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Old 30-03-2016, 22:54   #1
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Hatch on Curved Deck

Hi all,

Have pulled out a hatch to try to get rid of a nagging leak. Not sure of the model of hatch but it has a square deck opening of about 530mmx530mm. Hatch is through bolted onto the deck.

The deck where it is located has a slight curvature. Previously the hatch was sitting atop an epoxy "flange" which created a nice flat bed. This flange varied in thickness from about 12mm to around 2mm.

This epoxy looks like it was poured into a mould of some sort directly onto the non skid gel coat that surrounds the cut out. The bond between the epoxy and the gel coat looks like it failed almost the whole way round hence the leaking. This epoxy flange was also cracked in several places and cannot be reused.

Ok, so how do I go about mating and re bedding the hatch with the curved deck? When I place the hatch into the cutout dry, there is virtually no fill required on the fore and aft ends with maybe 10-12mm of fill along the port and starboard sides. Do I:

1. Do the epoxy mould method adding some fibre to the epoxy for some added strength. Re bed hatch onto that with butyl tape.

2. Shape up some timber and glass that over and onto the cutout surround to build up a flange. Re bed hatch onto that with butyl tape.

3. Squeeze on a heap of Sika 291, plop the hatch on and do up the bolts.

4. Any Other unknown method you are willing to share

Number 1 seems relatively straight forward but need to make sure if an epoxy over gelcoat bond is possible or recommended.

Regards to number 2, shaping a flange accurately is going to be quite a bit of mucking about and I am not experienced with fibreglass work ( but can learn if necessary)

Number 3 Obviously the simplest and quickest and need to know why it may not be the best solution. Would Sika 291 be the sealant of choice, if not, then what?

Thanks in advance for any assistance.

Winf
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Old 30-03-2016, 23:03   #2
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Re: Hatch on Curved Deck

Cut out a 1/2" plywood mould using the hatch as a template, grease the inner edge and use it as a mould to contain the Sika 291 so that you get a nice vertical edge when you emplace the hatch, give it a day or two to harden and pull the plywood mould from around the hatch and trim up the Sika with a Stanley knife.
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Old 31-03-2016, 07:39   #3
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Re: Hatch on Curved Deck

Any glue will eventually leak. You need to rebuild the epoxy flange, but this time grind away the gelcoat and build it onto the glass of the deck. Then recoat the whole thing with gelcoat before installing the hatch.
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Old 31-03-2016, 08:27   #4
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Re: Hatch on Curved Deck

I would go with option #1. I would grind off the gel coat so that the epoxy bonds to the underlying laminate. Butyl tape is a great way to bed hatches and makes it possible to remove them in the future.
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Old 31-03-2016, 09:57   #5
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Re: Hatch on Curved Deck

Was the flange original, or a previous owners idea to deal with the leaks? If not original, maybe you could find out how it was meant to be?

How often does this hatch need to be accessed? Does the water it keeps out have an easy means to leave? (I.E. the hatch is not in a cockpit sole or other well area that may have standing water for a time?)
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Old 31-03-2016, 12:48   #6
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Re: Hatch on Curved Deck

Option 2, but make the timber (teak) frame say 25 mm thicker so the hatch stands above the deck a little. Make a cardboard template of the deck curve. Mitre the corners and Bed and bolt the frame onto the deck and Round off the outside edges. Make sure you seal the mitre joints absolutely thoroughly. Also, why glass the timber over? Why not just varnish it and leave it exposed as a feature?

You might guess I have a hatch just like that on my coachroof ....
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Old 31-03-2016, 13:06   #7
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Re: Hatch on Curved Deck

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Originally Posted by Clivevon View Post
Option 2, but make the timber (teak) frame say 25 mm thicker so the hatch stands above the deck a little. Make a cardboard template of the deck curve. Mitre the corners and Bed and bolt the frame onto the deck and Round off the outside edges. Make sure you seal the mitre joints absolutely thoroughly. Also, why glass the timber over? Why not just varnish it and leave it exposed as a feature?

You might guess I have a hatch just like that on my coachroof ....
You describe the standard way that everything used to be bedded to boat decks.

Now people seem to think the whole thing has to be difficult and full of various chemicals and googes

We have numerous hatches, fittings, a chimney, and whatnot all with a wood pad fitted to the deck and providing a flat surface for the flat item to be bolted to.

Here's a pic showing wood blocking under a deck mote mounted next to a removable butterfly hatch (that also has an angled bit of wood blocking). And here's a link to pics of the install of the deck mote wood blocking as well as how it ended up looking.

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Old 31-03-2016, 13:37   #8
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Re: Hatch on Curved Deck

Would be nice to see a photo but rather than wood, why not a flange made of a thick synthetic like Starboard cut to match deck arch and bolted on the deck with something like LifeCaulk? Starboard takes paint well and new hatch can be through-bolted to deck. I'd expect that to be leak-free for many years.
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Old 31-03-2016, 13:56   #9
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Re: Hatch on Curved Deck

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Originally Posted by Don C L View Post
Would be nice to see a photo but rather than wood, why not a flange made of a thick synthetic like Starboard cut to match deck arch and bolted on the deck with something like LifeCaulk? Starboard takes paint well and new hatch can be through-bolted to deck. I'd expect that to be leak-free for many years.
I agree that on a plastic boat, plastic is probably sensible but finding a material that won't degrade or warp or cause problems in another unexpected way can be difficult. Dimensionally stable, rot resisting woods (e.g. teak, mahogany) can last 100 or more years in service aboard a yacht. How long does Starboard last? With heat or UV (even while painted the UV can get through) will it degrade over a few years? Wood is by no means perfect but many people know how to deal with it and it does last and last and last. The hatch next to the deck mote in my photo--it was built in 1930 and while it has been well varnished and taken care of some of the time since then, there was a good 40 years of abuse--no varnish, no oil, no nothing...and it's fine. Most of it's parts are 3/4" or 1-1/4" thick teak.

What is the composition of LifeCaulk? We frequently use Tremco (brand that is owned by the same as Sitka just different trademarks) silicon-modified polyurethane for bedding things to deck. It must be painted (or varnished over) because it won't last forever in UV but it does do well and had a good modulus of elasticity (unlike 3M5200 or 4200 which don't have sufficient expansion/contraction for bedding). When in doubt about how long we'll keep something on deck or we think we'll be removing to maintain, we use Dolfinite which is an old-fashioned bedding compound that works well between wood, metal, canvas, a wide range of materials. It is not adhesive in nature, bedding only, and it lasts about 10 years before drying out.
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Old 31-03-2016, 14:22   #10
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Re: Hatch on Curved Deck

I've done this exact thing.

You want to use thickened epoxy and build up the areas such that you have a nice flat surface, or the hatch will never seal.

My technique:
I cleaned off all the old 'goo, where for years, instead of building a flange, PO's had just tried to make up the space with lots, and lots, of sealant. Clean off your hatch, also.

Once everyting is clean, take your hatch and lay it where it'll go, put in a couple of the bolts to square it, and trace around the hatch so you'll know where to put your new built-up area. Take note of about how much you'll need to fill in to make it up flat.

Tape that area off, sand within your marked off area it to key the substrate for the new thickened-epoxy buildup you're installing.

Take ordinary Johnson's floor wax or some sort of release agent and put it on your hatch flange where it'll meet with the new raised-up area. This is so you can make damn sure, by using the hatch, that you'll have an exact fit.

Mix up some thickened epoxy. I used WEST System. Make your mix fairly thick so it doesn't sag nor run off. Put your thickened epoxy onto your taped-off area, and you can make a 'dam' or sort of mold out of blue painter's tape to hold in your epoxy, but you probably won't need to do that.

Gently place your WAXED hatch over the thickened epoxy, press it down a little, and let the stuff cure.

If you didn't mess up with the wax (don't be shy with it) once the mix cures, you should be able to just pop off your hatch and then sand your built-up area to fairness. Of course if you're a Tape God, you might have it already faired. Paint your built-up area if you want, or you can wait till you rebed your hatch and tape off and paint. I think it goes without saying, but you shouldn't need to sand the area where you molded the hatch flange to your buildup, although you do need to wipe it carefully with acetone to remove the release wax.

be sure to use acetone etc and get all the wax off your hatch flange, rebed, and you should have an exact fit.
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Old 31-03-2016, 15:57   #11
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Re: Hatch on Curved Deck

We make a frame, bed it in epoxy, then fiberglass it. We have a couple post with pictures showing the steps here:

http://sailingdawntreader.com/2015/08/09/forward-hatch/

And additional pics and info here:

http://sailingdawntreader.com/2015/08/09/vents/

For slight curves you can bed the flat frame in epoxy to fill the gaps. Otherwise you can scribe the curvature of the deck onto the frame, then grind/cut out the curve, then bed with epoxy. Finally fiberglass to keep the epoxy from cracking.

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Old 31-03-2016, 23:58   #12
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Re: Hatch on Curved Deck

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Originally Posted by Don C L View Post
Would be nice to see a photo ...
I agree, or at least let us know how your taste runs. Me I'd do a wood frame formed to the deck curvature... But my plastic boat is from 1974 with a fair amount of wood... if I owned a 2000s Hunter I might choose another solution...
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Old 01-04-2016, 02:26   #13
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Re: Hatch on Curved Deck

Thanks for the responses everyone, much appreciated.

Am going to go with something similar to the epoxy method as suggested by AD28. Ground off the gelcoat around the opening lip today and will hopefully get it done over the weekend.

Although I love the look of timber frame method I just don't want any more varnish work having just redone what varnish I do have and I like the minimal protrusion of the hatch.

I have some Collinite Fleet wax. Will that do for a release agent?

Winf
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Old 01-04-2016, 03:21   #14
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Re: Hatch on Curved Deck

With due respect, you'd be better off doing something along the lines suggested by Dawn Treader.
As, without a mold to contain an epoxy pour, thickened or not, you're going to wind up with; drips & runs which need sanding, as well as very uneven sides to your epoxy "base". Which, frankly, are a nightmare to try & sand into a uniform & even shape. Especially given the tolerances to which you'll be working, & coupled with how tough it is to use power sanders right at deck level. Without removing some of the deck in the process.

That, & cured epoxy is tough stuff to sand, to begin with.
Plus, for things to have truly proper structural integrity, you'll want some fiberglass cloth/tape, as part of the hatch's base. Securing it ot the deck, as part of the raised base's structure. Thus making it/them, integral to the boat.

Also, the thicker one pours epoxy, the greater the risk of it going exothermic. And 10mm - 12mm is definitely thicker than that threshold.

There are some good project guides at www.Epoxyworks.com & www.WESTSystem.com Including the option to download all of the product guides for free, as well as the excellent book On Boat Construction. Which covers a variety of methods of installing hatches, & "bedding hardware", which is what installing a hatch is, in truth.

They're Definitely worth the time to read; the basics, & also, the relevant chapter(s) which will help with your hatch. As done right, the hatch's base is an integral part of the boat, & should live just as long (ergo, the above mentioned structural taping).

And one other thing worth doing, & thus factoring in, is to install breakwaters around 3 - 4 sides of the hatch. With or without the built in faciliites for incorporating storm covers/sun covers, into the breakwaters.

As, not only do they prevent boarding, green water from striking the seals of the hatches, & the bases which they're mounted on. But if you make them a few inches wide, & just a touch taller than the mounted hatch, then they become the spots which are commonly stepped on, instead of the edges of the hatches. Thus prolonging the life of the hatch gaskets, & also the hatch's mounting bases.

If you do a search on here, there are a few good threads covering hatch breakwater construction. And info on them can be found in many other places as well.


PS: Milled, or Chopped Glass fibers mixed in with epoxy make a great structural blend. Though it is one of the tougher ones to sand.
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Old 02-04-2016, 06:58   #15
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Re: Hatch on Curved Deck

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I have some Collinite Fleet wax. Will that do for a release agent?
I think that's thicker than the ol'timey Johnson's floor wax I used, can't see why not. Be generous with application

I just recalled I have pictures

This is the demolition/cleaning of the hatch area


This, the taping off and sanding of the substrate


This, the bog/fill laid in and hatch pressed over it


Completed, painted, and hatch rebedded
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