DIY Chainplates – Choosing your materials

6 Mar

I’ll start right out with this: don’t make your own chainplates. At least, don’t insist on doing all the work yourself. Well, not unless you already know what you’re doing. Or maybe if you’re really set on it. I mean, you will be able to manage it. So I guess do make your own chainplates, but…

 The one thing I can tell you with authority when it comes to crafting your own chainplates is that if you do it the way I have it will cost you more money and far more time than it would if you get at least some professional help. These chainplates have been the single most challenging task I’ve yet tackled, they’ve cost me far more money than expected plus a huge investment of time and they’re still not quite finished! On the other hand, in the process I’ve learned a ton about working with metal, acquired a couple very fun tools for my shop, and I made my own damn chainplates! That feels pretty good. Along the way there were a lot of errors which made the process slower, more difficult and more costly. In the next couple posts I’ll show you how I’ve made them. At the very least it should help anyone attempting the same to avoid some of the pitfalls I struggled through!

Building your own Chainplates:

The first step is to decide on your material. For the DIYer there are basically two choices: bronze or stainless steel. There are plenty of factors to juggle:
Bronze: Pros- Easier to work with, corrosion free. Cons – Far costlier than SS, finish quickly dulls
Stainless: Pros – Cheaper, Shinier. Cons – Harder to machine, more prone to corrosion, must be polished.

 Old bronze chainplates (above) and new ones made of 316SS Source:

Doesn’t seem like a clear-cut choice, does it? In the end I decided on SS but on an almost daily basis I wish that I hadn’t. Having gone the SS route I would strongly suggest that if you are doing this work yourself it is worth it to shell out the extra money for bronze. As a relative novice with imperfect tools I found stainless steel extremely difficult to machine and spent a lot of money in tools and consumables when working on it. Worse is the polishing. Polishing stainless is an arduous task and the tools and materials for it are not cheap but for its ‘stainless’ properties to work it must be polished. Bronze does not require polishing. Plus polished 316SS should last decades but quality bronze will last longer with none of the nagging fears of invisible corrosion that come with SS. So why are the vast majority of boats fitted with stainless steel chainplates? It pretty much boils down to two things- stainless is far cheaper for a production builder and most boat buyers prefer the look of polished stainless to the patina of bronze. Whichever material you choose there are a couple things you should know:

Stainless Steel:
There are many grades of stainless but for chainplates there is but one choice, 316. They are occasionally made of 304SS but I just can’t understand why any DIYer would do this as 316 is undeniably superior and only costs a little more. 316 is one of the most corrosion resistant grades of stainless but like all stainless it must be well polished. Stainless steels get their corrosion resistance from the inclusion of around 10% Chromium. As I understand it when this Chromium is exposed to air it forms a layer of Chromium-Oxide that protects the steel from corrosion. This reaction requires oxygen so if a tiny crevice in the material is able to trap water this layer can be compromised and the stainless will begin to corrode inwards. Though this corrosion is often all but invisible it can eventually weaken the metal enough that it will fail. This is why all stainless on a sailboat is polished- sure it looks good but it also ensures there is no marring on the surface that could become a point of crevice corrosion. .

 Crevice Corrosion leads to chainplate failure. 
There’s a good explanation of the process at the source.

Not having actually worked with it I can’t tell you a ton about bronze but I do know there are a few things to avoid. Mainly you must navigate the archaic terrain of bronze alloy nomenclature. Do I want aluminum bronze, silicon bronze, or phosphor bronze? Certainly you want to avoid the poorly named ‘bronze’ brasses which are not real bronze at all and have no place on a boat. If you’re going with bronze I would suggest this thread as a starting point.

Once you decide which metal to use two questions remain before actually getting started: how to size your chainplates and what state to buy your raw material in. These are the first two big mistakes I made. Or I suppose I could say the first mistakes we made as the first one was my father’s fault!

When I was getting started on this and looking around for where to buy materials I gave Nigel a call to ask about sizing. It was a rather brief conversation that went something like this: Me: ‘What size do you think I should make them?’ Nigel: ‘Oh, two inches wide should do it. Maybe a bit over a foot long and 1/4″ should be thick enough.’ So I went out and bought some 2″ x 1/4″ 316 Stainless bar stock and had it cut to 18″ lengths just to be safe. Turns out these things are enormous for my little boat! I forgot that my father hasn’t worked on a boat smaller than 40′ in a long time as, apparently, did he. I learned after buying my stock that there’s a handy sizing table in Brion Toss’ book Rigger’s Apprentice.

Next up is what grade of material to buy. If you’re going with bronze this is easy as you’re not likely to polish it much anyway. With stainless you have a few choices although you’re probably not going to find all of them locally. I just went to the local stainless place and bought the SS flat bar that they had. It was hot-rolled flatbar and cost about $100 for a 12′ length. The problem with rolled flatbar is that it is not actually flat. As it goes through the rollers it gets a slightly cupped shape to it and suffers quite a bit of surface pitting from the rollers. This means plenty of work when it comes to sanding and polishing. What I now wish that I had done is to look around for cold finished stainless bar. The cold finish means it is truly flat with square edges. Another option is finished or semi-finished stainless sheet which can then be laser or CNC water jet cut. This would certainly cost more than $100 but as it turned out I spent far more money on equipment and consumables for sanding and polishing than I did on the actual material. More on this later. However you choose to do it you’ll need enough to make all your chainplates and a little extra in case you mess one up isn’t a bad idea. I couldn’t find anywhere local to sell me less than 12′ of barstock so I had some extra anyway. I had the shop I bought it from cut it into 18″ sections which saved me some work.

The bar on the left is hot rolled SS flat bar while the one on the right is cold finished. The hot rolled bar is a different color in the center because this is actually a depression – the edges, which are higher than the center, have been somewhat polished by the rollers. The cold finished bar looks uniform because it is truly flat. It will be far easier to polish.

With twelve foot of stainless barstock in hand I was ready for the machining but that will have to wait for the next post. Time to go do a few things on the boat.

This article was syndicated from Safe At Harbour But Meant For The Sea: DIY Sailing with Paul Calder


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