Do I need a paddlewheel log?

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burgundyben

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If I had a GPS plotter and a handheld GPS as back up would I need a paddlewheel log?

On a sailing boat where one might be making 6 knots in 4 knots of tide I can see that the speed through the water is important, but on a boat where I'm unlikely to be doing less than 20 knots, the effect of tide and hence my speed and direction through the water is less of a factor albeit still there.

If the GPS system went down, I'd know my engine revs and hence speed, the longest leg out of sight of land where I need to do navigation rather than pilotage is Needles to Alderney, that is capped by range, so, never more than about 1hr 20 mins from sight of land, unless foggy I guess.

Worst case scenario, both GPS and both mobile phone GPS fail, or GPS system is shut down, visibility drops and I'm mid Channel. I know my course to steer as its on my passage plan, I know my speed derived from engine revs, I know the time I left my past estimated or known position. I have depth gauge.

Thoughts?
 
funnily enough I was thinking about this the other day and I don't think you do any more. as you say you know speed through the water from experience of engine revs, unless its a very strong tide you are probably more accurate than a paddle wheel log. I find them very inaccurate at planning speed if calibrated at low speed and vice versa. I no longer bother cleaning my paddle wheel sensor.
 
I don't have one at all. I despecced it in the boat build. Easy to add one if needed but I've never wanted one because it doesn't bring anything to the party. I'm in non tidal waters though.
 
No paddlewheel log on my boat; have a Garmin 820xs which reads out speed through the water, depth, distance to destination etc. and I know what speed a given RPM gives me.
 
AllanG said:
I thought GPS only measures speed over ground, not speed through the water?
Click to expand...

Mea culpa - across the ground, NOT through the water; I blame insufficient coffee for the error. Having said that, in a faster planing boat the difference is less critical than it would be in a 4-6kt sailing boat. Having said all of that, there is a section within the 820xs that gives the tidal info, so you can get the exact difference, should you want it.
 
No problem, Dick, as I just wanted to check if my understanding was correct...anyway, it sounds like your Garmin 820xs gives you all the information you need.
 
brand new airmar triducer installed.
1st Sept boat in water for the first time after the rebuilt, stupidly inaccurate readings (about 1/2 to 1/3 of GPS speed on flat calm seas and no currents/tide -that was even at D speeds!)
8th Sept after 40odd nm wheel stopped registering anything, totally pointless, wouldn't bother again.

V.
 
Like most people, we have one.
It always gets fouled up
But now it is now nice and clean - all nicely cable tied up in the engine room - been like that for 6 years.

I can think of a reason for using one though.
In tidal areas when you want the vectors and wind calcs to be correctly displayed on the plotters.
 
Vas - apologies if I am teaching you to suck eggs,but you do know you need to calibrate them for them to be accurate?
 
julians said:
Vas - apologies if I am teaching you to suck eggs,but you do know you need to calibrate them for them to be accurate?
Click to expand...

:D

no, you are right, only problem is I couldn't find a way to do it via the GMIs and by the time I figured out how on week 3 it had stopped registering any speed whatsoever on week2, if that's not pointless I don't know what is...
Mind I didn't a/f it as I couldn't figure out how to do so with all these thick paints on this delicate wheel without restricting movement.

Anyway, temp and depth works, so I'm happy with a 66% success rate :p

V.
 
Hurricane said:
Like most people, we have one.
It always gets fouled up
Click to expand...
+1.
Not that it really matters to me, anyway - in fact, I could easily reach it, pull it inside and clean it, also with the boat in the water, but can't be bothered.
It gets cleaned once per season, when the boat is on the hard, it works nicely for the first few weeks after she's back in the water, and that's just about it.
One thing is for sure: if I would think it's useful for my cruising conditions - even if just potentially, i.e. fog in tidal waters or whatever - I would spend a few more quids for an ultrasonic sensor, rather than a paddlewheel.
 
MapisM said:
+1.
Not that it really matters to me, anyway - in fact, I could easily reach it, pull it inside and clean it, also with the boat in the water, but can't be bothered.
It gets cleaned once per season, when the boat is on the hard, it works nicely for the first few weeks after she's back in the water, and that's just about it.
One thing is for sure: if I would think it's useful for my cruising conditions - even if just potentially, i.e. fog in tidal waters or whatever - I would spend a few more quids for an ultrasonic sensor, rather than a paddlewheel.
Click to expand...

You don't need one - your water is so clear you could just count the number of stones on the sea bed as you pass over them :D
 
burgundyben said:
If I had a GPS plotter and a handheld GPS as back up would I need a paddlewheel log?

On a sailing boat where one might be making 6 knots in 4 knots of tide I can see that the speed through the water is important, but on a boat where I'm unlikely to be doing less than 20 knots, the effect of tide and hence my speed and direction through the water is less of a factor albeit still there.

If the GPS system went down, I'd know my engine revs and hence speed, the longest leg out of sight of land where I need to do navigation rather than pilotage is Needles to Alderney, that is capped by range, so, never more than about 1hr 20 mins from sight of land, unless foggy I guess.

Worst case scenario, both GPS and both mobile phone GPS fail, or GPS system is shut down, visibility drops and I'm mid Channel. I know my course to steer as its on my passage plan, I know my speed derived from engine revs, I know the time I left my past estimated or known position. I have depth gauge.

Thoughts?
Click to expand...

I gave up on paddlewheel logs 10 years ago and have not regretted it. They were always getting fouled and now have one less hole in the hull.

Colin. Www.solocoastalsailing.co.uk
 
Nope never had one, can't imagine they'd likely be closer than 5% to true through the water speed and that's not good enough for accurate navigation is it?

Anyway if it all goes tits up on the way to Alderney surely the best plan is to turn left a bit and head for Cherbourg.
 
If you use your boat where there is any tidal flow, speed through the water gives you totally different info to a GPS which is speed over the ground and your position over the ground.

You don't want a paddlewheel which as you say are accurate only the day they are launched, but then foul up.

I have the a standard Raymarine Tridata with the speed transducer (electronic speed sensor) on the hull which has no moving parts (no paddle wheel). It appears very accurate to waves, hull fouling and resulting speed loss etc. This I use for my vessel performance and speed through the water and eventually my fuel and range calculations.

The only sensible range monitor in a motor boat is how many litres of the pink stuff to do a nautical mile Through the water.

After 6 months in the water I can see my speed reduce and fuel burn per mile increase until a scrub or a scrub and antifoul when it goes back to best reading.

Reading both Log speed and SOG from GPS gives you a good understanding of which way the tide is running as well during a trip. Around the CI's the tide generally is 1 to 6 knots.

What's the Point in having the best electronics, temperature sensor, fish finder, etc. If your electronics don't tell you the most basic thing "speed through the water".
 
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Bandit said:
I have the a standard Raymarine Tridata with the speed transducer (electronic speed sensor) on the hull which has no moving parts (no paddle wheel).
Click to expand...

I thought the standard Raymarine Tridata used a paddle wheel transducer, so would be interested to hear which model of transducer (Airmar?) you have fitted?
 
I am based on a river so we deal with flow all the time , including tidal flows in an upstream direction .
Sometimes it is important to meet the tide with reasonable accuracy in order to arrive at certain destinations at a favourable state of tide and to avoid running too shallow. To judge progress along the river it is SOG we need.

Speed through the water does have a use but only out of interest to see when the tide is against or assisting us but to be honest that can be seen by looking out of the window or by observing how sog changes at a set engine revs.
 
AllanG said:
I thought the standard Raymarine Tridata used a paddle wheel transducer, so would be interested to hear which model of transducer (Airmar?) you have fitted?
Click to expand...

I checked today and I have been exposed as a fraud, I actually have a paddlewheel!

My preference would be for a non paddlewheel sensor, but I stand by what I say about needing a speed through the water read out.
 
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