Solar Panels

Fitting a solar panel mount on a ketch rigged sailboat is challenging. On a sloop or other rig without a mizzen mast the panel mount can be far aft and above the level of the main boom. On a ketch or other rig with a mizzen mast, the mizzen extends aft of the transom. Putting the solar mount above the mizzen boom is not possible. Putting it below the mizzen is also not practical because the mizzen boom is often low and the mainsheet extends far enough aft to leave very little room for panels.

The only practical way to mount large solar panels on a ketch would be either the foredeck or between the main sail traveller and the mizzen mast. There is generally too little room aft of the mizzen mast. The foredeck would allow only one large solar panel athwartship if a large panel would fit at all. This space is usually reserved for storing the dinghy while underway. Only the option of putting solar panels under the main boom remains.

Solar Panel Placement

On a ketch the best place to install large solar panels is below the level of the main boom and off to either side. The panels must be behind the main boom traveller. Interference with the mizzen boom or stays must also be avoided. One this boat the split backstay chainplates are far enough aft that there is no interfere with solar panel placement. The mizzen mast itself plus its stays are the limiting factor aft.

Another constraint is avoiding interference with jib sheets. The forward feet must not extend too far forward of the sail tracks. The panels themselves can extend further forward since their height will keep them out of the way of jib sheets. This will put the feet such that an athwartship bar will extend over the companionway. The bar will be a potential head strike hazard but should be sturdy enough to serve as a handhold when entering or exiting through the companionway.

Overall Design

Two residential grade solar panels will be used, mounted with the long side fore and aft and mounted below tha main boom and on either side of the centerline, pushed outward as far as practical with a gap between them. Four vertical posts and feet are placed on the side decks as far outboard as practical.

The gap between panels serves two purposes. Pushing the panels out insures that at any given time at least one panel will not be in the shaddow of a mast. Another benefit is the space above the cockpit sole is less impeded due to the gap between panels. Athartship tubing near the mizzen mast and above the companionway would minimally impeded the space above the cockpit. When seated in the cockpit the panels will be overhead, providing shade. The frame extending forward will provide a useful handhold when exiting the cockpit to go forward on the side decks.

Another consideration is interference with jib tracks, jib sheets, and other running rigging led aft to winches in the cockpit. The vertical legs have to be far enough aft to avoid jib sheets and have to be pushed close to the toe rails due to the jib tracks. The gap between vertical legs needs to be kept clear to avoid interference with winches mounted on the coamings and winch handles when in use.

A crash bar was considered, forward of the panels and above them. The purpose of the crash bar would be to protect the panels from damage if the topping lift was released with sails down. After careful measurement is was determined that there simply is no room for a crash bar. This problem can be avoided with a stopper knot in the topping lift. It might also be possible to provide a second topping lift that cannot be released but is slack enough to avoid interference with sails but tight enough to prevent damaging the panels.

Shading Limitations on Output

There simply is no way to avoid shading problems on solar panels mounted on a sailboat and particularly a ketch. The best that can be done is maximizing the output and then keeping to realistic expectations on the output.

If panels are connected in series and one cell of one panel is mostly shaded, output will be reduced to near zero. If the two panels are in parallel, then one panel will produce full power and the other near zero. The output of a partially shaded panel with no cell fully shaded can be improved by putting each panel on a separate MPPT solar controller. The MPPT voltage of the partially shaded panel will be less than that of the panel that has less obstructed sun.

Underway with sails up, it is possible for the mainsail to shade both panels. Output can be expected to be low or negligible in this case. Nothing can be done to avoid this other than taking down the mainsail and sailing on jib and jigger (a headsail and mizzen). Underway and heeling away from the sun the panels will be tilted away from the sun with one partially shaded. Very little can be done to improve this other than allowing the panels to be tilted side to side which may be possible but impractical.

The shadow of the stays is likely to reduce the solar panel output, but only slightly. Tests results online confirm that as long as no cell has a high percentage of shading the panel performs well.

Output can be expected to be better at anchor, mooring or dockage with sails down, no heel, and little roll. The primary sources of shadow will be the masts and the main boom. If the sun is in line with the centerline, then neither panel will be shaded, except by stays. If the sun lies to either side of the centerline, then only one panel will be shaded by the masts and/or boom.

Measurements and Approximate Placement

Measurements of the cockpit and cabin top provide the means to plan for a more exact placement. The first constraint is that the panels must be at a safe distance below the boom. This safe distance would be at least 6" to 9" below the boom, which is below any bails that would pass over the panels.

The centerline of the main boom is about 3' above the cabin top, about 5'6" above the cockpit seat tops, and about 7' above the cockpit sole. A grating on the cockpit sole reduces clearance by 2 ½".

At 9½" below the boom a sloppily reefed sail might brush the panel but that is not likely to damage the panel or sail. Lazy bags would eliminate this problem. Higher placement reduces boom shading and also leaves more headroom in the cockpit but reduces margin for error in measurement. The bottom of the boom is about 3" below the centerline and 1½" is allowed for panel depth.

At 9½" below the bottom of the boom the bottom of the panels would be 1'10½" above the coachroof and 5'10" above the cabin sole (allowing 2½" for the grating). Using a double tubing frame with over and under tubes and less than a foot between them could be used to used to reduce the stainless steel tubing diameter needed but would also reduce headroom. The current plan is to put a long slight bend in the lower tube to reduce the loss of headroom and with short vertical supports improve strength relative to two straight tubes.

The beam of the boat is just over 10' at the mizzen mast and increases forward until the traveller where the full 11'6" of beam is carried. Using 10' of width and allowing 42" for each panel (they are less wide) allows a 36" area directly beneath the boom when over center. Since the panels will be forward of the mizzen where the beam is slightly wider, the panel frame could use up to 10'6" without extending noticably beyond the beam and allowing 42" between panels.

Pushing the panels to 6' above the cockpit sole and just forward of the mizzen mast would interfere with the traveller as it is currently rigged unless the panels were mounted quite low. Using a crash bar forward and above the panels would interfere with the main sheet so is not an option. A stopper knot in the topping lift would help avoid having the boom hitting the solar panel glass but a boomkicker would be a more reliable solution.

There are four boom bails on the main mast. The first (closest to the gooseneck) is used for the boom vang but also has a single block on it and is the forward main sheet attachment. The second and third have single blocks and are the remaining two main sheet attachments. The furthest aft is likely a remnant of the original traveller arrangement which is on the aft edge of the bridge deck. The forward of the two for the traveller is almost directly above the traveller and the aft of these two is aft just over 3'. The block on the traveller car is a double with becket. The three mainsheet attachments to the boom are spread too far apart. If there is interference with the panels and main sheet, then the aft boom bail can be moved forward more than a foot (or yet another bail added leaving the old one in place).

This arrangement of bails and blocks implies the line runs becket to aft block, back to the traveller block, to the block above the traveller, back to the traveller block, then forward to the block on the vang bail, then down to the block just aft of the main mast. The block on the vang bail mostly brings the mainsheet up before reaching the block behind the boom. This is a 5:1 when the boom is out (6:1 if you count the line to the base of the boom) but with steep angles it is effectively less than 4:1 when sailing to windward.

As rigged, the solar panels would interfere with the mainsheet where it extends from the traveller to the aft boom bail and back unless the panels were lowered. A distance of 65" is allowed fore and aft for the panels and frame. This is 62.6" for the panel plus on either side a nylon washer, ⅛" angle stock and ⅞" tubing.

Any sailer is reluctant to drill more holes in the boom or worse yet the deck or hull. It may be worth it to move the aft of the two traveller bails forward to about 18" aft of the other traveller bail rather than 3' aft of it. This would improve the downward force on the boom and also allow the solar panels to be raised to about 6' height above the cabin sole without resorting to pitching the panels fore and aft to clear the mainsheet boom to traveller line.

Approximate Placement of Feet

A set of measurements was made to determine where to place the mounting posts and feet of the solar panel frame. The aft mount on the port side is the most problematic due to crossing jib sheet, staysail sheet, and roller furler line. The mounting pole should not interfere with the use of the winches.

The mizzen chainplates are about 6' aft of the front of the mizzen mast. Immediately forward of these chainplates are side deck drains on each side. The aft feet can be placed just forward of this drain where it is wide enough that the feet do not interfere with flow along the side deck to the drain. This puts the center of the aft uprights 8'9" apart and just 1¼" from the front of the mast.

The forward feet are at a beamier part of the hull. They may be pushed inward from the toe rail about equidistant from the jib track and the toe rail and each about 4' from the aft foot on the same side.

Design of Solar Mount

There have so far been three solar mount designs. The first was designed to be as wide at the aft feet spacing. The second design was very similar but designed to be as wide as the forward feet spacing. This design would extend a few inches beyond the hull, a risk near a tall bollard. Both or these designs would be difficult to fabricate due to numerous critical bends. The third design was a simplification with the goal of reducing the number of bends and carefully matched peices and making the design easier to fabricate.