Windy
Active Member
Are expensive speed/log instruments relevant now that GPS is available?
Speed/Log instruments
- Thread starter Windy
- Start date
chrisc
Well-Known Member
GPS does not give you the same information..ie. speed over ground as opposed to the speed thru water.
john_morris_uk
Well-Known Member
[ QUOTE ]
GPS does not give you the same information..ie. speed over ground as opposed to the speed thru water.
[/ QUOTE ]I agree - although you will find a few forumites declaring that
1. They can't bear the thought of another hole in their hull.
2. The log is redundant because it gets fouled or needs calibrating..
I maintain (STRONGLY) that if you have GPS and log, it tells you firstly how fast you are actually going (as against what the tide stream and you are doing...) and secondly, you can tell what the tide is really doing when you compare SOG and LOG.
No contest - a log is not redundant. (and we carry a Walker mechanical trailing log for when all else fails!)
Of course if you are not a commerical vessal, you can take your pick. Its a free country and its your choice what instruments you put on your boat.
GPS does not give you the same information..ie. speed over ground as opposed to the speed thru water.
[/ QUOTE ]I agree - although you will find a few forumites declaring that
1. They can't bear the thought of another hole in their hull.
2. The log is redundant because it gets fouled or needs calibrating..
I maintain (STRONGLY) that if you have GPS and log, it tells you firstly how fast you are actually going (as against what the tide stream and you are doing...) and secondly, you can tell what the tide is really doing when you compare SOG and LOG.
No contest - a log is not redundant. (and we carry a Walker mechanical trailing log for when all else fails!)
Of course if you are not a commerical vessal, you can take your pick. Its a free country and its your choice what instruments you put on your boat.
homa
Well-Known Member
Depends what you want it for.
As already mentioned, when the log speed is compared with the GPS (ground) speed it will give a good indication of the current.
Something else that the log speed is very useful for is speed input for a radar for MARPA.
A log speed should always be used for this otherwise you will not get the true vectors of the other vessels (if there is any current).
Personally I'd consider fitting a speed log before a fixed GPS.
As already mentioned, when the log speed is compared with the GPS (ground) speed it will give a good indication of the current.
Something else that the log speed is very useful for is speed input for a radar for MARPA.
A log speed should always be used for this otherwise you will not get the true vectors of the other vessels (if there is any current).
Personally I'd consider fitting a speed log before a fixed GPS.
pvb
Well-Known Member
Sure?
[ QUOTE ]
Something else that the log speed is very useful for is speed input for a radar for MARPA.
A log speed should always be used for this otherwise you will not get the true vectors of the other vessels (if there is any current).
[/ QUOTE ] Sure about that? Raymarine reckon that SOG is vital.
[ QUOTE ]
Something else that the log speed is very useful for is speed input for a radar for MARPA.
A log speed should always be used for this otherwise you will not get the true vectors of the other vessels (if there is any current).
[/ QUOTE ] Sure about that? Raymarine reckon that SOG is vital.
homa
Well-Known Member
Re: Sure?
Yes I'm sure
It's not so much speed of other targets that so important as their aspect relative to you. If you only use SOG and therefore COG, with no allowance for current then you will only have a rough idea of the other vessel's Heading and aspect. This is rather important when interpreting the Col Regs.
I would say that for small boat radars then it is less vital as their acuracy is lower.
On commercial ships we tend to use log speed where possible.
Yes I'm sure
It's not so much speed of other targets that so important as their aspect relative to you. If you only use SOG and therefore COG, with no allowance for current then you will only have a rough idea of the other vessel's Heading and aspect. This is rather important when interpreting the Col Regs.
I would say that for small boat radars then it is less vital as their acuracy is lower.
On commercial ships we tend to use log speed where possible.
beneteau_305_553
Well-Known Member
Yep
I reckon you don't need them now. GPS are so good and reliable and so much cheaper. I still have one though.
I reckon you don't need them now. GPS are so good and reliable and so much cheaper. I still have one though.
pvb
Well-Known Member
Re: Sure?
Raymarine use SOG and COG as the basic inputs for MARPA. Within a smallish area, current can be expected to affect all vessels similarly.
Raymarine use SOG and COG as the basic inputs for MARPA. Within a smallish area, current can be expected to affect all vessels similarly.
Windy
Active Member
[ QUOTE ]
Yep
I reckon you don't need them now. GPS are so good and reliable and so much cheaper. I still have one though.
[/ QUOTE ]
Well so far we appear to be outnumbered
/forums/images/graemlins/grin.gif
Yep
I reckon you don't need them now. GPS are so good and reliable and so much cheaper. I still have one though.
[/ QUOTE ]
Well so far we appear to be outnumbered
/forums/images/graemlins/grin.gif
Sultans_Kapitein
RIP
Er what happens if your GPS fails, antenna breaks etc etc. Belts and braces are best to make sure you dont get caught with your trousers down. Ditto I will be fitting mechanical log as well as GPS.
Mal
Mal
William_H
Well-Known Member
It depends a lot on where your boat is. For example mine lives in an area of relatively warm water and little tidal currents. So the GPS tells me how fast I am going while the log paddloe is always fouled with little beasties. So I removed it and filled the hole. olewill
john_morris_uk
Well-Known Member
William, you always tell us how you have filled your log hole in when this subject is raised. Try sailing in the English Channel where there is always some current. Even my mooring has one or two knots flowing past the boat on spring tides.
I once did a lot of practical examining of people's sailing and navigation in the Med' (No tides and usually no current to speak of). For someone like me who has been brought up sailing in tidal waters with strong currents, navigation became ridiculously easy. If you point the boat South and cruise at 5 knots, you end up 5 miles South of where you started. Try doing that in the Channel - your boat is invariably effected by the tidal stream.
Perhaps this explains our different view points on the merits of logs and GPS. Of course you might argue that the GPS will tell you what is going on, and you are never lost, but for those of us who sailed before GPS, I think we remember how utterly stuffed we were without some tide tables, and a LOG to tell us how far we had travelled through the water.
Anyway, as I have said before, its a free world and people can fit what they like.
I once did a lot of practical examining of people's sailing and navigation in the Med' (No tides and usually no current to speak of). For someone like me who has been brought up sailing in tidal waters with strong currents, navigation became ridiculously easy. If you point the boat South and cruise at 5 knots, you end up 5 miles South of where you started. Try doing that in the Channel - your boat is invariably effected by the tidal stream.
Perhaps this explains our different view points on the merits of logs and GPS. Of course you might argue that the GPS will tell you what is going on, and you are never lost, but for those of us who sailed before GPS, I think we remember how utterly stuffed we were without some tide tables, and a LOG to tell us how far we had travelled through the water.
Anyway, as I have said before, its a free world and people can fit what they like.
bedouin
Well-Known Member
I have a log fitted but it frequently gets fouled up and so is almost useless.
I would think nothing about setting out on a coastal / cross channel passage without the log working and I certainly consider it much less important than GPS these days.
The one I wouldn't be without is the depth sounder. If all else fails with a chart and a depth sounder, and a rough idea of where you are, you should always be able to get to safety (although the constant reduction in the number of nav aids these days makes that less certain than it used to be)
I would think nothing about setting out on a coastal / cross channel passage without the log working and I certainly consider it much less important than GPS these days.
The one I wouldn't be without is the depth sounder. If all else fails with a chart and a depth sounder, and a rough idea of where you are, you should always be able to get to safety (although the constant reduction in the number of nav aids these days makes that less certain than it used to be)
andy_wilson
Well-Known Member
Yes, if you care at all about trimming your sails, even if you do it rather poorly.
ColinHuggins
N/A
I have a similar heritage to John above, (with Walker log as back-up. too!) and quickly augmented the existing gps with a 'proper' log. It didn't need another hole 'cos I ripped out the fishfinder . . .
I was apalled when Raymarine told me how to calibrate it using . . . the gps. Mind-boggling ignorance.
Anyway, my raison d'etre is to stay on the right side of the law - it's very easy when cruising around at 10 knots to continue at that speed right up the harbour. Oops! Actually you can in Pompey, but not in many other places.
Of course I like to know the effect of tide which causes the disparity between SOG and STW, and there is also that immediate indication if the engine is under-performing.
No, I don't work up the reckoning these days - but I could if need be (he says with fingers crossed . . .)
Regarding fouling, the ST40 set expressly advises pulling out if left unused for a few days. I don't, but have had no problem here in Chichester.
I was apalled when Raymarine told me how to calibrate it using . . . the gps. Mind-boggling ignorance.
Anyway, my raison d'etre is to stay on the right side of the law - it's very easy when cruising around at 10 knots to continue at that speed right up the harbour. Oops! Actually you can in Pompey, but not in many other places.
Of course I like to know the effect of tide which causes the disparity between SOG and STW, and there is also that immediate indication if the engine is under-performing.
No, I don't work up the reckoning these days - but I could if need be (he says with fingers crossed . . .)
Regarding fouling, the ST40 set expressly advises pulling out if left unused for a few days. I don't, but have had no problem here in Chichester.
Danny
Well-Known Member
I discovered a new (to me) method for calibrating my log weekend before last. We were on the pontoon at the Folley on Sunday afternoon and this became just about empty around teatime. I tried a sort of variation on a "Dutchman's log". I timed some bits of rubbish (plenty of these about) floating down the Medina on the ebb. Nice long visitors pontoons so I could do this over a fair distance. Got an average speed for the current, turned on the log, a Stowe paddle wheel type, and compared the two. Adjusted the log to be as near as possible to, but slightly more than, the measured speed.
I must have been bored...
I must have been bored...
