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*What is a persistent shift?*

Anyone who has read race the sailing tactics manuals for a windward leg

will understand the significance of the statement, "It's a persistent

shift". Broadly it means that when you are on a tack sailing upwind to a

windward mark, and you experience a header, rather than tack on the header,

it can often pay to hang on as you get headed and make the last tack into

your windward mark at the last moment when you find the layline.

This is all fine in practice on a windward leeward inshore race with a leg

of 1.5 miles and you can see everything around you. It is a different

matter and much harder to judge when you have 300 miles to the windward

mark and you need to decide to tack with 50 miles still to go.

Classes 1-3 boats are currently reaching up the leg to Muckle Flugga in WSW

winds (15-25 knots) and as I write this they have 350 to 400 miles still to

go to get there. On current performance the Class 2 boats will round

Muckle Flugga around 2200 on Thursday 14th August (A level results day).

Class 1 will be a bit ahead and class 3 will be a bit behind.

*Weather Forecast*

The weather patterns remain dominated by the residue of Bertha. The eye of

the low pressure is currently over Shetland at 60 23.00N and 001 01.00W.

As predicted yesterday this low pressure now stops moving North, it

changes direction and starts to head SE by

- 1000 on Wednesday it will be around 58 40.7N and 000 19.00E

- 2000 on Wednesday it goes E to 58 08.0N and 002 51.00E (and has a

large area of very light variable wind to the North and E of the centre of

the low

- By 0400 on Thursday the centre of the low is just off south coast of

Norway 57 55.00N 005 25.00E

This winds that classes 1-3 can expect are broadly that it will stay above

20 knots WSW tonight until around Midday Wednesday. Then it will veer a

bit to 265 from 0800 and then drop to 15 knots from Midday and start

veering to 350 and dropping to 10 knots by 2100 on Wednesday. then from

0800 on Thursday it will stay due North but will build again to 20 knots.

It even builds to 25 knots and veers a bit further to 010 as the boats

approach Muckle Flugga around 2200 on Thursday.

*What happened today?*

At the moment the boats are on a reach. As this low pressure moves SSE the

wind will Veer to the NW and then to the N turning this leg up to Muckle

Flugga into a beat. The fast boats have been able to take advantage of the

winds to the north of the low pressure and went around the top of it to

get favourable winds on the approach to Muckle Flugga. The Class 1-3 boats

will be too late to do this, they will have to beat their way up to the

windward mark. But as I said, it looks like there will be a persistent

shift that will start to affect them from Midday Wednesday as the low moves

SSE and then E.

*What will the navigators and skippers be thinking about?*

This suggests that navigators will be focused on making as rapid progress

to Shetland as they can tonight by sailing at maximum speed directly to the

windward mark and covering as much distance as possible before they get

headed by the veering wind much later on Wednesday. As this header kicks

in they will be slowed down. But if the weather forecast is right and this

shift is a persistent shift will they continue to point their boats at the

windward mark or will they tack on the header. So the question will be

"when to tack".

Now the sail up wind becomes a standard windward leg. The winning boat

will be the one that judges the tacks right. If the wind delivers a

persistent shift from WSW to N then sailing into the header on port and

waiting to tack onto starboard only when it is clearly the making tack

seems like the conventional option. Anything else is quite a gamble, but

they may see things on the water that suggest alternatives. But tacticians

know you should take the pain early on in a persistent shift. they also

know you cannot be sure the shift is a persistent one, so it is a tricky

judgement.

So I am sure the navigators will be watching other boats wherever possible

to see what they do as well. The most important thing in a race is to

remember you are not racing the wind, you are racing the other boats, the

relative position to other boats matters.

They will also be watching the weather forecasts to see if this persistent

shift will happen or will it change and lead to a different strategy.

More on this persistent shift tomorrow as the weather models get updated

--

Kind regards

Chris Radford

http://chrisradfordnav.wordpress.com/

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