Glen-L.com

that is the question. Sounds a little indecent... but it's a serious one. Here's why:

My Glen-L 15 build requires 16' lengths of bottom and side planking.
I could scarf together two 8' pieces of ply to get the full length in one piece...
but they'd barely fit in the door of my shop -- and i suspect, it would be a
true bear to set 'em rough in place, measure, mark, cut, reset, glue, trim, etc, etc...

On the other hand, there's a handy frame member just about 7' from the transom,
right at the beamiest part of the hull. So I thought:
Why not take 1' from one piece of ply and scarf it to the other, to make 7' and 9' pieces?
Then I have a manageable size to work with, and i can join them at the #3 frame.

Ah, but then I have a butt joint. This is frowned upon by some because it may not
yield the smoothest curve.

What do you guys think? Would a butt joint be objectionable at that location? Are there ways to make it look smoother -- or should i just bite the bullet and scarf the full length?
I'm aiming to sail this boat, not spend my life putting a finish on it like a bowling alley!
But I sure don't want my boat to look like a piece of origami!

Your comments will be appreciated.

A scarf joint can be done on a full sheet in about five to ten minutes, fitted outside on a set of sawhorses with two 2 x 4s for support. Then you can temporary fasten them at the seam and then cut the bottom shape and take apart and glue in place after you take the two seperate pieces inside and place them in place. Mark with a sharpie your corresponding seams and mark lines across the rough in scarfed seam so that you will have a reference area when you glue them in place on the boat jig and frame.

Its really easy to back the scarfs up temporarily with plastic and a temporary type butt block fastened at the edges and clamped down using another 2x4 across the seam to apply pressure until the glue dries. Then you can just clean up the leftover thickened glue. Then glue them down as you normally do. The less obstacles you have on the inside, the less areas that you have to block and hold any bilge water that may get into the boa in that region even from rain if stored outside..

sorry if I'm a bit thick, oyster -- let me see if I understand your suggestion:

1) cut scarf for full length pieces of ply outside shop
2) attach pieces of ply together temporarily (how?)
3) bring inside, place on frames, mark up
4) take apart scarfed ply
5) cut to shapes required
6) glue scarf in place (on hull)
7) glue ply to hull

is that correct?

[quote="babyorca"]sorry if I'm a bit thick, oyster -- let me see if I understand your suggestion:

1) cut scarf for full length pieces of ply outside shop

This step 2 is done after you mark and do your scarfs outside on the work area. I use sawhorses with two long boards to support them long ways and then use a stiffening board under the edges when scarfing each piece. I then mate them together laying flat along the horses and boards. I did not see what type of boat you are building. But if you are building a vee hull then cut your pieces outside. I run sheetrock screws at the outside edge to hold the two roughed in scarf pieces mated together and then mark and cut to fit, leaving about one inch fat if at all possible. Then remove the pieces, unscrewing them after you have done the marking along the scarf ends. This gives you a great reference point when you put them back together on the jig frame inside or on the boat skeleton.
2) attach pieces of ply together temporarily (how?)

Then do the glue process since you were concerned about carrying the mass unit on one piece. Tell me the boat again and this could change my thoughts too.

my build is the glen-l 15 sailboat.

i guess i wanted to get a sense of whether a butt joint would be acceptable in the location where it would occur on this boat -- namely, amidships, near the broadest part of the beam.

it sounds like you're thinking it wouldn't -- and i should try & find some way (such as the method you describe) to avoid it. is that correct?

Normally joints are not secured on frames, if thats what you are also considering. The hard point for the short seam will always give you some grief, hince the reason for butt blocks. Even butt blocks do not fair out as nicely, so when you have a chance, scarfing is much nicer to the eye too under shiny paints. My preference anyway..

also,when you scarf two pieces of 8',you will end up with less than 16' total because of the overlap at the joint

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

upspirate is right. Joining two 8' sheets yielded me about 15' 10"

There have been several really good discussions on scarfing here on the forum. Here are a couple of links to two previous discussions (one about scarfing plywood and the other about scarfing thicker lumber).

Hope this helps.

http://www.glen-l.com/phpBB2/viewtopic.php?f=4&t=9934&p=68182&hilit=scarf#p68182
http://www.glen-l.com/phpBB2/viewtopic.php?f=17&t=10050&hilit=scarf&start=15

_________________
Bill

I told my wife we needed a three-car garage for my projects...she told me to ask her for permission next time before I buy a house.
http://www.unitybuild.net

ok, you've convinced me.
(i also re-read the glen-l literature about not fastening to frames at all, due to stress, cracking, etc.)
thanks for your advice -- it really helps avoid the "seemed-like-a-good-idea-at-the-time" blues.

For what it's worth, I am nearing completion on a Glen-L 14.

I had the same questions.

I have no real previous woodwork experience. I work in Software.

I did the scarfs. They required a little thickened epoxy in places, but turned out just fine.

Dave

_________________
Hey! I built a boat ! No Really, I did !
http://davesboat.blogspot.com/

Has anyone tried to scarf a joint by using a router and stepping the joint with successive passes? Is this an alternative or just not practical? Seems a board clamped to the plywood could be moved incrementally to result in a stepped joint that would lock in as well or better than a bevel. Just wondering.

Roberta

_________________
Roberta
Built Zip "Oliver IV" and Super Spartan "Jimmy 70"

When you use step scarfs, the adjoining pieces cannot be off that much with the interlocking pieces thats creating a component. Many CNC routers cut them but most has been trued in the programming stage so that by the time you get out to the running length end, things fit acordingly. Without knowing your previous experiences I can only reply with the worse case scenerio.

The bevel just gives you more "jiggle" room and if you end up off a bit (sometimes if you scarf in place no matter how careful you are something ends up just a little "off") you can sand the joint flush on one side and fill the minor gap on the other.

If you use epoxy, once it's (dry) your joint will be significantly stronger than the plywood itself - so a stepped scarf is not needed for added strength - it's not going to come apart.

There was a good article about "birdsmouth" scarfs (that kinda lock together) in Woodenboat magazine sometime last year. But those were used because the restoration project was using traditional glues which are not strong enough on there own to provide all the bond strength required.

_________________
Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

I know scarf joints are preferred by many but I have to admit I have yet to scarf a sheet of plywood. Both my Cabin Skiff and the True Grit have all butt joints. When building the Skiff my lack of experience pushed me towards butts and I have to say they have served well. Looking at the exterior I don't think anyone would be able to see the joint. And as to strength the poor little boat has been beat hard in chop on many many occasions and proved the joints are up to the task.

It was because of my experience with the Skiff I decided to butt the panels in the True Grit. I was somewhat concerned about this because the forward joint was in and area that is forming a fairly strong curve coming from the bow. But it all worked out fine and to my eye reveals no flat spot. I personally think the reason some builders have a problem with flat spots is they over do the butt block. Here the thinking bigger is better is definitely not the case. If it is overly wide or overly thick butt blocks it will stiffen the joint and produce flat spots. On my 1/2" panels I used a 1/2" thick butt block that lapped each side by 4".

I have to ask - when you scarf the joints are the panels assembled and then installed in one piece OR are the joints glued as each panel is installed? I was thinking they were assembled first and it was that procedure that had me considering the problems dealing with a 4' X 28' sheet. Using butt joints I was able to install one 8' panel at a time and make the joint as each plywood sheet was secured to the battens.

I have to admit because of the high stress on the forward joint I ended up having to drill through the ply and the butt blocks and use some 1/4" bolts and fender washers to pull the joint tight (bolts removed and holes filled later). Assembling the first two sheets and then installing would have made a lot more sense BUT because the adhesive I was using had a very short set time it would not allow me to do more than one sheet at a time.

_________________
So Many Rivers,
So Little Time....

I used a combination of pre-scarfed and scarf in place on my sides.

I needed a 26' long panel, and as you note the idea of trying to manuver 26' feet of plywood is not practical in a couple of areas - even if you get a few buddies to help move it around, the thought of trying to get all the epoxy mixed and properly applied before it starts to set-up on you, and get all the fastening done, then clean up the squished out epoxy (or forming fillets with it etc) all the while doing acrobatics trying to squeeze in and out of the frames whose access is now severely blocked by the panel itself - just not practical.

Even with a helper I found it challenging to work with 16 feet, but kinda needed to do that due to the severe bend coming into the stem. On mine the 8 foot mark from the very front was still well in the (curve). So I pre-assembled a 16' (almost - lose about 3" with 3/8" panels) and glued/fastened that one and then scarfed the remaining 10'ish foot panel in place.

Scarfing in place, especially in a flatter section is just as easy as doing it on a bench (or the ground) - the only difference is that if you are working with sides it's vertical. That issue is overcome by dryfitting and fastening dry (with screws) before you attempt to glue things up - then you just use an extra bit of thickened epoxy (apply on both scarfed panels), because you are going to "drag" your joint a little no matter how careful you are getting the locating screws refastened.

You can always back up the scarfs with temporary butt blocks (covered with wax paper or plastic so the epoxy won't stick to it) and temporary screws until the epoxy is cured if the joint is being a little un-co-opeative - otherwise a few staples through the joint which you will later remove is usually enough to keep the joint "clamped"...

In hind sight I would have even gone a little shorter than 16' - 12 or 13 would have probably got me past the worst of the (bend). That would have resulted in a little more panel cutting and an extra scarf, but would have made the bonding/fastening to the frame a whole lot less "hairy"....

_________________
Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it