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Old 20-07-2018, 06:49   #1
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Installing hatch on sandwich deck

So on my boat(Rainbow42) there are no deck hatches(Lid to store ropes etc..) which are really unpractical. So now I am going to install some, however the deck is sandwich, glass with 30mm divinicell core, so how do I best install a hatch?


* Drill a hole with a 10mm metal drill bit
* Then put on a metal blade on my ryobi jigsaw, cut it out.
* Then add tec7 to the lip and put in place
* Drill holes(6mm metal drill bit) for the lip and install screws
* Wait 24 hours and then ready to use?

Or do I need to fiberglass divinicell edge before gluing it in?

link to my hatch:https://www.maritim.no/abs-luke-355-...-#.W1Hn6dUzZaQ
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Old 20-07-2018, 07:11   #2
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Re: Installing hatch on sandwich deck

You must remove. The core around the opening and make the deck to inner skin both waterproof and structural. I believe you can find how to video on YouTube or We$t Marine.
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Old 20-07-2018, 08:58   #3
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Re: Installing hatch on sandwich deck

The question was how to make it watertight, is the tec7 and the plastic edge on hatch enough or do I need to something in addition
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Old 20-07-2018, 11:04   #4
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Re: Installing hatch on sandwich deck

If the hatch frame completely covers the exposed deck edge, then properly bedding should be OK, as long as there's sufficient material for fastening.
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Old 21-07-2018, 08:15   #5
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Re: Installing hatch on sandwich deck

We recommend routing out the exposed core about an inch deep and filling the resulting channel with thickened epoxy. Cabosil or fumed silica works well in these situation because the putty it makes is resistant to sagging.
I read your note indicating that your inquiry is about waterproofing, but with the skins and the cores no longer firmly connected/separated, the skins may deform as you tighten down on them, making a good seal almost impossible. In addition, over time, water will penetrate the deck to hatch seal, and if the core is exposed, delamination will take place and the strength of the deck will be severely reduced.


It's all in the preparation.


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Old 21-07-2018, 09:28   #6
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Re: Installing hatch on sandwich deck

There have also been MANY cases of the deck getting floppy due to the material removed to install a big hatch. The hatch does NOT add support. Have sister boats added hatches? How do we know the designer allowed for this?



It can be beneficial to add a laminated reinforcing ring on the inside. I've done this a few times. Look at big oil tanks; it's in the code. It all depends on the safety factor.


Replacing a hatch is different, even if a slightly different size. This is what most posts and videos describe. If I were the designer, I'd want to know if someone was planning to cut a 2-foot hole in my boat.
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Old 21-07-2018, 11:43   #7
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Re: Installing hatch on sandwich deck

Quote:
Originally Posted by JOHNMARDALL View Post
We recommend routing out the exposed core about an inch deep and filling the resulting channel with thickened epoxy. Cabosil or fumed silica works well in these situation because the putty it makes is resistant to sagging.
I read your note indicating that your inquiry is about waterproofing, but with the skins and the cores no longer firmly connected/separated, the skins may deform as you tighten down on them, making a good seal almost impossible. In addition, over time, water will penetrate the deck to hatch seal, and if the core is exposed, delamination will take place and the strength of the deck will be severely reduced.


It's all in the preparation.


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This^^^^^ +1
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Old 21-07-2018, 14:02   #8
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Re: Installing hatch on sandwich deck

The top and bottom skins constitute a structural couple but only if well attached to a shear layer, the core. Once the penetration is made, the integrity of the bonds of skins to core are compromised. There must be a structural connection added. For this, remove core all around the cut edge and add structural filler to both seal and bond the skins together as noted by others. I prefer to use glass and epoxy jammed in. Leave a gap to fill with Cabosil or other material. I suggest the glass epoxy packing to be a width at least two times the gap height. The sealer should be about even in width and height. Consider that you will likely bolt through the hatch and both skins so you want solid material to prevent crushing core and distorting the deck. It is a given that water will eventually find its way to the edges of your deck cut out so preventing water from entering the core is critical.
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Old 21-07-2018, 17:10   #9
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Re: Installing hatch on sandwich deck

I would never fit hatches unless to improve living space light and ventilation.. Instead, I would install deck lockers on a cruising vessel. They double as seats and spray deflectors, and can be lockable and keep equipment dry.

However, if you must proceed, the foam has to be replaced where the hatch base bolts to the deck, and the deck itself has to have reinforcements in layers of glass above and below the deck where the hatch frame will land. I buy rolls of heavy glass bi-axial or tri-axial tape--one wide band with a smaller one on top both sides. it is VERY strong. Overlap the two layers when making the square around the hatch opening. While wet, cover them with Peel Ply, then roll them flat all around where the frame is to land, saving a lot of sanding later.

The foam has to be replaced with the same thickness in plywood. Lots of luck chiselling it out, and finishing the job with a divot so that the foam remaining has a groove to take the taper of the plywood replacement where the frame must be bolted.

The reinforcements added to the deck glass must extend beyond the plywood insert, and be glued with epoxy glue such as Araldite or any good resin mixed with cabosil and a slow hardener. Get as good a fit as you can, then add glue with a syringe, push in the ply allowing the resin to squish out above and below the plywood, which should of course have been treated with an epoxy penetrating timber preserver after shaping it and before fitting it.

All you need do once the epoxy has cured is to pull off the peel-ply and if necessary, sand the edges of the tapes to a fine taper into the existing structure and paint. You can even avoid much of this sanding if you use an epoxy fairing compound and fair the edges with it. All it needs then is a slight sanding and paint.

I use a dust extractor on my sanding machines. Spicules of glass are the last thing one needs on skin or in lungs and eyes.
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Old 21-07-2018, 20:15   #10
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Re: Installing hatch on sandwich deck

I'm with Thinwater. My recommendation would be to contact the N.A who designed the boat. Failing that, at least discuss it with a N.A. & yes, you'll probably have to pay for his advice.
I knew of a fellow bought a Vega 27' & later decided he really needed a 30 footer. He cut the Vega athwart the center & realised he had bitten off more than he could chew. He then went in search of a boat builder to add a 3' section in the newly created space. He was unsuccessful in his search because no self respecting shop would do the work unless it was designed & approved by a N.A. or professional yacht designer . . . His wife abandoned him & he abandoned the project. The Vega became SCRAP & I purchased the hardware, spars & sails for very few dollars, reselling them at a handsome profit.
. . . Yeah, Some mothers do have 'em don't they???
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Old 21-07-2018, 20:19   #11
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Re: Installing hatch on sandwich deck

Quote:
Originally Posted by Sailorbob8599 View Post
...My recommendation would be to contact the N.A who designed the boat...
For a 1' x 2' hatch? Come on!
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Old 21-07-2018, 21:57   #12
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Re: Installing hatch on sandwich deck

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Originally Posted by Terra Nova View Post
For a 1' x 2' hatch? Come on!
I'm not a N.A. so modify an engineered design structure at your own peril. Did you ever hear about disastrous square windows on a British airliner?
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Old 21-07-2018, 22:37   #13
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Re: Installing hatch on sandwich deck

I think there would be a lot of pissed of designers if everyone contacted them every time they wanted to install a hatch in a deck they have designed. I have installed plenty of hatches and not once has it ever crossed my mind to contact the designer.
When he cuts the hole there is probably going to be some camber in the deck that is going to need a custom ring made so the hatch can sit flat.
The hatch should come with a plastic insert for the underside so removing a bit of that foam core and filling it is no big deal. The insert is going to hide any raw filler.
For me the fastenings holding the hatch just keep it level until the sealant drys. It’s bloody hard to break a well sealed hatch out of its hole when good sealant has been used.
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Old 22-07-2018, 01:14   #14
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Re: Installing hatch on sandwich deck

Check out “Life on the Mold” video channel on YouTube. He is building a Cat to commercial specifications. In one area he had to remove core and go to solid laminate. He gives lessons on the new layup schedule and the reasoning for it (designed by an NA). Just a suggestion for how to think about the project.
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