How To? Hard Top Dodger/Bimini

Discussion in 'Fiberglass and Composite Boat Building' started by aybabtme, Apr 22, 2020.

  1. aybabtme
    Joined: Apr 2020
    Posts: 7
    Likes: 1, Points: 3
    Location: California

    aybabtme Junior Member

    Hi folks, new here. I have something that will probably come across as a stupid idea, and I'm very ignorant of all things composite. Please don't call me names! I'm mostly trying to learn and have some fun. Here's the TL;DR of what I'm asking, if you don't want to read all the details:

    How you would build this piece? I'm thinking of using a foam core (PVC, urethane or ??) that I'd trim, glue together and shape by sanding, and then do a handlay of fiberglass (I don't know anything about selecting weights, types of clothes and overall thickness). I want to be able to walk on the bimini to access the boom (and clean the solar panels on the arch). I have never done fiberglass/composite work before and want to learn. I've watched some YouTube about it and that's it.​

    The Details:

    I've had in mind for a while to fabricate a hard top dodger/bimini to add to my boat. The goal are (in order of priority):
    1. To learn how to build something significant in fiberglass.
    2. To make the cockpit more comfortable at anchor.
    3. To make the cockpit more comfortable when sailing in bad weather.
    4. To add more surface for solar.

    (updates) A few things I forgot to add in the original post:
    1. I want to design the thing so it's easy to remove, if an eventual purchaser wants it gone (I designed the solar arch this way).
    2. It should be cheap, and light (too much weight on the stern already).
    3. I'll be custom making solar modules on the top surface of the dodger/bimini (using flexible SunPower cells and probably ETFE for lamination). So far, I consider this a separate project, since the solar modules will have at most a 10y lifespan before needing replacement. I wouldn't want to have to redo the dodger/bimini just because the solar panels turned bad.


    I'm talking about a dodger/bimini because I have in mind something that is like a dodger, but with a very long "tail", which would usually be covered by a bimini. Basically a pilot-house without walls? Here's the initial CAD sketch I made for it (it's missing side windows and support poles at the back):

    [​IMG]
    It's about 0.9cm (35") in height, the width is ~2.40m (96") and the length of the top surface also ~2.4m (96"). I've built a mockup with 2x4 lumber and some plywood panels to test it out while sailing, and the current mockup looks like this (say hi to my last learning experiment, the custom stainless steel solar arch):

    [​IMG]
    It's pretty high and big. Not pictured here is the panels I added to the frame, to simulate windows and "walls". When I went to sail with it, it was obviously a bit bulky, but it worked out just fine in the end and the cockpit felt a lot more cozy. Upwind sailing was noticably slower, but I eventually got it sorted out to a point where I was satisfied with my speed. Things I learned from it:
    1. My windows should be removable to reduce windage: I'd put either soft windows that can roll up, or hard windows that would lift up somehow.
    2. The traveller was much harder to work with.
    3. I don't think I need a window to peak at the mainsail on the top, I managed to handle my mainsail just fine without it.
    4. I'll probably make the final structure 1 or 2" lower to leave more clearance for the boom (it's pretty flush).
    Recap:
    How would you build this?
     
    Last edited: Apr 22, 2020
    DogCavalry likes this.
  2. bajansailor
    Joined: Oct 2007
    Posts: 1,161
    Likes: 304, Points: 83, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum Aybab.
    This looks like a very interesting project. I am sure that we will all take a keen interest in seeing it progress.
    Fallguy on here will hopefully be along soon - he has a lot of experience of cored composite construction (he is currently building a 32' Skoota power cat) and I am sure that he can give you some useful advice.
    What is the current headroom under the mock-up that you have built? And how tall are you, or the tallest member of your crew?
    I am thinking that it would look a lot better if you could reduce the overall height by a few inches at least.
    It will also look less 'bulky' if the side windows are 'soft' rather than 'hard'. In the same fashion as so many powerboats of similar size - they have 'soft' isinglass wheelhouses (for want of a better word) with tubular aluminium frameworks which do not stand out as much as a 'solid' wheelhouse would.
    I am wondering if it would be possible to increase the angle of the port and starboard front windows relative to the centre window, so that they are 'swept back' (in plan view) a bit more?
    Could you post a photo or two showing the current arrangement of halyards, winches, jammers etc port and starboard of the companionway please?
     
    Last edited: Apr 22, 2020
  3. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Senior Member

    First thing to keep in mind is that the dodgers walls need to angle more inwards then the cabin sides do. This is so that it looks "right".
    Seeing that you can already bend and weld stainless I would say do support structure with pipe and put a composite panel on top. The sides I would make out of sunbrella with PE windows.
    What goes on the top panel? Rigid solar panels and 100kg of crew?
    Panel can be PVC foam with fiberglass or carbon, or plywood/beam-foam/plywood, or aluminium plate.
     
  4. aybabtme
    Joined: Apr 2020
    Posts: 7
    Likes: 1, Points: 3
    Location: California

    aybabtme Junior Member

    Thanks folks! A few things I forgot to add (I'm updating the original post for future readers):
    1. I want to design the thing so it's easy to remove, if an eventual purchaser wants it gone (I designed the solar arch this way).
    2. I'll be custom making solar modules on the top surface of the dodger/bimini (using flexible SunPower cells and probably ETFE for lamination). So far, I consider this a separate project, since the solar modules will have at most a 10y lifespan before needing replacement. I wouldn't want to have to redo the dodger/bimini just because the solar panels turned bad.
    Thanks!

    I'm 6ft and I currently need to bend to fit under the mock-up. I could remove maybe 6" before it gets really annoying. For some reason I have many measurements but I don't have the "cockpit floor to ceiling" one. I'd say it must be about 60", since the boom is usually just at the right height to knock my head right off my body..!

    I think I understand what you mean, would that look similar to the CAD model I shared? Hard front windows, soft side windows? If you have some links to wheelhouses you have in mind, that'd help me visualize better.

    Do you mean, similar to the CAD model? If so, I agree. It reduces the surface available for solar, but it would look a lot less bulky.

    Here's more pictures that I cropped from videos/previous pictures. I'm 1h30 away from the boat right now so I can't get fresh pictures.

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]




    I'll experiment with that, I'd like to reduce the "bulky look" a bit. However if I have to make the decision, I'll maximize surface area for solar at the sacrifice of aesthetics.

    I'd like to do this part mostly using composites. I've had my fill of metalwork, and I can only do it from a shop that's quite far from hom, which is going to make my wife unhappy. =P

    That's about right! Worst-case scenario if using off-the-shelf rigid panels, I expect about 70kg worth of panel in there. Quite a lot less if I make custom flexible solar panels to fit on it (which is my plan).

    Which would be the cheapest/lightest? The stern is already quite heavy from the arch + dinghy setup, I want to minimize adding more weight (I'll also probably revisit the arch/solar one day to shed some weight there).

    Would it make sense to try to do this project in multiple part, using vacuum bagging or vacuum infusion (I'm looking for an excuse to learn this as well)?
     
  5. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Senior Member

    Cheapest and lightest don't go together. Cheapest is ply/XPS/ply with some wooden frames. Lightest is carbon/PVC foam/carbon.
    To be removable the dodger needs to only be bolted to the boat at a few points. Can you make such a structure to be entirely composite panels? Yes, but it's easier with pipe the way I described. You could use carbon tube for it.
    If you want infused panels I would infuse flat panels on a table or buy them premade. Then it's stich and glue, sand and paint.
     
  6. aybabtme
    Joined: Apr 2020
    Posts: 7
    Likes: 1, Points: 3
    Location: California

    aybabtme Junior Member

    I figured there's a spectrum where you can get something light that's 80% of the way, while being reasonably affordable? Maybe using a cheaper foam core and fiberglass? On that end, I'm not sure what sort of foam and sandwich is needed to support the weight I envision. I like the idea of getting premade panels/components where it works, assuming I can find a source locally (shouldn't be too hard in the SF Bay area?).
     
  7. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Aluminum tubing and fabric/isinglass really fits the bill here, especially in terms of weight.
    If you’re dead set on fiberglass, do as Rumars suggests above, flatmold panels, stitch/glue together, flange at bottom to bolt on.
    I’ve done projects like yours utilizing a build in place female mold of Mellamine, but that’s really a lot of work and extra materials, doesn’t seem justifiable for your project.
    Do keep weight in mind, it is a safety consideration, as well as performance.
    The pictured solar/dingy davit structure looks extremely top heavy, Will that be coming down?
    Or redesign it to incorporate your dodger?
    My crystal ball is seeing a bigger boat in your future!
     
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  8. aybabtme
    Joined: Apr 2020
    Posts: 7
    Likes: 1, Points: 3
    Location: California

    aybabtme Junior Member

    So something like cutting pre-made sheet stocks like this fiberglass/foam panel? Sandwich Panels | Fiberglass/Foam Sandwich Panels | ACP Composites https://store.acpsales.com/products/2343/fiberglass-foam-sandwich-panels

    Or something else? These panels look pretty expensive.

    The solar panels are indeed very heavy up there (150lbs total), I'd like to replace them with lighter flexible panels down the line. For now, they're doing fine.

    Yup, in 18 to 24 months, we'd like to get our hands on a ~44ft catamaran. The goal with this current boat was always to learn what can be done system-wise: what sort of system/customization we care about, how can we have an entirely electric setup (galley, water heater, AC/heat, watermaker) without using an alternator/generator as much as possible. It's a learning platform to test out a bunch of ideas for us, while having fun on the weekends and becoming better sailors. We're staying mostly inside the SF Bay, so I feel it's a good place to make mistakes, we're never too far from help if we end up way out of our depths. And I get to learn how to DIY things I never thought about before. Hopefully that'll make things easier in a couple years when we're cruising.
     
  9. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    You could lay up your own fiberglass panels, it just requires a smooth, flat surface like a Formica covered tabletop.
    If you’re just looking to get some hands on experience with fiberglass, you should start with small projects like a dock step or a cooler, or something else that’s useful, but less complicated.
    Again, though, this method will add weight and complexity, reduce visibility and hinder access to the foredeck.
    Having easy access to all your sail controls is necessary to sail safely, and you have already stated that the traveler is restricted, Not good!
     

  10. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    "Yup, in 18 to 24 months, we'd like to get our hands on a ~44ft catamaran."

    In view of this event which will be happening fairly soon, if I was in your shoes I would be reluctant to start making drastic changes to your Hunter.
    She is a pretty sailing yacht without all the additions, and (to be blunt) the extra appendages do not really help to improve her looks.
    Fine if you intend to keep her for the next 10 or 15 years and you want to go cruising with her, but you might well find that that the wheelhouse structure that you (eventually) build will hinder rather than help the sale of the boat.
    Unless you plan on removing everything (including the solar arch and dinghy davits) when you come to sell the boat?

    A cat will be a totally different set up again - you will probably have a MUCH larger bimini to play with for installing solar panels, and the spray dodgers are often just positioned around the helm console poking out above the bimini.
    Maybe best to concentrate on improving your sailing and navigation experience with the Hunter - these can all then be applied usefully to the cat when you do acquire her?
    (Do you have a particular type of cat in mind yet?)
     
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