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Thread: Knoticator Info?

  1. #1
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    Default Knoticator Info?

    I have, and love using, a "Knoticator", built by Olympic Instrument Laboratories, of Seattle. It's a variety of speedometer: a 20' length of 1/4" cotton braid, at the end of a monofilament leader, provides drag to actuate a spring-loaded gauge and indicate speed through the water. The more speed, the more drag, the harder the cord pulls against the internal spring, and the needle moves across the dial. Very simple, very clever, and the speed range is from zero to six knots --perfect for my small sailboat.

    I suspect mine needs calibrating. It has gotten a bit mushy at the low end of the speed range and I'm concerned that the springs are getting "tired". (It's probably at least 50 years old.) I've pulled mine apart and found that it was built with a means to adjust it, and it doesn't seem to require any special tools to do so, but I don't know either the total spring weights (in case I need to replace them) or the calibration weights for given speeds, to adjust it internally with the original springs.

    Does anyone here know anything of the Knoticator's technical details, or could anyone point me toward someone who might? Alternately, does anyone have the ability to crunch numbers and give me the spring weights that would allow me to callibrate it?

    All I can find of it came from this archived 1946 issue of "Here And There On Puget Sound", where it seems to be new to the market: http://www.baxterandcicero.com/6metr...hwest-1946.pdf It was apparently invented by Carlyle "Cris" Cracelius, a Seattle aeronautical engineer, and marketted through A. D. Hewitt Company, Seattle.

    And no, I don't need to hear about how awesome GPS is. I have used it, I know of its precision and simplicty, and no, I have no interest in moving away from my analogue instrumentation.

    Ahead of time, thanks.

    Alex

  2. #2
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    Default Re: Knoticator Info?

    Hi Alex. In all honesty, I believe that there are so many variables involved in this analog instrument that it would be silly to put much effort into "restoring" it to prime time condition. If anything, I'd wager that any weakness of the springs would yield quicker and higher readings at obviously low speeds. If it were me, I'd clean it up as you are doing, lubricate if possible and possibly replace pivot bushings if deemed necessary. A new trailing line might be in order…. possibly try a longer one.

    As to calibration… I think the best thing to do is for me to come down for a sail. We'll set up the Knot-O-Meter, you will busy yourself with the helm and keep your eyes on the forward horizon. I will quietly take out my portable gps meter, no no belay that… I'll take out my analytical instrument, and compare the analog reading with "something else" in the cosmos. I will then adjust your device accordingly. Of course we will drink a nice IPA to celebrate a job well done.

    Jeff

  3. #3
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    Default Re: Knoticator Info?

    Jeff, I like your plan very well! Even the part about calibrating it against, ah, celestial standards. We can check my "new" taffrail log at the same time. I differ with you in your assessment of the futility of restoring the Knoticator to accuracy, but oh well, as my father says, that's why they made horse races.

    The new deck is on, the new cabin is under way, and with any luck she'll be back in the water this summer. I'll plan on a "calibration voyage" then!

    Alex

  4. #4
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    Default Re: Knoticator Info?

    Quote Originally Posted by Pitsligo View Post
    with any luck she'll be back in the water this summer.

    YES!

    Jeff

  5. #5
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    Default Re: Knoticator Info?

    Got any pictures of this thing? Anything like this?

    http://www.knotstick.com/



    This particular one uses a stainless steel spring that the company says never need adjusting.

    The calibration is totally permanent. We have tested knotstick in a number of ways. One test involved tying a unit off at full scale and letting it sit for several months. The result was that the spring did not change at all. The calibration was not affected. The spring in the Knotstick is so far over designed that no amount of use will ever change the calibration.


    I am still hoping yours is some fancy bronze device but this thing looks like something that could be cobbled together as an unnecessary toy for my little boat. A GPS and the right size disc should get me close enough for my own needs or rather wants. Even without a calibrated scale, just knowing if I'm moving faster or slower could be interesting if not helpful. I'm less than a novice when it comes to sailing so that information could be useful for tuning the sail and boat for maximum speed.



    Sea Dreams A.K.A. Brian

    P.S. You can probably guess what I'm thinking. When you have a hammer, everything looks like a nail. When you have a foundry, everything looks like a potential casting.

  6. #6
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    Default Re: Knoticator Info?

    That's a neat idea Brian , one I hadn't seen before.

    I have one of these, a Knotmaster. Something that might appeal to Alex.

    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

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    Default Re: Knoticator Info?

    WOW Peter where'd you geddit

  8. #8
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    Default Re: Knoticator Info?

    Ebay, kinda cheap too.
    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

  9. #9
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    Default Re: Knoticator Info?

    I am still hoping yours is some fancy bronze device...
    It is, in fact, a snazzy bronze device! How'd you guess!? I have virtually zero patience with the internet gymnastics necessary to post photos on the forum, but I'll try to remember to get a photo and send it to you. You may post it here as you see fit --or not bother, if it's a nuisance.

    Aside from that, though, it's virtually identical in principle to the Knotstick: something dragging astern pulls against a spring, moving an indicator along a scale. The faster you move, the greater the drag on a given object --an object I am always tempted to refer to as the "pièce de résistance". In the case of my Knoticator, the spring is linked to a needle on a dial.

    You can probably guess what I'm thinking. When you have a hammer, everything looks like a nail. When you have a foundry, everything looks like a potential casting.
    Hurray! That one made me laugh. I will warn, however, that the Knoticator is entirely formed of either sheet or machined rods; there isn't a casting in it. But don't let that discourage you!

    I have one of these, a Knotmaster. Something that might appeal to Alex.
    Ooooooh yes. Those *definitely* appeal to me. I think you suggested one to me back here: http://forum.woodenboat.com/showthre...for-Small-Boat but I never managed to find one that lay inside my price range. I got a little tired of getting out-bid on eBay --all bad timing, all my own fault, since I only watch the auctions every so often. (Ooo! Ooo! Are you offering to send me that one as a gift!? How nice of you, Peter! No? Oh... )

    However, I recently came to own a Negus taffrail log --another snazzy bronze device!-- which was one of the few old models intended for use on small boats. As I mentioned on that other thread, which I just resurrected, I'm now keeping my eyes open for more Negus spinners. Spares are imperative, in the realm of big fish.


    As for the Knoticator, what makes me suspect the spring is tired is that its action gets mushy down at the bottom of the scale, at 1.25kts or less. The spring just doesn't reliably pull the needle down to zero. HOWEVER, given that the markings on the dial jump from a range of around 3/16" of arc of needle travel between 0 and 1 knot, to more like 1" of arc of needle travel between 5kts and 6kts, it's obvious that the gauge was always far more accurate above 2kts, and that the designers knew that.

    So is that mushy-ness of gauge movement evidence of a tired spring (it's a pretty burly bronze spring), or just a function of the gauge's movement being at the absolute bottom end of spring travel? This fits with the principle that any gauge is most accurate in the center of its range.

    And here's the next question: it looks like I could adjust the gauge to take the "lash" out of the system, tightening the spring against the needle linkage so that there was always just a smidge of tension on the needle, resulting in a more positive return to zero. I suspect that's what the gauge's internal adjustment screw is there for: to do so "at the factory". BUT, assuming (perhaps incorrectly) that the spring has relaxed over the years --it is probably at least fifty years old-- and that the bottom range is the part of the spring most affected, would that ever-so-slight pre-loading then skew the reading when the spring tension is in the upper range?

    These are things of which I am ignorant. I have lots of guesses, and a few opinions, but no genuine knowledge. Unless someone comes along with that knowledge, to better guide me, I will probably just leave it alone and see how it reads when Jeff comes down for our calibration voyage.

    Alex

  10. #10
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    Default Re: Knoticator Info?

    Alex, regarding Ebay. It's possible to set up a standing search that will last 3 months? Every time on comes up, Ebay tells you. Recommended.
    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

  11. #11
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    Default Re: Knoticator Info?

    Quote Originally Posted by Pitsligo View Post
    As for the Knoticator, what makes me suspect the spring is tired is that its action gets mushy down at the bottom of the scale, at 1.25kts or less. The spring just doesn't reliably pull the needle down to zero. HOWEVER, given that the markings on the dial jump from a range of around 3/16" of arc of needle travel between 0 and 1 knot, to more like 1" of arc of needle travel between 5kts and 6kts, it's obvious that the gauge was always far more accurate above 2kts, and that the designers knew that.
    Alex, is it possible that some deterioration in the bearing surfaces of the instrument are resulting in some kind of 'stick/slip' action? That could account for the observed mushiness and inaccuracies at low readings, I think.
    When I first joined WBF they made me write a book to prove I was a real yachty. I was so gullible.

  12. #12
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    Default Re: Knoticator Info?

    It's possible to set up a standing search that will last 3 months...
    I'll go check that out. Thank you for the info. I'm still a bit dull on the details of internetting.

    is it possible that some deterioration in the bearing surfaces of the instrument are resulting in some kind of 'stick/slip' action?
    That's a good thought. It is possible. The pins all look tight in their seats, no obvious wobble or wear, but there are several points of articulation where plates are pinned together, and it's entirely plausible that a tiny bit of corrosion has built up between the bearing surfaces. However, I've just lubricated them (clock oil), and while I don't notice any immediate difference, perhaps it takes a little bit of time and working to get the oil everywhere it needs to go. I'll spend some time on that.

    It would be awfully nice if that was the solution!

    Alex

  13. #13
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    Default Re: Knoticator Info?

    Quote Originally Posted by PeterSibley View Post
    That's a neat idea Brian , one I hadn't seen before.

    I have one of these, a Knotmaster. Something that might appeal to Alex.

    Sadly, the Knotmaster does not give you a direct speed reading. It reads distance, which gives you average speed over time. Not useful for sail trimming info.

    BTW, I bought my Knotmaster (which I really like) for $75 on ebay. Complete and almost unused.

    Norm

  14. #14
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    Default Re: Knoticator Info?

    There's also the manometer option, if I can't get my Knoticator working and I don't want to trade over to a Knotstick, but the Knoticator is both self-tending and elegant.

    A Knotmaster may not give a direct speed reading --I've heard a few electronic taffrail logs do, but otherwise they generally don't-- but distance made good through the water is still pretty important for DR.

    I need to be especially mindful of boat expenditures, these days --the boat's 30-year major overhaul is not a small project-- so new toys on the magnitude of a Knotmaster, even at excellent prices, aren't really in the budget right now.

    Alex
    Last edited by Pitsligo; 02-01-2016 at 09:58 AM.

  15. #15
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    Default Re: Knoticator Info?

    Okay, so I just figured out how to approach this:

    If the resistance of a given object being towed through the water at 2kts is X, what then is the resistance to the same object being towed through the water at 3kts, 4kts, 5kts, and 6kts? (Sub 2kts, I don't think the gauge can give an accurate reading.) The nature of the towed object is irrellevant: it's a constant. What matters is the resistance, X, and the progression upward from there. From that, I can both calibrate whether the Knoticator is, as it sits on my bench, accurate, and determine whether the spring has retained a counter-resistance on an equivalent scale; i.e. whether I can adjust it to accuracy or if it has gotten too tired to be accurate at all.

    So what is that formula for determining the progressive resistance? Does anyone speak applied physics? Fluid dynamics?

    Alex

  16. #16
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    Default Re: Knoticator Info?

    I embarassed myself a little in Post #9, grousing about how little patience I have with the Forum's photo-posting protocol. If others take the time, I ought to. So here's my attempt at photos of my Knoticator --yes, a snazzy bronze device-- starting with the dial. You can see how the increments between indicated speeds increase as the speed increases. The increment between 0 and 1 is only about 1/8":



    When I got it, it was attached to a bracket that was apparently meant to be permanently mounted to the boat. I didn't like the idea of just leaving it out in the weather, so I built my own bracket, and mounted it on a pin that fits into the oarlock socket. The pin is a piece of red brass pipe turned down to 1/2" diameter. Through the pipe runs a piece of 1/4" rod, that at the top has a knob (ipé) and at the bottom screws into an expansion plug, so that when it's in place in the oarlock socket, I can turn the knob to tighten the screw, expand the expansion plug, and lock the whole thing in place:



    The little twist of wire is where the drag-line attaches (with a fishing swivel) to the protruding actuator pin, that is in turn attached to springs and linked to the gauge needle.

    Anyway, for today, I adjusted it so that the spring tension relaxes to nothing as the needle reaches a speed of zero knots. And unless I can come up with a good formula for adjusting it with more accuracy, I'll wait until I can inveigle Jeff south for a calibration cruise and then work by the highly precise, tried and true, scientific method of trial-and-error.

    Alex

  17. #17
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    Default Re: Knoticator Info?

    I like it. I'm curious that the dial you have is from somewhere though, a log of some sort, and so will be calibrated to whatever log it came from...so how will you adjust it to suit your own particular constant drag weight?

    Im no fluid dynamics expert, but I have a feeling twice the speed will be four times the drag force.

    A radial spring scale could work too, such as to weigh a suspended weight, if you painted over the dial knot for knot.

  18. #18
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    Default Re: Knoticator Info?

    I'm curious that the dial you have is from somewhere though, a log of some sort, and so will be calibrated to whatever log it came from...
    I lucked out: I have the original instructions. The drag is to be 20' of #4 (1/8")(I misremembered it, at the top of this thread) braided cotton line at the end of a long monofilament leader. Unfortunately, the instructions say nothing of how to calibrate the gauge after 50+ years.

    I also lucked out in finding 1/8" 100% cotton braid. It isn't available in the US, but Cancord, Inc., in Canada carries it, and when I contacted Wendy Johnstone, at Cancord, she VERY kindly supplied me with a couple hanks. It's item #11-040-05, if anyone needs it --or it was six years ago.

    And for those who wonder, I ran tests with it when I got the cotton cord (in 2010): I built two drags, identical except that one was with cotton cord and the other with nylon. The nylon drag registered about 20% slower, once the cotton line had been in the water a little while and had had a chance to "take up."

    I have a feeling twice the speed will be four times the drag force.
    That sounds vaguely familiar.

    A radial spring scale could work too, such as to weigh a suspended weight, if you painted over the dial knot for knot.
    There's a little bit of slop in the holes for the screws holding the face to the gauge, so I can shift it around a little during calibration. The dial is beautifully enameled copper sheet, so I'd hate to change it.

    Alex

  19. #19
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    Default Re: Knoticator Info?

    Old Thread but did you guys see the knoticator now on ebay? Looks to have instructions, original box, etc...

  20. #20
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    Default Re: Knoticator Info?

    Good to see that even though Alex hasn’t posted in years his latest activity was just a few weeks ago.

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