Chain Plate Fabrication for Island Packet

[bobconnie]

I personaly love external chain plates, much easier to keep an eye on, and on our colvin, easy to change, the boat we are trying to buy, has Huge external chain plates, I cked in side and all bolts are easy to get to by just removeing what evers in those compartments. po says they are original on a 1984 vessel I cked them with a glass and could not find any problems but the surveyer will ck further, but it sure makes for easy changes and all are the Same !! hooraw. I guess I vote for external change over for this boat, if its possible to do!! just my 2 cents

[lovinlifebda]

Hannah, Greg et al - thank you for your offers of help and for the input. Really do appreciate it! Cruisers Forum is wonderful for information and opinions - and all valuable as you try to find your way along the learning curve.

In spite of the obvious allure of external chainplates (especially after what we're about to go through) we've decided to stick with the Island Packet design. They're now making them from 316L and have doubled the size as well. We've had independent industry professionals tell us that the new method of glassing the chainplates allows for more than adequate drainage and oxygen.

Yes, all three shrouds are welded to a steel bar - all welds are annealed for further protection against corrosion is our understanding.

One of our reasons for staying with the IP design is resale. One day we won't have this lovely girl any longer. Not sure if you all have noticed, but IP owners (like most) are homers! If you're buying an Island Packet you want an Island Packet.

Once again, thank you all for your input. At this point, unless someone knows of a fabricator that already has the IP 40 (1995 model) specs for the chainplates then we'll sit tight on IP to get back from their annual hiatus.

Cheers,
Sharna

[sailinman]

call up jsi in st. petersburg, fl... they have drwgs on a ton of boats.... I would be surprised if they didnt have them.. they also have a full metal workshop and can turn stuff around pretty quickly unless they have some huge project on the tables...

good luck, and btw, that is one piss poor design...

[Cheechako]

If IP is annealing after welding kudos to them! Not sure why you should glass them in though... wouldnt it be better to "let them breathe"?

[Stumble]

Originally Posted by Cheechako

If IP is annealing after welding kudos to them! Not sure why you should glass them in though... wouldnt it be better to "let them breathe"?

Theoretically if they are hermetically sealed they will be protected from the environment. but this is next to impossible to get perfect. Heck if glass work was perfect noone would have blisters.

It is generally considered good practice to allow as much air as possible to the part to allow the chromium to oxidize.

[Cheechako]

Yeah, the deck penetration is likely to leak just a little at times...if the force is trying to pull the chainplate through the deck, just a couple of little f'glass tabs should be fine....

[Ian R]

Because of these problems with stainless, we recommend that our clients pull and inspect any chainplates that haven’t been out of the boat in ten years or so. Even sooner if the boat’s been South, or if there is any evidence of water intrusion belowdecks. We also recommend that, if you install stainless chainplates, you make them out of 316L stainless, polished (not electropolished) to a mirror finish. The idea is to make a low-corrosion material as smooth as possible, leaving less surface area and flaws for corrosion to propagate in.

The above is from the link in post 7 by Stumble. Why not electropolished ?

[Stumble]

Ian,

Is the fact that it was Brion Toss said so acceptable? He is probably the best rigger working today, and his books are pretty close to gospel for me (and have been for a long time). However I had no idea why he rejected electropolishing, so I have done some research. The following are the results...

The best I could find indicates that 316L sufferes from sulpher leaching when electropolished. This causes discoloration, and surface pitting that can lead to accellerated crevice corrosion.

But I am not a metallurgist, and can't really say. This was just the best info I could find. It is pretty interesting, so I may ask Brion what his thinking was. If I get an answer I will report it here.

[Cheechako]

Electropolishing is usually not as smooth and crevice fee as true polishing just based on what I've seen. However EP can be very good looking if the material is very smooth to begin with. If say tubing with a ground OD or extruded is simply electropolished, you will still see some of the scratches in the shiny surface. Grit polishing removes material and those scratches entirely.
316L is the low Carbon variety of 316. Lower carbon means higher resistance to rusting. It's also better for welding for the same reason. When the metal is welded, it precipitates out carbon, so the heat effected area becomes very rust prone. Annealing puts the carbon back into solution in the mix.

[Nicholson58]

I just went through this on our 1984 Camper Nicholson 58. I was re-coring wet deck and had to dismantle cabinets. Main plates looked questionable so I removed them. It took a polish (D-A sander & 600 grit) to reveal microcracks on both sides of each plate on a line inside of the deck. I work in a machine shop so it cost me a few cases of beer to have new grade 5 titanium plates made CAD-CAM plus 202 boat bucks per plate for material. (1/2 X 2-1/2 X 24). No inspection required ever again.

Comments above "don't say it is for a boat" is totally correct. Prices for the plates varied 2:1. I bought from a supplier in Cleveland - shipped form NJ to our shop. You can polish using the DA sander & 600 grit but do not lift the pad or oxygen gets in and the surface gets hard.

[sabray]

I went 316L hand polished the crap out of them. What I found on the original 1979 plates was terrifying. They looked fine at surface. Below where the passes through deck they were spent as we're the bolts. Heads of bolts looked fine there were signs of leaks. Did not pull the mast. I did a few at a time. Not a fan of a welded section chainplate.

[Stumble]

Nicholson,

Nice job on those plates. Honestly though as long as the temprature is keys below 600F oxygen embrittlement isn't a problem. (it's actually higher, but 600 gives you a huge safety margin). Since I am not sure it's possible to get it that hot with a sander, I wouldn't worry about lifting, and if you do get it hot enough to worry about, a pad won't help much anyway. Titanium has to be worked hot either in a vaccume, or an argon rich environment.

Did you switch to titanium bolts and fasteners as well, or just stick with stainless?

[Stumble]

Originally Posted by Stumble

Ian,

Is the fact that it was Brion Toss said so acceptable? He is probably the best rigger working today, and his books are pretty close to gospel for me (and have been for a long time). However I had no idea why he rejected electropolishing, so I have done some research. The following are the results...

The best I could find indicates that 316L sufferes from sulpher leaching when electropolished. This causes discoloration, and surface pitting that can lead to accellerated crevice corrosion.

But I am not a metallurgist, and can't really say. This was just the best info I could find. It is pretty interesting, so I may ask Brion what his thinking was. If I get an answer I will report it here.

This is bad information. I just heard back from Brion and he said

Hi there,
How embarassing. In the draft I meant to say "or", and also meant to expound a moment on the differences between the two treatments. Either will do nicely for chainplates, though regular polishing is usually easier to come by. Electropolishing is very handy for odd-shaped objects, with crannies that are difficult to get at manually. It also passivates the surface, though this can also be done easily with various acid treatments.
Fair leads,
Brion Toss



So there is no issue with electropolishing in chainplates or otherwise he is aware of.

[Ian R]

Thanks Stumble , I will go back to plan A and get my plates electro polished.

[Nicholson58]

Originally Posted by Stumble

Nicholson,

Nice job on those plates. Honestly though as long as the temprature is keys below 600F oxygen embrittlement isn't a problem. (it's actually higher, but 600 gives you a huge safety margin). Since I am not sure it's possible to get it that hot with a sander, I wouldn't worry about lifting, and if you do get it hot enough to worry about, a pad won't help much anyway. Titanium has to be worked hot either in a vaccume, or an argon rich environment.

Did you switch to titanium bolts and fasteners as well, or just stick with stainless?

Bolts all in good shape - at least as strong as the fiberglass bulkhead. I wanted to make sure I would never have to worry about the plates. Heat on polishing using a DA orbital by hand is not a problem. The plates barely got warm. The trick is to keep the pad working and in contact so the surface is workable and air is generally excluded. I tried the Scotch Bright wheel at the shop but the results were ugly and the surface was work hardening. In this case, slow & easy wins. Machining in the Mazak required speeds about 1/4 that of comperable steel and DO NOT stop in one spot or it gets very hard. Lots of cooling fluid - flood the surface. Use only new, sharp carbide bits.