Anchoring off... working out distances.

Nostro, your ability to over think a problem exceeds even that of Sheldon from the Big Bang Theory!

1. You cant get closer (assuming you don't drag) to any obstacle than the length of chain plus the length of boat
2. Things always look closer from the boat than they really are (see how close an anchored boat that is worrying you actually is when you look at it from the shore)
3. With your draft you wont be messing around in water so shallow that you might run aground within a twenty or thirty meter distance.
4. If you really are feeling that brave that you anchor really close to a rock, you are going to set the kedge.
5. If you are worried about going aground because of being blown onto a lee shore, then you are in the wrong anchorage so move
6. If you think you might be to close, then no amount of measuring is going to convince you otherwise so you would not sleep anyway

As a general point, if its forecast to get windy then we set a wind alarm, shallow and deep anchor alarms, and sometimes a GPS alarm, but that is to detect a dragging anchor which is a different problem. If strong winds are forecast then I want to be blown out to sea without hitting anything.
 
Nostrodamus said:
Just out of interest how hard does it have to blow to stop the chain keeping you where you are so you are relying on the anchor. I know it depends on the length and weight of chain out, windage etc but I was wondering.. when does the anchor take over from the chain?
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Nostrodamus said:
Just out of interest how hard does it have to blow to stop the chain keeping you where you are so you are relying on the anchor. I know it depends on the length and weight of chain out, windage etc but I was wondering.. when does the anchor take over from the chain?
Click to expand...

So the general gist of your question:

What would be the formula for working out the force required to pull the entire length of chain taught and thus pull the anchor clean out of the seabed?

Force/Mass x Acceleration ?

PS The anchor and chain work together, at no point does the anchor "take over". Ever dropped out 50 metres of chain without an anchor to see what happens? :-)
 
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SeamanStaines said:
Nostro, your ability to over think a problem exceeds even that of Sheldon from the Big Bang Theory!

1. You cant get closer (assuming you don't drag) to any obstacle than the length of chain plus the length of boat
2. Things always look closer from the boat than they really are (see how close an anchored boat that is worrying you actually is when you look at it from the shore)
3. With your draft you wont be messing around in water so shallow that you might run aground within a twenty or thirty meter distance.
4. If you really are feeling that brave that you anchor really close to a rock, you are going to set the kedge.
5. If you are worried about going aground because of being blown onto a lee shore, then you are in the wrong anchorage so move
6. If you think you might be to close, then no amount of measuring is going to convince you otherwise so you would not sleep anyway

As a general point, if its forecast to get windy then we set a wind alarm, shallow and deep anchor alarms, and sometimes a GPS alarm, but that is to detect a dragging anchor which is a different problem. If strong winds are forecast then I want to be blown out to sea without hitting anything.
Click to expand...

I am glad you said all of that.

I would add:

1. Time spent in recce is seldom wasted. Cruise around until you find a good weed free area of sand. I would rather be in the middle of the Cala than anywhere near rocks.

2. Assuming the depth is, say 6m, drop the hook, feed out another 10 - 15m or so of chain until the anchor is properly set whilst gently motoring astern.

3. Then give it some wellie until the chain takes the strain then let out as much chain as you can whilst still motoring gently astern without hampering other anchored vessels.

3. Note the position of your anchor relative to land features. You can then inform arriving vessels if necessary. Do not be tempted to use an anchor buoy, somebody will pick it up at dusk - whilst you are ashore in the beachside bar.

4. When it is all settled down, snorkel and check the anchor has set. If not.....repeat as necessary. Then put a snubber on the chain (any old line with a chain hook will do).

5. If there is an offshore wind, fine. If there is not, you should not be there. Consider your options if the wind shifts and puts you on a lee shore in the middle of the night.

6. Also consider the direction of swell, including the swell rebounding from rocks.

I would also add that, assuming you will be doing the donkey work forwards, you should invest in a couple of those cheap walkie talkie thing so you can communicate between helm and bow. At least, that way, any audience will not hear your caustic and sarcastic comments: 'Astern.......astern........ASTERN!!!!......THATS ****ING BACKWARDS YOU STUPID MARE'.

Trust me.
 
chinita said:
At least, that way, any audience will not hear your caustic and sarcastic comments: 'Astern.......astern........ASTERN!!!!......THATS ****ING BACKWARDS YOU STUPID MARE'.

Trust me.
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To which she replies "park your own damn boat" and stomps off down below leaving the boat still going astern as the chain flies out the locker ..... I knew we were being watched :-)
 
We are going to use mobile phones with handsfree kits to improve anchor-helm communication.

It is so cheap now to do this n Euro land it stops the need for fancy dedicated systems and best of all, only the two of you are in the conversation :-) not an army of marina boats on 'scan'
 
chinita said:
At least, that way, any audience will not hear your caustic and sarcastic comments: 'Astern.......astern........ASTERN!!!!......THATS ****ING BACKWARDS YOU STUPID MARE'.
Click to expand...

I once heard of a husband-and-wife crew making a minor hash of mooring their Fisher style motor-sailer, complete with the classic "bossing the missus around" comments from hubby. What made it interesting was that he was giving these orders from inside the wheelhouse, using the VHF loudhailer!

No doubt this is somewhat practical if you have an enclosed steering position, but being bossed around over a loudhailer must be even worse than being bossed around normally, plus the whole harbour was treated to a running commentary of the cockup in progress :)

Pete
 
We nose in, circle around, sensitive position instruments in hand.... hand signs- DROP NOW! ....we have 5 bars of wifi signal.....

Actually we just anchor a million miles away from the beach/rocks/other boats and spend a fortune on petrol getting ashore. I wish I was joking. Still, not hit anything YET.....
 
Jamesuk said:
So the general gist of your question:

What would be the formula for working out the force required to pull the entire length of chain taught and thus pull the anchor clean out of the seabed?

Force/Mass x Acceleration ?

PS The anchor and chain work together, at no point does the anchor "take over". Ever dropped out 50 metres of chain without an anchor to see what happens? :-)
Click to expand...


Here's some info about the maths of chains:

http://www.math24.net/equation-of-catenary.html

enjoy!
 
Thank you everyone for your advice and help.
I normal circumstances anchoring has been ok.
There are those occasions though when you want anchor close to a beach or cliff and you would like to wake up still afloat and without a rock sharing your cabin.
All your advice should help.
 
chinita said:
I would also add that, assuming you will be doing the donkey work forwards, you should invest in a couple of those cheap walkie talkie thing so you can communicate between helm and bow. At least, that way, any audience will not hear your caustic and sarcastic comments: 'Astern.......astern........ASTERN!!!!......THATS ****ING BACKWARDS YOU STUPID MARE'.

Trust me.
Click to expand...

We now have those walkie talkies after the whole of Fiskardo heard me 'suggesting' that the anchor might be made off now as I fended the boat of the quayside with my feet whilst she was 'looking at the pretty fishes'...
 
I remember dropping the anchor when going in stern to and motoring back to the quay side to tie off. All was going well when we suddenly stooped 10m short. I asked the wife what was wrong and she just said "well i let out the same amount as I did in the last place so you must have got the distance wrong"
 
Nostrodamus said:
Is there a technique you use for working out the nearest place you can anchor off a cliff or beach or anything?

Do most people just guess?

Sometimes you like to anchor in as close as possible when tides or winds change and swing you round you don't want to end up hitting something or going aground.
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generally I look at the contours on the chart, check the bottom type, make sure at low I stay afloat, check the tides, then anchor in my spot and hope I got it right!
 
lenseman said:
Blimey Mark !!! How close to the cliff were you ?? :D



.
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Close enough but not so close that we would be in trouble if we swung. The wind that night was blowing us off but the air dropped over the edge like a ton of bricks. Strange thing was this happened not around sun down but 2am.
 
Maybe katabatic winds ?

These happen at places with high hills and blow down vertically, on the leeward side ( known to glider pilots as ' rotors ' ) not along, so a boat heeling does not let the air spill up from the mast but instead presents more area for the force to act on.

Well known in the Med' but I remember two nasty occasions in Studland Bay when this happened, we weren't that close to the hills but it was certainly frightening, we took anchor watches all night.
 
Seajet said:
Maybe katabatic winds ?

These happen at places with high hills and blow down vertically, on the leeward side ( known to glider pilots as ' rotors ' ) not along, so a boat heeling does not...
Click to expand...

They blow vertically down until they meet the sea surface, then they cannot go down any more, and blow along like your common or garden wind. The sea surface is where most boats are found.
 
AngusMcDoon said:
They blow vertically down until they meet the sea surface, then they cannot go down any more, and blow along like your common or garden wind. The sea surface is where most boats are found.
Click to expand...

Here we go again !

Most boat RIGS are not found on the sea surface, if they are it's a message that something may be wrong.
 
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