Swiftsure 2014

24 05 2014

The 2014 Swiftsure starts this morning. Weather looks great for the start, with things getting a bit interesting out at the entrance to the strait. There looks to be a shift to negotiate on the way home, a decision made more difficult by significant contrary currents.

There’s lots of good info posted at http://www.swiftsure.org/ for anyone interested in playing along or just following the race. Live video of the start and tracking should come online in a few hours.

76T will be shadowing Farr 40 Occam’s Razor.

17 07 2012

Griddle me this

9 12 2010

Just some pretty pictures… 7 day average windspeed, and a crop showing 3 days at higher res.

Ramblings on Routers

29 11 2010

Laughing Sally posted a question on SOL’s forum recently asking how much of a difference use of software routing makes and whether using one is a pre-requisite to winning in online sail-races. I drafted a reply, getting partway into it before completely losing track of what I had started out trying to say. Editing wasn’t going to save the response, so I moved it here… It’s still long and rambling, but at least the page format doesn’t highlight that quite so badly.

I’ll take a stab at this one. Nicely posed question.

There are several sub-classes of routing software (and I suppose routing or potential-routing SOLers):

A handful of “super-routers” are using custom software. This gives two distinct advantages – they can take into account the way SOL works, and they understand what the software is doing from the inside out. “Can” doesn’t translate to “do”…

It used to be that the big (huge?) edge was the weather. It’s well known that SOL’s weather doesn’t match up perfectly with public sources and this means that although you can use commercial software for overall strategy you shouldn’t steer by it. Two changes have erased this – brainaid is making SOL’s “grib” available, and SOL has changed the way it sources and resamples the wind. Both are very welcome! Using brain’s weather (and polars for that matter), the gap to commercial software is pretty much erased. There are some very powerful free alternatives now too.

A “perfect” router will give you a perfect solution inside the 6h update interval. This means that races that can be broken down are easier to route with certainty. If there is a waypoint before the next update both the course and arrival time can be “known”. This is maybe closest to the “they just do what the computer tells them” complaint, though a fair number of boats that “could” win these quite handily either don’t bother with this sort of race, don’t route at all in these circumstances, or only use software minimally. I guess it needs to be pointed out that inside of 6 hours the good SOTP guys are very fast as well – it’s a much simpler problem. I can intuit a short leg awfully close to the perfect track, and if you want to work things out with more precision the ideas presented in my blog will squeeze out the last tenth of a percent.

If the forecast didn’t update, there would only be one solution for every race – many boats could make a pretty decent go sailing by feel, while someone with enough ambition could work it out fully by hand. The software guys could just push a button and set some DC. If all three methods were perfectly executed (this decides many short races) the results would be near-identical. I’m pretty sure that with *really* accurate timing you could tell what software someone was using… zero difference in real life.

The fun comes when the changing nature of the weather is taken into account. Every time the weather updates a new “perfect” solution is created, and the old one becomes sub-optimal. On a small shift, a boat that that was “behind” by the old weather can get promoted. On major changes whole races can be flipped upside-down. From this viewpoint, there is little reason to sail the supposedly perfect routed track – it’s guaranteed to be wrong. If you watch some of the best sailors go toe-to-toe (oh for replay) you can see a layer of tactics/strategy at work that makes for most of the game. It can be pretty subtle, but there is constant jockeying for position, gambling when there are decent odds, hedging against loss… It really never makes sense to sail the routed solution. You can’t pass a boat that way and you can’t hold a lead either. There’s a whole lot more racing going on than might appear.

Learning how weather systems behave can have a big impact on how you use routing software. I don’t think that any of the current routers have much in the way of statistical analysis built in – they give a single solution for weather that is assumed to be fixed. Pretty crude. If you can see that a weather event 5 days off is impacting a decision in the next hour or so you need to be pretty sure that it’s a stable/predictable  before you wager too much. A random windhole in the wrong place at the wrong time can disqualify a winning line through some islands for no reason. The software doesn’t know any better. The wind we use is a pretty impressive forecast, and betting *against* the weather rarely works, but there are lots of ways to add value to the routed solution. What are the odds if you sail a little higher or lower than the calculated track? Where does that put you relative to the fleet? Some routed tracks are very risky (though fastest at the time) but going slightly wide is often almost as fast but much less volatile. The unpredictability of the weather is somewhat predictable. Google “ensemble forecast” for some fun reading. How serious to take this?

Long ocean races are particularly interesting due to the lack of accurate long range forecasts. SOL weather only goes out 7 days. It’s far more important to understand what is likely to happen when you get to the trades than what the current model says. There’s a place in all this high-tech stuff for pilot charts.

Depending on the router, identifying options may be particularly difficult. If the router presents the fastest track but there is another wildly different one that is predicted to arrive just a little later you had better take a pretty close look. Even worse are solutions that alternate between two approaches on every update. Think of some of the races we’ve had with competitive splits – the fastest boats are the ones that set a strategy and then look to the router, not the other way around.

There are a few tricks to working with gribs that routing glosses over. Everyone knows that the NOAA data doesn’t match real life perfectly (or at all!) on a small scale, but there are clues “hidden” in the nice smooth weather that are relevant to offshore sailing strategy. The solution needs to be adjusted based on the navigator’s knowledge of how weather works and what is really likely to be there. Shear lines show up as impassable walls, unsettled areas interpret as jumbled low-wind areas where they likely have squalls. If the Navigator is avoiding a 400nm stretch of ocean because the software thinks there is a phantom obstacle there he’s not doing a very good job. The situation in SOL is different in that we sail the actual forecast and that impassable wall really is impassable. It’s somewhat predictable though, and knowing how SOL works can present options that the routing is blind to.

What running routing software does do very well is relieve some of the drudge work of calculating courses. The mechanics of HOW to get from A to B can be handed off, leaving the crucial decision of WHERE B needs to be to the sailor. The “game” that the best routers are playing is not “how to negotiate this shift” but how to set up for the best possible odds vs the fleet. “How to negotiate this shift” is an important lesson that SOL offers, but it’s not a tactical decision.

Routers are very useful for setting DCs, and knowing with some certainty where your boat will be in the morning. They also make snap decisions when you don’t have time for all of the above easy. It might not be the best track, but just doing what the voices tell you won’t lead you too far astray if you’re SOLing while juggling lunches and rushing people out the door in the morning.

Finally – routers are a fantastic way to learn more about sailing and navigation. The absolute biggest advantage that learning to use a router can give is better understanding, even if you never switch it on during an online race. If you like this sort of stuff, you can play for days with different scenarios, see how different boats handle the same weather, watch how the solution evolves over time. Some of the visualisations give you a whole different outlook on the game. Plotting isochrones shows all sorts of information – the weather, polar, obstacles and course are all handily summarized. Time contours plotted backwards from the finish let you assess fleet position. Combined, you can identify areas where potential gains might be made, where it’s safe to deviate from track to try an attack, evaluate risk on laylines… Some software allows you to simultaneously display the fastest track to every point on the course – this highlights the “seams” where there are multiple options, and those are critical areas on the map.

Do you need one to win – absolutely not.

How much difference do they make? – it’s a very useful tool. There’s nothing that the software does that can’t be done by hand, but you can solve in 30s what might take hours. Using the result effectively needs skill.

Disadvantage? – qualified yes? There is a reason that software routing has become a major part of offshore racing. That said, the difference between a well-routed and a good SOTP time is usually far less than the margins of victory while the strategic stuff really adds up quickly. The fleet has boats using identical software that finish very differently, and usually with dozens of places between.

Phew… back to the discussion on SOL.

Polar Hop #1

4 05 2010

Here’s a quick one from today’s practice race. On the downwind leg from Ile d’Aix to Ile Madame, the direct line put you at a twa of 148°. Normally with no shift, the straight line is the fastest, but looking at the polar we can see that 148° is in the middle of a “dent” in the curve.

The black arrow on both the above map and the polar diagram below shows the direct line. We need to avoid that dent to sail the leg as fast as possible, so we “bridge” the gap with the two angles that are tangent on either side. In this case they work out to around 139°. and 167°. We can sail the higher angle until we reach the layline that will take us to the turn on the deeper one, shown by the pink arrows.

How much faster is it? You can find the average speed over and two directions on the polar by connecting the points with a straight line. The yellow line above bridges the “humps” on the polar (but is offset a bit for clarity) you can see that the two-angle strategy gains about a 1/3 of a knot made good. Gain on the leg is around 80 seconds or 0.16 nm!

Fastest route to the finish line

4 05 2010

This situation presented itself during one of the increasingly popular practice races that a dedicated group of SOLers are organising in the time before the official race starts. Races are arranged on the fly, and usually use some interesting courses and are of relatively short duration. Everyone is welcome to join in – it’s a good opportunity to test out setting Delayed Commands, work on boat handling and ask some questions!

In last night’s race, the finish line was defined as the beach just East of the island shown below. The length of the line and the angle of the wind made for an interesting decision at the turn – which angle will get you to the finish fastest? The shortest distance is straight to a point perpendicular to the line, a little ways above where the fleet has gathered for the next race, but sailing lower might give more speed.

One way to approach this problem is to use the steering tool to measure distances and speeds to each end of the line, and do some quick math to find out which end is favoured. (distance is shown with more precision in the upper right corner of the map window, and speed in the lower right of the polar) This works most of the time, but for long lines, the best point might be somewhere in the middle. We can use the VMC concept to pretty accurately pick the fastest angle straight from the polar diagram without any math.

In the screen capture above, I’ve laid in a line defining the finish line and extending a ways beyond the edges of the beach. The beach is angled slightly @184°. The shortest distance is to the point perpendicular to the beach, or a CC of 94° from the boat, and defines our VMC target direction. You can eyeball this angle – use the steering tool to lay in this line and the resulting TWA will be shown on the polar diagram.

The black line on the polar above is the TWA for the shortest distance, and the windcurve we’re on is the black one just outside the red 20kn line. We want to pick the point that is “furthest forward” along that line. If you visualise a line at right angles to the target direction, the point where it touches the windcurve is our fast VMC angle. If you have a small piece of card or tear the corner off a sheet of paper, you can hold it up to the screen and use it like a little set square. In the example, the solution works out to around 93°.

Use the steering tool to set your TWA to your fast angle, and if the predictor hits the beach (or the finish line) enter that course and click “send” 🙂 In this example, the landing spot is marked by the red dot in the first picture.

We can also do the math as a double-check and to see how much we stand to gain: The shortest distance option gives us a speed of 8.36 knots over 4.89 nm, while the second results in a speed of 8.77 knots over 4.98 nm. This gives us times of 35m 6s and 34m 4s. The VMC method gains just over a minute, or  0.15nm – not a lot, but more than enough to decide a race. The top 5 boats finished inside that window last night!

What if your fast VMC angle ends up missing the line? Then you target the pin at that end of the line. This is much more common.

Final Results

23 02 2010

Final results table (I think… will double check calcs) Read the rest of this entry »