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Old 01-25-2009, 08:23 AM   #1
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I'm a bit of a newbie to posting but have been watching for a while and thought you guys may have some answers regarding these questions.

I have just replaced the 3 'keel' bolts that hold an approx 200kg lead bulb onto the retractable centreboard on my 28ft trailerable 'Spyder Besyder'.

The bolts that came out , 2 with alot of vocal encouragement and 1 that broke off and had to be drilled out, were I/2 " BSW mild steel threaded rod and were heavily corroded. These were screwed into what looks like stainless steel nuts welded to the base of the centreboards internal stainless steel frame. After a bit of searching I found some 316 stainless steel threaded rod with a BSW thread(apparently BSW is being phased out in Australia and most threads are UNC OR METRIC). I have used this with an anti seizing paste for the new 'bolts'.

I've always thought stainless shouldn't be used underwater for electrolysis reasons ,and have had stainless rudder brackets and pintles underwater on another boat that did suffer from this, but was fixed by attaching an anode to the affected area. SB is usually stored on a trailer so I hope not to have this problem and the existing SS in the centreboard looks ok.

Has anyone had experience with this ?

I have also always been told that stainless steel nuts and bolts under load can sieze and be very difficult to undo , especially rigging screws which is why they are normally Bronze or Gal steel.

Why then don't smaller SS nuts and bolts seem to suffer from this as they normally come apart easily?.... Size?

I'm thinking that siezed SS keel bolts might still be easier to undo than the rusted mild steel ones that came out. I am a little concerned that with the anti seize paste they may loosen themselves over time with a not very nice outcome. At least I can check them regularly when on the trailer.

The last question is, what is the difference in strength between theaded rod and round bar only threaded where it enters the nut?

I didn't fancy theading stainless rod although I don't know how much more difficult it is than steel . (maybe this is the last question )

Also I couldn't buy a 1/2" BSW die locally.

Thanks very much

Muz
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Old 01-26-2009, 06:50 PM   #2
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Has anyone had experience with this ?

Muz
Hi, Muz,

The SS will likely have a few problems of corrosion and yes, it tends to bind up on itself (galling). In above water applications, one can use a silicon bronze nut/washer on a stainless bolt but this cannot be recommended for below water use due to the dissimilar metals having galvanic corrosion. The seized SS bolts won't be any eaiser to undo than the carbon steel.

Depending on how much steel (stainless or other) exists on your boat (underwater) which would cause galvanic corrosion wasting away the bronze, you might just consider using silicon bronze rod and threading it yourself. Get the bar stock and thead only the ends--stronger for sure and less corrosion surfaces. Here in the USA, most tool places can order you a needed die. You can do your own threading of SS rod, but I'd suggest a machine shop for that. Even the bronze (of size) is physically heavy work, but lasts quite a long time in the lead keel and in theory will be more easily removed than that of SS or carbon steel. The raw material costs of the bronze will be more than SS but you can thread it yourself easily whereas you'd have to add in the cost of theading the SS bar at a local machine shop. We recently replaced 75 year old keel bolts in our 11,000 lb lead keel and had to do the threading ourselves as mentioned. We had various bolt sizes of 1/2" through 1" diameter and lengths ranging from 1.5 ft to 4 ft so they were quite large. Ours had nut and washer both top and bottom, btw. Our original keel bolts were a mix with every-other-one being galvanized and every-other-one being tobin bronze (which is another name for Naval brass). The galvanized ones were quite rusty and the bronze ones were quite pink from the zink coming out due to galvanic corrosion.

Threading keel bolts



Below is a galvanic series chart which shows the various alloys and their position in the series. Those alloys to the left of silicon bronze will cause the silicon bronze to degrade in the presence of seawater and stray electrical current; those alloys to the right will not. Essentially it works this way for each alloy. Just look at where it is in the series and know the relationship of which will waste away first.

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Old 01-26-2009, 10:32 PM   #3
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Thanks for the info redbopeep.

I hope tol be able to regularly withdraw and inspect my bolts as they are only around 120mm long and I have used antigall paste . Although I don't know how the paste will last being submerged for periods .

Previously the recessed lower nuts were faired over with what looked like auto putty (easier to remove than epoxy I guess) which made them impossible to inspect. I will be leaving them exposed.

I have 2 bronze thru hulls approx 400mm away from the bolts that I will keep an eye on as well. It is rare for SB to be in the water for more than a week or so at any time .

The galling of the SS is interesting . Do you know what kind of conditions promote this. Is it not as noticable on smaller nuts and bolts because of the size of tools in relation to the nut and bolt. (More leverage)
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Old 01-28-2009, 01:03 AM   #4
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I'm sorry I don't know much of it. Actually the corrosion if two different kinds of stainless steel are used together is probably most worrisome--if you use 316 make sure you stay with it, or if you use 304, then stick with 304 for all. I believe--but have not fact basis for this--that simply having the two identical metals of same strength, toughtness, etc may create the opportunity for galling. The same is true (or worse) for bronze on bronze which can gall if in a friction loaded bearing situation (example, rudder stock in gudgeon). But, in any case, best of luck in putting it all together. I also suggest that you consider a heavy lanolin grease which may actually last quite long submerged for periods as your bolts will be.

fair winds,

Brenda
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Old 02-22-2009, 09:48 AM   #5
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Thanks for the info redbopeep.

The galling of the SS is interesting . Do you know what kind of conditions promote this. Is it not as noticable on smaller nuts and bolts because of the size of tools in relation to the nut and bolt. (More leverage)
Hi Muz, Just read your post. I ran a SS fabrication business for many years, we always understood that the heat that comes from the friction causes the galling, it is much worse with nyloc nuts and the larger the bolt the more prone they seem to be. The bolt supplier always told us to NOT mix steel types as this would promote galling.

I don't how true any of this really was but copper paste was used on every SS bolt/shaft/assembly that we made. You don't need very much at all.

As for your keel, I would inspect the bolts every now and then and if there appears no issue's, which I doubt, fair them off with a plug of silicon (good stuff, Dow Corning 732) and then it should be good for years.

BTW is your boat a spider 28?? I had one of those for 7 years.
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Old 02-24-2009, 05:38 AM   #6
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YES , a SPIDER 28 she is. Great boat for round the cans . Enough volume for limited cruising for one or two although a bit tender shorthanded.

Where did you sail your spider?

From what I can figure SB was built in the early 90's ,not sure exactly but she has skite plates from races in 1994 in port Stephens, and has also been sailed out if Darwin , Cairns and Tin Can Bay .

Our cruising has been limited to between Bundaberg and Moreton Bay and shes been great for that. She is currently at Manly in Brisbane for a bit more cruising around moreton bay.
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Old 02-27-2009, 08:00 AM   #7
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YES , a SPIDER 28 she is. Great boat for round the cans . Enough volume for limited cruising for one or two although a bit tender shorthanded.

Where did you sail your spider?
I sail on Port Philip.

Mostly round the cans but a few times a year we would head down to the Gippsland lakes with the wife and 2 kids for a bit of cruising. Good boat mine was a MK4 which had a smaller rig than yours would have. I bought a no4 jib which was great for cruising, only 6m2, that and a reef in the main and she was a lot of fun in 35knot gusts.

I wouldn't get too stressed about the SS keel parts on a trailerable. I made my keel from #304 garde SS sheet and #316 welding rods as is normal practice and had no corrosion issues.
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Old 02-27-2009, 08:02 PM   #8
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The bolt supplier always told us to NOT mix steel types as this would promote galling.

I don't how true any of this really was but copper paste was used on every SS bolt/shaft/assembly that we made. You don't need very much at all.
Hi, Ghost!

I always thought the reason NOT to mix SS types (e.g. 304 with 316) is that there will be corrosion. When I don't know which stainless steel I have on a bolt, I use a silicon bronze nut to ensure no corrosion. Same situation that some people do with rigging screws/turnbuckles--they'll use a combo of bronze and stainless on the body and pins to keep the rigging screw from the SS (even if same alloy) seizing due to corrosion.

The use of copper paste to prevent galling makes sense. And, since a marine ss like 316 would be more noble than the copper, you don't need to worry about the galvanic corrosion you'll have in a salt water environment with this.

Thanks for your post
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Old 01-05-2011, 06:45 AM   #9
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We think you use same materials such as silicon bronze or monel.

This will bring better result.
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Old 05-13-2013, 04:52 AM   #10
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Old thread I know but I thought you would find this useful. Galling or 'Cold-welding' is in the nature of Stainless Steel - any grade. Less RPM and heat will help, but it can still happen just due to the properties of the Stainless. The rougher the threads the more likely. For this reason it is always important to lubricant Stainless Steel fasteners with a Nickel based lubricant. Ideally Nickel based rather than Copper. Some people like using opposite grades, like 304 bolts with 316 nuts. The important aspect is using a bolt/nut mate with differing hardnesses. So 316 Bolts with Duplex 2205 Hex nuts even better. But lubrication should do the trick with a 316 Bolt and 316 nut. Here is a good overview on Stainless Steel Galling. With regards to Keel Bolts, 316 really isn't up to it. It isn't ideal to be submerged in Salt Water or without Oxygen which Stainless needs to repair itself. So if any water gets into the Keel, there is no air and the bolt is 316 things won't turn out well. Ideally Monel or 2205 Duplex Stainless is best. Here is a good overview for Stainless selection for Keel Bolts. And yes as already mentioned as soon as you put too alloys together with a gap on the Galvanic Series chart, this would lead to Galvanic Corrosion with an electrolyte present like salt water. This is why Stainless Screws tend to eat Aluminium masts badly. Best they are isolated with Tef Gel or Durlac or something like this.
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Old 06-14-2013, 02:52 PM   #11
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Old thread I know but I thought you would find this useful. Galling or 'Cold-welding' is in the nature of Stainless Steel - any grade. Less RPM and heat will help, but it can still happen just due to the properties of the Stainless. The rougher the threads the more likely. For this reason it is always important to lubricant Stainless Steel fasteners with a Nickel based lubricant. Ideally Nickel based rather than Copper. Some people like using opposite grades, like 304 bolts with 316 nuts. The important aspect is using a bolt/nut mate with differing hardnesses. So 316 Bolts with Duplex 2205 Hex nuts even better. But lubrication should do the trick with a 316 Bolt and 316 nut. Here is a good overview on Stainless Steel Galling. With regards to Keel Bolts, 316 really isn't up to it. It isn't ideal to be submerged in Salt Water or without Oxygen which Stainless needs to repair itself. So if any water gets into the Keel, there is no air and the bolt is 316 things won't turn out well. Ideally Monel or 2205 Duplex Stainless is best. Here is a good overview for Stainless selection for Keel Bolts. And yes as already mentioned as soon as you put too alloys together with a gap on the Galvanic Series chart, this would lead to Galvanic Corrosion with an electrolyte present like salt water. This is why Stainless Screws tend to eat Aluminium masts badly. Best they are isolated with Tef Gel or Durlac or something like this.
Old thread or not, very good info, thanks.
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