Yawing at anchor and dragging

[markc]

Yesterday we were in the Lerin Islands for the day and stayed the night. Wind was forecast to be very light, if any at all. However, at about 9.30pm it became very windy. I don't really know how strong, but it was enough for the wind to keep picking up one of our paddleboards that was floating behind the boat.

For the next couple of hours I kept watch on our position as we were quite close to shore, and for some reason we were yawing a lot. This seemed to induce creeping in the anchor that had been set all day, and we were getting uncomfortably close to a neighbour, so at midnight I moved the boat.

I have never experienced this type of yawing, which did seem quite violent at times, and I'm wondering what caused it and if there was anything I could have done to prevent it. Was it just the type of wind event? Could the other paddleboard which was tied to the rails on deck towards the bow, act like a sail?

FYI, 33kg Rocna anchor, 4m water, 17m of chain out, plus anchor seemed well set when we lifted it to relocate, although we had clearly crept about 20m or so

 

[jointventureII]

You'll need way more chain out when it blows, I'd say triple that at least.

With 17m chain out and 4m depth, you'd have max 10m chain in contact with the seabed which will drag easily.

The yawing is something that will occur with high winds. I drive a Pershing 108 for a living and it ends up at 90° to the wind all the time, snatches terribly and drags in 20 knots of wind if I've got less than 4 x depth out.

The paddleboard would have had very little / no influence.

 

[Forty_Two]

I'm in La Napoule & it was a surprise lump of wind. My sun screens were snatching in the gusts so maybe down to how gusty it was. I hadn't reset my wind speed since the storm but guess twenty odd knot peaks.

Seems to me you handled it in a pro way. Sometimes circumstances happen.

With my binns looking at the islands it was a "fairy light" sight so busy as usual i imagine. Laying out enough chain is always a compromise at the Lerins.

 

[markc]

Yes it was pretty busy, and some boats were close already, so letting out loads of chain wasn't practical, especially knowing many people are on really short rode. I was wondering if I could have mitigated the yaw but rigging up my anchor snubber to a side cleat.

Heading to La Napoule in a couple of hours, so might bump into you!

 

[Forty_Two]

I always use a snubber to a bow cleat. What makes me yaw sometimes is the windage of my fly bridge being well forward. I used to counter it with my steadying sail but can't use it now due to my aft sun cover over the boom.

 

[mcanderson]

We arrived last night in Beaulieu and were woken about 1am when it really started to blow. Not ideal after spending all day driving down. Today is much better.

 

[Portofino]

There can be surprising amount of current through those islands .
Maybe when the wind eased if the wind wasn’t parallel to the main channel the current moved the boat ?

 

[Hurricane]

The only time that we overnighted in the Lerin Islands, we started dragging at about 5am.
Wind came up unexpected.
Didn't notice any yawing.
So we "upped anchor" and headed into Antibes.
That was in the days of our old useless Delta and light weight chain.

 

[Dogone]

Moving windage forward as opposed to aft increases yawing, so try moving stuff aft if you can.

Also short scope decreases anchor power. Under 3 is bad unless using a very heavy anchor or well dug in or in very light winds. 4 is minimal and 5 a good target. In a blow, 6 or 7. You were in 4m of water and with say 2m water up to the bow, that’s 6m With 17m of chain your scope was below 3.

 

[Greg2]

As already said, my first thought was not enough chain out. We work on 3:1 for a short term (lunchtime) anchorage in decent conditions but up that to 5:1 for overnight and would think about more in poor conditions / a more exposed anchorage. Our chain markings relate to depth from the waterline i.e. the first mark includes the height from the bow to the waterline.

 

[Dogone]

Our chain markings relate to depth from the waterline i.e. the first mark includes the height from the bow to the waterline.

What’s the point of that?

 

[Greg2]

What’s the point of that?

So that whatever mark is on deck we know that it denotes what is actually in the water i.e. no need to deduct the height of the bow from the water or to lean over the guardrail to see if the mark is on the waterline. Not a biggie but keeps things simple - what we see on deck is what is in the water.

 

[trapper guy]

not sure if this is relevant to this situation.
but during an episode of very poor conditions at anchor off bognor regis, the lifeboat guy told me about sea anchors, para anchor was the term he used.
i'd never heard of a para anchor, but he said when deployed from the bow, it keeps your bow to the wind at all times.
i had heard of drogues for use in high wave situations to prevent capsize from going sideways into a trough.
but a para anchor was something entirely new to me.

 

[Hurricane]

So that whatever mark is on deck we know that it denotes what is actually in the water i.e. no need to deduct the height of the bow from the water or to lean over the guardrail to see if the mark is on the waterline. Not a biggie but keeps things simple - what we see on deck is what is in the water.

Or a chain counter that does this!!!



I can't claim the length in the water idea was mine - it was a poster on these forums who talked me into writing that extra bit of software.

 

[Dogone]

So that whatever mark is on deck we know that it denotes what is actually in the water i.e. no need to deduct the height of the bow from the water or to lean over the guardrail to see if the mark is on the waterline. Not a biggie but keeps things simple - what we see on deck is what is in the water.

Sorry, I don’t get it. I don’t think you ever need to know the measurement from the water to the anchor. The only measurements you need are from the bow roller to the anchor and the bow roller to the seabed (their ratio being scope).

 

[WhiskeyTownRacer]

Sorry, I don’t get it. I don’t think you ever need to know the measurement from the water to the anchor. The only measurements you need are from the bow roller to the anchor and the bow roller to the seabed (their ratio being scope).

'Need' perhaps not, but wanting to avoid a (albeit simple) calculation each anchoring is surely personal preference. Bow to water is fixed, the other is variable therefore for differing scopes the calculation changes. Personally I'd see it more simply where one takes the approach Hurricane and others do, effectively eliminating one variable so you only need to decide on the scope based on a multiple of chain in the water. Perhaps this also makes making a mistake less likely, maybe even more relevant where you're in a situation requiring more chain for changing conditions where it may be easy to forget fixed vs variable factors. Each to their own I guess.

 

[Dogone]

'Need' perhaps not, but wanting to avoid a (albeit simple) calculation each anchoring is surely personal preference. Bow to water is fixed, the other is variable therefore for differing scopes the calculation changes. Personally I'd see it more simply where one takes the approach Hurricane and others do, effectively eliminating one variable so you only need to decide on the scope based on a multiple of chain in the water. Perhaps this also makes making a mistake less likely, maybe even more relevant where you're in a situation requiring more chain for changing conditions where it may be easy to forget fixed vs variable factors. Each to their own I guess.

Ok ‘need’ wasn’t the best word. We only need drink, food and shelter. What I meant to say was the only measurement we need when anchoring is bow to seabed and bow to anchor. I suggest those that use other measurements are probably working with muddled logic. I can’t see the point in knowing Hurricane’s chain in water numbers either. Maybe he can explain.

So by example: Say you anchor in 3m of water and want a scope of 4 then you want 12m of chain. Going off the measurement from the water you will have that 12m at the first chain mark with a 2m bow height. What you actually have though is a scope of 2.4. (12m/5m). That’s not safe anchoring.

 

[dunedin]

not sure if this is relevant to this situation.
but during an episode of very poor conditions at anchor off bognor regis, the lifeboat guy told me about sea anchors, para anchor was the term he used.
i'd never heard of a para anchor, but he said when deployed from the bow, it keeps your bow to the wind at all times.
i had heard of drogues for use in high wave situations to prevent capsize from going sideways into a trough.
but a para anchor was something entirely new to me.

A para anchor is a type of sea anchor. And possibly of use in a seaworthy yacht (with no large windows) mid Atlantic - but not a lot of relevance to the OP anchoring in a small bay

 

[dunedin]

'Need' perhaps not, but wanting to avoid a (albeit simple) calculation each anchoring is surely personal preference. Bow to water is fixed, the other is variable therefore for differing scopes the calculation changes. Personally I'd see it more simply where one takes the approach Hurricane and others do, effectively eliminating one variable so you only need to decide on the scope based on a multiple of chain in the water. Perhaps this also makes making a mistake less likely, maybe even more relevant where you're in a situation requiring more chain for changing conditions where it may be easy to forget fixed vs variable factors. Each to their own I guess.

Unfortunately the bows to water distance isn’t “fixed” as far as chain is concerned. In a bit of a blow, the chain pulls pretty straight. So it aiming for a 5:1 chain to depth ratio, there would be another 10m of chain needed from a 2m high bow before the chain reaches the water.
But as one should NEVER anchor with the strain taken directly to the windlass, our simple approach is to set the chain scope calculated from the waterline, then attach the rope snubber there and pay our more till the hook is well forward and the chain slack.

 

[WhiskeyTownRacer]

Unfortunately the bows to water distance isn’t “fixed” as far as chain is concerned. In a bit of a blow, the chain pulls pretty straight. So it aiming for a 5:1 chain to depth ratio, there would be another 10m of chain needed from a 2m high bow before the chain reaches the water.
But as one should NEVER anchor with the strain taken directly to the windlass, our simple approach is to set the chain scope calculated from the waterline, then attach the rope snubber there and pay our more till the hook is well forward and the chain slack.

Outside of pitching, and if you want to be really pedantic wave height, the distance bow to water is fixed. I think you misunderstood my point in this regard. I wasn't attempting to infer anyting about chain, merely distance in the vertical between the bow and the water.

As to your second point, you are seriously conflating two things, in order to be relevant to the responses made to the OP, the discussion is the omission of bow to water from the scope calculation and the impact that has upon said calculation. In that context, and that alone, the assertion that over a 2m bow to water distance you need another 10m of chain due to the elimination of catenary is an 'interesting' claim. Removal of catenary over the entire chain length, I won't argue, but that isn't the context of the discussion. I think we are just discussing slightly different issues.