In navigation, the role of the winds is very crucial. During the Age of Sail, which lasted almost 400 years, wind forces served as the primary means to power vessels, ranging from commercial to military. Over the years, though the wind action in sailing vessels as the basis for propulsion became supplanted by motorized propulsive systems, their effect remains relevant in terms of various aspects ranging from maneuvering and seakeeping behavior to resistance characteristics, according to Marine Insight.
Understanding Winds and Wind Action
In the context of wind action, there is always an associated direction of wind flow. For instance, we say that it is a northern wind when the wind flows from the geographic north, and is an eastern wind, when the wind blows from the east side.
In practical real-world scenarios, at any particular location in space and time, wind mostly flows from random directions in varying degrees, thanks to the complex interplay of meteorological and physical factors, and the component of the wind force vector that has the highest intensity is mostly felt.
Thus, when we say that there is a ‘nice breeze blowing from the south,’ the component of wind forces wafting from the southern direction is most prevalent, whereas other wind force vectors are present in lesser magnitude.
Windward and Leeward
The understanding of this is analogous to that of upstream and downstream. If a body is floating in a direction same as the water flow, it is said to be moving in a downstream direction, and if it is floating in a direction opposite to that of the water flow, it is said to be moving upstream.
On similar lines, when we move against the direction of the wind, we are said to be moving in an upwind direction, and when we are moving in the same direction as that of the wind, we are moving in a downwind direction.
In vessels, the side facing the direction of wind flow, or more accurately, the direction from where the wind originates is known as the windward side, and the other side that faces away from the wind action is known as leeward.
For instance, if a vessel is going in a north-south direction towards the north, and a gust of sea wind is blowing from the east, the starboard side of the vessel is the windward side, and the portside is the leeward side.
However, consider another vessel heading towards the south on the same route. For that vessel, the port side is the windward and the starboard side is the leeward.
Similarly, now consider that for a vessel, a gust of wind blows from the front side or against the direction of the vessel’s forward path. In this case, the bow region of the vessel is known as the windward and the aft region as the leeward.
Hence, if you stand on the main deck right in front, against the rails and above the prow region, you are essentially on the windward side, and if another person stands in the aftmost region facing the propeller wake of the vessel behind, he or she is well-positioned leeward.
Vessel and landmass
An interesting set of nomenclatures arises when a vessel is in the vicinity of a landmass or shore, based entirely on the physics of reference points. When we talk about a vessel close to a landmass, irrespective of the current time-varying weather conditions, the windward side of the vessel is always historically the side facing the sea or away from the shore.
The other side of the vessel facing the land is the leeward side. Now, to someone on the land at any point on the shore from which the vessel can be viewed, he or she is on the windward side as this side faces the sea. However, to someone on the vessel, the same person on the land is standing on the lee shore side as his position lies in the leeward side quadrant of the vessel’s point of reference!
Things get even more interesting and complicated when the situation in question is an island! Assuming the island as a circular mass for our simplicity, this nomenclature system then becomes partly dependent on the direction of the wind at that instant.
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Source: Marine Insight
