Anonymous wrote:
Please post pictures as you build.
Some questions:
- Will this mizzen ever be used to produce power or is it only used as a windvane? (aside from at anchor)
- Where do the control lines go? You mention sheets. So does that mean the control lines affect the sheets of your main or was the sheet to tiller idea just the starting point?
- My imagined answer is that the mizzen is effectively a large windvane so that other torque increasing methods like trim tab or servo-paddle are not needed. In which case, is the sail/windvane going to be more rigid/flat than a driving sail to be more sensitive to angle changes?
- Any bungee cords to adjust trim involved?
Sorry, Len, I have almost completed the build, and I haven't taken many photos, but it is so simple, a few photos when it's completed will show everything quite well. I should be able to do that tomorrow.
To your questions:
This mizzen will be purpose built as a weather-vane self steering system, with the added benefit of being able to weather-cock the boat at anchor or while "hove to". I deliberately made the sail cut flat and taut to enhance the weather vane effect. I don't need the sail to drive the boat under most conditions, with the only exception maybe when on a downwind run, it might add a little driving power, but it would even then probably be best used in it's self-steering mode to avoid accidental gybes.
A bit of background. I built the boat with a balanced lug as per the plans, and have now retro-fitted a junk sail. I did employ a mizzen with the original sail, mainly as a balancing-driving sail, and to offer weather-cocking when anchored or "hove to". But the junk sail is at least 40% larger in overall sail area than the lug, mainly due to increased height. So I don't need the extra driving power of the mizzen. I like to take multi-day cruises where I may need to hold a course for several hours at a time. I don't anticipate doing any truly blue-water cruising where I am on the sea for days at a time, but several hours is still a long time. I have successfully used bungee-type self steering in the past, but I have never been able to achieve true course-holding self-steering for more than a few minutes to maybe an hour in very steady wind So this system seems to offer a very cheap and easy to build method of approaching what other wind-vane methods do. (Of course this is yet to be proven!)
Back to the design. On David Omick's design the control lines go from the aft end of the mizzen boom, through blocks either side of the cross piece, then cross over to opposite sides of the cockpit, through blocks, and then to the tiller. So the lines (mizzen sheets) are alternately activated as the mizzen engages due to directional changes viz-a-viz the apparent wind. The sail only acts to engage the tiller to turn the boat opposite to the alteration cause by the increasing and decreasing wind pressure on the sails.
My version has the control lines starting from the cross-piece, driven directly from the swiveling outer mast. This eliminates a bit of friction by eliminating one set of blocks on the cross piece. It also allows the cross piece to be aligned parallel to the transom virtually regardless of the wind direction using a simple ratchet clamp and a "clutch disk" fixed to the swiveling outer mast.
Fixing the mizzen to any given angle as a fixed weather-vane can be easily achieved by cleating the mizzen sheets in fixed positions rather than having them freely running.
I don't anticipate needing any shock cords or bungees etc. in this design, although it would still be possible to use these as part of the system if desired.