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Todd D
03-21-2009, 09:19 AM
Within the next month I expect to be replacing a few planks on the hull of my 32 footer. Most of the plank runs consist of two planks with a but joint. Individual planks are up to 24' long. All the butt joints fall on frames. Since the frames are only 1-7/8" wide, it seems to me that the doubling of the number of screws in the frames with but joints must weaken the frames at those spots. My question for the forum is as follows.

Is there any reason that when I replace a plank that I shouldn't scarf it into the other plank in that run to give one continuous plank that runs the length of the boat with no butt joint? The planking is all 1" douglas fir.

If you think this is a bad idea, please tell me why you feel that way.

johngsandusky
03-21-2009, 09:56 AM
I think it will be fine, it's a common repair technique. You might glue the scarf in place, so you won't have to handle a 32' plank. You could also change the butt location to the frame bays, and use butt blocks. I've done that, it works.

Todd D
03-21-2009, 10:05 AM
The plan is to do the scarfs in place. It seemed to me that the hull would be stiffer with full length planks than with butts.

outofthenorm
03-21-2009, 10:37 AM
No reason at all not to do it. Much better than butt blocks. The DF will glue perfectly with epoxy. Make the scarf about 12:1 ( or even longer) and it will likely span 2 frames. Stronger then ever.

- Norm

Plover
03-21-2009, 10:47 AM
Todd,
Scarfs are OK above the water line any thing below should be butted with a backing butt block, much stronger and easier on the leakage assuming it is carvel planked. Simply make the butt block 1 to 2 inches wider (up and down) then the plank to be replaced and give it 6 to 8 inches of both sides of the joint or go rib to rib with it (frame to frame) fair it to the hulls shape use no glue and get 5 to 6 screws on each side of the joint with decent spacing and only screw to the replacing plank and nothing else! use a block plane before all that happensand bevel the exterior top 1/3 of the plank for the caulking, if you miss that step just use a butt iron (or dumb iron as its called) And smack that in there to open up the joint for the caulking, smear it with Interlux brown, let it dry, prime and paint, and you should have a very leak free job!
Best of luck to you!
Paul

Green Boat
03-21-2009, 06:39 PM
we just planked a 27 foot sloop with long scarfed cypress, the planks need 3 people to hang them but no butt blocks make for a very clean looking hull.

Todd D
03-21-2009, 07:23 PM
Plover,

Why don't you like scarfs below the waterline. They seem to be very common in plywood construction. Why not in carvel planking, particularly when they will be held together with screws through the planks to the frames.

RFNK
03-22-2009, 05:48 AM
Just butting in here - plywood is very stable, it doesn't swell or shrink much so a well-made scarf is fine below the waterline. With planks, you have the swelling and shrinking placing a lot of uneven pressure on the glue joint and it's likely to fail. The butt block arrangement allows it all to be caulked and the joint to be free enough to accommodate swelling and shrinking. Rick

floatingkiwi
03-22-2009, 05:55 AM
I would take the advice of Rick here, mate.

Plover
03-22-2009, 09:43 AM
Hey Todd,
As said, scarfs are OK for ply! (And I am one that does not like PLY!) Main reason, If you look at the length of the scarf and where the screws are going in to it, number one, the screws are going to be below the scarf depth, so how is that stong? The other thing is that wood is a natural material that absorbs moisture and swells and contracts, I really don't think there is a glue in the world that can hold up for long, just by the nature of things. Sure, a glued joint would look great and be leak free for a while but certainly not forever! And as said, it takes a few people to line it up and start screwing. A butt block on the other hand, is the most traditional of all, and some out there have lasted a hundred years! Tell me what glue will do that? Please believe that I mean no ill will here, I just believe that its more work for a scarf then it is to butt block it and have it last and last. Hungover with 2 broken index fingers and you can still get it right with out tying to hard, trust me on that one! How its done is always the mariners choice, saving time and money has always been mine. And besides, why complicate things? if it under water and no one see's it to apraise such a fine joint, why waste the time?
always, best of luck!
Paul

outofthenorm
03-22-2009, 10:32 AM
You guys make it sound like there are no issues with butt blocks - 'taint true. Blocks are weak points, not strong points. They are dirt and water traps and if they are under a ceiling, they can block air flow. If an old vessel with blocked planking is leaking, there is a strong possibility that it's leaking from the butts.

I am not an "epoxy-boy", but there are some applications where epoxy's ability to permanently bond 2 pieces of wood has already been tested and proved. This is one of them. A long scarf in properly prepared DF will last just about forever - or at least as long as a butt block ever will - and has some real advantages. What does properly prepared mean?
- the two pieces should be equally dry to the right moisture content
- the grain orientation should be matched
- the epoxy/aggregate mix should be tuned for the application
- the pressure used to clamp the joint should "just right" - a fine glue line with no starvation.

- Norm

Todd D
03-22-2009, 12:12 PM
plover,

I wasn't attacking your position, I just wanted to know your reasoning.

seo
03-22-2009, 01:01 PM
Making a scarf joint in place would take a lot longer than making a butt block. I agree with the comment above that butt blocks are prone to collect dirt and cause rot, and for that reason I keep them 1/2" away from the frames.
Butting planks on the frame is common in sawn-frame construction, and doesn't seem to cause huge problems.
Because the use of butt blocks is almost universal on high grade bent frame boats, I make the assumption that the Herreshoffs and Lawleys of the world knew what they were doing.
On the other hand, if you have a boat that was built with planks butted on frame, that's what you have. Changing a few butts to either scarfs or blocks isn't going to change the overall strength of the hull, and won't even get rid of the extra screw holes in the frames where you make the change; it's just that they'll be empty or plugged-off screw holes now...

Todd D
03-22-2009, 04:04 PM
Seo,

I am not concerned with time spent. I have plenty of time. In addition, I am reframing most of the boat and all the planks I am replacing will be attached to new frames. Cost is also not a factor since reframing and replanking are cheap compared to the repower. My concern is to make the hull as good as it can be.

Todd D
03-22-2009, 04:06 PM
For got one other point. Herreshoff and Lawley didn't have epoxy.

floatingkiwi
03-22-2009, 04:58 PM
But we do.

davetuemmler
03-22-2009, 09:44 PM
Last summer I did a total refastenining & a partial replanking on my 1956 Holiday 30. Starboard planks were in great shape but the port planks were looking tired. I replaced 6 full length planks that had been scarfed with 5-6 inch scarfs. I replaced with a 20 inch scarf. I figured it lasted 50 years with minimal scarfs, not to mention that in todays world we have epoxy for the scarf joints. While I was at it I replaced 43 ribs. It was a 2 person job to handle the planks and lots of clamps but really not to bad considering it was my first time. I used the old planks as a rough template and scribed in place. I'd like to say I'm finished but I'm not. I've done a rough fairing, ready to glue in bungs and do a final fairing which I think is going to be brutal. Then I find a waterline. After that I need to rebuild the interior that I ripped out to do the work. Hopefully it will be ready for another 50 years. I've had her for 27 years. Here's a link if you want to see photos.

http://holiday30.shutterfly.com/

Plover
03-24-2009, 06:43 AM
Dave, real nice work!

Todd, I didn't feel as if I was under attack, so have no worries there! Perhaps I was a little out of line! And as I said it is always the Skippers choice how he or she repairs their craft, simply. The dirt thing collecting on them is about the only real issue with them and after reading that I have just learned something, I have taken forgranted, from here out, frame to frame has always been the norm for me. So now being as I do my own work and its my ass if I screw up, I'm going to 45 the ends and top and stretch the top a little higher up the plank above it. Good idea or not I don't know, time will tell! I figure that the water sloshing around down there will be moveing sediment all the while, so why not use it to wash the blocks? I wouldn't make them knife edged, just a slight 1/8 inch reveal or so. Seems to make good sence to me.
So I can say Outofthenorm, you have taught me something that I have always over looked and never even thought to address it, Thanks.
Paul