Monel or Stainless Rivets in my mast ?

Hi everyone, I am in the middle of a refit of my 1971 Swan 55 Walross III.

One of the bigger jobs is a complete refurbishment of her mast. After drilling out all 1000 (!) rivets, we have removed the tracks of the mast in order to properly sandblast it and give the mast a fresh coat of awlgrip.

The alu mast tracks will be anodized again and then attached back on the mast.

I have had some conflicting advise on the type of rivet to use for this job (so alu track on alu mast).

I landed on stainless rivets, dipped in tefgel before inserting/clamping, but I have not bought them yet, so still a small window of time to get expert 2nd opinion from yourselves....

Any thoughts ?

Dear Michael,

my preference would be for Monel rivets.

matteo (47/069 Vanessa)

Cia Matteo, thanks for your quick response. Can you help me understand why ? I am being told that SS will have LESS galvanic corrosion with an alu mast and Calude corroborates this..IDK ?

In my experience, TefGel and stainless works great but (and that is a big but) the TefGel washes out with time. So while I use TefGel with bolts, e.g. for the winch bases which are removed regularly (and the TefGel renewed), I have not used TefGel on rivets which I hope I never need to touch again.

Fair winds,
Martin (Vellamo, 48/039)

Dear Michel,

originally our masts had Monel rivets, and there is no corrosion even after a few decades (while there is often corrosion under the stainless steel plates, which were not well separated at the time, alas, but this is another matter), by the way I agree with Martin, I would not be sure Tef-gel wont be squeezed out with a rivet.

Is it not possible to install the track with threaded bolts (and Tef-gel of course)?

matteo (47/069 Vanessa)

I advise against tapping the mast for a mainsail track (if that was proposed). The aluminum wall is too thin to provide sufficient thread engagement. An M6 bolt engages only about one thread per millimeter, which results in significantly lower pull-out strength than rivets.

Corrosion is also an issue. Galvanic corrosion will degrade fine tapped aluminum threads much faster than the large clamping surface of a rivet, even with Tef-Gel. Furthermore, tapping is a non-standard procedure. If a thread strips during installation, the hole is ruined. If a rivet fails to set, you simply drill it out and install a new one.

We attempted a tapped installation for a storm trysail track on our boat, Bacchus, with D-Marin. The threads proved unreliable during installation. We abandoned them and went back to rivets to ensure adequate strength.

Br,

Tapio