'The Casting of our
We would not have tackled this project if it were not for Mr. Michael Verney's article, taken from the May 1963 edition of 'Yachting Monthly', titled, 'For the Amateur Boatbuilder No 3.' - 'Casting Ballast Keels'. This gave us the advice on how to go about such a task. (This article is reprinted in Michael's book, 'Boat Repairs and Conversions. J. W.).
Our caldron was a length of scrap 3/8th steel irrigation pipe, 24" x 15" deep. We welded a sloping bottom to it and attached a 2" barrel nipple for an outlet. The caldron was built into a furnace , the bricks being laid with a mixture of pit sand and soil taken from a white ants nest!! for mortar. On top of the furnace wall, about 3" above the caldron we placed a 3/8th steel plate with an opening for a 12 foot chimney, and another for feeding ingots of lead into the caldron. A lid was placed over this hole when the caldron was full.
Our furnace proved most efficient, taking only 3/4 hour to complete the task. For fuel we used logs of local timber, 'Mopane' (Colosphospermum) and coal.
For the building moulds we were able to purchase a quantity of timber, 10 ft x 5 1/2", planed to a fraction under 3/4" for a song, the left over timber was used to make the keel pattern. Ten planks were screwed together in sandwich fashion. The final measurements were 9'7" long, as per the plan but only 5 1/2" wide at the top and 5" at the bottom, allowing for the one in twenty slope as in Mr. Verney's article. It was 7 1/4" deep.
Along the top were attached six by 1 1/16th" diameter core prints where the bolt boles will be, as per plan. Six by 2 1/4" core prints along the bottom of the pattern to accommodate the heads of the bolts. The fastenings will be drawn 'brass'. ( Note. this should be bronze. J. W.) We spent hours sanding down the pattern to a glass like finish, finally completing the job with several coats of shellac. Smooth!
We dug a hole in the ground for the mould box. The 'stabilised sand', Mr. Verney's article, is a mix of fine quality pit sand and Portland cement at 15 : 1, using very little water to obtain a 'dry mix'. The mixture was rammed in all round the pattern.
Now the moment of truth. Would the pattern come away without damage to the mould? My willing helpers, see photos, all gave a concerted jerk and away came the mould slick as a whistle. Eureka! We had been working in nearly 100 degrees F. all day, the iced beers that were served rounded the day off with sighs of much satisfaction. We will use the pattern later to position the bolt holes along the keel, as well as to guide the auger bit whilst drilling the holes.
The mould was allowed to dry out thoroughly and then painted with a mixture of shellac and graphite powder. The steel cores were also painted with this mixture and then positioned along the bottom of the mould in the holes left by the 2 1/4" diameter core prints. Over the mould a 3/8th steel plate was placed, holes having been drilled to correspond with the spaced steel cores which now stood proud of the plate. In an open type mould this steel plate is needed to flatten the lead meniscus, otherwise, without it a convex meniscus would have resulted, requiring many hours of filing to obtain a flat surface.
Before pouring the lead, red hot coals were placed on top of the steel plate to warm up the mould, steel cores and to dissipate any moisture around the mould. After pouring the lead we allowed a week for it to cool down before digging it out. The result was near perfect. Unfortunately the steel plate on top of the mould buckled in a couple of places due to the heat, allowing the lead to spill. However, a spot of filing soon trimmed off the unsightly areas. On giving the steel cores a sharp whack with a 14lb hammer, they popped out like champagne corks, the graphite powder being the magic ingredient. The finished lead ballast weighed 1,454 b. (The latest plan weight is 1,660 lb. J. W. 1996.)
We have finished the hog, gluing together three runs of 3/4" Iroko. It was a time consuming job as they were 10 foot lengths. The making of the scarf joints took a long time (for me anyway), to fit perfectly. I think more progress on the boat can be made now that the hog has been completed.
Mr. J.H.Goss has given me food for thought after reading his article in Y. M. the July 1973 edition. In stalling a 'Fairey Hydraulic Drive' immediately abaft the keel, this allows the are of metal skeg to be increased. (In the latest version of the plans the keel and deadwood is continued aft to the rudder. J.W.) This improved the performance of his vessel without unduly increasing the weight of the craft.
'Chala' is at the stage of construction where a decision must be made as to any keel modifications. As I do not wish to increase the weight to any great extent, but I never the less would like to carry out any modifications to improve the performance.
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