Newbie questions (swim platform)

Discussion in 'Fiberglass and Composite Boat Building' started by freddagg, Aug 17, 2018.

  1. freddagg
    Joined: Aug 2018
    Posts: 4
    Likes: 0, Points: 1
    Location: Sydney

    freddagg New Member

    Hi all,
    I am new here - complete novice.

    I want to have a go at making a swim platform for the rear of my 7.0m (23') cruiser. The boat is 20+ years old and the original manufacturer of the swim platform no longer has any moulds

    The design is such that half of new platorm will be supported by an existing smaller platform already moulded into the rear of the boat with the remaining half being cantilevered.

    On other boats on this same model, the cantilever may be supported by by 2 struts - but usually it is not.

    The platform is not in contact with the water when stationary or moving forward (on or off the plane). It does get wash over it when coming off the plane but drains away very quickly.

    I am thinking I have 2 options:
    A) Make up a timber platform from 6mm (1/4") marine ply encapsulated in fibreglass,
    or
    B) Make up a simple mould and manufacture 100% fibreglass


    From what I have been reading, I see the following issues
    Option A) Plywood
    1) I need to glass both sides - but will only need 2 layers on each side
    2) Glassing both sides will require me to turn the timber over
    3) Wrapping glass over/around the 6mm (1/4") edges will add to the overall width. As the new platform must fit inbetween the vertical faces of the existing transome, what deduction in timber width should I allow?

    Option B) Mould
    1) Sounds the simplest and easiset to fabricate
    2) All the layers applied from the same side - I don't need to turn the platform over
    3) What thickness / number of layers would I need?
    4) If thickness is a problem I might try to stiffen by encapsulating pieces of ply but I would be concerned about adhesion to the underlying laminate (top laminate would be OK)

    I would prefer to fabricate from epoxy and paint with 2 part polyurethane paint. I don't want to bother with gel coating
    It seems expensive to try and create a non-slip pattern in the glass so will probably paint a surface or use the stick-down anti-slip surface material

    Any suggestions / guidance will be appreciated

    Thanks
     

    Attached Files:

  2. BlueBell
    Joined: May 2017
    Posts: 1,039
    Likes: 158, Points: 63
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Welcome to the forum.

    I guess you've looked for a used, production one from a wrecked model?

    How about someone who's made a mould and can sell you an after-market swim-grid?

    You didn't mention what boat you have...

    And you didn't mention why... perhaps a smaller platform would suit your needs?

    You've listed several pros and cons but only you know which method is best for you based on oh so many variables.

    Are you sure you want to have this hanging off your transom?

    I once saw a swim grid slide an inch under the fuel dock in Victoria harbour while fueling.
    A seaplane landed nearby and sent out a two foot wave as it transitioned from planing to displacement mode.
    When the series of waves reached the dock, they lifted the hull and pushed the grid down with enough force to push all the supports right through the transom flooding the hull. The boat sank. I'll never forget that sight, the cause and the anguish on the owners face.

    To answer your question, finally, I would choose Option A.
    1.) No biggie
    2.) I don't get it... so you have to turn it over...
    3.) I would allow slightly more space than the manufactured unit.
    Attaching a 1" x 2" trim edge, vertically, would add strength and give you room to radius (fillet) as glass wont do sharp corners.
    You could also run a few 1x2 stringers (vertically) on the bottom to add strength as well, radiusing all the corners.
    If your glassing both sides, thinner ply may be sufficient.

    Clean sand may be sprinkled on uncured surface finish to give non-slip.
    Paint over top.
     
    Last edited: Aug 18, 2018
  3. Blueknarr
    Joined: Aug 2017
    Posts: 746
    Likes: 131, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    Welcome.

    All of the platforms are supported with struts. Some internally others externally.

    Moulding will at least double material expenditure and triple labor requirements. Moulds are only profitable if multiple copies desired.

    What is the problem with flipping plywood over?

    Have you considered using solid wood?
     
  4. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Go solid wood.

    Might find one at a boat salvage yard that needs slight mods. Teak is about 25$ a bdft here.

    Moulding is a definite no thanks. Lotsa work for a one off.

    Plywood has too much opportunity to delam there.

    Finish is up to you. Teak can go to gray.
     
  5. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    What is the aversion to turning something over?
    It's not clear what you're planning, but a mold for this could be as simple as plastic sheeting covering a piece of plywood on sawhorses, with a simple frame screwed to it and clay fillets or caulking to round the edges.
     
  6. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    I was thinking the ones with all the openings like hardwood.
     
  7. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Something like this? That does look pretty simple and easy to do.
    [​IMG]
     
  8. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Yes. You get more points than me, I sort of took it for granted the OP would understand.

    I don't know if you are being sarcastic, but it would be easier than building the same thing with a mould and looks a wee bit nicer than all glass, imo.

    The construction isn't too bad really, you just use G2 for joinery on these. The first part is made to fit the boat (with a jig) and the rest of the parts added and kept flat on a plastic sheet on a table. You just keep adding parts and clamp at each spacer location (x4) with a 2' pipe clamp and some weight to keep them down. Once glued together, you bandsaw and router around the outside edges top and bottom for radiuses and the part is done save fastenings and finishing. I have watched a few guys making them, but never needed one myself.

    Of course, the teak isn't free. At $25, bdft, that looks like about ?15 bdft or let's say about $300 in teak. Gorgeous when done.
     
  9. freddagg
    Joined: Aug 2018
    Posts: 4
    Likes: 0, Points: 1
    Location: Sydney

    freddagg New Member

    Thanks for your comments.
    Yes I have been looking for a wrecked boat for over 2 years.

    The boat is over 20 years old. The extension in the photos was an original option by the boat manufacturer (Whittley). They now longer have the moulds.

    I have been quoted A$5,000 to have one made and fitted but this is ridiculous.

    I have sourced an aftermarket one from USA and one from Canada but with freight, exchange rates, duty etc. they run about A$3000, so i figured i would have a go myself.

    I was concerned about the time to turrn it over. If i had to wait until it was cured on one side it would be difficult to bond or wrap the edges. I thought new layers had to be put on whhile the resin was still tacky. I imagined it would be easier in n a mould just laying up from one side.

    I was intending to stiffen as your suggestions

    Any ideas on number of layers, weights etc.?

    Thanks again
     
  10. freddagg
    Joined: Aug 2018
    Posts: 4
    Likes: 0, Points: 1
    Location: Sydney

    freddagg New Member

    Not sure my woodworking skills are up to makind a teak deck.
    My biggest problem would be making brackets an fixing to the rear of the boat. Access in there will be aproblem.

    A glass one will allow to cantilever off the small platform already moulded in the rear of the boat and be much easier to fix. It will still be bolted and access at that point is a breeze. This is what the original boat manufacturer did (but they no longer have moulds for either the boat or the platform)
     
  11. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    If you insist on glass; make a template out of cardboard and blank it out in 3/4" plywood.

    Use a router and put a 1/4" radius on all the edges, top n bottom.

    The glass will not wrap easily around the edges so you need to expect that.

    I would use a 17 oz no mat glass.

    I would probably use an electric planer and put a 2" wide rebate or relief on the top edge. It should be about 0.100". That way you can laminate the bottom and bring the bottom glass around. Let it cure and sand out imperfections; then glass the top and fill the rebate with fairing.

    This is the simple version. If you need edges done like the picture; you need to consider that as well.

    Epoxy here. Any holes in the glass will allow ingress and rot the platform, so a few overcoats of epoxy can't hurt.

    Plywood needs to be precoated to avoid dry sucking the laminate of resin.

    This is not a very complex project.
     
  12. BlueBell
    Joined: May 2017
    Posts: 1,039
    Likes: 158, Points: 63
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    You're welcome, glad you found it helpful.

    No idea on the number of layers.
    It depends on what weight you're using.
    I'd use thin ply, just keep layering until you're comfortable with the level of rigidity.

    For turning, you could drill and screw in a #6 screw at each end at the balance point and suspend it.
    Simply rotate the slab, and point support it from underneath to work on the other side.

    Looking again at your pictures:
    How about just a simple aluminum extension bolted to the existing platform?
    You could pepper it with holes to make it lighter, quick draining and non-slip.
    Welded stringers underneath.

    I'd sure lean towards an undersized, pre-made grid and just bolt it on.
    But, I'm not you, nor is it my boat.
     
    Last edited: Aug 19, 2018
  13. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    Those varnished strip built platforms are just awful. They are almost impossible to maintain (you have to varnish them every few years and with all the slots it's impossible to sand them properly and prep them). You have a sterndrive so your transom should already be pretty beefy. Some inboard boats need transom reinforcement when doing a project such as yours. Cantilevering adds a lot of stress and there is an engineering concept called moment-arm. Lift a 5 lb weight with your arm out stretched versus bent at the elbow and you'll see what I mean. I'll post a link to a thread that I started a few years ago when I built and installed a platform for my small cruiser. It might give you some ideas. There were a number of people who thought that a solid platform would cause problems in rougher water. I haven't had any problems. Aside from a couple of insignificant scuffs, that are easily repaired with a little epoxy, sandpaper and some paint, maintenance is a breeze.

    Keep in mind that my platform carries a LOT of load as well as twisting forces from the use of the outboard. Depending on your usage you might not need quite as much support.

    New swim platform for a 1973 Silverton Sedan https://www.boatdesign.net/threads/new-swim-platform-for-a-1973-silverton-sedan.56033/
     
    Last edited: Aug 19, 2018
  14. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Varnish on teak?

    Wood platforms look better than glass, imo.

    But I agree the maintenance is generally less on the glass. Just paint when the boat gets done.
     
    BlueBell likes this.

  15. missinginaction
    Joined: Aug 2007
    Posts: 793
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    Location: New York

    missinginaction Senior Member

    Up here most of the platforms I see are mahogany. I suppose you can just let teak weather but with the exhaust being there and the proximity to the water whatever kind of bright finished or unfinished wood that's used gets ugly rather quickly. That's why I like 2 part LPU paints. They're so hard, at the end of the season I just have a go at that platform with some Softscrub cleanser and I'm good for next season.
     
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