I have just seen a range of low-loss thin ad flexible 50 ohm coax -
aircell 7, ecoflex 10, ecoflex 15. If its as good as it claims to be,
i would be great for use on boats for both HF and VHF. Has anyone used
it?


Yup, great stuff. Not as flexible and thin as RG-58, but a lot more than
RG-213 (?).

As an installer and repairman, we used foam dielectric coax once in a while
for cell phone antennas because of UHF loss problems. It isn't as durable as
RG-213 (the standard for most installations around salt water, as it crushes
and flattens easier than solid dielectric.

There were some brands of foam dielectric coax that absorbed moisture that
degrades coax very quickly.

RG-58 is ok for short runs of 25 watt VHF, but in tall masts, it just
doesn't cut it. Also, it is a little light weight for 100 watt plus HF
installations.

The obvious weak link in most masthead installations is in the PL-259 coax
connector installation. There are not many out there who can do a proper,
watertight soldering job up at the top of a wavering, windy masthead. Been
there, done that, was not always proud of my work.

Old Chief Lynn, W7LTQ, PG-13-20604