Glenmar Sailing Association
Sailing the Chesapeake Bay

Static Righting Moment

If at the dock a sailboat is pulled over by its mast, there exists a transverse force which tries to set the boat back to where it naturally wants to be. This force is named the static righting moment. It is related to, if not identical with, the Euler force. Somewhat obvious to anyone who may have tried to pull over a boat from the top of its mast, the size of this force varies according to the angle of heel. Furthermore, every boat design is different from all the others. This is a classic example of my general rule for what makes a boat go fast. The rule is “Everything matters”, but that’s a different topic and not the subject of this post

For a particular sailboat, the force changes as the boat is tipped over. When floating upright in dead calm water, the force is zero. Likewise, when capsized, the force is again zero. In between is the problem.

From figure 1 we see that righting moment (RM) can be calculated as moment arm length times displacement force. Here, displacement force is mass (displacement in \( kg \)) times gravity. Thus the units of a righting moment are \[ kg \cdot\frac{m}{s^2}\cdot m = N \cdot m. \] Since the magnitudes of these values are essentially meaningless to everyone (not just Americans), we often see graphs with the righting arm length graphed on the y-axis versus degrees of heel on the x-axis. These graphs, which are called “GZ curves” essentially describe the yacht’s stability. Gz is the traditional yacht designer’s designation for the value that I labeled d in figure 1.

Fig 1. Righting Moment. CG is the center of gravity, CB is the center of buoyancy, and d is the distance between these two forces. In most sailing calculations, variable d is named GZ and referred to as the “righting arm”. Righting moment is the product of the moment arm length and the boats displacement force.

As an example, we have the GZ graph for a J105 in figure 2. Clearly, the righting arm is very small with a maximum deviation of only a little over an inch. We also see that beginning around 130 the graph goes into negative Gz territory. That point is called the “angle of vanishing stability” with all of the values below zero termed “inverted stability”. The good news for this J-boat is that the region is quite small and it is likely that a wave would push the boat back into an area where it would get righted.

Fig. 2. GZ graph for the J105.

GSA Burgee

The distinguishing flag of GSA is composed of a black air foil surrounded by a thin yellow slip stream and laid onto a field of blue (as in sky).  The exact wording is “The burgee shall be triangular in shape and shall consist of a black airfoil section, such section to be outlined by a band of bright yellow, and the whole to appear on a blue-gray field.”  Presumably, this comes from about 1965.  Although the club was founded in 1947 by a group of employees at the Martin Company, it was not incorporated in Maryland until 1965.  Because the Martin Company was all about airplane flying, it is appropriate that the club burgee would be an airfoil.

Importantly, there was never an official artistic rendering of the burgee. Nor did anyone, nor any document state that the colors were to be given in PMS, CMYK, RGB, or HEX. Currently, I only have four versions available. One is the burgee which is manufactured and given to new members. The other three are artistic renderings. There have undoubtedly been others, but they are not available. Unfortunately, I do not have artist credits. We do not know who drew these? If you know of another image, or know the artist, leave a comment below.

Despite these ramblings, I do have a comment about the airfoil.  It seems to me that it is too symmetrical.  That is, if we built it, it wouldn’t fly.  The thing about an airfoil is that it must be asymmetrical so that air will flow around it going further in one direction than in the other.  Here is a sketch of some historical foils.  This came from https://www.century-of-flight.net/history-of-the-airfoil/.   (Link only so that I do not use their copyrighted material.)  If you follow the link and look at these foils, you will see that none are symmetrical.

Should we consider a slight design change to reduce the symmetry? Our founders might not have approved of an airplane wing that wouldn’t fly, considering that they came from one of the greatest American flight manufacturers of all time.

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Henry’s Basement

A few nights past, I was knocking about in Henry Roesner’s basement and we came across a Courseboard that I hadn’t seen before.  Henry told me where it came from.  I don’t rightly recall where that was, but it reminded me that there is quite a collection of them on this site and I requested that one to add to it.  Now there isn’t anything particularly special about this Courseboard.  It is dated April, 1989.  By then, I had been a member for a few years and many of you had been a member for eons.

Anyway, I went online today and added the document to our online Courseboard library (https://glenmarsailing.org/dropdown_form.php ) but was more than mildly annoyed to see that I couldn’t fetch it back again.  This led to a little poking around in some files and discovering that none of the last 5 Courseboards could be fetched as a historical document (as in using the link above).  All of the old ones worked just fine, but nothing new.  After a short but intense session relearning how to debug php code, I was able to find the problem and apply a band-aid.  Interestingly, however, the fix is truly just a band-aid.  We have WordPress code piled on top of php code piled on top of html code, and spread out all over the place.  I always think “Well one these days I’ll go in there and clean it all up, but just like the second garage, those days just don’t seem to be coming.   If you’ve lived in a place long enough, there are buried treasures that you may dig up and know for sure that you’ve seen them before, but have no clue why you still have that stuff.  In a website, the same thing occurs, but if you throw it out, not only might you need it the very next day, but worse, you may find that you were using it all along and just didn’t know.

That kind of happened with this Courseboard.  I found a couple of files (real important ones as it turns out), that were quite literally in the wrong place and were in use.  I know they need to be moved so that me, or any other half way competent coder would know where to look,  but – they work fine where they are and who knows what would have to change if I relocated them.  Maybe someday I’ll clean it all up.

About that Courseboard, April, 1989.  I took the time to read it and guess what.  It’s no more interesting than the current ones – probably less so.  Here is a direct link if you are also inclined: https://glenmarsailing.org/wp-content/plugins/Courseboard/docs/CourseBoardArchive/1989%20-%20Apr%20Courseboard.pdf

There were a few other things that we came across at Henry’s place, and I will comment about those in a future post.

Big Boats can go fast!

Check out this clip.

Members Flea Market

This is an idea I have had for a while and I would like to hear your feedback. Please leave me comments.

Suppose that we had a section of this website that permitted registered members to post items for sale? There need not be any charge for it, since the work of creating the ad and posting it would be done by the member. Here is how it might work.

A “signed in” member would click on this hypothetical Want Ad tab and then then click on post and then like I am doing now, they would type in their advertisement, and of course, add a picture or two and give the contact method of their choice. This would be a tiny bit like Craigslist, but on a far more local level. Payments would always be between buyer an seller and not ever online. Your have to meet to make the exchange.

The ad could be viewed by anyone on the site, although you should consider that the most likely purchaser of your stuff is someone else in GSA, since they are nearly the only real people who ever come here. As an alternative, we could make the want ads exclusive to registered members. The only reason to do that would be to allow you to restrict who can see your contact information. With some thought, it might even be possible to have it both ways!

I assume that we would want the ads to be for “boat stuff”. How should we regulate that? It really isn’t intended for selling your business products and services.

Would you want the ads to be searchable? Probably easy, but I am not sure.

Would you want the ads to expire and then disappear? Again, probably easy but I am not sure.

Please leave comments. If you don’t see the comment box below, click on the title of this post.

Docking

Regardless of your skill at boat handling, the event may come to pass when you try to pull along side a dock and the wind causes the nose of the boat to blow off. Meanwhile, the stern people have easily passed a dock line from the stern to a dockhand (OK so maybe a crew jumped onto the dock) and the stern end is secured. It seems silly to me that this situation can cause panic on the bow as there is an ultra-simple solution. First, since the stern is secure, the most the wind can do is blow the bow to make the boat perpendicular to the dock. If it can blow the bow further around than that, maybe you dock to starboard!

Solution 1: Take a long line, something barely longer than your boat. Hand one end to the person on the dock and then walk the other end to the person on the bow. Now the bow can be pulled in.

Solution 2: Undo the bow line from its cleat and carry the entire line to the stern. Hand one end to the person on the dock and then walk the other end to the bow, pulling the boat in as you go.

Solution 3: Have a good shouting match and let the conversation end with “Don’t you ever talk to me that way again”. Get a new spouse.

Race Committee

Last Wednesday, Rose Hoffman used her Catalina 34 Beeleaved as the PHRF race committee platform. We really appreciate the effort that members make to help out our programs and providing a committee boat is a big help. Although my computer is named Jesus, neither it nor me have quite mastered walking on water, thus someone always has to position a boat on the starting line.

Kevin Irwin has taken on the responsibility to find members like Rose, who will help us out on Wednesday nights. This effort allows racers to race. If no boat is available, one of them must abstain from racing and use their boat for the committee. This year, we are trying to get a non-PHRF committee boat for just a few Wednesdays in the season.

A long time ago, there was a member named Bruce Baty (his wife Lois is still a member!). Bruce had assembled a regular race committee that would start races off of Log Point across from Bowleys. Back then, the Thursday night fleet, composed of Portsmouth rated boats, were also given Wednesday night starts and everyone raced and partied together.

Around 1986 (I am not 100% on the year), we found a boat, Alert, run by Paul Fitzgerald, and for another decade or so a semi-regular race committee would take that out to set a start line in the same area that we race in today. The smaller, Portsmouth, boats wanted to find their own committees since they were correctly concerned about venturing out into the mouth of the river. Toward the end of the Alert era, we were having trouble getting regular race committee and it became necessary to ask racers to give up one race per year and use their crew to conduct the races.

PHRF Racing participation has reduced. This is hardly news to anyone in the sport, but it has impacted GSAs membership. At this time, the after race beer drinking is down to once a month (the boat owners are older) and racers have to give up their racing slightly more than one time per year in order to have enough committee.

I will post more about later. For now, I am just presenting the problem. The Portmouth fleet has found a temporary solution, but the PHRF fleet could still use some good ideas.

Welcome to the New Glenmar Website

Glenmar has recently updated the website to include a WordPress format with all of the good and bad features that lie therein.

  • It is a membership site. If you are a member of Glenmar, you can join the website to see protected content. I have to approve the members and I do not know everyone, so please be patient.
  • Any member can post content, such as this and any member can comment. There is a member registration in the dropdowns
  • There is a calendar, and any member can post an event.
  • When viewing the calendar, click on the words “Events In” and a popup will let you choose the month. Everything else about the calendar is semi-obvious.
  • When you write a post, there is information on the right of the screen that lets you pick a ‘category’. If your post fits into one of the categories, then check the box. It will help later and may help with searching as well.
  • The ability to contact GSA via this website is locked to members only. On the officers page, there are email links which are currently open to all. That may change.

If you are a regular user of the site, you may find some features that were previously there to be missing. We will get to those but it may take a few weeks. If there is something that you want right away, let me know in the comments. If you can’t comment, it is either because you haven’t yet registered or you aren’t a member.

Portsmouth Brunch

The Portsmouth sailors had a very successful organizing brunch at the home of Terry Westhead and Mark Roesner last Sunday. There was a lot of food but somehow we ate most of it. A few changes were discussed about starting location and boat storage at the sailing center, but I will leave those details to the Portsmouth Captain.

PHRF Scoring

I am inserting an excel sheet that will score a GSA race, or for that matter, any PHRF time on distance race, although it is limited to just a few boats per division. I could easily expand it to larger fleets.

GSA has and really needs an official scorer. A widget like this is just a tool not a scorer. You can’t invent a hoe and expect a garden to just appear. Currently our scorer is Gary Moler. The reason a scorer is so important is the principle of garbage in garbage out. It is seemingly obvious that to get the right outcome one has to input accurately the following data:

  • Start time
  • Boat name
  • PHRF rating
  • Course distance
Soooo simple, but chances are you may mess it up. That is one of the reasons, and there are others, that we occasionally have to post corrections. I will link to the widget. If I get feedback and think it is worthwhile, we can put it into a more permanent link. You have to have excel on your computer to use this, although anybody can look. Also, there is not any way to save the data on this site, but it can be saved on your own computer. There are some internal macros in the sheet and most versions of Excel will disable those by default. In fact, there is a sort button for each division and I don’t even see the button in the wordpress rendition of excel. On the upper right, you should see a DOWNLOAD button. After downloading, the macro buttons show up, but still you will have to enable macros. A pop up will help with that. You do not have to enable them or even use the macros ! They sort the boats after the scoring is done. Just putting in the data causes the boats to be scored.

How the scoring is done; A bit of math.

The time-on-distance formula is:
TA = ( D x PHRF ) / 60
TA = Time Allowance in minutes
D = course length in nautical miles
PHRF = rating in seconds per mile (the number we all use),
Subtracting the time allowance (TA) from the actual time it took the boat to sail the race (elapsed time or ET) equals the corrected time (CT).
However, there is a reason that just any third grader can’t score us. That would be because time is in base 24 and base 60 and our calculators use only base 10 (or sometimes 2, 8 and 16). In other words, adding together hours minutes and seconds will produce nonsense unless we carefully think it through.

One final point I would like to make is that we all measure race starts and finishes to the nearest second, not tenths of seconds. However, when that wee bit of math from above is applied, the corrected time will often come out in tenths of seconds. It is all because 60 does not go evenly into some numbers.

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