Casting The Keel

The aluminium tear drop pod is designed to accommodate a variable number of similarly shaped lead ingots which locate on the mandrel each side of its centre. Allowing that these would be a handleble 25- 30 kg these were cast in sand so they would be approx 2cm thick. Anything new is bound to be a little worrying and the first casting of these was
no exception. The lead came from my roof as opposed to some local church roof, kept under lock and key since I had the roof replaced.
The former or mold was made from 2cm mdf and all the edges relieved by 7degrees to allow extraction from the sand without damaging the impression. A central handle was vital to ease the mold from the sand.

Important in casting lead, I guess any metal for that matter, is its temperature at the time of pouring. I learned that using strips of sheet lead let in at the time of the pour will give a good idea of the state by way of melting away and at the same time act to cool down the melt - the lead at the edge of the container should just  be beginning to crystalise.

Important, in fact vital, is to wear total face and hand protection and ensure that the sand is not too damp and that tool to be used are not wet and ideally warmed if not heated.

In the picture above we can see the crystallisation of the lead in tail of the casting due to relative rapid cooling where the  blue bloom on the right is a function of the slower cooling mass allowing oxidizing of the surface. It is interesting too to see the shrinkage of the casting from the surrounding sand as the casting cools. Such shrinkage allowed the casting to be carefully removed without shattering the mold such that it allowed ten castings to be made from it after a little tidying up of the mold each time.

The above shows the casting placed into the 'pod' and sitting neatly on the mandrels. The lifting of the casting from to and fro was fascilitated by the T shaped handle that was screwed into the casting after drilling and tapping - (8mm metric).

The little cauldron above was made from a dicarded 'Creuset' found in the street on to which has been attached a bar from its handles. The two cuffs of wood at each end were free to rotate so that when held in pouring the bar on the right can be used to rotate the cauldron to empty its molten contents into the mold. The support underneath was made from a short length of 'I' section onto which two pieced of angle iron have been welded to support the cauldron. A brick was used to close off the back. The curved dish shown conveniently sat around the lip of the cauldron when removing slag from the top of the molten lead.

The space heater in the background, without the heating, provided an indirect draft accross the furnace by hitting the wall, bouncing off and moved fumes toward an open space.

Making the Keel Housing Safe and Finishing the Deck

This week I finished the decking in that the overlap of the ply on the framework was trimmed (routed) off.
What is interesting about the decking is its cross-sectional contour - exactly opposite to a normal boat where the profile is flat or convex down - mine being convex up. This profile is not of particular interest for motor vessels but very pertinent for small sailing craft which on long tacks will have a more level standing platform on the windward side - so helpful in travailing the vessel under way.  Also the curvature of the deck in this way makes it exceptionally strong and stiff offering in its own way a complete member to the boat's structure.
The other thing I am doing to finish the gunwhale region is running a length of triangular shaped meranti on the edge of the gunwhale to offer a positive toe-hold both for both lee and windward sailing. What is a challenge for boat builders is bending wood. A particular challenge here is to bend these triangular in section lengths. What happens is they 'jump' out of place to find the easiest lie - here not being what is wanted.
The mounting of the keel housing has been boxed in - the struts to the hull being a serious source of injury if they were not so boxed. The boxing offer too a platform and compartment at the same time and its top will be nearly though not quite a continuation of the floor of the boat that has yet to be finished. Of course the lids of the box can be opened quickly up from the centre as an inspection hatch - important because the stresses on the keel, especially if going aground or hitting rocks etc could make that area of the hull bottom tear open or split.

Cabin Window Detail

I chose Perspex for the cabin windows because of flexibility and safety and workability as well. At 6mm of thickness it is easy to cut on the bandsaw and a linisher used carefully makes the edges tidy if slanting is needed.
I might just touch on a matter of boredom in fitting the windows is that they are framed up and the trim added only to be disassembled later to allow sealing and painting of the infrastructure and surrounding deck.
Certain psychological issues arise when a project is long drawn out. and many of which can be related to the nature of what is proposed.

Here I set out to build a large model of a smaller model that worked well. I approached the test tank people in Southampton and they priced testing a 3ft model at £2000. Foolishly I thought for that sort of money that I could build a large one which I could actually be a passenger to do real testing. In reality I was sort of correct in terms of materials incorporate in the boat but optimism forgot the time factor and the cost of housing the project in London's expensive space.

Unlike the right angled nature of cabinet building boat crafting has complex angles

Putting a plywood skin on the wooden bones of the deck

A task I was dreading was decking and the attendant 'hardship' of making patterns from thin hardboard to develop the deck panels from 9mm 5 ply, not a British Standard ply but 'Hardwood WBP ( water boil proof glue). It was suggested by the suppliers,Ferguson Timber, Acton, London, that it is likely that it is the same glue as is used in marine grade ply eg. BS 1088 except that the former's provence is not known and the layers of veneer are not of a single piece but rather assembled like a patch work quilt. This, however, is not apparent on the surface layers of the ply and the appearance was perfect. Allowing that there is a considerable price difference, that in my inexperience spoiling a sheet or two from poor workmanship or poorly cut out pattens was/is a distinct possibility and that this whole project is really something of a test bench makes using the cheaper item a reasonable choice.

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Here a single 2450 x 1225mm (8'x4') sheet is bent around the foredeck framwork with some difficulty in getting cramps to have points of purchase due to the overhang which was necessary to get the sheet close to the underlying frame. I suppose I could have use a Spanish windlass but found a stout rope around the sheet and the hull and its looped end over the jaws of a long friction clamp did the job and achieved the required apposition.

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Here interdigitating the side and foredeck panels is tricky and takes a bit of patience getting a reasonable fit as the hardboard pattern on the left shows. Not shown here but there was no attempt to match the ply colour as it is all going to be painted.There was no chamfering of edges here as the beam underneath was  wide enough to provide a good seal for both panels.

However the junction of the deck panels, here seen in the far lower left hand conrner of the lower of the two  pictures, had but a 20mm spar thereunder and so these I chamfered, fore panel overlying rear.

Sikaflex 291 Marine Sealant Trials And Tribulation On The Use Of

This shows the keel housing components seperate and in the order of assembly minus the bottom of the boat which will be between the housing and the lower compression plates. Both larger components are bent as best could be as to as least approach conformity with the bottom of the boat. It is the difference in conformity that require a good spread of 'filler' or sealant and the philosophy is essentially to put on more rather than less.

This shows the bottom of the boat ready to receive the housing. Cleaning is important and the maker of Sikaflex suggest that solvents leaving a residue be avoided. We used isopropyl alcohol, a good general spirit industrial cleaner. It might have been appropriate to have roughed the area with course wire wool but this was omitted. Perhaps somewhere in the back of my mind there was a worry of detritus from such cleaning getting into the proposed work.

The Sikaflex is 'toothpasted' on in runs of approx. 7mm thickness so each of the hole is surruounded.

The messy scene after bolting down with me inside and my friend under the boat. The central plates secured with 6mm ss hex head set screws/nuts and the marginal sections with 5 mm ss cuphead hex. recessed machine screws/nuts.

Pretty much the same situation under the boat. As we worked tightening the sealant bulged from the margins and from the holes yet unfilled with bolts in no uncertain manner. This Sika flex is expensive and it was a shame to see the waste but inevitable if we were to ensure filling of any potential points for water ingress.

This would logically suggest we should have worn gloves and it is advised by the Silaflex makers. However sensible gloves would have made the job impossible, given tactile finess, the shear number of scews to brought into place with attendent washer, spring washer and Nyloc nut, and the time for my friend under the boat to capture the head for me to tighten up. The work as a piece would have failed had the set time been exceeded and as it was it became quite difficult towards the last insertions of screws. Has we had cleaned our hands at short interval with mineral turps we might've not had the dreadful affliction to our hand seen here but time for that would have been lost to the job in hand. Normally the sealant is removable from the hands IF IT HAS NOT YET CURED. Thereafter one has to wait till it can be peeled or falls off from by mechanical means from attrition. Certain web advise suggested using razor blades but this did not appeal. In our case it took THREE DAYS to dissappear. We suffered no ill effects that we could ascertain though it is mentioned that skin reactions can occur. Of course the appearances made us feel like social outcasts. 

Fitting the Central Keel Housing

As the name implies 'housing' is apt in that the hefty aluminium item at the top of the first picture accommodates the keel shown in earlier posts. The space between it and the lower two  plates is for the bottom of the boat, drilled and cut out to accommodate the two posts on the keel as seen in the second of the pictures.
This will now form the sandwich, brought together with stainless steel bolts and button head machine screws, with of course a healthy layer of marnine grade Sikoflex between each plate.
Interestingly the makers of this mastic recommend firm initial tightening followed by a final tightening after 24hrs.

Getting a sense of the completed article

Having been built upside down suspended from the ceiling of the workshop mezzanine, then lowered to the

floor and turned, cabin frame added, it was most pleasing to get a view of what the boat might eventually look like.