Monday, May 17, 2010

Addendum to: An Expression of Doubt — How can Hydrovane Self-Steering really be any good?

I’ve written this post as an addendum to my earlier piece,  An Expression of Doubt – How can Hydrovane Self-Steering be any good? in part because someone questioned whether it was fair for me to criticize a product with which I have no experience. And in principle I wholeheartedly agree. Yet in my defense,  I made it clear I had no personal experience a Hydrovane. I confessed that I could not understand how it could work very well. The questions I raised were based not on pure speculation but on the promotional material of the product itself – they are the kinds of questions that I would like to have resolved before I would purchase such a unit.

But I do so much prefer talking about stuff I really know about, so I’m taking a different approach this time.  I’m revisiting the Hydrovane promotional material again, but this time I'm looking at the way it represents its primary rival, namely servo-pendulum self-steering gear. Hydrovane makes some rather grandiose claims about its superiority vis-à-vis servo-pendulum gear, but they are based on gross misrepresentations which bring up basic issues of credibility.

A major claim that they make repeatedly is that servo-pendulum gear doesn’t work well in light air. They say, for example, "we have too often heard owners of servo pendulums that are very proud of their units but advise that they only work, when off the wind, in a minimum of 15 or 20 knots of wind!!" But this can hardly be true, or at the very least it is the product of extremely selective hearing. If the servo-pendulum is set up correctly, it should not require any more wind to steer the boat than a Hydrovane. In fact, the windvane on a servo-pendulum actually does less work than the windvane on a Hydrovane. On the Hydrovane, the windvane has to turn a rudder – a rudder that’s smaller than the boat’s own rudder, but which is nonetheless much larger than the steering oar of a servo-pendulum gear. After all, this rudder is steering the boat. On a servo-pendulum gear, the function of a windvane isn’t to steer the boat but to turn a small, balanced oar, which in turn harnesses the power of the water rushing past the boat. In effect, the windvane on a servo-pendulum only needs enough wind to send a signal to the steering oar; the windvane on the Hydrovane needs to get all of its power to steer the boat from the wind. Indeed, this is why the windvane on a Hydrovane is significantly bigger than on a servo-pendulum gear.

A boat with a servo-pendulum needs to be moving through the water for the gear to work. I would estimate that once our boat reaches, say, 2 ½  knots, the gear can steer the vessel without any problems. I can imagine that a Hydrovane might be able to steer a boat that is moving slower than this, though this would also mean that there was very little wind. But a more likely scenario would feature a boat sailing dead down wind in light conditions. The faster the boat moves, the less apparent wind is experienced by the boat and by the windvane. In such conditions, a servo-pendulum will have plenty of power to steer the boat – the tricky part is having enough wind to send a signal to the steering oar (sometimes we’ll increase the area of our vane by clipping on a piece of cardboard). But I imagine that the Hydrovane would have an even more difficult time, for it needs the wind not only to send a signal but also to power the rudder.

Another point the manufacturers of Hydrovane repeatedly stress when comparing their windvane with servo-pendulums is that their unit has “very little friction” and thus performs better in light air. They add, too, that if there is any “excess friction in the system - stiff rudder, arduous connecting lines” then the servo-pendulum unit suffers all the more. This is most certainly true – but it is also misleading and largely irrelevant. To meaningfully discuss of the role of “friction” in a servo-pendulum system, one must distinguish between that part of the system powered by the wind and that part powered by the water. If anything, the part of the servo-pendulum system powered by the wind should generate less friction than the hydrovane – it performs less work. The part of the system that is powered by water – from the lines through the blocks, to the tiller/ wheel, from the wheel, to the cables, to the rudder – obviously generates a lot more friction than the Hydrovane. But it shouldn’t matter. Given the amount of power generated by the oar in the water, that friction should be easily overcome.  If  “excess friction in the system - stiff rudder, arduous connecting lines” – is really limiting the effectiveness of the gear, then something is seriously wrong.

A third misleading point made by Hydrovane is that “all servo pendulum systems, when matched against a Hydrovane, are comparatively unsophisticated. Once engaged they do a meandering sort of course correction without any means of tuning or straightening its course.” Frankly, this assertion is so divorced from reality that I hardly know what to make of it. The manufacturer at this point in its promotion is really trying to emphasize Hydrovane’s own “sensitivity adjustment” of its vane axis and its three different “rudder settings.” To set up a striking contrast, the manufacturer wants you to imagine that its servo-pendulum rival has “no means of tuning.”  How ridiculous. Our Sailomat (which like all decent servo-pendulum gear begins with a sophisticated geometry) can be “tuned” (from the top down) as follows: changeable windvane sizes, moveable counterweight, adjustable windvane lever arm, adjustable push rod, adjustable lever arm at the steering oar, selection of line attachment points at the pendulum, a wide range of block configurations for the lines, adjustable lines for balancing the helm. Some of these things are adjusted when one sets up the gear; others can be used to adjust the gear for different sailing conditions. I will concede the point that “all servo pendulum system lack this [namely Hydrovane’s specific vane axis] adjustability for sensitivity,” but we are talking about different kinds of systems here. Kinda like criticizing an orange for not having apple seeds.

A fourth misleading point made by Hydrovane pertains to the way the boat’s rudder is utilized by the Hydrovane and by a servo-pendulum unit. The Hydrovane needs to set the main rudder in a certain position that balances the boat so that its own auxiliary rudder is effective. The manufacturers then criticize the servo- pendulum system because it cannot balance the rudder in the same way, but they misrepresent the way the system actually works:

A servo system cannot match the configuration of locking your main rudder to render your boat perfectly balanced.  …  A servo pendulum system must perform a lot of steering that a Hydrovane does not have to do. … On every turn it must deal with the forces of any weather helm or lee helm – not so for an auxiliary rudder system which has no weather or lee helm to deal with as the positioning of the locked main rudder compensates for such ‘pulling’ by the positioning of the main rudder – neutralizes any weather or lee helm!   … a servo pendulum can struggle with the forces of weather or lee helm on every turn. …  Comparatively, a servo pendulum configuration requires a lot of extra steering.

Hydrovane wants you to believe that a servo-system oversteers because it cannot balance the rudder. But in fact, trimming the lines that connect the servo-pendulum to the wheel/ tiller – that is to say, balancing the rudder – is a critical part of properly setting a servo-pendulum gear for the sailing conditions. The rudder is trimmed to balance the boat, neutralizing weather or lee helm, and the lines to the gear are trimmed so that the gear is a neutral position. The servo-pendulum then steers the boat by moving the rudder in relation to this “balanced” position. What Hydrovane has done here is to describe the wrong way to use a servo-pendulum unit and then criticized its operation. They might as well be telling you that shoes don’t protect your feet because you wear them on your hands.

And this misrepresentation leads nicely to the next one, in which servo-pendulum gear is portrayed like some kind of savage brute. The passage is worth quoting at length:

If you have ever had the chance to see a servo pendulum operating in bad weather you would better appreciate where that comment about its power comes from. Its activity can be described as perhaps violent as it wrenches the wheel/tiller from one course to the next. One certainly wants to stay clear of that section of the cockpit. We do suggest that there is some overkill in that performance. … The comparison [between a Hydrovane and a servo pendulum] is like the difference between the less skilled hard working rookie and a skilled athlete that makes a play look so easy …

Now, I actually have seen our servo-pendulum operating in bad weather.  And I never noticed that it “wrenches the wheel/tiller from one course to the next.” Properly trimmed, it ticks gently back and forth, keeping the boat on course. But when boat get smacked or falls of a wave, and veers in the wrong direction, the servo-pendulum shows its strength, vigorously spinning the wheel to bring the boat back on course, making good use of the boat’s own rudder – an athlete to be sure. At this point, I imagine the Hydrovane would be calling out for help from the autopilot (although I confess I wouldn’t know, because I’ve never used one).

I'll close with final quote from Hydrovane's website that attempts to portray a stark contrast between the pathetic inadequacy of servo-pendulum steering gear and the magnificent superiority of the Hydrovane:

A servo pendulum cannot be adjusted for conditions. It cannot help but to over-steer or under-steer. The activity of the main rudder flapping back and forth exacerbates the steering difficulties of a heavy sea. If the same boat had its main rudder fixed it would be far more stable.  These issues are complex and hard to understand. I am guilty of a bit of hyperbole in making my point but the concept of the stability of auxiliary rudder systems is well worth appreciating. It alone makes the auxiliary rudder concept superior to any other method of self steering. Adding to that the sophistication and the unmatched versatility of the Hydrovane..........[sic]

Guilty of a bit of hyperbole?   You betcha!!  I can almost hear maniacal laughter.