Helicopter Rescue off Dover

[RobbieW]

Not only does pressure increase something like exponentially with speed, it also increases with a decrease in temperature. Air density increases as the temperature lowers so a winter wind/gale/storm carries more punch than the same in summer.

 

[Blueboatman]

I would just add to that that air is compressible, water not so.

So, horizontal rain squalls in a full gale not only steal body warmth, sting and rob you of vision, they add pressure ( and weight) to the sail area . Nice, eh?

 

[jimi]

Also I've always felt an easterly has more "weight" than a westerly, probably cos the easterly tends to be associated with high pressure whereas westerlies are associated with depressions and thus lower air pressure. Higher pressure will lead to denser air.

Is there some sort of calculator that will take windspeed,temperature and pressure and convert it to a force/m2? That would be interesting!

 

[RobbieW]

Dynamic pressure

Here's a start, what I dont know is how to allow for the compressibility of air in the equation. I'm also not convinced that a percieved difference betwen an easterly and westerly is down to the originating weather system, more likely to do with the temperature of the air mass flowing.

Is there a physics teacher in the house? I'll also spin off a new thread for this.

 

[marklucas]

Some figures

The density of air is as follows:

0C 1.293 kg / m^3
20C 1.205 kg / m^3
40C 1.127 kg / m^3

e.g. every 20C decrease is ~ 7% denser in typical temperatures, and so the wind is 7% more powerful.

In addition, in winter conditions, higher, colder (and so denser) air is more likely to sink from higher, faster moving levels (top of the mast) and mix with air close to the sea / air boundary. This increases the speed at lower levels (which is what you actually feel standing 1m above sea level). As the power of the wind increases with the square of speed (remember the formula for kinetic energy of a moving body?) only a slight increase in speed puts quite a bit more power into the sails lower down.

If it's any corollary, glider pilots also recognise that their stall speed goes down in winter for the same air density reason.

Hopefully useful.

 

[Blueboatman]

This information is all part of the Commercially endorsed Rock jock teaching ticket from the RYA I assume. Thems going winter sailing an all..

 

[Vara]

Fascinating stuff, I'm sure.

It will be one of my priorities, when I'm next caught out in a force 10.

Measure wind speed, temperature, humidity, barometric pressure. Consult spreadsheet and communicate the force per square metre to my gallant crew, they'll be really impressed.

This will be done while counting my rosary and whistling "for those in peril on the seas".

 

[jimi]

Fascinating stuff, I'm sure.

It will be one of my priorities, when I'm next caught out in a force 10.

Measure wind speed, temperature, humidity, barometric pressure. Consult spreadsheet and communicate the force per square metre to my gallant crew, they'll be really impressed.

This will be done while counting my rosary and whistling "for those in peril on the seas".

I would'nt whistle if I were you, that's just asking for trouble!

 

[alant]

Too right.


Wind Type___________________Wind pressure in lbs sq ft on:

___________________Round surface__________ Flat Surface


Gale___________________ 2.8___________________ 4.0

Strong Gale_____________ 4.2___________________ 6.7

Whole Gale______________ 5.8___________________ 9.0

I simply square the wind speed & compare those.
Don't know how that matches up with your figures.

 

[Koeketiene]

I would'nt whistle if I were you, that's just asking for trouble!

 

[bigwow]

Fascinating stuff, I'm sure.

It will be one of my priorities, when I'm next caught out in a force 10.

Measure wind speed, temperature, humidity, barometric pressure. Consult spreadsheet and communicate the force per square metre to my gallant crew, they'll be really impressed.

This will be done while counting my rosary and whistling "for those in peril on the seas".

Took the words right out of my mouth!! well almost

 

[Tidewaiter2]

It is old sailing knowledge...

This information is all part of the Commercially endorsed Rock jock teaching ticket from the RYA I assume. Thems going winter sailing an all..

The old time Thames Bargemen had a saying;
"Cold winds knock yer dawhn. mate!"

Of course, some hard grafting, hard drinking, baccy chewing, 'Mirror' newspaper stuffed up the front of his guernsey and donkey jacket, varnished bowler/flat capped wearing bargee ( at the job since he was 14), slogging round the Naze and upwind in Black Deep in January, knew b***gger all about wind, tide, and when not to sail, compared to the present day 'Zero to ?ero' HPX encased, Endorsed GRP Jockey hard wired into the 'net & Met, Tweeting both broadsides simultaneously???

BTW, I think I was lucky to be sworn at/clipped round the ear by one or two of the former at the tender age of 11 helming an Montagu Whaler, (nb; we do not mention the Norwegian timber ship 'incident', one windless Sunday pm in the old working West India Timber Dock, do we, or how I learnt my first words of a Scandanavian language, either, do we)

 

[Twister_Ken]

I wonder whether all that dense air, travelling at F10 velocity, is enough to bend a spot welded wheel? I think we should be told.

 

[Tidewaiter2]

No, But..

I wonder whether all that dense air, travelling at F10 velocity, is enough to bend a spot welded wheel? I think we should be told.

10stone or so of unbraced Helm hitting it hard at 10mph will do it, if the welds are poor in the first place, or corroded.

 

[Seajet]

The old time Thames Bargemen had a saying;
"Cold winds knock yer dawhn. mate!"

This is of course why a lot of traditional working boats sent down their topmasts for the winter.

 

[Tidewaiter2]

And a lot of pubs in East London and Essex were called.....

The old time Thames Bargemen had a saying;
"Cold winds knock yer dawhn. mate!"

This is of course why a lot of traditional working boats sent down their topmasts for the winter.

...the Anchor & Hope.
And why they watched the skies and sea surface like a hawk, and made sure they were tucked up on the leeward side of a sandbank or up a creek whenever possible.
Not to mention the best ground tackle they could get the Owner(or 'er in doors) to pay for.

 

[TSB240]

10stone or so of unbraced Helm hitting it hard at 10mph will do it, if the welds are poor in the first place, or corroded.

Surely this thread is a recipe for how to turn a "day skipper" into 10 stone of Dazed and Diced kipper.

 

[Tidewaiter2]

There are always carrots!!!!!!!!!!!

Surely this thread is a recipe for how to turn a "day skipper" into 10 stone of Dazed and Diced kipper.

Which is what the poor bod felt like after being slung against that wheel, I bet

Was on an murky xManche cruise ex-Chi Hbr, a few years ago, in coy with another boat.
Got a SW Gale 8 Warning 'Soon' about 12nm Sth the Nab, SWMBO and I were just trying to raise t'other boat to say"Lets Run away to Gosport Fleshpots instead", when I was slung across cockpit by a giant hand, winded and bashed about, which made our minds up 100%.

Sod the VHF, saw the other boat heading towards us thru the murk, closed and yelled; "We are running away, NOW".
Lots of nodding heads, no sign of their Skipper(like me, no feather), all slog back to Haslar and ice & pea packs on the bent bits. Seems the same wave that chucked me across our cockpit from behind wheel, slung their Skipper into chart table edge, bent it, and him painfully & U/S for x Manche job, and thats just the forerunning wave energy from an 8 on two strong, well built and padded fairly experienced helms still fairly fresh and cheery and not tired, cold, wet, and a bit puky, if not worse.

 

[blacksheep509]

The AIS station for that area is at Fairlight near Hastings.... It was working perfectly that day...

 

[blacksheep509]

I sent my eldest son with Hot Liquid last year, in spring to do his Comp Crew. His skipper was the guy that got into trouble on Goodwin Sands on the way back from the Boat Show. I found out after I had let my boy go ith them. I know this because he was telling the story to the crew. In his version he said he was asleeep at the time, so it was not his fault. He was a young chap, apparently a nice gyy, but no way a mature skipper.

I don't agree with charging for rescue. That way people will die because the skipper doesnt want to face a bill. I guess their insurance will go up, so perhaps that might make them think about better planning in future?

I was thinking of using them for my Coastal Skip courses and a coulple of day courses. Now I am thinking again. I don't want to put money in the pockets of people who take unreasonable risks with customers (and their own) lives.

Last point, I live just outside Southampton. For the last three days the fields around us have been full of seagulls, taking shelter from the coming storm. If even dumb birds can see its unsafe to be at sea ......

I would strongly recommend Southern Sailing.... friendly and Very professional !