no paddle wheel speed transducer

[Troy Scott]

Folks,

Have any of you used one of the new "no moving parts" speed transducers? Do they work OK? How does the price compare to the paddle wheel variety?

[Warren Kaplan]

I haven't. I don't know about the rest of you but my paddlewheel transducer either fouls and/or breaks each year from barnacles and the like.

A few years ago I came to the conclusion I really didn't need it anymore because my gps (and probably everyone's gps) gives speed over ground, which our onboard paddlewheels do not.

Since I'm 99% interested in speed over ground rather than speed through the water I decided not to fix my transducer a few years ago. I can honestly say I have not missed it one little bit.

So, not meaning to hijack this thread, I'm just interested if others have come to the same conclusion, paddlewheel or non paddlewheel transducer.

[Neil Gordon]

I have the paddle wheel. Sometimes it works, sometimes it doesn't.

When it does work, I can never be sure how accurate it is. It was callibrated as per the instructions, but in between zero and functioning normally, I'm sure a little bit of crud slows it down a little bit. I think accuracy varies over my speed range.

Also, is there a difference between port and stbd tacks? Different discussion, perhaps but as the hull becomes asymetrical due to heeling, does water flow down both sides of the hull at the same speed?

All this said, I still like having it. I generally eyeball the GPS vs. the paddle wheel so I have a good idea of how they compare without current. I never use the total miles log because I never remember to reset it and I can't be sure it's accurate. GPS has pretty much replaced that need. On occasion I use the countdown timer and the water temp. feature is handy if you're planning a swim.

[Troy Scott]

Warren,

My brother feels the same way. He uses the GPS for speed and sees no value in having a knotmeter. My problem with that is: How do you know how you're being affected by current? If you can get ACCURATE speed through the water, ACCURATE wind angle, etc., then modern, integrated systems can calculate water current direction and speed, true wind direction and speed (rather than just apparent), etc.. (I know everybody knows this, I'm just stating the obvious as basis for discussion). On the one hand I really like the simplicity of telltales and a handheld GPS. On the other hand, I am fascinated by knowing things like water current speed and direction, actual wind speed and direction, etc.. It's not just interesting; it can be really helpful to know these things. But, the basic sensor information has to be excellent for these wonderful calculations to be accurate, and they have to be accurate to be useful.

I need to do more research, but I think probably the non-paddle-wheel type sensors electronically measure the velocity of the bubbles passing the sensor, and I'll bet it's less sensitive to fouling. I'm sure this has the potential to be more accurate, especially if the setup includes a thorough calibration regimen.

I'll bet somebody here knows more about this!

[Neil Gordon]

Troy,

It's all about the degree of accuracy that's required for safe navigation and simple (or complex) enjoyment of the sport. They might be the same or they might be different.

>>How do you know how you're being affected by current?<<

If the buoys and lobster pots are leaving a wake, there's current. If the wind is light and you're ghosting but the scenery is flying by, there's current.

>>If you can get ACCURATE speed through the water, ACCURATE wind angle, etc., then modern, integrated systems can calculate water current direction and speed, true wind direction and speed (rather than just apparent), etc..<<

How about ESTIMATED speed, EYEBALL wind angle, etc. An old fashioned maneuvering board with vectors drawn with a pencil will tell you about the same thing.

>>I am fascinated by knowing things like water current speed and direction, actual wind speed and direction, etc..<<

Agreed. But I'm also fascinated by the loss of traditional skills and the dependence upon gizmos. It's like the joke about the guy who gets stuck on the escalator when the power goes out.

[John Ring]

Troy,

Where are you seeing these speed transducers? I've heard of them, but haven't seen them for sale yet. From what I hear, they operate more like a depth transducer, measuring the speed of particles going by in the water. This of course, eliminates the need for the problematic paddle wheel.

As a side note, I just installed a removable paddle wheel knot meter in Tantalus. Most of the new ones come with a flapper valve set in the thru-hull that stops most of the water from flooding into the boat when you swap the dummy plug and tansducer. Keeping the dummy plug in the hole and storing the actual paddle wheel in the boat (dry) keeps it the paddle wheel clean and weed free until you put it back in next time.

John Ring
CD28 Tantalus

[Anthony P. Jeske]

Like John Ring on TANTALUS, I too remove my paddle wheel when not sailing. On my boat, it's easy to get to and so only takes a minute to swap out and results in an always working speedo; which I find is easier to read than the speed on my GPS.
Tony Jeske

[Troy Scott]

Neil,

I've done it both ways, traditional observation and electronic. I used a lead line for years. I used to tow a "knotmeter" that had a tiny drogue connected to a "meter" that consisted of a spring in a tube with marks on the side. (It was obvious when THAT picked up seaweed!) I've laughed at folks who've looked at my Windex-free masthead and asked me how I knew which way the wind was blowing. I sailed for years with paper charts, parallel rules, etc.., and finally got an ADF to play with. But a few years ago I had a boat partner who liked gadgets. I didn't really want to bother with that stuff, but we installed the latest Raymarine MFD with moving map and connections to everything, including the autopilot. Because of the integration, it was able to do the calculations and tell me things I really hadn't even worried about before. The newest ones will even overlay radar and current weather on the map page, which is really a SAFETY thing, and few among us will argue that we should be Luddites when it comes to safety.

Please don't get me wrong. I'm still opposed to clutter. I don't want a boat loaded down with gadgetry. I would be embarrassed to have my pedestal guard looking like the helm of the starship ENTERPRISE. Many times I've been annoyed by some new feature that exists because it can be done, not because anybody needs it. However, adding a little integration to the instrumentation most of us already have takes up no additional space and can provide a lot of derived information. I can still observe the current flowing past the bouys. I can still confirm by looking that the hurricane has just ripped the wind sensor from my masthead.

But if I can eliminate that pesky paddle wheel.....

[Troy Scott]

John,

My CD36 has the same flap to seal off the paddle wheel receptacle. Like wheels on suitcases, why on Earth didn't we have THAT long ago?

I'm not sure where I've seen those paddle-wheel eliminators. I thought about it last evening and started looking. I did find some references to the technology, but none for sale so far. Somebody here will find it and let us all know.

[Russell]

If the buoys and lobster pots are leaving a wake, there's current. If the wind is light and you're ghosting but the scenery is flying by, there's current.

That only works near shore. Offshore it is difficult to tell other then estimate based on known current data. This is indeed where a knot meter, that is clean and calibrated, becomes very handy.

That said, I am lazy, to keep the knot meter working properly it requires weekly removal and cleaning, which I hate doing. Like most, I rely on the GPS, and with that, you can compare true heading with magnetic heading and known variation, and know if the current is affecting you. But GPS goes out and its back to dead reckoning, well, you dont have anything to compare the knot meter to anyways so you are still back to estimating it based on piloting data.

I think these days the only people who make real use of traditional knot meters are round the bouys racers, since the knot meter gives instant (as opposed to GPS delayed) speed down to 1/100th of a knot.

A knot meter with no moving parts that does not foul sounds terrific, I know nothing about them (must be spendy??). If I was doing a refit right now, and such a beast existed for a reasonable price, I would certainly look into it myself.

[Troy Scott]

Google

Airmar Ultrasonic Speed Sensor CS4500

[Russell]

Interesting. Being airmar I bet it will work with some existing knot meters. But that price tag is not for me, maybe in a few years when prices come down.

[Warren Kaplan]

I do 99.9% of my sailing in my local home waters. So one look at the tide table and I know which way the currents are going and approximately how strong those currents are during the tide cycles. I know what to expect when I'm sailing and I can tell just by the boat's performance whether I am being helped or hindered by the current by my gps reading of speed over ground.

So, for sailing in my own well known waters, the paddlewheel knotmeter doesn't really tell me anything I don't already know just by watching how the boat is performing.

Certainly if you should venture out of your well known home waters then you could glean some info from the knotmeter as to current effects. Again though, most of us check tide tables and Eldridge for currents when in unfamiliar places and that alone can give us a pretty good idea of what's going on with our boats at any given time.

[Troy Scott]

Today I spoke with Airmar (the manufacturer) and Gemeco (their distributor). The untrasonic senders are compatible with standard knotmeters. You have to order a specific model number, determined by whatever meter you plan to use it with. It is considerably more expensive than a paddle wheel, but I want to replace the sender anyway since it's a cheap plastic unit in a plastic thruhull. I will buy the bronze unit with the bronze sender, but first I have to decide whether or not I'm going to keep the Raymarine 60 Series instruments. They're nice, but it may be a year or more before I need them. By then, who knows what will be available.

[Russell]

If its a year before you need insturments, why not wait till then to order the transducer too? It may come down in price as well.