Masthead Antenna Orientation

[svHyLyte]

This AM I was stopped by a friend at our YC who needed some help with a replacement Masthead Bracket for his yacht. Last year his masthead antenna was hit by lightening, which fried all of his electronics. He is concerned about a recurrance and has decided to remount the antenna with the whip pointing down, along the side of the mast, rather than up and is convinced that with such orientation he's less likely to be hit; and, if hit, the dischagre is more likely going to pass through the mast to the keel than through the VHF Coax to the electrics. Will one of the electronic wizzards hereabouts kindly comment on the efficacy of the foregoing including the effects on transmission capability, if any?

Thanx...

[senormechanico]

I doubt it would make any difference in lightning damage avoidance.

[btrayfors]

....but it WOULD make a difference in VHF reception and, especially, transmission.

Dumb idea.

Lightning's gonna hit where it's gonna hit. Period. Nothing you can do with a VHF antenna's going to make a difference.

Bill

[GordMay]

Originally Posted by btrayfors

....but it WOULD make a difference in VHF reception and, especially, transmission.
Dumb idea.
Lightning's gonna hit where it's gonna hit. Period. Nothing you can do with a VHF antenna's going to make a difference.
Bill

Methinks, that in the interest of politeness, Bill understated the objections (with which I concur).

[sandy daugherty]

Reassure your friend that lightning can strike twice in the same place. Suggest he raft up next to a much taller mast.

Science has long overlooked the fact that lightning is merely one of Mother Nature's ways of expressing herself, and she has a lot to say about many things. Perhaps the most egregious provocation is the mistaken assumption that something we invent will shut her up. You need to be married to understand this, but its far better not to do that.

[svHyLyte]

well. Those answers are rather what I expected but with some people, one is wise to keep one's own counsel...

...Suggest he raft up next to a much taller mast.

Ah.. No... That might be me!

Thanx All...

[bill good]

Why not mount it in the centre of the spreader? It would not matter whether it is up or down but more which way is clearest from other metal parts of the boat.Some shielding will occur but I doubt you will notice any major loss of range. Leave a sacrificial vertical whip grounded on top of the mast for lightning protection. If you look at the damage done by the strike you will find the whip prob. "vaporized" without any other visible damage to the top of the mast. (which proves it works).The coax cable to the radio should include a gas discharge lightning protector bonded to mast & earth plate. Other wise go with the "look for a taller mast" advise!!
Bill

[FSMike]

[QUOTE=bill good;367913]Why not mount it in the centre of the spreader?
Bill[/QUOTE

The lower the antenna the shorter the transmission range. That's the reason for the masthead installation in the first place.

[denverd0n]

Originally Posted by bill good

Some shielding will occur but I doubt you will notice any major loss of range.

I think that if you spent some time working with any of the better antenna modeling software that is available, you would change your mind. Even being next to the shroud wire is enough to create significant lobes in the antenna's radiation pattern. Being next to the mast? You will no longer have an "omnidirectional" antenna by any stretch of the definition of that word. You would probably get an improvement of range in one or two directions, but a drastic loss of range in other directions. This is not how you want your VHF to function.

The VHF antenna needs to be at the masthead, mounted in the clear, up above the mast. If you have any other antennas up there, they need to be adequately separated, depending on the frequencies for which they are used.

[bill good]

FS MIKE & DEVERDON. Yes there will be some degraded performance but the increased protection is what I am looking at!! The line of sight cal. is only one part of the equation & this drop of height is practice is about 1mile in 20. If the antenna is located on the top spreader & actual field strength test conducted you may find the results a more than acceptable. How do I know well I have done it. How many boats have lightning protection put into the coax of coax outer bonded to the mast & earthed to a proper plate not many!! About the same number of boats recording lightning strikes I suspect. It might not prevent damage but it is better than putting up a come & get me rod on top of a mast!!