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**StuM** · 07-07-2018, 02:21

Quote:

Originally Posted by Brady 50

We have class B AIS it uses WiFi AND SAT

"uses" for what?

Please tell us make and model number of your WiFi/SAT Class B AIS system.

AIS transmits and receives VHF signals, essentially line-of-sight.

Satellite AIS (S-AIS) is a system which uses sensitive receivers to detect these VHF trnmissions from space. There is no provision within AIS for any other type of communication protocol.

**StuM** · 07-07-2018, 02:25

Quote:

Originally Posted by KJThomas

Note. Marine traffic from AIS, gives a totally false impression of traffic density in the open ocean. It depends on shore based receivers. AIS has limited range.

You may like to look at

Satellite AIS - Addressing Misconceptions | BigOceanData

However, around ten years ago various organisations discovered that, much to everyone’s surprise, these short range signals could in fact be picked up from above the Earth’s atmosphere. This was not expected as the maximum horizontal range at sea level is around 50 nautical miles (74 kms), yet these same signals could be received on the ISS, 400 kilometres up. The thinner atmosphere, with no atmosphere at all above, provides far less resistance to the VHF signal. The result is that, since 2005, AIS receivers, which can be very compact and weigh just a few kilogrammes, have been mounted in increasing numbers in low earth communications satellites, creating the satellite AIS (S-AIS) network.
The advantages of S-AIS
The key advantage of S-AIS over terrestrial AIS is that, with sufficient, suitably placed satellites, the entire surface of the earth can now be monitored for AIS transmissions, removing the dependence on terrestrial receiving stations. Each individual satellite can also cover a very large area. The result is that individual vessels or entire fleets can now be monitored wherever they are in the world, be it the middle of the Pacific Ocean or in the most isolated inland sea, as long as each has an AIS transponder fitted and operational.

Brady 50 · 07-07-2018, 05:18

We have both. We have a special 2.4 metre Ariel on top of the 20 metre mast that gives use upto 250nm distance. That system was not cheap at AUD670.00. The AIS system has it's own GPS dome on the upper deck.
Trust this info helps.

**StuM** · 07-07-2018, 05:55

Quote:

Originally Posted by Brady 50

We have both. We have a special 2.4 metre Ariel on top of the 20 metre mast that gives use upto 250nm distance. That system was not cheap at AUD670.00. The AIS system has it's own GPS dome on the upper deck.
Trust this info helps.

Both what? Please tell us what you Class B AIS transceiver is that "uses WiFi and SAT"

The GPS dome just provides data to the AIS system which is then transmitted over VHF.

A 2.4m metre (8ft 6db gain) aerial is a fairly standard VHF antenna size. No way will it give you 250nm range - more like 25m when mounted at the top of your mast.

And AUD670 is a lot to pay for one unless that included installation. Even a top quality marine one should sell for 1/4 to 1/3 of that price.

So once more, what's the make/model of your Class B AIS transceiver that "uses WiFi and SAT"?

ErikSteenberg · 07-07-2018, 06:35

Quote:

Originally Posted by gmakhs

So in case of a vessel without AIS like let's say my boat you would t be alarmed .

Why would you sail without AIS? In that case I hope you’ve got competent crew who keep a good watch so you avoid collisions with singlehanders like me... Its easy to call me irresponsible for sleeping 8 hours every night (in open ocean, outside shipping lanes) but exhaustion can get a person killed and I didn’t choose sailing as my way of life just so I can be a nervous wreck who suffers from sleep depravation...

ErikSteenberg · 07-07-2018, 06:37

Quote:

Originally Posted by StuM

Both what? Please tell us what you Class B AIS transceiver is that "uses WiFi and SAT"

The GPS dome just provides data to the AIS system which is then transmitted over VHF.

A 2.4m metre (8ft 6db gain) aerial is a fairly standard VHF antenna size. No way will it give you 250nm range - more like 25m when mounted at the top of your mast.

And AUD670 is a lot to pay for one unless that included installation. Even a top quality marine one should sell for 1/4 to 1/3 of that price.

So once more, what's the make/model of your Class B AIS transceiver that "uses WiFi and SAT"?

I’ve seen 250nm distance on class B AIS... I think the data relays via sattelite

gmakhs · 07-07-2018, 07:27

Quote:

Originally Posted by ErikSteenberg

Why would you sail without AIS? In that case I hope you’ve got competent crew who keep a good watch so you avoid collisions with singlehanders like me... Its easy to call me irresponsible for sleeping 8 hours every night (in open ocean, outside shipping lanes) but exhaustion can get a person killed and I didn’t choose sailing as my way of life just so I can be a nervous wreck who suffers from sleep depravation...

Why? Simple reason budget .
My problem is not that you sleep well , my problem is that you relley on AIS alarms , a lot of vessels out there have no AIS. If you did the same with a radar I wouldn't comment .

cfk0jmz · 07-07-2018, 08:03

In my humble opinion, single handed cruising while sleeping should not be encouraged. It is unsafe for you as well as others. I have seen the damage done when a boat without someone attending the helm interacted with an innocent cruiser. It is not responsible to do this anywhere near the coast during night or day.

With that said, there are professional captains that will assist in your needs and they have reasonable rates. Most will allow you to assist so the duties can be shared. Two six hour shifts during the day and four 3 hour shifts at night provide adequate rest periods and assurance that someone is alert at the helm at all times.

I have used Captain Blane Parks for this purpose and recommend him without hesitation. I am not affiliated with him or his business, other than as a customer.

thomm225 · 07-07-2018, 08:11

Quote:

Originally Posted by cfk0jmz

In my humble opinion, single handed cruising while sleeping should not be encouraged. It is unsafe for you as well as others. I have seen the damage done when a boat without someone attending the helm interacted with an innocent cruiser. It is not responsible to do this anywhere near the coast during night or day.

With that said, there are professional captains that will assist in your needs and they have reasonable rates. Most will allow you to assist so the duties can be shared. Two six hour shifts during the day and four 3 hour shifts at night provide adequate rest periods and assurance that someone is alert at the helm at all times.

I have used Captain Blane Parks for this purpose and recommend him without hesitation. I am not affiliated with him or his business, other than as a customer.

Sort of ridiculous for some singlehander on say a 27' sailboat barely big enough for one to hire another person to sail it for him while he's asleep.

They just completed the 2018 SHTP Race from San Francisco to Hawaii (a distance of 2,120 miles) and all the racers sailed singlehanded and they all slept. And btw, the lady on the Freedom 38 is a CF Member

http://sfbaysss.org/shtp2018/racers/

http://sfbaysss.org/shtp2018/

As do all the singlehanded circumnavigators and ocean crossers

ErikSteenberg · 07-07-2018, 08:13

Quote:

Originally Posted by gmakhs

Why? Simple reason budget .
My problem is not that you sleep well , my problem is that you relley on AIS alarms , a lot of vessels out there have no AIS. If you did the same with a radar I wouldn't comment .

Mostly fishing vessels and coastal sailors don’t have AIS. I’ve never come across a boat in the open ocean that doesn’t have it. I have a receiver only (reason budget) but its good enough for me. I trust my gut feeling and get up to have a look around whenever I’m in doubt, but keeping 24hr watch is not only impossible - it’s not enjoyable either. Radar is expensive and drains batteries too quick, so from a practical point of view and taking my personal experience into account I think I’m doing the best I can. If I were someone who only needed 4hrs sleep every day I’d do that, but I’m not so I don’t. Try sailing singlehanded across an ocean then tell me if you still hold the same views on AIS. I can personally say that without it I wouldn’t be doing what I’m doing

**StuM** · 07-07-2018, 10:03

Quote:

Originally Posted by ErikSteenberg

I’ve seen 250nm distance on class B AIS... I think the data relays via sattelite

Nope. A standard AIS transceiver can only receive data via VHF, not data from messages picked up by S-AIS. S-AIS only transmits to the owners of the satellite based receivers - using entirely different technology. (That's what you see when you go to sites like MarineTraffic)

You'll only see those long range vessels under two conditions:

1. where atmospheeric conditions are conducive to tropospheric ducting - in which case it is possible to pick up VHF/UHF signals from hundreds (and sometimes thousands) of miles away.

2. when close to shore where you are within range of an on-shore AIS repeater. And you will only see other vessels that are within range of one of the AIS repeaters in a network.

AIS Basic Repeater

zboss · 07-07-2018, 10:09

Quote:

Originally Posted by hellosailor

Either you take on at least one other person to keep an adequate watch while you sleep, or you sail without insurance, against the laws, and with some extra risk, no matter how many bells and alarms you have set.

If you get squashed by a tanker moving 25 knots while sleeping, I’m not sure anyone would even know you are gone or have the insurance companies quiz you on your alertness.

ErikSteenberg · 07-07-2018, 10:17

Quote:

Originally Posted by StuM

Nope. A standard AIS transceiver can only receive data via VHF, not data from messages picked up by S-AIS. S-AIS only transmits to the owners of the satellite based receivers - using entirely different technology. (That's what you see when you go to sites like MarineTraffic)

You'll only see those long range vessels under tow conditions:

1. where atmospheeric conditions are conducive to tropospheric ducting - in which case it is possible to pick up VHF/UHF signals from hundreds (and sometimes thousands) of miles away.

2. when close to shore where you are within range of an on-shore AIS repeater. And you will only see other vessels that are within range of one of the AIS repeaters in a network.

AIS Basic Repeater

Fair enough, this was in the Mozambique Channel where I saw this range in AIS. So 150-200nm from shore was probably close enough to communicate with shore based stations. Thanks for the info (we joked onboard that the earth might be flat afterall)

GrowleyMonster · 07-07-2018, 11:12

Quote:

Originally Posted by StuM

Nope. A standard AIS transceiver can only receive data via VHF, not data from messages picked up by S-AIS. S-AIS only transmits to the owners of the satellite based receivers - using entirely different technology. (That's what you see when you go to sites like MarineTraffic)

You'll only see those long range vessels under two conditions:

1. where atmospheeric conditions are conducive to tropospheric ducting - in which case it is possible to pick up VHF/UHF signals from hundreds (and sometimes thousands) of miles away.

2. when close to shore where you are within range of an on-shore AIS repeater. And you will only see other vessels that are within range of one of the AIS repeaters in a network.

AIS Basic Repeater

And Stu gets the cigar. Keep in mind also that this is digital communication, and brief, intermittent, repeated flashes of data can be combined into useful communication, given time. I often see other ships on the ECDIS at 100 or 200 miles, even though VHF is generally regarded as a line of sight band, only. No satellite is involved in AIS propogation between ships. Inside 15 to 25 miles, the system works as advertised. Outside that range, knock on wood. Occasionally you will see another vessel. More often, not.