Fiberglass help & information

Discussion in 'Fiberglass and Composite Boat Building' started by Moonshine, Feb 7, 2012.

  1. Moonshine
    Joined: Feb 2012
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    Location: Palm Coast

    Moonshine New Member

    I am a new member, and hope I am posting in the right section,
    I would like to cut a hatch into an existing fiberglass cockpit floor.
    Stage 1, I propose to mark out and cut the hole in the floor.
    Stage 2, I need information regarding the edges, if possible I would like to reuse the existing piece that I cut out as the hatch, or would it be more practical to mold a new hatch?
    As the deck and hatch piece will have plain saw edges, I want to build some form of mating lip on both sides.
    I am concerned about making these lips, am I going to need some sort or form for these, what would members recommend I use?
    I can’t seem to find anything with the right profile; I am favoring a u section on the deck section and an inverted u on the hatch, I had a power boat with hatches that had a lip that seated on a rubber seal in a u section that worked well.
    n--------n hatch
    u------- deck
    How would you advise I construct these?
    Would fiber glass alone be strong enough? Or would I need metal inserts. And if so can I use mild steel or aluminum encapsulated?
    would the form have to add strength or just used to form the profile.
    I have hand laid fiberglass in the distant past, but never done any mating new to old fiberglass, I am concerned about the strength of the joins
    I don’t have a problem with the span or anything else just deciding on the lip is my problem.
    Idea would be to purchase a custom hatch inner & outer frame but have no idea of where to start on that,

    I would like the recommend fiberglass build hopefully to finish with gel-coat.

    any help or advice would be really appreciated


  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    What is the purpose of this exercise ?
  3. Moonshine
    Joined: Feb 2012
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    Location: Palm Coast

    Moonshine New Member

    What is the purpose of this exercise ?

    The purpose is to simplify access to the engine room, current access is below the cockpit via gangway.
    But its meant to be a study in general of hatch fiberglass edge design and bonding techniques.

  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    You could bond from below, all laminate, forming drip edges, hatch lands, supports, etc., leaving the textured (assumed) cockpit sole surfaces, relatively intact. You would need to ease the sawn edges a bit, but with some care and well placed masking tape, you could have a nicely rolled edge on both the hatch and surrounding sole. A little paint on these edges and it'll look pretty much like it did, except with a flush hatch.

    The hatch lands and sole supports would have to be worked out, for practicality and stiffness, as would a sufficient perimeter drain for the hatch, so you wouldn't flood your engine bay after a boarding wave or wash down.

    Techniques would vary to a degree, depending on the situation. The edges of the opening and hatch would be tapered down and reinforcement, supports, drip rails, etc., built up from laminate. You could also incorporate dimensional lumber and or sandwich construction, to save some laminating. A 1x2 bonded on edge, to the perimeter of both, would go a long way toward restoring the stiffness issue, for example.

    A lot depends on how much room you have for these additional materials, your skill set, tools, familiarity with the various techniques, etc., etc., etc.
  5. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    This is not an easy job with the engine in place as you can not get at the under perimeter of the cutout. Here's how I would do it. Remove the engine before hand. The area you select to cut out should be flat on the underside say 2in. beyond the perimeter of the cutout to allow the attachment of the support lip (outlined by the dotted line and the crosshatched inner area on the drawing. You might have to grind some of the rough underside of the existing area smooth depending how even they laid it up at the factory. If the support lip can be installed, (slid from the cabin approach in one piece then you can make it up in one piece. If not make it a two piece unit cut mid point on the short dimensions. The support lip flange can be glassed up on an MDF mold of the same shape. Simply glass it up in layers on top of the MDF --pop it off and trim the edges. The MDF mold surface should consist of two levels. The area under the floor should be say 1/8 or so thicker than the cross hatched area to compensate for the thickness of the hatch to opening rubber gasket. That way when the gasket is laid on the supporting lip and the hatch is bolted in place the cockpit floor to hatch joint is level. I would mix up a batch of thickened epoxy resin and use it as a glue to fasten the support flange lip to the bottom of the floor cutout. In addition i would bolt it in place using carriage head stainless bolts. Add some 5200 under the head flanges. Dont overtighten the fasteners and create a starved epoxy glue joint. Simply clean up the squeezed out epoxt with a plastic broadknife and wipe up with acetone creating a smooth filled in joint. I would use mechanical fasteners in addition to the thickened epoxy because i don't think the epoxy would be strong enough alone. The flange lip has to support the wieght on the hatch which could be a cockpit full of water as well as any crew in it up to their knees. I would also fasten the hatch down with low profile torx pan head machine bolts. The nuts should have 1/8 dia. rod welded to them in wing fashon and glassed in to the underside of the flange.Possibly you could find these specialized nuts made up. The idea of the wings is to make sure they don"t break out and free turn when you're removeing the hatch fasteners from above. With a little radius sanding on the cut edges and a little paint as suggested by PAR it should look ok. Fastener heads will be showing but if spaced and lined up they shouldn't be too offensive. This is just one way (my way to do it) I'm sure other people will also have some good ideas--- Geo.

    Attached Files:

  6. Moonshine
    Joined: Feb 2012
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    Location: Palm Coast

    Moonshine New Member

    Thanks for the info,
    I was expecting to bond from below, as you suggested.
    I have seen badly bonded repairs that have come apart at the bond point, can you suggest a mix or product to assure a good bond.

    also on the deck edge/perimeter drain I wanted to form a solid (as in strong) channel that would mate with same profile but inverted on the hatch.
    Rather than trying to form the channel freehand I wanted to insert some form of profile to carry the early coats of wet fiberglass.
    Assuming I have a good bond to the old fiberglass, and I was to sit a light metal profile on it, what type/size fiberglass should I use? cloth / chop
    and what resin mix?
    are several thin layers considered to be better then a few thick ones?
    is there a chart the tell how many layers to the 1/4 inch?

    I am looking for a procedure, something like...
    grind/ clean of old surface and prepare
    use xxx or resin mix to wet down
    1 layer x oz cloth whetted with xxxx resin mixture
    5 layers of x oz chop/cloth
    1 layer of (fine?) to build up to a paintable finish for
    paint or gel-coat

    also I see a type of powder added to the resin to make a filler type compound, what is that powder called?
    I need someone in the trade to tell me what are good brands and where to buy.



  7. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    Hard to understand what the hatch is for. and its size...

    Hatches are complex and the whole assembly should be fabricated on the workbench.

    One way to set a flush hatch into a solid laminate cambered cabin house or cockpit is to first take a mold off the inside of the deck.

    cover the underside of the deck with brown mylar packing tape as a mold relaese .

    cover a thin piece of plywood with plastic sheet.

    Lay several layers of mat and cloth on this sheet of ply, impregnate, then Jack it up into the hatch position and bond it to the understide of the deck.

    Once cured remove this lamination and use it as a form to build your hatch subframe and waterways onto.

    Cut the deck hole to the finished hatch demensions.

    The finshed hatch assembly , with its six inch or whatever is suitable ,perimeterr flang will then be epoxy bonded to the underside of the deck.

    Ive only used this technique for small cabintop flush fit hatch frames and windows.

  8. viking north
    Joined: Dec 2010
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    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    Moonshine i think you're design vision of U shapes and draining channels is far too complicated for the average person as yourself who doesn't have a good working knowledge of this product. The other design feature of your cockpit floor I overlooked was: Is it cored. If so this creates another Pandoras box of design and proceedure problems to overcome. If the cockpit floor is solid and of a sufficient thickness min. 1/2in. the proceedure I posted is the least complicated. However after re-reading you post I have reservations on your experience to tackle this job.(no insult intended, we all have to learn) I was assuming you had already surveyed the structure or had it surveyed by an experienced or qualified person on the feasibility of the modification. If not have this done before moving any further. If the structure is solid glass and heavily built in the form of a large flat area to facilitate the cut out, no big deal as per my prev. post. At that you still might need some structure re inforcing. If it is cored or lightly built using glassed in supports or shaped for strength you have a bit of a hornets nest on you hands. On second sober thought if you are determined that you need this mod. Have a designer or an experienced builder look at it and hire an experienced glass worker to give you a hand.---Geo.

    PAR you old owl reading between the lines, I have learned another piece of wisdom from you posts, a little more on tecnical, a little less on details is a wise, look before you leap, message. :)
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