AUXILIARY WIND PROPULSION SHIPS

General

This is not an idea for a “return to sail” ocean carrier, but for a sail-assisted cargo motor-ship.

Some day, cargo ships will run on clean fuel. While we wait for that day, we might already be avoiding 50% of harmful emissions by the use of auxiliary wind power.

Reluctance to invest in wind assistance is not surprising, since the contrivances being proposed for simply catching wind are unrealistically expensive. This is because they are intended to work at the flick of a switch, involving no extra crew. The clothes-line rig is comparatively very cheap to set up and maintain, and over a ten-year period, when the push-button wind gear would be beginning to need replacement, the cost of an extra few hands would be infinitesimally small.

Another reason which must be putting off ship managers is the incompatibility of rigs of any sort with bulk cargo handling machinery at terminals. Both these problems are addressed here.

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The proposed rig

Does require specialised extra crew. According to ship size, from 3 to 5 a.b.s could cope with the sail area involved, if the handling procedure suggested further on is followed.

The masts are deck-stepped triangular section lattice towers, braced at mid-length by tubular bipods. Their heads are stayed in the transverse plane, with tubular spreaders.

The “clothes-line” stay linking the mastheads is given a generous dip, which in a funicular polygon such as this, significantly reduces tension. A lighter stay would link the mastheads directly, possibly with some provision against overload due to hull flection in extreme conditions.

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The second drawing shows the ship ready to receive shore machinery. To get the sails out of the way for harbour operations, they would each be lowered complete with all their gear onto a broad canvas strop laid out on the hatch cover, and the primary halliard transferred from the sail to the eye of the strop for hoisting aloft.

Sail handling policy:

The sails (all identical) would have full length battens (more than shown), in p.v.c.pipe, which would extend the leech and also make dousing these very large sails easier. The centre batten would be in heavier pipe, having the function of a boom. There would be two sheets, one to act as preventer when required, also to assist the downhaul in subduing the sail when dousing it. Each sail would be hanked to its own, very light, guidance stay, and would have its own (secondary) halliard. All this gear would first be hoisted by a primary halliard rigged to the clothes-line, with its fall led along the clothes line to to the nearest mast and thence to multiple winches on deck. The guide stays need not be rigged very tight.

The intention is that these sails would all be set as soon as the ship cleared harbour, remaining so throughout the voyage.

Since the sails are free to rotate forward of their stay, and uncontrolled floggig is inhibited by the battens, the way to cope with squalls would be to slack off sheets until undue pressure was off the ship, even to fully feathering them if required.

Generally, line squalls don´t last very long; this practice would avoid the labour-intensive task of reefing or furling conventional sails and then re-setting them son after.

Sailcloth could be quite light in view of not having to stand up to strong winds, their luff and leech reinforced with kevlar tape. If doused at sea, they would be triced down on top of the hatch covers.

The lower terminal of each sail´s stay would be shackled to an eye in the centre of a strop spanning the hatches or deck load and secured at each end to the scuppers, taking advantage of the extra strength of the underlying structure.
Windward performance is never going to be brilliant in a rig with many sails in a row, so the fact that the luffs will be somewhat short of dead-straight loses relevance.

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Down-wind, it would be possible to goose-wing the sails on alternate sides, with some benefit.

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The fourth drawing shows the same total area split into six sails instead of five, making each sail 17% easier to handle and lowering mast height.

How much or how little driving power can a total sail area such as illustrated provide?

The ratio to displacement to the 2/3 power (metric) is 4.4 in the non-dimensional example shown. The 1903 five-mast er “Preussen” had a value of 9.6 under full sail and 6.4 under working rig.

One problem remains: low bridges!! Although it would not be impossible to solve this.

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pgoodeamrina@gmail.com
Palma de Mallorca, Spain, February 2015

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