Speed and distance logs-do we need them?

[ffiill]

Given the variety of GPS receivers most of us have aboard is there any real need for stand alone paddle wheel,mechanical or trailing logs given the amount of time spent persuading them to give an accurate reading.
I have a fixed GPS aboard and ones in both my phone and tablet as well as navigation Aps in both.Plus a full laptop based system with its own GPS receiver.
Whilst I have a good paddle wheel system aboard half the time it end up weeded up and I am no longer sure of its use particularly when if like me your sailing is mainly Brest to the Elbe so to speak.
If GPS is ever turned off that will probably reflect the end of our civilisation anyway and in the meantime it has become an integral part of our technological society.

 

[affinite]

I no longer use a mechanical log but then my boat is in the Med so I rarely (if ever) sail in any significant tide or current.
If I was still in the UK I think Id want to know Speed over ground and Speed through the water.

 

[JumbleDuck]

I have a paddle wheel log which is invariably jammed up with little mussels after four weeks afloat. I'm far too scared to remove and clean it, so it stays that way, and I don't feel any loss. Quite the reverse, really, as I prefer to sail with as few instruments as possible. I use a Walker's log for longer trips, mainly for fun. GPS does all the important stuff.

 

[jwilson]

I sailed lots of miles without any electronics at all, so no I don't need the speed log: you can guess boatspeed accurately enough for reasonable DR if you have to. I don't bother to put the impeller in if it's just me sailing. If I leave it in when on the mooring it's reading slow in under a week and stopped after ten days with tiny crustacea.

There are times when a speed/distance log is nice, but rarely is it vital. I'm not a Luddite: I love chartplotters and the ability to easily and instantly work out VMG. But speed logs and windspeed instruments I can happily live without.

 

[Pye_End]

GPS does not give the same information as a log - having an accurate log may lead you to make different decisions than being without.

As you say, there can be difficulty is with accuracy. The Raymarine can be kept out of the water and just put in when needed quite easily, but this still won't help with the effects of fouling on the hull. Additionally logs may read differently on both tacks, and seem often poor at lower speeds. However, I also find GPS speed unreliable - I have several sets, and they all give different speeds, and play as I might with the smoothing I cannot to get them to read the same.

However, on balance, I miss being without a log when it is not available. It gives useful relative information, even given its inaccuracies.

 

[Giblets]

I have a paddle wheel log which is invariably jammed up with little mussels after four weeks afloat. I'm far too scared to remove and clean it, so it stays that way, and I don't feel any loss...........

I'm glad I'm not the only one then. Being a bilgy I must have a go at this drying out lark to clean the little beastie out!

Another vote for the Walker log.

 

[Georgio]

I would not like to sail without a log, yes it is a pain to keep it weed free but knowing what's going on with the tide can make such a huge difference to passage times it's really worth comparing SOG to LOG.

If nothing else it will help when coming into a berth and you want to know what the tide is doing.

 

[nigelmercier]

If nothing else it will help when coming into a berth and you want to know what the tide is doing.

So will popcorn thrown on the water.

 

[Georgio]

So will popcorn thrown on the water.

so will looking for the flow around a fixed object like a mooring pile.

There are many ways to skin a cat and using the log to check for tidal flow is a useful tool to have in your bag.

 

[Nigel-in-Oxford]

My NASA log is a PITA. Works for a couple of days after cleaning, but always reads low (varying amounts) I find I can guess within a knot just by looking at the water. Everything I need is on the chart plotter, or the iPad, or the H/H gps, or the iPhone........

 

[awol]

If you ever sit your Yachtmaster practical it will come in useful. My examiner was awfy keen on hiding me below pretending I was in thick fog with only the compass, depth meter and log to guide me - GPS was verboten.

For the OP, there are enough war games up in your neck of the woods when GPS gets jammed to make having a plan B a reasonable contingency.

 

[westhinder]

GPS does not give the same information as a log - having an accurate log may lead you to make different decisions than being without.

As you say, there can be difficulty is with accuracy. The Raymarine can be kept out of the water and just put in when needed quite easily, but this still won't help with the effects of fouling on the hull. Additionally logs may read differently on both tacks, and seem often poor at lower speeds. However, I also find GPS speed unreliable - I have several sets, and they all give different speeds, and play as I might with the smoothing I cannot to get them to read the same.

However, on balance, I miss being without a log when it is not available. It gives useful relative information, even given its inaccuracies.

+1
I would not be without my log.
I do not see the problem with fouling either. Whenever I leave the boat I remove the impeller. That does not cause a severe ingress of water, you are not going to sink the boat. On my first boat the through hull did not have one of those flaps to minimise the amount of water, but a quick action with the plug was all that was needed. Mopping up a few cc's of water is no pain. My paddlewheel has never needed more than a thin coat of antifouling at the start of the season.

 

[MoodySabre]

The only useful information is SOG. Will I get back to the marina in the tidal window? When will I cross a sandbank? If you need a log to know what the tide is doing then why don't you know that already. An East coast passage without knowing the tides would be barmy.

 

[Rigger Mortice]

My NASA log is a PITA. Works for a couple of days after cleaning, but always reads low (varying amounts) I find I can guess within a knot just by looking at the water. Everything I need is on the chart plotter, or the iPad, or the H/H gps, or the iPhone........

You're better than I am. It's easy enough to make a guesstimate when there is a fixed object on the water, but out at sea when on passage?

 

[Deleted member 36384]

Given the variety of GPS receivers most of us have aboard is there any real need for stand alone paddle wheel,mechanical or trailing logs given the amount of time spent persuading them to give an accurate reading…

There never was a need for them, they were just aids that increased the accuracy of navigation but one could still navigate without them, obviously. On the other hand do we need large varieties of GPS receivers on our boats? I don't!

 

[Athene V30]

The only useful information is SOG. Will I get back to the marina in the tidal window? When will I cross a sandbank? If you need a log to know what the tide is doing then why don't you know that already. An East coast passage without knowing the tides would be barmy.

Agree SOG from GPS is useful for knowing if going to achieve stages of the route plan but wouldnt be without my log for speed through the water so I can tell if I am sailing the boat efficiently.

Am fortunate that the raymarine log I have has a flap to close the hole as you withdraw it so not a lot of water comes in making removing the log when away from the boat much less stressful!

 

[Nigel-in-Oxford]

You're better than I am. It's easy enough to make a guesstimate when there is a fixed object on the water, but out at sea when on passage?

I chuck a crisp in the water and "time" it going past the cockpit

 

[AntarcticPilot]

If you're interested in the boat's response to sail trim, you need one. GPS is slow to respond to changes in speed - the interval between fixes is two seconds, and internal filtering of the positions to increase accuracy means that the speed output will be even slower to respond accurately to changes in speed. A paddle-wheel log responds pretty much instantaneously to changes in sail-trim, you can see the effects of your latest tweak immediately. If you rely on SOG, the wind may change over the period that it takes for the GPS to respond to your adjustments.

As others have said, it measures a different thing from your GPS SOG, and that may well be useful, especially if sailing in an area where there are back-eddies and turbulent flow below the resolution of tidal charts - most of the tidal gates on the West Coast of Scotland are like that. Knowing the tide vector is a different problem to knowing the height of the tide and is a much more difficult problem, and less tractable using tables etc. Combining log and GPS means you have potentially complete knowledge of the various vectors affecting your boat.

 

[ffiill]

GPS does not give the same information as a log - having an accurate log may lead you to make different decisions than being without.

As you say, there can be difficulty is with accuracy. The Raymarine can be kept out of the water and just put in when needed quite easily, but this still won't help with the effects of fouling on the hull. Additionally logs may read differently on both tacks, and seem often poor at lower speeds. However, I also find GPS speed unreliable - I have several sets, and they all give different speeds, and play as I might with the smoothing I cannot to get them to read the same.

However, on balance, I miss being without a log when it is not available. It gives useful relative information, even given its inaccuracies.

My st60 raymarine unplugs with ease. Why did I never thing to unplug it when not in use?

 

[JumbleDuck]

If you're interested in the boat's response to sail trim, you need one. GPS is slow to respond to changes in speed - the interval between fixes is two seconds, and internal filtering of the positions to increase accuracy means that the speed output will be even slower to respond accurately to changes in speed.

Speed is available directly from GPS using doppler analysis of the signals from the satellites in use. It can be done from differentiating positions, but that's a pretty crude method (differentiated error is never pretty) and I'd be mildly surprised if any GPS sets today did it that way.