DESCRIPTION OF TIG RIG SAIL SYSTEM
The Tig Rig (TR) sail system consists of square rigged sails each set in self contained units attached to the sides of existing sea going vessels. TRs are deployed in arrays along the sides of the hull. The drawings show the design installed on a Green Dolphin 575 Handmax (GD 575). This requires 9 units per side and a bow unit to total 19.
The TR is a roller blind design of sail (in this description 16m wide x 15m high) which can reef from full up to full down in increments of 10ths of sail drop. The unit has a mast that can rotate and be fixed in position through 360o. In the schematic example on the front cover the TRs are set at the angle of 115o to the wind. Both the reefing and the angle of the mast can be controlled through control cables, cogs and worm screws in three ways:
- centrally/electronically from the bridge
- by an operator at the unit electronically
- by an operator at the unit purely manually
However overriding all these controls the TR units have automatic mechanical safety devices for automated reefing and automated mast release. These mechanical safety overrides prevent damage to ship, mast or sail through excessive wind however sudden.
The units are mounted at set mounting points around the hull but the mountings are interconnected by rails which run all around the ship. Along the side of the hull the top rails are flush with the deck edge and the bottom rails protrude at most 250m (9”) and so are easily fendered/yokohama’d. The rails allow the units to be rolled around the ship and out of the way for regular dockside operations in port. This operation is very common sense, low tech and easy for the crew to learn. Dockside clearance on a ship this size (190m long) should take two crew members at most half an hour. It is also straightforward to get the units out of the way on both sides for passage through Panama and Suez canals.
Wind tunnel tests were conducted on a 1:150 scale model in Kiel, Germany by Prof Kai Graf. The raw data was then used to produce routing analysis by Rogier Eggers of Marin, the Dutch National Maritime Institute for N Atlantic and N Pacific routes in both directions for the ship travelling at 12 knots (see below). These both gave average thrust savings of 8%. These thrust savings rise by 3% for every knot decrease in sailing speed.
The top row of MEPC 62/INF.34 results are the internationally agreed global wind probability that should be used for assessing wind assisted devices for EEDI savings. The figures are smaller than the prime northern ocean routes that were done but at 4% thrust savings at 12 knots they compare favourably to the sort of savings gained from propeller improvements and hull coatings at 3-5%.
The key point here is that the Tig Rig system is all above the water line and so doesn’t need dry dock to be installed. The installation of the rail mounting system and the computer control hardware will cost we think between $200,000 to $300,000 depending on the size of the ship. In effect the owner is getting the ship set up for similar savings for $300,000 capital expenditure.
The business plan then envisages the operator renting the units on a profit share basis and so being cash flow positive from day one. We feel this presents a very low risk entry for wind assist.
Using the data from the wind tunnel and routing above we can make guesstimates for ships of other sizes using approximations based in the sail area to displacement ratio (SA/D). This allows a comparison table to be drawn for a 40,000 DWT ship of around the same length like the Green Dolphin 38. With 2/3rds the weight we produce the table showing thrust gains of 20%.