Paddle wheel speed sensor, who needs ‘em!

[Dockhead]

Originally Posted by noelex 77

I find ground wind very useful, particularly when combined with apparent wind. Ground wind keeps track of the environment (what is the wind strength is the wind increasing, decreasing or changing direction).

Apparent wind, both strength and direction is used to trim the sails.

The combination works well.

Give it a try.

I often have no choice, as valid STW data has been hit and miss for me since my CS4500 speed log went down a couple of years ago.


Of course, Ground Wind is useful -- it's the actual weather. You must have this if you want to know how the True Wind will change when the tide changes. I have Ground Wind permanently displayed at the nav table, together with a 60 minute plot of changes of direction and speed, on a Maretron display.



But Ground Wind is useless for finding a layline or planning a tack, or avoiding a gybe. Your pilot uses True Wind when sailing downwind, and needs True Wind -- real True Wind, not pseudo-True Wind derived from SOG -- to steer properly downwind. Near DDW Apparent Wind is highly unstable and flips right around before you can react -- only accurate True Wind tells you how close you really are to DDW and only accurate True Wind will allow your pilot to steer a competent downwind wind-following course. It's the very devil to sail with a racing spinnaker near DDW without accurate True Wind.

[valhalla360]

Originally Posted by sailorboy1

Well i haven't removed mine. But i pulled the sensor out around 8 years ago and the plug has been in ever since. I changed the meter to display SOG from the chartplotter

Yep, if you are racing, getting all the details may buy you that extra 0.01kt that wins the race.

For cruising, it's OK but just not that important. Cross currents are easy to pick out by watching compass heading vs COG. Once you have a good feel for your boat speed, larger head or tail currents can be picked out. Obviously it won't be as accurate but again, if you aren't racing, it won't make a big enough difference to really matter.

Certainly no need to fuss about true wind relative to water vs ground.

[sck5]

Sailing in the tropics means the paddle wheel gets gummed up pretty quickly. And why did we want to know speed through the water, set and drift in the first place? So we could calculate course and SOG!! Now that we can get that directly from the GPS the paddle wheel isnt as important. Nice, but not essential.

[Na Mara]

On my present boat the damn thing is a PITA. It keeps getting gummed up and so constantly under reports boat speed. This is more than just annoying in places with substantial current or tide as without knowing speed through the water you can't workout what the current is doing to your boat. And then there is dead reckoning. I'd love to remove the thing, but the thought of being without the possibility for dead reckoning in the event of loss of satellite uplink, though I carry two GPS aboard, leaves me with a cold sweat.

[Dockhead]

Originally Posted by Na Mara

On my present boat the damn thing is a PITA. It keeps getting gummed up and so constantly under reports boat speed. This is more than just annoying in places with substantial current or tide as without knowing speed through the water you can't workout what the current is doing to your boat. And then there is dead reckoning. I'd love to remove the thing, but the thought of being without the possibility for dead reckoning in the event of loss of satellite uplink, though I carry two GPS aboard, leaves me with a cold sweat.

You might try an ultrasonic or electromagnetic one.

I had pretty good luck with the old CS4500 ultrasonic one. You are supposed to antifoul the sensor face, and I had almost no trouble with fouling and it was mostly quite accurate.

When that died after many years I replaced it with a UST850, which is not as accurate as the CS4500 was. I now have, at last, the long awaited DX900+ which is electromagnetic instead of ultrasonic, and measures leeway directly. I haven't installed it yet to see whether it's any good. I'll report when I have some experience with it.

Note that for really accurate STW you need not only a good and clean transducer, you also need to compensate for heel angle. I've bought a B&G H5000 Hercules computer to try to manage that. We'll see whether it works.

Several cruisers have opined in this thread that you don't really care about any of this if you are cruising as opposed to racing. Well, it depends on how keen a sailor you are. I do do some racing, where it's really important to understand the True Wind, without which you don't have laylines and can't do tactics, not to mention sailing downwind. But even cruising, decent True Wind data really helps you sail better. It's not a "mere 00.01 knots" -- it can be all the difference in nailing your tack or blowing it, the difference between being able to sail safely downwind or not, etc. etc.

[Na Mara]

Its an idea and if there is no improvement this year I might just decide to do that as, as I mentioned above, I view the speed log as an essential bit of safety gear. So long as I have that and a compass I am confident I can get across any given body of water. With just the compass it gets dicey as I'm not a sufficiently skilled celestial navigator to be able to accurately figure longitude and attitude from a chronometer and sextant.

[goboatingnow]

Originally Posted by Na Mara

On my present boat the damn thing is a PITA. It keeps getting gummed up and so constantly under reports boat speed. This is more than just annoying in places with substantial current or tide as without knowing speed through the water you can't workout what the current is doing to your boat. And then there is dead reckoning. I'd love to remove the thing, but the thought of being without the possibility for dead reckoning in the event of loss of satellite uplink, though I carry two GPS aboard, leaves me with a cold sweat.

Which is despite 4 GPS , and a paddle wheel I carry my trusty Walker speed log.

Equally you can estimate speed by timing a piece of paper in the water passing the length of your hull. !!

[Pizzazz]

The utility of the sensors depends on cost and accuracy. This is why GPS position, course and speed is so useful - it is cheap, available and accurate. I would say that for the casual sailor a GPS is all that is needed.

I find true wind very valuable for sailing downwind but it takes some effort to clean the sensor. It is also useful for tracking other boats on radar while racing and estimating their speed relative to water (sea-stabilized radar). I find ground course, wind and radar stabilization very useful because we leave port and come back to port. It does not matter what happens on the water. Currents are overstated. People who sail in high current areas know them by heart, so you do not need the log to tell you the current.

So, it is really up to you how geeky you want to get.

[donradcliffe]

I have this argument with myself every time I race out the Golden Gate I use the true wind speed and true wind angle and true wind direction (not ground wind) for sail selection, polar performance, and wind shifts. I use the SOG and COG to detect changes in current. I want both, and have them displayed side by side. I still watch the relative speed and direction of the other boats scattered across the inlet, the wind and waves on the water, and the predicted changes in the tidal currents. I still learn something new every time I do it, and its a lot of fun.

[noelex 77]

Originally Posted by Dockhead

Your pilot uses True Wind when sailing downwind, and needs True Wind -- real True Wind, not pseudo-True Wind derived from SOG -- to steer properly downwind. Near DDW Apparent Wind is highly unstable and flips right around before you can react -- only accurate True Wind tells you how close you really are to DDW and only accurate True Wind will allow your pilot to steer a competent downwind wind-following course. It's the very devil to sail with a racing spinnaker near DDW without accurate True Wind.

When using wind mode on the autopilot, apparent wind is better when sailing upwind and true wind or ground wind is better when sailing downwind. Modern autopilots can be programmed to automatically make this switch based on the wind angle.

I am surprised that you find ground wind poor in this application. In my view it works better than true wind on most cruising boats.

If there is negligible current the ground wind and true wind readings are the same. In this case for cruising boats ground wind is always going to be better for directing the autopilot to hold the correct course. This is because of the inherent accuracy and correct calibration of gps derived speed that is used to calculate ground wind. While the true wind reading should be identical, in practice the poorer calibration together with the multiple factors that effect the paddle wheel mean the STW data and therefore the true wind data is not as accurate and this will be reflected in the autopilot performance. The exception is boats with old gps units (these had a slow refresh rate and poor speed accuracy) or boats with gps units that have a poor view of the sky (this has a significant effect on speed accuracy even if position accuracy is still deemed acceptable).

If there is significant current there are pros and cons for using either true wind or ground wind (assuming you have a paddle wheel that is working at least reasonably, so have access to true wind data). The advantage of ground wind remains in the inherent accuracy and consistency of the data. The drawback is that current will create an offset in the wind direction. This is something you need to be aware of, but creates few problems. In practice rather than sailing directly downwind and always selecting 180°, the wind angle will be chosen to keep the sails setting correctly and this angle will be dependent on the sails chosen, swell etc etc. So while the wind angle chosen will be different for true wind and ground wind when sailing in current this angle will simply be chosen to keep the boat performing well and the difference is of little consequence. The advantage of true wind over ground wind occurs in situations of varying currents. Here the ideal sailing angle will change as the current changes when using ground wind but will stay steady if using true wind. This is an advantage for true wind although in practice as the current changes so will other factors such as the wind speed, COG, sea state etc and this usually necessitates an adjustment in wind angle even when using true wind.

[Dockhead]

Originally Posted by noelex 77

When using wind mode on the autopilot, apparent wind is better when sailing upwind and true wind or ground wind is better when sailing downwind. Modern autopilots can be programmed to automatically make this switch based on the wind angle.

I am surprised that you find ground wind poor in this application. In my view it works better than true wind on most cruising boats.

If there is negligible current the ground wind and true wind readings are the same. In this case for cruising boats ground wind is always going to be better for directing the autopilot to hold the correct course. This is because of the inherent accuracy and correct calibration of gps derived speed that is used to calculate ground wind. While the true wind reading should be identical, in practice the poorer calibration together with the multiple factors that effect the paddle wheel mean the STW data and therefore the true wind data is not as accurate and this will be reflected in the autopilot performance. The exception is boats with old gps units (these had a slow refresh rate and poor speed accuracy) or boats with gps units that have a poor view of the sky (this has a significant effect on speed accuracy even if position accuracy is still deemed acceptable).

If there is significant current there are pros and cons for using either true wind or ground wind (assuming you have a paddle wheel that is working at least reasonably, so have access to true wind data). The advantage of ground wind remains in the inherent accuracy and consistency of the data. The drawback is that current will create an offset in the wind direction. This is something you need to be aware of, but creates few problems. In practice rather than sailing directly downwind and always selecting 180°, the wind angle will be chosen to keep the sails setting correctly and this angle will be dependent on the sails chosen, swell etc etc. So while the wind angle chosen will be different for true wind and ground wind when sailing in current this angle will simply be chosen to keep the boat performing well and the difference is of little consequence. The advantage of true wind over ground wind occurs in situations of varying currents. Here the ideal sailing angle will change as the current changes when using ground wind but will stay steady if using true wind. This is an advantage for true wind although in practice as the current changes so will other factors such as the wind speed, COG, sea state etc and this usually necessitates an adjustment in wind angle even when using true wind.

Well, if you use COG for "True Wind" -- and if it's expressed as an angle to the bow, I think it's better to think of it as pseudo-True Wind rather than Ground Wind -- it will be actually dangerous in my opinion to sail very deep with the pilot. It only takes a little bit of current to throw off the true wind direction quite a bit when sailing deep -- the effect is magnified at deep angles.



We don't sail DDW all that much since broad reaching and gybing is usually faster, but there are times when it's nearly unavoidable. Our A2 is about 250m2 and with the cutter rig, we can't gybe the pole without completely disconnecting it, so we typically gybe by bringing the kite all the way down and then resetting it on the other tack. This is a long process and costly when racing. So sometimes we run DDW for some intervals just to avoid a gybe -- trying to thread a needle in the islands, for example.


We could not really do this without feeding True Wind to the pilot; steering by hand is not on because the Windex will flip right over too fast to react to.



Sailing more conservatively, 15 or 20 degrees off DDW, and not using wind mode for the pilot if there is much current, I guess you can do without it. But you will still not get usable laylines without good True Wind data, so tacking, where precision is required, is also problematic without this data.


As you say, the pilot won't care once the wind is forward of the beam, because it switches to apparent wind. But sailing deep, watch out.

[wingssail]

For many years we've used TWS and TWD as calculated by the instruments using the paddle wheel for boat speed input. Today we sailed 15 miles using SOG for the calculations. The paddle wheel was clean but it was reading way low; I guess that the hull is dirty near the paddle wheel, so I switched to SOG.

I was thinking of this forum.

I've read many of you say that SOG is good enough, that you have stopped using the paddle wheel years ago, but I can tell you that I really missed my accurate boat speed and True Wind Speed and Direction. I know my boat and I can accurately judge it's speed and the wind speed. Today nothing seemed right.

Maybe I care too much about how we're doing and what the numbers are, but it takes a lot of the fun out of it for me when I can't trust what the instruments are saying.

We're at anchor now and tomorrow I'm diving on the boat and I'm going to give the hull around the paddle wheel a really good cleaning.

[PineyWoodsPete]

Originally Posted by goboatingnow

Glad your not instructing on navigation then

...for my obstinate ignorance about this fine point of sailing in currents. I would never think of instructing navigation, much less racing nav. on SF Bay!

Our first "serious" sailboat was a new '77 Endeavour 32 CB, which had only a paddlewheel speed/log sensor and a masthead wind-fly, which we took from NW FL to Bahamas and as far N as Newport, RI and back over a year in '79-'80 with our then 11 and 14 year old daughters. Most of this was per the Ditch. We did use an RDF crossing from W. Palm to the Bahamas' West End, but our triangulation was pretty much right on assuming a 4kn N current and our 6kn motoring speed and main only in the light breeze.

We've done a fair bit of cruising with just GPS and wind sensor, with computed Ground (called True on inst.) wind-speed and Point in our'93 FP Antigua 37 cat, sans analog water speed input: From two summers in the PNW, as far N as 50 deg. (Alert Bay) big currents, with little wind in the summers, but one memorable long spinny run down Johnstone Strait. Then to SF Bay for a summer riding the weak Humboldt current down, and boomer of a gale from Cape Mendocino almost to SF Bay, running under Solent jib only, 10-16 knots, and AWS rarely under 25.

Then S of the border to the Canal over a year, wending our way up to Isla Mujeres, and then hopping in and out up the Stream, with Newfoundland's 50 deg. N an objective. We fell short by about 150nm due to deteriorating weather, turning around in the upper Bras d'Or lakes of Cape Breton Is. And back to NW FL, ultimately delivering "Tango" to Annapolis in 2000 where the FP dealer had a full-price offer sight unseen.

Somehow we never seemed to get lost or miss waypoints...but there was one unintentional jibe (vanged down) with a sudden wind-shift in rough waters running AP at 135deg. windpoint in the E Santa Barbara Channel S of Ventura - not an area with significant currents AFAIK - but could have been part of the problem.

[donradcliffe]

I never use either apparent or true wind speed mode on the AP when off the wind. The damping on the wind direction makes the autopilot response too slow to avoid major roundups and roundowns. I remember from my control theory courses that lag is the enemy of stability.

[goboatingnow]

Originally Posted by donradcliffe

I never use either apparent or true wind speed mode on the AP when off the wind. The damping on the wind direction makes the autopilot response too slow to avoid major roundups and roundowns. I remember from my control theory courses that lag is the enemy of stability.

Me neither , I tend to just use heading or hand steer if deep downwind or avoid the point of sail