Bow and Stern or Two Bow Anchors?

[belizesailor]

Originally Posted by illiniphoenix

Thanks all for the advice! I went with one anchor, as seemed to be the consensus.... it was a magical way to spend the night. I can't wait for the next time!

Glad it went well.

Just for future reference: Bow & Stern (not to be confused with Bahamian Mooring as some do), you would normally only use in very protected (minimal wind and waves) anchorages with minimal swinging room. For example, anchoring in a narrow stream.

[heatherbrie]

Glad things went well for you! In case you plan to head further afield, you may want to practice bow and stern anchoring for the future. In our current anchorage in Curacao, it's an absolute necessity as the anchorage is crowded, winds are flukey, coming from any direction in sudden gusts or dying altogether, and there are reefs. In other Caribbean anchorages, a bow-an-stern setup might be the only way you get any sleep in the unrelenting swell. Just a thought.

Also, one trick that we use when the winds are likely to shift is to not just set the anchor alarm, but also hit mark when your anchor hits bottom. Measure the amount of rode/chain you have out, and name your mark anchor-50, for example. Then, if you wake up in the middle of the night with a changed perspective, all you have to do is click on the mark, and your GPS will tell you exactly how far you are from your original anchor drop site -- an excellent way to know if you've dragged or not. Finally, in a crowded anchorage, you can also set a radar proximity alarm, though leaving your radar on all night just gobbles energy.

[noelex 77]

In a crowded anchorage your boat needs to swing and move like the other boats around it. This means you need to match their anchoring technique.

Anchoring so your boat is fixed in one position will cause contact with other boats if they are not anchored in the same way and the wind or current changes.


The gps alarm is ideally centred over the anchor, but the gps aerial is situated well back from the bow (30 feet) on most boats. If you can set an anchor alarm from a waypoint (sometimes called an offset anchor alarm) this is ideal.
If you cannot do this setting the anchor alarm when you drop the anchor will result in a lopsided swing circle.

[foolishsailor]

The advice on this thread is sound.

Especially the advice regarding mirroring the anchoring styles of other boats in the anchorages.

One word of caution however. As you skills amd experience amd hopefully knowledge build remember to trust your instinct. If you pull into an anchorage and you feel the conditions or future conditions warrant anchoring in a way different to your neighbors that do what is right for YOUR boat.

Just make sure that when you make a decision to deviate from the herd that you will be clear from the differing swings of anchor and more importantly that you will be upwind of all the people when the weather you think is coming hits.

[heatherbrie]

Originally Posted by noelex 77

In a crowded anchorage your boat needs to swing and move like the other boats around it. This means you need to match their anchoring technique.

Anchoring so your boat is fixed in one position will cause contact with other boats if they are not anchored in the same way and the wind or current changes.


The gps alarm is ideally centred over the anchor, but the gps aerial is situated well back from the bow (30 feet) on most boats. If you can set an anchor alarm from a waypoint (sometimes called an offset anchor alarm) this is ideal.
If you cannot do this setting the anchor alarm when you drop the anchor will result in a lopsided swing circle.

Absolutely, you have to pay attention to the boat around you!

Good point on the ariel being situated further back, something folks should definitely keep in mind. In general, we've found that we can account for that when we've swung with a quick mental calculation, and since we don't have the offset anchor alarm, this "back of the envelope" method just gives us a good sense of whether we're swinging or dragging when a sudden blow comes up.

Of course, in all our time out, we've dragged twice, once when we were exhausted and mis-calculated the scope, leaving only 3-1 (we start at 4-1 normally) and a sudden squall came up, and the other in a holding that proved untenable because of coral rubble and grass. The funniest part of this one was that we were off the boat when it happened -- thank God for our friends who re-set our anchor after dealing with theirs -- but when we came back to the boat, we were in the exact same position relative to everyone else, so didn't understand what was going on, until we realized that EVERYONE had dragged the same amount, and the anchorage looked exactly the same! Luckily, there was lots of space as everyone slid back 300 feet, so there were no collisions and we were able to head to a better anchorage pronto.

[noelex 77]

Originally Posted by heatherbrie

Absolutely, you have to pay attention to the boat around you!

What we do is mark the anchor placement, then read the GPS when we're digging in -- we run the engine in reverse at 1500 rpm for a good 10-15 seconds once the chain is taut -- and then look at our distance from the anchor. While the GPS is further back, and therefore the distance is actually more than the number we record, this ensures that the distance between the boat and the mark is constant, no matter how we swing.

Yes that's very much what we do although generally higher revs in reverse.

For the distance to be constant as the boat swings the gps aerial needs to be over the anchor when the mark is created. You can achieve this by displacing the anchor watch waypoint on some chartplotters. This is very helpful. If the wind reverses you can tell imediatly if you are dragging.
If you set the anchor alarm waypoint without taking the position of the aerial into account you will swing 2x the bow to aerial distance more on one side of the circle than the other.
If anchoring with 30m of rode with an aerial that is 10m from the bow you will be 30m from the anchor waypoint on one side, but 50m away on the other side. (assuming the chain is stretched, you haven't dragged and the small effect of using the hypotenuse instead of the base of the triangle).

This is a signifficant difference and people can become concerned their anchor is dragging when that is not the case.

[micah719]

Resolution of gps would have to be factored in as well, yes? I hear civilian gps is about +- 10m. Or, the cheaper yet precise solution of a beercan on a string. Tough call, having to empty the can just for anchoring....but difficult problems require stern measures. Have courage! Cshhht!

[BobH260]

I like to turn on our handheld GPS as we come into an anchorage, it plots our track as we come in, drop the anchor and back down on it. Then as time passes we get a nice averaged track of our position. At any time I can turn on it on and see if we have moved at all. If the wind really comes up I'll keep it running and take a glace every once in a while to be sure we have not started moving. Easy to do from your bunk.
Bob

[Normanby]

Newbie question:
I use a handheld GPS and paper charts, and have only spent a couple of nights at anchor, each of them nervously.
The thing is, I only think about the anchor alarm on the GPS after I've anchored.
So if you've anchored already, how do you set the anchor alarm later?
Also, does everybody have their rode marked in some way, so you can tell how much scope you've put out?

[Astrid]

A common practice is to tie different coloured strands of canvas to your chain or line at regular intervals (fathoms, meters, whatever you are comfortable with). One could also use paint as I know some have done.

[noelex 77]

Originally Posted by Normanby

Newbie question:
I use a handheld GPS and paper charts, and have only spent a couple of nights at anchor, each of them nervously.
The thing is, I only think about the anchor alarm on the GPS after I've anchored.
So if you've anchored already, how do you set the anchor alarm later?
Also, does everybody have their rode marked in some way, so you can tell how much scope you've put out?

Marking the rode is essential. Astrid has mentioned several ways.
When you have anchored you can still set the anchor alarm correctly. You want the centre of the circle over the anchor. This is only possible (once anchored) with the GPS if it allows you to set a remote waypoint as the centre. About 1/2 the GPS units allow this.

Look at the trace on the plotter in the above photo. You can see where the boat reversed and the anchor was dropped. The trick is to get the antennae over this spot so the best waypoint is about 30 feet in front of the boat changing direction.

An alternative if the chain is stretched out is to note the compass bearing to the anchor ( normally direcly upwind) and set a waypoint in this direction with the rode length (or a bit less) plus the bow to GPS distance.