Thursday, September19, 2019

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Calibrating a Marine Compass

Everyone understands that a marine compass needs to be calibrated. I am not an expert on compass calibration but got interested in the question when a club member asked me if I had an article on the subject on this web site. It is easy enough to find articles on how to calibrate a marine compass but I found them lacking in two areas. First, they did not explain what was really going on such that I could understand why things were being done. Second, they all recommended you don't actually do the calibration yourself but rather hire an expert. Of course, because I only was presented with a how and a recommendation not to do it, I did not have the knowledge to judge if the procedure was going to be error prone if I did it without some of the fancy tools the professionals have. I kept thinking about it and doing a few experiments until I felt I understood what the goal of all these measurements was and how accurate they needed to be. Of course, I would be a fool if I didn't give the same advice, have an expert do the job for you. But after reading this you might at least understand what is going on and be able to judge for yourself if you think you know enough to calibrate your own compass.
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7-Day Tide and Current Forecast

Improved 2/27/2013 - Graph now goes midnight to midnight. Added title to each section.

Tables and graphs for selected tide or current station for the week ahead.
Table shows high and low times for tide, slack and peak for current. Also shows sun and moon events. Graph is as shown below. The final table shows the hourly values.

Sorry tide depth graphs only, please select another station.
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Low Friction Rings Mechanical Advantage

Using Low Friction Rings instead of Blocks
I recently saw a picture of a three stage cascaded block system using low friction ring instead of blocks. This article analyzes such a cascade and shows how to calculate its effective mechanical advantage. The techniques shown can easily be extended to other systems. I will discuss one such system that I use on my boat.

Mechanical Advantage
To analyze a system like this you need to know the efficiency of a single stage, extend that to the the efficiency of the entire system, and translate that to mechanical advantage. For reference lets consider the following sketch.

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Make Your Own Telltails

By: Ed Sinofsky

I admit it, this is sailing nerdiness at its extreme. When I was a teenager I was a sailmaker at Spencer sails in Huntington New York. That was almost 40 years ago! I used to make the telltales when I worked there. It was always fun bringing pockets full out to customer's boats and giving them away like bringing cake or wine to a visit.

I'm no longer a sailmaker, but over the years I have fine-tuned the design. As winter sets in, I always like to make a nice big batch just to keep myself occupied. I thought some of you might be interested to see how I do it.
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2013 Racing Rules of Sailing -- When Boats Meet

With a new year comes new rules. Nothing major changed this year, just clarifications and a few changes to keep people from "working the rules". If you sailed to the intent of the old rules, nothing changes. Here is a link to just the definitions and section 2, When Boats Meet. This is the part every racer needs to know and the source of most discussion of the rules.

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GPX and CSV Waypoint Editor and File Converter

  • Input GPX or CSV Files
  • Add any number of additional waypoints
  • Edit any name, location, or symbol
  • View location of waypoints on map
  • Download as either GPX or CSV The file at the left is an example of the map view of a file about to be edited.

    This tool can be used to convert any Garmin gpx file to a StartLine csv file. In addition, you can use this to read your gpx files into Excel or Word processor for analysis, viewing, or editing.
    GPX -> EDIT -> CSV
    GPX -> EDIT -> GPX
    CSV -> EDIT -> CSV
    CSV -> EDIT -> GPX

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    Buying New Sails?

    by Harry Pattison

    New sails represent one of the biggest investments you make in your boat. So when getting ready to make that purchase what things should you consider to make sure you get the product that best fits your needs and to insure you spend your money wisely?

    First make an honest assessment of what kind of sailing you will be doing. Broadly sailing falls into four categories; offshore cruising, local cruising and recreational sailing, cruise/race, and racing. The type of sail material, type of construction, and the price to some extent will be determined by this decision.

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    Stray Current Can Drop your Mast

    You would think that having researched and witting an article on galvanic corsion that I would know better. But when I installed my antenna on the pulpit thus grounding it, I was only thinking about the VSWR and antenna performance. Little did I know I was going to cause a failure that not only could have but probably should have taken my rig down.

    The coorsion was caused by a 20mA current that was sourced by the potential difference between my newly cleaned (after inspection) bronze chainplate and the zinc on my prop shaft. The path was the bolts holding in my chainplates to the chainplate to the shroud to the bronze ring around my lifeline to the lifeline to the stern pulpit to the antenna ground to boat ground and finally to the zinc on the prop shaft. The connection between the shround and the lifeline was the same as it had been for 50 years but I guess this time it make electrical connection or perhaps it was the different type of twine I used to lash it. That could have held water where the old twine didn't. In any event, in just a few months (May to September) this damage occurred. It is truly amazing that during the race we did the day before ...

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    Rock Box Blue - First Look

    It will not come as a surprise to readers of that I was a little disappointed to see that there was no "time to line" function (yet) in the new Rock Box Blue. But if you watched any of the Olympics or the America's Cup you see that the vast majority of starts today have boats lining up at a distance from the line and starting their accelerated run seconds before the gun. For those kind of starts, the Rock Box is a perfect match. Having a 50+ year old 12,000 pound boat, I want more than that and the developer of the Rock Box points out that there is more to come on this really solid platform.

    That said, the new Rock Box is an impressive product. The waterproof case, O-ring sealed looks solid and well made. There is more to this product than just the start function as I will explain below.

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    Buying Used Sails

    by William Posner

    sail Given the cost of purchasing new sails for your boat these days, some are turning to the used sail market. Here at Pacific Sail Trader we wish to give you the lowdown on how best to do it. Purchasing a sail without seeing it in person is the greatest concern of most buyers. Not being able to actually touch it seems to be the missing sense.

    Will it fit correctly? Of course a seller that will provide not only accurate measurements with the sail pulled taught, but showing photos of the good and the bad can help as well. If there are patches or repairs, are they shown? Seeing the corners is key. Often the original owner, especially if a racer will have written the luff , leech and foot measurements as well as the date those measurement were taken. Getting the build date is a plus! Let's say you see that the corner rings are reinforced with leather.Well that's a clue as to the age as it has been many years since that was a standard feature seen on sails.

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    Phone or Tablet On Board?

    Using phones and tablets for marine applications is very attractive. Applications are a fraction of the cost of dedicated marine products that seem to perform the same function. But the marine environment is very difficult and there are problems with both phone and tablet applications. There are many articles on the Internet showing you which 10 apps are the best. This is not one of those articles. This article explores some of the problems people don't talk about and points out what to look for to get the best experience with your phone or tablet. The things that turned out to be important onboard were not the things that seemed important checking out the application at my desk.

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    Starting Line Apps

    I had intended to review both iRegatta and BC Racer. Both are excellent well done apps for smart phones and tablets.

    After testing both, I decided not to review the programs themselves, but to talk about limitations on this class of device. Perhaps you can overcome these limitations but after reading this you will at least you will know what they are.

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    Starting on Time with GPS -- Getting to the line at the gun going fast

    This is the first of a series of articles on using GPS devices to get to the line on time going fast.

    Wouldn't it be great to have an application or device that would get you to the starting line right at the gun going fast. There are several phone/tablet apps that say they will help you do that and a few dedicated boxes that say they will do it better.

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    Weather Page Updates

    It has been about a year since I reported on the Marine Weather page. There have been many improvements to the page in that time that I want to share. The page has been well received and has hundreds of users. I thought it would be useful to point out some of the improvements for those of you who have not tried it recently.
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    The information on this web site has not been checked for accuracy. It is for entertainment purposes only and should be independently verified before using for any other reason. There are five sources. 1) Documents and manuals from a variety of sources. These have not been checked for accuracy and in many cases have not even been read by anyone associated with I have no idea of they are useful or accurate, I leave that to the reader. 2) Articles others have written and submitted. If you have questions on these, please contact the author. 3) Articles that represent my personal opinions. These are intended to promote thought and for entertainment. These are not intended to be fact, they are my opinions. 4) Small programs that generate result presented on a web page. Like any computer program, these may and in some cases do have errors. Almost all of these also make simplifying assumptions so they are not totally accurate even if there are no errors. Please verify all results. 5) Weather information is from numerious of sources and is presented automatically. It is not checked for accuracy either by anyone at or by the source which is typically the US Government. See the NOAA web site for their disclaimer. Finally, tide and current data on this site is from 2007 and 2008 data bases, which may contain even older data. Changes in harbors due to building or dredging change tides and currents and for that reason many of the locations presented are no longer supported by newer data bases. For example, there is very little tidal current data in newer data bases so current data is likely wrong to some extent. This data is NOT FOR NAVIGATION. See the XTide disclaimer for details. In addition, tide and current are influenced by storms, river flow, and other factors beyond the ability of any predictive program.