When to Turn the Mill
Google document - When to Turn the Mill - Draft 2
Guidance on When to Turn the Mill due to a Forecast of High Winds - Draft 2
This document is intended to set out principles to consider when high winds are forecast and is intended as guidance for use when an experienced volunteer’s input is not available. Experienced volunteers may want to use their judgement and go outside the guidance referenced in the document.
Objectives:
- Minimise the load on the mill structure by orienting the mill so that the front (narrow, angled face) of the mill faces the wind. Note: wind hitting the sails other than directly straight on, may cause the mill to turn to an undesirable orientation. If a mill is subjected to wind from the tail end it will subject the windshaft to unintended axial loads and could push the windshaft out of the mill.
- Minimise the water ingress to the mill. Note the weather boarding at the front of the mill overlaps the weather boarding on the sides and the side boarding overlaps the boarding at the rear.
During the Winter Months (October to March):
In October the mill should be oriented facing SW (the direction of the prevailing winds) and staked in this position to prevent the mill moving.
During the Summer Months (April to September)
Whenever the mill is turned it should be left in the orientation facing the strongest winds forecast for the following 14 days.
Any Time of the Year:
Weather forecasts should be monitored on at least a weekly basis. If there is a wind of over 40mph forecast during the forthcoming week, there should be close monitoring of the forecast daily.
If there is a wind of over 40mph forecast for a significant period:
- The mill should be turned to face the forecast wind direction and staked in place. Winds varying by less than 45 degrees either side of the actual mill orientation should not increase the risk of water ingress because of the angle at the front of the mill.
- Where the wind direction varies by less than 45 degrees, the mill should ideally be oriented to face the direction midway between the two extremes, however if the current orientation of the mill is somewhere between the two extremes, it does not need to be moved.
- Where the wind direction varies by more than 45 degrees, consideration should be given to turning the mill from the initial wind direction to the new direction, at approximately the time that the wind direction changes.
