Laser 28 - Excellent example of this great design Hamble le rice |
![]() |
Rossiter Pintail Mortagne sur Gironde, near Bordeaux |
![]() |
Laser 140101 Tynemouth |
![]() |
List classes of boat for sale |
Wind |
Post Reply ![]() |
Page <1234> |
Author | |
Hobbo ![]() Far too distracted from work ![]() ![]() Joined: 02 Jun 06 Location: United Kingdom Online Status: Offline Posts: 211 |
![]() ![]() ![]() ![]() Posted: 11 Jun 06 at 4:21pm |
The anamometer picks up local conditions and what the wind "appears" to be like right? So therefore it is elementary whther it is reading 16 knots in colder or denser airs as the anamometer is reading the force going into it, accounting for the local air pressure. Therefore i think the effect of the wind would be the same in both - in your scenario twenty knots, however the true windspeed in the denser air may not be that speed the denser air is just casuing it to appear faster.
That's jsut my line of logic, may be complete bollocks and i'd be happy to be proved wong ![]() |
|
Contender GBR 362
Osprey 1318 - IVplay SSC |
|
![]() |
|
gonzo ![]() Far too distracted from work ![]() ![]() Joined: 30 Oct 05 Location: United Arab Emirates Online Status: Offline Posts: 236 |
![]() ![]() ![]() ![]() |
One example i have heard is that an aeroplane that takes off in dubai mid summer must have a higher take off speed to get the lift than it must in the uk where the air is denser. So for colder denser wind do we get more power per knot of wind than in a hot country with lower density.
|
|
Go Big or Go home or sail a 49er!!!
|
|
![]() |
|
Ian99 ![]() Posting king ![]() Joined: 07 Apr 05 Online Status: Offline Posts: 138 |
![]() ![]() ![]() ![]() |
The effect is far more noticeable with altitude. Try sailing at nearly 6000 feet above sea level and wind speeds of 25+ knots become far more manageable.
A decent anenometer should measure the actual speed of the air movement and shouldn't be affected much by air density - there's only the resistance of the bearings providing any kind of load. If however, you use beaufort scale to measure wind strength, a force 5 will always feel the same regardless of altitude, temperature, humidity etc. The beaufort number is classified by the effect the wind has on the sea (or objects such as trees on the land). The wind speeds in knots at sea level on a British summers day (I'm guessing they used a British summers day!!) which have this effect are only there for convenience. |
|
![]() |
|
gonzo ![]() Far too distracted from work ![]() ![]() Joined: 30 Oct 05 Location: United Arab Emirates Online Status: Offline Posts: 236 |
![]() ![]() ![]() ![]() |
thanks for that it has cleared some of it up. So an anamometer built in the uk set to measure wind on a summers day at sea level in the uk is not accurate anywear else. And yes i agree the beaufort is what on what you can see not a measurement. |
|
Go Big or Go home or sail a 49er!!!
|
|
![]() |
|
Prince Buster ![]() Really should get out more ![]() Joined: 15 Dec 05 Location: United Kingdom Online Status: Offline Posts: 1146 |
![]() ![]() ![]() ![]() |
yeah i suggest doing a search mate.....there's loads of this stuff on the forum that's been discussed before.....
|
|
international moth - "what what?"
|
|
![]() |
|
Medway Maniac ![]() Really should get out more ![]() ![]() Joined: 13 May 05 Location: United Kingdom Online Status: Offline Posts: 2788 |
![]() ![]() ![]() ![]() |
I read Ian99 as saying that a decent anemometer will measure speed not force. As such, it would be equally accurate anywhere. Of course, it depends on how you define 'decent'. I'd have thought that a good rotating turbine-style of anemometer would have such minimal bearing drag that the turbine would always effectively spin at a rate proportional to the windspeed, regardless of the air density, i.e. it will be accurate everywhere. An instrument that depends on the pressure force exerted by the fluid - e.g. a vane with a pointer that moves against a spring or gravity, will depend on density and therefore be less accurate. That said, anybody who's used an anemometer will know that the fluctuations are usually so great, gust to lull, that such inaccuracy would be hardly noticeable and thus irrelevant, or so I'd have thought... |
|
![]() |
|
Skiffman ![]() Far too distracted from work ![]() ![]() Joined: 27 May 04 Location: United Kingdom Online Status: Offline Posts: 291 |
![]() ![]() ![]() ![]() |
no offence really to Julian beithewaite because he has designed some of the best boats in the world, but from past experiance i do not think you would think hes god if you met him. At the 29er Worlds in 2005 julian made up a rule that we had to measure the spreader hieght that wasnt in the rules, and he also said that you weigh a 29er with the pole in which is not correct (but julian said so, so it was done). There was hardly any boats underweight and most were 1.5kg over which is about the weight of the pole. back to the topic, i agree that when it is warmer the wind is not as powerful for its speed as a cold UK winter breeze. |
|
![]() |
|
tack'ho ![]() Really should get out more ![]() ![]() Joined: 08 Feb 06 Location: United Kingdom Online Status: Offline Posts: 1100 |
![]() ![]() ![]() ![]() |
When thinking about this just remember being hit by a fly doing 30 mph hurts a lot less than being hit by a HGV doing the same speed!
|
|
I might be sailing it, but it's still sh**e!
|
|
![]() |
|
49erGBR735HSC ![]() Really should get out more ![]() ![]() Joined: 30 Mar 05 Location: United Kingdom Online Status: Offline Posts: 1991 |
![]() ![]() ![]() ![]() |
Haha, that reminds me of one of the boats our uni crashed at BUSA, we were trying to work out the extent of the damage and reckoned the forces involeved were on par with crashing a Transit van into a wall doing about 30mph. Back on topic, its all good to consider the pressure differences but with the size of the sails on our boats and the slight differences involved with varying pressure, is it worth really getting too caught up on the subject. Yes there will be a difference but its not as apparent as for air-crafts because they have massively more efficient wing sections. My theory is that I will consider all aspects before going out on the water but we generally try and head out early to make sure the boat is feeling right and get a general idea for what is happening wind and tide-wise in the race area. I won't be thinking about the fact that one day is warmer than another on the course, but I will be picking up constantly feed back from the boat to see if its tuned properly, whether she could be doing with more power or slightly less.
|
|
![]() |
|
gonzo ![]() Far too distracted from work ![]() ![]() Joined: 30 Oct 05 Location: United Arab Emirates Online Status: Offline Posts: 236 |
![]() ![]() ![]() ![]() |
And all your tuning efforts are worthless when you go arse over tit in a gybe and end up swimming or have to spin after hitting the mark. My veiw spend more time on your boat handling skills than worrying about which country you well get most wind. |
|
Go Big or Go home or sail a 49er!!!
|
|
![]() |
Post Reply ![]() |
Page <1234> |
Forum Jump | Forum Permissions ![]() You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |