Mooring weight question??

[Gatto Nero]

I built mine with 3 bags of concrete, which I poured into a duck tape reinforced cardboard box. Mine is in 25' of water, and I didn't want have to do it twice, so I sunk a stainless eye bolt into the middle of it. I built the whole thing on my raft at the shore then floated it out to its final location and pushed it overboard with chain attached. I have a 24' boat at a very windy location and it has never moved as far as I can tell.

[Dave R]

Originally Posted by Gatto Nero

I built mine with 3 bags of concrete, which I poured into a duck tape reinforced cardboard box. Mine is in 25' of water, and I didn't want have to do it twice, so I sunk a stainless eye bolt into the middle of it. I built the whole thing on my raft at the shore then floated it out to its final location and pushed it overboard with chain attached. I have a 24' boat at a very windy location and it has never moved as far as I can tell.

I hate to be the bearer of bad news, but stainless steel was a bad choice and you should not trust the mooring. Google "crevice corrosion on stainless steel".

[Gatto Nero]

Originally Posted by Dave R

I hate to be the bearer of bad news, but stainless steel was a bad choice and you should not trust the mooring. Google "crevice corrosion on stainless steel".

I Googled. Here is what I found.

"Crevice Corrosion

The corrosion resistance of a stainless steel is dependent on the presence of a protective oxide layer on its surface, but it is possible under certain conditions for this oxide layer to break down, for example in reducing acids, or in some types of combustion where the atmosphere is reducing. Areas where the oxide layer can break down can also sometimes be the result of the way components are designed, for example under gaskets, in sharp re-entrant corners or associated with incomplete weld penetration or overlapping surfaces. These can all form crevices which can promote corrosion. To function as a corrosion site, a crevice has to be of sufficient width to permit entry of the corrodent, but sufficiently narrow to ensure that the corrodent remains stagnant. Accordingly crevice corrosion usually occurs in gaps a few micrometres wide, and is not found in grooves or slots in which circulation of the corrodent is possible. This problem can often be overcome by paying attention to the design of the component, in particular to avoiding formation of crevices or at least keeping them as open as possible. Crevice corrosion is a very similar mechanism to pitting corrosion; alloys resistant to one are generally resistant to both. Crevice corrosion can be viewed as a more severe form of pitting corrosion as it will occur at significantly lower temperatures than does pitting."

Not sure I follow what the problem is. I figure my other choice was a galvanized eye and I don't see how that would be any better.

[Dave R]

Originally Posted by Gatto Nero

I Googled. Here is what I found.

"Crevice Corrosion

The corrosion resistance of a stainless steel is dependent on the presence of a protective oxide layer on its surface, but it is possible under certain conditions for this oxide layer to break down, for example in reducing acids, or in some types of combustion where the atmosphere is reducing. Areas where the oxide layer can break down can also sometimes be the result of the way components are designed, for example under gaskets, in sharp re-entrant corners or associated with incomplete weld penetration or overlapping surfaces. These can all form crevices which can promote corrosion. To function as a corrosion site, a crevice has to be of sufficient width to permit entry of the corrodent, but sufficiently narrow to ensure that the corrodent remains stagnant. Accordingly crevice corrosion usually occurs in gaps a few micrometres wide, and is not found in grooves or slots in which circulation of the corrodent is possible. This problem can often be overcome by paying attention to the design of the component, in particular to avoiding formation of crevices or at least keeping them as open as possible. Crevice corrosion is a very similar mechanism to pitting corrosion; alloys resistant to one are generally resistant to both. Crevice corrosion can be viewed as a more severe form of pitting corrosion as it will occur at significantly lower temperatures than does pitting."

Not sure I follow what the problem is. I figure my other choice was a galvanized eye and I don't see how that would be any better.

"To function as a corrosion site, a crevice has to be of sufficient width to permit entry of the corrodent, but sufficiently narrow to ensure that the corrodent remains stagnant."

In this situation, the water is the corrodent and the concrete allows water in but not to flow, so it remains stagnant. This makes the SS corrode very quickly and invisibly (it's invisible because the corrosion can only occur within the tight confines of the crevice, if it's plainly visible, there will be no corrosion).

Here's a nice example of a stainless bolt compared to bronze bolt:

[SIKSUKR]

Sounds like evelyn has the best set-up.I can see where more wear on the chain can occur but at least it can be seen and corrected unlike eyebolt that breaks off.

[LIforrelaxin]

Originally Posted by Dave R

I hate to be the bearer of bad news, but stainless steel was a bad choice and you should not trust the mooring. Google "crevice corrosion on stainless steel".

I hadn't heard of this before.... indeed not good....

Now the concrete block we made, with rebar has been at the bottom for ummmmm I think about 25 years now.... the chain has been replaced several times, but the rebar is still in great shape.

now someone else mentioned granite..... I have heard this is much better then concrete, and I know on Lake Champlain, is very popular for moorings....

[Pineedles]

didn't the same site being copied and pasted also say....

Crevice corrosion occurs in stainless steel and other metals when the metal is covered, but immersed in a corrosive liquid such as seawater.

[Dave R]

Originally Posted by Pineedles

didn't the same site being copied and pasted also say....

Crevice corrosion occurs in stainless steel and other metals when the metal is covered, but immersed in a corrosive liquid such as seawater.

Trust me, rain water and lake water will do it too. Most crevice corrosion takes place well above the waterline on boats due to rain water leaking past SS fasteners and into the core of the deck or superstructure. There's very little stainless steel crevice corrosion with underwater parts because builders know not to use it wherever it would be a problem.

[ApS]

Originally Posted by NoBozo

"...ALL Galvanized chain, shackles, and fittings are far superior to Stainless Steel..."

Not all galvanized steel (or stainless) is of high quality, so I wouldn't make that generalization: for example, I gave my BIL a one-inch solid diameter galvanized eye bolt for use in his concrete mooring block. After only about eight years in the lake, it got very ugly, and we're not trusting it another four or five years in this lake.

A ½-inch diameter galvanized U-bolt used on our original mooring block has disappeared entirely after 54 years. (Well, there are two brown spots remaining. )

As to narrow anchorages, a new Chapman NIB text—marked "100" at a yard sale, which turned out to be just $1 —suggests three mooring blocks. Two should be placed to the strongest wind direction and all three attached together with chain with a central shackle pickup point.

Chapman advises "hot-galvanized" steel, which may be that process that wrinkles the galvanized finish to a thicker coating.

Chapman also suggests switching mooring chains end-for-end each season. (Although a heavy nylon line should be fine for a 19' sailboat mooring). A friend just ½-mile from me has been using a stainless steel mooring cable—for 40 years! (For a 19' Cape Dory Typhoon sailboat).

For confirmation of the suggestion found in Chapman, check out this chain: http://www.winnipesaukee.com/forums/...06&postcount=5

Originally Posted by Dave R

"...Most crevice corrosion takes place well above the waterline on boats..."

Crevice corrosion was covered in a recent copy of Sail magazine.

Since I seek-out new (and used) stainless steel objects at every opportunity, I discovered some deep crevice corrosion on a very important object that hasn't been covered in this thread.

That piece was a boat's 2nd-hand bow eye!