Does anyone know of an inexpensive device to measure speed over water? (Other than a log attached to a knotted line.) I have a small sailboat, and it's not worth investing in electronics. Thanks everybody. Dick
Speed indicator
- Thread starter Dick Westwood
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Cheetos!
Cheetos and a stopwatch
! Drop a cheeto at the bow, start watch. When the cheeto reaches the stern, stop the watch. Speed is: .6 x boat length / time in seconds The speed given is in knots. Works best if you have a crew - like a kid - to drop the cheeto at the bow while you watch the stern with the watch. Unless the cheeto gets eaten first . . . Cheers and Best o' Luck!
Cheetos and a stopwatch
! Drop a cheeto at the bow, start watch. When the cheeto reaches the stern, stop the watch. Speed is: .6 x boat length / time in seconds The speed given is in knots. Works best if you have a crew - like a kid - to drop the cheeto at the bow while you watch the stern with the watch. Unless the cheeto gets eaten first . . . Cheers and Best o' Luck!
What if the cheeto surfs the waves?
Thanks, OldCat. This may be a little lower tech than I have in mind, though. What I want to do is to optimise sail trim (cunningham, vang, and all that) by monitoring effect on sow. I'm figuring I need to measure tenths of knots, and that the drag coefficient on a Cheeto won't permit this. Dick
Thanks, OldCat. This may be a little lower tech than I have in mind, though. What I want to do is to optimise sail trim (cunningham, vang, and all that) by monitoring effect on sow. I'm figuring I need to measure tenths of knots, and that the drag coefficient on a Cheeto won't permit this. Dick
Cheetos Sound Good to Me
That may be low tech, but with a stop watch, it would be very accurate. The biggest problem is dropping it accurately and actually determining when the Cheeto is even with the stern.
That may be low tech, but with a stop watch, it would be very accurate. The biggest problem is dropping it accurately and actually determining when the Cheeto is even with the stern.
Cheeto Accuracy
What? The cheeto is time honored seamanship! Required for a Pirate hat ! You mean you can't drop the cheeto exactly at the bow & get the watch to the millisecond? Or, your kid ate the cheeto so you got no measurement? Well, I understand! The cheeto boat speed log is taught in navigation classes - as a way to do it w/o the boat's electronics. If you are sailing with small currents - then a cheap GPS may well suffice. Only $100 or so. Even in a current, where GPS speed is over ground and not over water - it will still record changes in trim and their effect. Just realize that port and starboard tacks may record differently due to the effects of current. Good trim should still be faster than poor trim as long as the comparison is close in time, location (these 2 so current effects stay similar) and windspeed. Cheers!
What? The cheeto is time honored seamanship! Required for a Pirate hat
! You mean you can't drop the cheeto exactly at the bow & get the watch to the millisecond? Or, your kid ate the cheeto so you got no measurement? Well, I understand! The cheeto boat speed log is taught in navigation classes - as a way to do it w/o the boat's electronics. If you are sailing with small currents - then a cheap GPS may well suffice. Only $100 or so. Even in a current, where GPS speed is over ground and not over water - it will still record changes in trim and their effect. Just realize that port and starboard tacks may record differently due to the effects of current. Good trim should still be faster than poor trim as long as the comparison is close in time, location (these 2 so current effects stay similar) and windspeed. Cheers!Speed tube
Years ago I had a device that was a plastic tube with an "el" on the bottom, open; and graduations up the side of the tube. You'd stick the open end of the tube into the water and a floating ball would float up the tube with the distance being determined by your speed -- and you read your boat speed off the graduation closest to the ball. Real simple. I haven't seen anything like that in years, tho'Good luck!
Years ago I had a device that was a plastic tube with an "el" on the bottom, open; and graduations up the side of the tube. You'd stick the open end of the tube into the water and a floating ball would float up the tube with the distance being determined by your speed -- and you read your boat speed off the graduation closest to the ball. Real simple. I haven't seen anything like that in years, tho'Good luck!
Had a Speed Stick too
I also had a speed stick about 15 years ago. It worked fairly well, but like the other poster, I haven't seen one in several years. Steve Alchemist
I also had a speed stick about 15 years ago. It worked fairly well, but like the other poster, I haven't seen one in several years. Steve Alchemist
Confessions of a sail trim fanatic ...
If you soak the cheeto in beer, you get better results. Measuring tenths of a knot was my goal a year ago. Does not work, forget measuring your speed with each sail trim change. Been there, done that, there is a much better path to happiness. I have become a fanatic when it comes to sail trim, have gone the route of using a GPS to measure speed (does not get much simpler) but was still dissatisfied ... as wind speed and angle changes as often as every 3 minutes or less. Not having a constant wind speed makes it very hard to adjust two or more controls (e.g. boom vang & sheet tension) and know if the speed change was from good sail trim ... or change in wind. I got satisfaction instead by: 1. Understanding what my desired sail shape is for a given wind and sea condition, e.g. where do I want the draft positioned on the mainsail, leech open/closed, how much jib sag, etc. in 1 foot chop at 10-15 knots of wind. 2. Understand which sail controls ideally affect sail shape on my boat (to move my draft forward, etc.) Note: no matter what book you read, your boat may handle differently ... which is part of the fun/art. 3a When sailing alone: My challenge becomes to find which sail control adjustments get me the desired sail shape (and hence best speed) ... such optimization is less sensitive to small wind changes and provides instant feedback (I can see the draft, twist, etc. on the sail) and gratification (or fustration), and assurance that my success/failure is due to me alone, a feedback loop that the GPS, log, or cheeto, cannot give me (remember the instrument cannot tell me if I did good vs. the wind changed). 3b. Alernating with 3a above, when sailing against other boats of my type, the boats next to me become a much better comparison of my sail trim, and provides instant gratification that my electronic instrument can not give me (remember the instrument cannot tell me if I did good vs. the wind changed). When there isn't much wind, I then also get additional gratification when I sail circles around the other boats (when your good, you can eaily double your speed in light winds at or under 4 kts vs. trim challenged individuals) 3c. Repeat steps 3a & 3b, re-read the text books, and incrementally get better. This is an experiened based learning process. 4. That said ... it does help to refer to a GPS or a Cheeto, once you think you have achieved great sail trim ... to provide a reality check. Then you can say to yourself, I remember last time in simliar conditions I was slower, so this last idea I got out of the book is working for me ! Happy sailing!
If you soak the cheeto in beer, you get better results. Measuring tenths of a knot was my goal a year ago. Does not work, forget measuring your speed with each sail trim change. Been there, done that, there is a much better path to happiness. I have become a fanatic when it comes to sail trim, have gone the route of using a GPS to measure speed (does not get much simpler) but was still dissatisfied ... as wind speed and angle changes as often as every 3 minutes or less. Not having a constant wind speed makes it very hard to adjust two or more controls (e.g. boom vang & sheet tension) and know if the speed change was from good sail trim ... or change in wind. I got satisfaction instead by: 1. Understanding what my desired sail shape is for a given wind and sea condition, e.g. where do I want the draft positioned on the mainsail, leech open/closed, how much jib sag, etc. in 1 foot chop at 10-15 knots of wind. 2. Understand which sail controls ideally affect sail shape on my boat (to move my draft forward, etc.) Note: no matter what book you read, your boat may handle differently ... which is part of the fun/art. 3a When sailing alone: My challenge becomes to find which sail control adjustments get me the desired sail shape (and hence best speed) ... such optimization is less sensitive to small wind changes and provides instant feedback (I can see the draft, twist, etc. on the sail) and gratification (or fustration), and assurance that my success/failure is due to me alone, a feedback loop that the GPS, log, or cheeto, cannot give me (remember the instrument cannot tell me if I did good vs. the wind changed). 3b. Alernating with 3a above, when sailing against other boats of my type, the boats next to me become a much better comparison of my sail trim, and provides instant gratification that my electronic instrument can not give me (remember the instrument cannot tell me if I did good vs. the wind changed). When there isn't much wind, I then also get additional gratification when I sail circles around the other boats (when your good, you can eaily double your speed in light winds at or under 4 kts vs. trim challenged individuals) 3c. Repeat steps 3a & 3b, re-read the text books, and incrementally get better. This is an experiened based learning process. 4. That said ... it does help to refer to a GPS or a Cheeto, once you think you have achieved great sail trim ... to provide a reality check. Then you can say to yourself, I remember last time in simliar conditions I was slower, so this last idea I got out of the book is working for me ! Happy sailing!
Should be precise when using the Cheeto Speedo
You can not start timing when you drop the cheetos. You can only start timing when the cheeto hits the water. You do not want to include the cheeto flight time to the speed calculation. In additin, the different cheeto shapes will have different flight times. Also make sure you are using the correct cheeto launch location, depending on if you decide to use either LOA or LWL, and adjust your calculation formula as needed. It is also better to toss the cheeto far away from the hull, since the boat waves will impact the cheeto flow time. Also, you may have to repeat the test if there are fishes or seagulls around that steals the cheetos. ;d
You can not start timing when you drop the cheetos. You can only start timing when the cheeto hits the water. You do not want to include the cheeto flight time to the speed calculation. In additin, the different cheeto shapes will have different flight times. Also make sure you are using the correct cheeto launch location, depending on if you decide to use either LOA or LWL, and adjust your calculation formula as needed. It is also better to toss the cheeto far away from the hull, since the boat waves will impact the cheeto flow time. Also, you may have to repeat the test if there are fishes or seagulls around that steals the cheetos. ;d
Knotstick
Dick... I found it. Or something very much like what I used to have. It's called a KNOTSTICK. You can see it at www.knotstick.com Looks like $39.95 -- pretty good and accurate. Best regards, Bruce
Dick... I found it. Or something very much like what I used to have. It's called a KNOTSTICK. You can see it at www.knotstick.com Looks like $39.95 -- pretty good and accurate. Best regards, Bruce
Cheetos reality
According to my calculations for a 24 foot boat doing 5 to 6 knots, an error of +/- one foot in the landing point of the Cheeto at the bow and clicking the watch at the stern is about 1/2 a knot. At the same time, an error of +/- 0.1 seconds in clicking the stopwatch is also about 1/2 knot in error. So, the accuracy of this could be as much as 1 knot. Not nearly enough, I'd say, even if you cut my error factor by 1/2 or more. The KnotStick link claims 0.2 kt accuracy, and that they use these to calibrate electronics. Of course, in this case, it's not the absolute speed we care about but the change that occurs as you make a sail trim change. The knotstick would seem a good option, perhaps beter than GPS if you have current to factor out. The winds on my lake aren't steady enough even for the 3 seconds it would take a Cheeto to pass by! I make a trim change and the boat slows down. I put it back where it was and the boat slows down some more. Or vice vera, _and_ vice versa, and everything in between! I have an electronic AutoHelm Bi-Data with 0.1 increments, but I think I only make progress learning about trim changes when I'm neck-and-neck with another boat when their crew is watching me and not touching their trim. And even that doesn't last long, as I sail by leaving them in my wake.... ;-) ...RickM...
According to my calculations for a 24 foot boat doing 5 to 6 knots, an error of +/- one foot in the landing point of the Cheeto at the bow and clicking the watch at the stern is about 1/2 a knot. At the same time, an error of +/- 0.1 seconds in clicking the stopwatch is also about 1/2 knot in error. So, the accuracy of this could be as much as 1 knot. Not nearly enough, I'd say, even if you cut my error factor by 1/2 or more. The KnotStick link claims 0.2 kt accuracy, and that they use these to calibrate electronics. Of course, in this case, it's not the absolute speed we care about but the change that occurs as you make a sail trim change. The knotstick would seem a good option, perhaps beter than GPS if you have current to factor out. The winds on my lake aren't steady enough even for the 3 seconds it would take a Cheeto to pass by! I make a trim change and the boat slows down. I put it back where it was and the boat slows down some more. Or vice vera, _and_ vice versa, and everything in between! I have an electronic AutoHelm Bi-Data with 0.1 increments, but I think I only make progress learning about trim changes when I'm neck-and-neck with another boat when their crew is watching me and not touching their trim. And even that doesn't last long, as I sail by leaving them in my wake.... ;-) ...RickM...
Speed Tube
I have one of the speed tubes. I didn't know it had a name. It came with the boat. The problem with it is that it is very sensitive to how deep you put it in. It has a guide, but water builds up around the front, making the depth guide somewhat ambiguous. I occasionally use it, but I doubt that it is terribly accurate.
I have one of the speed tubes. I didn't know it had a name. It came with the boat. The problem with it is that it is very sensitive to how deep you put it in. It has a guide, but water builds up around the front, making the depth guide somewhat ambiguous. I occasionally use it, but I doubt that it is terribly accurate.
Three options
Thanks everyone for some great input. There seem to be two mechanical approaches. The knotstick that capnbruce located seems to be a disk, thrown overboard, attached to a spring in a tube onboard. The spring extends as the disk creates more resistance by being dragged faster through the water; the tube calibrates this in knots. It's about $40, and I think I'm going to get one. The 'l-shaped tube' seems to be something called a pitot tube. I found one on a Hobie pedal kayak site (I've attached a link to it). Water pressure in the horizontal part of the tube (underwater) forces a ball up the vertical part of the tube (on deck) and again it's calibrated to read in knots. They seem to use a similar system in aeroplanes (but they replace the ball going up a tube by a dial). Other than the Hobie, most of the marine devices I could find deal with much greater SOW than my 20 footer can achieve - 80 knots and such! On the non-mechanical front: I'm also going to get a handheld GPS. That should do it nicely. That and a lot of Cheetos. I'll use these to validate the precision of the other instruments, and to recalibrate the GPS and knotstick readings to Cheeto equivalents. Thanks again Dick
Thanks everyone for some great input. There seem to be two mechanical approaches. The knotstick that capnbruce located seems to be a disk, thrown overboard, attached to a spring in a tube onboard. The spring extends as the disk creates more resistance by being dragged faster through the water; the tube calibrates this in knots. It's about $40, and I think I'm going to get one. The 'l-shaped tube' seems to be something called a pitot tube. I found one on a Hobie pedal kayak site (I've attached a link to it). Water pressure in the horizontal part of the tube (underwater) forces a ball up the vertical part of the tube (on deck) and again it's calibrated to read in knots. They seem to use a similar system in aeroplanes (but they replace the ball going up a tube by a dial). Other than the Hobie, most of the marine devices I could find deal with much greater SOW than my 20 footer can achieve - 80 knots and such! On the non-mechanical front: I'm also going to get a handheld GPS. That should do it nicely. That and a lot of Cheetos. I'll use these to validate the precision of the other instruments, and to recalibrate the GPS and knotstick readings to Cheeto equivalents. Thanks again Dick
4th option
I'll admit that while I had been taught the Cheeto Speedo in sailing class - I had never stopped to calculate its accuracy - suspected it was a bit variable, but not actually calced it out until it was pointed out here to do so. So - here is a 4th option. A chip log. Usually these are a triangular piece of wood on a small diameter line. You throw the chip off the stern, and time the length of time it takes for the line to pay out. You need to have the line flaked well so there is little drag at the boat. It is more accurate as you can use a longer line than the boat length - say 100' or so, maybe longer on a big boat. The extra length reduces the errors, the formula is the same as the Cheeto Speedo, but use the line length payed out. Something else to play with!
I'll admit that while I had been taught the Cheeto Speedo in sailing class - I had never stopped to calculate its accuracy - suspected it was a bit variable, but not actually calced it out until it was pointed out here to do so. So - here is a 4th option. A chip log. Usually these are a triangular piece of wood on a small diameter line. You throw the chip off the stern, and time the length of time it takes for the line to pay out. You need to have the line flaked well so there is little drag at the boat. It is more accurate as you can use a longer line than the boat length - say 100' or so, maybe longer on a big boat. The extra length reduces the errors, the formula is the same as the Cheeto Speedo, but use the line length payed out. Something else to play with!
Error Calculation OK, Logic Flawed
The problem with the logic is that the calculations were made for a boat close to its hull speed. I rarely worry about a tenth of a knot when I am near hull speed. I do worry about a tenth of a knot when I am crawling along at a knot or two. Then the Cheeto becomes very accurate.
The problem with the logic is that the calculations were made for a boat close to its hull speed. I rarely worry about a tenth of a knot when I am near hull speed. I do worry about a tenth of a knot when I am crawling along at a knot or two. Then the Cheeto becomes very accurate.
The 'chip log' is the traditional method
of measuring a ship's speed. Perhaps the name 'log' was given because they actually used a log. I suspect that the Cheeto is going to be subject to many different forces - the bow wave, current, and even the wind are going to affect it's journey to the stern. Cheers, Bob s/v X SAIL R 8
of measuring a ship's speed. Perhaps the name 'log' was given because they actually used a log. I suspect that the Cheeto is going to be subject to many different forces - the bow wave, current, and even the wind are going to affect it's journey to the stern.
Cheers, Bob s/v X SAIL R 8speaking of which,
the knot was, as I learned, named for the knots tied in the cord used on the log, so many knots in X time meant that was the speed being made, part of the reason that the knot doesn't directly translate into land based measure. My boat has an old knotmeter mounted that I'm thinking of reworking for use, it's the old style with a finger protruding from the hull under the cockpit, connected with rods and gears to a scale mounted (not so conveniently) at floor level, people I've talked with said they are reasonably accurate for speed over water, sounds like it functions the same way as the speedstick described above. Ken.
the knot was, as I learned, named for the knots tied in the cord used on the log, so many knots in X time meant that was the speed being made, part of the reason that the knot doesn't directly translate into land based measure. My boat has an old knotmeter mounted that I'm thinking of reworking for use, it's the old style with a finger protruding from the hull under the cockpit, connected with rods and gears to a scale mounted (not so conveniently) at floor level, people I've talked with said they are reasonably accurate for speed over water, sounds like it functions the same way as the speedstick described above. Ken.
knot a land mile
The knot is longer than a land mile because it is exactly the distance of 1 nautical mile or one degree of latitude travelled in one hour, ie one minute of latitude. (1/60 of a degree). The actual ratio is 1.15 to one statute mile. That doesn't disagree with the number of knots tied in a line that pass out of hand in a given amount of time. Interesting lore.
The knot is longer than a land mile because it is exactly the distance of 1 nautical mile or one degree of latitude travelled in one hour, ie one minute of latitude. (1/60 of a degree). The actual ratio is 1.15 to one statute mile. That doesn't disagree with the number of knots tied in a line that pass out of hand in a given amount of time. Interesting lore.
Chip Log
The historic "Chip Log" utilized a wedge of wood about 18" in size (chip); which was tied to one end of a long ropel, which had knots tied into it about every 47' 3". The length between knots was based on converting 1 nautical mile per hour to feet per second(fps)], and then multiplying fps by 30 seconds (which was a practical time to spend counting knots with a sandglass). The result was the calibrated length in feet at which to tie the knots for a 30-second run of the chip log (1 kt = 47' 3" in 30 seconds). For a photograph and brief explanation of the chip log, goto: http://www.tallshipbounty.org/Demos_ChipLog.html Because the definitions of a second, and a nautical mile have changed (since the 17Th century), the log must be recalibrated to about 28 seconds. The "chip" is the wedge of wood, and the "log" is the notation in the log-book.
The historic "Chip Log" utilized a wedge of wood about 18" in size (chip); which was tied to one end of a long ropel, which had knots tied into it about every 47' 3". The length between knots was based on converting 1 nautical mile per hour to feet per second(fps)], and then multiplying fps by 30 seconds (which was a practical time to spend counting knots with a sandglass). The result was the calibrated length in feet at which to tie the knots for a 30-second run of the chip log (1 kt = 47' 3" in 30 seconds). For a photograph and brief explanation of the chip log, goto: http://www.tallshipbounty.org/Demos_ChipLog.html Because the definitions of a second, and a nautical mile have changed (since the 17Th century), the log must be recalibrated to about 28 seconds. The "chip" is the wedge of wood, and the "log" is the notation in the log-book.
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