Attached are pictures of our chainplate replacement project for our 1979 
T-37 MISTRESS (Hull number 215).  The original chainplate bolts had 
become badly corroded from water intrusion through the deck and into the 
sealed plywood "pockets" that housed the bolts.  This is a very common 
problem in T-37s, so if you haven't checked yours yet, your rig may be 
living on borrowed time. Below are some thoughts on material and design 
of our replacement chainplates.


1.  Material – My original plan was to use silicon bronze because it has 
a better long-term track record than stainless, even 316 stainless.  
When I priced silicon bronze, however, it looked like it was going to 
cost over $700, plus shipping, just for the material (you have to use 
thicker material for bronze because it is roughly 30% weaker than SS), 
so I bought 316 stainless for about $200.  What I didn't figure in, 
however, was the extra labor needed to polish the stainless (you must 
bring the chainplate to a high polish to gain stainless steel's anti-
corrosion benefits).  If you farm out the polishing to a professional 
metal finisher, it will cost you about $100 per chainplate; if you 
polish them yourself, you're in for many, many hours of very tedious 
labor.  Moral of the story: go with bronze unless you object to it for 
aesthetic reasons (I happen to like the traditional look of unpolished 
bronze).  Alternatively, you could use the bronze and have in chromed. 

2.  Design – I decided to mount my new chainplates outboard because (a) 
outboard mounting with internal backing plates is an inherently 
stronger, time-tested design; (b) it was easier to increase the length 
of the plates by placing them on the outside (the original chainplates 
are a little too stubby in my non-professional opinion); and (c) because 
of the working of the chainplates, it is extremely difficult to prevent 
water intrusion any time you route the chainplates through the deck.  
(The only through-deck chainplate design I've ever seen that looks like 
it will not eventually leak is on some of the newer Pacific Seacraft 
boats – their chainplates have rectangular collars welded onto them 
where they intersect the deck, so there is a lot of surface area for 
caulk to adhere to where the collar meets the deck – (there is a picture 
of one in Calder's new cruising book, I believe).  I'd be surprised if  
those collars didn't add at least 100 bucks  to the cost of each 
chainplate, however.)

    If you do decide to go with the outboard mounting method, it is not 
too hard to notch the existing wood trim to accomadate them; however, 
you will have to spend a fair amount of time ensuring that the camber of 
the chainplates and backing plates inside the hull match the curve of 
the hull.  This is important to ensure that the forces exerted on the 
chainplates are spread over the largest possible area and do not distort 
the hull shape.