I have noticed some posts on the GPS Team Challenge web page. Where some sailors ( not many ) have posted a 5x10 Average speeds lower than their Nautical Mile speeds for the one session. Is this correct
I thought it would be impossible to have a lower speed 5x10 Average than your nautical mile. Being, it would take you longer than one minute to sail the Nautical Mile. So anyone posting a session with a lower 5x10 Average than their Nautical Mile is incorrect?
Does any one know the facts
Please note I just corrected my post.
Goomba, I think you misunderstand, how the 5X10 works.
It's the average of the best 5 separate runs.
A 10sec run is only going to be 200 to 300 metres. so it's quite possible to get very high 5X10s and not have enough room/wind/energy to do a full NM.
Posting a higher NM score than 5X10 would be very rare.
I think I've only done it once, when the wind dropped out after 1 long run.
In fact I think you'd better have another look and make a list of all the NMs that are higher than the 5X10 in a session, we could take a bet on how many you find.
I'll go for 5 over the whole 4 years we've been posting. (Any takers)
Sorry Hardie & Decrept, I ment How can you have a lower speed 5x10 average than your Nautical Mile speed in the same session?
Hi Vando,
Wouldn't you do your 5 Top 5x10 speeds,(which then get averaged) in your best nautical mile? The average would have to be equal or above your nautical mile speed? I have never had a 5x10 average less than my nautical mile.
The computer knows that if you turn 90 degrees, or slow to below say 10 knots, that a new run has started.
But if you keep going in a straight line for 5 km, that's counted as 1 run.
So let's say I'm slogging, get planing for 5 minutes (and go in a straight line to the other side), and then slog the rest of the session then it works out as:
Nautical Mile: 20 kn
10 sec runs: 22 kn (while planing), 12kn, 11kn, 10kn, 9kn.
This works out as a 5x10 average of 12.8 knots.
So you're left with a session where the nautical mile (20 kn) is higher than the 5 x 10 (12.8 kn).
Billabog, If you look closer at my post you quoted, you'll see I underlined and emboldened separate runs!!!
Decrepit, I checked some of my sailing sessions where I did only had 1, 5x10 speed recorded. The other 4 were Zero. It gave me a 5x10 average less than my nautical mile because I never recored a score for the other 4, 5x10. I have found 7 sessions in my sailing records. All sessions in light winds where the wind died.So if you have one or more 5x10 Average reading zero you most likely will have a faster nautical than your 5x10 Average.
I see what you mean cheers
Yep, the moral of the story is, if you're going for 5x10s, do lots of shorter runs in the fastest part of the course, (make sure you get 10s of max speed in of course).
@neb
did pc know difference between jibe and tack
for example:
you run 250m then tack then run 250m to the start point
did pc takes that like @500
or you really need to run 250 then jibe then 250 back to start ?
just wondering ???
same thing at gps results
thanx for answer, i was not shure about it
for @500 tack and jibe counts then ;)
KA72.com also doesn't care if you tack or gybe. As long as you return to within 50m of your starting point.
Oh, and Alpha500 means "up to 500m" not "exactly 500m."
This was an issue when I first coded the Alpha calcs on KA72.com. I assumed that the Alpha500 track had to be 500m long
. In reality, it can be a lot less. Different software deals with this slightly differently I've realised, so some short alphas will be discarded by some software and accepted by other software.
Since shorter Alphas tend to be a little slower than longer Alphas, this isn't necessarily a problem. But if you are going very fast into a gybe, then crash on the way out, you won't record an alpha in some software (sorry I can't remember which was which and how they all worked, but I ran a lot of tests on this at one point.)
Dylan.
for an alpha, is it approx 500m from starting point of your run to the point of the gybe, or 250m to the point where you gybe and back again which add up to 500m "ish" in total?
and how lenient either side of the '500m' is the software are we talking 2% or 20%?
also if anyone can give me an explanation as to why it is not calculated exactly at the 500m point and at a variable amount, this makes it harder if you were estimate where to meet back 50m from original position.
The rules say, a total distance not greater than 500m and a diversion at the start and finish points no greater than 50m. That's the way Mal conceived it (I think it's Mal's idea).
The GPS we use record data at 1 or 2 second intervals, so it's impossible to get exactly 500m, apart from the very odd time, 500m coincides with a measurement. That may have been Mal's reason for not saying exactly 500m
So no software is lenient on the plus side of 500m. I think I've seen an alpha as low as 70m on realspeed, that wasn't shown on GPSarPro, but I can't tell you what the minimum distances any software allows.
