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Kedging Cannon
The real key was inventing the windmill-powered winch.
Title text: The real key was inventing the windmill-powered winch.

Explanation

Ambox notice.png This explanation may be incomplete or incorrect: Created by a HEADCANNON. Do NOT delete this tag too soon.

Sailing vessels can navigate upwind through a technique called tacking (or "tacking against the wind") which involves zigzagging across the wind's direction. However, this comic describes a fictional scenario where a ship's captain, unfamiliar with tacking, has developed an alternative method based on kedging (also known as warping).

The basics of kedging are not dissimilar to the comic: a boat affixes a rope or chain to an anchor point (such as a literal anchor) and winches itself closer. Traditional kedging involves deploying an anchor from the vessel, either manually or via a smaller boat, and then winching the ship toward the anchor point using ropes or chains. The anchor points often utilize natural features such as trees or reefs. Kedging is a real historical technique, but has definite limitations compared to tacking, typically reserved for specific situations where conventional sailing methods are impractical, such as in calm waters, during precise maneuvering, or against strong opposing winds or currents. In this comic, the captain has modified this technique by inventing a specialized "kedging cannon" to project the anchor greater distances.

In places with a large depth, an anchor cannot be used, but a so-called sea anchor could solve the problem... somewhat.

The title text indicates that the captain's system has evolved to incorporate a windmill mechanism that harnesses wind power to draw in the kedging rope, which might be intentionally ironic -- given that the captain knows that windmills work, they could presumably have used that knowledge to reinvent tacking. Additionally, this makes the solution even less efficient, given that wind could be used for tacking.

Speed and economic analysis of dual wind-winched kedging cannons compared to tacking

A dual-anchor kedging cannon system for sailing upwind, consisting of:

  • Two kedging cannons firing 16 kg anchors
  • 6-meter diameter windmill powering winch system
  • Dual-winch setup for continuous operation
  • Operating in 15 knot headwind conditions

Vessel specifications:

  • Length: 30 feet (9.1 meters)
  • Displacement: 10,000 lbs (4536 kg)
  • Sail area: 600 sq ft (55.7 m²)
  • Wetted surface: 40 m²
  • Frontal area: 8 m²
Wind power generation

Available wind power is given by: P = ½ρAv³η where:

  • ρ = 1.225 kg/m³ (air density)
  • A = π(D/2)² = 28.3 m² (windmill area)
  • v = 7.72 m/s (wind speed)
  • η = 0.245 (combined efficiency)

This yields 1.95 kW of usable power.

Drag forces

Total drag combines water and air resistance: Fdrag = Fwater + Fwind where:

  • Fwater = ½ρwCdAwv²
  • Fwind = ½ρaCaAfv²

Using:

  • Water density (ρw) = 1025 kg/m³
  • Hull drag coefficient (Cd) = 0.04
  • Wetted area (Aw) = 40 m²
  • Air density (ρa) = 1.225 kg/m³
  • Air drag coefficient (Ca) = 0.8
  • Frontal area (Af) = 8 m²

Total drag force = 1053.4 N

Anchor ballistics

For 300 m range with 45° launch angle:

  • Required velocity = 54.7 m/s
  • Launch energy = 23.7 kJ
  • Black powder energy per shot = 680.4 kJ
  • Launch efficiency = 3.5%
System performance
  • Winch speed = 3.60 knots
  • Cycle time = 194.7 seconds
  • Effective speed = 3.04 knots
  • Compared to tacking speed = 4.95 knots
  • Speed ratio (kedging/tacking) = 0.61
Economic analysis
  • Shots needed per nautical mile: 6.1
  • Black powder cost per shot: $10 (0.5 lbs @ $20/lb)
  • Cost per nautical mile: $60.76
  • Powder consumption: 9.2 lbs/hour
  • Operating cost: $184.90/hour

Example 100 nmi journey:

  • Total powder cost: $6,076.12
  • Journey time: 32.9 hours
Conclusion

The dual-anchor kedging cannon system is both slower and significantly more expensive than traditional tacking:

Speed disadvantage:

  • Achieves only 61% of tacking speed
  • 100 nmi journey takes 32.9 hours vs 20.2 hours tacking

Economic disadvantage:

  • High powder costs ($60.76 per nautical mile)
  • Requires significant powder storage (303 lbs for 100 nmi journey)
  • Additional wear and tear on mechanical systems

Key limiting factors:

  • Limited wind power available (1.95 kW from 6 m windmill)
  • High drag forces (1053.4 N total)
  • Poor ballistic efficiency (3.5% of powder energy converts to useful launch)
  • Long cycle times due to realistic winching speeds

The system could potentially be improved by:

  • Larger windmill (though practical size limits on boats)
  • More aerodynamic anchor design
  • More efficient powder-to-launch energy conversion
  • Reduced transfer time between anchors

Therefore, given both the energy constraints and economic factors, traditional tacking remains far more practical for upwind progress. The key insight is that while the kedging cannon seems to "cheat" the wind by going straight upwind, it actually requires converting wind energy to mechanical work less efficiently than a well-designed sail plan, while also consuming expensive gunpowder. The indirect path of tacking makes better use of the available wind force with no consumable costs.

Transcript

[A two-masted sailing ship with its sails up is floating on a calm sea with tiny waves. Two tiny figures can be seen at the ship's bow. One of them is speaking. In the next panel it becomes clear this is the captain.]
Captain: I hope someday someone invents a way to sail upwind.
Captain: Using the kedging cannon just wastes so much gunpowder.
[Close-up on the deck of the ship, showing two persons behind the taffrail. Cueball is standing behind the ship's captain and talking to him. The captain is wearing a black bicorne navy hat and aiming a cannon containing an anchor forward. Chains are draped from the cannon.]
Cueball: The what?
Cueball: Wait, do you not know how to sail upwind? Is that why your ship takes forever to--
Captain: Stand by...Fire!
[Distant shot showing the anchor and its chain being launched out in front of the ship, towards the right of the panel. Cueball and the Captain can still be seen behind the cannon. The cannon has exhaust fumes coming out in front and the sound it makes is indicated:]
Cannon: Boom
[Same setting but the anchor is now under water and the chain has become taut as the ship is dragged forward to the right. Movement lines behind the ship indicated its progress and it is also further into the frame than the previous panel. The movement is caused by pulling the chain back in on the ship. This produces a series of sounds:]
Dragging chain: Click click click


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