Anchoring off... working out distances.

[AngusMcDoon]

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.

If you think that you have vertically moving wind within the height of your piddly mast, what is it, 16', then you are as deluded as ever. Air at atmospheric pressure and atmospheric velocities is effectively incompressible - air won't be compressed at the bottom of the downdraft so has to spread out. The effect of being under a downdraft at the sea surface is serious directional and speed instabilities. Vertically descending wind within the height of a yacht's mast - not a chance.

Maybe I should offer some of my aviation experience as a helicopter pilot as you seem to have a bit of difficulty differentiating meteo effects as they affect aircraft and boats. If a helicopter gets caught in a downburst, it will lose height rapidly until within 100-200' of the surface. It doesn't crash into the surface quite yet because the air stops moving downwards at this height. However, it becomes extremely turbulent and unpredictable in direction and strength. It's this effect that can cause a loss of control and subsequent unfortunate meeting with the hard or wet stuff, not the downdraft itself. That's why if you are unfortunate enough to get caught in one you use all your power and time to fly out of it forwards rather than fight the loss of altitude.

 

[Seajet]

If you think that you have vertically moving wind within the height of your piddly mast, what is it, 16', then you are as deluded as ever. Air at atmospheric pressure and atmospheric velocities is effectively incompressible. The effect of being under a downdraft at the sea surface is seriously directional and speed instabilities. Vertically descending wind within the height of an average yacht's mast - not a chance.

Angus,

I don't know where you get your ideas from but the Anderson 22 mast is 25'6" long and stepped about 5' above the waterline; why the hell should you think I'd make up stories about katabatic winds ?!

When you get to try the experience you'll know it's rather real.

 

[AngusMcDoon]

why the hell should you think I'd make up stories about katabatic winds ?!

I have no idea what motivates you, but it keeps us all amused, so carry on.

 

[Seajet]

So you don't know a proper answer then ?!

 

[lenseman]

Ohhh goodie, deckchair time again!

.

 

[AngusMcDoon]

So you don't know a proper answer then ?!

I've given the established view of what happens at the base of a downdraft. If you want to believe your pseudo-science, that's up to you.

 

[Twister_Ken]

In the interest of interest, I offer an interesting observation.

Offshore wind coming over a high hill, Greece.

Calm for a few yards out from the shore, then an unpredictable series of 'wind bombs' on the sea surface, sometimes one, sometimes several at the same time in different places, with the resulting surface winds blowing in various directions, as evidenced by the effect on yachts in a mooring field in the bombardment zone.

Interesting, I thought.

 

[noelex]

If you think that you have vertically moving wind within the height of your piddly mast, what is it, 16', then you are as deluded as ever. Air at atmospheric pressure and atmospheric velocities is effectively incompressible - air won't be compressed at the bottom of the downdraft so has to spread out. The effect of being under a downdraft at the sea surface is serious directional and speed instabilities. Vertically descending wind within the height of a yacht's mast - not a chance.

Maybe I should offer some of my aviation experience as a helicopter pilot as you seem to have a bit of difficulty differentiating meteo effects as they affect aircraft and boats. If a helicopter gets caught in a downburst, it will lose height rapidly until within 100-200' of the surface. It doesn't crash into the surface quite yet because the air stops moving downwards at this height. However, it becomes extremely turbulent and unpredictable in direction and strength. It's this effect that can cause a loss of control and subsequent unfortunate meeting with the hard or wet stuff, not the downdraft itself. That's why if you are unfortunate enough to get caught in one you use all your power and time to fly out of it forwards rather than fight the loss of altitude.

Wind with a vertical component all the way to the water is seen in some anchorages, particuarly those with steep terrain.

This phenomenon is known by various names depending where you come from, but I like the descriptive Australian term for these winds. They are called "bullets"

 

[SamanthaTabs]

Just asked the Boss to explain katabatic winds to me, fortunately logical enough to understand before diagram sketches commenced, talk about a Michael Fish moment.. Any room in that deck chair Lenseman??

 

[lenseman]

Just asked the Boss to explain katabatic winds to me, fortunately logical enough to understand before diagram sketches commenced, talk about a Michael Fish moment.. Any room in that deck chair Lenseman??

I have just found a spare one for you Sam.

.

 

[Nostrodamus]

You can call them anything you want but in an otherwise peaceful bay the wind howled through the rigging from nowhere.

 

[lenseman]

You can call them anything you want but in an otherwise peaceful bay the wind howled through the rigging from nowhere.

When you can hear the wind in my rigging it is Force 5 and / or greater.


.

 

[Nostrodamus]

Blimey Mark !!! How close to the cliff were you ??



.

Just updated the blog and maps on our site. We were anchored at flag 76 (www.cygnus3.com)
Apart from a mostly naked hippy commune there were tall, steep cliff on two sides and it was a very hot day.