Traditional Lapstrake Question

[tapsnap]

With traditional lapstrake construction is it customary to use red lead primer, bedding compound and cotton string caulking between each strake or is that not necessary?

[James McMullen]

It depends on several things:

Whether the boat stays in the water all year, or is a boat that is launched occasionally.

What kind of wood it is planked with.

How good you are at planing a perfect winding bevel.

I use nothing at all between the laps of my lightweight, cedar planked small boats but bare wood and good intentions--getting excellent results so far. I have also sailed on a 40-footer fir planked boat that used actual copper pennies for the roves that was payed with cotton for all the strakes above the waterline and tar and oakum for the underwater bits, and it seemed to be as dry as could be. I think it depends on what scale of boat you are talking about. For small boats, nothing.

[JimConlin]

... I have also sailed on a 40-footer fir planked boat that used actual copper pennies for the roves ...
Kids, don't try this at home.
US pennies are now zinc.
What about Canadian pennies?

[tapsnap]

It's a 16' rowing boat. Eastern white pine for the strakes. It will be frequently in and out of the water - mainly freshwater.

[Thorne]

I'd be tempted to go fully traditional at first, using either the cotton string or nuttin'. If that isn't working after the first season, you can always consider putting a thin line of flexible caulking along the edges of the laps.

Don't forget this -

http://images.trademe.co.nz/photoserver/tq/51/89859251.jpg

[JC 72]

tapsnap, What James said. Merryrows has nothing between her plank lands. The first time we got her wet she seeped at first. Just beads of water laying in the laps. After a couple of hours we bailed out several gallons. This got slower and slower over the next two days. The hull is western red cedar, with two coats of paint outboard and oil finish inboard. 11' LOA .She is stored dry and trailered. Hope that helps. John

[Clinton B Chase]

Tapsnap, Use Walt Simmons method for caulking the laps. I'd look up his site, Ducktrap Woodworking and order his boat on building lapstrake boats or contact him and see if he'd be willing to send you the diagram that shows how he does it.

Clint

[tapsnap]

Tapsnap, Use Walt Simmons method for caulking the laps. I'd look up his site, Ducktrap Woodworking and order his boat on building lapstrake boats or contact him and see if he'd be willing to send you the diagram that shows how he does it.

Clint
Does it involve putting chamfer on the lapping bevel to create a "V" groove when the two planks are riveted together and the grooves are then filled with caulk when the whole boat is together?

[dmede]

Tapsnap, Use Walt Simmons method for caulking the laps. I'd look up his site, Ducktrap Woodworking and order his boat on building lapstrake boats or contact him and see if he'd be willing to send you the diagram that shows how he does it.

Clint

My recommendation as well, and how I did it on my 14' skiff (WRC planks, traditionally planked with copper rivets - no leaks, lots of in and out of the water).

No need for a diagram, this should be pretty easy to grasp. You take a flat-head screwdriver and run it down the length of the lap joint on the outside of the hull (right where the planks meet at the lap). This puts a small groove down the line of the lap, around 1/16" wide and deep. Next run a bead of your favorite caulk down this groove and smooth over with your finger. Let dry and paint over it. Done :D The caulk seals the lap pretty well and flexes with plank movement, but because it's not IN the lap you can easily reef it out and reapply if needed.

[dmede]

Does it involve putting chamfer on the lapping bevel to create a "V" groove when the two planks are riveted together and the grooves are then filled with caulk when the whole boat is together?

Read my post above, the V grove is the result your going for but you do not need to cut this in before planking, just groove it after your done.

[Thorne]

What Dave describes above is largely what I did in my dory skiff restoration. Reefed out the old caulk, re-caulked with Vulkem116, no problems with drysailing the fir over oak hull.

http://www.luckhardt.com/scraper1.jpg

http://www.luckhardt.com/primer1.jpg

[tapsnap]

So, is this better to do before the boat goes into the water for the first time or should I wait and use this caulking technique when I notice the boat leaking too much after a few seasons?

[dmede]

So, is this better to do before the boat goes into the water for the first time or should I wait and use this caulking technique when I notice the boat leaking too much after a few seasons?

I'd do it before. Were talking about a very small bead of caulk, I think the best results will be had if your planks are clean and dry, no paint, oil, shmutz in the joint or grain. Don't think of it as leak repair or cover up for shoddy work, think of it as just another finishing step.

[Yeadon]

I don't have an exact opinion on what you should do, but can tell you what I did on my lapstrake peapod.

After I beveled my laps, I took a rat-tail rasp and created a small cove straight down the middle of the lap. Then I ran a small bead of a silicone-type sealant in that cove. Afterwards, when I clinched nailed, I got a bit of a squeeze-out that I had to clean up.

Getting your bevels right is the main trick. Trouble is, you'll be much better at it by the time you're well above the waterline. So a bit of silicone sealant in your laps under the waterline probably isn't the worst thing in the world.

When I build another one, I'll probably do it the same way. Though, when I get up above the waterline, I'll likely skip the sealant. I thought it was a pain to clean up.

Edited to add - my boat is dry sailed off a trailer, a lot. So it is always getting wet and drying up. Those planks are in a constant state of flux.

[tapsnap]

I'm pretty confident about getting a flat rolling bevel - I have over 20 years woodworking experience. However. I have no boat building experience.Until now none of my joinery has had to be watertight.

[tapsnap]

Thanks for everyone's advise. Now I have another question. How should I join the scarfed planks? I'm cutting nib end scarfs at a 1:12 angle. Should I just glue these or use the method I saw used in the Traditional West-Norwegian Row Boat thread, where they riveted the planks together and used the cotton string dipped in boiled linseed oil as caulking?

[Pugwash]

I'm pretty confident about getting a flat rolling bevel - I have over 20 years woodworking experience. However. I have no boat building experience.Until now none of my joinery has had to be watertight.

That's funny.

I kept a piece of the keelson from my Tammie Norrie, that I had to replace, after I asked a friend of mine, with 40 years "woodworking experience" to come out and work with me on my boat. He doesn't know, and I would never tell him.

:)

[dmede]

Thanks for everyone's advise. Now I have another question. How should I join the scarfed planks? I'm cutting nib end scarfs at a 1:12 angle. Should I just glue these or use the method I saw used in the Traditional West-Norwegian Row Boat thread, where they riveted the planks together and used the cotton string dipped in boiled linseed oil as caulking?

Unless your building a historical replica, just glue them. You can only take "traditional" boat building methodology so far. There is a happy medium where traditional methods and materials can get along very well with modern methods and materials. Taking the adherence to older methods too far results in more work than necessary and less function or reliability. It's been said on this forum many times, if the old-timers had epoxy they probably would have used it.

RE the "20 years wood working experience " and flat bevels, you may be right but unless you've had some experience with boat construction in the past I think you'll be surprised by how little your previous knowledge will come into play when dealing with boat layout and construction.

[Yeadon]

Unless your building a historical replica, just glue them.

If it's plywood he's using, then sure, glue away. But if he's using actual milled wood for his planks, then gluing the laps will destroy the planks as they begin to work and move over time.

[dmede]

If it's plywood he's using, then sure, glue away. But if he's using actual milled wood for his planks, then gluing the laps will destroy the planks as they begin to work and move over time.

unless I misread his question he is asking about glueing the scarf not the plank laps. you can indeed glue solid wood scarfs (depending on species and grain).

[Yeadon]

Hmmm ... now you've got me wondering. I do think it's laps he's talking about, versus scarfs. I'd definitely agree that epoxy on a scarf joint would be the right choice.

[tapsnap]

In this second question I'm asking about the scarfs to join the planks end to end to make longer planks.

[James McMullen]

You can glue the scarphs with thickened epoxy--a perfect boatbuilder's glue, strong, waterproof. Do not glue the laps themselves in any way if it is a solid timber plank.

[Eric Hvalsoe]

For many years I built cedar lapstrake with dry laps. I took great pride in producing dry boats, or boats that seal up in short order after a brief bit of weeping through seasonal moisture changes. And I took great pride in teaching my students these skills with the same results. I came up with the idea years ago that Yeadon mentions of running a little hollow along the lap with a rasp - this a variation of another idea I saw years ago of running in a slight hollow with a thumbplain. Maybe the thumbplain was in one of Simmons or Culler's books. At some point, as a courtesy to my clients, I decided to try to insure a watertight boat year around under any circumstances by running a bead of caulk. The theory of a slight hollow is applicable to either dry or caulked lap. I have tried different caulks. These days I am incllined to use either Boatlife or one of the Sika's. Rich Kolin use to recommend tub and tile caulk. I tend to use the expensive stuff. Caulked or dry - either way is legitimate. The main thing is to get the bevels right or darn close in the first place, this simply takes practice. My 16 lives on the trailer.


I hope I've got this right, was the original post in regards to traditional lapstrake? I don't think you need a 12/1 scarf. Something like 8/1 is adequate. Do the spiling, figure out the overlap of your two pieces of plank stock on the bench, spile, get out the planks, do the gains, cut the scarf, plank up. Glue up on the boat. Use epoxy, most convenient thing is Gel Magic in a tube from System Three. Close the scarf with clench nails.

Eric Hvalsoe