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21-03-2010, 09:41
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#1
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Registered User
Join Date: Jun 2008
Location: Houston, TX
Boat: Columbia 8.7m, Rol'n Rose
Posts: 91
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SS and Aluminium
Hi all,
Ive made a anchor roller platform out of aluminium which will be bolted through the deck. I was plannin on using SS bolts and am wondering about the possible consequences of corrosion. I could use nylon washers to prevent contact between the dissimilar metals. is it a bad idea to go this route? how back would the cossion be? i've seen it in the past as a light white dust, nothing major. but being on the bow and being exposed to seawater, I am thinking that it will be worse. The backing plate is also alumium.
hank
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21-03-2010, 09:51
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#2
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Registered User
Join Date: Mar 2007
Location: Tavernier, Fl
Boat: Outremer 50
Posts: 750
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Use Tef-gel between the ss bolts and the aluminum. Fantastic product.
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21-03-2010, 12:22
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#3
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Senior Cruiser

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 51,775
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Since Stainless is more noble than Aluminum, a small stainless bolt in a large aluminum structure, is the right proportion of metals to limit the galvanic corrosion. A dielectric grease, like Tef-Gel, will further limit any potential corrosion.
The major problem is galling (which prevents easy removal of the fastener), occuring with stainless fasteners threaded into aluminum hardware. Through-bolted stainless fasteners are ok on aluminum.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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21-03-2010, 18:35
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#4
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 21,171
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Well, the alloy will be the loser, so ... huge dia alloy fasteners can be used.
Or else - I-S-O-L-A-T-E.
Tef-gel. Lanocote, washers. And a lot of them.
b.
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21-03-2010, 18:47
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#5
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Moderator Emeritus

Join Date: Sep 2007
Location: Eastern Tennessee
Boat: Research vessel for a university, retired now.
Posts: 10,405
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I have used both nylon washers and Tef-gel doing essentially the same thing. No problems, even years later. In my experience, Lanocoat is not as good as Tef-gel.
__________________
David
Life begins where land ends.
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21-03-2010, 18:50
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#6
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,558
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G'Day All,
A real world observation:
Maxwell windlasses, cast aluminum body, have s/s bolts securing them to the deck. The OEM provides plastic sleeves with integral washers to isolate the s/s from the powder coated aluminum. I just assisted a friend in the removal, overhaul and replacement of a 2200HWC which had been on deck for 15 years. There was noticeable corrosion around all four bolts... enough to breach the powder coating, but there was no serious erosion of material, and I believe no perceptable weakening of the structure.
So, in the case of the bow roller structure, the use of nylon washers under the heads of the attaching cap screws, plus the use of reasonable clearance holes in the alloy with the voids filled with sealant of some sort should give good service. Inspection during use should show up any corrosion developing, and renewing the sealant might be required now and then. Or, one could perhaps buy the appropriate sleeve/washer isolators from Maxwell (or other sources).
Good luck with it all.
Cheers,
Jim and Ann s/v Insatiable II lying Church Point, NSW, Oz
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21-03-2010, 18:53
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#7
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Registered User
Join Date: Dec 2009
Posts: 2,959
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FYI - Backing plate could be steel. Generally use aluminum for strength, and steel for stiffness ... kilo for kilo ... until carbon came along ...
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22-03-2010, 01:33
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#8
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always in motion is the future

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 20,107
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Yes, TefGel is much better than Lanocote. I use Lanocote for SS to SS to prevent galling and lubrication. The reason is that it is cheaper (I'm Dutch :-) because I think TefGel would be better for that too ;-)
cheers,
Nick.
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23-03-2010, 19:39
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#9
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 21,171
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lanocote vs. tef-gel
Quote:
Originally Posted by s/v Jedi
Yes, TefGel is much better than Lanocote. I use Lanocote for SS to SS to prevent galling and lubrication. The reason is that it is cheaper (I'm Dutch :-) because I think TefGel would be better for that too ;-)
cheers,
Nick.
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I use -
:lanocote - where there is movement, (e.g. joints)
:tef-gel - where there is no movement (e.g. ss crews into alloy) (esp. if painting over)
plastic washers - where I cannot use tef-gel or lano
When using plastic washers I will still supplement them with one of the goos.
b.
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23-03-2010, 20:25
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#10
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Registered User
Join Date: Sep 2009
Location: Houston
Boat: ‘01 Catana 401
Posts: 9,627
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and lanocote smells like sheep...........kinda soothing in a way.
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05-04-2010, 19:27
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#11
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Registered User
Join Date: Jan 2010
Location: Wells, Vt
Boat: 42ft Colvin Gazelle - TLA HLA
Posts: 503
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If you want to keep things simple you can use hot dipped galvanized steel nuts and bolts. Mild steel is very close to aluminum on the galvanic scale being slightly more noble. Zinc (galvanized) is just below aluminum bieng slightly less noble. Stainless should not be in contact with aluminum as it is way, way away on the galvanic scale.
Galvanic corrosion is not the only type you should be worried about with aluminum. Anywhere moisture can be trapped or held can present a serious problem. If certain alloys are allowed to be primarily in the presence of oxygen aluminum can be very corrosion resistant. If in a salt environment use 5000 series. In any case, if the aluminum will be bolted down to something make sure you paint any surface (imediately after sanding it to remove the oxide) that may trap moisture. A good bedding will help also.
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06-04-2010, 06:06
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#12
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Registered User
Join Date: Jan 2010
Location: Usually where the boat is...
Boat: Pearson 40
Posts: 557
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Hank
Since you will not be removing the anchor roller platform anytime soon, here is a procedure that will work in the long term: do not use delrin washers as they distort under pressure and also absorb moisture over the years. Use ss bolts that are truss head (they have a slightly larger head diameter). Each bolthole has to be cleaned out well of any grease, cutting fluid etc.
Clean each bolt and backing fender washer in acetone and let dry without touching with bare hands.
Now apply a good amount of Lifeseal (from Boatlife) to each bolt and the inside of the hole. Insert bolt, apply lifeseal to washer side that will go against the aluminum and tighten the nut. Lifeseal on the thread is OK as it will prevent the nuts from loosening.
Cleanup is with mineral spirits. Make sure you clean all traces of bedding because it is almost impossible to take off after it's dry. A roll of paper towels will work wonders.
The lifeseal bedded under the truss heads and washers will work as a capping barrier, sealing moisture away from the contact point of aluminum and ss. The bond is also permanent. Tuff gel works well also but not for as long.
This procedure is an old trick riggers use on alum masts where screws are tapped in aluminum where there is a potential for galvanic corrosion.
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06-04-2010, 06:11
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#13
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Registered User
Join Date: Jan 2010
Location: Usually where the boat is...
Boat: Pearson 40
Posts: 557
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[QUOTE=ConradG;431295]If you want to keep things simple you can use hot dipped galvanized steel nuts and bolts. Mild steel is very close to aluminum on the galvanic scale being slightly more noble. Zinc (galvanized) is just below aluminum bieng slightly less noble. Stainless should not be in contact with aluminum as it is way, way away on the galvanic scale.
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The only problem with zinc dipped is if one scratches the zinc coating during tightening on the nuts, the fastener will start becoming active in that spot. A small scratch is enough on an anchor roller as this sees a lot of salt spray....
Coating will help but it is not easy to paint alum properly
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06-04-2010, 07:58
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#14
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Registered User
Join Date: Jun 2008
Location: Houston, TX
Boat: Columbia 8.7m, Rol'n Rose
Posts: 91
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Thank you all for your insights/ advice.
Hank
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06-04-2010, 16:33
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#15
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 21,171
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Quote:
Originally Posted by Sailmonkey
and lanocote smells like sheep...........kinda soothing in a way.
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Only if you are from the land down under. ;-))))
b.
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