Sunday, 17 May 2015

VOR Leg 7 - T-0 - How hairy will it be?

Significant change?

The early part of Leg 7's outlook is quite different than the last report, with the L developing over NE now moving offshore and away from the coast faster than the fleet can. Therefore a change in route optimisations favouring again the shorter N option and staying as close as possible to the GC route.

Runs, as always, done with www.expeditionmarine.com, and with GFS 0.25 and www.tidetech.org currents



The route suggests that through Monday the fleet will be punching into a solid NE flow of winds making their way down from Newfoundland - nice and uncomfortable and probably quite cold.
00z Mon

The trick is going to be trying to stay in the NE winds ahead of the region of H pressure coming in from the NW.
00z Tue

And by Weds, nice light airs and shortest distance sailing
00z Wed

Currents

A few trails from the Gulf Stream to play with, bright red is 2-3 kts, not insignificant, will possibly provide some lumps and bumps with wind over tide.


TWS Distribution

This shows the winds across the route Isochronically from the start, and early indications with the Az H being quite well established bringing a good blow for the fleet coming into Lisbon.

Sensitivities

Testing the route with % changes in polar and TWS, if the TWS was at 110% of forecast, or you could sail at 110% of your polar, the S route shown comes into play as you can get to winds associated with the L system
Polar %

TWS %

Forecast accuracy

Not having studied the Ensemble member variances, running the route through the GFS Ensemble members shows that the forecast has some uncertainties - would be interesting to analyse the EC and other models to see what variances/differences are present in the models.
Ensemble runs

Wind Distribution

Not looking as much fun as the previous run!


Thursday, 14 May 2015

VOR leg 7 preview - chasing the Low

Leg 7 a sprint, with an early blast?

Looking at the leg ahead starting at 18z Sunday 17th, the fleet will primarily be focused on hooking into the back of a L moving slowly E, and will eventually make their way S of it before tackling potential H systems for the 2nd 2/3 of the leg.

The overall route, with 0.25 deg GFS winds, and www.tidetech.org currents.
Of note is that with these models, the ice limits will not feature in the route.

18 hours post start

36 hours post start

 54 hours post start

Gulf stream currents are significant, but overridden by need to get SE for the winds related to the L

How sensitive are the routes?

A Pol % analysis (sailing slower or faster than polars) shows that the route is not remarkably different in shape, bar the 110% sailing a shorter course.

A TWS analysis (ramping up and down the forecast TWS) shows very little variance in the shape of the route.

TWS shading shows the first 1/4 of the leg in the most pressure, and thereafter moderating bar one section near the Azores. It is quite apparent that the first section id chasing the pressure.

Route statistics - bar the D&P show around the bay before being set free, nothing forward of the beam - wish all transatlantic trips looked like this!:

Sunday, 29 March 2015

VOR 2903 - Let it rip!

800nm to the Horn, and will be one hell of a ride...

Looking at the 0040z sched, there is nothing in it, with the exception of SCA1 who have dropped off the train, and may be punished for this with their slightly N and W position as the front rolls in.
Nothing in it
ADOR and TBRU are registering as 12nm DTL, however are set up to the S and W of the leaders and as the routing results suggest this is negligible in terms of time to the mark at CH.

0040z run, GFS model

Point it at the mark and let it rip



The rest of this portion of the leg is going to be all about sailing minimum miles (with the exception of SCA1).

The first boat to Cape Horn is going to be the one who can keep their foot down and not trip over it as the VO65 appears prone to do.

One wipeout at 20kt boatspeed is a loss of between 10 and 20nm.

Keeping the rig pointing at the sky...

Chinese Gybes were a hot topic last week, and this week will possibly be even hotter. However the rest of the leg looks like sailing hot angles rather than VMG mode which may be better for keeping the wet bits under the boat.

The dynamics of these boats is very different to a conventional yacht. The VO65 keel pins are slightly off axis (4deg from memory) - so at full cant the leading edge of the keel is tilted up. This is a performance enhancer - reducing displacement (think foiling but only about 1% of the way there). A side effect is reduced righting moment.

Rob G's comments after the MAPF wipeout was it happened ploughing into the back of a wave. Imagine the scenario with surfing down a wave, the rapid deceleration at the back of the next one...and a keel canted out to weather

  • The boat parks in the wave and decelerates
  • A ~6T bulb canted out to weather wants to keep going - spearing the boat off to leeward
  • Apparent wind speed spikes & angles changes instantly
  • Righting moment and displacement change due to the canted keel 'tilt'
No bloody wonder they are hard to hang on to. Wouldn't help if the rudders are too small or not very 'grippy' - not suggesting they are...

Weather

The boats have a cold front approaching from the W. GFS model suggesting sustained 26-30 kt. My bet is this will be 30-40, possibly +20% with gusts, and if the front itself catches up then potential for a lot, lot more.

However, doubt the boats will be going any faster in 40 than in 30. In fact maybe slower.

No accounting anywhere here for waves/sea state etc...

Here is a run, with the cold front evident in the second half with the predicted rain highlighted.

Thursday, 26 March 2015

VOR 2603 - a whole lot of ocean

Middle of nowhere, but nowhere to go

The fleet is banging off of the edge of the ice exclusion zone which must be maddening for the teams, however they will be released soon from this virtual fence...but will be interesting to see where they go from here.

Routing over the last couple of days has suggested that a NE route is fastest to the Horn, however not by a great deal.

1840z pos, GFS

The SCA1 route in timing terms gets them into CH with pretty much the same time deficit as they currently have - however sail fewer miles. Probably more maddening miles though sailing 1000nm down the edge of the exclusion zone.

For the leaders, the SE route is only 3hr slower in theory than the optimal NE route. I expect to see the fleet juggle themselves somewhere in the middle of the two options, playing it safe and conservative.

Results to CH

Roller coaster ride

The two options are driven by quite different systems. NE to tap into the back of a L system, SE to hook into a cold front.



Running hard

Route output shows a fun ride for all...
TWS down, TWA across. Data in hours.

Wednesday, 18 March 2015

Expedition Seminar

I will be hosting a seminar in Lymington, focused on the features and functions of Expedition Navigation Software.

Download information here.





Monday, 16 March 2015

VOR Leg 5 - T-2 (again)...Should I stay or Should I go now?

Big brother meddling

So the Start of Leg 5 has been shifted out bit by bit. Initially prudent I believe with the uncertainty of the impact that STC PAM could have had on the fleet. I doubt a single person would deny that it was a good idea to wait and see how it panned out since a scenario could have arisen whereby the boats had no escape route.

Am sure there would have been a full consensus amongst the competitors that this was the right thing to do

However, IMHO, this power (that of the RC) has been taken too far by delaying to Weds (NZT). Now the fleet could potentially face what may be boat breaking conditions, without much wind to speak of.

As soon as the centre of PAM had passed the approx Lat of Akl or at least East Cape, the boats would have plenty of sea room to be the masters of their own destiny. Get N and diverge from the system for less winds, or charge on in and hang on for dear life. At the sole discretion of the skippers.
Findamental rules of the RRS


PAM, where has she gone?

Screen shots below show a start point at Coromandel, for ease of running the route. This is ~45nm from Akl, so even ignoring the dog and pony show loops around the harbour the boats would take a while to get to the 'start' of my routing.

Start -24hr...nice breeze out of AKL

Start -12hr...still not bad out of AKL

Start...mmmm...bugger, missed the train.

Start +12. Still sitting at the station. 

What does the rest of the leg hold?

Not entirely clear, but the navigators will have their work cut out this leg, with the first corner some 4500nm away.

At the preset times for the weather files downloads, the send/receive button will be getting pretty hot, the guys willing the files down over the FB units. Anyone with comms issues on this leg will be at a serious disadvantage.

High pressure, MSLP or BP?

Out the back of PAM an expansive H region establishes. Going to have to push hard, very hard to try and stay in touch with PAM. Anyone who gets across the H well and manages to stay on the back of PAM will take off. Get dropped, and you are toast.

The H could be a big part of this leg

What will the future hold?

Reasonably uncertain for the 2nd 2/3 of the leg. Don't wear out those send/receive buttons boys.

GFS (red) and GEM (blue) Ensemble plot 7 days from now

Whole route...

Not sure the image below is of much value. Two wx models disagree. Will just have to wait and see how it plans out. Lets just hope the AIS tether gets broken early and se can see some more freestyle Ocean Racing Navigation...

The GFS (American) model - might need to check the sunscreen stocks. GEM (Canadian) model, not as afraid if ice.

Tuesday, 10 March 2015

VOR Leg 5 - T-5. This is was what was in the brochure

Record breaking or boat breaking?

A very quick review of Leg 5 weather outlook and the fleet could be in for one hell of a ride...

TC PAM coming into the mix so early on in the leg will sort the men from the boys. 

Expedition run GFS

Quickly looking at the transit across the top of PAM, one 24hr period reveals a potential 675nm run from point to point - not distance covered over the ground but a straight line between two points.

This is not necessarily achievable as the polar is suggesting sustained speeds of 25-35kt, no account for crashes, there is a gybe in the mix and Sig wave height at the position of the screenshot below is over 9m.
Transiting PAM, a record?
Significant Wave Height

Statistics

~60% of the leg to the Horn is sub 25kt, but what is more interesting is that ~60% of the leg is at TWA125 or wider. Thats what you sign up for in this race!


Testing the routing

Re running the opt route with a spread of TWS and Polar % reveals the dominant effect of PAM in the first half of the leg, the second half is to be fair too far out to draw any conclusions.

Route options with a spread of TWS % adjustments. 



Route options with a spread of Polar % adjustments



Finally, what impact on routing has the Ice Limit had?

The Ice limit looks like a get out of jail free card, but limits the routing options. With the limit in place the fleet is 'forced' to go over the top of PAM. Without the limits, fastest route is S, a long way S...but only a couple of hours in delta at the Horn.

Even without the lice limit, I know which way I'd go...