How Necessary is a Knot Meter ?

[Ex-Calif]

Originally Posted by bobconnie

As JDS61 said I use my Taff Rail log for not only speed but distance run in 24 hrs, and still use DR everyday!! along with noon sites offshore. of course I use a GPS but don't need it LOL I to don't really like NEW Things Ive had to many of them go belly up on me over the last 50 yrs LOL so I Stick with what I know works and has worked for 1000s of sailors before me and I hope a few after me !! Just my 2 cents Bob and Connie

A log will tell you (water) speed not distance or ground speed.

A gps will tell you distance and ground speed not (water) speed.

Statistically a gps beats a speed log 2:1 for utility - LOL

[Wotname]

Originally Posted by Ex-Calif

A log will tell you (water) speed not distance or ground speed.

A gps will tell you distance and ground speed not (water) speed.

Statistically a gps beats a speed log 2:1 for utility - LOL

Err...I haven't seen a log that doesn't tell you distance (through water) and most give you STW, but maybe there are some around that are as you have described.
My Walker trailing log only gives distance and no speed (water referenced of course).

[mrohr]

The spinning paddle gives an instant read out as to the speed of the water moving past the hull yes? Therefore I Can see if my latest sail tweak is helping .

My Gps computes the boat speed of the boat relative to the earths surface (o.k., really 4 dimensional space time but lets keep this simple) ,but the read out on the screen is only an average of the periodic inputs from the gps satellites and is not continious ( I don't know the intervals ,but suspect they even vary somewhat depending on the satellites being tracked and their movements.

Am I splitting hairs here ? I Just want to sail as fast as I can if one of those black holes Ive heard tell about is chasing me.

[denverd0n]

Originally Posted by Celestialsailor

As far as trimming...I usually go by sail shape.

There have been many, many times when I have found that I can go .5 to .75 knots faster by adjusting the sail to a shape that does NOT look quite as good, with the telltales NOT streaming quite as perfectly. I would not have discovered this, and I would not have made nearly as good of time, if I had not had the knot meter to truly tell me what my sail changes were doing.

Again, I think the problem that most people have is they consider the knot meter to be useless because it is not accurate. They want it to tell them how fast they are going, but it doesn't do a very good job of this. The REAL value of the knot meter is in showing a relative change, and it really doesn't matter at all how far off it is from your actual speed through the water to be useful for this.

[nautical62]

My current boat does not have one, and I don't really miss having one at all. My GPS gives me everything I need to know.

At times, it would be handy for calculating current speed (difference between GPS and knotmeter), but that's more out of a curiosity than any actual need.

[MarkSF]

Originally Posted by four winds

I agree, that would be for just long enough to clean it.

I would look for a new proper plug.

So the impeller threads into the housing? And turns out for cleaning, not pulled straight out?

I'm still looking for the paper manual, I think I have it somewhere.

Normally the impeller is held in by a pin that's an interference fit. Or are you referring to the whole body with the impeller in it? Never heard of that being threaded, there's normally a captive nut on top of the knotlog that engages with a thread on top of the through-hull.

[Ex-Calif]

Originally Posted by Wotname

Err...I haven't seen a log that doesn't tell you distance (through water) and most give you STW, but maybe there are some around that are as you have described.
My Walker trailing log only gives distance and no speed (water referenced of course).

With a log in current you can't tell how far you have travelled over the ground.

If you are doing 8 knots on the log against a 2 knot current you will travel 6nm in an hour.

The gps will show 6kt speed and 6nm distance after an hour. If the log records distance it will show 8 but the 8 is meaningless...

[C4 King Cobra]

The more information you have the better the outcome of your decisons. The average of all will give you superior choices over one source. A little of this and a little of that. Look at it all and decide for yourself based on what you see. IMHO.

[four winds]

Originally Posted by MarkSF

Normally the impeller is held in by a pin that's an interference fit. Or are you referring to the whole body with the impeller in it? Never heard of that being threaded, there's normally a captive nut on top of the knotlog that engages with a thread on top of the through-hull.

Mark, mine has a pin located horizontally across the top of the housing which retains the impeller insert. It has a ring on each end to remove, then pull the pin. The housing itself appears threaded similarly to a through hull fitting with external exposed threads.

So I was inquiring if, after removing the pin, the impeller insert merely pulls straight out for cleaning. Which I suspect it does.

If I had a plug for the housing after the impeller is removed I would investigate further.

Pretty busy cleaning the bilge, rebedding ports, removing old wiring, relocating VHF, and other inexpensive maintenance. But would like to explore the possibility of using the speed log if I could develop a best practice for keeping it working.

It's already there, might as well see if it adds any value to my sailing.

[matauwhi]

G'day, mate. Been sailing successfully without ours installed for years now. But, it is still lying next to the thru hull fiting just in case the day comes when those GPS satellites, that we all take for granted, somehow quit sending us the required data transmissions. Cheers.

[wolfenzee]

I have heard knot meters defined as "Just another hole to be glassed over when I haul the boat next". My knot meter is off by a known amount, the amount is is off changes as the speed of the boat changes.. of course this assuming the paddle wheel is clean, to clean it while the boat is in the water requires pulling the wheel and replacing it with a plug...always a bit unnerving.

[Wotname]

Originally Posted by Ex-Calif

With a log in current you can't tell how far you have travelled over the ground.

If you are doing 8 knots on the log against a 2 knot current you will travel 6nm in an hour.

The gps will show 6kt speed and 6nm distance after an hour. If the log records distance it will show 8 but the 8 is meaningless...

I gotta agree that you can't read gound miles numbers right off the display but I was surprised with your comment " A log will tell you (water) speed not distance or ground speed" as all logs I have ever seen give you distance (travelled though water of course). In fact early logs only gave you distance, to get a speed (STW), you had to take two log reading (distance) over a time interval and do the maths. Granted the very early ones gave you only speed as the knots slipped though your fingers out astern while you watched the hour (1/2 minute?) glass but in fact they were measuring the distance of the string and did the calculation for you (ie number of knots).

I know you know this stuff as I bet you learnt to navigate the same way me, indicated airspeed, true airspeed, forecast winds aloft, actual winds, watch, compass, 1 in 60 etc. It was all good training for when I translated to water (pre GPS) using STW, Distance through water, charted currents, predicted tides, time intervals, doubling the compass bearing and so on and so forth.

So the quoted "but the 8 is meaningless..." is not true when it becomes a component of the bigger navigational solution but hey, thanks to GPS, we can now use the time which was taken to complete the solution to do other stuff like tweaking the sails or sitting and thinking or better yet, just sitting...

[Ex-Calif]

Originally Posted by Wotname

I gotta agree that you can't read gound miles numbers right off the display but I was surprised with your comment " A log will tell you (water) speed not distance or ground speed" as all logs I have ever seen give you distance (travelled though water of course). In fact early logs only gave you distance, to get a speed (STW), you had to take two log reading (distance) over a time interval and do the maths. Granted the very early ones gave you only speed as the knots slipped though your fingers out astern while you watched the hour (1/2 minute?) glass but in fact they were measuring the distance of the string and did the calculation for you (ie number of knots).

I know you know this stuff as I bet you learnt to navigate the same way me, indicated airspeed, true airspeed, forecast winds aloft, actual winds, watch, compass, 1 in 60 etc. It was all good training for when I translated to water (pre GPS) using STW, Distance through water, charted currents, predicted tides, time intervals, doubling the compass bearing and so on and so forth.

So the quoted "but the 8 is meaningless..." is not true when it becomes a component of the bigger navigational solution but hey, thanks to GPS, we can now use the time which was taken to complete the solution to do other stuff like tweaking the sails or sitting and thinking or better yet, just sitting...

Sometimes when one tries to say less, as in a shorter post, it ends up all out of context and dragging on over several days and a dozen posts.

Going back to the original post - my opinion is that no instrumentation is "necessary" to make a boat sail.

In my opinion a speed log is useful and a gps is useful as they do different and complimentary things.

To try, again, to clarify my previous posts - Because when we sail the intention is to get somewhere "on-earth" a speed log cannot tell you how far you have travelled over the ground. So if the speed log reads 8 knots and you are bucking a 2 knot current it is useless in the context of telling your wife what time you will be home for dinner with accuracy.

Otoh anyone trimming sails based on gps speed is just doing it wrong. I am currently working with a skipper and trying desparatey to break him of this very bad learned habit. He thinks something is wrong with his rigging because we are faster on one tack vs. another as we sail around in a 2 kt current...

[Wotname]

Originally Posted by Ex-Calif

Sometimes when one tries to say less, as in a shorter post, it ends up all out of context and dragging on over several days and a dozen posts.

Going back to the original post - my opinion is that no instrumentation is "necessary" to make a boat sail.

Gotta agree

In my opinion a speed log is useful and a gps is useful as they do different and complimentary things.

Gotta agree

To try, again, to clarify my previous posts - Because when we sail the intention is to get somewhere "on-earth" a speed log cannot tell you how far you have travelled over the ground. So if the speed log reads 8 knots and you are bucking a 2 knot current it is useless in the context of telling your wife what time you will be home for dinner with accuracy.

Now that is both funny and a great way to describe it - thanks for the smiles

Otoh anyone trimming sails based on gps speed is just doing it wrong. I am currently working with a skipper and trying desparatey to break him of this very bad learned habit. He thinks something is wrong with his rigging because we are faster on one tack vs. another as we sail around in a 2 kt current...

Well good luck with that one - sounds like you need to start him off again with the basics but it is funny how many of us resist learning basics once we have "made it" . If you could only demonstrate that today it is the port rigging that is crook but last week it was the starboard rigging or whatever

[wolfenzee]

Granted a knot meter only tell speed through the water, but some applications require that (like trimming sails and figuring out which sail combinations work best when etc..)