New possibilities... 

  Engineered for superior
  performance and

• Improved aerodynamic efficiency
• Easy control with minimum crew
• Safe mechanized handling

Indosail suspension bridge effect diagram

The INDOSAIL Utility Sailing Rig

Inspired by the principles of suspension bridges, suspension sails are a step forward in technology and efficiency.

By separating the functions of horizontal profile control and vertical twist control, the enormous vertical control forces are carried by strong vertical luff and leech ropes. Consequently, suspension sails may be made of conventional woven sailcloth.

Modular Concept

The objective of the INDOSAIL-Project was to develop a Prototype Cargo Sailer for the Indonesian inter-island trade.
Based on a four-masted standard design, a modular system was conceived, to derive a smaller and a larger version by subtracting or adding a standard section consisting of one cargo hold and one mast module, without modifying the basic elements of the hull and the rig. At a common beam of 12 m and draughts around 5 m, the main particulars are as follows:

LOA:      63 m
LPP:      50 m
Displ.:  1700 t
Dwt:     900 t
As:       1050 m2


LOA:     78 m
LPP:     65 m
Displ.:  2450 t
Dwt.:    1550 t
As:        1400 m2


LOA:   93 m
LPP:    80 m
Displ.: 3200 t
Dwt.:   2200 t
As:       1750 m2

INDOSAIL configuration

Reasonable Sail Configurations — never without Jib!


All sails are made of soft UV-resistant cloth. They are of flat cut with a hollow curved leech seam. The sails under wind load are suspended by a strong, curved leech rope similar to a 'suspension bridge'.

In a multi mast sailing rig—as with an aircraft wing in the start or landing configuration—the optimum adjustment of the sail- or wing elements to the local flow conditions is resulting in a fairly open sheeting of the jib and a progressively closer sheeting of the following sails, with the mizzen sheeted closest. The purpose is to force the wind flow—step by step—to turn its direction closer to the midship line, for optimum propulsion thrust and even distribution of the contributions of the sail elements.

A fore-and-aft mainsail attached to the mast or a luff roller close to the mast is suffering from disturbed flow on its most critical leading edge. The gap between mast and roller is marginally improving the flow but a considerable improvement is found from the slipstream of a jib sail in front. Thus the propulsive effect of the combination is much more than the sum of the effects of the individual sails. Consequently, to open the gaff sails only is not an efficient configuration. It is suggested instead, to open the jib and mizzen sails first and to open the gaff fore and mainsails then to a degree compatible with the course and wind conditions. With increasing wind speeds, the gaff sails should be reefed progressively with the jib and mizzen sails still full.

Unexplored Potential

The positive handling experience and the success of the INDOSAIL Prototype Vessel show the technical advantages provided by a modern, efficient, and easy-to-handle soft-sail rig. They also hint at yet unexplored potential in the technical and operational field. 

The collected experience of now four years of cargo service has proven the potential of a modern utility sailing rig:
+ easy and safe handling by a small crew,
+ efficient sailing on all headings,
+ well controlled sail trim in every sheeting,
+ easy control of pre-tension by frequency-check,
+ short-term sail opening, continuous reefing and fast furling,
+ safety by ‘sheets-off’ function,
+ flexible level of mechanisation, from hand-winches to semi-automatic operation.


Get in touch with us


We will reply as soon as possible


Peter Schenzle
August-Krogmann-Str. 155
D-22159 Hamburg

Peter Willcox
PO Box 66 
Islesboro, ME 04848-0066, USA

We encourage anybody who likes the idea to use it!