Mounting things on an alloy boat?

[Recutter]

Just wondering...
What is the procudure to attach accessories to an alloy boat? I am thinking specifically about downriggers on the gunnels, a small rack for knife/pliers/etc, and also maybe a pvc bracket to hold dive tanks.
Is it a simple drill and bolt?
Thanks guys!

Dave

[Kern O]

What you need to keep in mind is that stainless and aluminum are dissimilar enough that they create galvanic action between them. So, anywhere you have a stainless screw into the alloy, it either needs to be sealed very well with something like 4200 or the fasteners need to be sprayed with a zinc compound such as ECK. ECK is basically powdered zinc in an oil base that serves as a sacrificial anode. It is primarily used in the alloy truck body realm. So, if you can't seal it, ECK it.

[Daddy'O]

Dave,

You want to isolate dissimilar metals to avoid galvonic corrosion. This can be accomplished in several different ways. A common way is to use a marine grade anti-seize in conjucntion with plastic or teflon washers. Of course there are other techniques which I'm sure other forum members will recommend.

Wayne

[Daddy'O]

Dang Kern O!

You're up late and beat my reply.

See Dave, I said you would get the answers you needed.

Wayne

[peterbo3]

Dave,
Mounting items which exert flexing stress onto your alloy can be risky. I am referring to downriggers. The length of the arm coupled with the weight of the ball & the motion of the boat will, in time, damage the metal. Could I suggest that a piece of alloy plate be welded to your gunnel ,or, if your boat is painted or you do not want any welding done, mount the downrigger base onto a piece of starboard or the like. I would also suggest some form of backing plate under the gunnel if you go with the starboard.
As for isolating the SS fasteners, there are plenty of products out there but definitely use one of them. Another way to go may be monel rivets, which from memory, do not react with aluminium.

[welder]

Order your boat with the out rigger plates on the gunnels as for the rest , MEASURE 10 times and DRILL once.

Piece of cake.

Lester

[offshore]

Tef-Gel works great and I have never had a problem with galvanic reaction. This is what Birdsall reccomends when using stainless and aluminm together....mark

[Recutter]

Thanks guys!!!

A question about ECK: If this acts as a sacrificial metal, does it have to be re-applied after time? For instance, if I bolt something to a console or to the transom of an 5086 alloy boat, do I periodically have to take out the bolts and ECK again?
Sorry if these seem like stupid questions.

For downriggers - I think that Les and Pete are right, have the mfr weld in reinforcement.MC