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  Topic Review (Newest First)
12-23-2012 11:17 AM
Re: Heavy winds?

With an anemometer the cups are pushed, on the 'wrong way' side of rotation you're fighting the drag.. I think the density difference will even out/cancel in this case.

Bernoulli is an 'easy' way to explain lift but it's not the true science.

As an extreme illustration, think of standing on a dock with 5 knots of wind.. no problem... then go stand in a creek with 5 knots of current running... good luck staying on your feet. Same velocity a lot more force....
12-23-2012 08:01 AM
Re: Heavy winds?

My question about the anemometer - mine is three little cups on short plastic arms, all of which rotate about an axle. When the wind is making the whole mess rotate, it's more or less "filling" one of those cups at any time, but the other two are heading (backwards) back into the wind. Maybe nice weather stations take temperature into account when converting shaft rpm into wind speed?

Air feels a whole lot heavier when riding a motorcycle without a windshield. 23 degrees is the coldest I've ridden any real distance. Noticeably different lean-forward angle compared to 95 degrees. Not that I care at 23 degrees. I'm just cussing and hanging on for dear life.
12-22-2012 11:59 PM
Re: Heavy winds?

This is way out of my limit . Bernoulli did most of his work of I think in fluid dynamics. Fluid that you can not compress. Air can compress more than fluid. Some fluid can because it has gases inside. I fly, I sail I fit pipe with fluids and gases and changing of state from gases to fluid super heat and so on. This could be the point when we need to ask the PE to explain. I will just have to take his word he will pull out a lot of math with letters an such, I will stay with my first and the majority. Cold air has more lift and power. Any PE want to jump in this? Regards ,Lou
12-22-2012 08:27 AM
Re: Heavy winds?

Originally Posted by lapworth View Post
I was out the other day with a cold North wind on the bay. There was only a few white caps so I believe the wind was around 12 knts at most. I like to get the boat moving between 3.5 to 2.5 knts. I am trolling. Almost all summer there in these conditions I would use small jib and main. Yesterday with this setup I was doing almost 5. So I reefer and that only slowed me down to 4-4.5. Finally decided to drop main. Now I was sailing at 3-3.5 knts. Are cold winds heavier then warm winds making your boat sail faster. Also i was sailing across channel so current would be a very small factor.
To answer your question, air density at 80 degrees is 0.070 lbs./cubic ft. while at 30 deg. it's 0.081lbs. But since the major driving force was the Bernoulli effect, I think that the cold air gives a different perception, imho.
12-19-2012 12:00 AM
Re: Heavy winds?

Originally Posted by Cruisingdad View Post
Please make sure to emphasize "... YOU ARE the "BEST LOOKING..." SOunds better that way. Also helps to keep my fellow male mods (the not good looking ones) in check!!

"WHO" claims you to be the BEST looking MALE mod?!?!?! not me!

Winston is he best looking MALE mod! Didn't know he was a mod did ya! Time to delete ol CD with that spikey collared ugly thingy of a dog! Yep. that is my story and I am sticken to it!

So with that, when do you come up here to the NW next?

12-18-2012 10:29 PM
Re: Heavy winds?

Originally Posted by sealover View Post
Alright, would my little home weather station (or your mast top anemometer) read higher wind speeds on a colder day? But a little dandelion poof blowing in that same wind would be going the same 12 kts regardless of temperature?
The change in density produces more force for the same velocity... the anemometer speed is based on the velocity...I doubt it's affected by density changes.
12-18-2012 09:12 PM
Re: Heavy winds?

Alright, would my little home weather station (or your mast top anemometer) read higher wind speeds on a colder day? But a little dandelion poof blowing in that same wind would be going the same 12 kts regardless of temperature?
12-18-2012 09:06 PM
Re: Heavy winds?

I like that Jkemp. Testing would be very hard but looks good enough on paper. I am not sure about the beer and the BBQ but that test might be more fun? Regards, Lou
12-18-2012 08:32 PM
Re: Heavy winds?

I had to get some numbers. I would not stand behind this "science", but I had to get this out of my system. I used this site Air Density Calculator to figure out air densities. I used this site Airplane Aircraft Wing Lift Design Equations Formulas Calculator - Force to calculate lift of a wing. I used 1.5 for Cl for a sail.

So the jib on my Sabre 28 would theoretically have 10% more lift in 45 degree 40% relative humidity air than it would have in 85 degree 60% humidity air. That was fun.
12-18-2012 01:03 PM
Re: Heavy winds?

Originally Posted by Faster View Post
Problem is, Brian, the waste heat from your BBQs will undo all the good that cold beer did, esp considering the beer probably didn't last more than a few boatlengths!!
I added a fan too. And everyone knows that a fan will make you sail faster.

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