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View Full Version : Heresy? Glue-on Butt Blocks?



chuckt
11-20-2013, 06:53 AM
I was thinking. Wouldn't it be better to epoxy on butt blocks? Instead of putting 10 bolts through your plank ends and the block? I guess a downside is if you ever need to remove the plank. But seems like epoxying on the butt block would be a superior arrangement.

Brian Palmer
11-20-2013, 07:17 AM
Bolts tie the inner and outer surfaces of the block and plank together, preventing the block from splitting.

Brian

chuckt
11-20-2013, 07:30 AM
yes--I know that Brian. Just seems like epoxy and clamping might be better than all those fasteners.

Actually, I do not plan on doing this but am wondering why it wouldn't be a better way.

I suppose if you were just replacing the block from the inside you would need at least some fasteners to draw everything tight while your epoxy cures.

slug
11-20-2013, 07:48 AM
Epoxy does a good job of sealing butt block end grain. You can also run a nice big fillet on top of the block to keep water from standing there.

it would be unwise to rely on epoxy without fasteners on planking.

Ian McColgin
11-20-2013, 08:22 AM
If you're going to epoxy, you might go with the repair technique that Gannon & Benjamine call "hide-a-butt". In essence it's a third short piece scarfing together the two planks. Proper 8:1 and all that. The hide-a-butt is especially handy when making repairs in places where the butt is not accessable from the inside for conventional butt blocks.

The big advantages of conventional butts over the proposed epoxy method are speed, economy, greater ease to do the job right, and greater tolorance of the joint to progressive minor failure. Epoxy (My name is Ian and I am an epoxyholic. I have been epoxy free for ten hours.) is lovely but it's expensive. If you make an epoxy butt, then all activity in the area halts till the glue is fully cured. Getting the fit really good and the clamp pressure correct - which can be hard to feel if the clamps are also dealing the the stress of bending the plank - is a major pain. And when a glued joint fails, it all goes. When a screwed in butt block starts having trouble, one has at least a small chance of seeing it during the spring haul.

G'luck.

wizbang 13
11-20-2013, 08:30 AM
Even the last few guys building on the beach in Carriacou are scarphing planks, on the frames , no butt blocks. Epoxying them right in place
I have come to feel that using a little epoxy here and there is not a good thing .
So , I would tend to build a traditional butt, but I would not build a traditional boat. If that makes any sense.

debenriver
11-20-2013, 08:41 AM
I'm another epoxyholic! But with traditional carvel planking I don't think it is a good idea to epoxy bond the butt blocks.

On a new build we fitted the butt blocks after planking was complete and before caulking etc. They were generally copper clench fastened rather than bolted, because the other structures, planking etc. were copper clenched. Because the butt is caulked along with all the other plank seams I think you need to retain the same type of fastening structure, so as you caulk the structure can move very slightly to tighten everything up. The butt blocks fit between the steam bent frames and have a beveled top and a good waterway at the back each end so that water can't sit on the top. I'm talking sail boats here in the 25' - 55' range.

In new wood-epoxy construction we do still use butt blocks in place of scarph joints sometimes (specifically on decks and sometimes on chine hulls) and then they are epoxy bonded with the rest of the structure.

I reckon a good rule generally is to keep structures consistent – don't introduce sudden changes of system!

George

chuckt
11-20-2013, 09:29 AM
All that makes sense. "I would tend to build a traditional butt, but I would not build a traditional boat." LOL--I like that. And it makes perfect sense. I absolutely would scarf if I were replanking with new wood. I'm putting back on the old planking which is in near-perfect condition. My old blocks were clench fastened. Over the years, many of the roves have corroded away and some even disappeared! The butt blocks above the waterline seem fine. I've been replacing with bolts. More expensive but easier to do.

Dave Diefenderfer
11-20-2013, 09:42 AM
I had to replace a section of the garboard on a sailing Barnegat Bay Sneakbox I refurbished. I intended to hunt it from a trailer, so the carvel plank/swelling was not a real option. The daggerboard truck was rebuilt and I used butt blocks to fit in the new garboard section. Using thickened epoxy and SS screws. Once the epoxy cured, I removed the screws and filled the holes. The hull then got 2 layers of 6oz cloth. I break ice with this hull underpower in the dark, so I wanted a bulletproof hull. Of coarse, this is a 12ft hull, with a 15hp outboard, not much "working" of the hull anymore with the 2 layers of glass, and Ipe ice runners bolted and glued to the bottom.

Dave

Andrew Craig-Bennett
11-20-2013, 09:47 AM
I'm another epoxyholic! But with traditional carvel planking I don't think it is a good idea to epoxy bond the butt blocks.

On a new build we fitted the butt blocks after planking was complete and before caulking etc. They were generally copper clench fastened rather than bolted, because the other structures, planking etc. were copper clenched. Because the butt is caulked along with all the other plank seams I think you need to retain the same type of fastening structure, so as you caulk the structure can move very slightly to tighten everything up. The butt blocks fit between the steam bent frames and have a beveled top and a good waterway at the back each end so that water can't sit on the top. I'm talking sail boats here in the 25' - 55' range.

In new wood-epoxy construction we do still use butt blocks in place of scarph joints sometimes (specifically on decks and sometimes on chine hulls) and then they are epoxy bonded with the rest of the structure.

I reckon a good rule generally is to keep structures consistent – don't introduce sudden changes of system!

George

Well, George's Dad built Mirelle in 1937 and all but two of her copper clench fastened butt blocks are still there. The two that were replaced were replaced because the strake of planking between them was replaced after heavy weather damage.

So +1 for George's advice!

Gabriel Sky
11-20-2013, 10:21 AM
I am epoxyphobic... it is wonderful as glue (in most woods, teak being a notable exception), but I have failed to see it superior as a coating or sealer.

That being said, we did an experiment when I was building yurt door frames. We mocked up a door frame and epoxied the half lap both sides as normal, and installed the 5 fasteners on only one side. Once cured, we clapped on a come along and tightened to the point of failure. The side with fasteners and epoxy failed.

I thing a properly prepared epoxy but block would work, but is it superior, simpler? Prolly not for repairs, perhaps for new construction.