Current tactics under the coast
There is more tidal current further out to sea (in deeper water) than close to the beach. Slack starts close to the coast. When the current is against us, we prefer to sail close to the coast. When the current is with us, we opt for deep water further out to sea. See, for example, the illustration below.
In estuaries and channels, most of the current is always in the middle of the channel or in the deep outer bends.
Tidal current turns on 1 course
If, for example, we want to sail from IJmuiden to England and we can sail on a beam reach course, it is better not to correct for current, because we do not necessarily have to stay on the ground course. We prefer to keep as much as possible to a fixed true water track and thus also a fixed course on the compass and thus let the current move us, for example, 6 hours north and then 6 hours south again. The ground course then does not remain a straight line, but the path through the water does and is therefore the shortest path. And after all, we sail through the water, not over the ground. Due to wind farms, shallows, recommended crossings for traffic separation schemes, this tactic is not always possible, but try to take advantage of it when you can.
wind from current
Apparent wind is the result of true wind, speed wind and current wind. Current wind is straight against the current and is as string as the current rate. On a crossing to England where we have to beat against the wind, we always keep current at leeward. That way the apparent wind comes in with a bigger angle and is stronger so the VMG (that is the speed straight towards our target) will be higher. The course high to windward is also more towards our target and we stay close to the rumbline. When the current turns we tack.
If we expect the wind to turn due to the movement of a high or low pressure area, we always make the turn first in the direction to which the wind will turn.
Oscillating wind shift
Oscillating wind shifts are rhythmic wind shifts. If, when beating against the wind and the wind turns to our disadvantage, increasing the angle to our target, we call it a header, the opposite a lift. On open water, we can see these wind shifts on our compass. We tack at a header and take advantage of any lift.
Wind under clouds
Cumulus clouds are formed by rising air. The wind therefore blows towards the cumulus cloud (counterclockwise, as in a low-pressure area). The air rises, cools and condenses. But once the cumulus cloud is formed and develops further and also gets higher, this reverses. This is because once developed into a high cloud, a shadow is created below the cumulus cloud, causing cooling and thus falling air right there again. With high, developed cumulus clouds, the wind actually blows away from the centre again.
Gradient wind
The high-altitude gradient wind runs parallel to the isobars and is much stronger than the surface wind. Due to instability, the gradient wind comes down, this produces gusts and the wind veers. The surface wind is the wind at a height of 10 metres. The rougher the surface the more the wind shrinks. So at sea, the wind veers and on land the wind backs.
On Starboard tack through a squall
In the squall, the gradient wind comes down so the wind veers and becomes gusty. So when beating, we always sail over starboard tack into the squall. Then the wind shrinks back to the normal surface wind.
Convergence and divergence
Convergence and divergence occur because the wind at sea veers compared to wind on land. Convergence means the wind is compressed along the coast and thus increases. Divergence means that the wind splits apart along the coastal strip, leading to decrease in wind along the coastal strip.
The image below shows an island with convergence on the east side and divergence on the west side.
windshift
This effect occurs because the wind on the water veers compared to on land.
Another example you may encounter is when you want to enter a harbour on a windward shore or if you want to round a buoy during a race. In the picture, you can see that you have to take into account that the wind will back just below the shore.
Coastal winds
Coastal winds consist of sea breezes during the day and land breezes at night. These are created by the temperature difference between land and sea. on a sunny day, a thermal layer forms over the beach, the thermals create a kind of underpressure that will be supplemented by the sea breeze. These winds sometimes extend several miles out to sea (the more stable the further) and is several Beauforts strong. These coastal winds may also cause winds (caused by a high and low pressure area) to change along the coast in both strength and direction.
Land effects
Land effects such as kaape effects and funnel effects, for example between islands, can strongly influence winds and also currents locally. This can be taken advantage of or you can be hugely inconvenienced.
Questions & Answers
Question 1: You sail from Scheveningen to IJmuiden. The wind is northwest 3 bft. The current is southwest. Are you going to sail close to the coast or are you looking for the deep water?
a: Further out to sea
b: Close to the coast
Question 2: Where do you expect the slack to start first, under the coast or in deep water?
a: Further out to sea
b: Close to the coast
Question 3: On a trip from The Netherlands to the UK, we sail a compass course of 270 degrees. The current is north. The apparent wind east-northeast. Do you expect the wind to veer or back after the slack?
a: Back
b: Remains the same
c: Veer
Question 4: You are crossing from Hoorn to Lelystad against an easterly wind. On port tack, you sail a compass course of 135 degrees. After a few minutes, you will see that the compass course has become 145 degrees. Is this a header or a lift and what do you do?
a: Header, tack
b: Lift, keep course
c: Header, keep course
Question 5: You are sailing from IJmuiden to Scheveningen. The wind a few miles offshore at sea is south-southwest. Will the wind back or veer close to the coast and so what do you do?
a: Stays close to the coast
b: You are heading further away from the coast
Question 6: You have your back in the wind and the shore on the left, is there divergence or convergence?
a: Divergence
b: Convergence
Question 7: In the summer you sail in front of the Maas estuary, the river water is relatively warm. What will happen to the offshore wind in front of the Maas estuary?
a: Becomes stable
b: Becomes unstable
c: Remains the same
Question 8: Two boats are cruising towards a harbour. They are now downwind over on port tack. A squall is coming. Only 1 boat just tacks in the squall and tacks again after the squall. Which boat will be in port first?
a: The boat that went on starboard tack through the squall.
b: at the same time.
c: the boat that went on port tack through the squall.
Question 9: In the summer you make a night trip from IJmuiden to Scheveningen. It is very bright, so it cools down considerably at night. The wind is west-northwest and is weak. Is it wise to sail just below the coast or a few miles off the coast?
a: There is more wind further out at sea
b: There is more wind close to the coast
Question 10: If you are cruising against a north wind and there is a westerly current, over which bow is the VMG WIND the fastest?
a: On starboard tack
b: On port tack
