Radar Mast Construction

[wkd928]

Here are the details for my solution to a radar tower/mast. Not happy to pay the money asked for a proprietary product i decided to have a crack at sorting something out myself. These are pics of the bracket i have had fabricated in alloy to support the radar mast where it emerges through the deck, the plan is to cut a hole in the deck and bury the tube with another bracket against the hull bottom.

The mast itself will be 4" diameter with 1/4" wall thickness alloy tube, the bracket pictured has a 4" internal diameter to act as a sleeve around the mast. The bracket will bolt against the cockpit sides at the open transom. Here are a couple of pics, comments welcome:

[James S]

Looks like nice clean work.
Are you OK with getting the bolts through the mounting holes to the out side of the bracket..or do the nuts go from that side?
It looks like a substantial bracket.
Those bracket plates look like they're about 9 or 10 ins high by about 6 wide...are you sure the mast needs to go through the deck and fix to underside...if the cock pit side that you're bolting to is substantial enough, I wonder if the bracket would do the job by its self....I hate cutting holes through the deck if its not absolutely necessary.
Are you planning on being able to remove the mast from the bracket?
Are you putting any thing els on the mast like GPS or other antennas?

[wkd928]

James - this is all guess work. The piece in the previous pics is about 17" wide and the largest mounting flange 12" high. Im attaching a pic of the cockpit where this will mount - on the starboard side aft of the runner winch about where the black rope bag is hanging - where the transom starts to slope away and hence the asymetry in the bracket.

Any idea how i would determine if this bracket is sufficient in itself? Im picturing the tower itself being about 8' above the deck or thereabouts. I will probably have a branch sticking out from it with a few small antennae on there.

The plan is for the mast to be dismountable if necessary. As mentioned in the thread on the bow roller - i hadnt got hold of CAD when i came up with this and so i had left some of the further details out ie how to ensure it clamps sufficiently tightly etc.

[James S]

Man...if that bracket is that big it sure seems a plenty.
Unfortunately I don't have a scientific way of determining if its enough...I'd bolt it on...drop the mast in it....stand on the combing...grab the mast as high as possible and try and rip it off with all my might....if it stays...I'm thinking its OK.
Sorry mate...thats about the full extent of my engineering calculations!

[wkd928]

That sounds like a suitable empirical test.. good advice! I will give it a go when im installing. If it works out that will save a hole in the deck as well as buggering about inside the boat too much back there - its tight!

[Blue Stocking]

Very Impressed!!

I am not an engineer, but would think that the oscillating loads on the fasteners will be considerable. What were you thinking of for back-up plates. Even though that is a 2-plane mounting, I would think it is going to "work" that glass moulding pretty hard in a seaway.

[wkd928]

the boat is constructed in alloy so i was thinking of alloy plate 1/4" thick for backing plates. i agree about the oscillating loading in a seaway, my original idea was to bury the tube through the deck as well in an effort to make sure it would hold.

[Blue Stocking]

Sorry,--I did see on your other thread that the boat is alloy. It would be nice to not have to cut a hole, but the up side is that you could tube the inside of the mast, and possibly gusset it under the deck. I do note where you said space is limited under there.
Very impressive work

[ConradG]

I can't see the through deck part of the mast...keeping water out is a concern of course. A drip cap on the mast would probably do. And a closed off top. Leaving the open seam in the step will let any moisture that makes its way between the metals out and even painting the surfaces that might hold moisture between them might be good. The concern would be "crevass" corrossion...But it sure looks mighty rugged! The bending force required to distort that size pipe in that span is readily available and the forces exerted by the weight of the unit and the surface area exposed to a given wind can be calculated, I'm sure. But I think you have a brick sh@# house by the looks of it! Those prefabricated masts of light stainless appear dwarfed by comparison and you have eliminated the stainless and it's potential problems with alloy!

[wkd928]

just had two pieces powder coated - this and the bow roller (pics in other thread). it turned out nicer than i expected and overall im quite happy. thanks to the feedback here i will install initialy without putting a hole through the deck and see how that works out.