Scarf joints

I am about to get started on a SW17 from plans. I've got 3 sheets of 4x8 Okuome for the hull. To avoid major alignment problems I am considering scarfing all 3 sheets prior to tracing the lines and making cuts. (this way I will have true factory edges to line up prior to gluing)  A 4x24 ft sheet of 4mm plywood sounds intimidating though. Any suggestions on a better method?  Also, the plans talk about using a layer or 2 of fiberglass to renforce of other types of joints ...i.e. butt joints and the factory cut puzzle joints. But there is nothing about using this technique for scarf joints....any thoughts?


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RE: Scarf joints

Topper,

A 4x24 sheet does not have to be intimidating as long as you have the space to handle it. I used 3 sheets of 4x20 for my schooner. The main thing is to have a large open area, clear of any obstacles.

You also want to avoid flipping the sheet as much as possible, though if you have a helper it's not a big deal. The main thing I wished I had was a waist-height table big enough to hold the full sheet. I did all the joining, layout and cutting on the floor and my bad knee was not happy about it.

That said, at least hundreds of SW17s have been built by scarfing after the cutting, so I don't think you really have to worry about it.

A properly made scarf joint is as strong (or stronger) than the original wood, so it doesn't need the fiberglass reinforcement. Butt joints and some puzzle joints just don't have the same bearing area as a good scarf, so they need the glass to distribute the stress. The CLC precut finger joints for joining multiple sheets of plywood do have enough bearing area and don't need the glass, either.

Say hi to the Kerbys and Neil for me,

Laszlo

http://www.morocz.com/BoatBuilding/SchoonerBuild.htm

 

RE: Scarf joints

If I recall correctly, the layout allows you to cut the sheets in half the long way before scarfing them together. That will make them much easier to handle. My own experience is that butt joints are cleaner and much easier to do, and plenty strong enough for our purposes. You can see examples of both on the kayak pages of my site www.twofootartist.com -Wes

RE: Scarf joints

Thanks for the words of wisdom guys. Wes- it was your blog that got me interested in the Shearwater. I bought plans the week after reading it. I like the look of the Sapele deck but not the $100 price tag on 1 sheet of it. I am entertaining the idea of putting a red mahogany stain on a pc of Okuome for the deck. It's kind of waxy though, probably need to seal it with something prior to fiberglass and epoxy...?

Also, Wes- I believe you covered the entire interior of your SW with glass instead of just the cockpit am I correct?  If so, Do you know how much weight it added?

RE: Scarf joints

Hi Topper,

  I scarfed up a 4'x24 and it went well. You may alreadfy have a method for cutting scarfs on 4' ply sheets, but FWIW I made a really simple jig/fence for my skilsaw from a length of 2x4". It took only minutes to make, and cuts really nice scarfs in seconds. Give me a yell if interested in details.

The idea of ripping the ply lengthwise may be useful, here is another trick I used. The hull I was building had hull panels layed out on the ply symmetrically either side of the centreline. I only marked panels on one side of the centreline. My first cut was made along the bottom edge of the panel nearest centreline - effectively ripping lengthwise. I then flipped one half on top of the other, taped long half sheets together along straight edges (clear packing tape, 6" lengths, at about 1' intervals), and cut panels in pairs. The paired panels are now same shape. Tape pairs together along one edge (as you go). A few F clamps along that taped edge and the pair is held together in alignment and will sit up on edge. Now fair edges with plane and or sander, tape faired edge, remove tape from other edge and repeat. After this you will have perfect matched pairs of panels ready for wiring.

  cheers, Dave P

RE: Scarf joints

I agree with Dave P about cutting identical panels together if you can. That's what my daughter and I did with her Ganymede.

As for glassing the inside, I used cloth only in the cockpit and underside of the deck. The rest of the seams used tape.

-Wes

RE: Scarf joints

Thanks again for the advice. I like the idea of cutting and shaping 2 identical panels at once....I will definitely try this method. Waiting for the rain to stop here in Oregon so I can do a mock lay up to see if the pattern can be put on 2'x8' plywood strips. Definately sounds easier to manage. I just finished sealing my 15'x19' covered patio for the build...realizing that I need to extend it by a few feet in order to accommodate 24' at least for a day or two while I glue and cut the panels.

Wes, I have read so many blogs in preparation for this, now I can't recall where I read the one with the full glass interior....After using your boats can you think of a benefit for doing this?

RE: Scarf joints

I completely glassed the inside of my WD12 and am doing the same for my schooner. The reasons were abrasion protection, extra strength and assured interior waterproofing.

The extra cost was mostly in epoxy. I used up everything in the kit and had to buy an extra quart (since that was the smallest unit sold). The extra weight was managed such that the boat still came in under the design weight.

It's not necessary for a successful build, but I planned to use the boat in high choppy waves, carry all sorts of stuff inside and use it in rocky areas. I also like to hose out the interior after a paddle. The extra glass mainly gives me reduced maintenance.

Hope this helps,

Laszlo

Click on images for larger pictures.

 

RE: Scarf joints

Helps a lot. Thanks! If you had a choice between 3.7 oz or 5.8 oz glass which would you choose? The plans call for 4oz but for some reason the local plastic shop only carries these 2 options plus a few heavier ones.

 I am also using a graphite finish on the bottom thanks to all of the testimony.     Also considering a water based stain....maybe a 2 tone red and black. Not completely sure. I love the look of wood but want stand out from the crowd a bit :^)

RE: Scarf joints

The 3.7 ounce. It's the closest to what the plans call for. Alternatively, you could order the glass from CLC. Since they can ship it rolled or folded (depending on the size) the shipping costs aren't too bad and you end up with exactly the right stuff.

Laszlo

 

RE: Scarf joints

So frustrating....For some reason I am having the hardest time making scarfs. I am soooo glad I bought some cheap 1/8" to practice on. I made a jig, bought a new blade for the saw and they still come out looking poor. I even tried the block plane method but found it too difficult to get everything even. Maybe try an electric sander next....if that does not work I'm going with butt joints. Laszlo, I read your posts and looked at the pics...butt joints definately look cleaner. I think I will try to find data on how much stronger scarfs are than butts...

RE: Scarf joints

oops. Actually it was twofootartist who posted about the joints. Thanks to both of you anyway. I found some good info on Pygmy's site concerning their decision to only use butt joints. I think this is the one for me.

RE: Scarf joints

Hi Topper,

  what kind of jig did you make for scarfing? Mine was quick to build, easy to use, worked great. Then again butt joins sound even quicker and easier!

 

FWIW:

 

Here is a test result:

RE: Scarf joints

 Hey Topper,

 I feel your pain. Up until this morning I've hated scarfing. Tried the electric planer, router, worm drive and block plane, still had a hard time getting to sleep the night before scarfing. I caught a video on UTube where a fellow used a mini grinder and sanding disc, no jig and no sweat he had a nice scarf in no time at all. So this morning I was at the big box and picked up a disk for the mini grinder, it looks like a lot of small pieces of sandpaper glued together to form a circle and is rigid. This works like a champ for me!

 Also I have done butt joints on other projects where the outside bulge (from the extra glass cloth) would be faired out and it worked very well. I don't know how it would look in an area that was going to be left bright though.

RE: Scarf joints

Davep,

I have noticed that most builders are using a skill saw to do their scarfs...I wonder if that has anything to do with it? I have been using a wormdrive. Not sure why that would make a difference. I followed an example I found on line using 2 pcs of MDF and some bracing. Since I was going to scarf 4x8 sheets my jig is 54" long.

Thanks SSkiff, I will try that next. I know the disk you are referring to, I have one on my grinder now and was using it to shape a paddle I am building. I did a mock lay up using a butt joint last night, waiting for the epoxy to cure so I can try and break it.

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