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Old 14-02-2020, 11:23   #1
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AIS registration

I am about to purchase an AIS transponder. The registration form asks for the length of the vessel. My sailboat is 47’ LOD, but has a bowsprit and boomkin that results in a LOA 55’

Which measurement should I use?
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Old 14-02-2020, 11:53   #2
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Re: AIS registration

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Originally Posted by crazyoldboatguy View Post
I am about to purchase an AIS transponder. The registration form asks for the length of the vessel. My sailboat is 47’ LOD, but has a bowsprit and boomkin that results in a LOA 55’

Which measurement should I use?
Well you have 3 different measurements. 1. 48' listed under your avatar, 2. 47' lod or 3. and loa of 55'

Is your boat documented? Would go w/that length to be consistent.

Our boat is 57' loa, but it really is a 49' hull w/junk off both ends.
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Old 14-02-2020, 13:59   #3
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Re: AIS registration

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Well you have 3 different measurements. 1. 48' listed under your avatar, 2. 47' lod or 3. and loa of 55'

Is your boat documented? Would go w/that length to be consistent.

Our boat is 57' loa, but it really is a 49' hull w/junk off both ends.

Generally agree - I have gotten answers from both ends of the spectrum. The purpose of the measurement is so folks can tell how much space your boat takes up. Bowsprits are part of that. Think of a square rigged vessel - it could have 150’ of LOD with a bowsprit of 40’ of bowsprit. That could affect maneuvering by an oncoming vessel.

If I place the GPS antenna at the end of the bowsprit of my vessel and then report on the required form that it is 52’ from the stern but the length I give is 47’ that might make some heads scratch.

I am not trying to be silly. Just trying to use some “logic” here since I can’t find the any info in the regs to guide me.

Common sense can be used to justify using either LOD or LOA.

Thank you for responding.
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Old 14-02-2020, 14:11   #4
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Re: AIS registration

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Originally Posted by crazyoldboatguy View Post
I am about to purchase an AIS transponder. The registration form asks for the length of the vessel. My sailboat is 47’ LOD, but has a bowsprit and boomkin that results in a LOA 55’

Which measurement should I use?
IMHO, if you value any or all of the parts at the ends that factor into the LOA then I would use the longer length. If you don't care about your bowsprit or davits then use the shorter LWL.

Not unlike determining the length of your boat when you request a boat slip. It is inappropriate to hang bits and pieces out into the fairway or over the dock where they can collide with other boats or persons.
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Old 14-02-2020, 14:15   #5
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Re: AIS registration

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IMHO, if you value any or all of the parts at the ends that factor into the LOA then I would use the longer length. If you don't care about your bowsprit or davits then use the shorter LWL.

Not unlike determining the length of your boat when you request a boat slip. It is inappropriate to hang bits and pieces out into the fairway or over the dock where they can collide with other boats or persons.
That’s pretty much my thinking. Thank you for responding.
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Old 14-02-2020, 14:25   #6
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Re: AIS registration

You aren't registering your boat to fit in a slip, you are measuring your boat for the FCC ship's license.
Since this is federal, the logical/consistent thing to do would be to measure as you would for USCG documentation using their simplified measurements
As you can see, for L they exclude bowsprits, swim platforms, etc. and only measure the boat.
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Old 14-02-2020, 15:38   #7
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Re: AIS registration

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You aren't registering your boat to fit in a slip, you are measuring your boat for the FCC ship's license.
Since this is federal, the logical/consistent thing to do would be to measure as you would for USCG documentation using their simplified measurements
As you can see, for L they exclude bowsprits, swim platforms, etc. and only measure the boat.


If only we can be sure the FCC agrees with the USCG.

That diagram is quite helpful, nonetheless. Thank you for commenting.

When we went to document the vessel we ended up re-documenting as a previous owner (the US Navy) had already done so, so the particulars were already in the system and we didn’t have to fill out the form.

The functions of the 2 registrations accomplish different things so it’s possible the FCC has different requirements. Thank you for commenting.
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Old 14-02-2020, 20:09   #8
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Re: AIS registration

It makes no difference which length you use. The length is broadcast over AIS to other ships. The receivers make passing decisions based on the general size of the vessel. It doesn't make any difference if they see 40ft vs 50ft. It does make a difference if they see 33ft vs 150ft.
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Old 14-02-2020, 20:42   #9
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Re: AIS registration

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It makes no difference which length you use. The length is broadcast over AIS to other ships. The receivers make passing decisions based on the general size of the vessel. It doesn't make any difference if they see 40ft vs 50ft. It does make a difference if they see 33ft vs 150ft.
Well, of course the length is important - if passing vessels are to make crucial decisions based on the “general size of the vessel”. And the guiding regulations should indicate that. I realize the difference between 47’ and 54’ isn’t all that much but it would be nice to know what is expected.

Thank you for responding.
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Old 14-02-2020, 20:54   #10
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Re: AIS registration

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Originally Posted by crazyoldboatguy View Post
Well, of course the length is important - if passing vessels are to make crucial decisions based on the “general size of the vessel”. And the guiding regulations should indicate that. I realize the difference between 47’ and 54’ isn’t all that much but it would be nice to know what is expected.

Thank you for responding.
Come on, what possible change of plan in real life would be different if an AIS target said it was 47ft vs 54ft? This isn't precision machining, it's piloting a vessel on the water. Way different than an internet forum.
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Old 14-02-2020, 20:57   #11
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Re: AIS registration

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Come on, what possible change of plan in real life would be different if an AIS target said it was 47ft vs 54ft? This isn't precision machining, it's piloting a vessel on the water. Way different than an internet forum.
.
There is a qualifying regulation somewhere. I agree that the difference is minimal - I’m just looking for the actual regulation language. Bureaucracies thrive on that, don’t ya know.
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Old 14-02-2020, 21:42   #12
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Re: AIS registration

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There is a qualifying regulation somewhere. I agree that the difference is minimal - I’m just looking for the actual regulation language. Bureaucracies thrive on that, don’t ya know.
Except there are no Bureaucracies that spend time checking the boat specs broadcast on class B AIS. The main issue with these is having a properly assigned and programmed MMSI number.

Sometimes we can get a bit too anal.
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Old 14-02-2020, 21:45   #13
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Re: AIS registration

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Except there are no Bureaucracies that spend time checking the boat specs broadcast on class B AIS. The main issue with these is having a properly assigned and programmed MMSI number.

Sometimes we can get a bit too anal.
You are misunderstanding what I am saying. I am not worried, just curious. Whether I am anal or not, or there are agents looking for me or not - the regulation and language exists.
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Old 14-02-2020, 22:05   #14
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Re: AIS registration

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You are misunderstanding what I am saying. I am not worried, just curious. Whether I am anal or not, or there are agents looking for me or not - the regulation and language exists.
Unlike position where the quality spec is +/-10m, there is no quality spec for length and beam in the Solas chapter 5 annex 17.
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Old 14-02-2020, 22:18   #15
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Re: AIS registration

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Unlike position where the quality spec is +/-10m, there is no quality spec for length and beam in the Solas chapter 5 annex 17.
Section 5.3 “Ships dimensions” is still somewhat confusing. It calls for “overall” length but the diagram shows length on deck.

As you said, the difference of 8’ in length is negligible when compared to most larger vessels.

Thank you for providing that. I had been looking for it but wasn’t using the right language in the search box.
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