By Kaare   |   2023-07-03

Solar Arch

Solar arches, or targa arches, are something which divides sailors into two groups: those who thinks arches should be banned because they are extremely ugly, and those who can’t live without them. Let me be honest - I am in the latter category, but that does not mean that they are always pleasing to the eye.

If you are cruising long distances solar panels are a must. Yes, it is true that you can also charge your batteries with a generator, but that way you still rely on fuel, and generators are always a bit noisy. Today you do not see any serious cruisers without solar panels. The best way to mount these panels without doubt are on a solar arch. For a more detailed discussion see the section on solar panels.

However, a solar arch can be more than just a way to mount solar panels. On IRIS the arch also serves as:

• davits for our dinghy
• mount for the satellite antenna
• storage nets for fruits and vegetables
• hanger hooks for drying wetsuits and BCD’s
• anchor point for the sunroof (the bimini extension)

You should carefully think about what your arch needs to do before finalizing the design. However, for many reasons do not over clutter the arch, and do limit the items which rises above the arch.

Some feel that the arch is the perfect place for all their antennas, including a huge radar dome. However, all the stuff which rises above the arch will cast a shadow on the solar panels. Since even a small shadow on a solar panel will severely limit the output from that panel, all such shadows should be eliminated.

When designing an arch there are some guidelines which can help you make the arch aesthetically pleasing, they are as follows:

• the forward frame should be angled to the rear at an angle of approximately 20 degrees.
• the rearmost frame should be angled approximately 5 degrees less than the forward frame.
• the width of the two frames at the top should be the same.
• the forward most frame should be a little wider than the rearmost frame, however not excessively so.
• the distance between the frames at the top should be approximately 500mm.
• the distance between the frames at the bottom should be approximately 700mm.
• the extension of the dinghy davit’s should not exceed 500mm 

The Hallberg Rassy boats differ from the more modern boats in that they do not have a very wide stern. The narrow stern makes for a bit more challenging design of the arch. You want to have an arch which is as wide as possible in order to fit enough solar panels, and also to be able to carry a decent size dinghy.

The width at the top is governed by the rearmost frame. We designed our arch so that the rearmost frame sits on top of the toe-rail. In order not to have too extreme an arch we put the feet of the forward most arch on the deck itself.

Each of the feet ends in a Ø100mm plate with 3 countersunk M10 mountingbolts. Because the rearmost feet sit on top of the toe-rail these bolts need to be very long - in our case 160mm. It is very important that you remember a load spreading plate underneath the deck, so that when a support comes into tension the load will be spread evenly to a large area of the deck.

Our arch is designed for solar panels. In order to facilitate the cables from the panels the forward frame has a been opened up at the top on the underside of the tube. That way the cables can enter into the 40mm tube which makes up the frame. The footplate of the frame has also a 30mm hole in the middle so that the cables can exit the frame and be ducted into the interior of the boat. That is a nice way to hide the cables.

We have provided the arch with a number of eyelets so that we can hang items on the arch when at port or at anchor. The eyelets are quite simply a stainless-steel ring cut in half and welded onto the 40mm tube.

Finally, the arch serves as anchor point for our solar roof. As a traditional Hallberg Rassy IRIS is equipped with a center cockpit, and the mainsail sheet is run from a point just aft of the cockpit. This has the consequence that the Bimini cannot extend aft because it then would collide with the mainsail sheet. In order to provide the aft deck with some shade when we are not underway, we can run a solar roof from the Bimini and aft to the arch. This gives us a fantastic nice shadowed area and a nice extension for the cockpit.