No-tilt sail


No-tilt sail – the movie

A No-Tilt Sail is specially designed so it does not make the ship tilt, regardless of the size of the sail, or the direction or strength of the wind.

Abstract
Idea
Sail size vs. fuel savings
Is tilt a serious problem?
Formal status

Abstract

While engine-powered ships burn tremendous amounts of hydrocarbon fuel, wind may still offer those vessels a supplementary method of propulsion. However, sails not only push a ship forward: they can also tilt it. This is usually unacceptable, as it may damage the cargo. In our design, the sail does not make the ship tilt, regardless of the size of the sail. This is achieved by a design mounting the sail on the windward side, tilted forward and to the leeward side.

Idea

Figure 1. No-tilt sail
Figure 1. A ship with no-tilt sail from three perspectives
Figure 2. Element of a No-Tilt Sail. The sail is drawn transparent

Elements of a No-Tilt Sail visible in the figures.
H – ship’s hull
S – sail
W – wind
F – the resultant force of the wind acting on the ship
A – forward, lower corner of the sail
B – top sail corner
C – rear sail corner
4 – mast
5 – boom
45 – top tenant
6L, 6R – left and right sheets of the sail
7L, 7R – left and right boom sheets
8L, 8R – left and right attachment point for 6L, 6R sheets to the hull
9L / R – left and right attachment point for 7L, 7R sheets to the hull
10 – additional anchor point

The sail is on the windward side, tilted forward and to the leeward side. The figure below depicts the resultant force of the wind acting on the ship, demonstrating that the wind’s force does not tilt the ship. Insted, it pushes the ship forward and presses it into the water, thereby acting as a ballast.

Figure 3. The resultant force (F) acting on the ship

Figure 4 below demonstrates setting the sail to the wind.

Figure 1
Figure 4. Setting the sail to the wind

In the figures above, the sail is rather short to clearly demonstrate its ability to not cause the tilt at all. However, if the tilt is admissible, then our sail can be just larger than a typical and cause the same tilt. Also, the boom can act as a ballast on the windward side. In this way, a typical sailboat can have larger sails and be faster thank to the No-Tilt Sail.

Analysis: sail size vs. propulsion and fuel savings

Here we consider a realistic large cargo ship and analyze how large sail would be required to give this ship a propulsion equivalent to that given by the engine. Then, we conclude how a sail of any size reduces fuel consumption of the ship.

Assumptions about the ship:
– fuel consumption: 100 tons/day (typical for very large container ships)
– fuel energy density: 43 MJ/kg (typical for diesel)
– fuel energy to push efficiency: 33% (good for modern ship propulsion)
– cruising speed: 24 knots = 12.3 m/s (typical for large cargo ships)

Consequently:
– the engine pushes the ship with a force of 1.35 MN (137 tons).

Assumption about the wind:
– air speed perpendicular to the sail = 10 m/s, this gives a pressure of 60 Pa (the global average 10-m wind speed over the ocean is 6.64 m/s, which gives a pressure of 25 Pa).

The size of the sail that would be pushed with the force equivalent to the force produced by the engine = 22500 sq. meters. For instance, this could be a rectangular triangle with a height and a width of 212 meters. For comparison: The length limit for ships traveling through the Panama Canal is 1200 ft = 366 m.

Conclusions: In moderately favourable wind conditions each 225 m2 of sail reduces fuel consumption by 1 ton a day.

Is tilt a serious problem?

When we consider installing sails on a cargo ship, we may think that its tilting/heeling is not a serious problem, because such ships are very heavy. This intuition is wrong. However heavy the ship is, it needs proportionally high force to push it forward. If this force is produced by a typical sail, this sail also produces a proportional force that pushes the ship to the side. The latter force operates above the center of the mass of the ship, thereby tilting the ship. Consequently, regardless of the size and weight of the ship, the tilt problem is the same. This problem only ceases to exist when the sail is so small that it only marginally contributes to the propulsion of the ship.

Figure 5. Tilting sailboat

Formal status

A patent for this invention is pending.