Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 26-04-2011, 06:24   #1
Registered User
 
DevoDave's Avatar

Join Date: Nov 2009
Location: Circumnavigating Australia, currently Melbourne
Boat: Seawind 1160
Posts: 74
Mounting Antennas on Spreaders: To Drill or Not to Drill ?

Looking at installing a 3G antenna on the spreaders of a Seawind 1160 (38 foot) catamaran.

Is drilling spreaders something that is or isn't advisable?

What are the alternatives?
__________________

__________________
DevoDave is offline   Reply With Quote
Old 26-04-2011, 06:28   #2
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: Mounting antennas on spreaders? To drill or not to drill?

Thanks for posting this. I have exactly the same question.

I have three new antennae to mount -- a WiFi antenna (with Bullet), a 3G mobile phone antenna for my GlobeSurfer, and a spare VHF antenna for the AIS receiver I am planning to buy. I already have a number of antennae on the pushpit -- satphone, gps, navtex. I thought about an antenna pole on the after deck but baulked at the windage, cost, and clutter. I think the first spreader will be the right place for these. Does anyone know any disadvantages?
__________________

__________________
Dockhead is online now   Reply With Quote
Old 26-04-2011, 06:37   #3
Registered User
 
DevoDave's Avatar

Join Date: Nov 2009
Location: Circumnavigating Australia, currently Melbourne
Boat: Seawind 1160
Posts: 74
Re: Mounting antennas on spreaders? To drill or not to drill?

One piece of advice I have picked up... mount them on the bottom of the spreaders pointing down. That way if a halyard gets caught up by one, it should fall out without too much drama.

Hopefully someone with rigging knowledge will be along shortly to advise if we should pull out the ol' drills.
__________________
DevoDave is offline   Reply With Quote
Old 26-04-2011, 07:01   #4
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: Mounting antennas on spreaders? To drill or not to drill?

Quote:
Originally Posted by DevoDave View Post
Hopefully someone with rigging knowledge will be along shortly to advise if we should pull out the ol' drills.
I think there may be ways to mount them without drilling. Depending on how the spreader is constructed, perhaps a clamp would do it?
__________________
Dockhead is online now   Reply With Quote
Old 26-04-2011, 07:04   #5
Freelance Delivery Skipper..
 
boatman61's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Jan 2010
Location: UK/Portugal
Posts: 20,210
Images: 2
Send a message via Skype™ to boatman61
pirate Re: Mounting Antennas on Spreaders: To drill or not to drill?

Keep em to the wide bit close to the mast and you'll be fine.... as long as its not a 10ft whip arial...
The mount on the underside is a good idea as well..
boatman61 is offline   Reply With Quote
Old 26-04-2011, 07:22   #6
Registered User

Join Date: Apr 2006
Location: Muscat, Oman
Boat: Roberts, C45 Spray - EDM
Posts: 80
Re: Mounting Antennas on Spreaders: To drill or not to drill?

Just break in mind that if you ever come to use your spare VHF Antenna - if you have placed the other two antenna's in very close proximity then the electrical equipment connected to the (WIFI and AIS) will be getting a very large amount of RF - which typically does not do sensative electrical things any good.

I realise that you asked a question regarding holes in spreaders - apologies for drifing a little off topic.
__________________
deepstar is offline   Reply With Quote
Old 26-04-2011, 07:43   #7
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: Mounting Antennas on Spreaders: To drill or not to drill?

Quote:
Originally Posted by deepstar View Post
Just break in mind that if you ever come to use your spare VHF Antenna - if you have placed the other two antenna's in very close proximity then the electrical equipment connected to the (WIFI and AIS) will be getting a very large amount of RF - which typically does not do sensative electrical things any good.

I realise that you asked a question regarding holes in spreaders - apologies for drifing a little off topic.
Good thing to keep in mind. But if I'm using the spare VHF for transmitting on the VHF in an emergency, as opposed to merely receiving AIS which is its main function, I think interference with mobile phone and WIFI signals is not going to be high on my list of things to worry about.

In any case, it's not too hard to obey the required separation distances.
__________________
Dockhead is online now   Reply With Quote
Old 26-04-2011, 07:56   #8
Registered User

Join Date: Jul 2010
Location: ft.myers,fl
Boat: rhodes,seafarer,28
Posts: 137
Re: Mounting Antennas on Spreaders: To drill or not to drill?

Physical mounting on spreader arms on most boats presents no problem. The problem is the close proximity to the aluminum mast. What is the wavelength? Can you mount the antenna 1/4 wavelength away from both the mast and the shroud? If not, you'll set up standing waves and at best the antenna will not work efficently,at worst, you'll destroy your transmiter.
__________________
capt.bobfm is offline   Reply With Quote
Old 26-04-2011, 08:44   #9
Registered User

Join Date: Jun 2008
Posts: 264
Re: Mounting Antennas on Spreaders: To drill or not to drill?

Quote:
Originally Posted by capt.bobfm View Post
Can you mount the antenna 1/4 wavelength away from both the mast and the shroud? If not, you'll set up standing waves ...
Oooh, I've wondered about this. Should the antenna be exactly 1/4 wavelength away? At least 1/4? A multiple of 1/4? Is the mast and shroud the only concern? What about other antenna?
__________________
JayH is offline   Reply With Quote
Old 26-04-2011, 08:48   #10
Registered User

Join Date: Apr 2006
Location: Muscat, Oman
Boat: Roberts, C45 Spray - EDM
Posts: 80
Re: Mounting Antennas on Spreaders: To drill or not to drill?

I would think you want to avoid 1/4 Wave spacing, as this configuration is often used in phased mono-pole's installed on terra firma.

AIS/VHS has a freq of what 162Mhz - which will be about 1.84M - so I would think you need to be at least 55cm apart and closer than 90cm
__________________
deepstar is offline   Reply With Quote
Old 26-04-2011, 09:07   #11
Registered User

Join Date: Jul 2010
Location: ft.myers,fl
Boat: rhodes,seafarer,28
Posts: 137
Re: Mounting Antennas on Spreaders: To drill or not to drill?

If you can set up your mounting so that you have a 1/4 wavelength space between your antenna and another (longer) piece of metal(mast) the mast will act as a reflector element of the antenna and direct your signal in more of an eliptical patern rather than a round omnidirectional whip antenna alone.However,if your shroud (which is also a piece of metal longer than the whip) is there,the signal will reflect back again. Now you've set up a standing wave that's probably not good for you.
__________________
capt.bobfm is offline   Reply With Quote
Old 26-04-2011, 09:30   #12
Registered User

Join Date: Sep 2008
Location: Camden, ME
Boat: A Thistle and a Hallberg-Rassy 36
Posts: 664
Although nearby metal will affect radiation/reception patterns, and antenna impedances will be affected to some extent, unless the antenna is very close to the mast or shroud, it probably will not cause a problem with the transmitter. If you want to be safe and sure, you would want someone with an antenna analyzer that covers vhf frequencies to check it for you. That is what I would do, but I have and use one already.

You could also use a vhf swr meter to check your install - that would be a bit cheaper than the analyzer.
__________________
SoonerSailor is offline   Reply With Quote
Old 26-04-2011, 10:04   #13
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: Mounting Antennas on Spreaders: To drill or not to drill?

Quote:
Originally Posted by capt.bobfm View Post
Physical mounting on spreader arms on most boats presents no problem. The problem is the close proximity to the aluminum mast. What is the wavelength? Can you mount the antenna 1/4 wavelength away from both the mast and the shroud? If not, you'll set up standing waves and at best the antenna will not work efficently,at worst, you'll destroy your transmiter.
The longest wavelength used by mobile telephone/3G signals is 37.5cm. A quarter wavelength would be only about 4 inches.

The longest wavelength used by WiFi is about 12cm.

The longest wavelength used by VHF is about 2 meters, so a quarter wavelength would be less than two feet.

I don't think this is going to be a big problem.

Frequency - Wavelength Chart
__________________

__________________
Dockhead is online now   Reply With Quote
Reply

Tags
antenna

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Electric Drill Winch gettinthere Deck hardware: Rigging, Sails & Hoisting 57 02-10-2012 19:49
How to Drill Parallel Holes ? ShipShape Construction, Maintenance & Refit 27 25-09-2010 05:51
USN Honour Guard Drill Team knottybuoyz Off Topic Forum 3 10-05-2009 18:38
Man Overboard Drill Ex-Calif The Sailor's Confessional 1 13-07-2007 22:10
Spreaders Islandmike Construction, Maintenance & Refit 7 16-05-2006 13:14



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 09:58.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.