Metalwork fixings for Carbon spar

[Delfini]

Ive recently bought a new VHF antenna to replace a very old stub at the masthead - the original bracket was fixed to the carbon mast with 3 x self tapping (now rusty) screws

Is there a preferred fixing for stainless metalwork into carbon spars - Ive read you can get carbon friendly rivets ?

 

[William_H]

Carbon fibre is an electrical conductor so there for gives a concern re electrolysis. Certainly ali and cheap steel rivets should be avoided. Monel might be OK I don't know. However use an insulating paste or sheet under the bracket. CF might tend to be a bit softer than ali so some risk of pop rivets pulling through. You might consider drilling more holes in the bracket and epoxying the bracket to the mast. A true cf solution but do clean the base cf well. ol'will

 

[Ian_Edwards]

My boat has Selden Carbon mast and boom, looking at what Selden use during manufacture and fit out, it's a combination of Monel pop rivets, SS self tapping screws and nuts and bolts and SS threaded inserts.
For things like VHF antenna I prefer to use threaded inserts, simply because they need to be replaced periodically and if you take SS self tapping screws in and out they become loose over time.
Although Carbon fibre is conductive, Selden don't seem to use Duralac or similar insulating paste, and there doesn't seem to be any obvious corrosion between SS fixing and the Carbon fibre mast in a 2007 mast, although I don't think using Duralac would do any harm.
If you really want a strong fixing, then using epoxy to bond it onto the mast and then laminate carbon epoxy over the top of it, but that would be overkill for a VHF antenna.
On my boat the VHF is fixed to a section of aluminium channel which is bolted as a "T" onto the cap on top of the mast with SS nuts bolts and washers, on one side there's the VHF, on the other a SEA-ME radar transponder, the aluminium section simple gives some physical separation between the two antenna.

 

[Delfini]

In case anyone finds this thread of interest - I initially bought carbon friendly 5mm rivets at £1 each but when it came to it, the section of carbon at the top of the mast where I wanted to fix the VHF antenna was too thick for a rivet and I was left with a deep 5mm hole - the boatyard rigger advised me to tap the hole to M6 for a stainless bolt and if that worked to drill and tap for all 3 bolts in the same way - the carbon was tricky to tap but it worked a treat - I tightened up all 3 x bolts absolutely solid with a bit of Duralac behind the bracket and in the holes - job done