Different metals on Mast & Epoxy Question?

[SeacretSailor]

Need to ask 2 quick questions relating to my med size trailerable sailboat:1 - I'm mounting 2 small bronze block/pulleys on my aluminum mast and I'm wondering about "dissimiliar metals" problems. Would the bronze & aluminum effect each other thru galvanic corrosion resulting in mast corrosion problems? If so, I can put a rubber gasket between them when I mount them on.2 - I need to install two small metal "L" brackets on either side of my rudderpost on the interior in the lazarette. They'd run up & down so I can install pulleys going to a quadrant for a tiller/wheel conversion. Can I epoxy or resin these onto the transom bulkhead and not add fiberglass cloth to it? I do not want to drill my transom and bolt it thru, but want to epoxy/resin them in?Any thoughts would help...Kevin B.

 

[Ross]

Vinyl electrical tape is good for isolating

aluminum from foreign metals. I like a little glass cloth with my resin if strength is an absolute.

 

[Dave]

Yes and No

Dissimilar metals will react due to a difference in electrical potential between them. You need to isolate them from each other. Don't forget the fasteners, you can put a gasket and yes electrical tape will work for that but the fasteners will still provide a current path maybe. So you also need to add some method of isolating the fasteners. Are you using rivets or screws? If threads you might consider zinc chromate primer, used on aerospace applications, should be easy to get. For rivets if they are aluminum maybe coat them prior to installation.Raw epoxy will not have the strength you need to take all the load from your rudder to a steering wheel, no way this will work. Either use fiberglass cloth and bond the brackets to the boat or bolt them to the transom. If you use cloth make sure you make the laminate thick enough and large enough, you need to spread the load over a wide area to reduce the stress (Stress = Force/Area). In a GRP (glass reinforced plastic) construction all the strength comes from the glass, the epoxy is just to hold it all together and the higher the glass to resin ratio the better. Straight epoxy has almost no strength for structural work so definitely do not try it.Regards,dave

 

[Fred]

Kevin, If there's any strain on the lines that go

through your bronze blocks, go buy plastic blocks, with stainless straps if needed. Any tape or even plastic bushings you use to insulate the bronze from the aluminium will wear through quickly. If it'a a flag halyard, a good bushing may work, but electrical tape will wear through just from the weight of the block.Rudder pulley brackets;If you really don't want to use glass cloth (not even a little cloth tape? You can saturate it before you slap it in place. Four or five 4" x 2" tapes in epoxy would not be too hard) OK - no cloth, then; You can glue a piece of wood to the hull so you get a lot of surface area for the glue, then screw or bolt (if you put the bolts in from the back side before you glue the wood down) your brackets.I would just bolt them through the Hull. Use good bedding and big washers. If it drips a bit it's easy to see and fix. That's what most yacht builders would do. More complication is just, well.... more complication.