Bimini canvas replacement

Discussion in 'Materials' started by jimbo2010, Jul 12, 2019.

  1. jimbo2010
    Joined: Sep 2010
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    jimbo2010 Junior Member

    I was looking at this polycarbonate hard top

    Tech Info | Hard To Top http://hardtotop.com/tech.html

    made like this [​IMG]


    they want over $1,000

    They have withstood 80 mph storms

    I would use the existing frame which is 1" and very strong

    So think I could use plywood core glassed on both sides and attach the same way to the frame

    Then thinking perhaps sandwich or balsa core may be lighter/stronger

    upload_2019-7-12_19-50-42.jpeg

    the size is about 110x120

    Any suggestions
     
  2. jimbo2010
    Joined: Sep 2010
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    jimbo2010 Junior Member

  3. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Sorry jimbo

    Canvas bimini frames are not strong enough to properly support hard tops.
    You will also need to re-engineer the deck connections.
     
  4. jimbo2010
    Joined: Sep 2010
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    jimbo2010 Junior Member

    It's done all the time did you read Tech Info | Hard To Top http://hardtotop.com/tech.html

    I know people that have done it and it been reported on several forums with that system
    I can literally hang on mine

    I was looking for advice on how to fabricate a light weight skin like the one made out of polycarbonate
    I'm not concerned with it ability to support it.

    Found Nida-Core, not sure how to layit up with what weight glass?
     
  5. Chuck Losness
    Joined: Apr 2008
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    Chuck Losness Senior Member

    I made a hardtop for the bimini on my sailboat using two layers of 1/4 plywood attached to the existing 3/4" frames. It has withstood winds up to 50/60 knots. But it is not strong enough to stand on. I can provide construction details on how I made it if your are interested.
    IMG_3425.JPG
     
  6. jimbo2010
    Joined: Sep 2010
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    jimbo2010 Junior Member

    looks good

    I would like to know the layup on using say 3/8" core materiel, don't need to support a person

    I was thinking of taking the Bimini frame adjusting it to be level across the 3 bows

    Then taking a piece of ply or something inexpensive in 4x8 laying it across setting the core materiel in place.

    Glassing it with (what weight cloth?) want it light as possible but not flimsy.

    So need opinions on that. was thinking one layer of 6oz????

    But read that although carbon costs more it requires less resin so there's an offset to the cost, not sure

    Next

    Flip it over after it cures and glass the under side.

    Again with what layup

    Thanks for any input


    .
     
  7. Chuck Losness
    Joined: Apr 2008
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    Chuck Losness Senior Member

    I can't help you with a layup schedule. Once you have the layup figured out you should compare the finished weight to a plywood top like I made. There might not be enough weight savings to justify the extra cost and complexity of making the top out of foam covered with cloth and resin. Fiberglass cloth and resin is pretty heavy at around 90 lbs or so per cubic foot. Plywood is around 40 lbs per cubic foot. You will have to make a mold to start with and you will need either solid glass or plywood blocking at the attachment points. It will not be easy to make with the bimini on top of your flybridge. You will most likely have to make a stand that duplicates the location of the bimini attachment points to the flybridge so you can work at ground level.

    With a plywood top you will be able to do the initial construction with the bimini in place on your flybridge. Then remove it to do the finish work. One tip that I got from a friend of mine who had spent his whole life working on boats was that the front of the bimini needs to be lower than the back. Without this slight downward slant the bimini will look like the front is much higher than the back.

    Good luck with your project.
     
  8. jimbo2010
    Joined: Sep 2010
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    jimbo2010 Junior Member

    Chuck what weight cloth did you use?
     
  9. Chuck Losness
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    Chuck Losness Senior Member

    This is how my friend and I made the top. A 4x8 sheet of plywood turned out to be the perfect width, 4', in the fore and aft direction. My top has two bows, 3/4" OD. First the bows were laid on the dock and the forward bow was bent slightly to match the aft bow. The dodger had support struts going back to the cockpit combing which you can see in the above picture but no supports going forward. Front supports were made by a local stainless shop. The front supports are hidden by the canvas in the above picture. The bows were positioned so that the front bow was slightly lower than the aft bow. Sorry but I don't remember by how much. The aft bow was positioned so that there was 6' head room. This gave me standing headroom.

    A hole for a 10x24 machine screw was drilled on centerline in each bow. Both pieces of plywood were centered athwartship on the bows and positioned so that the front edge over hung the front bow by 3". The plywood was held in place by a 10x24 machine screw through each bow. The bottom piece of plywood was bent to follow the curve of the bows and held in place by simple u brackets. I wasn't concerned by having screw holes in the underside of the plywood because I planned to paint the underside. Epoxy thickened with cabosil was spread between the pieces of plywood and starting at the center and working out the top piece was screwed to the bottom piece. We only put screws along the outer edge of the plywood. Some clamps were used to help keep the plywood together while the screws were driven. Time for lunch. After lunch we worked on the the curves at the outer corners. We taped paper to the plywood and drew the curves on the paper. Then cut out the inner pieces of the paper. The white paper against the plywood gave a very good visual on how the top would look. We worked on this all afternoon. We first determined how wide the aft corner of the plywood needed to be to afford convenient access from the cockpit to the side deck. Next was the front corner which needed to be narrower than the back edge both for access and to look right visually. A large pot was used for the curve at the back corner and the largest mixing bowl that we could find was used for the curve at the front corner. The front edge was curved to match the curve of the front bow and the back edge was curved to match the curve of the back bow. This took most of the afternoon. Done for the day.

    The next morning we drilled a hole for a 10x24 machine screw as far out as we could to where the plywood still touched the bows and screwed the top to the bows with 10x24 machine screws. Fender washers were used under the screw heads on top and just nuts were used on the bottom. The screws were broken off and filed smooth. Six 10x24 machines screws hold the top to the bows. We removed all of the screws holding the plywood together and the u brackets. The top was cut to the lines we had drawn the day before and the edges were rounded using a router. A layer of 6 oz cloth was set in epoxy over the top. The weave was filled with epoxy thickened with cabosil. Done for the day.

    I was on my own after this. Removed the top from the bows and applied two coats of epoxy to the bottom of the top. The mahogany looked so nice that instead of painting I put on two or three coats of varnish on the bottom side. The top was painted with Seattle Grey paint. This held up for years with only an occasional touch up with varnish and paint. Last year I removed all of the solar panels and painted both the top and the bottom with Seattle Grey paint. Probably good to go for another ten years.

    I have probably forgotten something but this is how I remember making the top.
     
    Last edited: Jul 14, 2019 at 9:33 PM

  10. jimbo2010
    Joined: Sep 2010
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    jimbo2010 Junior Member

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