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Old 04-09-2012, 07:43 PM   #15
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Hi, SV Adventure. Thank you for the detailed product information. Could you please introduce yourself-- explain who you are (SV Adventure) and your relationship to the company? That would be helpful to our understanding of your use of the product or your loyalty to the vendor.

Knowing how long it takes to get into harbor and back to one's slip or into a particular anchorage is a very good thing, yes.

Products such as this are extremely appealing to newbie weekend sailors who may be very frustrated when they misjudge the time they need to return to the slip. Often even very experienced sailors don't have sufficient experience with local wind and current conditions and miss deadlines/commitments because, well, the elements don't always cooperate, do they?

Fair winds,
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Old 04-09-2012, 11:28 PM   #16
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Thanks S/v Adventure. So my laptop with bluetooth and wifi will be able to use the nmea sentences as is or is there some sort of coding that procludes this? I guess you can tell I'm not a really savy computer geek. Polar Navy ( which is great) has instruments which use nmea sentences. The Sailcruiser software looks good also and I see radar will work with it as well.
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Old 04-10-2012, 10:07 AM   #17
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I recently had a look at the NASA current model for the planet which was interesting because it shows that mostly they travel in a cyclonic fashion..... seeing that I immediately thought of how my racing ferro travels faster on one tack than the other. I'm guessing the circular movement of the water may have a lot to do with this.

If a current is say half a knot against on one tack then most likely will make a one knot difference on the other.
We have a friend who used to track all our passages as we meandered across the globe. When we sailed from French Polynesia to Beveridge Reef we passed the Cook Islands. Our friend wrote to us asking how scary was it passing between two of the islands.

I was puzzled by his question since we never saw any of the Cooks as we passed by. Looking on one of our charts, it dawned on me that 70 miles (the distance between two of the islands) looked to be about a hair's-breadth on the chart he would have used, and sitting in one's home looking at sea maps could be confusing.

I think it's the same regarding the currents in the oceans. A picture on one's monitor isn't easily understood in terms of hundreds of miles of breadth.

SV Watermelon sailed a good half knot faster on a starboard tack than on a port tack. As diligent as I tried to be trying to distribute weight evenly on the boat, just the placement and configuration of our water tanks could make a 200 to 400 pound weight difference, translated into a few degrees difference in heel, on tack to the other. And no boat is perfectly symmetrical anyway, so there are lots of variables to how a boat can sail.

Gadgets. I like gadgets, but I am still skeptical about things like a tacking GPS for a cruising sailor. And for the day sailor as well.

For long distance cruising comfort and large-scale variations in wind and current have so much greater effect on one's time of arrival that the minor variations in speed wrt tacking are, IMO, immaterial. We used to joke that we could go for days on one tack, negotiating with each other about when we should flop over to the other tack.

For the day sailor, by the time he decided to head back to harbor his fate was sealed. Until he flopped over and settled onto a return tack to harbor, no device could tell him how long it would take. He had either given himself enough time to get back, or he hadn't, and a gizmo telling him he was right or wrong can't be that much help.

Experience is invaluable, and until a sailor gains that, all the electronics around can't bring him home safely.

End of today's stint as the curmudgeon.
J
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Old 04-10-2012, 11:59 AM   #18
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I read the manual and I'm excited by this tech. However If I had a $1500 windvane onboard maybe not. I've been saving for a vane and this little beauty is priced right and has the latest tech. This gps learns your polars and the skipper is its teacher so what it learns is under control.
For me its not so much about getting home for tea as choosing the fastest or most efficient route.
I agree JeanneP simitry is important and may indeed be the reason some yachts are faster on one tack. I've tried to centalise the weight on mine by putting the house batteries under the table and against the mast suport. still think the current will have a large effect on this but if its the same side that is faster constantly my argument falls flat on its face. I think most properly built yachts would be so close to symmetrical that it wouldn't matter at all but we have the situation where growth seems to like one side of the yacht more than the other. My experience of the great craftsmen who build these is of an accuracy and itegrity to the drawings that is astounding. These folks take a lot of pride in their work. Really interesting to see this NASA world currents research in action. Here's a link.......http://www.gizmag.com/perpetual-ocea...ization/22024/
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Old 04-10-2012, 12:43 PM   #19
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Danblu, As it notes on the website, the NMEA sentences are open and standard that are sent from the solar-powered, wireless SailTimer Wind Vane. So if other products like Polar Navy can read NMEA wind sentences, then they should be able to receive and display the wind data sent through the air via Bluetooth or wifi. (I don't want to document my own name for posterity here, but am just trying to offer any helpful clarifications about product details from the information available.)

Your comments were interesting JeanneP. I agree with your point that we don't want to take the fun or seamanship out of sailing. But when making our judgments about whether we can make it back to the dock by lunch or to the coastline before dark, it is important to have safe, reliable information. Not ETA. ETA does not account for tacking distances. And if it does not know how far you are going to travel, obviously it can't correctly calculate how long it is going to take. Tacking Time to Destination is a better measure for sailors. You don't want it to replace your judgment and seamanship, but you want to use your judgment based on correct information. :-)
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Old 04-10-2012, 04:29 PM   #20
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...and I think it would be good , especially for racers, but also cruisers if forced to go to windward. Apparently it calculates different tacks to see which is the fastest which for most people is a guess. App for ipad also but I have a pc onboard. I don't have any wind instruments onboard as yet so I'm waiting to see reports on this vane.
... there is absolutely no need to combine the GPS with a wind vane as long as the GPS has the VMG-Funktion (velocity made good) already built in. Even my small backup Garmin out of the late 90ies has this function. A good explanation is found here: Velocity made good - Wikipedia, the free encyclopedia

Yes, this sailing GPS might have the advantage that I don't have to tack to find out myself if the VMG on the other leg might better. But I could live with that...

And as wind direction and windspeed is just one factor that decides about the ETA, what about possible tidal currents that will change for sure later on? There is no sensor for that?

And what happens if the wind is veering or backing later on? Is the sailing GPS linked to any weather GRIP-data sources to be able to "look into the future"?

So, a fine toy on the hour out on the racing triangle, but not so necessary for longer passages...

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Old 04-10-2012, 05:57 PM   #21
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Hello Uwe, With respect, allow me to suggest a clarification... The VMG that you are referring to on your GPS is not actually an acceptable measure of velocity. You cannot, for example, see that your VMG is 10 knots, and calculate that since you have 5 nautical miles to go (in a straight line without accounting for tacking distances), that therefore you will arrive in 2 hours.

One problem with this is that it doesn't account for the actual tacking distance you will travel (or your actual boat speed during the length of the tack). Did you know that if you are on the correct tack going upwind with a constant speed, that the VMG you are referring to will decrease all by itself the longer you stay on the tack? It will go all the way down to zero, and even into negative numbers. Not a very good measure of velocity.

There is a detailed explanation of how this happens with Velocity Made Good (VMG), if a geometric proof is helpful, in this article from GAM on Yachting magazine (863 k PDF). Or, you can just try it yourself sometime and see it happen on your GPS. Tack to a waypoint upwind, and watch the VMG decrease even though your speed and heading remain constant, the longer you stay on a tack.

That is why it is better to see a display with your optimal tacks, the exact distance on each tack, and the Tacking Time to Destination (TTD).

You are right that The Sailing GPS does not account for GRIB data or water currents, although the same SailTimer calculations are in the full-featured chartplotter software from NavSim (for Windows) and MacENC (Apple) mentioned on page 1, and these do include many other parameters such as GRIB, water currents and AIS.
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Old 04-10-2012, 07:07 PM   #22
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SV Adventure--you are surely in love with the technology--that is certain

Can you please, as I asked you before, explain your relationship to the manufacturer? Also, in what sailing venues have you personally used the technology? Do you sail? I almost get the impression that you do not sail or at least don't cruise based on your responses.

Thanks.

VMG

I think of the times when wave conditions require us to change tack to non-optimal so we'll have a decently comfortable ride or not be soaking wet Also, the funny sails when the wind and waves are just right to generate the perfect sailing at hull speed one one tack and...70% of hull speed on the other tack

Knowing one's boat and that boat's responses to particular conditions makes a huge difference to knowing when one is going to arrive--and where!

Time is most definitely on the side of the cruiser. The cruising sailor is in luck, though, often our passages are long enough that we can adjust and trim to arrive to a port or anchorage during daylight hours vs in the night. Luckily, our "window" of daylight hours is pretty big. And, luckily, we can often choose to simply heave to and await the daylight hours, or the right tide to clear the bar on a harbor entrance, or what ever the challenge may be.

Winning a race, no we are not. Living a lifestyle at sea, yes.
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Old 04-10-2012, 07:32 PM   #23
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Default Other competing technologies

There are other competing technologies out there (for the wind indicator). The compass, gps, and wind instrument in the Airmar weather station, for example, can provide NMEA 0810 or 2000 data to your computer. I've been intrigued about the Airmar because the wind instrument can't be killed by a passing Osprey who decides to sit on it (as our last wind instrument was!). Having said that, we had the older version of this Airmar (ours a PB100) on the boat but we've never used it as our (new in 2009) wiring inside the mast is bad so we've not "fixed" it yet by running a new power line to it. That's on the 2012 list of things to do.
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Old 04-10-2012, 08:46 PM   #24
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Hi Aquaria, you r opinion regarding a combination of a windvane and a gps is opposite to mine. I think its about time and an excellent developement. Add some paper charts and you,ve got it covered.
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Old 04-11-2012, 04:32 PM   #25
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... s/v adventure,
I hope you find it okay that I put my answers right into your detailed reaction


With respect, allow me to suggest a clarification... The VMG that you are referring to on your GPS is not actually an acceptable measure of velocity. You cannot, for example, see that your VMG is 10 knots, and calculate that since you have 5 nautical miles to go (in a straight line without accounting for tacking distances), that therefore you will arrive in 2 hours.

you are right - absolute numbers do not really help and I do not get to know the ETA. But when tacking I can compare the VMG-data of the starboard- and port-tack and then I love to do the trial and error thing, which is acceptable to me: sailing on one tack for some time and when the VMG deteriorates under a certain number (which has to do with experience), I change to the other bow and check the new data and when they meet my expectations, I continue on this tack. SO, it's just another philosophy of tacking: I'm doing my legs to windward like I learned it before the time of electronic navigation devices, and then (GPS is a fine thing to have) I love to look at the GPS to see, if the VMG is better than before... and so on!

One problem with this is that it doesn't account for the actual tacking distance (...which I personally don't really need to know, tacking can be awful: double distance, triple time and four times as much hastle) you will travel (or your actual boat speed during the length of the tack (... I know my speed very accurately - either as speed through the water given out by the traditional speedometer or by GPS which shows the exact speed over ground!)). Did you know that if you are on the correct tack going upwind with a constant speed, that the VMG you are referring to will decrease all by itself the longer you stay on the tack? Yes. It will go all the way down to zero, and even into negative numbers.Right, and here has do be made a decision way before it reaches the Number Zero, as I explained above. Not a very good measure of velocity but a pretty good measure deriving out of experience over the miles you drive your boat to windward.

There is a detailed explanation of how this happens with Velocity Made Good (VMG), if a geometric proof is helpful, in this article from GAM on Yachting magazine (863 k PDF). Or, you can just try it yourself sometime and see it happen on your GPS. Tack to a waypoint upwind, and watch the VMG decrease even though your speed and heading remain constant, the longer you stay on a tack. ... yes and in this very situation I love to decide when to tack or not and (referring to Fig 2 on page 29 I know out of own experience and with a brief look into the chart that I should continue on the track, even though the VMG will deteriorate still below 1,5kn/2,6 hours, because after another mile the vmg will be at its optimum!!! For this I don't need a display and it's playing with the elements and leaving decisions to myself and not to the onboard electronic devices.
That is why it is better to see a display with your optimal tacks, the exact distance on each tack, and the Tacking Time to Destination (TTD). If the display leads to the situation that the helmsman never learns to decide himself when there is the best time to tack, it is not so good and has nothing to do with learning how to sail.

Maybe it might be a thrilling toy to test the own abilities and experience to drive your boat to windward, comparing the GPSs optimal tacks with our own decision.

But in normal sailing life these data would drive me nuts. It's okay to have navigational raw data to work with, but I love to work with them and do the decision making and the navigation.


You are right that The Sailing GPS does not account for GRIB data or water currents, although the same SailTimer calculations are in the full-featured chartplotter software from NavSim (for Windows) and MacENC (Apple) mentioned on page 1, and these do include many other parameters such as GRIB, water currents and AIS.

... so, interesting idea to combine wind data with GPS, but not really necessary...

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Old 04-11-2012, 05:48 PM   #26
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Well at least we are in agreement on the technical points, Aquaria. :-) And I agree that instruments are no replacement for good judgment and seamanship. The instrument readouts allow us to make good judgments.

Aside from all of the details though, for me one important thing is knowing when I am going to get there. Crew and family members may ask, too. It is difficult to give an accurate answer to that question when tacking upwind, no matter how much experience one has. You said you don't want to think about the hassle, which is fine for some people. But many people don't realize that ETA will not give an accurate answer, even though their GPS knows exactly where they are on the face of the earth. The Sailing GPS is an easy way to see what the correct Tacking Time to Destination (TTD) will be.

Different people have different preferences for how they like to sail, of course. (And however you approach it, it is good to know how to get the correct information if you do have to make a decision.) Thanks for sharing your approach -- it was interesting reading.
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