Stern Arch


When we bought Alba, there was a wind generator on a stainless steel pole on the aft deck, plus a small solar panel attached to the guard rails.  It soon became apparent that the solar panel was inadequate for our power requirements and the mounting method on the guard rails was flimsy and prone to catching the main sheet on a gybe.  I wanted to increase the solar panel area substantially, so I started to look at installing a stern arch to hold the solar panels and the wind generator.

I put together a list of requirements one of the most important was that it should look good.  Many arches on monohulls are square "goal posts" that have been bolted along side the existing pushpit and quite frankly look dreadful.  I spent a month going around anchorages and marinas in the West Indies, taking photographs and asking lots of questions to come up with my headline requirements:

  • look good
  • two solar panels (total area = 1.5m * 2.0m)
  • wind generator
  • four aerials
  • a crane to lift our 15hp outboard
  • fishing rod holders
  • fish cleaning table
  • davits to lift the dinghy

Conceptual Design

I researched other boats on the internet and came across a nice looking arch on a HR46 called "Grace" where the owner had removed the existing pulpit and incorporated the pulpit into the design.  Good idea - looks more like part of the boat. Other ideas included narrowing the frame towards the top with the side frames sloping in towards the top give it a more elegant appearance.  Sketches littered the chart table and then I used Photoshop to create visualisations to see the outline design. 

Original Side View

Visualised Side View

Original Stern View

Visualised Stern View

Practical Design

I discussed the design with several fabricators in the Windward Islands and decided to use Mitch at West Coast Fabrications, Chaguramus, Trinidad.  We agreed a price of $4,200 including the dinghy davits.  I really liked the guy; he had a good sense of humour and listened to what I was saying.  He came up with some good, practical engineering ideas including making the main frame from 1½” stainless steel tubing and putting in some extra strengthening bars around the inside of the main frame - both to make sure that the whole arch doesn't sway when underway.  I amended my drawings and drew up a list of the main design criteria, so that we both knew what we were working for.

The final design criteria were: 

1. The Arch replaces the existing pushpit.  

2. Main frame made from 1½” stainless steel tubing.  The top of the frame should be flat to take solar panels.

3. Structural side cross members made from 1½” stainless steel tubing.  Two cross members on each side above the pushpit.

4. ¼” mounting plates are to be welded to bottom of tubing to take 10mm bolts through the toe rail:

  • Aft Main Frame will have a plate with two bolts either side of tube 
  • Forward Main Frame will have a plate which will be welded onto the existing chain plate for running back stays. There will be one bolt aft of the upright.

5. Use the rear part of existing pushpit tubing. 

6. Pushpit horizontal cross members to be made from 1” tubing as per existing pushpit.

7. There will be four cross members on the top frame made from 1” stainless steel tubing to take mountings for the solar panels.  (No requirement for additional 1” rail on top to take solar panels.)

8. There will be a strengthening rail inside of the rear main frame.  This is made from 1” stainless steel tubing.

9. Use existing Outboard Engine hoist – mounted on the aft port side main frame.

10. Dinghy Davits made from 1½” stainless steel tubing with suitable bracing in 1½” tubing.  The length of the tubing going aft is about 800mm.  The dinghy is a Caribe 9.5 RIB with a 15hp outboard.  There will be suitable fittings to allow fitting of blocks to hoist the dinghy and to tie off the hoist rope. 

11. Dimensions:

  • Top of arch frame is 1,900mm above the deck.
  • The top of the frame is 1,780mm *  400mm (but need to allow clearance for solar panels 2,000mm wide)
  • The Front edge of the top of the frame is level with the rear of the toe rail in the centre of the boat i.e. is not over the aft deck.
  • The Aft edge of the top frame is level with the rear of the sugar scoop.
  • The Aft Main Frame sweeps in towards centre of boat by 100mm on each side. This starts at the height of the top of the existing pushpit.
  • The Aft Main Frame sweeps aft by about 700 mm and ends in line with the back of the sugar scoop. This starts at the height of the top of the existing pushpit.
  • The Forward Main Frame sweeps in towards centre of boat by 430mm on each side.  This starts at the height of the top life line (620mm).
  • The Forward Main Frame sweeps aft by about 950mm. This starts at a height between the upper and lower life line (470mm).
  • To make the frame look good, it is important that the side frames appear to converge from the bottom to the top

12. Cabling will be run down all four 1½” main frame legs from the various pieces of electrical equipment as per diagram.  The existing pushpit is held in place by 21.5 mm diameter stainless steel rods which are fibre glassed into the toe rail.  It is intended to drill the rod out using a core drill and rely on mounting plates to hold the arch in position.  If this is possible, then the cabling will exit through a 1” diameter hole in the bottom of each main frame leg, otherwise the cabling will exit through ½” holes positioned 4” above the bases.  

13. Solar Panels.  

  • There needs to be sufficient clearance to fit solar panels 2000mm wide.  
  • Cabling is 2-core, 10AWG (12mm * 6mm) and will lead into a junction box on the front port side underneath the front of the top frame then into the 1½” stainless steel tubing (Forward Port side).  
  • A 4” * 4” stainless steel plate is required to mount the junction box.
  • The cable exits through the hole in the toe rail and into junction box panel in the aft cabin.
  • The intended solar panels are 2 * 215W panels which are 1500mm * 990mm - making the total area = 1500 mm * 1980 mm.

14. The Kiss Wind Generator should be mounted on 2” stainless steel tubing on port side of the main frame.  

  • The bottom of the 2” tube is welded to a cross brace in a position to allow clearance for 2000mm solar panels.  
  • There are two 1” tubing struts which go to the front and aft main frames attaching just below the top of the frame and extending out to the main 2” support. (It must not impede the space available for solar panels.)
  • The main 2” support should be positioned so that the struts are equal length.
  • Cabling is 2-core, 10AWG (12mm * 6mm) and goes into 1½” stainless steel tubing (Aft Port side).  Cable exits through hole in the toe rail and into junction box panel in aft cabin.

15. Aerials.  Mounted on 500mm long, 1” tubing on the starboard side of arch.  Aerials will be attached in the following order – Aft first :

  • Wireless network (50mm wide bracket, cable diameter = 4mm)
  • Iridium Satellite Passive antenna (100mm wide bracket, cable diameter = 11mm)
  • Garmin GPS (120mm wide bracket, cable diameter = 5mm)
  • Navtex Antenna (80mm wide bracket, cable diameter = 5mm)
  • Navtex Antenna (80mm wide bracket, cable diameter = 5mm)
  • Antennas’ cabling goes into 1½” stainless steel tubing (a & b into Aft Starboard side;  c, d & e into Forward Starboard side).   Cables exit through a hole in the toe rail and into junction box panel in aft cabin.

16. The stern navigation light will be mounted underneath the centre of the aft top frame – the cable is 6mm diameter and will be run down the Aft Port side 1½” stainless steel tubing.  A stainless steel mounting plate is required which is 40mm wide and 100mm high.

17. Two deck lights:

  • Rear facing mounted on starboard side of rear arch support ( illuminates water behind boat)
  • Front facing mounted centrally on rear arch support (illuminates rear deck.)
  • The mounting method is to be specified after the lights have been purchased.
  • The Deck Light cabling is 6mm diameter and goes into 1½” stainless steel tubing (Rear facing into the Aft Starboard side and the Forward facing into the forward port side.) Cable exits through hole in the toe rail and into junction box in aft cabin.

18. Flag pole mounted on Arch – welded tube to take flag pole.  The position is to be decided.

19. Two fishing rod holders, welded onto arch on either side on the front main frames at a height to be determined.

20. Fittings on the starboard side frame to hold small table to be used for cleaning fish.  The working height for the table should be 850mm.

21. Danbuoy holder on Port Aft frame – clamps onto 1” tubing.

22. Hydrovane Wind vane steering – no change other than to shorten the vane which is made from ¾” aluminium tubing – can they re-bend for me? 


It wasn't an easy job to draw the three dimensional arch.  The first job was to accurately measure and draw the shape of the boat and the position of the existing pulpit (which was to be removed and incorporated into the arch).  An obvious datum was the centre line of the boat and I eventually ran a piece of string between the two forward edges of the pushpit, which gave me my second datum across the boat.  The vertical datum was the point on the deck where the two other datums crossed.    

Initial Sketch





Solar Panel Frame

Fabrication and Fitting

Once Mitch and I had agreed the scope of the project, he came around to measure the boat and verify my dimensions.  We then agreed a three week timetable and he was exactly on time with all deadlines.  Mitch built a simple jib in his workshop which accurately positioned the six feet and then worked from there.  I popped in occasionally, mostly to drop in things like spot lights, which had to have brackets welded to the frame.  Five days after he started the fabrication,  Mitch did an initial fitting to check the basic frame dimensions, then delivered the final arch just over a week later.  I then spent a week, running wiring and fitting the solar panels, wind generator, etc.  It took one month from my initial contact with Mitch to completing the job.

We had one little hiccup because neither Mitch nor I had noticed that the toe rail sloped up at the back. This meant that the whole arch was tilted forward by five degrees.  Not a huge amount but it was noticeable that the Solar panels weren't level. Mitch was great.  He came to look, agreed with me and then spent the day removing the arch, cutting just over 1 inch from the aft feet and re-welding it.  He did a great job and was a pleasure to work with.

Project Diary

This is a series of extracts from the Alba Chronicles, which give a blow by blow account of the process:

22 July. I spent the morning deciding how I am going to mount the solar panels on the arch and how I will wire everything up.  My biggest problem is where to put the regulator for the solar panels. It’s quite a big metal box, with heat sinks and the installation instructions say not to put it in an enclosed space.  It can’t be outside because it’s not waterproof, so it has to go in the back cabin somewhere.  I could bolt it on the outside of our beautiful mahogany cupboards, but it would spoil the “ambiance” of the master cabin (especially because it has a red display which will glow balefully all night.)  I’m thinking of putting it into a cupboard and installing cooling fans like they put into computers.  

29 July.  I removed the aerials, outboard and other equipment from the pushpit.  Taking a deep breath, I took down the wind generator and its support pole, which turned out to be easy enough.  With all this out of the way, I removed the pushpit away from the port side – the back deck looks very bare now.  The pushpit is held in place by six 7/8” stainless steel rods which are bonded into the toe rail.  My plan is to remove four of these, so that the wiring coming down the Arch frame will be able to go straight through the toe rail.  I’ve been worrying about this job for a few weeks.  I'm going to use a hole saw, which has an inside diameter slightly larger 7/8” and hopefully I’ll be able to drill a hole around the rods.  It will either go well or turn into a complete nightmare. 

30 July.  I decided that I need to extend the hole drill to allow me to drill out the stainless steel rods in the toe rail, so I dropped it around to Mitch who is going to cut it in half and weld a 4” extension tube, so that I have 6” clearance.  He’s started manufacturing our Arch, which was good to see. 

Solar Panels dominating the Saloon

Sorting out the Wiring

31 July.  I spent all day working on the wiring for the Arch.  I pulled all the wires out of the pushpit and lazarette ready to wire them into a wiring panel in the aft cabin cupboard - I found a few redundant wires running through to the main switch panel and removed them.

1 August.  I spent the day working on wiring for the Arch.  It never ceases to amaze me how long each job takes on a boat.  I’m installing the solar panel regulator into a cupboard and the installation instructions recommend that it shouldn’t be installed in an enclosed space.  So my grand plan is to install a cooling fan like the ones in a computer case and extract the hot air into a space at the back of the boat.  I bought some 2” ducting and a couple of fittings and it took me four hours to make two, 3-inch holes in the bulkheads to fit the ducting.  The rest of the day was spent tracing some more redundant wiring and working out how much cable I will need to buy.  

2 August.  I spent most of the morning running around buying marine grade wire and other bits while Glenys did a few jobs on the boat.  Mitch is progressing with the Arch and hopefully we’ll have the first fitting tomorrow.  After lunch, the heat was so intense that Glenys cracked up and went shopping in the air conditioned West Mall.  I tried to continue to do work in the lazarette, but it’s a tight space that I have to crawl into and after an hour my t-shirt was wringing wet with sweat.  I gave up, changed my t-shirt and went for a walk to buy a few more bits.

First Fitting

Drilling out the Toe Rail Posts

3 August.  Mitch came and did the first fitting of the Arch which cheered me up – the end is in sight.  The Arch fitted in the correct place - with a little bit of pushing and twisting.  Mitch said that the boat is out of square.  To which I replied, “Of course it is – nothing on a boat is ever square”.  The Arch looks to be the correct dimensions and looks good.  I fitted the ducting in the lazarette for the cooling fan for the aft cupboard.  It was a mission crawling into the lazarette, applying sealant and tightening bolts, while Glenys was in contorted positions below holding the other end of the bolts.  Now that we’ve done the first fitting of the Arch, I removed the four stainless steel rods that supported the pushpit.  I’d been dreading the job, but in the end, it wasn’t as bad as I thought it would be.  The extended hole drill worked very well and it only took me an hour to drill them all out.

11 August.  Mitch picked me up in the afternoon and we went through the final touches for the Arch, working out exactly where to put the lights and fishing rod holders, etc.  He’s certain that it will be fitted tomorrow.  Mitch is also making a pair of “storm drogue” chain plates for me.  These will fit under the aft mooring cleats and provide a strong attachment point for a “Series Drogue”.  I bought some 160mm long stainless steel bolts to fit the chain plates - I’m in shock because it cost me £55 for six bolts with washers and nuts.

12 August.  Mitch came at nine o’clock and delivered the storm drogue chain plates.  He still had a little bit of welding to do on the Arch and was having a problem getting bolts that were 7 inches long.  I spent the morning removing deck fittings from the aft deck and drilling the holes for the chain plates.  By lunch time, Mitch still hadn’t been able to find any bolts, but could get some by Monday.  I told him that he could use the ones that I bought yesterday to fit the Arch and I’ll do the chain plates on Monday.

Mitch arrived just after lunch and we fitted the Arch in position.  It was a laborious process but was all done by five o’clock.  It looks good and I spent the evening checking that everything was in the correct place.

The Arch Arrives

Final Bits of Welding

Nearly Done

Strength Test

13 August.  I was up at six o’clock this morning worrying about not being able to get the wiring through the inside of the Arch tubing - the last thing that I want to have to do is take the Arch off again.  It took me two hours to pull four “mouse” lines through, so that I can pull the wires through later.  Mitch turned up at eight o’clock and spent all morning attaching the back part of the pushpit to complete the job.  After lunch, I made some brackets for the solar panels and started to fit the wind generator.  I had a panic attack when I dropped the mouse line for the wind generator cable.  The path through the tubing is quite convoluted and I was in despair at how to get it back through.  Jimmy from “3/4 Time” suggested using a small fishing weight on a bit of fishing line.  Five minutes later, I had the mouse line through again – I owe Jimmy a six pack of beer for that tip. I didn’t quite manage to get the wind generator installed before I gave up at six o’clock. 

14 August.   I was up at half past six and spent all day fitting the various pieces of equipment to the Arch and running the wiring.  There are five aerials, two flood lights, a navigation light, two 185 Watt solar panels and a wind generator.  By six o’clock, I’d got everything fitted and wired up at the Arch.  All I have to do now is to run the wiring through the lazarette to the cupboard in the back cabin and connect it together.

15 August.  I woke up at four o’clock in the morning with the subconscious part my brain telling me that the Arch wasn’t square to the boat.  I climbed out of bed and stared at the vertical and horizontal sections of the structure and, sure enough, it looked to be about five degrees out.  In particular, the wind generator pole was definitely not vertical and the solar panels weren’t horizontal.  I spent an hour working out that we need to take just over an inch off the rear main support because the deck slopes up towards the stern.  

At nine o’clock, I went to see Mitch and he agreed that, if I thought that it needed to be done, then he would sort it out.  The dilemma was whether it was worth the effort of removing all of the equipment, removing the Arch, re-doing the welding work that we did two days ago and then re-running the cables – all for a small five degree slope.  Back at the boat, I discussed it with Glenys and we stared at the slight “lean” for about ten minutes before I decided that if we didn’t do it, I would spend the next ten years looking at a Leaning Arch.

I rang Mitch. He came over straight away and agreed that we should remove 1 1/8” from the rear support.  Glenys and I removed the solar panels, pulled the wiring up inside the tubing, leaving some iron wire that won’t melt when Mitch has to weld.  By lunchtime, we’d finished our bit and the arch was ready to lift off the boat.  Mitch arrived at one o’clock and worked all afternoon to cut out the small section of tubing, re-weld, re-polish and install the Arch back on the boat.  We finished at six o’clock and had a celebratory beer.

16 August.  I was up at half past six, sorting out the wiring.  The mouse wire for the wind generator snapped as I was pulling it down, so I had to remove the wires for the navigation light, the aft flood light and the wind generator and then use the fishing weight (again) to feed a mouse line down the tubing for the wind generator.  The rest of the wiring pulled though okay.  I fitted the various pieces of equipment to the arch and re-wired everything – 5 Aerials, wind generator, three lights.  Reluctantly, I crawled into the hot lazarette locker and spent an hour running the wiring through pipes into the cupboard in the back cabin.  I was then able to connect most of the wiring in the cupboard.

Fitting the Wind Generator

Wiring Cupboard

17 August.  I had a lie-in this morning and didn’t get started until seven o’clock.  My day was taken up with lots of small finishing jobs today – I fitted the storm drogue chain plates, fitted the solar panels and completed the wiring. I fitted the vane for our Hydrovane self-steering and, sure enough, it hit the Arch at many points of sail.  I chopped 16 inches off the frame and it clears most of the Arch.  I took the bits to Mitch and he is going to weld it back together to that it is 16 inches shorter and 6 inches wider.  Hopefully that will give us enough vane area for the Hydrovane to vane to work correctly.  

18 August.  I connected the solar panels and they were pumping 10 Amps into the batteries at eight o’clock in the morning.  At midday, they were putting in 23 Amps which should be more than enough to keep us going without running the generator every day.  I spent the day doing more finishing off jobs – mounted the barbeque, outboard and Danbuoy brackets on the Arch, fitted the guard rails, cleaned up the sealant around the deck fittings

19 August.  I spent the morning running about buying last minute things and finishing off a few essential jobs.  In preparation for the River Manamo, I bought a Fortress anchor which is supposed to hold well in soft mud.  I bought and fitted some blocks and rope for the davits.  I picked up the modified vane for the Hydrovane and the aerial bracket from Mitch.  My credit card was red hot by lunchtime.  Back on Alba, I managed to get the dinghy up on the davits – it’s not quite right, but hopefully it will be calm on the passage to the Manamo River tomorrow.

26 August.  I’m very pleased that we put davits on the Arch as the system works well both at anchor and when under way in calm waters.  I hoist the dinghy with two ropes and then use another two ropes to pull the dinghy in tight against the Hydrovane to stop it swinging from side to side. There are a couple of little niggles - the ropes that I bought are too thin and too short, so I’ll have to buy thicker rope when we get back to Trinidad.  The more serious problem is that the dinghy being worn by rubbing against protruding parts of the Hydrovane.  So I spent most of the day making a shaped teak pad, which I’ve screwed to the Hydrovane.  Hopefully, this will give a bigger and smoother surface to hold the dinghy in place without chafing.

Five Years Later

I'm really pleased with the Arch. 

  • The dinghy davits have been a god send - we pull the dinghy up every night at anchor, which keeps the bottom clean and stops any Rascals stealing it.  I initially thought that there should be an additional strengthening strut under the davits, but Mitch said it would be fine and it has been.  We put the dinghy on the front deck whenever we sail at night, but we've done some rough day passages and never seen the arch move at all, so the strengthening bars that Mitch suggested have worked. 
  • The little table is great.  It's good for cleaning fish, but is also a useful little work bench allowing me to clamp my small vice at a convenient work height.
  • The fishing rod holders have been very useful.
  • The solar panels haven't been touched for five year apart from the occasional cleaning.  One disadvantage is that Brown Boobies think that the solar panels are a great landing platform and we've had to chase quite a few off - dried Booby Poo is hard to clean off.
  • The wind generator has been good.  There is some vibration through the frame, but no more than the original pole.
  • Our little outboard crane work well.
  • Having two spotlights (pointing at the water and the aft deck) has been very useful.
  • I've got space to hang two outboards, a stern anchor, a Life Sling, a danbuoy, two fishing rods and a gaff. 
  • The cut down Hydrovane wind vane is working well.
  • There's quite a bit of stainless steel to clean, but Mitch used good quality 316 steel and it's as good as it could be. 

Aft View

Wind Generator Mounting

Side View

Underneath the Solar Panels

Starboard Lower

Starboard Upper

Port Lower

Port Upper