Olympic Triangle Course calculator
The Real Andy
triangles by GPS, but cannot find anything. I am not good at excel,
but I can write windows apps, so I thought of writing something where
you put in current location and wind direction and it calculates GPS
coordinates where you should lay the marks. If I do it that way then
no one can complain that one leg is to short or the reach is to tight.
Anyone seen a spreadsheet or should I push forward with my course
plotter app?
The Real Andy
To late, I wrote one today! Designed to run on pocket pc, but I will
also create a version to run on a laptop. Will create an installer in
the next week or so and put it up on the clubs website.
The Real Andy
<there...@nospam.com> wrote:
So took this out for a trial today. To hard to use. Ended up using a
mix between the old fashion way (using the elvestrom tactician +
compass) and the GPS for distance. I am going to order a bluetooth GPS
device this week to incorporate into the software I wrote. I think I
can make this one work.
Also learned today that my trig skills suck, poor lads had to sail a
much bigger course. Goes to prove the old eyeball measurement is
usually closer than you think. All this stuff just because we are
running the Aussie titles for the flying fifteens in January!
Jason Keats
An Olympic course is an equilateral triangle. You can just drop the
leeward mark, drive upwind for (say) 0.8 nm (taking a compass reading),
turn left 120 degrees (ie, subtract 120 from previous reading, and add
360 if it goes negative to get new direction), drive the same distance
and drop the wing/gybe mark.
No need for mathematics, just a compass and a log/odometer.
Jason Keats
>
> An Olympic course is an equilateral triangle. You can just drop the
> leeward mark, drive upwind for (say) 0.8 nm (taking a compass reading),
> turn left 120 degrees (ie, subtract 120 from previous reading, and add
> 360 if it goes negative to get new direction), drive the same distance
> and drop the wing/gybe mark.
>
> No need for mathematics, just a compass and a log/odometer.
>
>
It also helps if you remember to set the windward mark. <g>
jg
As long as you are not limited for width.
Another consideration is what sort of yacht - boats without spinnakers
like shallower reaching angles, heavy yachts with spinnakers might like
deeper angles.
What about when there is a course change and the RO is not at the pivot
mark, has to tell someone else how far in what direction to pull the
other two marks?
"Olympic course" these days seems to be anything you care to make it.
Jason Keats
>>
>> No need for mathematics, just a compass and a log/odometer.
>>
>>
>
> As long as you are not limited for width.
>
> Another consideration is what sort of yacht - boats without spinnakers
> like shallower reaching angles, heavy yachts with spinnakers might like
> deeper angles.
>
> What about when there is a course change and the RO is not at the pivot
> mark, has to tell someone else how far in what direction to pull the
> other two marks?
>
> "Olympic course" these days seems to be anything you care to make it.
>
>
I agree, it's a bugger when the wind changes direction.
Maybe a large-scale chart to plot the location of your marks and a
couple of GPSs is the easiest solution - just read off lat/long for
those laying the marks. It also makes it easy to measure/describe
changes in position of the marks, if the wind shifts.
However, if the wind's steady, then a table of distances/angles may be
all you need.
Eg: R = D/(2cos(X))
D\X 45 50 55 60
0.5 0.35 0.39 0.44 0.50
0.6 0.42 0.47 0.52 0.60
0.7 0.49 0.54 0.61 0.70
0.8 0.57 0.62 0.70 0.80
0.9 0.64 0.70 0.78 0.90
1.0 0.71 0.78 0.87 1.00
where D is the windward leg, X is the angle at the top/bottom mark, and
R is the length of the reach leg.
Then all you have to do is teach people how to use a compass and log.
jg
Simplicity doesn't really jump out at me here, you mean I have to go to
the windward mark, travel the distance at the angle, then try to work
out how to drag the wing mark to where I am without losing my place in
time and space, all before the leading yacht reaches the windward mark?
Surely nav aids would help, although I'm not sure how they tell you the
wing leg distances - you must always have to calculate those yourself?
The Real Andy
Actually, there is 2 variants, the equilateral triangle and the
45/90/45. We sail the latter.
When you set the course, and listen to them whinge cause one angle was
a bit tight then you will understand where I am coming from. Trust me,
a GPS is a good thing
The Real Andy
We have done it for years with compass and log, its not that hard. But
as things become more competitive, people will whinge when they lose.
The GPS sets it a lot better than I can plus I can take waypoints that
I can refer to in a protest.
Jason Keats
> Actually, there is 2 variants, the equilateral triangle and the
> 45/90/45. We sail the latter.
>
> When you set the course, and listen to them whinge cause one angle was
> a bit tight then you will understand where I am coming from. Trust me,
> a GPS is a good thing
Yeah, we sail the same course. However, I don't think anyone really
cares if one reach is different to the other - it makes it more
interesting. That often happens anyway, when the wind veers.
I believe those laying the marks used to use three nails in a plank of
wood to measure the angles, but the GPS has now taken over.
Jason Keats
> Simplicity doesn't really jump out at me here, you mean I have to go to
> the windward mark, travel the distance at the angle, then try to work
> out how to drag the wing mark to where I am without losing my place in
> time and space, all before the leading yacht reaches the windward mark?
>
> Surely nav aids would help, although I'm not sure how they tell you the
> wing leg distances - you must always have to calculate those yourself?
A compass and log ARE navigational aids.
D\X 45
0.5 0.35
0.6 0.42
0.7 0.49
0.8 0.57
0.9 0.64
1.0 0.71
For example, let's say we're laying a 45/90/45 triangle, the wind is
from 200 degrees and we want a windward leg of 0.8 nautical miles.
Drop the bottom mark first, then steer 200 degrees for 0.8 miles, drop
the top mark, turn left 135 degrees (because 180-45=135) so you're
steering 65 degrees (as 200-135=65) for 0.57 miles (see table) then drop
the gybe mark.
Is that so hard?
As mentioned before, if your calculations are in danger of going
negative, then you can add 360 degrees to start with. And, if you're
setting a starboard course you'll have to add rather than subtract 135.
jg
As a means of setting a course I'm not sure how else it would be done
accurately without those basic nav tools, but it relies on travelling
from the previous mark to set the next which while not a mental strain,
doesn't lend itself well to late course shifts or having more than one
course boat.
How often have I seen that race between the mark laying boat and the
fleet? How often a revised course so bad it might as well have been left
alone?
It seems to me the card calculator would avoid the simple mistakes I for
one might make. I have never used a GPS and they don't look too simple
to me, but I don't know anyone who doesn't say it's an all round better
way to set a course or navigate generally.
The Real Andy
I use a card calculator at the moment. Its an elvestrom tactician but
its about to be replaced with a musto compucourse because its buggred.
http://www.musto.com.au/productdetail.aspx?fromSearch=true&productId=1614
I tried using the GPS last course I set with some success, the biggest
problem is that the GPS is too hard to drive and it takes to long.
Using the compass I can lay a full 1nm course in maybe 10minutes. Its
also a lot quicker to adjust the couse when the wind shifts.
However, with all this in mind, and being a computer programmer I am
rolling everything I need into an application to make my life easier.
My first attempt failed (to hard to use) so now I am going back and
addressing all the issues that made it difficult to use. I am
developing it to rin on my windows phone at the moment. When I was at
the GPS shop I spotted a HP PDA with built in GPS. They also sell
these waterproof cases for them. Once I have the application to a
point where its usefull I will buy one of the PDA's for the club to
keep.