in its variations but not so easy without accurate cutting equipment.

 

A scarf is a lovely technique to learn.

 

Cheers

Peter HK 

Hi Peter,

Thanks for the tip, I was thinking Join, I incorrectly applied the term Scarf.

 

I set up everything to start creating the first scarf, by trying to sand using a 1/3 sheet finishing sander (the vibrating kind).  60 grit sandpaper.  Despite the coarseness of that paper, it was going impossibly slow.  Researching around I read that a planer or a belt sander should work.  Kind of sucks that I have to go out and buy one of those (even if used) just to form the scarfs, and only use it once.  But using a table saw would be kind of dangerous with those tall flimsy boards, and using a circular saw (which I don't have either) requires crafting some special jigs.

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I used butt joints. It took 1 minute with a wide squeegee to make the joint disappear. I'm not saying any other way is worse, but they are strong and quick.

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I used butt joints. It took 1 minute with a wide squeegee to make the joint disappear. I'm not saying any other way is worse, but they are strong and quick.

 

Thanks Steve.  Very curious...did you use fiberglass cloth to reinforce the seam, or did you just go au naturel with just the epoxy?  Some joining things I read said that if you want to do a butt, you have to also have a backing plate, or I guess the fiberglass cloth acts as that.  If I could just put the sheets end to end and use epoxy without glass, that would be sweet because it would avoid having that lump in the lines where the glass cloth is.

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Update, in case it helps future scarfers.  I bit the bullet and went out and bought a used belt sander off Craigslist.  Picked up a beast, a Makita 9924B, running 7.8 Amps.  Think the sandpaper was 50 grit.  Holy crap.  That thing was removing material like a possessed beast.  It probably took me 15 minutes to make 4" of extremely flat scarf angles across two board pieces.  The neatest thing was how once I started making progress, the different layers of the plywood began to serve as guidelines.  When sanded at that shallow angle, those vertical ply demarcations begin to show up along intervals horizontally.  So when you had a good angle, I would see about 6 different parallel lines running across the scarf mating surface, they looked like swim lanes, and after a while I began to just look at the swim lanes to see where I needed to remove material.  Once all the swim lanes were running at equal spacing, the angle was perfect.  Looking back on it that makes perfect sense, I just hadn't thought about it in advance.  A neat little trick.  The blow picture isn't perfect but you see the concept.

 

image1.jpg

 

The only problem now is since it is night and I had to work in the garage with the door closed there is now a layer of sawdust covering the wife's car.  That heavy-duty belt sander removes material, and places it anywhere it wants.

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I think you are now starting to realize that the real reason we build wooden boats is to justify buying more tools ;)

As I said earlier, learning to scarf is very satisfying as you've just found out. I find a power plane is even faster and, if you don't have a vacuum attached to it, makes even more mess. I can do 90% of a scarf in a couple of minutes with the power plane and then finish neatly with a hand plane or sander.

The lines in the ply provide a great guide.

 

Cheers

Peter HK

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