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Peterduncan
01-15-2019, 09:40 PM
I'm getting ready to build a strip planked Runabout. The thickness of the planks are to be 5/8 of an inch thick bye 2 in wide. My plans were to use a Cove and bead on the planks and glue them into place. Does anyone know if the cove and bead need to be the exact thickness in this case being 5/8 of an inch in order to be able to properly plank the boat

Ian McColgin
01-15-2019, 09:53 PM
Not sure I understand the question. The whole bit with cove and bead is that the seam between planks has good clean contact all the way. To get that fit with flat seams, you have to do fussy rolling bevels. You do not want radiuses anything like 5/16", giving a cove and bead radiused to the thickness of the plank. Something near 5/8" radius should work fine but you might even go bigger. Make some careful drawings, perhaps well expanded, of the planks joining at the sharpest curve, the turn of the bilge, and you'll quickly see a size that works. As shallow a cove and gentle a bead as you can make is the goal so you don't waste wood.

Peterduncan
01-16-2019, 08:28 AM
So I understand from what you're writing that the cove and bead must be large enough to allow the two adjacent planks just swing to be able to match the curvature of the hall

Peerie Maa
01-16-2019, 10:24 AM
So I understand from what you're writing that the cove and bead must be large enough to allow the two adjacent planks just swing to be able to match the curvature of the hall

That is the exact reason for cove and bead.https://www.guillemot-kayaks.com/Building/StripBuilt/CoveNBead/Comparison.gif

MN Dave
01-16-2019, 11:14 AM
I think that the question was about the radius of the cove and bead, If the radius of the curve is larger than half the plank thickness, there will be a small gap on the inside of the curve and a small bump on the outside. If the radius is half the plank thickness (same diameter as thickness) The outside of the curve will be smooth and on the inside there will be a very small area of interference where the edge of the cove side will have to bend.
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Peterduncan
01-16-2019, 11:40 AM
I think that the question was about the radius of the cove and bead, If the radius of the curve is larger than half the plank thickness, there will be a small gap on the inside of the curve and a small bump on the outside. If the radius is half the plank thickness (same diameter as thickness) Toutside of the durve will be smooth and on the inside there will be a very small area of interference where the edge of the cove side will have to bend.
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Excellent explanation!!! Thanks for your help.

Peerie Maa
01-16-2019, 11:57 AM
Excellent explanation!!! Thanks for your help.

You should be able to purchase ready milled to the correct profile.

Gib Etheridge
01-16-2019, 12:35 PM
Is your planned hull hard chined? If so you may or may not be able to get away with gluing 5/8 thick by 2" wide strips to the frames, depending on how much radius the side and bottom frames do or do not have. If they are radiused the 2" width will not conform to that radius unless you back them out. Even 1" will only make contact at the top or the bottom or somewhere in between, leaving a gap between the strip and the frame everywhere else. If the radius is slight thickened epoxy may be able to fill that gap.

If the radius is more pronounced, as in bent frames, you will encounter the same problem to a greater extent.

Either way it won't make much difference whether you use more or less radius for the bead and cove. Less will conserve a bit of lumber though.

If the hull is to be frameless you should be able to get nice tight bead and cove joints by allowing the strips to touch the mold at their mid width only as you lay them up, even if they are 2" wide, but there's no way you will be able to clamp one or the other edge of wide strips to framing and not get gaps in the edge joinery similar to what you would get with square edged strips.

I don't know how to draw it up on the 'puter like the more clever previous posters, but you should be able to draw it out by hand, or model small sections with frames or molds of varying radii.

Hope this is clear enough to be understood.

Lee Valley sells internal and external bullnose router bits.

Jay Greer
01-16-2019, 01:43 PM
When we glued up the Lapworth 36 hulls at Carl Chapman Boat Works the planking was close to 1 1/8" by 2 1/8" prior to running the profile through the sticker. This allowed good contact with the molds and enough depth for the ring shank nails that were run verticaly though each course though predrilled holes. The nails gave sufficient vertical force to bring the cove down onto the radius. Even so a lot of clamps were used to keep the courses in form. We used casein glue back then but a lot of the boats are still around and that was over fifty years ago! Fairing demanded a lot of skill and planing which brought the skin down to about 7/8". This is a messy way to build a boat but it gives a strong hull.
Jay

JimConlin
01-17-2019, 08:54 AM
It's OK if the diameter of the C&B is a bit larger than the thickness of the strips. 3/4" would be OK. If you can't find that large a fluting bit, use a round nose bit.

You might vary the width of your strips to suit the curvature of the hull. You can use wider strips in flatter parts if edge-setting isn't a problem. You might even spile a lenticular 'plank' of considerably greater width. As a rough approximation, the strips should not be wider than about 1/10 of the radius of the hull.

MN Dave
01-17-2019, 12:01 PM
It's OK if the diameter of the C&B is a bit larger than the thickness of the strips. 3/4" would be OK. If you can't find that large a fluting bit, use a round nose bit.

You might vary the width of your strips to suit the curvature of the hull. You can use wider strips in flatter parts if edge-setting isn't a problem. You might even spile a lenticular 'plank' of considerably greater width. As a rough approximation, the strips should not be wider than about 1/10 of the radius of the hull.
I played with my Excel sketch to see what the effect of C&B diameter looks like for fairing and plank thickness after fairing. I didn't expect much, but it looks like using a diameter larger than the plank thickness requires a little more stock removal and results in slightly thinner planking in the end. I drew a faired curve on the inside too, which I suspect is a waste of time and material. It does look like a larger diameter is OK. If you can find a cutter equal to the plank thickness, it will be a little easier to fair.

I have seen narrower strips used at the turn of the bilge on a stripper canoe with rather hard chines, maybe 3" radius. It looked like it would have been hard to make the boat any other way.
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