An easy DIY job in; aluminum, wood, or composite. And if you go the metal route
, there's nothing that says that it has to be round. Plus, the bracket needn't be fancy (read, a welded up job) neither.
You can build a bracket which simply bolts on, & or, is glued on (or both). Even using U-bolts on a round tube, or trailer clamp type bolts on a square pole.
Although me, I'm in favor of a DIY, swiveling/leveling mount. Be it self leveling, or one where you set the radar
at an average of your angle of heel. Via the mount being on a pivot bolt, with a set of remote
lines led to it for adjustment, from the cockpit
As to the bracket for the radar, it needn't be welded. Which cuts a lot of the cost out of things. You simply cut the pieces to size in your shop, or cockpit
. Bend them to shape, & bolt or rivet them together. With or without epoxy
Plus, any & all of the above mentioned materials can be used in combination. And wood or composite is as easy, or easier to work with than is aluminum.
Also, you can use Door Skins, & a Hot Glue Gun to make a mockup/patterns for the real thing. Or, use pre-fab composite plate glued or bolted together, in order to build the mount (out of). Including using pre-glassed 3mm - 6mm plywood panels
... with or without some Trick, geometrically shaped lightening holes.
FYI, 3mm aluminum angle makes great gusset material for bolting things together.
Too, for a KISS mount for the tube. Simply cut a hole in your deck slightly bigger than the pole. Make a GRP sleeve for the pole, long enough to go from just above the deck, to the bottom of your boat's inner hull
. And then glass it into place.
After which (or before), you put a small riser (epoxy or other) into the bottom of the sleeve, that's angled downhill towards the transom. And add a small drain tube from the sleeve, out of the back of the boat.
From there, simply use a few knees, bolted to the tube, to attach it to the deck. Or, a custom; composite, aluminum, or wooden bracket/flange if you like.
Ah, & the other option, is to make up a similar sleeve for the pole. And then using "shim blocks", to get things vertical & plumb, when you bolt the sleeve to your transom. Decorating it to look "shiny" (pretty) as you see fit.
Also, you can just bolt it to the transom with some supporting blocks, & then angle the mount in order to get the radar itself level.
Plus, of course, you can simply bond (glass) the mount to the boat's transom if you like. Using some pretty, clear coated carbon fiber for the last layer or three.
Not a tough job. And one with lots of options & solutions, so as to make it look FAR better than any stock mount. As well as being; lighter, cheaper, & stronger.
PS: IIRC, Bruce Schwab had a Trick, custom, semi foil-shaped, carbon fiber one on Ocean Planet. And it was plenty tall. Which is easy to do, particularly if you put a couple of stays on it.