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Paul,
Over the last 40 years, I've sailed with pendulums, trim tabs, auxiliary rudders; and vertical axis, inclined axis and horizontal axis vanes. My first choice would always be an inclined axis vane driving a pendulum, where the boat and her layout permit. An auxiliary rudder (eg Hydrovane) would be preferred where the rudder and wheel mechanism are stiff, or the wheel acts like a flywheel. A trimtab and vertical axis vane would be well down the list. It's no accident that the best-liked gears (Aries, Monitor, Cape Horn) are of the first type, but that there are also good opinions of the auxiliary rudder type. The natural selection process has been at work, and the trim tab is on the way to joining the Dodo.
Some thoughts about trim tab gears:
- They never steer as well as pendulum gears. This is principally because they rotate in the opposite sense to the rudder, and thus they reduce the effectiveness of the rudder. I found this when Tystie had a trim tab - the tiller would be up at a huge angle, going to windward, a much greater angle than when steering by hand, resulting in as much braking as steering.
- They need an exceptionally freely turning rudder to work well.
- Given that the correct negative feedback is put in, by having the linkage to the tab tiller at the correct distance aft of the rudder axis for the characteristics of the boat being steered, steering can be reasonably stable in good conditions, but in a seaway, a pendulum is better because it senses that a yaw is starting and immediately tries to correct the course.
- They steer adequately on long-keeled boats like La Chica, but never as well as a pendulum.
- The trim tab unit is likely to weigh as much as a well-designed pendulum like the Cape Horn.
- It's a continuing job to keep the barnacles and other wildlife out of an underwater bearing, and the slot between trim tab and rudder.
- They are less vulnerable to floating weed and lines.
Some thoughts about vanes:
- The vane unit with all its mountings is likely to weigh the same, whether it's driving a trim tab or a pendulum.
- A vertical axis vane always has to be much bigger than a horizontal axis vane, and this will become a serious problem on a short-ended, two-masted JR boat, with the need to have the after sail sheeted far aft. At times, the sheet and vane are going to intertwine, and I wouldn't want to have to unwrap the sheet from a big high vertical axis vane in a sloppy seaway.
- A vertical axis vane can easily its have course setting line lead forward to the hatch, using the worm and wheel method of the Hasler and some later gears.
- Vertical axis vanes and trim tab gears only go together because it's the easiest system to visualise, understand, design and make. A horizontal, or inclined, axis vane will always give a better result, with both trim tab and pendulum, but involves more work in designing and making the linkages.
Given that you have a Cape Horn gear all ready to install (I'm guessing that it's the Varuna model, meant for boats with external rudders), given its good track record, and given that you want to be afloat and sailing at the end of the year, I wouldn't be giving the matter any more thought than how to install it well, with convenient course setting, convenient connection to the tiller and some protection from the mainsheet, if possible.
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