Sailing Straight: Two Boats With a Lee Helm

Not too long ago I wrote excitedly about two new, free Tako-based boats: the BBK 137 and Nemo Nantucket. The boats differ in both their concept and construction, and I thought it was pretty fantastic that Kanker’s original ideas might live on in the creativity and enthusiasm of a new generation of boatbuilders.

While testing out those boats, I noticed that Nemo had a “Lee Helm.” It’s a small point, but this issue comes up in real life too and it may partly explain some of Nemo’s behavior, so I thought I’d mention it here.

First, to introduce the topic, let’s talk about helm ‘balance!

A Balanced Helm

JG-44 30R holds a course

When they try out a new boat in real life, many sailors will check how “balanced” the boast’s helm feels on different points of sail. After all, as Ben Franklin said, “A helm unbalanced is not worth sailing.” (or maybe that was Socrates… 🙂 )

Anywayz, a well-designed and well-rigged boat should feel at home on all major points of sail; if you set a heading of 40°, the boat should ‘dig-in’ and hold that course without much complaining.

Quite often however, boats end up unbalanced and consistently drift off course. The most common example of this is called a weather helm, where a boat sailing upwind continually wants to head higher into the wind; it tries to “sail to weather”.  A  skipper needs to constantly apply leeward pressure to the wheel or tiller to hold a ‘weather helm’ boat on a constant compass course. This is only a small irritation on leisurely weekend cruises, of course, but it can become a real pain in races when strong foul weather gusts dramatically amplify the forces on the boat. I’ve sailed races where I had to give up the helm because I didn’t weigh enough to control the boat; the weather forces transmitted to the helm kept lifting me in the air while I tried to hold the boat on course.

Luckily, most boats in SL are nicely balanced. You can set a compass heading, raise sail and let go of the wheel; the boat will faithfully hold it’s course. That’s good news, since most skippers end up busy enough sheeting to the apparent wind changes, switching the sails, reefing, and much, much more.

Click to enlarge

To illustrate this, I’ve added some images above from an Oceanis 160 on a beam reach; the Oceanis 160 is a good example of a BWIND boat with nice balance.  It’s also an easy boat to test, since it has multiple, detailed displays.

Using wind from the North at 15 kn, the first image in the figure above shows the boat heading directly East at a bare 1.63 kn.

JG-44 on beam reach; Wind dial shows AWA adjustment

That results in a real wind angle (RWA)= 90° and an apparent wind angle (AWA)= 84°, as shown. If you then trim the sails without touching the helm or changing course, the boat picks up speed and the  apparent wind direction appropriately shifts toward the bow (AWA= 55° in the middle frame above). After many minutes of sailing without changing the original heading, you can then drop sail and confidently find yourself on the exact compass course you originally set. Oceanis 160 uses BWIND brains for helm balance,  and the boat holds its own, sailing straight as an arrow… quite nicely, in fact.

Good balance is, of course, not a trait exclusive to BWIND or Oceanis.

I’m gradually going through the whole list of popular sailing vessels in  SL, and every boat so far in the Trudeau Fleet  and Juli Designs’ lineup shows a “straight-down-the-line balance.” If you set a course and take your hands off the wheel in these boats, they remain compass-true.

By the way, you can also add the Wildwind Fleet to the ‘balanced boat bunch’ too; I ran my JMO-60 through it’s paces, and got no more than a 2° fluctuation in heading while sailing a fixed course for three minutes. 

Two For the Lee Road

Ok, so my point above is that the large majority of sailboats in Second Life have what might be called ‘a balanced helm.‘ You can set a compass course and take your hands off the wheel;  your boat will sail true.

 This may seem like a small point, and you might even think it’s a pretty obvious one.  However, I’m bringing it up  here because there are two popular boats, the Tako 3.3 and the Nemo-N/R, that appear off-balance and seem to have a ‘Lee helm;’ If you set a course heading, these boats won’t sail a straight line; they sail an arc that gradually turns the boat away from the source of the wind. A skipper needs to invest extra time and tiller touch-ups to stay on tack.

Let me show you what I mean :

In the figure below I set my Tako on a beam reach (RWA=  89°) with a compass heading of  270°.  After sailing for nearly 4 minutes without touching the tiller or changing the heading, the boat had spontaneously turned 11° away from the wind.

Click to enlarge

Is an 11° deviance in four minutes a lot?  That’s for you to judge and it certainly depends on the context, but let me make these comments in that regard:

  • Columbus, Magellan and Cook would still be sailing slow circles in European harbors if they were even 1/1,000 so inaccurate 🙂 ;
  • Any Tako racer knows that even a 2° difference on close haul, say from 34°-36°, can have an enormous impact on boat performance;
  • None of the other boats mentioned above showed any helm preference, so it’s not an ‘artifact’ of the sims or system; and
  • Although a beam reach is a “special” point-of-sail for the Tako (the spinnaker inflates on that heading), the downwind drift appears to happen at all points of sail; its intrinsic to the boat and its power algorithm, not to any specific heading.

Behavioral Genetics

The recently-released Nemo-N/R has a similar Lee Helm propensity.

The figure below shows a series of six sequential Nemo images, while sailing a fixed course with the default 15 kn wind.

If you look at the circular guage, you can see the blue indicator shows the boat starting on a beam reach, with an approximate wind heading of 90°.

 As the boat picks up speed, look carefully at the next four frames. Even with a boat speed of 7.0 kn ( half the true wind), the blue indicator for wind angle stays locked at just about 90°.

 That looks like the Real Wind heading, not “Apparent Wind.”  Two weeks ago I concluded that Nemo’s sailing engine must be using a ‘Real Wind’ algorithm. Nomad Zamani (the boat’s  scripter) corrected me, however, revealing that the boat did use apparent wind, albeit an attenuated version of it (Apparent Wind Lite?).  I was sort of ‘flummoxed’ with that info, since I couldn’t show any upwind velocity-based angular wind swing toward the bow in Nemo (the definition of ‘Apparent Wind’).

It turns out Nemo’s Lee Helm may explain why ( at least in part).  

Click to enlarge

Take a look at the orange arrows in each of the frames above.  They indicated a fixed reference, the clock over the raceline in Farragut. When the boat’s at rest in the first image of the sequence, the bow is pointing slightly starboard of the clock. In each of the following frames, however, the boat’s heading falls further leeward and further to the port side of that heading relative to the clock.

That may explain the Apparent Wind confusion in the prior Nemo discussions; I didn’t appreciate Nemo couldn’t hold a heading. One reason Apparent Wind doesnt show the typical shift toward the bow in Nemo seems to be that Nemo wants to turn away from the wind; it’s heading spontaneously rotates downwind. The size of that angular fall-off is roughly equal to the maximum adjusted wind angle change (AWA) in the boat.

If you’re confused by this, so am I :-), I’m still looking at it, and I’m posting here to get more input and ideas. Hey, but don’t worry :-), the ‘Trouble with Nemo’ seems similar to what happens in the Tako, and that can’t be too bad. We all know that little unruly Tako showed it had the right stuff.

It proved to be the inspiration that lit the fuse for everything else in SL Sailing over the past four years.

So, that lee helm thing? It’s not a defect, it’s not a flaw…

It’s just personality!

7 responses to “Sailing Straight: Two Boats With a Lee Helm

  1. Chaos Mandelbrot

    “The distance run was twenty-seven hundred miles as the crow flies. … During those twenty-three days I had not spent altogether more than three hours at the helm, including the time occupied in beating into Keeling harbour. I just lashed the helm and let her go; whether the wind was abeam or dead aft, it was all the same: she always stayed on her course.” — Joshua Slocum “Sailing Alone Around the World”

    I think this is a good example of a balanced helm.

  2. There are 2 ways of making a boat heel over. The old Tako way was to apply force to it. But everyone that has struggled with rotating some construction they have build by setting the rotation by hand knows that the rotations over the 3 axis X,Y and Z influence eachother.

    As a boat builder you can try to figure out why and how heel over X + applying forward force to a boat will slowly result in an altered course and try to compensate it. (It is caused by applying forward force + the force caused by buoyancy both pointing a little bit off) Or you can choose the easy way.

    The easy way is not allowing the boat to rotate over the X axis (leeward heel) but change the reference frame instead. If you do that, all the computations by the SL physics engine remain unchanged, while the visible model of the boat heels over. If you apply force to it to make it go forward, the boat will only go forward and not try to change its course.

    For the scripters: llSetVehicleRotationParam(VEHICLE_REFERENCE_FRAME, new rotation)

  3. Thats actually one of the big “Immersion breakers for me” because the vehicle engine control acts like a switch (you’ve either got full rudder on or no rudder) you cant really have the rudder “over a little bit” – no idea why, but for both planes and boats thats the effect that tends to remind me I’m playing a computer game and kills my fun.

  4. Point well taken, Alain. I agree this is a big deal when sailing a boat with a ‘weather’ or ‘lee’ helm.
    In retrospect, there were many complaints over Tako 3.3 tiller control just prior to Kanker’s departure from SL. In the Tako, it’s my understanding the turn effect is modulated… at least in 2 steps: Holding down an arrow key causes a sharper turn than just ‘tapping’ the key. I never tested that, and I could be wrong.
    Your point is well taken, and might hopefully be addressed by boatwrights in SL.

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