Changing the Forward Hatch

[Mike and Theresa Vaccaro]

Replaced the forward hatch over the weekend and wanted to share some lessons with the corporate knowledge database...

Bomar makes a "drop in" replacement hatch.  This is a "Nibo" series hatch.  The new hatches use different arms, a thicker seal and have dogs that open from inside and outside.  The exterior dimension of the hatch is identical to the old hatch, but the lower flange is slightly smaller in outside diameter (i.e., you have about 1/4" less "overhang" on the outside edge, effectively reducing the sealant area a bit).  Additionally, the mounting holes in the flange are are slightly different than the old flange.  

Bomar has a full line of replacement parts available for their hatches, and I've noticed that the local BoatUS outlet stocks the most common ones (dogs and seals).  Bomar maintains a website at http://www.pompanette.com/bomar .  Something we learned is that Bomar maintains a "factory overstock" listing on their site, and their sales reps can also look through available hatches.  You might get lucky when you call.  We paid less for a complete hatch assembly than we would have for parts.  The hatch we purchased was returned to the company because there were some scratches in the frame.  Be sure that you've measured carefully, however, since once your order a "factory overstock" part, it's non-returnable.  Odds are higher that you'll find the smaller square hatch for the coachroof.

Changing the hatch.

Before you remove the old hatch, put down an outline of blue tape or use a sharpie to mark the deck for reference.  If you do this, odds are you won't damage any gel coat in the process.  Keep in mind the new lower flange may be slightly smaller than the old, so take your time and use care to avoid damaging any surface that may end up exposed.  

Our hatch was bedded with silicone at the factory, and there were no leaks of any sort around the flange when I removed it.  When you remove the hatch, you can leave it as an complete assembly, or you can remove the arms (two large screws at the lower end) where they mount to the lower flange and then remove the two inboard screws on each hinge and lift the cover of the hatch off.  Now all you'll need to do is remove the bottom (base) flange.  

To remove the hatch as an assembly, first remove the screws.  Don't forget the four screws on the outboard end of the hinges (two per hinge).  The next step is to break the seal.  To do this you'll need to use a glazing tool, hook blade knife or sharp putty knive.  The trick is to remove a small amount of sealant, allowing you to wedge a strudy putty knife or glazing tool underneath the flange and then GENTLY pry up the flange, working the tool around as you do.

If your flange was installed with silicone, you'll need to remove all of the old sealant.  I don't have any clever tricks for removing cured silicone, although a chemical may be available for that purpose.  The tried and approved method is mechanical removal.

The next step will be to lay the new hatch in place and check the hole pattern.  Use a sharpie to trace the holes and then remove the flange.  Compare the position of your markings with the existing holes.  You now have two options, fill all of the old holes with epoxy and re-drill, or as a minimum fill the holes that are very close and redrill, drill new holes were there are no clearance problems and fill the old holes with sealant.  The proper technique is to use epxoy filler to avoid any potential leak that could damage the plywood deck core.  Also note that "edge" disance for some holes is marginal so use care in drilling.  The new flanges are counter-sunk for #8 screws which merit a #29 wire size drill for the hole in the deck.

A trick to use when filling the old holes is to surround the hole with four pieces of blue masking tape, making a small exposed square.  This will make sanding the filler easy without damaging surrounding gelcoat.  The last thin layer of filler can be removed by hand without doing any harm to surrounding surfaces.  The filled holes will be covered by the new flange, so it's not necessary to do any additional work beyond faring.

After the new hole pattern is drilled, install the new hatch and install all the screws.  This will, in effect, "tap" the holes and allow you check alignment above and below deck.  Then, lay down a blue tape outline of the new flange, allowing 1/16" space between the flange and the tape for your hew caulk line.  Then remove the hatch and clean the flange and the edge of the deck with Acetone or MEK.  

Apply the sealant of your choice.  I prefer a removable polysolfide-type, and would recommend against a "permanent 5200" type since you may have to remove the hatch in the future.  Silicone will also work and held up well on our hatch for 18 years.  When sealing, be sure to apply a small dab to each of the screw holes and then put a bead on the deck around the opening.  Too much is better than not enough, but it's a fine line!  Fortunately clean up is fairly straight forward if you've outlined the hatch with masking tape.  Also, it doesn't take much sealant to make a water-tight seal.  Provided the parts fit well, only .004 inches is required!  Since the hatch is screwed to the deck vs. through-bolting, you can use your discresion whether or not you fully seat the screws during assembly.  Unfortunately, if you wait 24 hours for sealant cure prior to snugging, you can break the seal at the screw.  As an alternative, you can wait to snug and then remove and re-seal each screw individually, keeping in mind that the screw holes are somewhat protected by the "o-ring" of sealant around the parimeter of the lower flange as well as the rubber seal between the top and bottom flanges.  Be sure to fair the sealant and remove the masking tape before the sealant sets up for a neat caulk line.

After 48 hours, it's time for the hose check!  Flange leaks can be noted if the water is coming from behind the plastic fairing installed on the inside of the hatch cut-out.  Dog or main seal leaks are revealed by water dripping from the inside of the main seal or off a dog handle.  New hatches and seals sometimes require some adjustment for a proper fit and seal.  

These small profile hatches are adequate for knocking around the bay, souldn't be considered for off-shore work if there is a potential to truly bury the bow in green water.  A more robust hatch is required for that.

Cheers,

Mike

[APACHE]

Mike : Why don't you write this up and send it to Mark for the "projects".  If you have any pictures, he's like them also.

[SteveLyle]

With a few pictures this would be a great Mainsheet article as well.

All submissions gratefully accepted.

[Mike and Theresa Vaccaro]

Will do, but we're currently in the process of moving and having a couple of hurricanes...once things settle down and I figure out how to hook up the wireless router, we'll get back to it!

Cheers,

Mike