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Help please. I am right in thinking that I will have to have my boat lifted to have a speed and depth log fitted ?  I already have a fish finder fitted, could I not use the transducer from this to link to the depth log ? or am I being thick ? 

Any help suggestions and comments appreciated as always. Thanks 

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You can certainly get “in hull” depth transducers rather than the thru hull type.

Im not sure if the existing fishfinder transducer would be compatible with a seperate depth log (i would guess most likely not). 

The speed log may be more tricky, they are usually a thru hull paddle wheel device unless you opted for a gps unit instead.

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dnks34 has said it. I would add, "how often do you use your boat" ? I ask because paddle wheels do not like long periods of inactivity, they clog up. There are pressure speedos available ( bit like pilot-statics in aviation ) but Broads speeds are too low, they are designed for fast runabouts and do not "log" distance run. I would go in-hull tranducer for depth and GPS for speed.  I am a great fan of no holes below the waterline, I have owned two yachts, powered by outboard, with no holes and they were a joy. Other boats we had with logs, sea toilets, stern gear etc were a pain at times.

When distance sailing before GPS we would trail a Walker Log similar to this.

 

Screenshot_20190105-055751.thumb.png.e88bf5bf75454dfcb4b0c88bf9751fa5.png

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6 hours ago, ChrisB said:

Screenshot_20190105-055751.thumb.png.e88bf5bf75454dfcb4b0c88bf9751fa5.png

 

Ah, the Walker's Patent Log! A wonderful instrument which was used by ships for decades. What you don't show in the photo is the big brass flywheel which sat just behind the instrument, mounted on the aft taffrail and which allowed it to spin smoothly. The log-line itself was one of the only occasions when right hand laid rope was used on a ship as this allowed it to tighten up against the rotation and give an accurate reading.

The word "log" relates to the really old days, when they used to throw a log of wood over the stern attached to a long line with knots in it at regular intervals. As the line ran out, the number of knots which had fed out over a space interval of about 15 seconds, allowed you to calculate your speed in nautical miles per hour, which became known as "knots".

The nautical mile (more or less 2000 yards) is a "minute" of latitude. This means it is the only length measure which can be related directly to a distance on the Earth's surface.

 

Anyway, I digress!

I agree with others that it is very difficult, if not impossible, to be mechanically accurate at speeds of 5MPH or less so you would be much better to rely on a simple GPS App. Why not? Just don't forget that this will give you speed over the ground, but not "boat speed".

As to your depth, if you are going across Barton Broad and seem to think you are going a bit slower than usual, then you have no more depth under the keel!

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1 hour ago, Vaughan said:

The nautical mile (more or less 2000 yards) is a "minute" of latitude. This means it is the only length measure which can be related directly to a distance on the Earth's surface. 

1852 metres if I remember correctly, although a minute of latitude is a different distance depending on what latitude you are at due to the planet being an oblate spheroid.

 

1 hour ago, Vaughan said:

As to your depth, if you are going across Barton Broad and seem to think you are going a bit slower than usual, then you have no more depth under the keel!

There is no bottom on the east coast, the water just gets much thicker.....

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1 hour ago, Smoggy said:

1852 metres if I remember correctly, although a minute of latitude is a different distance depending on what latitude you are at due to the planet being an oblate spheroid.

That's why I said "more or less" 2000 yards and remember that they didn't work in metres in those days. A navigator will always read off a distance on the chart which is directly opposite his position on the chart, for that very reason.

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18 hours ago, Vaughan said:

A navigator will always read off a distance on the chart

"Left hand down a bit!"

 

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