Expedition Navigation Software 
1 of 1- pjl
- Expert
Offline - From: Lake St. Clair, MI
- Registered: 11/09/2015
- Posts: 113
Light air downwind optimum performance
My latest, probably harebrained, idea is that using Exp calculated VMC is a great guide to optimizing those frustrating situations when it is really shifty, light and probably dark besides. All other methodologies (TargBsp, VMG, polar%, etc) all seem to have more margin and opportunity for error IMHO.
Nick states that the VMC is the projection of the SOG and COG vector onto the bearing from the boat to the mark. Seems like a winner to me.
Any comments based on opinion or experience?
TIA, pjl
- sheldon.haynie
- Expert
Offline
- From: San Francisco Bay
- Registered: 1/13/2016
- Posts: 133
Re: Light air downwind optimum performance
Toss in Currents and VMC probably makes most sense, We sail SFBay and on Saturday, had a strong Flood with Set of about 60-75 degrees to the rhumb lines, crossing the South bay and drift rates of 1.5-2.5 kts based on H5000. Doing only 5-6 kt BSP, your fastest angles are going to be highly asymmetric and non-intuitive otherwise.
Semiconductor Development Engineer, Retired Viticulturalist, Occasional sailor
"Lioness" 1962 Hinckley Bermuda 40 Custom Yawl
- pjl
- Expert
Offline
- From: Lake St. Clair, MI
- Registered: 11/09/2015
- Posts: 113
Re: Light air downwind optimum performance
We sail Lake St. Clair with mostly wind driven surface currents except near the mouth of the Detroit River where current runs up to 1K. It's also inland lake with lots of light shifty stuff and shore effects. Hoping to see that the VMC theory holds up over time.
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