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      Abbreviated rules   07/28/2017

      Underdawg did an excellent job of explaining the rules.  Here's the simplified version: Don't insinuate Pedo.  Warning and or timeout for a first offense.  PermaFlick for any subsequent offenses Don't out members.  See above for penalties.  Caveat:  if you have ever used your own real name or personal information here on the forums since, like, ever - it doesn't count and you are fair game. If you see spam posts, report it to the mods.  We do not hang out in every thread 24/7 If you see any of the above, report it to the mods by hitting the Report button in the offending post.   We do not take action for foul language, off-subject content, or abusive behavior unless it escalates to persistent stalking.  There may be times that we might warn someone or flick someone for something particularly egregious.  There is no standard, we will know it when we see it.  If you continually report things that do not fall into rules #1 or 2 above, you may very well get a timeout yourself for annoying the Mods with repeated whining.  Use your best judgement. Warnings, timeouts, suspensions and flicks are arbitrary and capricious.  Deal with it.  Welcome to anarchy.   If you are a newbie, there are unwritten rules to adhere to.  They will be explained to you soon enough.  


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About Joakim

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  1. ORC inclining test method

    When I got the first inclinometers ready it was thoroughly compared to water scales, which is the other option in ORCi measurement. There was no difference in the results. A water scale should have a dampening screw, which limits the water flow from the "tank" to the tube. This stabilizes the reading and takes on average of some unknown period. Skill is needed to make the adjustment correctly and for reading the scale at the correct time. All this is very easy in totally calm conditions, but more demanding with waves or wind. E.g. the Finnish Navy made their own tests to compare with a pendulum and found the inclinometer to be more linear. For the pendulum a tank of water, oil or some other liquid is used to dampen its motion. It is often not possible to get a stable reading and one needs to take the average in the middle of min and max or do some other type of averaging. It is not uncommon to see rather much of rolling during the inclinining test. Often the range (max-min) is more than one degree and can even be over two degrees while averaging one angle. Still good repeatability can be achieved for inclining part, but measuring the freeboards becomes more demanding. Below are some real examples of normal, excellent and bad measuring conditions. Unfortunately it is not always possible to choose good conditions for the inclining test due to location and schedule. When the hull 3D form is know and freeboards have been measured the ORC software knows how the boat floats during the measurements and can calculate the shifting of center of buoyancy with heel angle. Thus it can calculate the location of the metacenter referenced to the 3D hull form. When inclinning test is done the software knows the moment needed to heel the boat to a known rather small angle. From this it can calculate the distance from M to VCG. With all this information the boat can be heeled in the software to any angle and full stability curve can be calculated. As said earlier the deck is assumed to be flat and accuracy of the stability curve starts to worsen when superstructure or cockpit touches water.
  2. ORC inclining test method

    I just noticed this thread. I have designed, manufactured and calibrated most of the digital inclinometers used for ORC measurement around the world. Here is a simple datasheet. The same inclinometer with a different software is also used by ship yards, design offices, notified bodies (e.g. DNV/GL) and measurers for measuring from small boats (CE marking etc.) to big ships. As you can see the accuracy is 0.5% + 0.005 degrees and the resolution is 0.001 degrees. These are about on par with a 3 m pendulum. The actual accuracy is even better, about 0.1% + 0.005 degrees in most cases. 0.5% takes into account a wide temperature range and also wide range of gravity (the inclinometer is based on measuring gravity). I have made these since 2007. I have tested several old ones and never found one out of specs. It is quite easy to test the accuracy with the help of a long bar or a laser pointer. The inclining test is meant to be done in the linear range, thus at relatively small angles. ORCi measurement uses only one angle (3-4 degrees to both sides for small boats and less for bigger ones), but the standard 8 weight shift system uses several ones leading to a line, which should pass through (or close to) all 9 data points. This makes it easy to see possible errors in the measurement. The boom inclining system for ORC uses four angles (boom on STB with and without weights + boom on PORT). One important benefit of an electronic inclinometer is the ability to average for a long period of time. In ORCi measurement each angle is measured 4 times and each measurement is an average of 600 measurements taken during one minute. For ships longer periods are used due to longer roll period. An experienced measurer can average a reading of pendulum or a water scale, but most of my clients have found that the digital inclinometer pruduces better linearity and repeatability. The measurement should be done with boat moored only from the bow and thus free to align with the wind, since not much wind is needed to heel a boat a few hundreds of a degree. When the boat turns freely the times having wind from STB will average out the times from PORT. As it has already been said the purpose of the inclining test is to find VCG, which then can be used to calculate the whole stability curve when 3D hull form is know. ORCi measures hull only to freeboard and assumes the deck to be flat. This typically lowers LPS/AVS. Depending on the superstructure this can be more than 10 degrees. Also ISO/STIX LPS/AVS can be clearly wrong or valid only for a specific model (keel, mast interior, hull construction). ORCi depends on the 3D hull form and can't thus use weight from the scale to replace weight from the freeboards. If freeboards give a wrong displacement, the offset file or the measurement is false. If both are well made, the displacement is within 50 kg from scale for a 40' boat. While a 40' boat has a sink of about 20 kg/mm, the freeboards are measured from 4 positions. To get an 200 kg error one would need to measure all four of the 10 mm wrongly to the same direction. If the conditions are even decent, 10 mm is a big error. E.g. for an X-41 a 10 mm error in all the four freeboard measurements in the same direction would cause a 225 kg difference in displacement and a 0.33% difference in rating. In a measurement protest an over 0.1% rating change would lead to rescoring all the races, but no penalty. An over 0.25% error would lead to a penalty. There have not been problems with these limits despite quite a few during the recent Worlds and Europeans. Most boat are within 0.1% and some 0.1-0.25%. Over 0.25% is a clear sign of a mesurement error (or cheating). Thus repeatability is good enough for this purpose. For comparison IRC has a limit of 0.005 in TCC thus about 0.5% and twice the upper limit of ORC.
  3. If the keel is the same as in 11/2012 Offset file it is 3.5 m deep T-keel with quite narrow fin and long bulb. In 1993 this boat had a much longer chord keel and only 2.5 m deep.
  4. Ultrasonic Wind Options and Questions

    The German Yacht magazine has tested wind sensors in 18/2013 and 7/2013. They measured the wind speed accuracy from 0 to 9 m/s. B&G Triton (608?), Nexus (now Garmin gWind), both Raymarines (their own and the one that came from TackTick) and NKE were all quite accurate from 1 to 9 m/s and showed very good linearity. For these I would argue the position of the transducer in the sail plan and calibration of upwash etc. are much more important than the lack of accuracy of the transducer. Then Garmin (not gWind, their own rotating cup version) and especially Furuno had clearly worse accuracy with quite much unlinearity. Also too ultrasonic ones were tested, VDO and Maretron. Both showed quite bad unlinearity, about equal to Furuno. About 1 m/s error from 3 to 6 m/s while being accurate at 1 and 8 m/s. They did not measure the AWA accuracy. Nexus was the only one with a propeller type. I had Nexus (standard one, not the Race one with longer vertical stand) in my previous boat and it was good. Usually the first to start rotating in light winds and seemed to give very reliable TWA and TWS, since polars worked very well and TWD was also accurate. I stored all the data and often sailed W/L races within 1-2% of the target from polars for the whole race. In heavier winds it started to show too low AWA and TWA, which I think was due to upwash being changed from trim changes. My current boat has ST60 system. I have added my own box that makes some correction to BSP and calculates targets from polars, I think even it is OK. Maybe not as good as Nexus was, but still targets work quite well.
  5. Airmar ST610 speed/temp transducer

    Which wind transducer and what info? If you mean the old Nexus/Silva one, it has 12 V power and 5 V open collector outputs with a pull-up in the server. The two outputs (A and B ) are 50%+30%*sin(a) and 50%+30%*cos(a) PWM. The frequency of both is 3.4 Hz/(m/s) and there is 0.3 m/s offset. This is for the old single fin two blade propeller transducer, which must use 1.50 as calibration coefficient. The two fin three blade one uses 1.70, thus it most likely has 3 Hz/(m/s).
  6. Airmar ST610 speed/temp transducer

    Nexus 42 mm sensor outputs seven pulses per meter, which equals to 3.6 Hz/knot. Power supply is 12 V (10-18 V) and output a 5 V square wave. 4.8 Hz/knot is certainly close enough to be calibrated, if the input and output voltage levels match. E.g. Raymarine ST60 has 11.2 V output, so it shouldn't be used directly with Nexus. I don't know about ST610 sensor.
  7. I'm even more skeptical about that. Most of the AIS MOB device manufacturer give about 5 miles range. It has the same power as AIS B of pleasure boats. I can't see pleasure boats (mostly with mast head antennas) from 5+ miles with my AIS antenna, which is about 1.5 m above waterline. I would guess someone has made a lot of testing, but could not find much with a quick search. I could find this test: http://www.yachtingworld.com/features/tested-ais-mob-devices-help-your-crew-to-save-your-life-69914 They did not test the limit, but found all the units worked from 3.5 miles to a 14 m antenna on open water. In harbour they lost the signal already at 0.5 miles.
  8. I read SeaTalk data from my ST60 system and then show corrected data on a NMEA display. For that b is 0.45 knots and speed is accurate down to 0.5 knots (compared to GPS, currents are very small around here). I have separate depth and speed sensors. I don't there is any offset in the SeaTalk data so 0.45 knots should be comparable with your 1.3 knots, which sounds very big. Have you cleaned the sensor well? Is the paddle wheel turning with low friction? I use exponential smoothing with 5 seconds time constant to get stable 0.01 knots reading. Probably could use smaller time constant, but I'm quite happy with the response rate.
  9. Just took a quick look at this. There seems to be a lot of different environment settings (temperature, humidity, duct profiles etc.). It would be nice to know how these work with different settings. It is well known that in good radio conditions you can reach very long distances, but it is more interesting to know the worst case. I don't think you can always get a connection to a handheld near water from 13 miles. Even 5 miles can be too much.
  10. What makes the system (path loss) asymmetric? 10' to 50' 33.1 miles (nautical miles???), but 50' to 10' 31.6. 3 dB is quite much loss. OSR states maximum 40% loss, which equals to 2.2 dB. At the same time 1 dB is rather small for a rail mount. You still need quite a long cable and you probably don't use as thick or high quality cable for the rail mount. E.g RG58 has about 0.18 dB/meter and you might have close to 10 m. What happens in 10' waves when the rail mount antenna is part of the time behind the wave? Or when there is an island in between? Long antenna with more gain does not work well when the boat is heeled. In my earlier boat I had this 15 cm antenna at the mast top with RG58 cable: http://shakespeare-ce.com/marine/product/ha156c-vhf-antenna-little-information/ Despite being quite equal to antennas used in handhelds it had a much better range, even at 1 W. What does the calculation show for two handhelds?
  11. Decoding tacktick micronet protocol

    Sailing instruments do not require much of a processing power unless you are doing something special not done by most of the systems. The fist microcontroller based marine instruments came in the 80's and at least in the early 90's they were able to process all the data at several Hz. I have made my own processing system that does everything needed at 4 Hz with a 8 bit microcontroller running at 2 MHz (this one could be run at 32 MHz, but there is no need for that). This includes calculating polars and calculating TWS, TWA and TWD etc. As a side job the processor also works as a solar power controller and battery monitor. It also drives a graphical display which I use to show all the data at the same time at the chart table. The same could have been done in the 90's easily. However it would have been more difficult to store all the data as my system does on a SD card. I think the only reason for slow rate of Tacktick is due to save power for solar power operation. Also 1 Hz is fast enough for most of us, if the raw sensor data is already averaged out before sending.
  12. Slug, if you replied to me, as I said I don't have an AIS transponder, just an AIS receiver. I'm never visible to other boats. I can't really see the point of seeing other points from more than 1-2 nm from you. Nor ships further than 5 nm away. They won't fit into my plotter display and I don't want to have collision warnings of vessels earlier than 10 min before.
  13. What do you consider as "closer range". I have only an AIS receiver. The antenna is in the cockipt locker against the wall of the head. I can see all the ships at 5 nm or so which is all I need. Many ships are visible already from 20+ nm, but I don't need that. Boats with AIS trasnponder are shown at least from 1 nm, which is again all I need.
  14. Torqeedo leg comparative drag

    So you are comparing the 2/4 kW Torqeedo model to the newest controlled pitch Oceanvolt model (Servoprop). The lowest power available from Oceanvolt is 6 kW. Servoprop must be much more expensive than the standard Oceanvolt drive. Torqeedo recommends 2/4 kW models up to 4 tonne boats. I think 4 kW is too small for 4 tonne. Are the Figures 1 and 2 of the Torqeedo claim available somewhere? The claimed "average speed loss" of 0.56% or 0.04 means that the speed was about 7 knots. Yes the loss will be low at such a high speed for a 30' boat. I don't know any Dehler 30', but looking at Dehler 29 it reaches 7 knots only between 75 and 135 TWA at 14 knots. At those points the speed difference between standard drive (VP or Yanmar) and no drive is less than 0.2% according to ORC VPP. So even if the Torqeedos claim is true, the drag is about 3 times more than the drag predicted by ORC VPP for normal drives. It is expected that the speed loss will be low when the boat has a high drag due to moving over its hull speed (about 6.9 knots for Dehler 29). Beat VMG at 14 knots wind is predicted to drop 0.6% and at 6 knots 1.4% (VP/Yanmar ORC VPP). These points Torqeedo will be addiotional 1-3% slower, if the Torqeedo claim is true. Torqeedo drive hub doesn't look at all well designed for low drag. The frontal area is huge (due to motor inside the hub), the tip looks too blunt and the diameter reduction towards the propeller hub way too fast causing flow separation. You can find the drag formula used in ORC from the VPP documentation (6.22). Note that the hub diameter (ST4) would be taken to be the end diameter, which is equal to propeller hub diameter. More realistic for Torqeedo would be to use the maximum diameter of the hub. The latter part of the drag area formula is dominent (0.4*(0.8*ST4)^2). For normal drives ST4 is from 85 to 112 mm. What is the maximum diameter of the Torqeedo hub? 200 mm would give 4 times more drag than 100 mm with that formula. Oceanvolt drive looks like to be as low drag as the normal drives.
  15. justice

    I think the wording is very clear in the current rules. If I remember correctly, it was way less clear long time ago (tack finished?). It would be very bad, if it involved sail trimming. What would happen, if a sheet is broken or slips through? You are tacking untill you got the sheet fixed? How tightly trimmed should the sails be? Usually it is very easy to say what is close hauled, at leas with 5-10 degree accuracy.