caulking planks

I'm in the "getting" information stage. I was thinking of caravel planking. I read that cotton was used so that the planks would swell when the boat was put in the water. If I use some "new" adhesive type caulking and sand, seal and or paint the hull,will the planks still swell when I put the boat in the water? I guess my confusion is the planks will be covered (paint) how does the water get to the wood to swell it ? Thanks

 

Paint is not able to perfectly seal the wood from moisture. Also there is water vapor in the air. The wood passes off moisture or absorbs it depending on whether it is wetter than the environment or drier. It is a lot like hanging your washed clothes out to dry on the line. It it's raining it will take a while.
I read comments from Phil Bolger that he tried using some modern caulking compound in a carvel planked boat, but it was a disappointment. He said he would not do it again.

 

There are several different techniques for caulking carvel planked hulls (in the 16' to 40' range) with planks of 1" thickness or less. Essential they consist of:
1. Use cotton caulking and apply a seaming compound of the traditional (oil based) type;
2. Use cotton caulking and apply a seaming compound of the polysulphide type;
3. Caulk totally with a polysulphide.

If you are building new, the polysulphide seaming/caulking is best. "Fresh" wood with no oil, etc. from a previous caulk job provides an excellent surface. The caulk will penetrate into the pores of the wood. A problem can be that if the wood dries excessively (like above the waterline in hot climes) the planks, in shrinking, will actually start to split about 1/16" to 1/8" back from the plank edge - the polysulphide caulk does not "tear". I have never tried using simply the caulking/seaming compound itself to make a seam watertight. I have talked with those who have done this and they say it works well. I have used the traditional method of caulking with cotton using proper caulking tools and setting the cotton approximately 3/16" below the plank surface, then applying the seaming compound, and immediately removing excess from the seam by going over it with a "tongue depressor" type tool. This creates a seam that, once the boat is in the water and the planking swelled, will not "pooch out".

The ONLY brand that I use is Boat Life "Life Caulk". You can find them by "googling". The factory is extremely helpful and - by following THEIR instructions - I have had excellent results for over 30 years! I do not like either Sikkaflex or the 3M line. Boat Life is more expensive, "messier" to use, takes longer to cure (but does have the nice advantage of curing underwater for emergency repairs - I know, I've done it) but gives a superior bond and retains its felxibility longer.

 

3M 101 will also cure underwater, as is my impression of other polysulfides, which use moisture to complete the cure.

There are several ways to caulk, but I don't recommend any process that doesn't introduce a mechanical linkage at the plank edges. Sealants are just that, a stuck-um that will keep two pieces dry and absorb some movement. Carvel planking will dance a jig without having something pounded into the seam to harden the joint lines. This can be wedges, one of the few different strings, etc., but the mechanical edge set has to be there. Without this linkage, the planks are free to move about under load, which will a lot, in a sea way. This tests the abilities of the planking fasteners, which will "egg" out their holes pretty quickly and things go down hill fast after that.

In other words, water tight is one thing, mechanically sound is another. You need both on a carvel hull, which can be accomplished a number of ways.

 

Hi all,
4 years later and I now have an issue. My boat starting leaking today. single skin kauri timber carvel planked. Above the water line, but below the bow wave. Is there a commercial sealant off the shelf I can apply to either the inside, or the outside?

 

I am sure there are sealants that you can try for this. Some are mentioned above.
A much more certain approach is to remove the old caulking (cotton or whatever) in the problem area and recaulk it and then apply a seam compound.
I assume that the seam has begun leaking because of the planks drying out to a level that is drier than when it was caulked before. This is quite common above the waterline. If the boat hasn't been used in quite a while (no bow wave) perhaps just keeping on using it could tighten it up by supplying moisture to the planks.

 

Thanks, exctly what I thought. I need o get out more

 

if i understand you correctly, it is caulked with cotton,
you can feed linseed oil in the interior seams, this may swell the cotton
if it still leaks after a few days, as Gilbert says, re-caulk it

 

The linseed oil solution sound like a goer. How would I "feed" it into the joint?

 

let it run in from above, push it back in with a knife or sponge

 

Thanks Peter. I'll try this during the week and do sea trials on the weekend to check.
Pierre

 

I've had the boat builder around to look at the leak. He was quite non-chalant about. Also says to get out more and get some good old salt water into the joints. Not worth a lift-out now, but next time she's out of the water, to call him and he'll re-caulk these joints. Anyway, I did spray heaps of linseed oil on the joints from the inside and will do so every day 'til the weekend. Weather looking good, so wwe will be away foir the two days - whoo hoo.

 

Sprayed another coat of linseed oil last night - Tuesday night. Am looking forward to Saturday for sea trials.

 

if you can mix linseed & beeswax, or tallow, not too hot,
& fill the seams from outside,
its hard to advise people from a distance
its not easy to get paint to stay on beeswax or tallow
but it should squeeze out if the seams swell,
its hard to know what finish you expect on your hull,
it can be a constant battle tending a hull
if you can feed sikaflex or other mastic in , good
but its all messy
i am hesitant to tell you do this or do that
because i dont want you to have to do an expensive hull repaint
possibly to match a slightly faded colour
which then requires an overall paint job
with oil/ beeswax or tallow,you can clean it off with white spirit/alcohol
without disturbing the paint job

 

Thanks Peter, what about Sikaflex on the inside of this joint? If I scratch the joint to expose fresh timber, say 3 or 4 mm deep and wide, and then squirt the Sikaflex in, will it stay in place and seal the leak?
Pierre