accessories

Guys, I'm headed up to Sandusky to work on my new E29 this weekend and am going to relocate my VHF antenna from the stern rail to the mast. What is the best fastener to attach an accessory like this to an Aluminum mast. Obviously you can't get to the inside of the mast to put nuts on the back...

I have a Datamarine 5100 unit (circa 1988) with the original remote cockpit unit, speed transducer, and masthead wind transducer for sale. Remote unit completely rebuilt by the Datamarine guys last year. I know there was some interest in some Datamarine stuff recently...