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Old 11-08-2013, 03:24   #1
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How to build a hard-top.

I recently built a hard-top for my Privilege 435. Having received a number of comments and requests for photos, I thought I’d post an account of how the top was constructed.
The previous top was made of a stainless frame with a canvas covering. It was O.K but it seemed to be a bit of a mismatch with the sleek lines of the boat. Standing on it in order to gain access to the boom required a balancing act that made me look about as cool as a newly-born giraffe.
My pre-requisites were that I wanted the hard-top to be a professional looking job with a glossy gel-coat upper surface. I wanted to be able to put solar panels on top and I wanted lights built into the underside. It needed to be strong enough for two persons to walk on whilst only being supported at the edges; one support at each side and a pair of supports at the front and rear.
The top is 12’ x 13’ so in order to keep the weight down to an acceptable level, and in order to get the shiny topside, the only real way was to make a mold and create the top using foam (Divinycell), gel coat and resin.
Here’s how it was done;
I started the mold by using a 12’ length of 10” x 1” plank and copied the curve of the coach-roof onto the board. I then cut out the curve and made another seven identical planks. I supported the planks using 4”x 2” and spaced them evenly so that the curve of the coach-roof was inverted to form one big bowl-shape. I then screwed some sheets of ¼” ply down onto the edges of the planks to form the bowl. At this point, it is important to get the bowl shape correct and smooth. Even though you will be covering it with laminate, any raised edges or indentations will show on the finished product and will be practically impossible to fix after the fact. Any screws that sit above the ply surface will be problematic so ensure that each screw pulls itself below the ply surface. Any indentations in the surface bigger than a screw head should be filled with spackling. If the curve of your top is gentle enough that you can use ½” ply go ahead and use that as it will form a better finished surface. After the top is finished, all of the mold will be discarded so use the cheapest products you can find to make the mold. There is no need for the added expense of micro-balloons, marine ply or stainless steel screws.
Bermuda day2Hard-top.jpg
Once you are satisfied with the shape and size of the ply mold, you are ready for the laminate. The laminate has a glossy surface and it is this surface that will act as a mold-release and give the smooth surface of the hard-top. Most hardware stores sell Wilsonart or Formica laminate. You need to purchase a dark color (Assuming that your top is white). The reason for this is that when you apply the gel coat, you will not see any thin spots or missing bits if your underlying surface is of a similar color. This is very important as the resin sets fairly dark in colour and any gel coat which is too thin will allow the resin to show through. (I used a couple of light coloured sheets for my project as seen in the photos as the hardware store had no dark-coloured sheets left).
Glue the laminate down onto your sheets of ply. Contact glue is the best glue for laminates but the only draw-back is that once it touches the ply, that’s where it’s going to stay. To make this process easier, once both surfaces have been coated with glue and have dried to the touch, place a number of dowels or pieces of 1” x 2” across the ply, laying the laminate on top. You can then remove one piece of wood at a time pressing down the laminate as you go, thus ensuring that the laminate does not stick to the ply before you are ready for it to do so.
Because you cannot move the laminate once it has been laid, it is very difficult to get the edges abutted perfectly. The design of my top allowed for a margin of error here. My top is 13’ wide and as the laminate is 4’ wide, I needed just over three sheets to cover the width of the mold. I knew that once finished, the middle portion of the hard-top would require a non-skid application to allow access to the boom. This would be put onto the top after it had been removed from the mold, so as long as any imperfections made by the joints were in the middle 5’ section of the top, they would be covered by the subsequent non-skid. This allowed for 4’ at either side of the top to be uninterrupted glossy surface. A tip here relates to imperfections which have to be repaired once the top has been removed from the mold. It is easier to sand down gelcoat and buff it to a glossy surface than it is to mix up filler and patch any indentations. Therefore, in places like joints in the laminate, if you fill it with spackling prior to gelcoat, it is better to ‘underfill’ the joint thus giving a raised portion of gelcoat on the removed top.
Once you have the laminate down, you will need to decide what sort of edge or lip that you want on your top. Having tried a few different shapes, I settled on a curved lip. I purchase a few lengths of 2” plastic plumbing pipe. I made up a jig on my bench-saw and cut it down the middle length-wise to give me one long continuous semi-circle. Having screwed down some wooden battens as a support for the pipe, I screwed it in place around the edge of the laminate.
Bermuda day3Hard-top.jpg
If your top is not square in shape, you will need to ensure that the pipe is flexible enough to take the curves without them distorting. I realized a mistake that I had made after having affixed much of the pipe. I found that the pipe would not bend around the sharper curves at the back of my top. I had to replicate the shape by building up layers of bondo and spackling and then sanding out the inside curve. Although I was happy with the outcome, it was very time consuming and took ages to do. To fill the very small gap between the pipe and laminate, I ran a very small line of caulking.
Once you are happy with the mold you are ready to apply mold release. Mold release wax is available and priced similarly to car wax. I read lots of different accounts of how to apply mold release wax and whether or not to use PVA mold release agent. The PVA is painted on and dries to form a film on the surface of the laminate. I had read a few reports which said that although the PVA always worked well, it was very difficult to get a perfect finish as it leaves small brush marks on the surface which are replicated in the top. As I had spent much time getting my surface perfect, I didn’t want to ruin it so decided to go without PVA. I applied the wax to the laminate in 5’ x 5’ sections at first, but found that it dried quickly and was difficult to remove even with an electric buffer. I reduced the size of the application to around 3’ x 3’ sections and by the time I had finished, it was ready to rub out. It seemed as though I was rubbing off all the wax that I had just put on and after two coats of it, I felt like that little fellow from ‘Karate Kid’. I applied two good coats on most areas and three on some. I also waxed the inside of the plastic pipe, paying particular attention to the bent edges. On the part that I had made out of filler (and then spray painted) I put three or four layers.
I was finally ready to start making the actual top. First up are a couple of layers of gel coat. Gel coat comes in two sorts, waxed and non-waxed. Waxed or non-waxed does not refer to the shine of the finished product. Gel coat when mixed with hardener never fully hardens when exposed to the air. For this reason, gelcoat is mixed with wax. As the gelcoat is applied, the wax rises to the surface of the gelcoat and seals it from the air allowing it to harden completely. The draw-back with this is that you now have a surface with wax on it so any further layers of resin or paint will have trouble adhering to it. When making a mold, you need the non-waxed gelcoat since both surfaces will be sealed; the bottom by the mold itself and the top by subsequent layers of gelcoat and fiberglass. Gelcoat can harden quite quickly so follow the mixing ratios and try a few quart-size mixtures first so you can judge the cure time based on your conditions. Having given the mold a final wipe down with a soft cloth to remove any dust I first mixed up a quart of gelcoat and brushed this onto the inside of the pipe, eventually building up several layers. I made sure that the areas which were curved had a few extra layers to allow me to fix any imperfections once the top had been removed from the mold. I found that I could mix up about two quarts at a time which would give me sufficient time to roll on the gel before it began to set-up and become gelatinous. If you roll the gelcoat on, be sure to use a short nap sleeve on the roller; you don’t want a heavy nap soaking up all your gelcoat. Also, ensure that the sleeve is designed for epoxy paints or it will dissolve and fall apart. I applied two layers to the mold which used up two gallons of gelcoat. Once the gelcoat has set you are ready for the fiberglass.
Bermuda day4Hard-top.jpg
Polyester resin is ideal for hard tops. There are a number of different types of fiberglass cloth. Chopped strand matt (CSM) is the fiberglass that has lots of little random strands in it. It flakes into pieces when you handle it and these tiny strands show up in your clothes, your tool box and several months later in your bed. It is strong when cured but not in any particular direction. Fiberglass cloth is much smoother to use and stays intact when handled. The cloth is made up of neatly crisscrossed strands and has greater strength in a lateral direction. Bi-axial cloth is made up of a combination of CSM and cloth and takes advantage of CSM’s binding abilities and cloth’s lateral strengths. For this project I used 1.5oz chopped strand mat and bi-axial cloth.
The first layer down on the gelcoat should be CSM. Lay it out, cut it to shape and roll on the resin. Keep the resin spread thinly, do not let it puddle or it will dry brittle and just add extra unwanted weight. A rule of thumb is that 1 gallon covers 4.2 yards of 1.5oz CSM. Put plenty of layers on the inside of the edges. These edges are likely to take the brunt of people holding the top or any impacts. Let the first layer cure.
You will then need to cut to shape the divinycell. This stuff is expensive but there is nothing as strong and light which will serve the purpose for a project of this size. I used ¾” foam to ensure the strength of the top. Cut the divinycell to size using a sharp knife or jigsaw and leave it to one side. Next up is a layer of biaxial. Lay it out in the same way and coat it with resin. Roughly 1 gallon to 4 yards. While it is still wet, coat the underside of the foam with a thin layer of resin and lay it down on the biaxial. You will need to weigh it down with blocks to ensure that it takes the shape of the mold and to ensure that it adheres to the cloth. Make sure that there are no spots where air pockets can form between the foam and the cloth as this will weaken the structure.
Bermuda day7Hard-top.jpg
After this has set overnight, you can apply one more layer of CSM and one more layer of biaxial in the same way.
A friend at the local boat-yard gave me another tip here. I cut a few 6” holes into the foam and discarded the round plug prior to laying it onto the glass. Once it had cured, I filled the hole with several layers of CSM and biaxial. This served to effectively bolt the foam down. The strength of the top comes from the laminating process whereby the different layers cannot move laterally independently of each other. These solid round plugs help to glue the foam down and ensure that it cannot move laterally. At two points at either side of the top where the supports were to be secured, I made it from solid glass, laying up numerous layers of cloth. This way, I can really screw down tight on the retaining bolts without flattening any foam.
On the underside of my top I added LED white lights and a set of RGB lights. The white LED’s that I used were ‘bright white’ which are good for lighting up the deck for projects or general lighting. I used six 3-watt recessed lights. In order to embed the lights into the underside, I applied another layer of ½” divinycell onto the mold as before leaving channels for the wiring for all of the lighting and for the solar panels. Once this was done, I covered the foam with another layer of CSM and biaxial. I am told that the ¾” foam alone would have ‘probably’ been strong enough to walk on, but as I needed the depth afforded by the extra ½” foam, I was happy to have the extra strength to tip the scales from ‘probably’ to ‘certainly’.
Bermuda day9Hard-top.jpg
Some finishing was required prior to the big day when I would try to pop the top out of the mold. I used a grinder to remove the fiberglass that had protruded up from the edge. I could finish the edges properly later but at this stage the plastic piping gave a good straight line to level the fiberglass. I did some grinding on the underside of the top to remove any imperfections and gave it a coat of oil-based undercoat paint. I was happy with the finish of the biaxial cloth and did not feel any need to fair the surface or have a perfectly smooth finish on the underside.
Next came the big moment when I would find out whether the top would pop out from the mold. I used a flat crow-bar to raise an edge and wedged a pool noodle into the gap. After three or four of these the whole top just separated from the mold without fanfare.
Bermuda day10Hard-top_1.jpg
The top turned out great with the glossy finish that I had hoped for and only a few small holes to fill around the edges. It weighs somewhere in the region of 250lb, which is a fair bit of extra weight to put on the boat, but with the benefits it affords, I consider it to be worth it.
Bermuda day12Hard-top1.jpg
I designed some supports for the sides and had them made up. I’m very happy with the finished product; it looks professional and I think that it adds to the aesthetics of the boat. I’ve added solar panels, a cradle for the boom and have yet to apply the non-skid finish; but that’s on the list of things to do…and it’s a very long list.
Bermuda day12Hard-top2.jpg
Bermuda day13Hard-top.jpg
Bermuda day13Hard-top_1.jpg
Bermuda day14Hard-top_1.jpg
Bermuda day15Hard-top_1.jpg

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Old 11-08-2013, 04:20   #2
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Re: How to build a hard-top.

I would have loved to see the pictures....but not being registered on the multiply hull forum I was not allowed....sounds like a very good job indeed.....sorry i couldn't see the final product.
I presume you can see the pictures of the one I built for my Mono hulled boat.

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Old 11-08-2013, 04:40   #3
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Re: How to build a hard-top.

Very nicely done. You just did your boat a big favor. I have a similar hard top and wouldn't know how to live without it.

I think I'll add a post on extending my hulls; a smaller project, but helpful for me.
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Old 11-08-2013, 05:48   #4
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Re: How to build a hard-top.

Photos aren't showing...when I click on them it takes me to a different website and says "you aren't logged in"
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Old 11-08-2013, 18:30   #5
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Re: How to build a hard-top.

Originally Posted by bryguy67 View Post
Photos aren't showing...when I click on them it takes me to a different website and says "you aren't logged in"
I would also like to see the pictures very much please, any change to post them direct here, Privilege?
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Old 12-08-2013, 15:53   #6
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Re: How to build a hard-top.

Privilige, I went to the website, registered, checked my email and activated my registration. It's very much like Cruisers Forum. Your pictures are excellent, and thank you, because I didn't even know Multihulls4us Forums existed. Now I do.

By the way, how much does the hard top weigh?
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Old 12-08-2013, 16:03   #7
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I would suggest as an alternative that the plug be built from cheap mdf. That can be routed and sanded as required then spray with ordinary nitrocellulose paints and finish accordingly, avoids the use of laminates like Formica , which are expensive and difficult to apply to complex surfaces.

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Old 12-08-2013, 18:36   #8
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Re: How to build a hard-top.

What a great job and useful write-up on how you did it. Well done.

I can see a similar project in my future.

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