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Old 29-09-2016, 08:09   #1
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VMG calculation software

Hi forum,

I'm trying to avoid paying the roughly $1200 for the Expedition software, as everyone I've talked to about it is pretty ambivalent about it's value. We're not racing, but do like to sail efficiently. We're still trying to get a good handle on downwind optimization, We're a fast boat, so we're always gybing downwind, but it's a bit hard to do a running 'back of the napkin' vmg calculation while we're on a downwind passage.

Here's our current electronic setup relevant to this question

B&G hydra 2000 system, 6MFD's. This is not interfaced with a plotter at this point, so I can't get VMG at the moment.

B&G Zeus touch. This is the previous version without sail performance functions.

I also have a separate PC down below, with a repeater screen in the cockpit, which might be the easiest device to get this working on, but it's not ideal, as one has to go to the nav station to do anything.

The ideal would be to be able to link the B&G plotter to the H2000, so that I can just set a mark and have the H2000 provide the info, but I'm not really sure if I can get that to network in the way I want.

So, if that's the case, I'm guessing a stand-alone program will do the job well enough. Any open-source (or at least not terribly expensive) options anybody can suggest? I would want to be able to input the boat's polars.

I hope that's concise enough to be understandable...

Thanks for the ideas. TJ
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Old 29-09-2016, 21:37   #2
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Re: VMG calculation software

qtVlm is free for PCs, and can do exactly that (vmg, laylines, target speed, etc).
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Old 30-09-2016, 00:32   #3
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Re: VMG calculation software

Thanks. I'll take a look at it.


TJ
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Old 30-09-2016, 01:46   #4
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Re: VMG calculation software

Maitai,

Hopefully you pass by this page again.

Ok, I downloaded the program. It looks like it will do the job. I can't figure out how to put my boat's polars in, however. Is there a way to do that? I looked on the forum, but am struggling with the French...

Thanks, TJ
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Old 30-09-2016, 02:04   #5
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Re: VMG calculation software

No problems

There is a directory "polar", just copy them here. Or use "import polar" from the boat settings menu (boat->boat settings)

There is a documentation in English here: http://www.virtual-winds.org/maitai/...ntation_en.pdf
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Old 30-09-2016, 02:22   #6
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Re: VMG calculation software

Quote:
Originally Posted by maitai View Post
qtVlm is free for PCs, and can do exactly that (vmg, laylines, target speed, etc).
Where does one look this up, & what specifically do you type into the search box?

To the OP. Can you not just set a destination point into say your handheld GPS, & then set it to display your VMG? That way you can see what's roughly the best course, in real time, to optimize your gains towards your destination or that entered navigation point anyway.

And I'm curious to know what I'm missing in terms of what you may be calculating other than the very basic info above.
I obviously know that VMG can vary greatly between the 2 tacks or gybes, due to currents, sea conditions, wind... And that you also want to use things to your advantage to get on the best side of weather systems. But... what specifically are you attempting to calculate?

Also, what's your instruments package, & what software is it's brain, as well as your PC running?

And with regards to your queries, have you tried asking them over on Sailing Anarchy Forums? It might be a good bet, given the racer geeks over there. Some of whom even write the kind of code you may be looking for.
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Old 30-09-2016, 02:28   #7
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Re: VMG calculation software

Quote:
Originally Posted by UNCIVILIZED View Post
Where does one look this up, & what specifically do you type into the search box?
If that is the question you can download qtVlm from here: https://sourceforge.net/projects/qtvlm/ (for windows/linux/macOs) or from the relevant stores for Android or iOS.
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Old 30-09-2016, 02:34   #8
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Re: VMG calculation software

I'll give it a try, thanks!
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Old 30-09-2016, 03:40   #9
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Re: VMG calculation software

Quote:
Originally Posted by UNCIVILIZED View Post
Where does one look this up, & what specifically do you type into the search box?

To the OP. Can you not just set a destination point into say your handheld GPS, & then set it to display your VMG? That way you can see what's roughly the best course, in real time, to optimize your gains towards your destination or that entered navigation point anyway.

And I'm curious to know what I'm missing in terms of what you may be calculating other than the very basic info above.
I obviously know that VMG can vary greatly between the 2 tacks or gybes, due to currents, sea conditions, wind... And that you also want to use things to your advantage to get on the best side of weather systems. But... what specifically are you attempting to calculate?

Also, what's your instruments package, & what software is it's brain, as well as your PC running?

And with regards to your queries, have you tried asking them over on Sailing Anarchy Forums? It might be a good bet, given the racer geeks over there. Some of whom even write the kind of code you may be looking for.

Hi Uncivilized,

You're right that SA is a better forum than this for performance questions, but I figured that someone here could probably point me in the right direction. Maitai has proved this supposition correct...

To answer your question, I was hoping for a simple (cheap or free) affair where I could input the boat's polars, put the cursor on the destinatinon, input the wind speed and get a target speed, optimum angles, and real-time VMG, just so I can see how I'm actually doing. We're not chasing 1/10ths of knots, just looking for a good data source to monitor general performance.

I'm not getting this info at all now, so everything's more of a mathematical/paper affair at the moment, and while I do know how to use a maneuvering board, it's really not my idea of a good time or an efficient way to do these things in 2016! Our ancient GPS doesn't really do what you're suggesting... Probably, I could set the B&G plotter up for it, but I'm looking for just a little bit more info.

I'm looking forward to getting this program dialed in and giving it a try.

TJ
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Old 30-09-2016, 13:42   #10
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Re: VMG calculation software

I'm glad to see that someone besides me still knows how to do manuvering board (solutions). By hand no less. Navigation is not dead!

Anyway, the reason that I asked what I did earlier, about using a handheld (or fixed) GPS to calculate some of what you're after, is that back in the early 90's, we did exactly what I described using a friend's handheld, when we were delivering his boat from San Diego to Dana Point.

It's an uphill trip (100% to weather), & we were on a Newport 30', so we could use all the help that we could get. And with both of us being serious racers, we decided to try some new toys & tools. Thus I showed him how to input Dana Point as our destination, & then pull up the various performance screens: SOG, COG, VMG, SMG, etc.

Then, with the GPS set to show VMG as the primary (info output), we played with footing off in 3-5 deg. increments in order to see what it did to our VMG. And similarly, whenver the AWS, or TW varied by any significant amount (2kts, or 3-5 deg.) we'd do the same thing with regards to our heading, & check our VMG again.

It was a fun experiment, & also gave us some quality time on the helm, practicing staying on course while using as little rudder as possible, with zero distractions. Unlike when you're racing, where sometimes there's too much noise, or information for a helmsman to fully concentrate on just steering.
While of course also letting us put together a mini set of polars for how his boat went to weather in the various conditions of the day. With his "enhanced" rig, & the main & the #1.

His rig was from a larger racer, & was about 10' taller than standard. Once we'd optimized it to fit with the sails that came with it, & made & fitted some shrouds to it. So we were curious to test it, & get some performance data.
It was fun day of testing (especially for a delivery), as until the advent of cheap GPS at that time, you needed a full B&G instrument suite in order to get the info that the handheld was giving us. And such instrument packages cost about what a mid-level new car did, back then.

Speaking of which, I'm curious to know what your instruments setup is like, if you don't mind. And posting it may also help some others to assist you in figuring out how to "wire everything together" in a manner that'll let you easily call up the data that you want in real time.
Especially as I'm 95% sure that you already have the capability onboard with the hardware & software that you currently have. It's just that I'm not fully up to speed on the latest stuff. Nor an electronic nav wizard.

That said, there are multiple ways to input Polars into OpenCPN. Here are links to a few of them, as found via the OpenCPN website's search function, where I typed in "Input Polars".
And no doubt, some other searches of the site, & software will turn up more info on this. Though this search also shows you how to sync up data from NMEA instruments. And by virtue of doing so, it'll create a set of Polars for the boat in your nav software.
Polar | Official OpenCPN Homepage
NMEA Instruments | Official OpenCPN Homepage

With all of the other bells & whistles that this software, & that which comes with instruments, etc. have, I can't imagine that your gear won't do what you're aiming for. Perhaps bribing the navigator from a racing boat's in order? And if you do, set up a video camera to "take notes" for you, about what they do in order to get more, & better information out of your system.

Also, I'd reckon that most of the instrument manufacturer's websites have a good bit of information on this, as well as relevant links. Especially ones like B&G, NKE, as well as the next tier down.
Plus again, there will be a plethora of info over on SA forums on these topics. On that I'd wager immensely.

Good luck, & have fun playing with the toys. Just don't let them boss you around in terms of telling you how to drive the boat


Edit: Here's another helpful search from the OpenCPN website on Polars Search | Official OpenCPN Homepage
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Old 30-09-2016, 14:24   #11
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Re: VMG calculation software

Uncivilized, we're sort of between generations on our electronics, and this is part of the difficulty. That, and I'm too lazy to try to get it all talking to each other. In reality, we have 2 pretty good computers on the instruments, which would both probably do the job if I could figure out how to network it all.

But, as I said, it's a matter of actually doing it and getting it to work. Sort of a work/reward question.

So, here's the setup on RS in more detail.

Our sailing instrumentation is the B&G Hydra 2000 system, about 2007 vintage. We have 6MFD's, one analog display, and of course the wind speed and depth/speed ducers are all H2000.

The autopilot is an NKE gyropilot. new last year. As an aside, this is the best performing pilot I've ever used. We're using a Whitlock electric drive. I think this thing's probably 15 years old and is still going strong.

This has a single MFD at this point. It's functioning as a standalone pilot, but it has wind angle/speed and boat speed fed to it via 0183 from the B&G.

The plotter/radar is a B&H zeus, first generation. No sailing functions here.

I also have a PC in the nav station. We're mellow enough about this VMG question that I would be fine with just having this function on the PC for now, at least until we ditch the H2000.

I'm not sure if the program we're discussing here quite does the job, if only because inputting the boat's polars looks like it's going to make me go cross-eyed before I'm a quarter of the way done. But, I'll try to take an afternoon and input it all and see how it works.


Longer term, the H2000 is getting a little wonky, but I'm waiting for it to die before replacing it. The replacement will be entirely NKE. This is for 2 reasons, one we already have a processor with the gyropilot, so we just have to add a few MFD's and ducers, and 2, it's just really good equipment if the autopilot's any indicator.

As far as bribing a racing navigator, you might be on to something! There are plenty of them around looking a bit bored in these parts. I think most of them have already put their boats away for the winter...

TJ
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