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Old 29-08-2018, 12:11   #1
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Fed up with paddle wheel logs

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.

I know there are untrasonic versions but the cost is putting me off. I have been discussing this with my son who like me is an eklectronic engineer and we have thought of the following solutions.

1. Pitot tube like aircraft but larger tube size.
2. Pressure transducer reading against a drum membrane
3. Rod with a stress sensor
4. Rod with a 45degree plate that rises with speed.

The question is, has anyone done the above or an alternative successfully?

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?
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Old 29-08-2018, 13:11   #2
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Re: Fed up with paddle wheel logs

We have a paddle wheel, but have never used it. We just use the gps. Several times I thought about getting an ultrasonic transducer, but always have gotten talked out of it, by some very good sailors who just use gps.
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Old 29-08-2018, 13:17   #3
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Re: Fed up with paddle wheel logs

Quote:
Originally Posted by FionaJC View Post
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.

I know there are untrasonic versions but the cost is putting me off. I have been discussing this with my son who like me is an eklectronic engineer and we have thought of the following solutions.

1. Pitot tube like aircraft but larger tube size.
2. Pressure transducer reading against a drum membrane
3. Rod with a stress sensor
4. Rod with a 45degree plate that rises with speed.

The question is, has anyone done the above or an alternative successfully?

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?
We have a (click on) Knotstick that we use to calibrate our Speedo. Very accurate and quite inexpensive. Easily deployed and recovered.

FWIW...
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Old 29-08-2018, 13:43   #4
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Re: Fed up with paddle wheel logs

Fiona, there are already pitot tube speed gauges for fast planning craft, but they just aren't accurate enough for slow speed yachts were you want to small increases perhaps for sail adjustments or in your case minor changes in revs. There were okay on dry sailed craft but the tube would surely block if permanently kept underwater on a yacht.

We have the Raymarine ST60 and keep the paddle wheel out most of the time, only fitting it when going on a longer trip. Like you we are UK based and the tides rule, so knowing SOG and comparing it with speed through the water is very useful.

If you could make a replacement sender unit for the Raymarine series then you would be on to something.
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Old 29-08-2018, 14:17   #5
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Re: Fed up with paddle wheel logs

Do you know why your paddlewheel stops working? Is it fouling, or mechanical jamming or whatever? I ask because with minimal attention, ours have worked for many years.

If fouling is the issue, I've found that putting a thin coat of antifoul paint, the same stuff as I've used on the hull, will keep beasties away for a few months. If mechanical jamming is the issue, perhaps the bore in the wheel is worn enough that it cants to the side and jams... replacement wheels are available, or you could use a slightly larger axle pin.

If the boat is only used periodically, removing the unit whilst the boat is idle always helps.

Don't give up! It can be made to work.

Jim
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Old 29-08-2018, 15:09   #6
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Re: Fed up with paddle wheel logs

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Originally Posted by Training Wheels View Post
We have a paddle wheel, but have never used it. We just use the gps. Several times I thought about getting an ultrasonic transducer, but always have gotten talked out of it, by some very good sailors who just use gps.

Yes I use GPS but when the wind is on the nose and you cant steer to where you want to go its nice to know if you are at max hull speed as the choice might be furl the sails and head where you want to go and ut the revs up.


You really need to know the speed through the water to make thioose decisons and SOG from GPS is not reacrive enough to tell you that.


It gets clogged within 30 minutes usually with seaweed wrapped around it. I am on the East Coast of the UK and I really need to scrub fortnightly but it still wont work for long. Its a NASA Log.
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Old 29-08-2018, 15:10   #7
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Re: Fed up with paddle wheel logs

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Originally Posted by Jim Cate View Post
Do you know why your paddlewheel stops working? Is it fouling, or mechanical jamming or whatever? I ask because with minimal attention, ours have worked for many years.

If fouling is the issue, I've found that putting a thin coat of antifoul paint, the same stuff as I've used on the hull, will keep beasties away for a few months. If mechanical jamming is the issue, perhaps the bore in the wheel is worn enough that it cants to the side and jams... replacement wheels are available, or you could use a slightly larger axle pin.

If the boat is only used periodically, removing the unit whilst the boat is idle always helps.

Don't give up! It can be made to work.

Jim

Its fouling, it hasnt turned much in ten years so it cant be wear!
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Old 29-08-2018, 15:27   #8
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Re: Fed up with paddle wheel logs

My paddlewheel turns, but much too slowly. Like it reads 3 knots when I'm doing 5. Also turns more slowly on one tack than the other. (It's on one side of the forefoot.) Since it used to do better, I suspect that this may be due in part to fouling on the hull around or forward of the paddlewheel disrupting laminar flow. Not on the wheel itself.
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Old 29-08-2018, 17:00   #9
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Re: Fed up with paddle wheel logs

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.
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Old 29-08-2018, 17:34   #10
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Re: Fed up with paddle wheel logs

I had a paddle wheel, I still do, it lies in the bilge where it can't give me inaccurate readings.

I would like a log to give me some insights into my speed through water but after trying for a few months to calibrate the thing, it was faster on one tack than the other, I gave up and have never really missed it.

Instead I use my understanding of the boat to know how well she is sailing. As for currents, close to the coast they are usually well charted on satellite weather webpages. Also you can use temperature to detect whether you are in a warm or cool current. To get a truly accurate idea of current flow, if I see a fishing float I can head closer to check it out. Here on the East Coast of Oz the currents are very easy to predict and you don't get much info from a log you can't get elsewhere.

Although it may be nice to have a paddle log, I have never missed it in 19 years of owning my boat.
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Old 29-08-2018, 17:41   #11
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Re: Fed up with paddle wheel logs

I once installed some nexus instruments into one of my boats. Because the boat had previously had a system installed, I used the original holes and installed a version of the instruments that used a separate depth transducer and a separate speed log. On relaunch, I soon discovered that the speed log didn't work properly. It was very haphazard. After some experimentation, I swapped the speed and depth transducers around (easy to do because they used the same through hull socket). Lo and behold, the speed log worked perfectly in one hole, but was a bear in the other.



Oddly enough, there was no obvious reason why the log should not have worked in it's original location. Both locations were located in an area with (apparently) clear water flow. I just attributed the fact it wouldn't work in the original location to either turbulence at that point and/or water flowing around the hole at an angle at that particular point that was too far offset for the speed log to spin up due to the hull form. It was a real mystery.


Moral of the story is that if your paddle wheel spins freely, the point where it pokes out of the hull might not have a good flow of water going past it when moving, even if it appears it should.
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Old 29-08-2018, 17:47   #12
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Re: Fed up with paddle wheel logs

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Originally Posted by billknny View Post

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.
I found the thermometer does just as good if not a better job of Gulf Stream detection.
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Old 30-08-2018, 00:03   #13
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Re: Fed up with paddle wheel logs

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Originally Posted by FionaJC View Post
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.

I know there are untrasonic versions but the cost is putting me off. I have been discussing this with my son who like me is an eklectronic engineer and we have thought of the following solutions.

1. Pitot tube like aircraft but larger tube size.
2. Pressure transducer reading against a drum membrane
3. Rod with a stress sensor
4. Rod with a 45degree plate that rises with speed.

The question is, has anyone done the above or an alternative successfully?

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?
Blacksmith age technology.

Electronics engineers + of the shelf ultrasonic transducers + microprocessors should + DIY electronic knotmeter.

I would use a two diaphragm (small and large on the same shaft) to multiply the pressure the pitot tube pressure and one of the small, cheap, low presssure transducers to provide a voltage signal rather than rod with load sensor.

You need a static tube signal to the back side of the large diaphragm.
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Old 30-08-2018, 09:32   #14
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Re: Fed up with paddle wheel logs

Have used paddle wheels for years and other than the occasional beastie that likes to be dizzy have had no real problems. In a lot of seaweed I have seen a knife like blade mounted a bit forward of the wheel. cuts the junk and doesn't upset the flow.


If it is bottom slime then Anti foul would be worth a try.


Hmmm, in the UK would that be counter foul?
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Old 30-08-2018, 10:34   #15
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Re: Fed up with paddle wheel logs

Anyone using the Airmar UDST 800?
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