st40 or st60 VMG to wind

[Quoddy]

Does anyone know if the Raymarine st40, (now i40) wind instrument will feed enough data into the Raymarine classic c70 for it to compute “VMG to the wind“? The c70 has a data field for a “VMG to the wind” readout.

The st 60 says it calculates and displays “VMG to the wind” on its own. I assume the pre-calculated data would also display on the c70.

I would like to get the i40 but wonder about its functionality.

 

[Bill Roosa]

The beauty of SeaTalk is it is designed to work with all Raymarine stuff.
If the device can display the data then plugging in a sensor that provides the raw data will make it work correctly.
Course I've never heard of VMG to the wind. Normally you don't want to sail "to the wind" but do want to get to that turnpoint/marker/harbor so most of us are interested in VMG to a Waypoint. Which is why VMG does not work when you don't have an active waypoint!!!

 

[Joe]

Actually there's two VMG scenarios that I know of.... one is a discription of how fast one is making progress to specific waypoint.

The other VMG is associated with optimal boat speed as related to true wind speed and true wind direction........ i.e polar charts.

There are others on this forum that have more expertise on this subject..... but I'm curious as to how a wind indicator can give you a vmg without some kind or data set, such as the polar chart, to base your target vmg on... Perhaps what you're really wanting to know is if the wind indicator can give you the "true" values necessary to determine which part of the chart to look at.... As far as I know, attaching the speed log to the wind indicator should give you "true" data... and the device's spec sheet should tell you that.

 

[Jackdaw]

It's simply using SOW to calculate VMG with respect to the wind direction, the second option Joe describes. Toward windward without respect to the mark, which would change the value as you moved towards the lay-lines. It's racing focused. Your knot log must be networked.

Because it does not access to your polars, it cannot tell you how well you are doing with respect to them, but in pure windward work is a single boat speed against any true wind speed, so you'll get that sorted pretty quick.

 

[Luca1467]

I have a similar set of instruments st60 based. I use vmg to maximise my upwind speed and my downwind ( -ve reading). Recently i installed an AIS transducer with a wifi output which outputs all my data to a software called inavx on my ipad. When i do not activate waypoints it therefore gives me vmg to/off the wind, and by using the tracking function i easily created a set of true polars for different conditions. Does this help?

 

[Quoddy]

Raymarine brain power

Thanks for the ideas. The vmg to wind shows how well you are moving upwind. The vmg to a destination can be misleading because as you get closer, say approaching the layline of your final tack your destination is off to the side and therefore your vmg to it is very low. Unless you are beam reaching to your destination you must always be working up wind therefore vmg to wind gives you a better idea of how well you are doing. As I understand it.

You must have some sort of speed input and you can use this vmg info to construct polars as was said.
I guess the basis of my question is: is the Raymarine classic C series smart enough to take wind and speed inputs to compute vmg to wind, as it can do with vmg to a destination?
Thanks again.

 

[Joe]

Thanks for the ideas. The vmg to wind shows how well you are moving upwind. The vmg to a destination can be misleading because as you get closer, say approaching the layline of your final tack your destination is off to the side and therefore your vmg to it is very low. Unless you are beam reaching to your destination you must always be working up wind therefore vmg to wind gives you a better idea of how well you are doing. As I understand it.

You must have some sort of speed input and you can use this vmg info to construct polars as was said.
I guess the basis of my question is: is the Raymarine classic C series smart enough to take wind and speed inputs to compute vmg to wind, as it can do with vmg to a destination?
Thanks again.

If your st40 can TRANSMIT true wind data, then your c70 should be able to perform........ if the C70 says if can provide the ubiquitous vmg to wind number, then it should be able to compute it use it's own boatspeed info in conjunction with true wind data from the wind instrument.... how else would it work?

So your question is: does the st40 TRANSMIT, rather than simply dispay, true wind data? Second question: part a) Does the C70 compute VMG to wind, part b) What external data does the C70 require for this feature?

Sounds like a visit to the Raymarine site to look at user manuals is in order.