Fed up with paddle wheel logs

[salfarina]

Hello Fiona - Just last night, I was searching YouTube for a visual on changing a Racor fuel filter and came upon a site that had what I was looking for, in addition to a few other "how to's". Coincidentally enough, it contained a video "How to fix a boat speed sensor". It's a interesting and helpful lesson and I was quite surprised to learn that the paddle wheel itself, over time fails and requires replacement. The You Tube "channel" is entitled "spelunkerd" and there are two videos applicable to your dilemma. The first is titled "How a boat paddlewheel speed sensor works" and the second video is the one I mentioned earlier.
Good Luck!

[Cheechako]

Make a chart of your boats speed in flat water at 10-15-20 etc wind speed. Look at your gps sog and estimate the current or etc. Close enough for cruisers. "Hmmm... my sog says 4 knots, but I know my boat goes 6 in 15 knots of wind"

The better way is to make a small line with a wood block on it. Make it with knots at equal intervals so that you throw it over and count how many seconds to go say 6 intervals. You then know your "water speed"

But I have to say, while paddle wheel logs can be problematic, they should work for quite some time, until you stop moving and anchor for too long. My B&G were pretty good, but eventually stopped.

[tml]

Telcor Instruments from California sold some very innovative knotmeter and wind speed instruments. We had them on a boat we bought in the late 80's that had been outfitted in 1978. We used them for several years and they worked very well.
The speedo transducer was a 3/8" ish rod that protruded about 3/4" from the hull. Water pressure against the rod increased as speed increased and showed up in the cockpit on an analog dial. I have been told the same instrument was used on submarines because of low drag etc.
Wind speed had no moving parts at the masthead;a small 3" cylinder had holes around the cylinder. A thermistor ( whatever that is ) inside measured temp that varied with wind speed,.for all I know it was magic but it worked.
Tom

[jmschmidt]

SOG data (Speed Over the Ground) from GPS and STW (Speed Through the Water) or Boat Speed from an in-water knot meter, with the exception of comparing the two to get a rough approximation of the effects of current, are used for completely difference purposes on a sail boat.

SOG data is primarily for making navigation calculations and estimates, Boat Speed data from an in water sensor is used to determine the need and effects of sail trim.

On a power boat the only reason to have both would be to estimate the speed and effect of any current.

[DMCantor]

We have used a standard Raymarine paddlewheel log for the last 10 years, with minimal problems. We maybe have to knock off marine grown every 3 months or so, less often if we're sailing every day. This is in the Caribbean where there's plenty of marine critters around. I think there must be something fishy about your specific paddlewheel if it fouls so quickly.

[JimsCAL]

Some random comments.
1. The techniques you list in the first post are all non-linear (basically square relationships). You might get them to work at high speeds, but not likely at low speeds.
2. I have a 30+ year old Datamarine knot/log unit on my current boat. Still works pretty well. Does require an occasional cleaning (depends on how much I use the boat). This season I've had to pull it once.
3. Be careful if you decide to try using an antifouling paint on the paddlewheel. Most sensors use a hall effect device to detect the spinning wheel and copper based paint will interfere with the sensor detecting this. A paint without copper or other metal in it would probably be OK.
4. If currents are not strong in your sailing area, you can get away with using the speed reading from the GPS. I still like having both however.

[jeff356]

Have the Raymarine standard paddle wheel log and find it works well when the wheel is free from growth, spins freely, the sensor is clean and the bottom in front of the sensor is clean.
Went out this weekend and had a good sail with my speed sensor running a knot or more slower than the SOG GPS reading. Anchored and jumped in to cool off and saw a scum line and some growth on the bottom even though we normally go out every weekend for multiple days. Used a deck brush on a pole and hit the waterline and as far under as I could reach, which hit where the speed sensor was.
Headed to port and for the first time in a long while the sensor speed was above the SOG, didn't think it was making a difference but it did.
As standard procedure I remove the sensor and put in the blank when leaving the boat for over a day as it clogs up or slows down quickly when sitting.

Jeff

[Steve Bean]

A simple way to get STW is just to throw a chip of wood, wad of wet paper, or something easy to throw, into the water at or near the bow, and use a stopwatch to find out how long it takes to sail past it. If you know how long the boat is, speed=distance divided by time.

[Jim Cate]

Be careful if you decide to try using an antifouling paint on the paddlewheel. Most sensors use a hall effect device to detect the spinning wheel and copper based paint will interfere with the sensor detecting this. A paint without copper or other metal in it would probably be OK.

Normal anti fouling paint does not have metallic Cu in it, but rather copper oxides. At any rate, I've been using various Cu based paints on my paddlewheel for several decades now with no issues other than over application which can bind up the wheel. A thin coat on both the paddlewheel and the cavity in which it spins will work to keep actual growth off. Can't ward off strands of loose weed getting tangled in the wheel, though. The "blade" ahead of the wheel helps with that, and we've had one on this boat since we bought her (installed by the PO).

Jim

[roverhi]

Have had paddle wheel transducer knotmeters on 2 different boats. Never a problem and worked fine for our ownership. I did pull the transducers after most sails so no problem with fouling except the few times I got lazy and left them in. After a couple of weeks in the water, the transducers did pick up some growth that didn't stop them from functioning just reduced their accuracy. Transducers were in the bigle so no problem with water ingress when changing from blank to the impeller.

New boat came with a dead impeller/log. Think it's transducer and probably the gauge that are both bad as they are vintage instruments from the last millenium. Will replace with a NOS Raymarine Knotmeter ST60 Plus system which still works fine on my other boat after a decade. The thru hull has a flap to restrict water inflow when changing the impellor/blank. Will be interesting to see if it significantly reduces water inflow as the PO located the old through hull in a locker that I don't really want water in.

[Kenomac]

Originally Posted by billknny

The idea that GPS SOG gives you all the information you need to do useful navigation is very shortsighted. Yes, it give you some useful information, but without a water speed sensor you are missing a LOT of vital data if you are doing serious navigation, and not just eyeballing it to the next anchorage.

The combination of Heading, STW, COG, and SOG allows your instruments to calculate and display the current affecting your boat. Knowing the set and drift of the current in real time is really useful and helpful. Of course for the resulting calculations to be accurate, the heading and STW must be accurately calibrated.

An example of when you would find real time current data important: You are making your way south along the east coast of the USA. You would shave hours, and maybe days, off your trip if you could keep yourself out of the Gulf Stream flowing northwards at 4 knots, and instead could stay in the shoreside countercurrent that flows south at 2 knots.

We use an Airmar CS4500 ultrasonic speed transducer in lieu of a paddlewheel. It has been reliable and accurate for the last 10,000 miles. Really nice not having to pull it and scrub before every sail for reliable numbers. Of course it doesn't work if it has a thick biofilm growing on it, but it is way easier to keep clean.

If your paddlewheel is not working even when clean, have you tried replacing the wheel and bearing pin? They have finite lives and need replacing occasionally.

I haven’t used a paddle wheel speedo in over 8 years and haven’t missed it one bit. ‘Guess I’m “shortsighted,” but always seem to know where I am on the planet to within 15 feet or so.

[sailorboy1]

Originally Posted by FionaJC

I know I can see the SOG using GPS but after an 8 hour sail against tide and into wind I wanted to know how much the wind helped and if I had reached max hull speed when the SOG was 2.6kts. Would extra RPM help. So many questions and only knowing the boat speed through the water could help.


Any ideas guys?

It comes down to how much that info is worth to you. Me I haven't clean my speed log in 7 years and just go with SOG

[fxykty]

Thread drift, but isn’t the reason to want STW is to get TWS and TWA?

Or is it more of a multihull thing to want TWS? I know ‘deep’ downwind (130+ TWA) we rely heavily on TWA and often set our pilot to TWA to avoid surfs taking us too far downwind.

[ranger58sb]

Originally Posted by FionaJC

Ok after 10 years I have had enough. I have a paddle wheel log and its never worked. I clean it each scrub and as soon as it goes back in the water it works for five minutes and stops.

Any ideas guys?

Some paddlewheel assemblies are meant to be replaced after X amount of time... See instructions for Airmar B774V and Maretron DST100, for example. Yours may be one of those, where cleaning isn't the answer.

-Chris

[ranger58sb]

Originally Posted by sailjumanji

Anyone using the Airmar UDST 800?

Ummm. maybe. We just last week replaced an ailing Maretron DST100 with a new Airmar DST800. (Not a UDST 800.)

??

Anyway, it seems to work. Only have the one return trip with it so far, though.

-Chris