304 vs 316 fasteners

What grade of stainless is recommended for replacing fasteners?

For example the strut with nuts that will be glassed in, and deck fittings like genoa track, padeyes, cleats, stanchion bases that will remain exposed

Is readily available 304 stainless adequate and is that what was used originally, or is it worth the extra expense to special order the 316 stainless?

Thanks

Tonyh 44/04 Hatha

Tony:

Lars may check in, and if he does, please pay heed. In the meantime, here's a few points I think are valid: as a material, 316 came after 304 and was developed to overcome some of the weaknesses corrosion-wise in the 304, and it does perform better. However, it is not immune to corrosion issues in seawater, just better than 304. Mechanical strength wise, they are close to one another. Depending on where in the world you are and the fastener you're trying to get, 316 is often now less expensive, simply because it is now made more often in large quantities. Now, having said all that, there are newer an/or better materials available that are superior to 316 for both corrosion resistance and strength, and depending on what fastener in the boat you're talking about, it may be worth spending big dollars for these materials - Nitronic 50/60 (same material as the rod rigging, typically, 254 SMo, a really great material, Hastelloy alloys, the list goes on. So to me the question is: what is the fastener we're talking about, how critical is the service, what are the supply issues where the boat happens to be in the world, and finally, if we have to make a compromise on material, are there other things we can do to mitigate the risk of fastener failure (eliminating crevices to prevent crevice corrosion, which can be sudden and very destructive), encapsulate, or just make the particular fastener very temporary until you can get the correct one. As an observation, I'd say that even 30 years back, Swan did a fine job picking materials, as we rarely hear of abrupt failure due to fastener problems, meaning the original selections weren't bad, and that's where the Professor will know more (actually he'll know more than I everywhere, I just meant I know absolutely zip in that regard). What are you trying to do in this case?

Fair Winds,

Geoff
Corazon 411 #41

Tony:

Lars may check in, and if he does, please pay heed. In the meantime, here's a few points I think are valid: as a material, 316 came after 304 and was developed to overcome some of the weaknesses corrosion-wise in the 304, and it does perform better. However, it is not immune to corrosion issues in seawater, just better than 304. Mechanical strength wise, they are close to one another. Depending on where in the world you are and the fastener you're trying to get, 316 is often now less expensive, simply because it is now made more often in large quantities. Now, having said all that, there are newer an/or better materials available that are superior to 316 for both corrosion resistance and strength, and depending on what fastener in the boat you're talking about, it may be worth spending big dollars for these materials - Nitronic 50/60 (same material as the rod rigging, typically, 254 SMo, a really great material, Hastelloy alloys, the list goes on. So to me the question is: what is the fastener we're talking about, how critical is the service, what are the supply issues where the boat happens to be in the world, and finally, if we have to make a compromise on material, are there other things we can do to mitigate the risk of fastener failure (eliminating crevices to prevent crevice corrosion, which can be sudden and very destructive), encapsulate, or just make the particular fastener very temporary until you can get the correct one. As an observation, I'd say that even 30 years back, Swan did a fine job picking materials, as we rarely hear of abrupt failure due to fastener problems, meaning the original selections weren't bad, and that's where the Professor will know more (actually he'll know more than I everywhere, I just meant I know absolutely zip in that regard). What are you trying to do in this case?

Fair Winds,

Geoff
Corazon 411 #41

Geoff

Specifically, I am re-installing the strut and all the deck hardware

I am in Southern California and have a good local supplier who has the 304 grade fasteners in stock. If I go to 316 they will need to be shipped from New York. Not a big deal for the bulk of the order but when we get near the end, needing small quantities of mixed sizes might get a little awkward.

Most importantly I want to use what the factory used unless there's a compelling reason not to in some case. Everything I have disassembled has come apart easily with more than surface corrosion appearing only in 6 or 8 of the bolts, and in various locations. One in the strut where I found that water had been getting trapped inside the glasswork, and the rest scattered throughout the genoa track, padeyes, and other deck hardware.

Thanks for your input

Tonyh 44/04 Hatha

Tony:

It will be interesting to see what Lars says about original materials - I'm guessing 316 on most mechanical fasteners exposed to seawater, intermittently or full time, but I cartainly have been wrong before. 

I wouldn't use the 304 on the strut or the decik hardware personally - unless you're talking about non-critical, non-highly loaded deck hardware, let's say the screws that hold the tank fittings in place, things of that nature - but anything that would cause a problem if it failed in service - that's a risk not worth the difference in material costs....there might be logic in upgrading from original materials from time to time when the upgraded materials can be had without breaking the bank, of course.

Sounds like you have a lot of work to do - best of luck and fair winds - (at least you don't have to wait now for winter to be over).

Geoff

Tony
Original fasteners are 316.
For deck fittings it is advisable that fasteners are not in contact with wet wood. For example bedding in sealant or treating the wood with epoxy would keep the fasteners dry.
Best regards
Lars

Thanks for the advice Lars. I have the 316 grade fasteners on order.

I would not have thought of sealing the wood to isolate the fasteners from the moisture, thanks for that! I will probably drill oversize, fill with epoxy, then re-drill the correct size

Tonyh44/04 Hatha