Log impellers

[cpedw]

As for these electromagnetic logs, are they the same principle as the Doppler logs commonly used on ships?

No. The NASA one uses Magnetohydrodynamics

 

[johnalison]

In order of usefulness electric instruments are as follows:

1 - Echosounder - have sailed many miles without one but do like to have it now especially with a deepish keel.
2 - GPS - there were times long ago when I'd have sold my soul to know where I was within a mile or two, let alone within yards.
2 - Speed log - inaccurate for long even after calibration but there are times it is useful, mostly to compare STW with SOG
3 - Wind speed/direction - why bother: you can feel the wind and know where it's coming from.

I'm not a total technophobe: I do dearly love modern plotters, though I hope I can still remember how to use leadline, sextant and compass.

If you do use a paddlewheel log pull it out and clean it regularly, especially if the boat has sat static for more than a day or two. You won't sink with a few pints of water coming in. You won't sink even if you waited 3 minutes with water coming in, let alone 3 seconds.

I think that I agree with your order, but not with your dismissal of the last two, even if your arithmetic is a little unconventional.

A log’s accuracy depends on the model and how well it is looked after, but it is still useful if it has a known error. My chief uses for it are to monitor my motoring performance and to assist with sailing close-hauled.

A Windex will do some of what a meter will do but at the cost of a stiff neck. When sailing close-hauled, I judge the wind largely by feel, as you suggest, but a meter allows for finer judgement. Knowing the wind speed can make decisions about sail changes much especially downwind. I also find it useful when motor-sailing. It sometimes happens that I am motoring on a long passage to keep up speed, knowing that I need about 15 knots wind from astern to make it worth cutting the engine. This is quite hard to judge by eye or feel, and a meter will tell me exactly when the wind is sufficient, and makes it easier to avoid make the change too late.

 

[Rappey]

Surely gps has be be no 1 as you can see your depth on the chart at your current location ?
I sailed portsmouth to Dartmouth with a stowe trailing log. When I arrived the gps told me something like102 miles, the trailing told me 101.6 . I was quite impressed.

 

[johnalison]

Surely gps has be be no 1 as you can see your depth on the chart at your current location ?

I would guess that you have never sailed on the East Coast.

 

[[70521]]

Surely gps has be be no 1 as you can see your depth on the chart at your current location ?
I sailed portsmouth to Dartmouth with a stowe trailing log. When I arrived the gps told me something like102 miles, the trailing told me 101.6 . I was quite impressed.

Only at the date of the survey and hopefully the chartmaker's pen did not slip when drawing the chart.

GPS is readily available, but not number one in my book.

 

[CM74]

Only at the date of the survey and hopefully the chartmaker's pen did not slip when drawing the chart.

GPS is readily available, but not number one in my book.

Exactly, and a difference between what it should be from the plotter, and what you are actually getting can be a useful indication of something wrong - whether it's your position being inaccurate (unlikely, but possible), the chart being wrong, or things having shifted since the last survey! It's all useful to know about.
And a lot of charts are not that detailed close inshore, especially drying areas so knowing the exact depth in that exact spot can be valuable in certain places.

I appreciate though that in some areas which are steeply shelving, rock rather than mud and generally deep - it's nowhere near as important as it is in a shallow harbour.

Which is why I'm getting very frustrated with my sounder, it's not in the best place and it seems the way the cable is routed makes it give all sorts of random depths with the engine running - which is precisely when it would be most useful for me!

 

[Daydream believer]

A GPS is not so important in an area littered with sand banks as one might expect.
I sailed the east coast throughout the 70s with an echo sounder & a compass. After a while I had a log & that was a revelation. I would go nowhere without the sounder working correctly & lots of spare batteries.
Earlier this year I watched 3 yachts aground in the lower sunk crossing. One had major rudder damage. One a 40 ft yacht ( Bavaria ? ) needed hauling for keel damage. The third , a 40 ft ketch, was Ok but was escorted to an anchorage. The life boat was called to attend.
The reason was a major shift in the sand. This was not marked on the chart & possibly not marked on the later chart issued shortly after the event. I know that the boat with rudder damage was looking at his chart plotter.

It is just not wise to sail the Thames estuary without some means of ascertaining depth quickly whilst under way. A lead line is NOT quick enough. Appearance of a quarter wave would sometimes wake ones senses to the falling depth.

I did have a 6 ft 6ins bamboo cane with 3 bands on it. All 6 inches apart, which I came quite adept at "rolling" as I sailed over flat shallow water sitting to leaward, tiller in one hand, cane in other hand over the side. This had a loop on the end, through which I passed my hand to avoid dropping it . 1st band =get ready, 2nd band= tack, 3rd band =too late (that was at 4ft 6 ins, the draft of a Stella)