Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 05-07-2015, 14:03   #1
Registered User

Join Date: Aug 2012
Location: New Hampshire
Boat: Gulfstar 50 ketch
Posts: 210
AIS antenna: masthead or rail mount

Is there a material difference in reception if the antenna is mounted on the masthead versus on the rail. Clearly it is easier to mount it on the stern pulpit if only until the next time I pull the mizzen mast. Thanks.
__________________

__________________
Calypso52 is offline   Reply With Quote
Old 05-07-2015, 14:13   #2
Eternal Member
 
monte's Avatar

Cruisers Forum Supporter

Join Date: Jul 2011
Location: Australia
Boat: Lagoon 400
Posts: 3,650
Images: 1
Re: AIS antenna: masthead or rail mount

Yes, big difference, try mount it as high as possible ASAP.
__________________

__________________
monte is offline   Reply With Quote
Old 05-07-2015, 14:13   #3
Registered User

Join Date: Nov 2011
Location: Oregon, USA
Boat: Shuttleworth Advantage 43
Posts: 200
Re: AIS antenna: masthead or rail mount

AIS and VHF isn't purely line-of-sight because the atmospheric conditions and sea state will affect if, but this distance to horizon calculator will give you an idea of the relative distances for different heights.
Distance to the Horizon Calculator

There is a lot more in this recent thread AIS Range
__________________
rgesner is offline   Reply With Quote
Old 05-07-2015, 14:35   #4
Registered User
 
Zanshin's Avatar

Join Date: Feb 2007
Location: Caribbean
Boat: Jeanneau 57
Posts: 1,621
Re: AIS antenna: masthead or rail mount

Mounting the AIS antenna higher will certainly make a big difference.


But does it matter if a ship sees you at 40nm or only at 15nm or vice-versa? I have my antenna mounted on the aft rail and have seen cargo ships on the open sea change direction to avoid me (I transmit as well) when about 15 miles away; I don't know if they saw me earlier, but that distance is more than enough for me.
__________________
-Zanshin (SV Zanshin)
Zanshin is offline   Reply With Quote
Old 05-07-2015, 14:51   #5
Registered User

Join Date: Sep 2011
Location: Germany
Boat: secondarily boatless
Posts: 178
Re: AIS antenna: masthead or rail mount

Calypso,

I had mine on the aft railing and I was pretty much blind forward. Finally I installed a splitter on the VHF antenna and now I can see (and be seen) roughly 30 nm.

Oliver
__________________
Oliver L. is offline   Reply With Quote
Old 05-07-2015, 15:08   #6
Moderator
 
JPA Cate's Avatar

Join Date: Nov 2011
Location: aboard, cruising in Australia
Boat: Sayer 46' Solent rig sloop
Posts: 10,685
Re: AIS antenna: masthead or rail mount

Calypso 52,

Friends have a stern mounted AIS. Ours is masthead ~66 ft., sharing the VHF antenna via a splitter. We consistently receive the signals from both class A and class B transmitters at significantly greater distances.

Ann
__________________
Ann, with Jim, aboard US s/v Insatiable II, in Oz, very long term cruisers
JPA Cate is online now   Reply With Quote
Old 05-07-2015, 15:09   #7
Long Range Cruiser
 
MarkJ's Avatar

Cruisers Forum Supporter

Join Date: Dec 2007
Location: Australian living on "Sea Life" currently in England.
Boat: Beneteau 393 "Sea Life"
Posts: 12,828
Images: 25
Re: AIS antenna: masthead or rail mount

I agree with Zanshin.
I have both mounts and can swap my antennas to either VHF or AIS.
At sea I always have the AIS on the masthead antenna, and in port if I have friends about I have the VHF on the masthead.
The effective range difference is about what Zanshin said. 40:15 miles for the AIS
__________________
Notes on a Circumnavigation.
OurLifeAtSea.com

Somalia Pirates and our Convoy
MarkJ is offline   Reply With Quote
Old 05-07-2015, 15:18   #8
Registered User

Join Date: Apr 2015
Location: Newhaven, UK
Boat: Bavaria 36'
Posts: 6
Re: AIS antenna: masthead or rail mount

We have ours on the pushpit rail, we get a good 12 to 15nm range (we receive only). We have arranged some additional coaxial in the line so that if the mast comes down we have an immediately ready VHF aerial.
__________________
Bill_Giles is offline   Reply With Quote
Old 05-07-2015, 15:34   #9
Eternal Member
 
monte's Avatar

Cruisers Forum Supporter

Join Date: Jul 2011
Location: Australia
Boat: Lagoon 400
Posts: 3,650
Images: 1
Re: AIS antenna: masthead or rail mount

I think it's hard to argue that seeing a target 40 miles out with a CPA of over an hour isn't safer than seeing it at 15 miles with a CPA around 30 minutes. We routinely see ships at 20 miles plus with a masthead antenna on a splitter, yachts at around 10 miles and occasionally yachts at around 1.5 miles. I assume the yachts at 1.5 miles have a low antenna or dodgy connection. Double the range = double the safety factor, so why wouldn't you, unless you sail in a bay 15 miles wide.
__________________
monte is offline   Reply With Quote
Old 05-07-2015, 15:46   #10
Registered User

Join Date: Apr 2015
Location: Newhaven, UK
Boat: Bavaria 36'
Posts: 6
Re: AIS antenna: masthead or rail mount

Where I sail in the English Channel ships are frequently changing direction, although predictably as they follow the TSS. I have never been troubled by only having 'sight' of a ship at twice normal visual range. I guess that we only have a small screen and having ships shown out to 40nm would be bad cluttering.
__________________
Bill_Giles is offline   Reply With Quote
Old 05-07-2015, 16:11   #11
Registered User

Join Date: Jun 2007
Location: SW Florida
Boat: FP Belize, 43' - Dot Dun
Posts: 3,428
Re: AIS antenna: masthead or rail mount

IMO, it's a waste of time making navigation decisions more than 10 minutes from TCPA. There are simple too many variables to use a AIS borne TCPA more than 10 minutes and then using that information to make changes to direction/speed.

If you are not confident to avoid a collision within 10 minutes, please keep the docklines on and don't venture out.

Point: rail mount AIS is all you need for collision avoidance. But, if you get off on seeing ships far away, certainly the top of mast will give you a much better range. But, choosing longer AIS at the determent of VHF comms* is completely foolish, again IMO.

*A buddy boat recently chided me for my rail mount AIS, he could only see me 8 miles out. Same friend then mentioned he could only hear my side of VHF comms when we were right next to each other. I had no problem carrying out VHF comms @ 20nm. He could not hear the other half but refuses to believe his antenna splitter has anything to do with it.

Using an X switch as MarkJ does is the best of all worlds, it allows you to manually switch between the 2 antennas.
__________________
DotDun is offline   Reply With Quote
Old 05-07-2015, 16:20   #12
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: Punta Arenas ahorra
Boat: 39' Westerly Sealord
Posts: 3,953
Re: AIS antenna: masthead or rail mount

Mine is taffrail mounted.... 'sees' ships at 20miles... as stated above by quite a few anything over 5 miles away is of interest but of no consequence.
Not worth the fuss and bother of sending another cable up the inside of the mast.
Some say they have seen ships alter for them when over 15 miles away on the basis of AIS reception... I think that is wishful thinking...
El Pinguino is online now   Reply With Quote
Old 05-07-2015, 16:46   #13
Eternal Member
 
monte's Avatar

Cruisers Forum Supporter

Join Date: Jul 2011
Location: Australia
Boat: Lagoon 400
Posts: 3,650
Images: 1
Re: AIS antenna: masthead or rail mount

Quote:
Originally Posted by DotDun View Post
IMO, it's a waste of time making navigation decisions more than 10 minutes from TCPA. There are simple too many variables to use a AIS borne TCPA more than 10 minutes and then using that information to make changes to direction/speed.



If you are not confident to avoid a collision within 10 minutes, please keep the docklines on and don't venture out.



Point: rail mount AIS is all you need for collision avoidance. But, if you get off on seeing ships far away, certainly the top of mast will give you a much better range. But, choosing longer AIS at the determent of VHF comms* is completely foolish, again IMO.



*A buddy boat recently chided me for my rail mount AIS, he could only see me 8 miles out. Same friend then mentioned he could only hear my side of VHF comms when we were right next to each other. I had no problem carrying out VHF comms @ 20nm. He could not hear the other half but refuses to believe his antenna splitter has anything to do with it.



Using an X switch as MarkJ does is the best of all worlds, it allows you to manually switch between the 2 antennas.

I guess you may be referring to vessels altering course with regard to the too many variables comment? And maybe the 10 minutes being close to shore or in high traffic areas? I certainly wouldn't want a 10 minute warning mid ocean or even close to shore. The longer the warning the better, but in built up areas shorter CPAs might be acceptable. 10 minutes to make collision avoidance decisions? Really, we start making those decisions as soon as possible and 10 minutes wouldn't be anywhere near enough time.
__________________
monte is offline   Reply With Quote
Old 05-07-2015, 16:57   #14
Registered User

Join Date: Jun 2007
Location: SW Florida
Boat: FP Belize, 43' - Dot Dun
Posts: 3,428
Re: AIS antenna: masthead or rail mount

Quote:
Originally Posted by monte View Post
I guess you may be referring to vessels altering course with regard to the too many variables comment? And maybe the 10 minutes being close to shore or in high traffic areas? I certainly wouldn't want a 10 minute warning mid ocean or even close to shore. The longer the warning the better, but in built up areas shorter CPAs might be acceptable. 10 minutes to make collision avoidance decisions? Really, we start making those decisions as soon as possible and 10 minutes wouldn't be anywhere near enough time.
I've sat and watch too many CPA of <.1nm at 15/20 minutes TCPA change considerable, ending up at >.5nm CPA without either vessel making course/speed changes. Hence, TCPA more than 10 minutes does not warrant navigation adjustments for me. It may very well be my chart plotter being unable to calculate good CPA at large distances.

YMMV
__________________
DotDun is offline   Reply With Quote
Old 05-07-2015, 17:49   #15
Eternal Member
 
monte's Avatar

Cruisers Forum Supporter

Join Date: Jul 2011
Location: Australia
Boat: Lagoon 400
Posts: 3,650
Images: 1
Re: AIS antenna: masthead or rail mount

Fair enough DD. We also see CPA changing over time and we (and most ships) generally aim for a minimum CPA of around 1 mile in open water. Obviously 1 mile isn't always possible in dense traffic. The sooner we can determine if course changes might be required, or contact with the other vessel might be required, the better as far as we are concerned. Here's a snap from mid Atlantic. Obviously most of the ships are of little concern but its still good to know whats out there and possible crossing situations ASAP, especially when horizon scans might be 15 minutes between. The range ring is 20 miles.
Attached Thumbnails
Click image for larger version

Name:	mid atlantic ships.JPG
Views:	106
Size:	36.6 KB
ID:	104741  
__________________

__________________
monte is offline   Reply With Quote
Reply

Tags
ais, antenna, head, mast

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
Best VHF antenna for masthead mount Bristol30 Marine Electronics 1 14-11-2014 10:53
AIS AIT2000 from Digital Yachts with GV30 GPS+AIS Antenna SFH Marine Electronics 1 16-02-2014 17:19
For Sale: AIS-MULTI AIS Receiver with built in Antenna Splitter kokomodenny Classifieds Archive 1 17-09-2013 09:53
Where to Mount AIS Antenna? Dockhead Marine Electronics 22 16-01-2013 06:45
Pole Mount for AIS Antenna timberboat Electrical: Batteries, Generators & Solar 7 22-07-2010 08:33



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 03:31.


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.