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Sabbatical II · 23-02-2011, 10:53

I would like to hear from some of those who use any type of alarm system to warn of the proximity of another vessel. I'm not really after a discussion on the rights and wrongs of single handing as I've been on one fully crewed boat where the nominated watch person has only transfered his sleeping position from the bunk to the cockpit. I just accept that if I want to get somewhere, sometimes it will be just me.

What works and what doesn't?

Greg

Sailmonkey · 23-02-2011, 11:03

We've got a CARD radar detector. In the busy port of Houston , TX it works all the time. I've detected CG helo's, ships going up and down the chanel...etc. I currently don't know if it has any real value out away from traffic (ie I don't know what sort of range it has.)
here's a link to the manu
C.A.R.D.

**David M** · 23-02-2011, 11:10

ARPA and I think most MARPA systems have the ability to set up a guard zone.

There is also AIS which detects vessels with AIS transceivers.

Combine them both and/or with a radar detector and you have a pretty nice detection system.

rebel heart · 23-02-2011, 11:34

I have a cheapo furuno radar that has "watchman" mode or something of that sort. It does a sweep every two minutes and if anything shows up in whatever range you have the display at, it starts beeping. Uses a lot less power than having it sweep constantly.

And while not whole heartedly engaging on the conduct of watchstanders I think anyone who's been offshore knows how empty it can be and they're a bold faced liar if they say that they maintain a constant lookout, scanning the horizon constantly.

I used to use an egg timer, and now use a phone or a watch, setting the countdown timer for ~10 minutes or so. I think 7 minutes is roughly as fast as a 25 knot vessel will take closing in on your dead ahead from over the horizon if you're making ~8 knots (I forget the math and should probably redo that equation).

Whether it's the radar sweep interval or a drowsy sailor waking up and scanning the horizon there's an amount of time where you can be relatively sure that if you go through it you won't slam into anything until the next sweep/awakening/both.

**David M** · 23-02-2011, 12:34

Using this chart, http://upload.wikimedia.org/wikipedi...he_horizon.png

If your height of eye is 3 meters above the water, then the distance to the horizon is about 4 miles. If a ship in the distance on the other side of the horizon is say for example 15 meters above the water then you add its distance to the horizon. You add its 11 miles plus your 4 miles to the horizon and your distance to the ship about 15 miles. A ship cruising at 24 knots covers that distance in 11/24's of an hour or about 27 minutes. This calculation assumes 15 miles of visibility or greater.

rebel heart · 23-02-2011, 14:15

Quote:

Originally Posted by David M

Using this chart, http://upload.wikimedia.org/wikipedi...he_horizon.png

If your height of eye is 3 meters above the water, then the distance to the horizon is about 4 miles. If a ship in the distance on the other side of the horizon is say for example 15 meters above the water then you add its distance to the horizon. You add its 11 miles plus your 4 miles to the horizon and your distance to the ship about 15 miles. A ship cruising at 24 knots covers that distance in 11/24's of an hour or about 27 minutes. This calculation assumes 15 miles of visibility or greater.

So out of that 27 minutes though (and I know this is worst case scenario) you add in your vessel cruising at hull speed (call it 8 knots), in the case of a head on collision. I thought the number was around 7-10 minutes.

S/V Alchemy · 23-02-2011, 15:14

Quote:

Originally Posted by David M

ARPA and I think most MARPA systems have the ability to set up a guard zone.

There is also AIS which detects vessels with AIS transceivers.

Combine them both and/or with a radar detector and you have a pretty nice detection system.

This is how I plan to go, as I find AIS and RADAR to be complementary, rather than replacements for each other (See: Satphone vs. SSB endless debate...).

The RADAR tells you "an object" is too close. AIS tells you if it's a ship, which ship and if it's moving and how fast and in what direction (RADAR can plot an intersect, too, obviously).

This saves you the embarrassment of trying to hail a waterlogged picnic table to "get out of the way".

conachair · 23-02-2011, 15:52

Quote:

Originally Posted by Eleebana

What works and what doesn't?

Well for me the first thing that works is get offshore!!! Coastal don't sleep. Again for me offshore means off the continental shelf, away from the fishing boats. Then radar alarm on maybe sweeps every 10 minutes, I usually set the guard zone between 1 mile & 5 miles. Radar's great for picking up squalls as well. And AIS is great, find out in seconds if the ship 5 miles away is something to worry about or will miss by miles. I like both but if i had to choose then it would be AIS, low current draw and (well, my cheapo nasa unit anyway) will work down to 10.5v.

barnakiel · 23-02-2011, 17:07

alarm zones on your radar - good,
CARD - good,
MerVeille - very good,
various AIS alarms - good to very good,
SeaMe (generic) - very good,

Personally, I would stick with SeaMe and some sort of class B transponder.

Why?

Because both warn you AND try to make you visible to others.

b.

**Jim Cate** · 23-02-2011, 17:43

G'Day Greg,

We've had two types of small radar sets: Furuno 1710 and Anritsu 24 mile. While they both had alarm features, we found that if you set the sensitivity etc up high enough to see small vessels then there were frequent (very frequent in rough wx) false alarms. Never were able to use them to our advantage. Newer and fancier radar sets may indeed be better, but some hands-on experience with a given unit might be worth while before buying!

Cheers,

Jim and Ann s/v Insatiable II lying Church Point, NSW, Oz

CarlF · 23-02-2011, 18:06

I've had the See-Me and the alarm function worked well offshore (too many false alarms near shore). The EchoMax is a newer unit and apparently has better specs - including a unit that does both X and S band radar. Don't ignore the great safety factor of a STRONG radar return. This will set off the ARPA system on the ship's bridge and get some attention. While I know some are skeptical about the quality of the large ship watches offshore - my experience is that they will respond quickly to a solid ARPA target.

The biggest problem with most passive radar reflectors is that they have a weak return when the boat is heeled - which is most of the time. These active reflectors do much better

EchoMax Radar Reflectors -EchoMax Products

I'd also agree that an AIS transponder is the first install. This will create a reliable "closest approach" alarm on your boats chartplotter and also set off an alarm on the approaching ship. Prices have come down. In the US, West Marine has an AIS transponder (not just receiver) for $499US.

WEST MARINE AIS 1000 Class B "Send and Receive" AIS Transponder at West Marine

Carl

barnakiel · 24-02-2011, 13:33

Quote:

Originally Posted by CarlF

I've had the See-Me and the alarm function worked well offshore (too many false alarms near shore).

The EchoMax is a newer unit and apparently has better specs - including a unit that does both X and S band radar.

(...)

I believe the Sea-me is now a dual band too:

Sea-Me Crew Safety. Dual Band RTE

Cheers,
b.