Log paddlewheels...why not copper?

The Smiths log did use a propeller-like turbine to drive a Bowden cable which connected it to the instrument dial - an inevitably inaccurate system. Walker type logs do not use a Bowden cable.

Impeller logs rely on the relative predictability of fluid mechanics, so that suitably sited, the boundary layer behaviour will be relatively repeatable and a single calibration coefficient can give reasonable performance across the velocity range likely, certainly for a small yacht. Of course at sufficiently low velocities, a turbulent boundary layer may not develop at the impeller, which would introduce a more substantial error. Not sure whether this would be a problem for an Anderson 22.

My boat has an Echopilot ultrasonic log - this has its own problems [especially sailing on the east coast], but it does not have an impeller to foul.

Recollecting my deep sea experience, prior to GPS and on ships not carrying Loran, Decca or Omega, we did not use a log as we could get quite close enough using the engine revolutions updated with sun and star sights. I believe "grey-funnel liners" used to use a Chernikeef[?] log which would be deployed through the ships hull - I believe this was a pitot/static type instrument mounted on a pipe that was extended through the effective boundary layer.
 
vyv_cox said:
Because I have a small tin of Velox for my propeller, which I find works well on other things too, like P-brackets, I also use it on my combined log/depth transducer, where it is very effective, even with a single coat.
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After you recommended this sometime last winter I did mine in April and for the first time I haven't had to get the lg out if I leave the boat for man than a couple of weeks, it's been a great success. Thanks for the tip.
 
Seajet said:
Woodlouse,

thanks; that amazes me, as I'd have thought one would want to avoid boundary layer effects ie towed trail log or on warships & subs towed array sonar.

I'd never use a paddlewheel log for navigation, but I suppose some punters just want a speed display; there's a story about the Concorde ' we're now doing Mach 2 ' cabin display - a crew member said " Actually we can wind it up to Mach 9.99 ! " :)
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You calibrate your log to read accurately at what will be your boats average passage speed. This way any inaccuracies will hopefully iron themselves out at slightly higher or lower speeds.

There is nothing wrong with a through hull log as long as it's properly installed and calibrated. Towed logs are also very good and require less calibrating than through hull jobs, unfortunately the spinners have a habit of being eaten which, along with the hassle of deploying and retrieving them, is why they are rarely seen these days.

Talking about towed sonar is a little off topic, but the reasons for it are to be able to deploy larger sensors over a larger area away from the noise of the vessel using them and while yes, warships and submarines make extensive use of towed sonar they also have the same capability, though less sensitive, built into the hull. It would surprise me if warships or submarines used trailing logs as anything other than an auxiliary back up to conventional through hull units.
 
The Smiths log on my Carter 30 was an in-hull paddlewheel job.

The log on the original Centaurs for instance was a little prop' driving a Bowden cable a la a car speedo and even less reliable.

I found the paddlewheel was very easily fouled by weed or wee beasties.

Anyone using an in-hull paddlewheel log for navigating more than a few miles deserves a gold medal for optimism; but trail logs are not foolproof, I find my Wasp job collects floating weed quite often so requires hourly checking and a good pull & jerk every hour or so; so do I but that's a separate issue.

BTW I was trained by and worked alongside Dunsfold Instrument Calibration Dept.
 
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Seajet said:
Anyone using an in-hull paddlewheel log for navigating more than a few miles deserves a gold medal for optimism.
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Every sailing school teaches DR and EP navigation, almost always based on logs that use paddlewheels. They work well enough for the purpose. Just because you don't have the maths capability to do it doesn't mean that the technique and the equipment are useless for everyone.

Are you as dismissive of pitot tubes used for air speed measurement in aviation, because they too are subject to their own inaccuracies and failure modes? Although in the real world almost all aviation navigation is now done using the various satellite systems the traditional methods of time, airspeed and wind compensation are still taught and required to be demonstrated in an air navigation exercise during the license test. If you were a pilot you would know that.

You are dismissing well established equipment and navigation techniques because you had a bad experience with equipment not made for 40 years. Strange attitude, but not unexpected in Andy's Weird World.

Post number 30 in this thread is relevant...

http://www.ybw.com/forums/showthread.php?244519-Crossing-Irish-Sea-without-GPS
 
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Seajet said:
The log on the original Centaurs for instance was a little prop' driving a Bowden cable a la a car speedo and even less reliable.

I found the paddlewheel was very easily fouled by weed or wee beasties.

Anyone using an in-hull paddlewheel log for navigating more than a few miles deserves a gold medal for optimism; but trail logs are not foolproof, I find my Wasp job collects floating weed quite often so requires hourly checking and a good pull & jerk every hour or so; so do I but that's a separate issue.

BTW I was trained by and worked alongside Dunsfold Instrument Calibration Dept.
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The sumlogs as originally fitted to centaurs should not be under estimated. The one fitted to my boat was within a mile and a half of the walker trailing log after crossing the North Sea from ramsgate to Norway.

Of course fouling is going to affect all types but you should not write them off because of your own bad experience. They are perfectly accurate enough for dead reckoning navigation and just as good as trailing logs although with a different set of drawbacks.
 
Seajet said:
The Smiths log on my Carter 30 was an in-hull paddlewheel job.

The log on the original Centaurs for instance was a little prop' driving a Bowden cable a la a car speedo and even less reliable.

I found the paddlewheel was very easily fouled by weed or wee beasties.

Anyone using an in-hull paddlewheel log for navigating more than a few miles deserves a gold medal for optimism; but trail logs are not foolproof, I find my Wasp job collects floating weed quite often so requires hourly checking and a good pull & jerk every hour or so; so do I but that's a separate issue.

BTW I was trained by and worked alongside Dunsfold Instrument Calibration Dept.
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A through-hull paddle wheel will indeed be operating in the boundary layer, and the recommended locations should ensure that the boundary layer is fully turbulent at the instrument unless the boat is moving very slowly.

A particular configuration might lead to the paddle-wheel experiencing a mean velocity of around 75% of the mean boat velocity. A variation in salinity from 0 to 30g/kg should cause a change in that velocity within a range of +/- 0.1%, a variation in temperature from 10 degC to 20 degC should cause a change in that velocity within a range of +/-0.6%, and a variation in boat speed from 1 to 10 knots should cause a change in that velocity within a range of +/-5%. Calibrated at a suitable speed for the boat in question, a paddle wheel log should be quite adequate whatever the variations in salinity or temperature.

The salinity change from 0 to 30 g/kg would give a change in density of about 2.3%. A common value used for density of seawater in the absence of better information is 1025 kg/m3, this would correspond with a temperature just below 0 degC for 30g/kg, or a temperature of over 30 degC for 40 g/kg.
 
My Airmar log demonstrated yesterday just how good it is. We motored and sailed down the east coast of Kalymnos in a lumpy swell from the north. There is some fouling of the hull, to which I attributed the fact that the log was consistently reading about 0.5 knots less than the SOG. First part in light wind, for about an hour 3-4 knots boat speed. Rounding the cliffs at the east side of the island the wind speed was up to 22 knots, boat speed about 6.5 SOG, a little less on the log. However, at the SE corner of the island the wind became far lighter and we were in waves that were nearly overfalls, obviously current flowing north against the waves. Suddenly the log was reading well over the SOG, both slowly under sail and when we turned the engine on as the wind died totally. We then motored across the enclosed bay towards Pothia, where the log and SOG were identical.

I am delighted with the performance of the log, clearly showing a true picture of boat speed throughout the trip. Wave action in the early part, between 3 and 6.5 knots, adding a little to the SOG, adverse current knocking SOG down. Calibration confirmed on the flat water at the end. The new Airmar design well thought out.
 
Seajet said:
If in-hull is so spiffing, how come all decent warships and subs use towed array sonar ?

:)
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Because they perform far more functions than simple log
Torpedoes are no longer fired in a single direction as in WW2 waiting for a target to run into it
Some torpedoes rely on picking up signals from the target in the same way as some missiles that home in on enemy radar signals hence a ship transmitting signals for anything from depth to search sonar makes the ship visible to the enemy once they can sort the frequencies being transmitted
The towed unit can be used to warn of torpedoes and can be used to send out spurious signals in the same way that fighters used to drop flares. By sending signals from the towed sonar the ( seemingly silent)ship can be half a mile away.
In addition the ship can send signals in conjunction with the towed sonar to triangulate an object for greater accuracy
None of this is needed on my boat although warning of Anderson 22's sailing in cloud cukoo land might be useful
 
vyv_cox said:
My Airmar log demonstrated yesterday just how good it is.
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Airmar have elevated the humble paddlewheel to a state-of-the-art device. All the major instrument manufacturers now use Airmar log transducers, because they're so good. Yet so many sailors still can't believe that paddlewheel logs are any good. Beats me!

Similarly, we keep getting posts saying the paddlewheel fouls up and has to be cleaned every few weeks. Several of us have been posting for years that the answer is simply to antifoul the thing, yet people still prefer to grumble.
 
Simply remove the log impeller when leaving the boat on her mooring (don't forget to insert the blank...!) then install clean, dry impeller when off for a jaunt or a cruise.

Simples.
 
FulmarJeddo said:
I also used a water based antifoul (ECHO) on my paddle wheel. After an initial bit of binding where I think I put a bit too much on, it has worked every time I have used the boat since I launched at Easter. I haven't had reason to pull the transducer out so couldn't say if it's still spotless or not. I thought £15 seemed a lot for the tiny pot, but from the results so far, it was money well spent. If it doesn't dry out the pot should last for quite a few years.
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As an update. After painting the paddle wheel with Echo water based antifoul before Easter, apart the initial binding I mentioned, I have had a complete season of trouble free Speed/log operation. I lifted out today, but didn't get a chance to take the transducer out to see how clean or dirty it was. Even today on the short trip from my mooring to the club slip the speed was displaying. Definitely £15 well spent.
 
Some confusion between the old Smiths paddle wheel log which I also had and the VDO log. The original VDO Sumlog had a long pitch screw driving a bowden cable to a log head. Later models used the same screw but put a magnet into it to transmit electric impulses. The screw type seemed more resitant to fouling compared to the paddle wheel. The Smiths type had a magnet in the rotating wheel which passed a reed switch to give pulses to the head. I found the magnet became tired and I replaced the reed switch witha Hall effect device and little amplifier which fixed it. However I finally removed the whole system because fouling just gave too much trouble. eg I have just had to wipe over the hull in water just 7 weeks after new a/f was applied. I expect to wipe it over every few weeks from now on. (warm water and coming into summer) good luck olewill
 
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