On KiteTugs©  copyright 1996, Dave Culp Speedsailing

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Current Status of Commercial Sail

Though numerous studies, proposals and tests have been conducted within the past 20 years 1, widespread commercial sail assist, whether conventional sails set on masts, wingsails, or powered Flettner rotors or aspirated cylinders, is not prevalent on commercial ocean going vessels today. While upwards of 25 vessels, from 50 to 50,000 tons have either been retrofitted or studied for sail retrofit 1,2, we do not see a viable sail assist industry today. The simple reason for this is the same as it was 100 years ago; fuel oil is inexpensive, powered vessels are not labor intensive and powered vessels' performance is both reliable and repeatable. For sail assist to make inroads, it must be cost effective, it must incur minimal degradation of performance, and it must not entail significant retrofit expense or increase in crew load.

Currently considered designs generally envision "assisting" a powered vessel's engines only; few envision pure sailing 1,2. There are several reasons for this. Retrofitting an existing vessel is expensive, hull shapes, control gear and deck space are not optimized for large pure sail rigs; capital cost and space limitations demand that the sail rig be as small as practical. Rig sizes are thus optimized for high winds, while the vessel's engines are expected to supplement them in lighter winds.

Thus, currently envisioned schemes result in average fuel savings throughout a vessel's voyage on the order of 10-30% 1,3. This is not enough saving to warrant re-routing vessels to the old windjammer trade wind routes, which further degrades savings available. The vessels travel more of their route on courses which do not benefit from sail assist, or even suffer degrading drag from the furled systems while under power alone. There's a "chicken and egg" issue here. If large, efficient, purpose-built sailing vessels existed, even if ship owners would not re-direct them on the old routes, then capital and operating costs of sailing vessels would compete favorably with powered vessels2. Indeed, this is the case in some parts of the world today. "Niche" markets, especially small ports located on trade wind routes, are currently profitably served by sailing vessels3. However, for the foreseeable future, except for these niche markets, retrofit is the likeliest route to sail assist.

Most currently envisioned schemes aren't reliably profitable. Often, the difference between 10% fuel savings on a voyage and 30% can be the difference between profit and loss on the sail equipment investment. Ship owners and operators incurr substantial financial risks in their day-to-day operations, and aren't interested in assuming new ones, so sail assist isn't currently popular. As fuel costs rise, sail assist becomes more and more viable. Historically, however, such costs are variable over time and again we see a reluctance to make the long term capital investments necessary for sail assist. This study assumes that the current world price of diesel oil is $1.00 US per gallon, or $320/long ton.

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