Wooden Ship Built By Iron Men 2
WOODEN SHIPS BUILT BY IRON MEN
Caulking and Pitching the Deck
By Trevor Watson
28th March 2007
I worked as a traditional timber boat builder in the 70s and 80s and have always remembered these years with mixed feelings. On one hand it was extremely interesting and I am thankful I was part of it and had the opportunity to learn so much. On the other, while not has hard as previous centuries, it was still hard, heavy and dirty work with little regard for personal safety. Very typical of the era in all trades.
In this story, I would like to give you some idea of how decks were laid, waterproofed, fastened and finished in the days before we had modern adhesives, sealants and other chemicals which I cannot pronounce. There was only caulking cotton and pitch or tar as it is sometimes referred to.
There are three options for a deck. Straight laid where every plank is laid fore and aft parallel to the centre line and running into the cover board or devil plank which runs around the outside of the deck. Cut to the shape of the outside of the hull and about twice as wide as the main decking. This is very plain and simple and common on work boats.
The second and third are sprung decks. That is, the decking is bent without the use of steam Etc. to follow the outside shape of the vessel either fully or partially. This is typically used on pleasure boats and the timber is much smaller. About 45 x 19 (1 3/4” x ¾”). The ends of every plank are then fitted (joggled) into the centre plank (king plank) and the outside plank (cover board) as in the image below.
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Example of a Joggled Deck
The timber we used mainly was Queensland Beech for it’s whiteness and durability. In addition we also used quarter cut Douglas Fir (Oregon pine) however only on work boats. Douglas Fir is also very durable in the weather but also a lot harder so ideal for work boats. This timber should not be confused with the timber which was being brought in from New Zealand also called Oregon Pine. It was very inferior quality and went rotten even in mild conditions in a matter of a few years if not months.
Depending on the size of the vessel and the use, decking ranged in size from 50 x 25 (2” x 1”) up to 100 x 50 (4” x 2”)
The first step:-
Plywood was laid over the cambered beams, nailed down with silicon bronze nails and the joints fibreglassed.
Next it was painted with bituminous paint, malthoid laid over the top and then another layer of bituminous paint. After all that the decking was ready to be laid.
The decking was rectangular in profile with a taper machined by spindle moulder using a set of ball race Tessman collars on the edges. This was to take the caulking after it was laid. The bevel went about 2/3 of the way down the side of the plank and when butted together left a gap suitable for the size of the decking. Usually between 4 and 6mm.
The decking was fastened down with either silicon bronze screws on the smaller profiles of gunmetal dumps. Gunmetal dumps were a cast nail 75mm to 100mm long (3” x 4”) and with about a 6mm (1/4”) shaft. Every plank was fastened on every beam with two fasteners. A countersink hole to take a plug was drilled with a Stanley Power Bore bit, (no longer available in Australia to my knowledge possibly because I have never seen one in a metric size. However far superior to a Forstner Bit)
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Stanley Power Bore Bits
Then a clearance hole through the decking and finally the pilot hole into the beam. The dumps were driven with a 4lb sledge hammer and a large punch to avoid damaging the decking. The screws were slot headed. To my knowledge phillips head screws were not available and certainly not in silicon bronze. The days of cordless power tools were long in the future so the weapon of choice was a spiral screwdriver. (again, a great product that has fallen foul of modern times)
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Stanley Yankee 1301A Spiral Pump
Action Screw Driver
Once the deck was laid all the holes were plugged, and there were thousands of them! Plug cutters were too slow to produce the plugs in the quantity required so one of the characters in the yard named Billy Loft took home a heap of beech offcuts and turned them on his lathe at night for extra pocket money. Of course, the material to be turned had to be cut across the end grain so the finished plug when inserted, followed the grain of the deck. He also turned a groove about every half inch so that once inserted, you could break the plug off in the hole and move on.
The adhesive, like most things which were glued in the yard was Urea Formaldehyde. A cream powder and a cream viscose liquid when mixed together hardened and dried like glass. Fortunately it had a long pot life so was ideal for this type of fiddly operation. After the glue has dried, the tops of the plugs were nipped off with a sharp chisel leaving them protruding just above the deck.
The next step was caulking and pitching the seams. Caulking cotton was used because oakum which was used below the waterline, eventually leached out the tar with which it was impregnated and stained the deck.
Again Bill Loft played a big part in the caulking process as he was a quiet man and bit of a loner. Sitting for hours on end day after day on a low stool caulking the deck was his thing.
Once the cotton was hammered in with special caulking irons and a mallet, molten pitch was ladled into the seam.
Pitch (Shell 75/25 from memory) came in a solid cylinder of cardboard about the size of a 20lt paint drum. Chunks were chopped off with an axe and placed into a cleaned (burnt) out 20lt paint container and then placed on an open fire. Melting the pitch was a bit tricky because if you got it too hot to the point of it smoking, you were burning the rosin out of it and reducing the quality. Also the risk of the pitch catching on fire was always present. However too cold and by the time you carried up the ladder/stairs (a bit of a dangerous operation really) to the deck where four or five apprentices were waiting, it was starting to become too thick to pour.
We made our own ladles out of an old jam tin nailed to a stick.
When the whole deck was done and the pitch cooled, the excess, and there was a lot as it was not a neat process, a pitch scraper made from a piece of flat steel about 50mm (2”) wide and sharpened one end was run along each seam. The pitch was quite hard and brittle once cool, it more snapped off in pieces rather than sheared off.
I hope you can imagine what the deck looked like at this point. It was not pretty. Tops of plugs sticking out everywhere and thin pitch stain either side of the seam.
How do you clean all this up to become a beautiful laid deck? You can’t use a sander as the friction melts the pitch again and clogs the belt making a terrible mess.
The answer is, get down on your hands and knees with garden hoses running on the deck and the good old No.4 Stanley hand plane. The water was to stop the friction from the hand plane melting the pitch and smearing it over the timber. It may sound a bit far-fetched I know but we all became so proficient at sharpening our hand planes just so, and using them, that the finished deck received no further treatment. Of course the process took days so not a job for the older guys.
The secret was being able to grind a very slight curve in the iron before sharpening. All done free hand as was the sharpening. This curve eliminated “tram tracks”; the two lines you sometimes get from the edges of the blade if not set up correctly.
The only respite was when you went downstairs to re sharpen you plane iron.
Thankfully oil was not allowed anywhere near the deck for fear of staining. As it was, if you left your hand plane sitting on the deck for too long it would leave a blue mark. The perfect shape of the sole or side of the plane.
I actually liked this job. It taught you a lot about using and sharpening your hand plane, it was cool kneeling in water as by this time the boat was out from undercover so you were working in the sun and lastly, when the deck was finished you saw a truly beautiful thing that you had been part of creating.
INTERESTING INFO.
· The caulking mallets we used were all made from she oak (Casuarina) by you guessed it, Billy Loft.
· A good mallets hitting the iron made a high pitched ringing sound which could be heard all over the boat yard.
· The best caulking irons were made by Ward and Payne in England.
· The saying “between the devil and the deep blue sea” I like to think comes from the devil plank on the side of the deck. So when you walked the plank, you were between the devil and the deep blue sea.
· You don’t use caulking cotton under the water line as it goes rotten very quickly.
· You don’t use oakum ( AKA tared jute pipe packing or plumbers hemp) on the topsides or decks. The tar will eventually leach into the surrounding timber.
· In days gone by many Cruise Liners and some merchant ships had laid teak decks.
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A typical design for caulking mallets with some irons form a set.
