karlh
New member
What are the pros and cons of using a gps only as a log? I need to fit a log to my trailor sailor and am thinking a cheap gps unit may be the way to go, no holes,no impeller cleaning,speed over ground.
GPS as log
- Thread starter karlh
- Start date
Joe_Cole
New member
It depends on the sailing you are going to be doing.
If you are going to be day sailing/coastal cruising then no problem just using a GPS. If you want to do "proper navigation" (which is fun!) then you'll need a log. If you want to get the best performance out of your boat then (in my view) you need a log.
I have no doubt that some will tell you that your GPS may pack up so you need an alternative method of navigating but, in my experience a log will be far more unreliable than GPS!
Having said all that I prefer to have both systems.
If you are going to be day sailing/coastal cruising then no problem just using a GPS. If you want to do "proper navigation" (which is fun!) then you'll need a log. If you want to get the best performance out of your boat then (in my view) you need a log.
I have no doubt that some will tell you that your GPS may pack up so you need an alternative method of navigating but, in my experience a log will be far more unreliable than GPS!
Having said all that I prefer to have both systems.
geoffatstanpit
Member
I have what could be described as a trailer sailer (but it's less hassle to have it on a mooring just across the road) and I have a GPS and a log.
I keep telling myself how good it would be to have both working so I could tell if the tide had turned and by how much.
But the GPS is so easy and I haven't got around to all the wiring and finding somewhere to fix the whirly thing. One day I might think it's important enough. Probably the day when I'm in the middle of the Channel in fog and George turns off the satellites.
Geoff
I keep telling myself how good it would be to have both working so I could tell if the tide had turned and by how much.
But the GPS is so easy and I haven't got around to all the wiring and finding somewhere to fix the whirly thing. One day I might think it's important enough. Probably the day when I'm in the middle of the Channel in fog and George turns off the satellites.
Geoff
VicMallows
New member
If I had to choose between the two, I'd pick a GPS anyday. Before it gave up altogether by thru-hull paddle was always fouled for around half the time, and even when it was apparently working I had no faith in its reading. I now have a CLIPPER DUET but havn't got around to connecting the log part as the paddle assembly is a different size to the old one and the boat's afloat.
Vic
Vic
Oldhand
New member
I'm surprised this question is asked. Surely you wish to check your are sailing efficiently and the sails are properly trimmed? /forums/images/graemlins/confused.gif The best indicator of this is your speed through the water thus a log is necessary. The effect of currents on your SOG makes a GPS useless as a log for sailing efficiency purposes.
mirabriani
New member
Right!
whenever I have keen dinghy racers as crew
they seem to do the tweaking and check the log.
Regards Briani
whenever I have keen dinghy racers as crew
they seem to do the tweaking and check the log.
Regards Briani
karlh
New member
Thanks for your advice.Thats why the question was asked.
webcraft
Well-known member
I disagree with the premise that GPS SOG is useless as a guide to sailing efficiency. In most locations trimming the sails will result in your SOG going up and down rather more immediately than the changes in tidal flow.
I like to have both, but the log packs up for longish periods of time and we manage to sail perfectly efficiently just using the GPS repeater. Of course, we know what the tide is doing, which helps. (And we regularly sail through places where the tidal stream runs at anything up to six knots).
If I had a trailer sailer I would be inclined to use GPS only and not put a hole in the hull.
- Nick
I like to have both, but the log packs up for longish periods of time and we manage to sail perfectly efficiently just using the GPS repeater. Of course, we know what the tide is doing, which helps. (And we regularly sail through places where the tidal stream runs at anything up to six knots).
If I had a trailer sailer I would be inclined to use GPS only and not put a hole in the hull.
- Nick
FlyingDutchman
New member
Interesting thread!
Does it mean that in a motor boat the choice would be the GPS as sailing efficiency is not an issue?
Just curious because I am planning to buy a GPS (Garmin 72) for my motor boat which does not have a log.
Best wishes to all,
Jan
Does it mean that in a motor boat the choice would be the GPS as sailing efficiency is not an issue?
Just curious because I am planning to buy a GPS (Garmin 72) for my motor boat which does not have a log.
Best wishes to all,
Jan
duncan
Active member
basically 'yes'
you won't find any planning motorboats using trailing logs (they won't stay in the water) and equally paddlewheel and pitot based systems are going to have errors.
you won't find any planning motorboats using trailing logs (they won't stay in the water) and equally paddlewheel and pitot based systems are going to have errors.
lockwood
New member
I have just bought a NASA log, after having used my handheld GPS for the past 2 years as a log.
I am a bit confused as to how the log will measure my speed, as I assume the current is enough to turn the paddle wheel of the log even when I am anchored.
Am I correct in thinking that if I take the SOG (from the GPS) and take the log (of the paddle wheel variety) away from it, I will get an indication of the tide speed?
I am a bit confused as to how the log will measure my speed, as I assume the current is enough to turn the paddle wheel of the log even when I am anchored.
Am I correct in thinking that if I take the SOG (from the GPS) and take the log (of the paddle wheel variety) away from it, I will get an indication of the tide speed?
whisper
New member
You are absolutely right. If the paddle wheel is showing, say 2 knots, when you know you are stationary then that is the speed of the current/tide. Similarly, as you suggest, the difference between the log reading and the GPS speed gives you the approximate rate of the tide/current that is affecting your forward progress.
William_H
Well-known member
I got so grumpy with my log in my trailer sailer (moored) that I have removed the paddled filled the hole and put a ventilator grill in place of the dial. It is most depressing having an instrument that won't work either due to failure of the paddle sensor or fouled with weed. I am not convinced that you need a log to trim the boat sails, you should know if they look right. Anyway I do use a little Garmin Etrex on occasions the only down side being that the read out of speed is rather small but the navigation function for finding buoys makes up for that. So don't buy a log look out for a GPS with big readout. (from one who doesn't have to battle tidal currents) regarsds will
Colvic Watson
Well-known member
IMHO the only real purpose of a log is to assist with DR navigation in order to confirm/call into question a GPS reading. I therefore wouldn't sail out of close proximity of land without a log. Having said that, 99% of my sailing is by pilotage, not navigation (i.e. within easy sight of land) and so unless it gets foggy I would back up a GPS with land sights / buoys. If it gets that foggy I would either trust the GPS or anchor. A log would mean a rather fraught bit of mental arithmetic using a tidal atlas etc for the kind of sailing we do. Plus the flippin paddle wheel will have got fouled anyway. /forums/images/graemlins/crazy.gif
milltech
Active member
This is what I do because the log has failed. The thing is I know how fast the boat is at given revs, so any difference is tide. I think there is a value is knowing how fast your boat is at different revs, but there are ways of establishing this either in non tidal areas or between the measuring markers here and there, (a bit of a time consuming pest though).