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Old 04-05-2010, 07:44   #1
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Running VHF Outside the Mast

I went to do the install on my VHF antenna yesterday and when I pulled the mast foot off I found nothing but urethane foam. I walked up the mast tapping it with my leatherman only to find it had foam in it the entire length. So much for my plans of running my antenna up the inside.

Does anyone have any pictures of an outside of the mast coax install? I need to find a way to do it that isn't super ugly. How would one fasten the cable to the mast in intervals?
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Old 04-05-2010, 08:01   #2
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You could always run it up one of the shrouds with wire ties. Barring that, just pop rivet on some of the fasteners designed to hold wire in place. Are there no wires, halyards, etc. inside the mast? If there are you could use one of them to haul up the coax. If not I'd be tempted to try to install some pvc the length of the mast (inside).
Usually foam is inside a mast for one of two reasons:
1) To silence wires, halyards, etc.
2) Flotation to prevent the boat from turning past 90 degrees in case of a knockdown.
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Old 04-05-2010, 08:02   #3
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I don't think there is a way. More important, if it is foam, take it out of the mast before you get some severe pitting/corrosion from the entrapped moisture.
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Old 04-05-2010, 08:32   #4
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Are there no wires, halyards, etc. inside the mast? If there are you could use one of them to haul up the coax.
There are but they are foamed in. Will that foam really cause pitting and corrosion? I was assuming it was in there to keep the moisture out.
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Old 04-05-2010, 10:09   #5
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I don't think foam will be a problem unless it is open cell foam. If someone dumped in urethane and let it expand--that's closed cell and impermeable to water. Running a cable outside will be problematic.

Maybe you could take a section of electrical conduit (thin wall pipe), file the edge sharp, and ram it down through the foam (from top & bottom) well enough to make a channel down through the mast?
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Old 04-05-2010, 10:43   #6
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When it was popular to make sailboards out of ABS plastic which had no easy way to seal the hull deck flange, most manufacturers glued a plastic strip onto the hull deck seam to keep water out of the closed cell foam inside the skin. One manufacturer that our club bought a fleet of sailboards from decided that since it was closed cell foam and inpenetrable to water that they only needed to put a decorative piece of plastic over the seam. More than one of those boards when they were retired weighed 90+ pounds. They had started out at 50 pounds. All were more than 10 pounds overweight. There was no free water to pour out of those boards.

Our club was having trouble sealing some of the masts of our Hobie cats. This is important for being able to right them from a capsize. Someone had a great idea of using closed cell foam at all points that had screws, rivets, joints, etc. About 5 years later one of those masts is now sitting in the to be repaired pile due to around 10 pounds of no free water in the mast. This makes it impossible to right without huge crews. 10 pounds at 15 feet (approx.) is 150 ft-lbs, divided by 3 ft (center of mass person) is 50 more pounds of crew needed to right boat.

I used closed cell foam to support my plastic holding tank at all points underneath as recommended by the manufacturer. I don't care if it eventually takes on 10-20 pounds of water. I'll never use supposedly waterproof closed cell foam anywhere on a boat where additional weight could be critical.

John
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Old 04-05-2010, 11:22   #7
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I don't think foam will be a problem unless it is open cell foam. If someone dumped in urethane and let it expand--that's closed cell and impermeable to water. Running a cable outside will be problematic.

Maybe you could take a section of electrical conduit (thin wall pipe), file the edge sharp, and ram it down through the foam (from top & bottom) well enough to make a channel down through the mast?
Why would running cable outside be problematic? They do it for SSBs. I've heard of other people doing it on this forum.

I inspected the foam at most of the junctures and it doesn't look or feel saturated in any way. There are other threads on this forum and a few others dedicated to arguing the integrity of closed cell foam. I was reading one of them where a guy submerged a piece of urethane closed cell foam in salt water for a year he took precise measurements. Over a year the piece of foam took on approximately 4% of it's own weight. I am going to go to the boat today and ram a piece of copper tube in there to take a "core sample". I will report back.
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Old 04-05-2010, 11:57   #8
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Problematic, as in you need to find a way to secure it. Without pinching it, without encircling the mast, without making holes in the mast (preferably), without fouling it. And then there's the aesthetics of, what, gluing it down the side of the mast? (G) If you can find a way that looks and works acceptably--including zipties down the shrouds if you prefer--it can certainly be done. Done well, neatly, durably, reliably, just takes a bit longer.

Urethane foam should dissolve real easily in the right solvent, xylene or gasoline might do it. So if you have concerns about trapped moisture...cap the ends, slosh some solvent in the mast, pour the goo in a big drum when it comes out. "Side of fries with that shake?" (G)
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Old 04-05-2010, 12:27   #9
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Problematic, as in you need to find a way to secure it. Without pinching it, without encircling the mast, without making holes in the mast (preferably), without fouling it. And then there's the aesthetics of, what, gluing it down the side of the mast? (G) If you can find a way that looks and works acceptably--including zipties down the shrouds if you prefer--it can certainly be done. Done well, neatly, durably, reliably, just takes a bit longer.
Oh yeah totally, I see what you mean. I just can't really fathom a bunch of rivets and a big coax cable down the side of the mast really looking all that great. If we did go with the back stay method would we have to keep the cable off of the stay like you do with a SSB antenna?
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Urethane foam should dissolve real easily in the right solvent, xylene or gasoline might do it. So if you have concerns about trapped moisture...cap the ends, slosh some solvent in the mast, pour the goo in a big drum when it comes out. "Side of fries with that shake?" (G)
That is the worst thing I have ever heard...yet strangely appetizing.
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Old 04-05-2010, 12:30   #10
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By the way I just got my fifth star. Newbs bow down to me!!!!!!
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Old 04-05-2010, 12:31   #11
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your mast can't be all that tall, why not bore a hole all the way through with a drill and some copper, then you can run the coax in the mast.
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Old 04-05-2010, 12:44   #12
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your mast can't be all that tall, why not bore a hole all the way through with a drill and some copper, then you can run the coax in the mast.
Huh? I am confused. My mast is maybe 27 feet
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Old 04-05-2010, 12:46   #13
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Ok, so buy three sticks of copper pipe, solder them together, chuck in a drill, ........you know, the more of this I type the worse it sounds
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Old 04-05-2010, 12:47   #14
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Probably (???) by drilling the smallest possible hole every (x) feet and attaching a tie-down point (e.g. on of those tie-wrap holder type) wit the smallest possible rivet. Then use wire-ties (they say black ones last longest). Then punch out the rivet core and fill with Sika/ duralac/paint over the hole.

I do not see any issues with outside mount, except probably the wire will have to be replaced more often.

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Old 04-05-2010, 13:24   #15
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Ok, so buy three sticks of copper pipe, solder them together, chuck in a drill, ........you know, the more of this I type the worse it sounds
Haha. Thanks for admitting it. I was all ready to go out and buy a bunch of copper pipe.
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