Is it safe to cross astern of a fast ship in open water with a 180 feet CPA

[Pelagic]

Unsafe!

[evm1024]

The crossing scenario is concocted but specific for a reason.

You are in open waters and doing 5 kts, there is a ship doing 20 kts slightly more than 4 miles away bearing 14 degrees forward of your beam. The bearing is not changing.

Is it safe to attempt to cross behind the the ship with a CPA of 180 feet?

[Shrew]

180 feet is too close.

[Pelagic]

Again...NO!....
At 4nm......180 ft is well within the error values of navigating and piloting equipment.... It should be viewed as a colision.

Proper seamanship would require a much greater CPA to be exercised and failing action by the Give Way vessel, a dramatic course change to increase CPA should be exercised at no less than 3nm

[sirfer]

Unsafe..

[puffcard]

Couple things we don't know, at night nope, Navy ship nope. We also don't know the size of the ship. The wake might be a bigger issue at 20kts for smaller boats. I grew up sailing in a very busy harbor, crossing behind ships doesn't seem like a big deal. One problem is you don't know what's is on the other side of the ship, as you cross. Could be another yahoo. Also be careful cutting tight behind towed barges, most have tagged lines dragging so the tug can pick them up when they make up behind or to grab if they lose the tow. But a calculated CPA of only a 180ft is a super tight crossing. The CPA can jump around alot, never seen one that tight. On the flip side I love guys on small boats calling me on the VHF asking what my intention are, with CPA of a half a mile.

[evm1024]

Originally Posted by puffcard

Couple things we don't know, at night nope, Navy ship nope. We also don't know the size of the ship. The wake might be a bigger issue at 20kts for smaller boats. I grew up sailing in a very busy harbor, crossing behind ships doesn't seem like a big deal.

Open water (think out of sight of land) and the ship doing 20 knots.

[Dsanduril]

You also have to remember that COLREGS isn't the be-all, end-all of regulations with regard to crossings. There are additional regulations by various territories that are dependent on what the ship is carrying - do you know its cargo?

For instance, in northern California waters 33 CFR 165.1183 specifies an exclusion zone of 500 yards ahead, astern, and along either side of a cruise ship, an oil tanker, or a "high value asset" (pretty much all warships and whatever other ships the Captain of the Port cares to designate). In these cases it might or might not be safe to pass within 180 feet, but it would be illegal.

These regulations were enacted mostly as a counter-terrorism tactic in response to events like the USS Cole, allowing (at least in theory) offensive action to be taken against vessels entering an exclusion zone.

There are similar rules in other territories and jurisdictions, and the IMO allows such local rules to present an exclusion zone of up to 500 meters. So, unless you know specifically that no such regulation exists for the ship you are intending to cross then you're better off assuming the 500 meter rule applies.

[puffcard]

Originally Posted by evm1024

Open water (think out of sight of land) and the ship doing 20 knots.

Yea I wouldn't in open water and the wife would be flipping out at under a mile.

I was the kid that the USCG took his rowboat away, after getting pulled off the Elizabeth River for the third time. The last time I drifted into the channel sound asleep. I was layup in the bow listening to the Indy 500. Woke up to a megaphone, blue lights and the bow of the Enterprise (aircraft carrier) over my head. They yank me out of that river so fast. Then they called my dad and said I was in big trouble, my dad asked if I killed anyone. They let the 13 year old walk home, to start building his next boat, with sails. Then I could drift with purpose.

[30yearslater]

Never believed in using Colregs. When I have I have screwed up by not taking prudent action well before they were needed. 180 feet is ridiculously close. Even on Lake Ontario where high speed is 12 to 13 knots the wake is staggering at 1/4 mile out. I have a Master Unlimited container ship captain who sails with me and has shared a bit of perspective. In one case he recommended turning back at a self unloading bulk carrier and passing port to port at 2 miles out. Keeping the wheel house in sight at all times and then crossing some 2 miles astern the wake was sufficient to send green water over the bow. A ship moving twenty knots? I'd reverse course and get the hell out of there pronto.

[TheThunderbird]

No. Never

And, WHY??

[four winds]

Originally Posted by evm1024

The crossing scenario is concocted but specific for a reason.

You are in open waters and doing 5 kts, there is a ship doing 20 kts slightly more than 4 miles away bearing 14 degrees forward of your beam. The bearing is not changing.

Is it safe to attempt to cross behind the the ship with a CPA of 180 feet?

Using only this quote as the facts of the scenario. And assuming a planned maneuver is required. Can only speculate the 5 knot vessel is under power and give way to the fast moving vessel to starboard. Just forward of the beam and constant bearing. Four miles out.

To immediately change course for close astern would be undetected by the fast ship. Non-compliant. And lead to no good when the fast ship gave up stand on status and turned to port. Not to mention such a move would be imposible to execute accurately by the slow vessel.

If the slow vessel waited until the course change would be obvious to the fast ship skipper it's way too late, too close to the ships path, and probably occurs after the fast ship gave up stand on and turned to port.

I see nothing safe about either chioce.

Motoring at 5 knots. Give way to a 20 knoter just ahead of the starboard beam. I see only one good choice. A ninety degree or greater course change to starboard and a good look at the aspect of the fast ship with binoculars. Then maybe a few more to starboard for good measure.

Cutting to idle would work, but why founder around for ten minutes waiting.

[newhaul]

Can't say in till I have more information . What kind and of ship? what is his hull shape?
Here we have all manner of ship from catamaran fast ferries to navy aircraft carriers. All of which present their own unique set of variables. The fast ferry I would have no issue even 100 feet from her . The carrier I would want to be at least 1500 ft away from her. So the answer I would give wasn't in the poll and that is " it depends "

[Captain Bill]

I'm assuming your 180ft cpa was determined by AIS as MARPA isn't going to get you that good of a plot and actually neither is AIS. Even AIS is giving you a distance from his AIS GPS antenna. Do you know where on a 1000 ft ship the antenna is located. Unless it's located on the tip of the stern (I doubt they ever are) you might well be running into some point on their hull rather than 180ft astern.

[newhaul]

Originally Posted by Captain Bill

I'm assuming your 180ft cpa was determined by AIS as MARPA isn't going to get you that good of a plot and actually neither is AIS. Even AIS is giving you a distance from his AIS GPS antenna. Do you know where on a 1000 ft ship the antenna is located. Unless it's located on the tip of the stern (I doubt they ever are) you might well be running into some point on their hull rather than 180ft astern.

myself I use the mark1 eyeball a hand compass and a watch with second-hand.
When close maneuvering is needed I also use the vhf