Face to face with a 747

I was sailing with my brother north of Coronado's Naval Base facility in San Diego Bay, and a 747 jumbo jet came in to land at the base. As my boat reached the threshold of the runway, we came face to face with the 747. The plane flared moments before it reached us, passing overhead some 200-300 feet from the water. It was an awesome sight! To make things even more cool, a gust of wind grabbed the sails of our boat and thrusted us forward in what must have been a record acceleration for a 25' boat. We felt like we were in a sports car!

Minutes later, I realized how lucky we were not to be on a lighter boat. The gust of wind could have capsized us.

AirForce One or WindForce One ?

I do a lot of sailing in the east bay area of Panama City. We get some pretty low flying F-15 and various other Air Force aircraft. Thankfully, they are not low enough the hit us with their jet-wash. I think we would be a grease spot on the water if one of those hit us.

We did a seminar once at Coyote Point in San Francisco. We were right under the landing path for the airport, and every time a plane came in to land the vortices coming down from the planes would automatically capsize a bunch of boats.

That's no fun. I assume you guys moved after a while...

Nope, we didn't move. Apparently, that is where they sail. Pretty exciting...and noisy.

Yeah, it's noisy alright. We usually sail down the bay a little to get away from them. When they are taking off with full afterburner, you can't even hear yourself think. However, it is pretty impressive. Sounds like... freedom.

Remarkable is that you will notice the big gust of wind that follows an airplane not immediately but after more than 30 seconds. This makes it much more difficult to anticipate on the big gusts.

Wasn't there a beach in The Antilles where sailing with a cat could be dangerous ?

Try landing a small aircraft behind those guys! Those twin horizonal tornados can extend a mile behind a landing aircraft on a calm day.

Race on Botany Bay in Sydney. Sydney International Airports runway stretches out onto the bay. Seen many of small waterspouts come down and catch unsuspecting boats, sending them swimming.

If you have a window seat on a jet next to the trailing edge of a wing, in certain atmospheric conditions you can see the vortices spinning down like ghostly whirling dervishes.

Heaven help me for asking this question of a bunch of engineers, but does this happen on a smaller scale off the trailing edge of a sail?

Here is an excerpt from an e-mail from a friend of mine, partially on this subject:

To answer your question Mary, yes, on a much smaller scale it does happen off the back and tip of a mast/sail. The reason you can actually see the vortex when seated by a window in an aircraft is the much greater difference in pressure from the bottom to the top of the wing, which causes a lowering of temperature in the vortex to the dew point, forming fog, as the compressed air on the underside of the wing expands and cools going over the top. If the air is humid (like in Florida, all the time) you can see the vortex as fog. (if you sit near the front of the engine you can also see fog inside the engine cowling as take off power is applied, due to the reduced pressure inside the intake during engine acceleration) You can also see this as two streaming trails of fog off the wingtips if you sit at the approach end of any runway where big jets land in humid air.

The vortex's are much bigger when the wing is at a high angle of attack and "dirty" (flaps down, for take off or landing) as the wing is creating the most lift then. You don't see them at cruise as the wing is "clean" flaps up, fast and low angle of attack in dryer upper air. The vortex is still there but you can't see it in the dry air.

I have often thought of putting an end plate up there at the top of the sail but as the boat heals over, I think the end plate might become more drag than lift. If you were to capsize, it might also be more of a hindrance to righting. If you could keep the boat sailing with the mast straight up all the time, in theory, it would help reduce the tip vortex drag...in theory.

It is nearly impossible to measure how much it would help a sail boat, as the boat bobbs up and down over waves, which negatively effects the flow, in addition to the healing.

I think development of a soft-hard wing sail could yeild results. By this I mean a mylar/dacron wing sail with removeable battens/ribs, that looks like a hard wing, ala C cats, but then could be collapsed like an accordian back on the beach, for storage. The mast would be enclosed by the wing which would be raised around the mast, using the mast for support as a normal airplane wing uses the spar to support the ribs.

This wing sail plus boards/foils that lift the hulls clear, and the T foil rudders I think would make the next big advance in sailboat speed. We still have to figure out how to make the hulls get over the waves that come with big wind though...the Moth sailing up in the air looks cool, but can it be done consistantly in rough seas?

Wow, that must be what makes the Hobie Wave so darned fast -- that Hobie Bob does wonders. And when capsized it makes the boat easier to right.
So proud of my High-Tech Wave.., hmm! sailing in the Wave HT Class. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
Rick