why are boat planks butted and not scarfed

[Dan Hobson]

Access to long stock isn't always there. Why is it not more common to find scarfs in boat planks?? The positioning of scarfs might need to be thought out just as well as a butt joint. But it seems to me that over time a scarfed joint might have fewer rot and fastener issues.

[nedL]

I'd say speed. Butt blocks are much faster than scarfs. Also with butt blocks you can trim the plank ends easily between frames after the plank is hung.

[imported_Jimmy]

I think (I'm guessing mainly) that butt joints are quicker and easier. Also, in the past, glues were not as good as they are now and you wanted the fasteners as a back-up anyway. If done right, a butt joint is just as good as a scarf joint, it just isn't as pretty (although you often can't see them anyway). Shorter planks are probably also easier to handle and fit.

My boat has the butt joints done in about the worst possible way, the planks are butted on frames. Despite this, the boat is holding together almost 80 years later. So even done badly it works. It does make me nervous though and I am planning on replacing as many of these improper butt joints with short double scarfs as shown in the last (aug 2005) issue of Wooden Boat magazine.

[Dan McCosh]

I stopped using butt blocks about 20 years ago, and still have my original effort in the hull--a simple ship-lap joint. Since then, I've done probably a hundred repairs with scarfs rather than butt blocks. I pulled more than 30 rotted blocks from the hull, replacing them with scarfs. The scarf strength is superior--a block is a relatively weak joint, due to the fastenings close to the end of the two planks being joined. The rot collection point is eliminated. I would use all scarfs in new-boat construction.

[jwswanboats]

I might wager to say that a well fitting butt block is not easier and quicker than a scarf joint. This will in all likelihood become another circular conversation, But a really good scarf joint (one where you don't have to worry about air pockets and glue failure) should not just be a slap-dash quick cut joint, relying on epoxy filler/hardener to make up for a poor fit. I think if a person has a good butt block schedule, and they fit tight (to both the plank profile and in relationship to plank thickness/frame spacing) and are bedded properly, they can last as long as a scarph. Additionally, in small boat construction, using jimmy steele's-the maine peapod builder-technique on small boat construction of a "belt" frame, or a frame wide enough for two plank landings is, i think, a really clever approach. anyhow, i am not writing this full of venom for the scarph joint, i use them quite a lot. I am just trying to give the butt block its propers (in the immortal words of aretha franklin). well, happy debating...
josh smile.gif

[Dave Fleming]

using jimmy steele's-the maine peapod builder-technique on small boat construction of a "belt" frame, or a frame wide enough for two plank landings is, i think, a really clever approach.What means 'belt frame'?
Got a drawing or web site to view one in use?

[Cuyahoga Chuck]

The glue that has sustained woodworking since the days of the Romans is "hot horsehide glue". It's a wonderful product and still in use for the most treasured wooden antiques. That's as long as the antique has nothing to do with water. I don't think there was a real waterproof glue until resorcinol came along. I'm not a glue historian ,but, I think that appeared only in the 20th century.
Charlie

[Dan McCosh]

Filled epoxy is the key to a scarf installed while the planks are already hung. Obviously traditional butt blocks work, but they inevitably collect dirt on top, plug the drain holes, etc. Also--the fasteners close to the end of the plank are prone to splitting, etc.--and you create large amounts of exposed end grain. I would argue that even a fairly crude scarf is better than a good butt block. As for what you can get away with--a surveyor pointed out what looked like a leaking butt block. It turned out that an old repair had been done with the plank butt seam landing on the rib with no fastenings at all, and the butt block had been screwed to the plank alongside the seam. It still didn't leak all that much, even under sail, and apparently had been there for years.

[Ken Hutchins]

Here is another option, an edge scarf with finger joints glued with resorcinol.
http://www.imagestation.com/picture/sraid81/p0a86206838a1833cc24385a518ebe544/fafd4aba.jpg

[Stiletto]

I found myself wondering whether the greater amount of exposed endgrain could be a problem with scarfs. Not important on an epoxy glued boat but potentially problematic on more conventional construction.

[Dan Hobson]

Conventional construction has an open ended board treated with lead paint and bedded in dolphinite then crammed with cotton or oakum more or less sealed with paint over the top. Water gets in and rot spores with it. Water travels through the caulking. But the scarfing isn't built that way. Glue seals the end of the plank as it bonds one board to another. It's engineered to stay dry and limit water incursion rather than welcome it in and plan on the planks expansion to make the seal tighter. I don't think I like the edge scarf as well as a nice long 2:1 or 3:1 plain scarf. The ratio of bonding area to edge makes more sense to me. The finger joints have a lot of bonding area. But they also have a lot more edge. All in all it probably works great anyway.

[Jack Heinlen]

In a word, glue. For centuries butt blocks were THE way, but with the advent of waterproof glue, butt's are less necessary.

There're also pragmatic reasons. In larger boats butt blocks make the building easier. Hanging a full length plank on a thirty footer takes a crew, whereas one man can hang it in sections. Getting a forty foot plank fair ain't a piece of cake either.

If done right, butt blocks still work, as they have for a long time.

[ 08-21-2005, 09:05 AM: Message edited by: Jack Heinlen ]

[carioca1232001]

...Hanging a full length plank on a thirty footer takes a crew, whereas one man can hang it in sections. Getting a forty foot plank fair ain't a piece of cake either.
To add to the above comlexity, consider scarf-jointing planks 6 " wide and only 5/8" thick.

The scarf-jointed 30 ft length of plank would be relatively light, but the scarf-joint would probably not hold up (under the weight of the plank)while fitting into place on the hull, with a person at either end.

Right or wrong ?

[Dave Hadfield]

It's just easier in small pieces. The planks often have to be fitted. That means putting them in place, marking, then taking them down and removing excess material. This is a whole lot easier with a 16ft plank than a 40ft one.

If the planking is oak or mahogany or some stiff wood, it may have to be steamed. Steaming a 40ft plank is awkward. The steam box needs to be a lot more elaborate.

Also, the planks may have to fit into a stem or stern rabbet or both. You only get one chance to do this right if the plank runs full length. You'd hate to spoil a 40ft plank, particlarly if it only fits in one spot on the curve of the hull.

[carioca1232001]

Now that just about sums it up !

[Klaus]

quote:

To add to the above comlexity, consider scarf-jointing planks 6 " wide and only 5/8" thick.

The scarf-jointed 30 ft length of plank would be relatively light, but the scarf-joint would probably not hold up (under the weight of the plank)while fitting into place on the hull, with a person at either end.

Right or wrong ?

Wrong, properly done, at a 8:1 or better scarf ratio, this join will easily support the weight of the plank. Actually, if over stressed deliberately, the wood will most likely break elsewhere, away from the scarf joint.
My boat has a scarf joined teak rub rail, of only 1/2" x 2" section (teak IS expensive). I made the 26'+ length up from 4 bits of teak, eg. 3 scarf joints. No problem handling this very bendy rail to fit it into place and no problems in the 6 years since launching, despite some hard meetings with jetty posts ;)

Klaus

[carioca1232001]

Klaus, I suppose you need to go by the book, no short-cuts allowed.

I scarve-jointed two long chine pieces, but did not comply with the stipulated 8(or12):1 ratio, so they went fut as I lifted the pieces :rolleyes:

[Dan Hobson]

Jack and Dave are on the mark I think. I wasn't considering the case of the fourty footer but more the situation of having the most cost effective stock only available in 8' 10' or 12' lengths. I was also thinking of the longer ratios put together with good epoxies as well so holding together is not really an issue. But as to fitting a plank, A butt block splice has to be fitted to a 16th of an inch. And in the radical case of an 8:1 scarph formed on the boat, it might allow you as much as a half of an inch of wiggle room fitting the end of that board with less than a sixteenth of an inch of variance in the final thickness at the scarf. A lot more room to be somethat less precise in measurment and cutting and final fitting.

By the way which is correct Scarf, Scarff, or Scarph??

[Ellis Rowe]

I scarph in place with a 12 to 1 plain scarph joint. I find that I can accomplish the joint about as quick as I could do a proper fitting butt block. Of course, I was much younger and inexperienced when I did butt blocks, so probably slower. One disadvantage of butt blocks that no one has mentioned is that they prevent the chimney effect ventilation between planking and ceiling, which is why I started scarphing in the first place.

[Ken Hutchins]

...Hanging a full length plank on a thirty footer takes a crew, whereas one man can hang it in sections. Getting a forty foot plank fair ain't a piece of cake either.
:confused: :confused:
Gee I wish you told me that before I planked my 36 foot TALLY HO II, I didn't know it took a crew :confused: I did it all working alone, including riveting. I had no trouble spiling, cutting, handling, fitting, fairing all full length planks. smile.gif With careful work many of the planks fit the previous plank within 1/32" along the entire length on the first fitup.
IMO full length planks are easier than having to deal with butt blocks. I only steamed the foreward end of 2 planks on each side, no steam box needed, I used my plastic bag method and steamed the planks in place. smile.gif

[carioca1232001]

So, to reiterate an old request, PLEASE Ken reeal your expertise in a book, Videotape or DVD.

[Paulyboy]

Originally posted by Ken Hutchins:
Here is another option, an edge scarf with finger joints glued with resorcinol.
http://www.imagestation.com/picture/sraid81/p0a86206838a1833cc24385a518ebe544/fafd4aba.jpgSeems there was a thread here about 14 months ago regarding the use of finger joints. The concensus was not good strength in the joint, but I would certainly think it would be stronger than a butt joint if the same adhesives were used.

[hikingchrs]

If you notice in Ken's pic he has cut the planks a an angle, it looks to me about triple the glue edge. plus the fingering this will never break.
Chris