I guess there are 2 kinds of people:
Those who can understand a polar and those that can't.

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Grantmac said..
I guess there are 2 kinds of people:
Those who can understand a polar and those that can't.

But the ones who do well in the saturday arvo race around the buoys are the ones that have the knack of taking sightlines on the horizon.

And of course a GPS generated polar will not be accurate when applied to the tracks of the skilful sailor who keeps his eye on the horizon and tacks on the windshifts.

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Gotta remember, VMG is BOTH speed AND angle. Net vector speed to the mark at whatever angle and speed we can muster. Yes, you have to enter the coordinate of the mark and let the gps device, if set to VMG, calculate and display your VMG to that mark.

Now we're onto VMG we'd better get it clear. VMG is velocity made good in the upwind (or downwind direction) not speed to the mark. The GPS can only calculate VMG if it knows the wind direction. Your GPS can easily calculate the velocity towards the mark but that's not allowing for the other tack - which old fashioned VMG does. As an example if your best angle is say 50 degrees off the wind when the mark you're heading for is directly abeam you're getting further from the mark each second, ie. a negative GPS velocity towards the mark, but still haven't reached the layline. Your old fashioned VMG is still a nice positive number, keep going.

AC75s no doubt have a mast head apparent windspeed and direction sensor. With boatspeed the computer can directly calculate VMG and true wind direction. The onboard computer, knowing the co-ordinates of the mark , the current performance of the boat, can then output the distance to the layline.

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Ian K said..

Gotta remember, VMG is BOTH speed AND angle. Net vector speed to the mark at whatever angle and speed we can muster. Yes, you have to enter the coordinate of the mark and let the gps device, if set to VMG, calculate and display your VMG to that mark.

Now we're onto VMG we'd better get it clear. VMG is velocity made good in the upwind (or downwind direction) not speed to the mark. The GPS can only calculate this if it knows the wind direction. Your GPS can easily calculate the velocity towards the mark but that's not allowing for the other tack - which old fashioned VMG does. As an example if your best angle is say 50 degrees off the wind when the mark you're heading for is directly abeam you're getting further from the mark each second, ie. a negative GPS velocity towards the mark, but still haven't reached the layline. Your old fashioned VMG is still a nice positive number, keep going.

AC75s no doubt have a mast head apparent windspeed and direction sensor. With boatspeed the computer can directly calculate VMG and true wind direction. The onboard computer, knowing the co-ordinates of the mark , the current performance of the boat, can then output the distance to the layline.

Guys with all due respect can you please take this discussion to a new thread with the appropriate title
Thanks TK

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Grantmac said..
I guess there are 2 kinds of people:
Those who can understand a polar and those that can't.

boardsurfer said based on the polar plot he was getting amazing angles, so are you telling me there is no angle information in the polar plot?

Select to expand quote

Ian K said..

Gotta remember, VMG is BOTH speed AND angle. Net vector speed to the mark at whatever angle and speed we can muster. Yes, you have to enter the coordinate of the mark and let the gps device, if set to VMG, calculate and display your VMG to that mark.

Now we're onto VMG we'd better get it clear. VMG is velocity made good in the upwind (or downwind direction) not speed to the mark. The GPS can only calculate VMG if it knows the wind direction. Your GPS can easily calculate the velocity towards the mark but that's not allowing for the other tack - which old fashioned VMG does. As an example if your best angle is say 50 degrees off the wind when the mark you're heading for is directly abeam you're getting further from the mark each second, ie. a negative GPS velocity towards the mark, but still haven't reached the layline. Your old fashioned VMG is still a nice positive number, keep going.

AC75s no doubt have a mast head apparent windspeed and direction sensor. With boatspeed the computer can directly calculate VMG and true wind direction. The onboard computer, knowing the co-ordinates of the mark , the current performance of the boat, can then output the distance to the layline.

thanks, that was very informative!

I've added an F4 review under the gear review forums..

Nice to see some F4 reviews. Just was going to say that berowne made a really good review. One thing to add is the mast is compatible with the free ride fuse (not like Moses race mast) or any other type of setup. Mast is good for all types of foiling. Wing connection is 5 M6 and free ride surf wings is 3 M8. Nice connection. Thanks for the review.