Clinker lands - how much tolerance?

[ARW123]

Just idly wondering if there is any acceptable tolerance across the lands (in terms of flatness) without affecting taking-up or watertight laps?

Planing and getting dead-flat bevels on a bench isn't a problem, but it's testing & time consuming adjusting plank bevels to achieve this on the boat.

[TerryLL]

If you're building glued-lap there's a lot of tolerance for lousy joints. But cutting dead flat lands on the boat is fairly easy. A low angle block plane honed to wicked sharpness will do the job.

[Peerie Maa]

Try to get the bevels right, or you can get crippled lands cracking along the nails. This risk can be reduced by staggering the nails either side of the nailing line. A bit of out of flatness is OK, providing the contact line is where the nails are.

[skaraborgcraft]

I guess it depends on how dry you want your bilges to be. What timber you use will also make a difference to how much tolerance and leakage you can get, softwoods will swell quite well and reasonably fast. Even oak will close up, but it can take a month or more in my experience. Just get it as close, and as best as you can, if you get a real bad edge,(or just want to play safe) you can always stick a light cotton soaked in pine tar in the lap,that will normally make up for any variation in tolerence. Cheers

[ARW123]

But cutting dead flat lands on the boat is fairly easy

Perhaps a few more years practice then, but using a plane upside down isn't my natural position

A bit of out of flatness is OK

So over a 3/4" land maybe a 1/64?

I'm slowly gaining confidence and being bolder... With my boat I can over-cut the bevels a bit because the bottom edge of the upper plank is also bevelled, so I can adjust the new plank after the lower one is fixed (I didn't engage brain at the time and so was too conservative - out of fear more than anything else!). This method of double bevels was employed at the time the boat was built and I am told is unusual - can't understand why it was; it's suggested perhaps to reduce the external appearance of the lands for aesthetic reasons?

[Peerie Maa]

This method of double bevels was employed at the time the boat was built and I am told is unusual - can't understand why it was; it's suggested perhaps to reduce the external appearance of the lands for aesthetic reasons?

I think that is called dory lap. It was also used to an extreme in the Adirondack guide boats IIRC. It is certainly twice the work and less strong.

[PeterSibley]

There is a jig which I'm afraid I'll struggle to describe, it's the Tom Hill jig I think .

A round batten ( long dowel ) is run on the lap point blow the bevel you are wanting to cut. Take an old plane and drill a hole through it from side to side with the bottom of the hole the thickness of the dowel from the bottom of the plane . Thread a long bolt through the holes and run the smooth section of the bolt on the dowel while planing the bevel .

That description was positively opaque! Sorry . Perhaps someone with better descriptive skills will turn up and offer a better explanation . If you have access to old copies of WB look here.Beveling, planks: plywood lapstrake/for ultralight canoe/Tom Hill, 54:74

[Gib Etheridge]

Any reason you can't put a thin bead of Sika 291 in the joint? Besides keeping water out of the boat and out of the joint it helps to prevent "crack along the dotted line". It also makes it more difficult to replace a plank someday, but then again it might save you having to replace that plank.

[James McMullen]

1/64 in 3/4 is perfectly acceptable in glued lapstrake but completely unacceptable in traditional lapstrake if you're building to a shipwright's standards. If you're building trad lap, it should be perfect. The secret is practice, and a really sharp plane.

I think Peerie is right that dory lap is more work to make yet less strong. I would save that only for the gains at the hood ends at most, unless you are really trying to be historically accurate in a specific replica. The near doubling of thickness at each lap effectively forms a structurally useful longitudinal stringer with standard lapstrake technique.

A -very- thin bead of Sikaflex 291 is probably fine, but shouldn't be used as a substitute for making a plank actually fit.

[ARW123]

Thanks for the replies. Having taken about 25lb of Sikaflex daubed all over the lands externally, I have vowed this will be a Sika-free zone for as long as I own her , but thank you all the same for your time.

Just to reiterate, I am achieving a flat bevel, I was just curious if I was being over fastidious.

Things are a little mixed up (bevel angle wise) as the boat - or the bottom at least - has been replanked maybe a couple of times, the first being at about the 75 year mark. When this was done I think they may have replaced planks the same thickess of those that were removed (about 3/8"); but this would have been after decades of sanding and so in all likelihood may have been thinner than the originals. My reckoning was that I couldn't imagine the original builders deliberately finishing a plank at 3/8", it seems such an odd thickness for a boat 30' long carrying 400+ sq ft of canvas - more probable that it was 1/2". So the planks I am putting on are therefore 1/2".

Now, if the angle of the bevel for a 1/2" plank was transferred to a 3/8" plank replacement, it's going to be over cut (in my mind) - so maybe the dory lap was a method of evercoming this in the replanking stage not the original intent? It has to be said that away from the ends the degree of secondary bevel is only about 2 - 3mm so there is not a huge amount of wood removed.

Thank you once again for your time gentlemen.

[robert666]

John Gardner wrote in Building Classic Small Craft something along the lines of; a lap that is tight inside and slighlty open outside is watertight and fine and the paint/varnish will fill the gap outside. I'm dealing with a similar problem, a 1960's mahogany on oak sailing dinghy with laps that have been gooped up with some rubbery crap. all the laps are tight inside, but outside there are gaps up to 3mm when the goop is removed! My research has lead me to belive she was built this way from new to allow sailing off a trailer without needing to take up.

Robert