Functions Page 5
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Performance

Boatspeed

is the most fundamental input to the Ockam system, and is the first thing the crew looks at when trying to make the boat go faster. It is also used by many many other functions.

Boatspeed is a primary input via the T2 interface.
Why you should use boatspeed sensors instead of GPS.

Current Set & Drift

The Ockam system computes current by comparing COG and SOG with Boatspeed, Heading, and Leeway. Calculated current may be overriden by the C= command. Current is used in laylines and opposite tack.

Current requires boatspeed, heading and COG/SOG.

Vmg

is the component of boatspeed in the direction of the true wind. When beating (or running) this is the number to maximize (or minimize) for best performance.

Because of the dynamics of ship's handling, Vmg is not a usable helming function (see Targets for an explanation).

A more practical way to sail optimum Vmg is to use target speed.

Vmg requires boatspeed and true wind angle.
10 knot polar

Vmc

is like Vmg except in the direction of the current rhumbline. Sailing maximum Vmc gets you toward the mark faster than sailing directly there, but at the cost of going off rhumbline. On a long course, the wind will shift and allow you to tack and consolidate back to the rhumbline.

On short courses, this may not be possible. However, you can still sail Vmc on an upwind leg by doing the wally.

Vmc requires boatspeed, wind direction and waypoint range & bearing.
Vmc
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