In anticipation of an on-shore wind at one of my local events, Graham Bantock suggested a possible layout for the start line.  The idea is to set a start line close to shore which can be managed by competitors and race officials, meaning that the fleet is sent off on a broad reach to a first mark which is nicely downwind of the windward mark.  From there, the fleet then has a fair beat.  The question is, what should such a start line look like?  Its general characteristics are illustrated in Figure 1.

Figure 1.  General layout for reaching start.

The offset of the starboard layline to the first mark (▲) is at α° to the wind. The start line to the first mark (▲) is set at β°. The actual distances and angles needed to suit the Class can be calculated from the polar diagram for Class boats.

For the 6M Class, Figure 2 illustrates a typical 6M polar diagram (the Simple VPP web page explains a polar).  Extracts from a professional VPP are shown in the table on the left for boat speed for different true wind angles and speeds.

Figure 2.  Polar diagram for typical 6M boat.

Using the typical boat speeds at different wind angles allows a sketch of some possible reaching start lines which give boats a more or less equal opportunity to get to the first mark.  These are illustrated in Figure 3 for wind speeds of 4 and 8 knots. 

Figure 3.  Possible reaching start lines

The start lines for a broad reach (70° to 90° to the first mark) suggest that boats starting anywhere along the line are about equidistant from the first mark  (▲), while the start lines for a close reach (40° to 60°) somewhat favour mid-line starts.  This suggests that the offset of the starboard layline to the first mark (▲), α° to the wind, could be conveniently set at 80°.  The result is illustrated in Figure 4, with a suggested start line of 20 metres and a distance of around 60 metres from the start to the first mark.

Figure 4.  Reaching start to suit 6M boats.

A pole in the shallows (or the shore if there is sufficient depth) allows quick and easy start line bias adjustment, essential to accommodate competitor reaction to a very unfamiliar course layout and a possibly variable wind.

Taking measurements off the sketch of the start line suggests that the angle of the start line to the first mark (▲), β°, would be 30°.  That is, the boats starting at the pin end would (and should) find a significant port-end bias.

The remaining issue is to illustrate the start line arrangement for different angles of the on-shore wind, between 110° and 70°, to aid the mark layer and Race Officer.  These arrangements are shown in the following series of diagrams.  Note that for on-shore wind at angles of 60° or less, a conventional start line can usually be set.

Changes for different Classes and/or fleet size

The above angles are broadly applicable for any Class of boat if their specific polar diagram is not available.  The distances are also generally applicable, but can be reduced or increased in proportion to waterline length if that seems useful.  Taking the LWL of a typical 6M at, say 1.2 m, a 12-boat fleet of IOMs could as well sail with distances 20% shorter.  And in the case of a larger fleet, multiply the distances up.  An 18-boat fleet would ideally need distances around 50% larger.

Attribution & acknowledgements

Concept, design, and calculations by Graham Bantock.
Diagrams by Lester Gilbert.
Ver. 1.04, May 2025.

©2025 Lester Gilbert