Traditional caulking sealant

[zoidberg]

Just an extract, and so's not to hijack an adjacent thread.....

This was/is a 1960s 31' wooden-hulled motor-sailer with a lot of £££ sunk into recovering her. As I understand it, she ( the owner ) bought it in South Wales for ~£16000, spent about that again over 5 years on getting the thing ready for re-launching - and she'd about run out of money. It was re-caulked about 18 months ago, but not so you'd notice. I was privileged to witness the tub being 'hung in slings' for an hour while the planking 'took up'. It took on water like a colander!

The involved shipwright demonstrated a technique I'd heard of but never seen - that of introducing sawdust to the outside of cracks and gaps sucking water in, to help seal the planks. He used a 1-litre plastic bottle with its top cut off, cable-tied to a long stick, as an applicator. It worked - although there was well over a foot of water inside by the time the pumps were keeping pace. The shipwright brought and used up a whole 20-litre tub of sawdust. He'd obviously done that job before! I knew, but didn't mention, I was aware that the sawdust would wash out of the cracks as the flow of water along the hull and working of planks steadily stripped it out.

Both electrical pumps kept pace with the slowly-reducing inflow while the engine was running. I secured at the Visitors' Pontoon/Dartmouth and stopped... in the nearby 'Ship In Dock' pub/hotel. In the morning, the ould boat was still afloat. According to the 'happy as larry' lady owner, both pumps had been working during the night. The shipwright, a local bloke and member of the lifeboat crew, was engaged for another am visit to rectify/rebuild the wheel-chain-minitiller steering mechanism. And some other small jobs....

As in that famous journalistic euphemism, "I made my excuses and left."

Thoughts on sawdust as a sealant for wooden hulls? Compared with CT1....?

 

[B27]

I've heard that tale many times in different forms over the years, from before there was a visitor's pontoon in Dartmouth,

I've seen people attempt the trick and fail.
I've seen people try it and it's been arguable whether the sawdust really helped much, or it just gives you something to do while the boat takes up.

I am of the opinion that sealants in wooden boats may do more harm than good, as they can hold the seams apart, preventing the planks from taking up and putting a lot of stress on fasteners as the wood swells.

These days I am somewhat distanced from traditional wooden boats. Last time I was involved, some American chap was suggesting a thick grease-like substance which would fill a gap, but squidge out of the way as the planks took up.

Best to not let the boat dry out in the first place.

 

[Hacker]

Never use any sealant on a clinker hull. Anything between the lands stops them closing properly. Carvel hulls should use a seam compound on top of any cotton/hemp caulking, traditionally this would be red lead putty. I’ve seen sawdust used and as it’s wood it does swell to close the gaps but the danger could be that a “clump” gets in and swells and holds the land open. Better to get the construction right first time and then staunch before launch and then keep it in the water.

 

[penfold]

These days I am somewhat distanced from traditional wooden boats. Last time I was involved, some American chap was suggesting a thick grease-like substance which would fill a gap, but squidge out of the way as the planks took up.

Tallow probably. Old wooden boats which have been ashore for years leak like sieves when they go in, TADTS.

 

[AntarcticPilot]

I've seen it done, and it works. My memory is very ancient - it was my father's clinker lifeboat conversion when I was about 9 or so, but it leaked badly on the quarter when launched after one winter ashore. A hessian bag of sawdust was introduced next to the area that was leaking, and it stopped leaking fairly promptly.

I think a copper tingle was placed there the following winter.

 

[Daydream believer]

Never use any sealant on a clinker hull. Anything between the lands stops them closing properly. Carvel hulls should use a seam compound on top of any cotton/hemp caulking, traditionally this would be red lead putty. I’ve seen sawdust used and as it’s wood it does swell to close the gaps but the danger could be that a “clump” gets in and swells and holds the land open. Better to get the construction right first time and then staunch before launch and then keep it in the water.

I disagree with that first comment entirely. Dry the boat out as much as possible so that more filler can be applied
I shot blasted a 26ft clinker hull inside & out to remove all the paint & exposed all the wood. I did this in my joinery works to get the wood as dry as possible. I then machined out the lands using a 6mm carving blade in an angle grinder going as deep as the roves. This left a 6mm X 6mm groove in the lands
I then filled & faired the resulting grooves with the West sytem. This is recommended by the Gudgeon Brothers
This meant that any expansion of the wood would grip very tightly on to the filler.

With a carvel hull. If the wood is wet to start with, there is nothing to expand on to any filler which makes the filler medium less effective

 

[zoidberg]

Well, the re-launch and move down river happened on Monday 11th. Not my boat. I was asked to lend a hand to 'do the moving'. The yard manager, the lift-rig hand, the owner, I and others watched with interest as the ould boat was lowered in..... the shipwright began inspecting the bilges, then doing his thing with the sawdust. He certainly expected a degree of water ingress, due to the volume of s'dust he'd brought - but there was little none of the 20 litres of s'dust left in the tub when he'd done.

As for "Best to not let the boat dry out in the first place" and "Better to get the construction right first time and then staunch before launch and then keep it in the water", gentle readers will recognise that was not an option I could exercise.

 

[jamie N]

Interesting thread Z'berg, but although sawdust might work, after the last couple of launches that I've had, I really don't reckon that it's how I'd want to go, as I just want to get it right this time. It's unfortunate that the boat does have to come out, and it's unavoidable that it will dry out.
B27 in post#2 stated something about an American putting on a thick grease like stuff. That's interesting because only yesterday I was told a similar story in Inverness, again without knowing the name of the stuff. To seal some leaks offshore, our American colleagues had stuff named 'Monkey Shit', a bit like denso tape, without the fabric.

 

[penfold]

Very likely to be tallow.

 

[Forty_Two]

Interesting thread Z'berg, but although sawdust might work, after the last couple of launches that I've had, I really don't reckon that it's how I'd want to go, as I just want to get it right this time. It's unfortunate that the boat does have to come out, and it's unavoidable that it will dry out.
B27 in post#2 stated something about an American putting on a thick grease like stuff. That's interesting because only yesterday I was told a similar story in Inverness, again without knowing the name of the stuff. To seal some leaks offshore, our American colleagues had stuff named 'Monkey Shit', a bit like denso tape, without the fabric.

He may have referring to "Slick Seam". I have a tub i imported a few years ago. Was recommended on the now defunct Grand Banks Owners forum by several woody owners.

It's just for below the waterline & is indeed a very thick grease like product. Works well over the cotton caulking giving a good surface to paint. Never goes hard will squeeze out as required. My GB42 is tight below the waterline, just occasionally need to replace a short stretch of caulking & finish with Slick Seam..

The tough part is above the waterline with the med sun drying the planks, especially just above the waterline. Can take a journey with the bow wash re-wetting them to tighten up. International don't sell their seaming compound in the UK. Sika is not appropriate, maybe CT1, will it stay flexible enough?

 

[tillergirl]

What are we talking about? a carvel or clinker hull. Caulking a carvel hull uses putty and red lead below the waterline, putty and white lead above the waterline. Clinker is never caulked, never ever caulked. Hacker is spot on. My first was clinker. The yard commonly used sawdust if we had had a particularly dry spring - the yard had an old tin (largish) on the end of an old broom handle. They would introduce the tin under the waterline adjacent to particularly vulnerable spot shaking the tin so as to encourage the sawdust to be sucking along the lands. I never saw them use the technique on a carvel hull but I suppose it could work - possibly

 

[zoidberg]

I hadn't actually mentioned I/we brought the old boat downriver from Totnes, where it had been out on the hard there for the past 2 years. I heard earlier this evening that the boat was 'halfway to Plymouth'.....

 

[Neeves]

This is how they do it, between the tides, in Manta (the largest tuna port in the world?) for the local tuna boats. Most of the tuna landed is from large Spanish (crewed and owned) boats considerably bigger and more sophisticated than this local example.





Jonathan

 

[zoidberg]

Yeah, I know.

That's why they invented GRP.

 

[zoidberg]

Caulk - Any one of a number of substances introduced into the spaces between planks in the hull and decking of a boat that give a smooth, finished appearance while still permitting the passage of a significant amount of seawater.