Saturday, June 1, 2013

Building a Hard Bimini for Galena

I decided to build a hard bimini for Galena.

When I bought Galena she had an open cockpit; No bimini and no dodger. After a year or so I decided I needed to get out of the sun and so built a soft bimini. It was made of Sunbrella stretched forward from the stern mounted boom gallows to a set of aluminum bows mounted on the coach roof. The bimini covered the enter of the cockpit and the companionway hatch.

This cloth bimini was about five feet wide and ten feet long and it worked fairly well. When new the Sunbrella fabric was waterproof and thus kept some of the rain out of the cockpit and companionway. But being only 5 feet wide it didn't really cover the 'seating area' of the cockpit. For those who don't know the design of a Westsail32 the cockpit is really just a footwell; you sit on the deck around the edges of the footwell. For the most part one was not under the bimini. The bimini did provide some shade for at least one side of the cockpit. I tried to use the bimini as a rain catcher; fresh water being somewhat scarce where I cruise. But being cloth it flapped in the wind, throwing any rain off before I could direct it into buckets.

Here are two photographs of the old cloth bimini. One from the outside and one from the inside.


The original cloth bimini. It gave some shade but little protection from rain.



This view shows the underside of the old cloth bimini


In the years after I first built that bimin I'd had to replace or repair it several times. The cloth would lose it's water-resistance and also it would eventually begin to tear from exposure to wind and sun. Also the main boom was low enough to allow the sail cover to rub along the top surface, wearing away the threads of the seams. Finally I just gave up on it.

For the past year I've sailed without any cover over the cockpit. The result has been lots of sunburn. Additionally, whenever it rains I have to close my main hatch and put in the drop boards and that really reduces comfort below. And I really need a rain catchment system as the local water is often unappealing.

Recently two of my cruising friends here in Fiji (s/v's Drifter and Mambo) decided to build hard biminis of fiberglass coated plywood for their boats. I watch Arnold on Drifter build his and then I watched as Heinz on Mambo began his design process. It didn't look all that hard. With so much expertise and help at hand I decided to finally build a similar top for Galena.

The first thing I had to do was to draw up some plans. This wasn't the first time I'd considered a hard bimini so I wasn't really starting from scratch. There were several considerations:
- For support I decided to use the existing aluminum framework along with the aft-mounted boom gallows. I therefore had to dimension it to fit in the same space as the old cloth bimini.
- On passage I carry my hard dinghy on the coachroof. When it's in the davits, the dinghy's stern extends over some of the companionway opening. I had to leave room for the dinghy to be hoisted into position on its deck davits. - I wanted something a bit wider than what I had before but I still had to be able to walk around the side decks. So the maximum allowable width would be about 6 feet.
- The bimini had to be capable of catching rain and directing that water into deck jugs; even when windy.

After taking a lot of measurements I decided that I'd need a bimini with a finished size of 6-ft by 10-ft.

The plywood was available locally. Using 6mm (1/4") sheets of exterior grade plywood would result in a nice compromise between strength and light-weight. Rather than minimizing waste, I decided to go for maximum strength and that meant minimum number of joints. To get that I'd need three sheets of plywood. The available plywood sheets, being cut to metric measurements, are just a little smaller than the standard 4' by 8' sheets I'm used to. The three sheets cost about US$ 90 total.

The epoxy resin was also available locally in the brand name of Resene. It is similar to West System but mixed at 4:1. Cost was US$ 125 per gallon. I'd need two gallons.

Fiberglass cloth was not available locally. The local hardware stores had glass mat and some heavy woven cloth available. But I wanted relatively fine 200g cloth. That I had to order New Zealand. While ordering the cloth I also ordered epoxy fillers. I'd need 8 liters of Microlight and 4 liters of Colloidal Silica. Cost including shipping was US$ 250.

One gallon of two-part polyurethane paint, white, was available locally at a cost of US$ 125.

Some lumber and incidentals added another couple hundred to the tab. Final cost was about US$ 800.

The construction took about 4-weeks working about 4 hours a day. There were two reasons for the short workday: I could only do so much before I had to stop and wait for the epoxy to go off, and it gets very hot in the afternoons here in the tropics.

Most of the work was done on the porch of the Savusavu Marina office.

I like my little marina, but before you get the wrong image in your head, let me show you the place.


This is the office for the Savusavu marina. You can see the biminis for Galena and Mambo on the porch 'workshop.'



And this is the marina's only wharf. To the far right is Galena at her mooring. And to the far left about 3/4-mile away you can see the Copra Shed Marina.


I also had the help of my good friends Jeff and Jose (s/v Stravaig). They are very experienced in fiberglass work. In fact they had built their own boat several years back. Jeff helped me with the details of the design. His wife, Jose, is an artist with glass cloth. In fact most of the glass work was actually done by Jose while I was relegated to mixing pots of resin and taking notes.


Plywood sheets.

The first step was to cut the plywood sheets to size. From the three sheets I needed thee sections: 6'x4', 6'x4', and 6'x2'. They would be joined on their long sides resulting in a single sheet 6'x10'. That also resulted in a lot of waste: three sections 2'x4' and one 6'x2'. The latter would be used to construct the cross beams so that one wasn't really wast.

Once these plywood sections were cut I laminated them on both sides with 200g fiberglass cloth. One of the first things I learned from Jose about handling fiberglass cloth was how to cut it. In order to get a clean and straight edge one first pulls a thread out of the weave at the place you want to cut it. This creates a line to follow along the weave of the cloth thus virtually eliminating fraying. Then one cuts it with very sharp scissors.


Pulling a thread out of the fiberglass cloth to make a cut line



Cutting the cloth along the line made by pulling out a thread


To laminate the plywood with fiberglass the wood is first saturated with epoxy resin. The mix is pure epoxy for flat surfaces. When the cloth must be contoured around a corner or other shape one thickens the epoxy with some colloidal silica. This thickens the epoxy and makes it 'sticky.' The cloth then adhears to the wood and wraps nicely around any curve. Next the cloth is laid in place. Finally more resin is squeeged over the glass saturating it and removing any excess resin. One has to take care not to distort the cloth. Jose was constantly scolding me for 'adjusting' the cloth after it was in place.


Jose and Jeff wetting-out the plywood and laying on the fiberglass cloth


Once all three sections were covered with fiberglass cloth on one side I had to wait until the next day to do the same on the other sides. This waiting for the resin to go off would be the project's biggest consumer of time.

Crossbeams.

I wanted the surface to be slightly curved from left to right while straight in the fore and aft directions. To achieve the desired curvature I raised the center of the bimini about 2". I planned to place four beams across the bimini to give support and form the desired curve of the surface. These beams were constructed from plywood arcs roughtly 1.5" high, 1/2" thick, and the full 6' long. I rough cut eight plywood strips in the desired arc with a jigsaw. Then I glued two 1/4 inch thick arcs together to form the four 1/2" thick beams. Using a Surform plane I carefully shaped one beam to the 'perfect' size/arc. Using that one as a template I went out to s/v Stravaig and used Jeff's router to machine the others to match.


Jeff using his router to shape the beams on board Stravaig.


Assembly.

In the yard next to the marina office was an large boat trailer. It's shape and size lent itself to being the initial construction bed for the bimini. By placing some weights in the middle the plywood it bowed nicely into almost the proper shape.


All the parts are laid out on the trailer. The three sections of plywood, the butt blocks, and the cross beams. I've also placed the boom gallows board at the far end and the bows at the near end. Yes, it's upside down.


I joined the three sections together using simple butt joints with 4" strips of plywood forming the butt blocks. These butt blocks were glued and glassed into position while the plywood sheets were held to the desired curve by the cross beams and some weights in the center of the sections. As with most of the construction I'd use stainless steel screws to hold the parts in place until the epoxy would set. Then the screws were removed and the holes filled with epoxy. Most of the epoxy used was first thickened with colloidal silica thickener (West Systems 406)

The aft-most beam was special in that it included a large surface that would be bolted to the existing boom gallows board. That would fix the bimini in place at the stern. It was also notched to provide clearance for the brackets holding the boom gallows board to the stainless steel arch at Galena's stern.


Here I'm putting a fillet of colloidal-thickened epoxy resin along the aft-most beam.


All of the cross beams and butt-blocks were covered in fiberglass cloth for both strength and weather-proofing.

Once all the epoxy had gone off I moved everything to the marina porch. There was an old wooden dingy on the porch and that would become my construction table for the rest of the project. In the picrure below my bimini is standing against the wall while Heinz (s/v Mambo) works on one half of his bimini. Mambo is a large catamaran so his bimini was almost three times the size of Galena's.


My bimini is against the wall behind Heinz who is working on half of the bimini for Mambo, his large catamaran


After placing a for-aft beam in the center of the bottom I used Microlight (West Systems 410) filled epoxy resin to fill-in the weave of the fiberglass cloth covering all the wood surfaces. A light sanding left a very smooth surface for painting.


Bottom surface after sanding the Microlight. Almost ready for paint.


The top side of the bimini required a raised edge on all sides to both stiffen it and to catch rainwater. I opted for a rail of 1x2 inch lumber. This was a bit of overkill. It should have been only 1-1/2 inches tall. Less than that would have let the water overflow in a downpour.

In order to get the front and rear end rails to bend to the desired curve I had to cut kerfs up from the bottom every 6 inches along their lengths. The side rails had their bottoms milled (using Jeff's power planer) at a slight angle to allow them to stand vertically on the edge of the sloping top surface. All the side and end rails were radiused on the top edge. I also added a glassed 1x1 inch foam beam (left over from Mambo's bimini) down the center to for additional stiffness.


Top surface just before wrapping the side rails with glass.


The glass that would wrap around the side rails would extend down and around the edge of the plywood. Therefore I had to radius the edges of the plywood to allow the glass to take that bend. Jeff helped by using an angle grinder to do the rough shaping and I followed up with a Surform plane to smooth it out.


Jeff radiusing the edge before glassing the rails. The glass would wrap all the way from the top surface, around the side rails, and on to the bottom surface.


The forward end of the bimini would be held up by the old aluminium bow system, but would be somewhat unsupported torsionally. I added some pad eyes at each forward corner to allow me to tie cross-brace lines down to the coach roof for stability.

Sanding and prep for painting.

Once the bimini construction and fiberglassing was finished I began the sanding phase. There is always some excess epoxy on the surface of the fiberglass. And that must be sanded off without cutting into the fiberglass cloth itself. Also at all places where the glass cloth overlaps other fiberglassed areas the exposed edge has to be reduced a little to allow feathering of the edge.

I used 60 grit sandpaper and a small block of wood to do all this sanding. Smoothing the large surfaces were easy. Mostly there were just a few drips and laps to sand. The problem was the corners. There were 18 corners on this thing and each was a pure pain the butt to smooth out. But all I had to do was knock off the high spots.

Speaking of the corners Jose showed me a neat trick for glassing a corner. First of all you stop the main glass running up to the corner about 1/2" from the actual corner. Then you cut a circle of glass cloth. The circle will, with a little dabbing from a 1" brush, form itself nicely into that corner.

Once all the high spots were sanded down, I started the second-to-last phase: filling.

To achieve a very smooth surface one has to fill the weave of the glass with epoxy and then sand that epoxy smooth. Pure epoxy is extreamly hard so one uses a soft powdery additive (Microlight, West Systems 410) to reduce the density of the epoxy making it much easier to sand. The process is to squeege the thickened epoxy (thickened to the consistance of peanut butter) over the surface being sure to press it into the cloth. Then wipe it away with a metal squeege leaving only the weave filled. Along the edges and in the corners I used my fingers to spread a smooth layer of epoxy.

Once this hardens (here with the high humidity it often took two days to become hard enough to sand) you sand it smooth. With 80 grit paper it sands very quickly. Most of what is applied is sanded away leaving a very smooth surface.

With every other phase of construction I always had the excuse that mistakes could be corrected or covered up with the next phase. When a piece of wood was cut too short I'd think, "It's OK, I can cover that up with fiberglass." When the glass was a bit wavy I'd think, "I can fill that later with the sanding filler."

But then I started the Microlight filling phase. Even I know that pain never hides or covers up anything. All it does is hightlight mistakes. I knew that I was going to be staring up at the bottom of this bimini for the next several years. I didn't want a badly filled seam shouting at me, "Why didn't you spend just a little more time on me? I'd have disappeared!" So I was determined to spend the time required to make this as 'right' as possible.

The process is: fill with epoxy. Wait for it to harden. Sand it off. Look for imperfections. Fill them with epoxy. Sand it off. Look for imperfections. Repeat.


Here's a picture of me sanding the Microlight filling epoxy off the top of the bimini.


And here I'm sanding a central corner on the underside of the bimini


While I was still sanding Heinz had finished his painting. Here he's joining the two halves of his bimini. It's about 20 feet wide and 7 feet deep.


Heinz joining the two halves of his bimini.


Painting.

Once the surfaces were as smooth as I could make them (actaully I simply got sick and tired of filling and sanding) it was on to painting.

Of course as soon as I was ready to paint Fiji suffered a week of squalls with high winds and heavy rain. But eventually things dried out and I got on with my project.

I used an APCO brand two-part polyurethane paint in white. Proper rollers are unavailable here in Fiji so I used what was at hand. The results were acceptable but not great.

I stood the bimini on it's edge against the poles on the porch. That allowed me to paint both sides at once, reducing the time spent waiting for the paint to dry. The only part I couldn't paint was the lower edge. When I had two coats on both top and bottom I placed the bimini back on the table and painted the edge.


Two views of the bimini after it was painted

Installation.

I brought my dinghy up to the dirt boat ramp. Hienz and I carried the bimini out and placed it on my dinghy. I fitted a lifting bridle in place and we towed it out to Galena. Once along side I used the main haliyard winch to hoist the bimini up and swing into position over the cockpit. It dropped into postion without any fuss.


The new hard bimini in place on Galena.


View from the bottom showing the structure and supports

I have about 2.5" of headroom when standing in the cockpit and that's enough.

All that is left is to secure it into place and install the plumbing for the rainwater. In the future I may install virtical supports at each foward corner. But aside from that it's done.