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Analysis of a Tack
Using GPS Tracking Data to Analyze Race Results |
Regular readers of L-36.com know that I am writing an Android application for racing sailboats. I have had the pleasure this winter of collaborating with a Dutch sailor who is practicing this winter in hopes of winning his class in a major regatta this summer. With their 9th place finish two years ago and their 4th place last summer, we believe it is within reach.
This article is an analysis of a single tack. It uses GPS tracking data to calculate the current and from that to calculate the expected tacking angle. The upwind leg is the leg of interest. We are analyzing the third from the last tack before the mark rounding. We want to know why the boat was not able to make the mark without the last two tacks. The ultimate goal is to come up with better on the water tools for calculating laylines when there is current. |
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Small Things - Big Wins
Do you ever wonder what the big difference is between the boats that consistently finish in the front of the fleet and the boats that don't? Sure, sometimes it is just one or two big things; maybe a brand new set of sails while your struggle along with sails 5 or 6 years old, or maybe you think they have some uncanny way of always being on the correct side of the next shift. But after years of racing in all kinds of fleets I can tell you without a doubt that 95% of the time it is nothing so simple but yet something that can be easily attained. The magic factor is really a combination of a whole lot of small things that add up to a big difference and a big winning percentage.
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The First Bend
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This bend has been tested. Sometimes it slips, sometimes it breaks. Either way it is stronger than a triple fisherman's. Amsteel is very slippery. It is difficult to test a knot that slips and even harder when it slips sometimes. If you pull and let it sit after it starts to slip, it recovers and ends up being strong, something above 40% of line strength by some tests. There are other knots that almost never slip, see the Last Bend but it is ugly and not near as simple or easy to tie as this knot. The standard for tying Amsteel or Dyneema together is the triple fisherman's knot. This knot slips less that a triple fisherman's so it is a step forward slipping or not. When it doesn't slip, it is stronger than the Last Bend. I present it here for your consideration. Both the First Knot and the Last Bend can slip at about 35% of line strength. When they don't slip, they are about 40% of line strength with the First Knot just a little above this and the Last Bend below this. There is another variation that slips at about 40% that I will show here as well. You can untie the First Knot, but not the variation. This knot can also be untied even after being loaded up near breaking. Just put a spike through the center to loosen it up and remove the tails from the knot center. The rest is easy. I am calling this knot the First Bend because by the time I was done testing dozens of variations on knots and never wanted to hear the word bend again, I called the final knot the Last Bend. It did well but upon considering this knot, the first one I considered, I came to appreciate it more. In fact, I am declaring it the winner of my search for the best bend for Dyneema. That said, the variation is stronger. |
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Knives on a Boat
Are you still using an old worn out knife? When I found it time for a new knife, I was amazed how much knives have changed. I recently purchased about half a dozen new knives as I explored the field adding to the way too many knives I already had. I scored the Internet for recommendations. I read reviews on Amazon. I tried knives at the local WestMarine (none were acceptable). In the end there were 5 knives I liked and would recommend. There are also whole classes of knives I would stay away from. This article will take you through the thought process and hopefully help you find the perfect knife for your application.Read More
Automatic GPX File Marker and Route Generator
The set of tools that will generate a GPX file for your GPS has been recently fixed and I thought it time to make people aware of this valuable tool again. With two map clicks you can get a list of all the marks in that area, select the ones you are interested in, edit their names, and download a GPX file to your computer. These are USCG generated locations from the many volumes for all US territories. The search through all the volumes is done automatically. In just a couple of minutes, you can do what might take an hour to do previously. Please enjoy these tools.
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Boating Electrical ABCs
Many sailors I know find their boat's electrical system daunting. The very same people who will tinker with practically every mechanical device on their vessel, will for some reason, shy away from the electrical side of things. Perhaps this view is shaped by those salty-dog authors who dismiss electrical systems as new fangled, and prefer stinky kerosene instead. Or perhaps, sailors have forgotten their high-school science, although it is hardly more complicated than Ohm's Law. Regardless, you have nothing to fear, as electrical systems are very straightforward and equally reliable when properly maintained. Read More
Basics of Sailboat Racing
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This articles has been floating around the web and reprinted by some yacht clubs. It is an "introduction" to sailboat racing. It claims to be simple but is a bit more detailed than a typical introduction to racing. As far as I know, Captain Kangaroo is a fictional TV character from my youth but that is the author sited in the article. The pictures included in the article on the web are included but are enough to frighten anyone out of every trying racing. If you are new to racing, please do not assume these pictures are anything but the most extreme pictures the fictional Captain impersonator could come up with. If you are an experienced racer, they add humor to the article. See if you can pick out the bowman in the last picture. You can't see much of him, but he is in there. I hope you enjoy the article. Allen |
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Velocity Headers
I don't think there is a subject so misunderstood than velocity headers. They can take an entire fleet and get them to all stop dead in the water where a boat that recognizes what it going on can sail right through them. I know because I have done it. We went from last to first to finish in a fleet where we were neither the biggest, fastest, or lightest boat and yet there they all were stopped as we went right by, sails luffing away.Read More
Unassisted Mast Climbing -- a review of 6 methods
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There are many articles reviewing different ways of climbing a mast. There are also articles where people tell how they do it, their pet way. After frustration that none of the ways I have tried over the years or read about doing as complete a literature search as I could, would meet my goals, I went out and tried to come up with a new way, something that would meet my goals. This article reviews six ways of climbing a mast without help form anyone else. It talks about the pros and cons of each system and scores them on a set of criteria. The high score system is one I developed using some mountain climbing gear. I tried almost every mountain climbing mechanical and non mechanical assist that I could buy before settling on the system I like. |
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How to Fly a Spinnaker - Updated 6/9/2014
This 8 page tutorial covers all the terms, positions, and tasks of flying a symmetric spinnaker using the end for end gybe technique.
I have had Papoose for 23 years and never used a spinnaker on her. Last two seasons we won the local beer can series using a free flying jib downwind sometimes along with our normal jib. But we always had to play catch up to the boats that used spinnakers. I decided to learn to fly a spinnaker so we could move to the next level.
I joined the crew of a very successful Tarten-10 for the winter series. I used a GoPro camera to document as much as I could. This training series of articles is the result.
Lazy Lightning (the T-10) uses end for end gybes which are said to be appropriate for boats up to 35 feet. It is much simpler to rig and execute than a dip pole gybe so is the preferred method for boats such as mine which fly smaller spinnakers.
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Tide Page
This new tide page will show tide chart, table, and hourly tide or current. Search for a tide station by entering part of the name. Select from the list of possible stations. There is a list box that shows nearby stations if you want to switch locations. A map shows where the station is registered.
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Using Bluetooth GPS Receivers with Android - UPDATED 7-13-2013
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To get the most accuracy from GPS based applications it is not enough to use the built in GPS in your phone or tablet because they do not have differential (WAAS) mode. Some applications can take advantage of higher update rates available in external GPS devices as well. In this article, I will explain why you might want an external GPS receiver, what the various Android drivers do, and why I picked "Bluetooth GPS Provider" as my preferred app. Finally, I will explain all of the Preferences in Bluetooth GPS Provider, something you will not find anywhere else. Note that as of Android 4.1 it is a little tricky to get these devices to work. Read on and find out what you need to do. |
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More Low Friction Rings
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In the first article of this series we gave results on using fairleads and showed how the added friction is not significant with low deflection angles. In this article we consider using low friction and other standard rings with high deflections and analyze how these can be used in systems to provide simple and inexpensive mechanical advantage. Again we used the digital scale shown on the right to make the measurements. This scale reads up to 220 pounds with 1/2 pound resolution. |
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Fairlead Friction Uncovered
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Have you ever wondered hom much, if anything, you are giving up by using fairleads instead of blocks? How much friction is there. How does this compare with a block? Does the style of the fairlead matter? This article attempts to answer these questions.
Using a digital scale, I was able to compare the no fairlead force required to just move my weight against the turning block that I had on the test bench to the force required to move the weight when there was a bend through one of two types of fairleads. I took data at many angles with both fairleads. I also took some data with different line types, specifically Samson XLS and Amsteel. |
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