Design ideas for davits/solar arch

[SY Kelpie]

Originally Posted by Cherod

Aalco in aberdeen will do you 41 X 2mm 316 @ ( +/- ) 5£ per foot. but as you suggest prob 38 mm will do. weight wise the 50' that i used ( of 41 X 1.5 mm ) ( or 2 mm i cant remember off hand )) on a 20' beam catamaran weighs less that my wife does . i used ss for ease of adding on lugs etc. at later stage is easy otherwise i would have used aluminium. if you know some " excellent welders " then there is no reason why they cannot weld the All,, other than that a more industrial type "AC" machine is needed , welding / fabbing Al is just as easy as SS, maybe even easier as it cuts easier and contraction is much less than with SS. re deck fitting, make as wide as poss and use throo deck bolts with big back plates,, all easy stuff.. i could prob lift my whole boat with mine !! ( but remember , without lots and lotsa work or industrial polishing facilities then show room finish is not possible . ) a finish polishing disc to fit on a grinder are 5£ a pop,, you will need about 5. and then some pickling paste which ( i think ) comes in £ 50 jars, about 2-3 pints.., you will need about a tea cup , bst if you know people from fish farms they can get small amounts. so you are prob looking around 200£ materials for 10' beam monohull , ( twin bar hoop ) + very best of " mates rates ".
(ps,, Aly would have to be 2" x 3mm )

That's all good info, thank you! Funnily enough £200 was my ballpark figure for the job, probably adding a couple of bottles of good whisky.
As to fish farms... as it happens, I'm a fish farmer myself, hence how I know some good welders...

[KP44]

The flat top of our arch will easily handle 400 watts of panels and they are far enough aft of the rig that they will seldom have shadows. The arch is almost 7 feet above deck. That lets us lift the dingy well above the reach of following seas.

Some have lost a dingy to thieves from lower davits. It is best to have the dingy up high. (And chain it to the boat.)

I have a monitor windvane but it is not installed while the davits are in use.

[Cadence]

Originally Posted by SY Kelpie

We're looking at buying a new boat and equipping it for bluewater cruising. On most boats we have considered so far, we would need to add davits and/or a solar arch. It seems to make sense to combined these functions into a single structure.
Just to complicate things, we will also be adding a windvane (probably a Hydrovane) so need to consider airflow around the stern of the boat. I am fully expecting that we only use the davits for overnight storage of the dinghy, and for use on shorter passages where we are happy to hand steer or use the autopilot. The Hydrovane would be used for longer passages where the dinghy would be on deck, not in the davits.

I would like the arch to support a minimum of 400w of solar, and a dinghy+ob weighing up to about 80kg.

What sort of tubing size (thickness and od) should I be considering? And how best to fabricate the attachment to the boat? Boat is likely to be a centre cockpit GRP design in the region of 38-40ft.

If anybody has pictures or description of a similar design that would be fantastic.

I think your question may be answered better with a particular boat design.

[SY Kelpie]

Originally Posted by Cadence

I think your question may be answered better with a particular boat design.

We're not going to narrow down to one boat design, but so far the likely contenders have been:
Moody 37, 376
Westerly Sealord, Oceanlord
Moody 41CC

All very similar boats really in the context of this question.

[KJThomas]

Originally Posted by SY Kelpie

We're looking at buying a new boat and equipping it for bluewater cruising. On most boats we have considered so far, we would need to add davits and/or a solar arch. It seems to make sense to combined these functions into a single structure.
Just to complicate things, we will also be adding a windvane (probably a Hydrovane) so need to consider airflow around the stern of the boat. I am fully expecting that we only use the davits for overnight storage of the dinghy, and for use on shorter passages where we are happy to hand steer or use the autopilot. The Hydrovane would be used for longer passages where the dinghy would be on deck, not in the davits.

I would like the arch to support a minimum of 400w of solar, and a dinghy+ob weighing up to about 80kg.

What sort of tubing size (thickness and od) should I be considering? And how best to fabricate the attachment to the boat? Boat is likely to be a centre cockpit GRP design in the region of 38-40ft.

If anybody has pictures or description of a similar design that would be fantastic.

Have you considered foam and glass?

[sailcrazy]

We had one custom made in The Philippines; the contractor chose s/s pipe. when we got to Marmaris, Turkey, we contracted with a local fabricator, and he made our current radar arch out of 2" s/s tubing....and it is sooooo much nicer!! Our arch has ajustable davits off the back, has an antenna farm on each side, holds 4-80w solar panels on top, and has a wind gen tube on one side. We also mounted a PA speaker and a transom light between the 2 center panels, and with some added rings mounted a pasarele on the stern (needed in the Medd.) that is suspended and controlled by the arch. We also mounted both a MOB pole and 2 Horseshoe rings on the side......and the whole thing looks good! Definitely use tubing, with enough bracing to keep it sturdy fwd/aft AND sideways. Ours is supported by 2 custom mounting plates on the aft deck, and 2 arms extending to and thru-bolted to the transom. We've had it installed for 7 years now, and it works great-don't know how we got along w/o it!

[sck5]

In case it makes a difference, hydrovanes dont have to be centered on the transom. Look at their website and you can see many examples. Hydrovanes are the greatest - I did a transatlantic with one and loved it. But it is a bit hard to visualize how it would work with a dinghy trying to get hoisted over the same space. Even without the vane at anchor they still stick up quite a bit.

Another option for the dinghy is to make a bridle that allows it to be hoisted on a halyard off the beam of the boat. Very easy to use once it is set up and allows the dink to be hoisted WAY high. Easy to rig some fairleads so you can use the primary winches.

[srt]

A year ago I fitted davits similar to what you are describing to my Beneteau Oceanis 370. I attach details and photo. The tubing is 32x3mm SS. The solar panel is 320watt LG which has worked very well. The Victron controller tells me that it produces up to 360watts. The davits do not lift straight out of the water but overlap the sugar scoop a little to minimise leverage. To lift I installed a $AU100 electric winch I bought on ebay which came complete with 2 wireless remotes as well as hard wired switch. I am very happy with the package and for me works very well.

[David B]

Originally Posted by SY Kelpie

We're looking at buying a new boat and equipping it for bluewater cruising. On most boats we have considered so far, we would need to add davits and/or a solar arch. It seems to make sense to combined these functions into a single structure.

What sort of tubing size (thickness and od) should I be considering? And how best to fabricate the attachment to the boat? Boat is likely to be a centre cockpit GRP design in the region of 38-40ft.

If anybody has pictures or description of a similar design that would be fantastic.

Our concern when considering exactly this was that the arch would be rock-solid, would not look like a 'tack-on'. and would aesthetically blend as well as possible with the design on the boat. To this end I went round looking at and photographing as many arches as I could find - homing in on what worked, what I liked, and what I didn't. The final design was an arch that replicated the curve of our 'targa' arch, integrated into the pushpit, and matched the solar panels I decided on so that it is not immediately obvious there are any solar panels (chose semiflexible to conform with the curvature of the arch). The attached pictures give you an idea of the construction process, and final result, with the aerial one showing the panels.

FEATURES:
rock-solid - I can climb it, jump on it, try to shake the boat with it - it just does not move.

davits of same material (50mm 316, 2mm wall) and I can hang off those and jump around, with no movement.

the arch replaces the forward and quarter stanchions of the pushpit, and is thus integrated, and also supported.

the mounting plates are 100mm diameter, 12mm thick, with three 12mm bolts going through the deck at each plate, backed by thick 316 body washers.

struts on the sides are spaced to replicate the pushpit rails and work well as ladder rungs.

apart from the panels, there are NAVTEX 4G, & WiFi antennas mounted at either side.

all cabling is internal, with WP junction boxes for terminations, mounted in the lazarette.

the solar panel cabling is under the panels before entering the tubes - therefore protected from UV as much as possible. I used the same cable as used on domestic solar installations, so it is designed for high-temperature/high UV exposure. I also painted (automotive black) the plastic termination covers on each panel to protect the plastic from UV - they were black before, they are black now, but I suspect without that paint, they would now (6 years on) be chalky grey

A solid cleat is welded (fabricated from tube and rod) to either side of the arch - handy for towing and crossed stern-lines.

lugs ('U' 316 rod) are welded to the aft horizontal tube - these are used for the passarelle.

similar lugs are welded to the fwd tube, facing the cockpit - these are handy to hold lines when we are rigging, or winterising etc.

lugs (316 bar) have been welded on the fwd verticals to mount the bimini bracing to (which used to go the to pushpit top rail - this makes the bimini very solid.

the solar panels are mounted to 60mm x 3mm bars welded between the fore and aft tubes (so a bar on the stb and port sides, plus two inner bars).
the inner bars support LED strips for illuminating the stern area, and yet to be fitted is an LED flood light for looking further aft. Switching for these is at the fwd end of the cockpit table where the existing cockpit light switch is located.

davit lines when not in use, are clipped to saddles on the stern. Cleats for the lines are welded (316 rod again) up on the fwd down-tubes for ease of cleating off the dinghy. Each line is a double block tackle - double/triple would be a little easier, but then there is even more line to deal with when the dinghy is right up. It's not too much to lift the dinghy with 4T 6HP outboard.

I cannot think of anything else to describe, but in conclusion, we were concerned as to how we would affect the function and aesthetic of the boat, but are very pleased with the outcome, have received favourable comments, and feel both function and aesthetic to be enhanced as a result of the arch.
One of the big things is that it makes a great extra handhold either side of the cockpit.

When the time comes to replace the canvas on our bimini, we will then look at taking it that little further to the arch - maybe, maybe not ….

I hope all of that that is helpful.

David
(FB pages 'Sharing Life')

[KP44]

Our arch is 1.5" stainless tube braced with 1" stainless tubing. The feet simply through-bolt to the deck. The backing plate for each foot has a 1.25" hole in the center so I can run wires down the leg. That is; the backing plates looks like a big washers instead of circles. I have solar, flood lights, outlets, and antennas on the arch. So several wires and I like having antenna leads separate from power lines.


As I said earlier, the top about 7' (or slightly shorter) above deck seems right. I can walk under the arch even with fishing poles stored under it. And the dingy is high enough to deter thieves.

We are a 45' center cockpit cutter.