Thread: Canoe Plank Scarf

Originally Posted by Anthony_C

Hello woodworkers,

I have started my first major project, a strip planked canoe that needs longest planks of about 5.3m. I plan to use WRC in 18x6mm bead and cove strips that I will mill. Of course I cannot find timber that will provide the planks in a single length, so I will need to creat my full length planks, scarfing.

I have some scarf questions.
- should the scarf be along the thickness (6mm) or width (18mm) of the plank? They both seem to produce the area of adhesive, but not sure which is best.
- I think it would be best to scarf before ripping the planks, so join the stock and then rip the planks, building fewer joins… thoughts?
- do I need to be careful about reversing the timber? That is should I make sure to join A-B to A’-B’, such that the two A ends are together, which ensures the joined ends are similar colours, but the grain is reversed, or join the A to B end so that the grain of the finished plank is in the same direction?

Finally, I would like to create a pattern. The patterns I have seen use a simple 45 degree along the plank width. Does that compromise the plank strength? Do I need to be careful?

thanks for any thoughts

Anthony

Also, what scarf length? I have read some technical documents that suggest plank scarfing should be 4:1 although other material suggests that 6:1 should be the minimum.

all thoughts welcome

Anthony

Hi Anthony, welcome to the forum, it's good to see another canoe build starting.

I don't have time to cover everything in your post at the moment but can offer a few bits of opinion/advice.

First, many people do not scarf all of the strips. I would scarf the sheer line strips then butt join the others with the very important proviso that the joints are staggered ie are not all in the same position longitudinally. This way you still get a strong hull with less work. Note that I have not done this with bead and cove strips - I have always hand bevelled the strips to fit when assembling.

Second. I recommend 8:1 scarf ratio. For orientation and a couple of photos see post number 3 in this thread: Paulownia/cedar fishing ski (woodworkforums.com) .

Third, I would cut the strips before scarfing for those that will be scarfed. Handling 5.3M strips is much more difficult than handling something in the 2 - 3 M range.

Will try to find some more photos and add a bit more later tonight or tomorrow.

Originally Posted by labr@

Hi Anthony, welcome to the forum, it's good to see another canoe build starting.

I don't have time to cover everything in your post at the moment but can offer a few bits of opinion/advice.

First, many people do not scarf all of the strips. I would scarf the sheer line strips then butt join the others with the very important proviso that the joints are staggered ie are not all in the same position longitudinally. This way you still get a strong hull with less work. Note that I have not done this with bead and cove strips - I have always hand bevelled the strips to fit when assembling.

Second. I recommend 8:1 scarf ratio. For orientation and a couple of photos see post number 3 in this thread: Paulownia/cedar fishing ski (woodworkforums.com) .

Third, I would cut the strips before scarfing for those that will be scarfed. Handling 5.3M strips is much more difficult than handling something in the 2 - 3 M range.

Will try to find some more photos and add a bit more later tonight or tomorrow.

Thanks Labr@,

When doing the scarfs would it be best to do the join across the plank thickness (so having what looks like a rightangle join) or along the width , showing a long angled join?

With respect to joining before planking, while handling shorter planks is easier, as I need to join about 60 planks, i figured that doing one big join and then cutting and milling the planks may make for tidier joins, and less messing about.


Anthony

Well I was surprised to realise that I last posted here nearly 2 weeks ago! Hope I can still be of some help.

Have a look at the diagrams below.

If you scarf the stock before cutting strips as in A then you will get the joints looking like B on the canoe. To me this appearance is just wrong - but each to his own.
The scarf faces will look like C with the direction of bend shown by the arrow.

Compare this with a scarf done on an individual strip as in D. I may be wrong but I have a perception that the scarf shown in C is not as strong as that shown in D. In addition to this there will be more wasted timber.

How will you cut the strips?

You mentioned patterns in your first post but I am not sure what you mean. Can you post some pictures of the type of pattern you want to do?

Bob,

Thanks for your thoughts. I had been figuring to do as you suggested and join the timber and then cut the planks from the joined stock.

I agree that the long slope is unattractive, so I figured the do the join such that when cutting the planks ( marked up A) it ends up like D, giving a straight join at 90o to the plank length.

I think the join area is the same as the joint in B, but the stress on the joint would be less where the plank is curving, as the joint is shorter.

Scarfs.png
I have done a test this afternoon, I will see how it goes and post the result.

Anthony

Originally Posted by Anthony_C

Bob,

Thanks for your thoughts. I had been figuring to do as you suggested and join the timber and then cut the planks from the joined stock.

I agree that the long slope is unattractive, so I figured the do the join such that when cutting the planks ( marked up A) it ends up like D, giving a straight join at 90o to the plank length.

I think the join area is the same as the joint in B, but the stress on the joint would be less where the plank is curving, as the joint is shorter.

Scarfs.png
I have done a test this afternoon, I will see how it goes and post the result.

Anthony

I finished the test and the pics are below. Once I cut them, i put them through the thicknesser to clean them up.

Generally, I was reasonably happy with the look of the joint, it worked OK, but think it could be better.

I used Epoxy for the join, at first I clamped to too much, which resulted in too much glue pressed out of the joint. Also, not sure that wood glue would not be better.

Also, see the small "trench" at the left hand end of the top of the join. Perhaps I went to hard on the Thicknesser? I think it should be smoother.
Top_Side Joint.jpg

Regs

AC

A few observations/comments-

- Assuming that you will fibreglass the hull, you don't need to use epoxy for the scarf joints. Interior PVA is adequate and is so much quicker and easier.
- The scarf ratio appears to be about 4 to 1 - I recommend 8 to 1.
- My interpretation of your post is that you put the individual strips through a thicknesser. I don't do this. Provided the strips are cut with a decent saw they should be ready to use. They will be sanded once the hull stripping is finished. It is important to have the edges smooth, not the faces, so you need to make sure the faces of the stock are smooth before cutting it into strips (the faces of the stock become strip edges).
- When clamping scarf joints it is important to clamp the two pieces to the bench (or whatever) with the tapers overlapped/aligned correctly before clamping the actual joint. This stops the sloped surfaces from sliding on each other and forcing the pieces apart. It is also a good idea to use a strip of timber between the joint and the clamps. I put a piece of masking tape on the joint to stop the padding strip from sticking to the joint.

There are lots of words and no photos in the above so please let me know if anything is not clear.

Originally Posted by labr@

Well I was surprised to realise that I last posted here nearly 2 weeks ago! Hope I can still be of some help.

Have a look at the diagrams below.

If you scarf the stock before cutting strips as in A then you will get the joints looking like B on the canoe. To me this appearance is just wrong - but each to his own.
The scarf faces will look like C with the direction of bend shown by the arrow.

Compare this with a scarf done on an individual strip as in D. I may be wrong but I have a perception that the scarf shown in C is not as strong as that shown in D. In addition to this there will be more wasted timber.

How will you cut the strips?

You mentioned patterns in your first post but I am not sure what you mean. Can you post some pictures of the type of pattern you want to do?

Bob,

here is an example of the pattern I thought I would try to create. Obviously, these joins are effectively butt joins. I have seen these created by gluing a number of pieces together, and then cutting the planks out of the glued stock.

Canoe Pattern1.jpg

Regards

AC

You would need to take some care in lining up the segmented strips when gluing to the hull and when handling them. Apart from that it looks fairly straightforward.

Keep us posted with some progress photos.