Replacing the Bristol 29 Chainplates

Home News Plans Dimensions Projects Modifications Sources Links About Site Map Search

Replacing the Chainplates

Ever wonder what 35 year old chainplates look like? Here is the starboard main removed...

This is the outside face; little rust and no obvious fractures from crevice corrosion. I will Magnaflux all of them before replacing them.

This is the inside face against the forward side of the knee. More rust staining shows, indicating that there was some water getting down the back side of the chainplate at one time. Everything was dry when I removed it, and no rot or softness is present in the knee.

Here is the aft face of the knee. And here are the three bolts holding the chainplate in place.

As far as I can tell Bristol made these chainplates; the dimensions and hole spacing do not match anything sold by Rig Rite, although the deck covers look like Rig Rite covers.

I will replace the mains with Schaefer chainplates # 84-90. According the Schaefer catalog, the stock Bristol chainplates are undersized for the main shrouds. As a matter of fact, according to Schaefer, the Bristol chainplates should be used with a maximum diameter of 3/16" shroud. My B29 came stock with 1/4" mains and I upgraded them to 9/32". The Schaefer 84-90's take 1/2" pins and will be sized correctly.

January 7

I removed the remaining chainplates today. All looked like the example photos above: none had serious rust or crevice corrosion issues; none of the bolt holes had soft wood or structural problems. I will fill all the existing holes with thickened epoxy and drill new holes for all the new chainplates. The mains will be located about two inches outboard of the existing slots in the side decks and those existing slots will be filled in.

You're looking at the new main chainplates getting sprayed with Nyalic fluoropolymer to protect them from any possible crevice corrosion. These are Schaefer #84-90's: big hurkin chainplates, twice the size of the originals, 1/4" thick and a hefty 1-1/2 pounds each. They attach with 5 1/2" bolts and are sized for 1/4 to 9/32 wire size (I have 9/32" wire for the main shrouds). To mount the chainplates, I ordered all new hardware: bolts washers, fender washers and nylon locking nuts, all of 316 stainless, from McMaster Carr.

New Backstay Chainplate

Since I added 3 inches to the taffrail I needed a new chainplate for the backstay. It needed the mounting holes moved, a larger hole for the turnbuckle clevis pin and I felt it needed to be beefier. So, I bought bar stock from OnlineMetals.com of 316L stainless steel, 19" long, drew up some plans for what I wanted and sent it off to the welder in St Pete, FL I have used for all my custom stainless on the Bristol, Embree Welding. They do the most beautiful work you can imagine--and designed and build the stainless surround for my bowsprit. If you are in the Tampa Bay area I would strongly encourage you to consider using Embree--they are absolutely the best in marine stainless construction. If you are outside the local area, as I am, draw up some rough plans, mail them and Embree will call you to discuss, build your item and ship it to you. Really great people!

Embree Welding, Inc.

690 43rd St S
St Petersburg, FL
(727) 321-8771

Here some shots of the new chainplate and the old one beside it.

Here you can see the difference in length. The mounting holes have been increased--all 3/8"--and the highest hole lowered so as not to mount it into the stern bulwark. Notice the level of polishing on the new chainplate--it is called a "mirror finish" for a reason. The old chainplate, from the Bristol yard, looks homemade in comparison.

You can see the added thickness of the new chainplate here.

This photo just shows off the gorgeous polishing that Embree does.

Look here for more rigging work.

Today I prepared the stern to receive the new chainplate. The steps consist of:

Marking the new holes with a center punch.
Overboring the holes all the way through the backing block with a 1-1/5" bit.
Filling the opening with Six10 epoxy.
Securing an additional fiberglass backing block to each side of the transom.
Remarking the mounting holes with a centering punch.
Drilling and tapping the new holes (five 5/16 x 18tpi bolts mount the chainplate)

First, I cut the new fiberglass backing plates from some 1/4" fiberglass stock from McMaster Carr and chamfered the edges. The outside and inside backing plates were epoxied in place after the holes were overbored and filled. With the new backing plates, the total mounting thickness is 2-1/2 inches.

Here is the new chainplate temporarily mounted. It looks longer than it is. It is about 4 inches longer than the stock Bristol aft chainplate.

Here is the inside plate with the mounting bolts screwed in.

Next, I addressed the shroud chainplates. The main issue with chainplates is that boat builders tend to cut oversized slots for the chainplates to pass through the decks, and to seal the holes with some sort of durrable caulking, suck as 3M 5200. The problem is that the chainplates will gradually work fore and aft inside the oversize slot and eventually break the seal of the caulking, allowing water to pass through. I will negate those issues by beefing up the bearing surface that the chainplate rides against, and make the slot an exact same size fit as the chainplate itself. Since there will be no wiggle room for the chainplate to work, the caulking need only to prevent water intrusion and there will be damned little room for water to get past the slot.

I plan to reinforce the exposed side of the chains and provide additional water proofing by fashioning a 3/8" fiberglass collars above the deck that the Schaefer chainplate cover will attach to. First, I cut all the collars the same size (since the Schaefer covers are the same size) slightly bigger than the Schaefer covers, beveling all four sides about 20 degrees, When all six were cut, I sanded the edges smooth with 220 wet or dry. Then I carefully cut them in the middle--all exactly the same. Once the chainplate mounting holes are finished, I will tape a Teflon form in place the dimensions of the chainplate, and glue the two sides of the fiberglass collar tight to each side of the form and fill the middle gap with thickened epoxy. Once the deck is painted, I will screw down the Schaefer cover over a thick bed of caulking. This method I believe will make as tight and strong an opening in the deck as I can achieve.

I decided to sister all of the intermediate shroud chainplate mounts. It can't hurt, it beefs up the mounts and makes a smoother surface for the Schaefer chainplates and the mounting hardware. Here is the port forward chainplate sister on the aft side of the bulkhead. It is glued in place.

Here is the port aft chainplate sister on the forward side of the bulkhead. Glued in place in thickened epoxy. I used a flush cutting Fein Multimaster metal cutting blade to cut the aft edige of the chainplate slot.

I taped in place a Teflon blank the same thickness and width as the chainplate and flush cut the other side of the slot.

Here are the two slots. I connect them with a drill bit the thickness of the chainplate.

The chainplate is positioned for fit. The Fein makes a very exact and neat slot.

You can see the two sides of the chainplate collar fitted in place.

And the Schaefer slot cover positioned.

Here is the aft intermediate chainplate taped in position,

.
I over=bored and filled the holes to screw down the slot cover.

Here is the aft sister glued in place. All the sisters are 1/4' McMaster fiberglass sheets.

Here is the forward sister glued and screwed in position.

The mounting face for the main port shroud chainplate was not close to fair, so I epoxied a 1/16 sheet of McMaster fiberglass. Then I recut the chainplate passage through the deck.

I filled the gap at the top with thickened epoxy, then opened the passage with a rasp. Here you can see the Teflon blank the width and thickness of the chainplate, ready for filling the gap and gluing on the fiberglass collar.

Here is one of the collars fitted to the Teflon blank, ready for gluing.

I filled each of the gaps between the blanks and the passages with thickened epoxy, then painted the under side of each of the collar sides with epoxy and pressed them into position. When the epoxy began to kick I mixed another batch and did a first filling of the gap between each collar side. This shot is the aft lower chainplate position.

Here you see the forward lower chainplate collar.

And here is the port main shroud chainplate collar. Once the epoxy hardens, I will tap the blanks out and fit the chainplates in position for drilling.

The following shots show the nice fit of the slot to the chainplate.

The finished port aft lower.

The finished port main.

The finished port forward lower.

Aft lower cabinside.

Aft lower chainplate, bolted in place.

Port main chainplate.

Port main chainplate.

Port forward lower chainplate.