Zamani Marine, Nantucket Yacht Club, 1st January, 2012
In yet another first, Zamani Marine has taken a boat built for the WWC wind system and converted it to use Global Wind. Like the Nemo, this modified WWC boat uses wind shadow and land shadow, and can shadow, and be shadowed by, other Windmaster-powered boats sailing nearby.
“It came about after I sailed the demo of the RM20 from Rene Marine, ” says Nomad Zamani. “I liked the feel of the steering because it really behaves much more like a real-life big boat. It was by far the best big boat I’ve sailed in SL, and I thought it would be great for cruising the SL oceans.”
“However, I’ve become accustomed to Global Wind when racing the Nemo, and it seemed natural to use that in a cruising boat as well. In fact, the reasons for inventing global wind apply just as much to cruising as they do to racing – in essence, in real sailing, the weather is master of all, and I wanted to experience that aspect when cruising in SL.”
Zamani started by making the boat communicate with the Windmaster networked wind system, and then feeding the wind parameters into the boat’s sailing engine. “I knew the trick was to modify the generic WWC scripts,” says Zamani, “but I’m not so strong on the mechanics of WWC. The boat was behaving strangely when I first tried it, so I got in touch with Rene Underby at Rene Marine in the hope of gaining a better understanding of the issue. It turned out that I was injecting the Windmaster data into the wrong place, and I’d like to thank Rene for her assistance.”
With the RM20 now talking to the Windmaster server, the system treated the boat just like a Nemo, meaning that it imemdiately used wind shadow and land shadow. It also meant that it threw a Nemo-sized wind shadow – not realistic for a boat that’s over twice the height. “I then modified the wind shadow model to account for the increased height. Basically, the RM20 now throws a much longer and wider shadow than the Nemo.”
Zamani didn’t stop there. “The Nemo sends telemetry data to the server to enable a good shadow model to be built,” he continues. ”This includes the boat’s heading and boom angle, which the server uses to calculate the area of sail presented to the wind by an upwind boat – it works out how big a hole it makes in the air.” This is straightforward in the Nemo because the data is already available in the Nemo’s sailing engine script. With the RM20, the internals of the sailing engine aren’t accessible (because it’s not built by Zamani Marine). Instead, the modified script looks at the current rotations of the boat and its boom, and uses this information to derive its current heading and boom angle, which are then sent to the Windmaster server.
“It works very well,” says Zamani. “The project led to me to reexamine the wind shadow model because I had to account for the new mast height of the RM20. This resulted in some reworking of the code to model the height component more realistically – up until then, the model was purely Nemo-specific, where all boats are effectively the same height.” There is still some tuning to do, however, and the modification is still very much a prototype. “At the moment, the WWC scripts still ask me if I want to use the settings provided by every wind setter that I sail past, which I ignore. I need to refine the code to handle that better (or eliminate it altogether). I also discovered that a Nemo sailing very close to the RM20 will shadow it rather too strongly – the shadow model doesn’t yet account for the taller mast ‘in reverse’.”
In other words, the RM20′s mast is so tall that a large proportion of its sail area is above the hole in the air made by the Nemo’s sail, meaning that it doesn’t lose as much power as a Nemo would in the same downwind position. (Addendum: Accounting for the reduced effect of a smaller boat shadowing a larger one has now been implemented.)
“I’m excited by this development,” concludes Zamani. “For the first time, a non-Windmaster boat has used the Windmaster system. On the one hand, it means that I can indulge in proper cruising using real wind, all without having to make a lovely big boat to do it in. On the other hand, the changes this has driven in the wind shadow model means that Windmaster now has increased flexibility – there is the potential for other boats to be modified in a similar way.”