Solar arch

We have been trying to work out a design for a solar arch for a very very long time. Designs have come and gone multiple times. When I wrote our Solar Plan back in September, I said “I haven’t quite given up on putting panels off the back of the boat” but at that point we hadn’t make the decision to go for an electric motor and we hadn’t connected the dots with self steering.

So we continued to think about what we can build. This video from Sailing Britaly has continued to be particularly helpful.

But a solar arch on Vida is very complicated 🙂

We have three things that together make it very complicated.

  1. As a typical cruising boat design from the 1970’s our Rival 38 has a relatively narrow stern. That obviously restricts the space available for solar panels compared to a modern design where the beam at the stern could easily be doubled on another 38 foot design.
  2. Then we make it worse by having a ketch rig. Not just a ketch rig but one with a mizzen boom that stretches past the pushpit rail to end level with the very end of the stern. So we need to position the panels to avoid the boom, it’s sheets etc.
  3. Finally the extra thing that makes it difficult is something we don’t yet have. A Hydrovane Self Steering system (I mentioned that this might be needed in Zero fossil fuel sailing). We need vane steering to reduce electric consumption to a manageable level (electric autopilots use a ton of power, I’m guessing a 42 year old even more than a new one). With a centre cockpit and the wheel in a wheelhouse any vane steering that connects to the steering wheel via rope is a non starter. We don’t have space under the aft cabin bunk for a Cape Horn system that connects through the stern directly to the top of the rudder stock. The Hydrovane has the additional advantage of giving us a spare rudder.

So the plan is to shorten the boom a little (120mm). That should work without re-cutting the existing sails. When we replace them we will have a fully battened mizzen with a fat head and a shorter foot so the boom can be shortened a little more (as well as the sail being more efficient).

We have sent the details off to Hydrovane for a quote. We think the unit can be mounted high enough for the van to be above the boom and not hit the sail. The only time it might touch is in very strong winds (when the vane leans over more), but by then the mizzen would be reefed or lowered out of the way.

So now we have been planning the final piece of the puzzle. The solar arch.

We are going to have 3x Victron 175 watt panels high above the stern. That means a rectangle approx 2m wide and 1.5m long. Unfortunately even above the complications that I have already listed we have added 3 more.

  1. As solar generation is so important to us we need to be able to tilt the panels towards the sun to increase their efficiency.
  2. We need to be able to move them forward and aft. In a marina as well as in a storm we do not want solar panels sticking out 1.5m beyond the stern of the boat. So we need a “parked” position where they do not extend beyond the stern but instead extend over the mizzen boom (obviously in this parked position we can’t use the mizzen, a restriction we are happy to accept).
  3. Our budget is limited, we can’t afford to pay a professional to custom build something beautiful in stainless steel. Due to the height and restrictions that reduce the opportunities for cross bracing we don’t think that bolt together fittings (such as used by Sailing Britaly) are going to work. We can only find the range of joint connectors we need, for 25mm tubes which we don’t think is going to be strong enough.

We will document our design as we build it (and I really want to get the mizzen mast up and the hydrvane fitted first to check clearances as we go). However, this is the basic idea.

Two carbon fibre “masts”. The bottoms will be halfway down the stern, one each side. They will be vertical fore and aft (positioned so that the shortened mizzen boom just misses them) and they will slope outwards as they go up. So approx 1m apart at the bottom and just over 2m apart at the top.

There will be a pair of cross braces as an X to hold them vertical side to side. Also each of them will have a pole from just under the boom going forward to the size deck to keep them upright fore/aft.

The 3 panels will be in a tray that fits between the mast tops. We have figured a way for the tray to move to the forward or aft position and also for the whole tray to tilt to face the stern or to face the bow.

Fortunately, we think it is going to be a lot harder to explain than it is to build 🙂

While the carbon fibre poles are quite expensive (over £700) everything else is going to be pretty cheap, so hoping to keep the total cost under £1,100. That for something that should be very strong, pretty light and give us really good functionality.

3 thoughts on “Solar arch

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