Logs - water speed & distance

[cpedw]

Prompted by Ockle Point's question in TOP, I was wondering about the types available. On three boats, I have had a paddlewheel, a mechanical towed log (like a Walker but it was another make, now forgotten) and a built-in mechanical log, make was I think VDO, which used a permanently mounted spinner connected by a flexible drive cable to a speedo/distance display.
Of these, the paddlewheel is a regular source of annoyance; two weeks away from the boat will ensure that it's full of beasts and doesn't work.
The towed log was always reliable but a bit inconvenient to use. Getting it back in required coming to a complete halt. Also, essential to remember to bring it in before close-quarters manoeuvering, especially astern! Apart from those, it was accurate and used no electricity.
The built-in mechanical thing was my favourite. It was always there, always worked and it was a good few years old when I first got the boat. I expect it could get jammed with weed or suchlike, the spinner was a spiral shaped thing on a mini skeg, but in 4 years of my ownership it never stopped. I don't think they are available any more; at least I don't know where I might find one.
Does anyone have a reliable log?
Derek

[DaveS]

I fitted a mechanical log such as you describe to my first boat. IIRC it was called a Wasp (the log, not the boat). It worked fairly well, but was a bit prone to rust (the Vivacity was a somewhat wet boat) so did need oil poured down its shaft / annual cleaning up. I have no idea if they are still made: probably not - much too simple and reliable!

I now have a paddlewheel and curse and fiddle with it like everyone else.

There is another type available, though I have no personal experience. Described as "electromagnetic" it has no moving parts at all so should, in theory, be ideal. I'm not even sure on what principle it works: I have in industry used ultrasonics to measure flow speed in pipes, but this sounds different. Perhaps someone else knows?

[ash]

I have in industry used ultrasonics to measure flow speed in pipes, but this sounds different. Perhaps someone else knows?

IIRC, it is exactly the same principle.

Ash

[aquaplane]

My dad fitted a Doppler log to his first boat in 1976 so there are/were some about.
It just had a transducer glued to the hull which bounced sound off the bubbles flowing past the hull, as I remember it anyway, I've slept since then. Nothing to foul and no holes in the hull, it sounds almost sensible.

It worked but I can't say how acurate it was. I can remember mucking about with a stopwatch off Arran tweaking it. I'll ask the Admiral if he can remember what it was called etc.

[ash]

......and Time Poor, here is the Airmar Ultrasonic Speed Tranducer

Ash

[Rowana]

When I was in the Merchant Navy, I remember we had 2 different types of logs.

The first was a mechanical spinner thing which was trailed behind the ship. I remember that when the spinners were polished up, they could be made into lovely table lamps when suitably mounted on a piece of wood!

The second type was a pitot tube that was pushed out through the bottom of the boat, and worked on a pressure differential.

When I did my bit for Queen and country with the grey funnel line, the log was a propeller thing that was lowered through the bottom of the boat.

How all these performed, I have no idea, as I didn't have anything to do with the reading of them. My only involvement was pushing the bits down into the water from the engine room.

On my boat, I have the usual paddle wheel thingy, which works for a few weeks after launch, then gets bunged up and stops working. The GPS gives me SOG and TTG to the next waypoint, which is all the information I need. I can't get too excited about the log not working.