max ebb — crew list party

Igo to the Crew List Party every September because of the venue: Two years ago it was Spaulding Boat Works, this year it's at the Bay Model, which will be switched on for observation. Also, if you get there early, there's a deck tour of the Matthew Turner, Sausalito's latest historical ship replica. "It's great to have another tall ship out on the Bay," I remarked to no one in particular as I stepped off the gangway onto the wooden deck of the ship. "Aye," said an old salt in a peacoat leaning on the bulwark near the top of the gangway. "But this ain't no 'tall ship.' That's reserved for full-riggers, my boy. A tall ship means a real sailing ship with t'gallant masts and skys'ls."

It had been many decades since anyone referred to me as "boy," but that was OK. My problem was trying to figure out if this was a planted character actor or someone who actually objected to the "tall ship" moniker. "It is kind of under-rigged," I agreed, as my eye caught a display showing the sail plan, which did seem a little light on mainsail area for this type of vessel. "That mule tops'l would be laughed off the water back East," the old man continued. "This vessel should have a gaff almost as long as the main boom, for a real mainsail. And then a proper tops'l over it to fill the space between the gaff and the mainmast." "I had that thought also," I confessed. "But they say they have photos of original local boats of the same genre, showing the same small main and the same funny extra sail they fly to extend the leech. Is that what you're calling a 'mule' topsail?"

"Darn right. It's a sexless mongrel." "Maybe back then, in the central Bay in the summer, boats like this had all the sail area they needed, without a gaff mainsail and without a normal topsail," I suggested. "Or more likely," answered Lee Helm, who had suddenly appeared from around the other side of the chart house, "they have to limit sail area to be certified by the Coast Guard to carry passengers for hire. That's why they have a reduced sail plan that won't, like, cause too much wind heel." "That might answer," the old sailor allowed, while sucking thoughtfully on a pipe that was apparently unlit in compliance with museum ship rules. "But let's not pretend these recreated utility boats are 'tall ships.' It ain't fair to the real thing." "Sure," I sighed, "but we've got this living-language thing to deal with. These days anything with even a single vestigial square yard gets to use the term, and though there's nothing we can do about it, the Turner, on the other hand, does have some very functional square sails on the foremast."

The old salt looked as if he was about to spit over the windward rail, but was brought up short when one of the museum staff, on board to host the tours and answer questions about the ship, came within easy hailing distance. "Ahoy Max! Welcome aboard, Lee!" he greeted us. "We're taking it out next weekend and have room for supercargo. Can I give you two a pair of VIP invites?" "G'day, mate," the old salt interrupted as Lee and I were eagerly accepting the invitations. "I like the way you set

The Bay Model, a 400-ft-by-320-ft analogue computer built in 1957.

her up the traditional way, without the gaff. It's a regional rig, but it's truly authentic for the Bay." "Thank you," said the staffer, as he turned back to talk to Lee. "Smart as paint," added the old sailor, who suddenly had nothing but compliments for the rig. "I'll bet that topsail really powers her up in a smoky sou'wester of a sea breeze, can't wait to see it fly." "Yes, we're very pleased with the Turner's performance under sail," said our host. "I got a collection of old sextants from the tall-ship era," the old salt added. "I can bring a few of 'em out for a sail, and I'll have your guests ciphering latitude by noon sight before we're back at the dock." "Can you really get a good noon sight inside the Bay?" I asked, thinking maybe I should run interference between this character and our host. "Don't you need a clear horizon for a celestial observation?" "Hell, no," he answered. "A couple of miles of water in the true south direction will do, we just figure in the short horizon correction and Bob's your uncle." "We'll talk," the staffer finally agreed, and they swapped contact info. "I had a feeling it would be worth showing up for this," I said as we walked down the gangway and over to the Bay Model, where the snacks were out and the party was already in progress.

The mix of Crew List Party attendees covered the full range of sailor résumés: There were novice sailors looking for crew spots, retired racers who had switched to cruising, new racers looking for experienced crew, and sailors of all stripes looking for partners with more than sailing on their minds. But the most interesting category comprised new sailors who had recently spent way too much money on a boat that was way too new and way too big. "We had a hull speed U.S. ARMY CORPS OF ENGINEERS of 8 knots to windward!" boasted one sailor whom I took to be a newly minted owner of a large, upscale cruising machine. "That was in 16 knots of true wind at an angle of 42 degrees." "You can always tell a sailor who skipped

COURTESY ANDY DAVIS

dinghies and learned onto a big boat full of fancy instrumentation," Lee whispered. "They only speak true wind angle and true wind speed, never apparent."

Lee did not have to explain her logic. A small boat has a masthead fly, and maybe some telltales on the shrouds, so all you get is apparent wind angle. A boat with instruments is using the measured apparent wind angle along with the boat speed and wind speed to calculate the true wind speed and angle, and unless both are well calibrated, which they usually aren't, the true wind readouts are wrong. Wind speed is particularly hard to measure accurately when the apparent wind speed is very low, as on a deep reach. "And like, this newbie has no idea what 'hull speed' really means," Lee added. "Don't be hard on the novices, Lee. They'll be looking up at the masthead instead of the instruments by the time they get to Cabo." "If their full dodger doesn't, like, totally block their view of the sails. But I'd still sign on. I can handle trading two weeks of sailing lessons for two weeks of ceviche."

The second star of the show, after the Matthew Turner, was the Bay Model. This is a hydraulic scale model of the Bay and Delta system, built in 1957 to study tidal currents and the effects of dams, dredging and Bay fill. "Amazing," said Lee as we gazed across the expanse of the South Bay, "that they built this simulation as a huge physical analogue."

"The digital models took over years ago," I confirmed. "Now this is just a tourist attraction."

Along with the crew seeking boats and owners seeking crew, among other attendees were a couple of racers who, we found out, just came to observe the current patterns in the model in preparation for Big Boat Series. "See how the South Bay ebb begins while the North Bay is still flooding?" one of them observed. "That's why the tide changes first along the Cityfront. There can be good tide relief in there long before it's slack at the Gate." "Must be because the South Bay is so much shallower," suggested another racer. "No, the North Bay is just as shallow," Lee corrected. "The difference is the tidal dynamics between north and south. The South Bay is like, in resonance, sloshing in and out like one end of a bathtub. That makes the current slack at high water or low water, and maximum current at mid-tide. Visualize the sloshing."

The sail plan of the 'Matthew Turner', showing the unorthodox main topsail. The rig is probably OK for San Francisco Bay in summer, but not enough mainsail area for light air. Inset: Photographic proof that this type of topsail was actually used at one time.

Theoretical behavior of the tides in South Bay compared with North Bay and Delta. The South Bay is a standing wave, like one end of a sloshing bathtub. The North Bay tides move upriver as a progressive wave, with water flowing in at high tide and out at low tide.

South Bay North Bay

High tide: Water has sloshed into South Bay, tidal current is slack.

Alviso San Mateo Bay Ocean Bridge Bridge High tide: Water runs into North Bay and elta ood current is maximum.

Ocean Benicia Tinsley Stockton Island

Alviso San Mateo Bay Ocean Bridge Bridge Mid-tide: Water is owing in or out tidal current is maximum. Mid-tide: Tidal current is slack.

Ocean Benicia Tinsley Stockton Island

Low tide: Water has sloshed out of South Bay, tidal current is slack. Low tide: Water runs out of North Bay and Delta, ebb current is maximum.

"Just like the western end of Long Island Sound," said one of the racers, who had apparently learned to sail back East. "But the North Bay doesn't slosh," Lee continued. "There's a lot more water in the Delta system. Think of an infinitely long trench. At high water in the ocean, the current flows in. At low tide in the ocean, the water flows out. Slack current is at the mid-tide level. But remember, in the South Bay, slack current is at the highs and lows. That puts the South Bay out of phase, leading by pi, or by one-quarter of the tide cycle." "But a complete tide cycle," asked one of the racers, "is a little over 12 hours, so shouldn't the South Bay be turning three hours ahead of the North Bay if your math is correct?" "It's closer to just one hour," said the other racer. "For sure," Lee admitted, "the models are, like, approximations. But the theory explains the phenom." "Maybe the model would be more accurate if it were correctly scaled," uggested another sailor. "The depth scale is a hundred to one, but the horizontal scale is a thousand to one. So everything is ten times as deep as it should be." "That's on purpose," said Lee. "Because at small size and low speeds, viscosity

has a much larger effect on flow than momentum. Increasing the depth by a factor of ten tries to compensate for this effect."

That seemed to answer the question, but Lee was not done. "Reynolds number is the way this is

Even without a gaff mainsail, the 'Matthew Turner' seems to have plenty of sail power for cruising the Bay when the summer sea breeze is turned on.

described," she continued. "It's basically speed times size. At the extremes, an airliner wing is very big and very fast; Reynolds number is high, viscosity is almost, like, entirely out of the picture and the wing is very efficient, behaving as if it's frictionless. Lift-to-drag ratio can be over 200. On the other extreme, a dragonfly wing is at such a low Reynolds number that it's dominated by viscosity, and the best wing shapes are strangely corrugated flat surfaces. They do well if they can get a lift-drag ratio of, like, ten to one."

We finished up with a pass through the new exhibits brought in for the event by the Sailing Science Center, where Lee was very much in her element. She naturally had the right answer to the Archimedes paradox, and we both had fun playing with toy anchors and chain in the anchor sandbox.

It was a productive evening: Lee ended up with a crew spot for Big Boat Series, I had a possible berth on a big new cruiser sailing to Mexico in the Ha-Ha, and we both scored an invite to sail on the "tall ship" Matthew Turner. — max ebb

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