Challenge: Reversing Waves

[witzgall]

Hi;

I have recently read a few accounts of quite scary conditions. In all of these, a boat settles into a nice, 3 side protected anchorage for the evening. At some point, the conditions reverse, and the sailors are faced with sometimes breaking swell entering the anchorage, against the wind. There is also a lee shore to deal with. All in all, a ship threatening situation where there was not one too long ago.

So I thought it would be good to start a discussion of the phenomena, the signs that this is going to happen, the conditions that need to be present for it to happen, and how to deal with it.

Chris

[SuddenVibe]

Thank you for posting about this!!

[Pelagic]

Whenever you anchor in a bay which is wide open in one direction, you should always have an exit strategy.

Anchor conservatively with sufficient space between you and a potential surf line and allow for drag, setting anchor towards the closest danger.

Before going to bed, set up parallel index lines on your plotter showing offsets from good radar targets and then duplicate those exit headings by Offseting your radar EBL’s to guide you out at night.

One of the primary reasons I always lift my tender at night

[thinwater]

Something caused that swell, generally a powerful storm system off-shore. If anchoring in that sort of spot, I try to check if there is potencial for weather generated swell. Not an exact science. Often surfer web sites can help.

Surf Forecast Mid-Atlantic (STORMSURF)

Also, anchor in water deep enough that the swell will not be breaking where you are (~ 4x swell height).

[Hydra]

One day, I was anchored on the lee (south-east) side of Sark, in the Channel Islands, in sufficient depth. At the end of the afternoon, when we came back from a walk ashore, the north-west swell came around both ends of the island, maybe because the tide had covered shoals that were previously blocking the swell.

We were not in danger but it would have been impossible to sleep in these conditions, so I decided to go and find shelter at St Catherine, on Jersey.

Without prior experience of this anchorage, I had no real possibility of forecasting the change in conditions resulting from the tide: the influence of underwater relief on swell is difficult to compute accurately. However, the exit route was wide open.

Alain

[hummingway]

One of the things I look for here in the PNW is driftwood on the shore. If it's there it means it becomes a lee shore at times with adequate fetch to blow stuff up it. There is a lot of wood floating around these waters so it's a reasonable test.

[barnakiel]

Originally Posted by hummingway

One of the things I look for here in the PNW is driftwood on the shore. If it's there it means it becomes a lee shore at times with adequate fetch to blow stuff up it. There is a lot of wood floating around these waters so it's a reasonable test.

! Great.

b.

[Minggat]

Originally Posted by Pelagic

One of the primary reasons I always lift my tender at night

Ok Pelagic, I'm ready to learn somthing. What exactly is your thought process here. I also raise my dink every night for a couple of reasons. Anti theft and anit bottom growth to be precise.

So you lift yours also so you can have it out of the way if you need to do some backing during your relocating process? What?

[atoll]

Originally Posted by Pelagic

Whenever you anchor in a bay which is wide open in one direction, you should always have an exit strategy.

Anchor conservatively with sufficient space between you and a potential surf line and allow for drag, setting anchor towards the closest danger.

Before going to bed, set up parallel index lines on your plotter showing offsets from good radar targets and then duplicate those exit headings by Offseting your radar EBL’s to guide you out at night.

One of the primary reasons I always lift my tender at night

totally agree with pelegic,have had this happen inside coral lagoons where there is no posability of escape untiil day light,2nd and third anchors with very long scope are an option with the motor running, setting gps track and scouting out opposited side of the lagoon when coming in to anchor and putting way points in should you have to move,if at all possable.

lifting dingy reccomended if you need to power out to sea,also prevents painter going round the prop etc etc

[Hydra]

Almost each evening at anchor, I have the boat ready to sail at short notice: dinghy deflated and stowed in locker, deck cleared of any gear, dishes washed and stowed, etc.

It's true that I rarely stay more than one night in the same anchorage, so the dinghy would be deflated and stowed in the morning anyway

I also check the escape route, taking the wind into account. And I sleep with my ears open. The motto is "be prepared".

Alain

[Pelagic]

Originally Posted by Minggat

So you lift yours also so you can have it out of the way if you need to do some backing during your relocating process? What?

Exactly!

KISS principle… If you are having to make a move in the middle of a night it is usually because of some kind of serious problem… ( weather, medical, security, stupid neighbor…etc )

You may be distracted by a bunch of things and are still waking up to the problem. (I recognize that my middle name becomes "Murphy" when still waking up lol )


I always have my radar course plotted to get me out of an anchorage at night before I go to sleep, and the boat ready to go with the tender lifted and secure.

Doing this I sleep better knowing I am prepared in case I need to make a move and have kept things simple.

Once you get into the habit… it is no big deal

[Pete7]

Originally Posted by Hydra

One day, I was anchored on the lee (south-east) side of Sark, in the Channel Islands, in sufficient depth. At the end of the afternoon, when we came back from a walk ashore, the north-west swell came around both ends of the island, maybe because the tide had covered shoals that were previously blocking the swell. Alain

Alain, had the same problem on the west side moorings. Tide turned and the waves started to reflect back off a nearby cliff resulting in a really horible motion on the yacht. Within half an hour 2 kids and the dog are sea sick

Had no choice but to pull out and go. We passed back the same spot later that afternoon and it was flat calm again.

Pete

[kenny chaos]

Originally Posted by Pete7

Alain, had the same problem on the west side moorings. Tide turned and the waves started to reflect back off a nearby cliff resulting in a really horible motion on the yacht. Within half an hour 2 kids and the dog are sea sick

Had no choice but to pull out and go. We passed back the same spot later that afternoon and it was flat calm again.

Pete

Is there any way to see that coming?

[boatman61]

Originally Posted by kenny chaos

Is there any way to see that coming?

Tide Tables....

[atoll]

when the sh one tee hits the fan the dingy is one less thing to worry about,be alert this world needs more LERTS