That's a pretty serious gust Andi!

The red line is actual and the blue is average for the period? Or what?

Note the approx 45 degree shift in direction at the gust followed by a 90 degree shift after it....

Doesn't that indicate some kind of mini tornado?

Hello All,

...sounds like fun!

..no waves, ( I mean a preotect body of water)

..what a dream!

..I have a smaller main built for 18+ mph. In 20-ish steady winds, the I-17 is a dream, no problem at all.

..the platform is very stable and unstability comes from too much sail,....make no mistake about that.

..now, If I could get rid of the waves, like you suggested, it would be smiles, grins, whoops and hollars all the way.

..if I had the stock main up (160 sf) , it would be a pain in the b_tt and probaly boaderline dangerous.

..the key?...to go sailing in high winds in protected waters?...sure...

..but not with a sailplan optimized for 8-10 mph,...that is kinda nuts......ask a sailmaker,....stock sails have a designated 'wind range'.....I know everyone is saying, ' no kidding'..then , why are 'high wind' sailplans not used?...oh well..they would be allowed under class rules because they are smaller than sailplan size limit.....yes?

..what the heack,...it is 15mph out of the east,...air temp 83f,...water temp 79f,...I'm going sailing this afternoon!


regards,

Bruce
I17
St. Croix
USVI

Ahh, don't speak nonsense mate. That is not what we are saying. We are only saying that you weren't sailing in 80 to 100 knots winds. Like the other poster said, there may have been that windspeed some 10 miles away but not were you were sailing.

I know some people survived pretty horrendous conditions but your claims are just beyond that.

I even don't doubt that you yourself honestly believe that you did sail in that. Problem is only that it is physically impossible to sail in that in any meaning full way without totally wrecking your sails, mast and what not else. Note that each sq. mtr of cloth in 80 knots wind can pull with 80 kg compared to ONLY 5 kg in 20 knots. The cloth will just rip itself apart and even the bare mast is in danger of collapsing to such abuse. Monohulls will capize under their mast alone (as happened in the Sidney Hobart you mention), catamarans and dinghies will roll along on the watersurface.

Sorry.

Wouter

It was actually a active cold front moving through. That's the 90° shift. We saw a very little tornado then, but he din't made it to the water surface.

the red line indicates maximum wind force and blue must be average wind force...

The great thing about the masts we have on beachcats is that they are quite flexible. By trimming the mast (and hence the mainsail), you can change your mainsails profile to fit both lower and higher windspeeds. Most sailors sail in various conditions, depending on thermals, weathersystems, geography etc. So instead of having one sail for each windspeed/windrange (as larger monohulls often do), we make do by trimming the sails and mast. This system is quite successful!
In competitions, you are often only allowed to use one set of sails. If conditions change and you measured in with the "wrong" sail, you loose..

If you sail in places where you have very similar winds every day, tailoring a sail for those conditions are a very good idea (as you said).
For the 2000 olympics in Sidney, the gold medalists in the Tornado class showed up with a deep and draft forward jib. This jib allowed them to punch trough the waves on the racing area better than the others and they won the gold. (At least, that was the story I read)

What kind of wind measurement instruments would a race committee use to measure up to 100 knots? How do you stand there and hold it?

Don't be stupid.

I've raced in 35knots on a Hobie 16 as read on the course. This was barely manageable(survival sailing). My wife and I,who are one of the heavier teams(through no fault of hers)were double trapped and very depowered and were blown out of the water by a gust that was probably just above 40knots. At this years worlds when they measured 48knots just before a race the boats were being blown over everywhere including the World Champion. I don't know the math but every knot at that level makes a big differance. For anyone to say they are out sailing in anything over 40 knots tells me they just don't have the right numbers.

did I say there wasnt damage?
Did I say we had an option?
Did I say we didnt swim?

I will remember next time that we only get light breezes here.

Im fine with knowing that we get only light winds..

That the fronts are really in my imagination.

Stewart: I wasn't addressing you, But

"as a kid I sailing in gusts of 80 knots under those conditions.. "

Those are your words. This would lead us to believe you were sailing in 80 knots. You can't break "The Law" (Physics) not that I could figure it out.. That's why we have Wouter (good info on wind power)

Squalls with winds of 80-100 mph are not uncommon on Lake Erie. They often come up out of nowhere, with almost no warning, and boats are not always able to escape them. Fortunately, the storm doesn't last long.

Stewart, I'm glad you said "did I say there wasn't any damage?"

Sailing all my life in the 3rd windiest state of 48, scientifically proven to be flatter than a pancake, we are acclimated (sp?) to high winds. On the big wind days there is always a cat, centerboarder, windsurfer, university team and/or kite boarder out. Someone's always breaking something. I've (we've) raced a whole day (five races) with peak gusts in low to mid 40 knots with no damage to our three year old boat. Just playing, this last October we lost the 20 y.o. everyday jib on the 18 in 35 knot peaks, with three aboard, two trapping off the wings. When we test the limits of physics stuff breaks, the price we pay for going as fast as possible

BTW I record settings and atmospheric info with the two closet airports (both more than 10 miles away) The Corp of Engineers site only gives the current wind and the peak gust at the lake. Getting a bag for the digi camera but until then no pics.

The effect of the wind on a surface is the velocity pressure. The formula is velocity divided by 4005, the quantity squared where velocity is in feet per minute, standard density of air is assumed, and the answer is in inches of water. Twenty miles an hour (1760 fpm) is a velocity pressure of 0.19 inches of water. that results in a pressure per square foot of 1 lb. A 250 sq. ft. sail would then have a pressure of 250 lbs. At 40 miles an hour (3520 fpm) the v.p. is 0.77 " of water. That is 4 lbs, per sq. ft., a pressure of 1000 lbs. on the sail. At 100 mph v.p. is 4.83" of water, 25.1 psf or almost 6300 lbs. on a 250 sq. ft. sail. If the boat is going with the wind you would have to subtract its velocity to get the relative velocity.

This will at least give an order of magnitude to the wind strength discussion. Basically force varies with the square of the velocity.

Howard

On one 5 knot wind day we destroyed a 3 year old torndao. Split both hulls down the centre after catwheeling. Not a lot was salvagable if I recall.. A few ropes and the main system..
The rest boat went into the skip..

That was also the day the neighbours not next door but one deside them donated their entire roof to my backyard.. Think it was a sculptural exercise.. Amazing what 5 knots will do..

hrtsailor is correct only in that the force increases as the square of the velocity. The absolute figures quoted are for a flat plate, perpindicular to the applied wind velocity.

Sails are foils (well, really just camber lines) and the forces are much different. They vary more with the angle of attack in a given wind velocity - but the force is still proportional to the square of the velocity.

100 mph wind has 100 times the force of 10 mph wind.

Stewart.

Grow up; You've been called out for suggesting you were sailing in 100kts, you know it's plain rubbish, we know it's plain rubbish. Stop being silly and just live with it.

Should read

... 50 m/s = 100 knots is right on the threshold of being able ....


Wouter

mbounds,

You are correct about acting perpendicular to a flat plan (or the projected flat area of curved surface) but a boat in 100 mph wind is not going to be pointing up or on a reach.

The foil, like an airplane wing, causes another force by converting static pressure to velocity pressure on the convex side which causes a difference in the static pressure on either side of the sail. That is an additional force on the boat to make it go forward but not applicable on a run.


My experience in wind forces is in HVAC, not in sail dynamics, but the idea is to give an order of magnitude to this discussion.

Howard

Stewart, could these values be in km/h rather than knots? 100km/h and 80km/h are 54 knots and 43 knots respectively, which are reasonable values for a severe storm (although still dangerously extreme if you're out sailing).

According to Bureau of Meteorology data, the maximum recorded three-second wind gust in the Perth area was 43.2 m/s (84 knots) on 20th August 1963. This was at the City West recording station which had a height above datum of 58m and a mast height of 22m. One would assume the gust speed at water level was somewhat less.

Statistical work by Geoscience Australia predicts that a 100 knot gust in the Perth area is a once in 500 year event:


Similarly, a 80 knot gust in the Perth Area has a predicted frequency of once in 50 years:


Source: Geoscience Australia: SEVERE WIND HAZARD ASSESSMENT IN METROPOLITAN PERTH (Large PDF)