Cowes Week navigation tips part 2

Jim Saltonstall gives his views on the wind and tidal charactertistics of the central Solent area

Solent central - north
Wind Direction

340-040 degrees: With the wind coming from the northern sector it is blowing over relatively low land. But it is still quite shifty and, as with any offshore wind, the closer you get to the land, the more unstable in both velocity and direction it becomes. It's important to get a fix on how big these shifts are on different areas of the race course. In lighter winds, the shifts can be as much as 20 degrees, maybe 10-15 in the mid-to-upper wind range. In contrast, up near the windward mark under the shoreline, the shifts in the light winds can be as much as 30-to-40 degrees, and in the mid-to-upper wind range 20 degrees. So get a feel for the numbers on the compass and the size of the oscillations. If the windward mark is within half a mile of the shore, look out for more lifts on port tack, during your final approach, as the wind veers to the right as it leaves the land to come onto the water.

040-110 degrees: As the wind is leaving the northern shoreline at a tangent, it normally pays to go left up the beat for the wind. The mainland shore has the convergent breeze. It should provide both more pressure and a starboard tack header as you approach the land, with the corresponding port tack lift as you sail away.

110-140 degrees: When the wind is in the south-east sector, it pays to go left up the beat for the wind, as there is definitely more pressure on the port side of the course due to the wind convergence.

140-220 degrees: The breeze is blowing off the Isle of Wight, and how steady it is will depend on how far you are away from the island. The River Medina will usually try to funnel the wind down its river valley. So if it's blowing from the south-east then expect a more southerly wind to be blowing down the river, and then fanning out into the area off Cowes harbour entrance. This shouldn't affect the area to the north too much.

220-250 degrees: The wind is now being channelled down the western Solent. There is a point effect off Cowes, the wind veering as it wraps around Egypt Point. This should only affect the course in a very stable breeze, when the wind bend may still be seen some distance downwind. In these conditions you should watch for a right hand shift as you head south and upwind.

250-310 degrees: The wind is now blowing from the land and water to the east of the course. This is the trickiest direction for this area of the race course. Generally you can expect the strongest wind to be blowing straight down Southampton Water, as the gradient will want to line up with this channel. The south shore of Southampton Water is also a convergent wind zone, while the northern shoreline is a divergent wind zone. The result is that you can expect to find stronger breeze offshore in this area, at least until you come under the effect of the shore between Calshot and Stansore Point to the south-west. The wind close to this shore is light and horribly shifty - but generally you can expect it to back significantly (from the effect of the land) as you go further south down this shore. The practical result of this is that the stronger right hand puffs from Southampton Water, and the softer left-hand puffs from the land often take it in turns to dominate on this piece of water - keep your eyes peeled! If the course is further away from this shore, east of the Brambles Bank, then you can expect the stronger north-westerly wind coming out of Southampton Water to dominate most of the time. But you can still expect it to be shifty, and in a dangerous sweeping generalisation - the further south you are, the more left-hand-shifted wind you will see.

310-340 degrees: In this sector the wind is more settled as it blows down Southampton Water. Not as shifty as for the above sector, but you can still expect to find better wind further offshore. This is again due to the convergence zone on the west shoreline of Southampton Water, and the divergence zone on the eastern side. Again, there is an unpleasantly light and shifty zone up under the Calshot-to-Stansore Point shoreline.


Sea Breeze

The central Solent is not renowned for its sea breeze, as there is often a fight between the thermal wind trying to come up the eastern Solent, and the sea breeze coming up the western Solent. This can often leave nothing much in the middle, from Cowes to Hill Head. Most Solent sailors will have spent a frustrating hour or even a day, sitting watching spinnakers coming towards them from the west and east - but with no breeze in the middle. If either of the two winds is going to win, it's normally the south-westerly sea breeze blowing down the western Solent. The reason being that this is the main sea breeze direction for the whole of the south coast. And, normally (if there is such a thing) this will eventually over-ride the more localized south-easterly sea breeze in the eastern Solent.

The best conditions for a strong south-westerly sea breeze setting up are the same as for the rest of the south coast. We're looking for a light north-westerly, or no gradient wind, and the land getting warmer than the water. The signs are the sky clearing as you look towards the entrance to the western Solent, and the development of cumulus cloud over the mainland. The sea breeze almost always rolls down the western Solent, arriving in a line from 220-250 degrees. When it fills in properly, it can blow plenty hard too, pushing up towards 20 knots. There is not much rotation with the sun however, as the wind is channelled down the western Solent towards this race area.

We shouldn’t ignore the impact of Southampton Water and the Hamble River either. Both these areas of water can produce very localized sea breeze effects. If the day is a good one for the south-westerly sea breeze, they will quickly be over-ridden by it. But if the main sea breeze doesn’t fill in, then these smaller local winds can last all day. This is a tricky area for thermal winds, because of the complex lay-out of land and water. There is a great deal to be said for keeping your eyes peeled in all directions to see what’s coming your way, or happening on the other side of the race course.

Tide

As with the western Solent, the tide is the all-important factor, playing a crucial role in our race strategy plans. As with our advice for the other Solent areas, we can't recommend strongly enough the various tidal guides and books listed. The broad outline is that there is a double high water in Southampton, the second high being one hour after the first. The effect is a prolonged period of 'high water stand'. The flood tide sweeps the north race area in a clockwise direction heading north-north-east past the Bramble bank, then swinging east to run south-east along the Hill Head and Lee-on-Solent shoreline. The ebb tide runs anticlockwise through the race area, and is met by the outgoing tide coming down Southampton water. These two flows meet near the north-west corner of the northern race area, and it's possible to see a tide line on the surface that indicates this coming together. An often ignored tidal effect is in the North Channel, where there is deeper water and slightly stronger tide.