Wooden Boat People
By McKenzieDriftBoat.com
multiple scarf joints
when needing a panel longer than 16ft where do you make your scarf joints? I was thinking a narrow section between 2 8' sheets, or would adding a little to one end after scarfing 2 8' pieces be better. (talking about plywood sheets) Also on a S&G boat is 8-1 enough since it is fiberglassed on both sides anyhow?
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Replies to This Discussion
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Permalink Reply by Mike Baker on
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Hey Robert,
Scarf the two 8' sections then a small piece on the end. You can use the triangle shaped cut off from the front to ad to the back to make up to 17'. According to west system an 8-1 scarf is strong enough, I always go 12-1 (I do use 8-1 for botton scarfs).
Mike
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Permalink Reply by Lawrence E. Long on
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Robert:Putting a scarf joint in the "midship" side of the boat subjects it to more bending stress than towards either end. I much prefer to have a solid 8' sheet in the middle of the boat and then add sections fore and aft to get the required length. In my build it it required slightly over 17 ' so adding 2- 5' sections to the 8' sheet got the required length. Don't forget to figure the added length to the sheets to allow for scarfs.Mike is right8/1 is good- 12/1 is better.
Good luck
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Interesting perspective. I have always thought of the middle of the boat as having the least amount of bending stress and the most at the front where the boat bends the most. Admittedly when I do a high side boat I do 4' at the front then 8' in the middle then whatever is needed for the total length at the back.
Mike
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Permalink Reply by Rick Newman on
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Mike, Robert, Lawrence and all, sorry for the partial hijack;
When Mike mentioned the West system it reminded me of the news I read on Woodenboat Forum this morning. I also confirmed the news that Jan Gougeon died yesterday on the Gougeon Brothers site. He was one of the three brothers that makes our boat building possible with the materials we now use.
WEST Systems orignally stood for Wood Encapsulation Saturation Technique soon after the start of the company began business around 1969. See the link for their history here: http://www.westsystem.com/ss/history/
Without the leading edge work by these guys we probably wouldn't be doing scarfs with epoxy. They enable many boats to be built and repaired.
Rick Newman
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Mike: There are a few ways to explain this without going back to structural engineering courses. When you are installing a full length inwale on a drift boat or peapod( which can be a real PITA with one man) and everything is slathered with epoxy- where will it snap? Unless there is some "wild grain" it will let go near the middle of the piece. Also if you take say a 6' straight edge in the middle of the boat and measure the "offset" from the inwale it will be greater than the same measurement at either the bow or stern-tighter "radius" and curvature and higher stress. Think of the side of the boat as a beam with fixed ends(the stems and or the transom can't move) and load it up with weights spaced uniformly along the side. Where will it fail?
I may be full of oatmeal- but thats the way I see it. Merry Christmas
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Permalink Reply by Dave Z on
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This could probably be debated to no end. But, I think most would agree that the strongest part on a scarfed panel is the epoxied joint itself if properly done. Put your scarfs where you want them, make sure your scarf is clean and slathered well with goo. If you are following the panel up with full on glass cloth, or better yet, both sides for a s&g boat scarf location matters even less.
I make my scarfs where material conservation makes the most sense. To eliminate waste.
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