What is more accurate for speed, navionics or nasa log?

[Chiara’s slave]

Mine is pretty new and can’t do that. And as for best tack etc, the system might know that, in the instant, you might better off on the other tack, but in coastal waters, a decent crew are going to do better than any instrument system. You might see wind on the water, be heading for shallows or a known back eddy, or that the tide is about to turn. On a long passage maybe instruments can do better, but inshore, you can’t beat local knowledge and keen observation.

 

[Rappey]

I replaced the paddlewheel with a nasa electro magnetic log. Accurate to 0.1knts ? Can be bought as pulse or nmea.
Fun to see the current when moored.

 

[Rhylsailer99]

NASA logs are notoriously unreliable. Mine works for 2 weeks after going in the water and then doesn't do anything for the rest of the season.

Pulling them out to clean always seems a risky procedure as well, having a bilge keel ,I much prefer to get underneath my boat when the water has gone to clean mine. I have read about them cracking and breaking when being removed from inside the boat.

 

[Daydream believer]

Speed through water is now of limited value except to measure change in boat speed, for example after changing sail trim or engine RPM.

I started out in the 70s with my sestral compass ( still use it)& a seafarer echo sounder. Speed was calculated by stuff chucked over the bow & timed with a stop watch as it went past the stern .I had a table written up to get an idea of speed. When i did get a log it was a revelation.
However, even now I really enjoy turning off the chart plotter or at least not using it. I do need it for AIS, so crossing shipping lanes , Dover Straits etc it is turned on.
But when going most places typically Ostend I love to get to the Longsand head, bear 127 degrees & see if I can still see the Centrum building where it is supposed to be. ( I am sure they sometimes move it out of spite)
It is all part of the joy of sailing.
Sailing round the Channel islands really puts one's skills to the test & when my wife used to go with me she would be watching the Yeoman plotter & seeing how well I was doing. Generally OK. Well we did not hit any rocks. But I have hit a few sandbanks in the Thames estuary. A lot in fact.

 

[john_morris_uk]

Pulling them out to clean always seems a risky procedure as well…

. I have read about them cracking and breaking when being removed from inside the boat.

Really? I’ve never heard of such a thing.

I’ve had crew who hated me taking the paddle wheel log out, so I understand the fear. However IMHO it’s an irrational fear as the chance of you sinking is vanishingly small. Even if I had to leave a fountain of water rushing in because of some catastrophic failure that stopped the blanking plug fitting, the boat wouldn’t be anywhere near sinking in the time it took me to get something else to jamb in the hole.

 

[Buck Turgidson]

Really? I’ve never heard of such a thing.

I’ve had crew who hated me taking the paddle wheel log out, so I understand the fear. However IMHO it’s an irrational fear as the chance of you sinking is vanishingly small. Even if I had to leave a fountain of water rushing in because of some catastrophic failure that stopped the blanking plug fitting, the boat wouldn’t be anywhere near sinking in the time it took me to get something else to jamb in the hole.

Mine comes out after every sail. Sometimes during if I forgot to take it out last time or as is more frequent, I forgot to put it back in!
Once you've done it a couple of times it's a none event. 1 cup of water max.

 

[Chiara’s slave]

I got an invitation to race on an 8m in British Classics week, a few years ago. I turned up with time to spare, at Cowes yacht haven. The owner blithely told me he was off to sign on, and to stick the log in the hole. Strange, valuable classc boat, afloat, swap from blank to paddle wheel. I did not enjoy that. All very well when it’s your own.

 

[john_morris_uk]

I got an invitation to race on an 8m in British Classics week, a few years ago. I turned up with time to spare, at Cowes yacht haven. The owner blithely told me he was off to sign on, and to stick the log in the hole. Strange, valuable classc boat, afloat, swap from blank to paddle wheel. I did not enjoy that. All very well when it’s your own.

I think the skipper had the right attitude. It’s not exactly a high risk activity…!

 

[Chiara’s slave]

I think the skipper had the right attitude. It’s not exactly a high risk activity…!

I was just a bit taken aback, I had to take up various bits of floor even to find the damn thing. Flattered he was confident to leave me to it I suppose.

 

[Refueler]

Speed through the water has immense value, at least to me. In terms of navigation over distances, naturally the ground speed takes priority and frees one from the need for dead reckoning. I use water speed for:
Getting True wind speed and angle
As my most important reference when close-hauled, almost more so than the wind angle
As a guide to how well my engine/prop are performing. There have been several occasions in open water when I have noticed my speed drop about a third of a knot due to weed fouling. This would not have been noticeable from the GPS and no vibration was felt through the saildrive, and a short burst astern cleared the fouling, allowing me to continue at full speed, important over a leg of perhaps 100 miles.

I also value STW a lot ... as another says - the tuning of boat shows in STW ...

But John ... I'm not agree about using STW to get True Wind Speed / angle ... surely you would use SOG / COG as the wind has no reference to water ....

 

[Refueler]

Navionics gives very accurate speed over the ground. Your log gives speed through the water and less accurate, Depends what you want.

Isn't accuracy based on what the reference is ?

Log can be accurate for speed through water ... regardless of its value compared to SOG ?

 

[Refueler]

As to OP ... I would suggest he adjust the alignment of his log after calibrating .. its surprising what speed variation can be achieved just by twisting it a few degrees ...

 

[Buck Turgidson]

I also value STW a lot ... as another says - the tuning of boat shows in STW ...

But John ... I'm not agree about using STW to get True Wind Speed / angle ... surely you would use SOG / COG as the wind has no reference to water ....

Depends on the definition of True wind.

 

[Chiara’s slave]

Depends on the definition of True wind.

Was about to say the same. The true wind you sail to is the wind after the tide has done it's dirty work, and maximising progress has to take that into account.

 

[Refueler]

Depends on the definition of True wind.

??

The deciding factor is in the word 'true' ?? I assume you are using data to determine the true wind direction and speed ...

Interested to hear of another 'true wind' ..... please - genuinely interested.

Of course there's always Vectors ... but they are another matter.

 

[Refueler]

Was about to say the same. The true wind you sail to is the wind after the tide has done it's dirty work, and maximising progress has to take that into account.

Surely you are now talking about vectors etc. ... different matter to TRUE wind

I still have a sailing calculator for that sort of stuff ... wind vectors to maximise etc.

 

[Buck Turgidson]

??

The deciding factor is in the word 'true' ?? I assume you are using data to determine the true wind direction and speed ...

Interested to hear of another 'true wind' ..... please - genuinely interested.

Of course there's always Vectors ... but they are another matter.

wind direction with reference to a stationary object on the ground. True wind relative to the vessel not making way.

Lots of threads on this topic.

 

[Chiara’s slave]

??

The deciding factor is in the word 'true' ?? I assume you are using data to determine the true wind direction and speed ...

Interested to hear of another 'true wind' ..... please - genuinely interested.

Of course there's always Vectors ... but they are another matter.

Of course theres only one ‘true wind’. It’s more accurate to say there are 2 apparent winds, I suppose.

 

[Refueler]

wind direction with reference to a stationary object on the ground. True wind relative to the vessel not making way.

Lots of threads on this topic.

So there may be .. but now as I mentioned - that is now in the realm of vectors .... and as Chiaras Slave has accepted - Apparent winds.

 

[Buck Turgidson]

Of course theres only one ‘true wind’. It’s more accurate to say there are 2 apparent winds, I suppose.

I used to agree this point and suggest "sailing wind" or some such. But as all the boat polars are called "true" but are really not the "true" one would expect when fixed I gave up.

"True" wind angle as used in sailing performance is the angle between the water vector and the wind vector as that is what drives the boat.