Popular Mechanics 1962 PM38 Build [SPLASHED 2017]

[jbcurt00]

Use a scarf joint.

Using either 8:1 or 10:1, cut, glue, align and secure the joint until cured. No permanent fastener required.
https://en.m.wikipedia.org/wiki/Scarf_joint

Turn the scarf so that when installed on the boat, water is going past the joint, not into it.

If you screw the chine to the boat, use 1 screw thru the center of the scarf

 

[Scott Danforth]

I would use a shaper style splice joint as a last resort. however prior to that, I would be on the phone with lumber yards across the US

 

[Woodonglass]

what kind of wood are you contemplating using for the chine log? Is it a True 1" or in fact 3/4"?? Do you have a Table Saw? Router?

 

[archbuilder]

I've seen scarf joints used in wood boats a lot. They are usually made up of really shallow long angled cuts, this allows a lot of glue surface parallel (sort of) to the direction of the grain. Sounds like that is what you are describing.

 

[pekstrom]

Thanks gm280 for your response. I see what you are saying. That does seem like a better type of joint than what I had in mind.

 

[Grandad]

If you can't find a suitable length, do what ya gotta do; make a scarf joint as suggested. I would do it at the stern end where the side and bottom are at the strongest, not forward where you're making a bend. - Grandad

 

[pekstrom]

Thanks guys for all your responses. I like the scarf joint too. To Woodonglass' question, it is really more like 3/4" when all is said and done. So I don't have too much material to play with. I do have a tablesaw and also jigsaw. No router though. But I would think I should be able to cut at an angle and end up with a longer overlap allowing lots of glue. I could place the joint across frame #4 (the one closest to the transom) and put a screw through the joint and into the frame.

 

[pekstrom]

If you can't find a suitable length, do what ya gotta do; make a scarf joint as suggested. I would do it at the stern end where the side and bottom are at the strongest, not forward where you're making a bend. - Grandad

Yes, I was planning on trying to get it as close to the transom as possible thinking none of the bending forces from the bow end would be there. And also possibly lining it up with the frame in front of the transom so I could pull a screw through the joint and into the frame.

 

[Woodonglass]

Scarf Joints are NOT the easiest Joints in the world to make. A Lap Joint is much easier and in this application will yield a perfectly acceptable strong joint. If you use 3/4" Yellow Pine, Douglass Fir or a Good Void Free Plywood, If you use a 12"x 3/8" lap joint and TiteBond III wood glue, and a bunch of clamps, that stringer will be as strong as any 14' one piece of lumber you could buy. Maybe even stronger!!!

 

[TruckDrivingFool]

While looking for pics I saw some elaborate locking scarf joints I would trust but would be hard to cut into a 1x4, so I'll stick to my original agreement with GM that a lap joint would probably serve you better.

 

[TruckDrivingFool]

Wow sorry missed that there was another page to the thread when I replied, so put me in agreement with all not just GM that said a lap joint.

 

[pekstrom]

I think a lap joint it is, if I can't locate 14-foot lumber. It seems like that would be easier to accomplish given that I have just under an inch thinkness to work with. And on that note, it seems the weather is getting warmer so I should be able to continue working now. Thanks everyone for your thoughts and advice.

 

[BottleBoss]

I came across this message board during an internet search. I built this same boat about 6 years ago. I had a little help from my father who had built one back int the 1960's. A man who runs the DIY wood boat forum made up a small page about it. I think he called it the PM38 club. Judging by the pictures you have posted I would say yours will be a fine boat when it is done! Thanks- Mark Reynolds, Harpers Ferry WV.

 

[pekstrom]

I came across this message board during an internet search. I built this same boat about 6 years ago. I had a little help from my father who had built one back int the 1960's. A man who runs the DIY wood boat forum made up a small page about it. I think he called it the PM38 club. Judging by the pictures you have posted I would say yours will be a fine boat when it is done! Thanks- Mark Reynolds, Harpers Ferry WV.

Hi Mark,

This is too funny. I actually came across the plans on that DIY wood boat forum you mention, and saw the pictures of your boat. Those pictures inspired me to give this a go. I'm trying to take my time and think things through since this is the first time I have ever done anything like this. As a teenager I dreamed of building a boat but never did. I'm hoping to have her ready by this summer so I can take the wife out on the lake nearby. Thanks for stopping by and by all means feel free to tag along if you'd like.

 

[Ned L]

As jbcurt00 said, you need to scarf your chines with a tapered scarf (12:1 would be ideally preferred, 10:1 would work). No fastenings are needed. For little sticks like your chine a hand plane is the quickest and easiest way to cut the tapers. With a 12:1 taper there is no need to be concerned about where it lands.
Please don't think about using a half lap scarf, it is not what to use here and basically you will be sorry (when it breaks).

Nothing wrong with scarfed chines.

 

[TruckDrivingFool]

Hopefully not too much of a detour for Pekstrom's thread here but hopefully we can learn -

Please don't think about using a half lap scarf, it is not what to use here and basically you will be sorry (when it breaks).

After seeing your work and knowledge of boat building I will take your advice as gospel (recanting my own) but could you expound on the reason of why the scarf is better? My furniture building experience tells me a lap joint is stronger due to long grain on long grain gluing vs. the end grain to end grain in a scarf.

 

[Ned L]

You are correct in that you want the "long grain on grain" area for gluing strength. However, with a half lap you have those two areas of 90 deg. cuts where you are effectively gluing end grain to end grain ( no strength at all there). When you try to bend the piece those areas will open right up (about the same as making saw cuts half way though a single piece of wood and trying to bend it),
A tapered scarf gives you that long area of glue surface without any end grain to initiate a crack from.
A proper tapered scarf will be stronger than the wood itself.

 

[TruckDrivingFool]

Makes sense, thank for the explanation.

 

[Ned L]

No problem.
And for something like furniture, where pieces are coming in at different directions and there is really no flexing and bending involved I would agree that half lap joint is the way to go. Certainly stronger than doweling ( which also have no place on a boat).

 

[pekstrom]

Yes, thank you for explaining that. I was wondering if those 90 degree sections would weaken the joint in an application like this. The stem section for this boat is cut out of the lumber in two pieces with a tapered joint like this. I didn't realize it was called a scarf joint but now I know. If I can't locate 14-foot length lumber I will make use of this type of joint to make one. I am learning all sorts of things during this project.