Project SQD”” 1. Assault a battery.
It’s all about heavy metal this week.
Perhaps the strangest start to a boatbuilding project , no careful lofting of lines, no screaming band-saws and not even a tea break but i sarted project SQD this morning by emptying and taking apart a pair of large 6 volt heavy duty lead-acid batteries.
It’s partially because i haven’t got any materials yet although when i did take a break from the morning’s work and checked my mail i did have a message and quote from the timber yard for the first round of materials ; principally the plywood, some hardwood for the lammells (word of the week) and the first of many cans of Epoxy resin. In the first order i’m buying in all of the plywood for the frames, bulkheads and skin , some glue and the hardwood stock to make the strips from that when all glued together will form the blank for the centerboard : that’s what the lammells are all about and no, i hadn’t heard the term before and it’ll make a lot more sense when iv’e got the material here and i’m making them.
My first project within the project is going to be making the centerboard and it’s case because it involves a lot of separate parts and processes that i haven’t done before….like gluing together a whole load of hardwood strips to make a long and wide board. There is a job within the job though that i hadn’t even considered i might have to do and that is to cast a heavy lead block which gets set into the board to act as a weight so that it will sink and not just float back up into the board case. The instructions call for a block of lead that comes out at around 20 Kg or 44 pounds so iv’e got to acquire at least that much lead, melt it , make a mold and then cast the lead : i just checked to find out…the melting temperature of lead being 327 c or 627 degrees Fahrenheit and that’s pretty damn hot.
Lead is surprisingly expensive stuff too which is why some builders and many in the huntin and fishin world collect and scavenge stuff like fishing weights to cast their own bullets and sinkers from. Once again i just checked and found that to buy loose lead shot to use as a casting material would cost just over £10 per kilo and as i mentioned above i would need 20kg of the stuff. As it happens though i may have that much lead laying around because i have 4 big and heavy lead-acid batteries kicking around from when i cleared the workshop out , in fact when i weighed just one of the big ones this morning it came in at 28kg wet and about 25kg once emptied out….it’s ok i had my ‘safety’ shorts on this morning for the job !. I know that there’s some loss of weight with the cases and the other plastic bits but even so when i broke one of them down this morning i still had a heavy bucket of just the lead plates……time to ‘bring the heat’.
Oh…..and did i mention that lead is unpleasantly toxic stuff ?….which is why both paints and petrol are now unleaded. I don’t quite remember the chemistry of lead-acid batteries either but it’s likely that the grey powdery build up on the plates is sulphur related, a lead sulphide paerhaps, so when i start to heat the plates in the melting process i’ll first have to drive off a load of moisture and then the sulphur salts : it should all separate though and i should just be left with lead but that still leaves the problem of handling 44 pounds of liquid metal at around 330 C.
What the experts say.
I did the obvious thing in the form of a search for blokes melting lead and casting stuff on Youtube and fair enough there are the keen shooters and fishermen out there casting bombs and bullets and a few of those making lead ingots first which is closer to what i intend to do. One of those was hilariously inept though as he chose to use a brand new cast iron frying pan over a propane camping stove and hadn’t thought considered ‘free surface effect’ of the molten lead or that he would then have to grab both sides of his frying pan as the free surface effect took over and tried to torque the pan handle out of his grip. Nothing i saw was anything close to melting and pouring 44 pounds of lead in one go except for a big jump to some much more knowledgeable backyard boatbuilders casting their own keels which involves structures (molds) more like concrete formwork set solidly in the ground and running the lead into channels from large containers with bungs that are just knocked out to make the pour.
Interestingly there is a professional outfit just down the road in Cornwall who can cast anything in just about any metal and it’s a fascinating process to watch a big winged or bulb keel being cast : years back i asked them about casting a small but complex bronze bow-fairlead and i don’t remember what happened with that project.
So, i SQD‘d it !
If you’re wondering what the project SQD is all about then this is my neat segue into that – SQD standing for ‘stupid question day’ which is my usual introduction to what has become my frequent post on designer John Welsford’s social media page (link below). You see, i figure that many of John’s builders could be like me – rookie boatbuilders who don’t know this stuff and don’t want to look like noobs on social media , me ….don’t care as i luckily came up with an attitude in nursing and medicine that says that there is no such thing as a stupid question – merely one that hasn’t been asked yet. It did also seem a good question for a discussion because everyone who has made a weighted centerboard will have met the same problem and had to create a solution so…..
This process is now somewhat circular as i’m both happy to ask a question/initiate a conversation (on SM) and return the compliment by adding to the conversation with my own content where it’s relevant or just plain interesting . With this kind of project post it becomes a feedback loop too as this is where i think out loud about some of the responses and answers….and then of course i’ll post this as i update the group with my own progress…..or a least the next question and a note about what i did about the last question.
With this question what i didn’t get was any response from a builder who had cast a heavy block of lead as per instructions rather what i got was 2 main lines of response : the first being ‘don’t go there if you don’t know what you’re doing because it’s dangerous etc’…..fair enough except that the same situation exists throughout this project because in many (most) cases i won’t know what i’m doing until iv’e done it at least once…..the second line of responses was to do the job in a different way and it was something that i’d thought about so here goes.
Years and years ago i had to do a keel repair on the OOD34 that i crewed on after the owner had bounced the boat off of a hard piece of underwater scenery, it was the yard that did the hull repair and re-fastened the keel but it was left to us to repair the toe of the keel where it had struck. It had never occurred to me that the keel wasn’t a solid lead casting but a hollow GRP shell that had been filled with a matrix of resin and lead shot…essentially a cold casting into a GRP mold formed by the skin of the keel. The repair was surprisingly easy as all i had to do was drill into the lead/resin mix, set some studs in there and then build up a new filler and shot ‘blob’ around them before shaping and fairing the whole toe and foot of the keel. Somewhere along the way i also think that iv’e come across the same way of making complex shaped ballast pigs for small boats and from memory i seem to remember that the job can almost be done in-situ by covering the area to be molded in plastic sheet and pouring the lead/epoxy gloop straight into that.
So that would be an alternative way of doing the job and my thanks go out to the guys who reminded me of that, in my case i could cut out the section of board, temporarily seal one face and then cold cast straight into the hole – the epoxy resin would hold everything together nicely and if i added high density filler into the mix i could then fair the ‘up’ face nicely as well.
The other alternative is to go right back to the drawing board and ask a different question : ‘ what was the designer trying to achieve and is there a different approach’ ?……well, i don’t intend to second guess John the designer in this case but that many boats exist that have centerboards and not all of them have weight built in ; equally , because this whole thing is a learning process i know where i have the information by which i could learn for myself how to calculate the buoyancy of the board and how much weight i would need to sink it or in an alternative approach what force i would need to apply to sink it. I’m thinking here and at this stage that the weight in the board does obviously apply a considerable force on the centerboard case if say the boat was completely on it’s side and therefore applying some righting moment but….one of my boat designing and building books says not to rely on relatively small amounts of weight in a board to give stability unless it’s a full-on heavy-metal keel/board and that’s a whole different thing to engineer. It might be better for example to treat the board like many racing dinghy’s do and have a downhaul, actually that would then be just like the rudder blade on my last boat….and put the lead in the bottom of the boat as ballast pigs.
Upsy-downs-y lines on the rudder of WABI”’
Next post….getting my head around the maths.