Hasler Vane Gears Obstruction to Airflow

The information below was written over 30 years ago and must therefore only be used as a reference guide.

PUBLICATION  V2SP November 1969

For the best vane steering it is necessary to ensure that the yachts structure or dodgers do not unduly interfere with the airflow reaching the vane. Such interference can be experienced even when the obstruction is to leeward of the vane, but a mast or normal boomed mainsail or mizzen sail does not act as an obstruction provided that the boom swings clear of the vane.
2. For the purpose of the following rules, an "obstruction" is defined as any structural surface or canvas dodger or similar wind baffle whose area is greater than 1 sq. ft. (0.1 Sq. metres). Watchkeepers and crewmembers should remember that they also act as "obstructions" to airflow when within, say 8 ft. of the vane, and should keep as low as possible when within this limit.

3. Minimum distance of obstruction from vane shaft should be four times the height of the obstruction above the level of the base plates.
4. Examples, with a type 17 or type 18 vane at the standard height (as in Fig.7): -

Height of top of obstruction Minimum distance of Above base plate level obstruction from vane shaft
6" (0.15m) 2ft. (0.6m)
12" (0.3m) 4ft. (1.2m)
18" (0.45m) 6ft. (1.8m)
24" (0.6m) 8ft. (2.4m)
30" (0.75m) 10ft. (3.0m)
36" (0.9m) 12ft. (3.6m)
If more than 12ft. from the vane shaft there is no restriction

High Vane Assembly
5. If the standard vane would theoretically be "obstructed" and you cannot, or don't wish to remove the obstruction (e.g. canvas dodgers could be cut down in height or removed) then the "High Vane Assembly" should be ordered as an extra: This may be used with either the type 17 or the type 18 vane and raised the vane by 16" (0.4m). The lower edge of a "High Vane" will then be 2'6" (0.75m) above the level of the base plates.
6. The assembly comprises an extra upper vane shaft bearing carried by a Stainless Steel support which is bolted to the standard bumkin frame (B) and an extra long vane shaft to suit.
7. With this High Vane assembly any "Obstruction" may be 16" higher (at any given distance) than shown on the table in para.4. For example:

    2ft. From the vane shaft an obstruction could be 22" high (6" +16")
    4ft. from the vane shaft an obstruction could be 28" high (12" +16") and so on.