VMG - formula and expanations for a study

[jac]

Much simpler to sort out what CMG you can make on the other tack, and tack when the mark is on that BRG.
Depending on wind or sea state, my boat will tack through anything from 75 to 95 degrees.

I race dinghies, and use a tacktick digital compass.
I mostly tack on shifts or in response to situations with other boats, the wind is rarely constant enough to calculate banging the corners of the beat exactly.
Also where I race, the tide is rarely constant across the course.

Best argument for going up the tacking cone rather than a long punt out to the lay line on one tack.

 

[Birdseye]

Hi,

Long story but my daughter is doing a dissertaion for Uni on yacht racing and she needs a clear explanation and the formula for VMG with ideally some worked examples. There is one on wiki but it doesn't give actual numbers. She has been told that this is covered in one of the RYA Yachmaster publications but the problem is which one?

Can anybody advise on the this and/or point us to the book we need to buy?

Thanks,

Dave

Its simple vector maths. VMG is the velocity made good towards whatever is defined as the target. So if you are sailing at X knots over the ground on a course that is at A degrees off the direct line between you and the target then the VMG V is V= X cos A

I have seen it wrongly described in sailing books.

 

[wklein]

To my mind vmg is mostly useful for passage planning. If your beating to portend bill it will give you some idea of eta once tide has been accounted for.

 

[johnalison]

To my mind vmg is mostly useful for passage planning. If your beating to portend bill it will give you some idea of eta once tide has been accounted for.

Yes, but the trouble is - you can't kid yourself, or more importantly, your wife that you will be arriving in time for supper.