Non 304 Stainless steel keel bolt

[Catketch]

I just got a replacement keel pivot bolt assembly for my M25 from Blue Water Yachts and, just for fun, put a [FONT=&quot]refrigerator[/FONT] magnet on it. It stuck! The pivot bolt is not 304 stainless. The nylon lock nut is 304 stainless and the backing discs are aluminum, but the bolt itself seems to be a lesser grade (It holds a magnet about as well as zinc plated bolts, but not nearly as well as common steel...sorry, I'm not a metallurgist and don't know how to describe it better than that).

I put the same magnet on the current pivot bolt in the boat and if fell right off (I lost it in the bilge as a matter of fact). I was going to pull the existing pin for inspection and thought it would be a good idea to replace it with a new one just to be sure I didn't have to pull it again anytime soon, but I'm wondering if I should just keep the original in place and only swap the rubber washers and aluminum backing discs, assuming that I find no problems with the original bolt of course.

Does anyone have any experience with a non 304 SS bolt in their boat? Even without being 304 stainless, will it take a lifetime for something this big to rust through, or might I have to replace it again within years? I'd hate to service the keel in a way that leads to failure down the road.

Thanks,
Dan

 

[jmczzz]

I think I would find a stainless bolt from a different source if necessary. seems odd that if the original is stainless the Mac dealer would sell a non stainless.
I just looked at BWY's parts list and the description says it is a stainless bolt?
1967 - 1987M25, V25, V24, V23, V22, M22, V21, M21, V17Steering CB Keel5304-1K0

KEEL, PIVOT BOLT ASSY
Notes: USED ON ALL KEELBOATS EXCEPT EARLY V-17 AND V-21, FOR THESE BOATS WE RECOMMEND DRILLING OUT THE PIVOT HOLE IN THE KEEL AND THE KEEL TRUNK TO ACCEPT LARGER UPGRADED BOLT ASSY. 5/8" X5 1/2" STAINLESS BOLT, LOCK NUT, 2 CUPPED WASHERS, AND 2 RUBBER WASHERS/GASKETS.

Kit Contents: BOLT, 2 RUBBER WASHERS, 2 CUPPED WASHERS, AND LOCK NUT

Shipping Weight: 1 lbs.
Packing Charge: $0.00

$ 26.00

300 series stainless steels are non magnetic. both 304 and 316, 316 is the preferred type for marine applications.
I would call them and ask whats up with the non stainless bolt? It may be a lessor grade like 200 series (cheaper, China knock off).
James

 

[Catketch]

I missed that claim of stainless steel in their description...I thought they didn't specify and I was making an unfounded assumption that it would be SS. It makes the matter even more curious. I have an email out to them but they don't open until Tues. I will post their response when I receive it.

While we're on the subject, does anyone have advice on what to use for a bedding compound? I was thinking of using 3M 5200, but that stuff has such good adhesion that it can be difficult to remove later on. Maybe plain old silicone sealant?

 

[Cruiser1]

Hi Dan,
I have seen so many differing theories and comments about stainless magnetism and have done so much experimenting that I am nearly over it. I test all bolts and fitting with a heavy magnet and if not magnetic they go in one container and if magnetic they go in another. At least if I have to use/replace something in a difficult/critical location I make sure it is non-magnetic.

Anyhow, to cut a long story short you spurred me on to do another web search and I came up with this one - it is interesting http://27.111.87.182/~australw/stainless-steel-magnetism-corrosion-resistance/

After reading that article I ran a moderate magnet over my kitchen sink and it was interesting to see how some parts of it are very magnetic and other parts not magnetic at all (most of it shows very little magnetic attraction) - sound like the above article may have it sorted.

 

[justsomeguy]

I missed that claim of stainless steel in their description...I thought they didn't specify and I was making an unfounded assumption that it would be SS. It makes the matter even more curious. I have an email out to them but they don't open until Tues. I will post their response when I receive it.

While we're on the subject, does anyone have advice on what to use for a bedding compound? I was thinking of using 3M 5200, but that stuff has such good adhesion that it can be difficult to remove later on. Maybe plain old silicone sealant?

4000, 4200, BoatLife caulk, Sikaflex, almost anything but 5200!

 

[caguy]

Do you have a picture of the original bolt? What condition is it in? You may want to try these guys. http://www.allen-industrial.com/ . They have a large stock of bolts and if they don't have it they can get it for you. They are the only place locally where I could find 3/8 ss lag bolts. They don't make the same in counter sunk screw so I had to turn my own. They are very helpful Burbank used to be an aerospace industrial meca back in the 70's when Lockheed moved out all of the support manufacturers and supply housed did too. These guys are the last of a dying breed.

 

[vizwhiz]

I was going to chime in...304 SS can often show magnetism, where 316 SS rarely does. BUT this even differs based on whether it is a cast form of the stainless or a wrought form also. Not good to assume that something is not 304 or 316 stainless simply based on magnetism.

 

[Catketch]

The article on SS and magnetism was an interesting read. Clearly I should stop getting my stainless knowledge from reading BBQ grill reviews, as I should have known that I needed 316 rather than 304 stainless. The article would explain why the bolt is mildly magnetic, although I do wonder why, if that is the case, all the smaller bolts in my toolbox are completely non-magnetic.

At this point I would feel better about installing the part if I were sure that it was 316, so I'll wait to hear from BWY before proceeding. The bolt head is stamped with "F593C" on the top and "THE" on the bottom...anybody have any idea if either of these denotes the alloy?

Caguy, I have not had a look at the original bolt yet but I'll post a photo when I do. I have never done a visual inspection of the bolt and bolt hole, but all the discussion of keel problems in the forums of late inspired me to take a closer look (it's a 30-year old boat after all). I did put a bottle jack under the centerboard when I first got the boat and pumped it up to verify that there was very little play in the pivot, but nothing puts the mind at ease like a good look.

Thanks for all the feedback. I'll update when I have new information.

 

[Cruiser1]

...........I should have known that I needed 316 rather than 304 stainless. The article would explain why the bolt is mildly magnetic, although I do wonder why, if that is the case, all the smaller bolts in my toolbox are completely non-magnetic.............

I tend to use 316 if the bolt is under the water or near the waterline. I understand 304 is fine for most other applications on the boat. I get the feeling that inspecting fittings regularly and systematically is more important than the difference in grades. When I take fittings off I examine the bolts and fittings with a magnifying glass - if in doubt I take a close up photo with the digital camera and enlarge the photo.

The attached photo is of a bolt on the bottom rudder post bracket of my boat (1 or 2 inches from the waterline). The corrosion was only just visible at the first look (mind you my eyes are far from perfect!). From the attached you can see what showed up with the enlarged photo. Click on it if you want a closer look.

As I alluded to before I think the magnetic test is only of limited use - there can be lots of variation due to the processing that the fitting has gone through. I take the attitude that if it is not magnetic (or showing very little mangetism) then there is a pretty good chance it is good quality stainless. Perhaps I am way off the mark but it makes me feel good and I can pretend I know something about what I am doing.

...............The bolt head is stamped with "F593C" on the top and "THE" on the bottom...anybody have any idea if either of these denotes the alloy?...............

Have a look at this article http://www.ebay.com/gds/Stainless-Bolts-Usually-very-weak/10000000001623345/g.html
The last sentence of the first heading "Stainless Steel is Stainless Steel" will explain the "F593C" bit - it says that stands for is 304. The 3rd paragraph from the bottom explans the "THE" bit - the Asian based manufacturer Tong Hwei Enterprises.

 

[vizwhiz]

Something else to mention is that 304 will show surface rust pretty "normally" where 316 does not. The other 400 series stainless steels, such as knife blades (usually 440C) and such will also rust. So just because something is called "stainless" steel doesn't mean it is going to stay pretty and shiny. But also worth knowing is that 304 and 316 are not the toughest of metals. They are alloyed for their corrosion resistance, not for strength, so you shouldn't assume, for example, that a stainless chain is as strong or stronger than a carbon steel of equivalent size. You have to look at the ratings of the objects you are using to be sure they are suitable for the task.

In the case of the swing bolt, someone else has already done the engineering on it and you should be able to depend on the size/strength being right.

 

[centerline]

does anyone have advice on what to use for a bedding compound? I was thinking of using 3M 5200, but that stuff has such good adhesion that it can be difficult to remove later on. Maybe plain old silicone sealant?

the rubber and cup washers doesnt need any bedding compound.
the idea of the cup washers are to squeeze the rubber inward and compress it around the bolt and the hole....
what can happen if you use a bedding compound that sets up is, it will glue everything in to place and deaden the rubber.... and it will be glued even if you want to ever remove it.
it is good to have a little bit of lube around the bolt so the rubber sets, but using a bedding compound will defeat the purpose of the design...
a bedding compound would be in order if you use flat rubber washers and flat backup washers, but not with the cup washers....
if you feel an urge to glue it in anyway, use silicone. it will lubricate and seal, yet you will be able to peel it loose when you need to. but still, additional sealer is not necessary. just tighten the bolt real well to compress the rubber inside the washers

 

[Catketch]

As far as the bedding compound is concerned, I was going by the printed instructions in the M25 manual. "Cover all washers with a liberal coat of good quality bedding compound" it says, although I'm a little fuzzy on what they mean by 'bedding compound' in this application.

 

[THECUSCUS]

I use Boatlife Lifecaulk. Put liberal amount inside the cone washer and on trunk around the hole. Then assemble, and tighten bolt. Make it tight, but be careful not to compress the rubber too much (if it starts squeezin out beyond the washer, its too much). You can then smear the excess sealer around the outside. Lifecaulk stays flexible, and can be applied to wet surfaces, so if you get a little drip you can apply more. Seal your lockdown holes good, put a long hose on the keel cable fitting and your bilge will be dry all the time.

 

[Catketch]

Thanks, Thecuscus, that's exactly the info I was looking for. Thanks to Cruiser1, we seem to have established via the stamped numbers that the bolt is 304 stainless, which makes the BWY description technically accurate (stainless bolt, although not marine grade 316 stainless).

My final question for this thread is what do you think about using 304 grade stainless below the waterline. I could care less if the thing discolors or develops a bit of surface rust, but I wouldn't want it install it if it has the potential to corrode all the way through.

 

[jmczzz]

The problem is the rubber washers and cone washers. No place to get them but BWY. Do they sell them separate or would do you have to buy the complete assembly and not use the 304 bolt and get a 316 bolt from elsewhere. Kinda costly but I am inclined to do that rather than use the 304 bolt. James's $.02

 

[THECUSCUS]

BWY won't sell just the washers and/or the rubber gaskets. I tried, and now have afew extra bolts & washers, since I don't like to reuse the gaskets. I wouldn't worry about using "their" bolt, they have been supplying Mac owners forever and I can't say I've heard of a bolt failing. I don't know for sure, but the 304 bolt might be stronger in shear than the 316, that might be why they use that alloy (chime in material engineers at any time here). Its all about trade offs with marine stuff.

 

[jmczzz]

oh yeah makes sense, I did not think about shear strength. I'll go with your experience.
James

 

[jmczzz]

Dan, I didn't mean to highjack your thread, but I am faced with the same keel stuff right now.
This is the final reply I got from West Marine Rigging shop FYI.
to me

[FONT=&quot]12046744 – 3/16 7x19 ss wire @ 1.80 per foot X 12 = $21.60[/FONT]
[FONT=&quot]115055 – 3/16 copper oval sleeve @ 2.69 ea X 2 5.38[/FONT]
[FONT=&quot]126771 – 3/16 ss thimble @ 1.49ea X 1 1.49[/FONT]
[FONT=&quot]158198 – labor/oval press @ 5.29ea X 2 10.58[/FONT]
[FONT=&quot] Subtotal not including tax or shipping $39.05[/FONT]
[FONT=&quot] To approve or if any question; please contact me at the listed toll free number or reply via email.[/FONT]
what do you think? [FONT=&quot][/FONT]thanks James

 

[Catketch]

West Marine prices always scare me away, but I do like to stop in every now and then to window shop. I'm sure you could get it done cheaper elsewhere, but the convenience of just ordering it and having it done by a professional may well be worth the cost to you.

I looked up the specs for 3/16 7x19 wire and it has a rated breaking strength of 3800 pounds. I couldn't imagine a scenerio where anywhere near that much stress could be put on the cable (certainly not without tearing the winch out of its mountings first), so please ignore my previous advice of "going a size up".

Thanks again to Cruiser1 for his exceptional internet search skills (I had absolutely no luck myself tracking down the bolt head code) and everybody else for their very helpful advice. I will post the reply from BWY just to close out the thread, but I think my concerns have all been addressed here in the forum.

Best Wishes,
Dan

 

[Catketch]

For those of you who have been waiting breathlessly for the official answer, here are the email exchanges between BWY and myself. The final email explains it all to my satisfaction and the new bolt will go in as soon as I work up the nerve to pull the old one.

Hello,

I just received my order of a Macgregor 25 keel pivot bolt assembly (invoice # 20088). It arrived surprisingly fast...thank you for the quick shipment. I was also surprised to find that the bolt itself was not 304 stainless steel. It holds a magnet about as well as a zinc plated bolt that I tested it against, but much less than the steel that my crescent wrench is made of, so I'm assuming it is either zinc plated or a lesser quality of stainless steel. Nowhere in your part description did you describe it as stainless but I assumed that it would be, as the current bolt it was intended to replace is completely non-magnetic and therefore, (I am assuming again) 304 stainless. Several years ago, I ordered a lockdown bolt assembly from you and it tested as 304 stainless (again, by using a magnet).

I am somewhat concerned with the idea of replacing a stainless steel part with non-stainless and am wondering if a mistake was made in the shipment, or if there is some logic behind your choice of material that I am unaware of. I am far from an expert in these things and would appreciate it if you would address my concern before I proceed with the replacement of the bolt.

Thanks,
Dan Resch

Hi Dan, We just tested the remaining bolts that we have and they are very slightly magnetic, almost non. But yes they are stainless bolts. Same purchase place we always have had, not specified any difference in quality. Many of these bolts have gone out. I do not expect a problem. So, yes they are stainless and some stainless is slightly magnetic.
Thanks, Cheryl

Thanks for the prompt reply. I posted the issue to one of the online Macgregor forums over the weekend and a bright fellow from Australia was able to identify the code stamped in the bolt head as indicating that it was 304 grade stainless steel. I was then reminded that marine grade stainless is 316 rather than 304. We were wondering why you chose 304 grade rather than 316 for that particular bolt?

Thanks,
Dan

Easy answer. First of all it is incorrect to refer to 316 as "marine grade" and 304 not. Both are commonly used in marine applications and both are essentially immune to structural corrosion. 304 is by far the most common on recreational boats, nearly all hardware as well as railings, ladders, etc are 304. The primary differences are: 316 has better resistance to cosmetic discoloration and has a slightly different (some would say prettier) look when polished to a high gloss, while 304 is stronger and more abrasion resistant. Since the keel pivot bolt is a high wear item and cosmetics is of no concern, 304 is the preferred option.


Cheryl