Two phone calls a day apart. Matt's from film company– "could you build a representation of a Neolithic boat to carry a bluestone to Bristol" answer "yes certainly" .
Second call was to me from chap with a blue stone same question response "why would you want to do that – there is no doubt it could be done see John Coates article on Ferriby boat" As it happens, John Coates was my boss at one time whilst working for the Darkside see http://www.ferribyboats.co.uk/reconstruction/index.html
Matt quoted and got the job. This is a brief account of the design and build and the compromises needed to meet the timescale. Three people deserve credit – Matt for taking such a vague contract well out of Swallow Boats usual genre, but most credit is due to the two guys who built her Doug Hanton and Jeff Henderson long time helpers at Swallow Boats who put in a huge amount of time researching and creating work-rounds. They also provided some of the pictures herein
Essentially a flat bottomed version of the Ferriby boat 42 feet long a bit like a sampan. In the Ferriby boat the bottom was 6 to 8 inches thick oak in three huge "planks" sewn together with yew withies. Such a structure was not feasible in the timescale. What was evolved with the film company was to build the bottom out of three laminations of Douglas fir all glued up as a solid structure.
There was some vestigial evidence of frames on the Ferriby boat but proper a frame structure was needed to transfer the stone weight (maybe 5 tons) to the structure, so imitation grown frames were laminated up to a common jig and cut to size on the boat with a long scarf as had been seen on Viking boats and still seen today. The structure is illustrated in the inserted drawing.
There was insufficient time to learn the intricacies of transforming yew withies into something that could take real loads (and obtaining yew without knots was impractical in the time) though there was a trial with withies about halfway through the build, sufficient to satisfy the proposition that with more experience the withies would be fine. Instead of withies modern imitation hemp was used to tie the structure together. The strength of the withies and rope were tested in a tensile test machine and found to be remarkably similar.
The Ferriby boats has quite sophisticated lashing arrangements for the planking intended to bury the lashing to protect it from grounding and a modern version of their method was adopted. See http://www.ferribyboats.co.uk/description/index.html
At the same time this boat was being built a replica of the Ferriby boat was being built at the Falmouth Maritime Museum using the tools and techniques of the time see a time lapse video of the build at http://www.falmouthphotos.com/index.php/bronze-age-boat-build-in-falmouths-national-maritime-museum/
This was not a Swallow boats computer driven project !. The basic shape and the stability calcs were all computer derived but the actual build was very much an "on the beach" job as there was no room in the main shed. A cantilevered roof structure was built on the side of the shed and the boat built under this.
The boat was built right side up on a jig as shown below, starting with the centre planks and working outwards. At the bow and stern the curve was too much for the methods available to bend our planks so the 38mm planks were reduced to 25 mm and scarfed into the 38mm planks. The subsequent "bump" was faired off. See drawing insert for an idea of how it was done. All the glue used was epoxy.
The curved planks of the bottom were extended the full length of the boat to ensure that the curvature was uniform along the length (left hand picture), and then subsequently cut to plan shape (right hand picture). Screws were used to hold things whilst glueing but all were removed as the build progressed.
The second picture also shows the 4 part chine logs. After the chine logs were glued in they and the bottom plank were cut to the correct bevel using a skill saw.
Frames were then added and lashed to the bottom "cleat planks" and the sides planks fitted and lashed together. The lashing is interesting. Originally it was thought that multiple lashings would be used but it was found that after the first round turns subsequent turns merely jammed. The solution was to use two turns and to tighten them with a lever on the outside, and then peg the rope in position with tapered dowels covered in pitch. This has worked fine
There was much discussion about pitch availability but pine tar + heat + rabbit droppings or other filler can be made into pitch see link below. Guess who was delegated to find the rabbit sh*t. It worked fine just like the man says, so when the euro jokers ban pitch you know how to get round them http://www.primitiveways.com/pine_pitch_stick.html
The knots were left long in case tightening was needed later but in practice none has so far been needed
A view of the interior showing lashings etc
The other point of interest was the caulking. This was made from a moss variety called "hair moss" which is in long strands. This was worked into twisted rope by Jeff's wife and forced into the outside seams with a wooden caulking "iron". For a history of caulking see http://anthropology.tamu.edu/papers/Franklin-MA1985.pdf
We were worried that when all the screws in the hood ends were released that the planks might spring out from the chine log. In the event this did not happen but as in the Ferribly boat a tourniquet round the bow sections was fitted. Please ignore the towing eyes – along with a incredible array of other "safety" items including two safety boats this was a modern requirement
Launch was on the 6th of August bang on schedule. Since it was also the landing of the Curiosity on Mars the name Holgar which is Welsh for inquisitive seemed an appropriate christening.