Knot Meter

[Curt]

I did not have one on the last two boats and don't have one now. Don't race and never really gave much thought to know how fast I was going as long as I was going. However, I am curious now that I have a Capri 22 with all the trim control. The more I tinker with sails and trim the more I wonder if I am making a difference. One way to know would be a knot meter.

Is there such a thing that does not need to be through hull? I absolutely do not want, and most likely will not put a hole in it for any reason. I could use a GPS on a smart phone if I had one, but that is speed over land and does not have a direct correlation to knots per hour. Although it may show a change in value if I improved the sail trim

I have to make an admission here, don't hate me. At one time for a short while, when my kids were young and hated being on a sailboat. We could only sail as long as the juice boxes and gold fish crackers held out. I had a 20 foot IO. I have to admit that as there was a transom mounted knot meter that was not through hull. It was externally bonded to the transom below the water line and the wire ran up the transom and through a vent hole. There was an short extension that extended down and as the boat moved forward the arm would begin to raise with speed rendering a signal that was converted and displayed Knots / hour.

I have never seen such an item for sailboats. Maybe sailboats do not move fast enough to make the system effective.

Thanks,
Curt

 

[NewportNewsMike]

Hi Curt - I see no shame in owning a "stink pot" as my wife called them when we first met. She was a sailor, I was not, but I soon became converted. I love to sail (and have become the biggest sailor in our family), but I also love to explore in my canoes and kayaks, as well as my "kayak I do not have to paddle", i.e. my motor boat.

The current motor boat (a Lund SSV 16 with 20 hp Honda) does not have a knot meter. I use a hand held GPS for the rare occasion that I need a speed reading to compare various settings, trim, et cetera.

I also use that same GPS for sailboat duty when the time arises. Most days, and sails, I do not have any real "need" to have a speed indication in my Capri 22, but it can be enlightening to compare the effects of various sail trims, boat heel angles, et cetera. And the handheld GPS is more than adequate for this. I have resisted putting in a "proper" knot meter because of need wanting to put holes in the hull, and not having to deal with installing the transducer for every sail, and re-moving it when completed. Our Capri 22 is wet slip stored, and here in the Lower Chesapeake Bay, paddle wheel transducers will foul enough to be in-operative a just a few short weeks. So it is install for use, remove for storage. Previous sail boats I have owned all had paddle wheel transducers in through hulls - and I do not miss them a bit on the Capri 22.

As to your question about why you do not see transom-mounted paddle wheels on sail boats, I think it is because of the heeling associated with sailing. On a motor boat, the transom is squarish and is just about always properly placed to have the paddle wheel in proper contact with the water. Not so on a sailboat that may have a roundish transom with one side more out of the water than the other when heeling - and then you tack and the low side is the high side - and on it goes. I guess you could mount in the middle, if you did not have a transom-mounted rudder.

And there may be that "not looking proper on a sailboat" thing that keeps many sailing people from trying one out.

Edited to add - In re-reading your post, I see that you were talking about a different type of speed indicator than a paddle wheel transducer. My comments about sensor placement still apply.

I have seen powerboat speed indicators "kinda" similar to what you describe - a plastic "wand" permanently mounted on the transom with a wire / tube running up the stern to a dash-mounted indicator. But with the ones I am familiar with, the wand did not get deflected upward as you went faster. The "wand" was fixed and was actually sensing water pressure (as speed goes up, the pressure of the water pressing into the hole on the end of the wand goes up) and transferring this increase of pressure through a tube to the indicator head in the dash. Like a pitot tube system on aircraft.

This type of system probably would not be all that accurate at sailboat speeds. Simply not a sensitive enough system to tell the difference between 4.0 and 4.3 knots.

 

[BillL Capri 22]

I know how you feel - changes should be measureable, notes can be taken and data evaluated. The engineer in me wants to do that too.

However, "a good sailor" should be able to feel the speed increase caused by trim changes.
Watch, listen, and feel for the changes. Change back and forth to verify. When looking for smaller effects, try doing two-boat testing. Two-boat-testing is an itterative process were the slow boat is trimmed until its as quick as the fast boat, then one or the other does a change and both boats see the effect. Keep the speedier changes, discard the pokey changes.

There are transom-mount sensors that work like a pitot tube that may not foul as much as a paddle wheel. There are also ultrasonic sensors (sequential sonar) offered by B&G, Raymarine, and a few other mfgs. If you don't want a transom mount or through-hull, there is a system out there that measures how fast the water goes by the hull using and electromagnetic sensor (a la MagMeter) that is mounted within the hull. I've only found one mfg though and its still an emerging technology.

 

[Charlie H]

Hi Curt,

I use a Velocitek "SpeedPuck":

http://www.velocitek.com/speedpuck/

I use it a lot and really like it. It uses GPS to calculate speed. My only complaint (aside from price) is that it has no back-lighting for use at night.

Charlie

 

[Curt]

Newport News Mike; Makes sense now that you point out the obvious. The unit would need to be mounted on the center line at the transom to negate the effect of heel. Thanks

Bill; I have had only one sailboat with a know meter or any other instrument for that matter. When I sail it is always by how the boat feels underway. The engineer in me wants to know all the variables because we are an anal bunch. However I try to leave that at work and sail for the relaxation and fun in taking friends out on the water. That said, with all the adjustments it is fun to tinker a bit. However, sometimes the reaction to a trim tweek is not always evident. A bit more heel may feel faster but is actually not. A knot meter would come in handy for verification. I won't take the"good Sailor" comment personally. Thanks for the tech on electromagnetic sensors, something to watch for.

Charlie H; The Speedpuck looks like a great idea and I may have to take a closer look. Since I am not trying to gain every last oz of speed and just want a reference not being backlit would not pose a problem. Thanks.

Cheers All,
Curt

 

[sinnettc]

If you're into through hulls then you could put in a paddle wheel. I've got a through hull one that I'm taking mine out as it's eventually going to leak and it's not hooked up anyway. I've also got a transom mount that came with my first Lowrance chart plotter; haven't hooked it up but I keep thinking about it, especially if I can come up with a way to do it without drilling any holes.

 

[shnool]

I'm going to say something not real popular...
Put in a good analog 12 knot knot meter, with paddle wheel... drilling a hole in a Capri 22 isn't a big deal. Use 3M 4200, level the glass, and tighten appropriately.

A knot meter, and a GPS do similar but different things. The stern mounted anythings, won't work well on a sailboat (turbulence, and such), and if you were to do GPS, then use a combo, Nav tool and GPS (to get MORE functionality to it).

I realize you are in non-moving water and all, so GPS SHOULD provide same info as a sumlog in that instance. Indeed, I've used my GPS to calibrate my sumlog.

But GPS doesn't really have the resolution to get you accurate enough numbers at VERY slow speeds... it can be off by as much as a FULL KNOT (you can usually tell when that is though).

Anyway, a good signet 12 knot, knotmeter will be the best purchase you can make for gauges for the boat. And as much as I agree, you should be able to feel a .2 knot difference in trim, even the most experienced sailors can't always tell (as much of what they feel is apparent wind change, and sometimes that can be misleading). Sorry, I am a HUGE fan of analog gagues.

 

[NewportNewsMike]

I will have to agree with shnool that the analog knot meter is nice to use. I had the Signet analog knot meter (SL 11) on a Tanzer 22 for a couple of decades - it was joy to watch the needle creep upward as you fiddled with sail controls.

But, and here's the big but, it was a pain in the butt to swap out the "dummy" plug for the paddle wheel plug. Sailing here on the warm water lower Chesapeake Bay, and leaving the boat in a wet slip, required that you swap out the paddle wheel with a dummy plug whenever the boat was parked a few days or so. Otherwise, the paddle wheel would fill with barnacles and become useless.

The first time I did it, and the water started pouring into the boat, even though I was "mentally" prepared for it, my eyes must have been eight-inches in diameter! You eventually get used to it, but you do learn not to dally while swapping the plugs. And then there is the salt water that needs to be removed from the bilge or what ever compartment it collects in.

Add to all that the fact that the most favorable spot for the paddle wheel to work (i.e. best through hull location) may not be the most accessible from inside the boat (for swapping plugs). Here's a video on youtube - not my Tanzer, but it gives the idea of what I am talking about: http://www.youtube.com/watch?v=dGFZ86yh4RQ

Some days I would decide I did not need the knot meter and would not install the plug, just because of the aggravation of doing so.

So, here is a partial support of shnool's thought. An analog knot meter can be very useful, if you can convince yourself that it is worth the aggravation. And Signets are good products. If you choose to go with their knot meter, they have matching depth sounders, et cetra. I love their depth gauge - looks good, works well, and there is no paddle wheel to futz with!

 

[BillL Capri 22]

I'm one for no thru-hulls.
The "good sailor" bs wasn't meant to be taken too seriously, thus the "quote marks"...
Just the same, two-boat testing is a lot of fun, especially if you can get your boat going faster. It's like doing a bunch of littl races.

 

[HERSH]

Yes; I had an analog MK-II from Signet on my San Juan 21. Yes-- fun to watch it creep up. But I too had problems with it fouling all the time. Hudson River -- fresh water --- most of the time.

I haven't studied the digital meters at all. But when one says "digital display" I suspect it is just a digital voltmeter across an analog output. I would think that a true digital would count the number of pulses in a given time period and scale the output accordingly. But this is just my thinking --- no evidence one way or the other.

I just was looking a a "new" boat in my club the other day. The knot-meter paddle hangs off the transom. I'll find out in the spring what brand it is. I do not like drilling holes in the hull.

Hershey

 

[Richard9547]

ANY gps will have a speed display.

 

[shnool]

keep in mind folks I am spoiled I am in VERY LOW fouling fresh water... I don't remove the paddle wheel ever... I am ONLY in the water for 6 months tops... at the end of 6 months I can wipe the algae off with a sponge.

I did paint the paddle wheel with VC17m.

 

[Chris Capri 22]

Get a smartphone. Then get a waterproof case. Download Race Q's App (free). Stick a piece of Velcro to it and attach it to the aft cabin bulkhead (the one facing you). It replaces that overpriced Velocitek Speed Puc and you can still use it to call your Momma. Look Ma, no holes!