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Old 07-10-2015, 08:53   #1
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How to build a hard-top.

I've constructed a hard-top for my Privilege 435. Having received a number of requests for photos, (and as my previous attempt to post them failed), 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.

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 colour (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-colored 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 gel coat 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 gel coat, it is better to ‘underfill’ the joint thus giving a raised portion of gel coat 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 purchased 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.

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 of wax.

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, gel coat is mixed with wax. As the gel coat is applied, the wax rises to the surface of the gel coat 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 gel coat since both surfaces will be sealed; the bottom by the mold itself and the top by subsequent layers of gel coat and fiberglass. Gel coat 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. I first mixed up a quart of gel coat and having given the mold a final wipe down with a soft cloth to remove any dust, brushed the gel coat 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 was 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 gel coat on, be sure to use a short nap sleeve on the roller; you don’t want a heavy nap soaking up all your gel coat. 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 gel coat. Once the gel coat has set you are ready for the fiberglass.

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 easier 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 gel coat 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.

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 extra depth afforded by the extra ½” foam, I was happy to have the extra strength to tip the scales from ‘probably’ to ‘certainly’.

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 edges. 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 the 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.

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.

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 cut out a section above the driving helm and made it into a sliding cover, 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.


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Old 07-10-2015, 09:11   #2
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Re: How to build a hard-top.

WOW! That is really nice.

Mind if I ask you about costs?

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Old 07-10-2015, 09:21   #3
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Re: How to build a hard-top.

I hadn't really worked it out. Materials to make the mold and prep; around $300. Gel coat; $100. Polyester resin; $30 a gallon. Fiberglass cloth; around $250. Wiring and lights; around $150. Divinycell sheets; around $700 + Extras (Paint, wax, brushes, rollers, cleaner etc...) My labor at $25 an hour; around $1million. A guess would be at the total cost of around one million and $2,000 - $2,500.

The aluminum supports will depend on where you get them done and how complicated your design is.
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Old 07-10-2015, 09:31   #4
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Re: How to build a hard-top.

Very nice hardtop build and an excellent step by step description of how you did it.

Well done! Thanks for sharing the process and tips here.
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Old 07-10-2015, 09:40   #5
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Re: How to build a hard-top.

Privilege- impressive work and an outstanding write-up. I have been wondering about finishing the edges and had not thought of the PVC pipe. Also like your side supports.
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Old 07-10-2015, 10:27   #6
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Re: How to build a hard-top.

Nice job on a very complicated project! Thanks for sharing.
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Old 08-10-2015, 08:26   #7
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Re: How to build a hard-top.

Very nice project. Thanks for sharing. I'm also looking for options in hardtops and the first quote didn't make it as they wanted $9500 for an all aluminum project. I'm set for my solar panels as they are on my rear arch / davit assembly.

I look to my hardtop as a rainwater collection system. I like the idea of prewiring and suggest to everyone doing this to remember that if you have wire channels don't forget to put a chase string into each for ease of adding more.

I hope others will share their adventures in hardtop design and acquisition.
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Old 08-10-2015, 08:32   #8
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Re: How to build a hard-top.

I am looking at this project closely as I will be building a hard dodger and hard bimini. Thank you for the detailed description - I, too, like the pvc pipe technique on the edges.

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Old 08-10-2015, 09:45   #9
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Re: How to build a hard-top.

Congratulation for a comprehensive description of a nice job.
I build a similar hard top for my own Privilege 435.
I believe I found a simpler way to build the mold ;
As shown on the photos, I built the mold from 4 vertical frames sawn to shape, onto which I screwed pannels of 12 mm thick melaminated pannel (I am not sure I translate properly the French word "panneau mélaminé" )
Another simplification was to make the mold for the underside, making it impecable when seen from below wheras the top was naturally non-skid.
Finally, the edges where simpler: The mold featured
a vertical edge coming down. outside the laminated hardtop I glued vertical bands of laminate rising 1" above the top surface of the hard top. This raised edge hides the rough top surface of the hardtop, and catches the Rainwater
Smooth mold side

Rain water drain

Laminated hardtop

Band of laminate
glued to the edge

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Old 08-10-2015, 21:04   #10
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Re: How to build a hard-top.

Not a bad amateur top. Next time, use melamine instead of p-lam on ply, as already pointed out. Big time and cost saver. Also, when routing channels in foam core for wireways, I always insert 1/2" OD PVC pipe for the wireways. This means the wiring can be replaced down the road. I usually just leave a string through each one, and pull wire after construction is complete. This means no wet resin or solvents around your wiring. Also, a flange will give a more constant edge thickness after trimming and facilitate mold release.

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