Another Scarf Joint Question

[georgeandpat]

I'm sorry if this question is dumb, but it is driving me nuts. On the strips, does the scarf joint span the thickness (1/4" side) of the strip thus appearing as a butt joint from the outside of the canoe? Or, does the scarf joint span the width (3/4") of the strips and appear as a diagonal line from the outside (or inside) of the canoe? I get conflicting impressions from the archives. I plan on ripping strips over the holidays. Thanks, George.

[Glen Smith]

I have used both types and I had better success with the width-wise scarf using a ratio of about 8 : 1.

[John K]

Hi George,
It should be in the thickness, although there are people who do the diagonal cut. That also seems to work, but I would think that it would be somewhat weaker. It is easier to do.
JohnK

[georgeandpat]

Thank you for the quick replies. It seems that using the 1:8 ratio would give you a surface area (of the glued surfaces) of 1.5 square inches in both cases but I would think that using the scarf joint across the thickness of the strip would be a stronger joint. However, after scraping, shaving, and sanding, I envision the joint line looking crooked and, as someone mentioned (I believe), the glue is more visible when the scarf is across the thickness? I like the clean, symmetrical look of butt joints but have the understanding that while stripping they might not be strong enough to take the twisting and bending. I also have the understanding that once the boat is glassed that the type of joint is irrelevant as far as strength is concerned. Would using small biscuits or dowels be an option to add strength to butt joints in curved areas?
I know I'm asking a lot of questions on this one topic, but because I'll be using a lot of short pieces, I'll be using a record number of joints in this project. Thank you.

[pawistik]

The fact is you can do it either way as Glen said. I did it across the width (3/4") and you are probably right, this way, though it gives a longer visible line, will likely look "cleaner" in the end and will be less likely to have as much glue showing and the joint line will remain straight in appearance after sanding, scraping or planing. I was looking at the diagonal joint on the sheer strip of my kayak the other day and now it is hardly visible under epoxy & glass.

Regarding the ability of the strip to accept a twist or bend, that is probably not be an issue assuming that the wood you are starting with is more than about 3 feet long. Just ensure that the joint does not end up too close to either end of the boat and you'll avoid the whole issue of requiring the jointed portion of the strip to have anything other than a gentle bend or twist.

For the shear strips (the first strips put on the forms), scarf yourself some full-length strips so that your first strips on the forms will have a nice fair curve over the whole length. For everything else just butt-joint them as you strip the boat. Again, you probably want to avoid having the joint in a section that is curving dramatically, but that can be easily accommodated. Put the joint at your stations is probably best & easiest, but you don't have to - I know I did a few between stations and did not have problems. If you chose to butt-joint on the forms as you go rather than pre-scarfing your strips, you have the advantage of being able to use shorter pieces of wood which are much easier to manoeuvre and handle in the shop, especially if space is tight. If you pre-scarf your strips, then you don't have to worry about trimming things up to prepare those butt joints while you are stripping. My kayak was stripped partially with full-length strips and partially with shorter material. For my next boat, I think I would probably look for 12' material and do the whole boat with that - I found that dealing with joints was easier than dealing with unwieldy long strips.

Cheers,
Bryan

[georgeandpat]

Thank you Bryan, You and the others here have given me much more confidence to start this project. I hope to post a progress report in a couple of weeks. George.

[ealger]

George, practice on some scrap strips will give you an idea whether to scarf vertically, diagonally, 8:1, or at a 45 degree. joining between the molds will let you stagger the joints somewhat. Don't try and put a staple through a scarf joint at a mold location.

You can join a scarf joint right in place, whether at the mold or in between, by placing a short strip over the top of the joint (dry) with tape to align the joint (assuming you are doing cove and bead).

Glen has a picture of his scarf examples elsewhere in this forum.
Ed...

[georgeandpat]

Thanks for the input Ed. Yes, I do plan on bead and cove. I just got my 7-1/2" Diablo saw blade this week and will start ripping strips from an old redwood swing set. Most of the pieces are going to be between 4 to 8 feet, hence all the questions on joints. George.

[ealger]

George, do you have a plan as how best to resaw your Redwood? Redwood strips, which end up being flat sawn, tend to show the wild grain on the face. You might consider resawing the Redwood so that the strips end up being Quarter sawn. (Perhaps you might like the face figure, that's your choice). Either way you choose to resaw, know that scarfing a quarter sawn strip to a flat sawn strip, the joint is going to show.
I built a canoe in Redwood in 1970 from all heart vertical grain material. I didn't know any better and the sides of the canoe show the wild grain. It is still floating, however.

[georgeandpat]

Ed, I am ripping many of these strips from 4x4s so I do have a choice about the grain. Thanks for the reminder. I'll do a search on the pros and cons of each before starting. George.

[garypete]

Non-full-length strips are a great advantage when it comes to closing in the bottom along the keel line. With full length strips, you must guesstimate how much length to add so the strips will fit snugly along the keel line. Canoecraft recommends adding about 5/8", but this changes as you get closer to the final "fill-in" strips that close up the hull.

On the other hand, using 2-piece strips for these special pieces makes the adding-length hassle a moot point. You simply cut the correct angle at the keel line on one end of both fill-in pieces, then establish the exact overall length by overlapping the other ends with the strips in place. Cut off the excess to eliminate the overlap and you have a perfect length at the butt joint.

You can also get the exact length to cut by using tick marks, but that's even harder to explain without pictures!

Gary

[georgeandpat]

Nice tip Gary. Thank you, George.