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TOPIC: 4788 Engine Room Hatch Modification

4788 Engine Room Hatch Modification 03 Feb 2008 19:11 #1

  • KennyFerret
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This is probably one of the best modifications you can do to your 4788 as the one downside to this model is engine room confinement for filter changes and other maintenance. ("The Tunnel Of Doom" is one term I have seen on the BOC!) This additional hatch allows you to stand comfortably between the engines and to work over or between the motors as required. An ideal time to do this is when you intend to replace the carpet.

The standard 4788/490 comes with the center area closed off with a plywood floor. Access hatches are provided only above the engines. This floor is a sandwich construction with 2x4's providing the frame and 1/2" ply sandwiched top and bottom. To begin with you need to get a skilsaw with a fine blade and cut out the top section of ply in line with the existing hatch openings. This with reveal the 2"x4" grid below with insulation packed in between. Remove the insulation. Then cut and pry off the plywood on the underside. The 2x4 grid on our boat was like a ladder section. Longitudinals ran fore and aft inboard of the engines with short cross members running across the boat between these longitudinals. These need to be removed. Ours were screwed in from either side of the longitudinals but on some boats they may be nailed and/or glued. Here's a photo of the engines with the grid removed (except the original) Note the 4 saddles welded to the original aluminium cross bearers.

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Once you have this out you can reframe the opening by fitting 2x4's to either end of the new opening. Fit them so about half of the front edge of the 2x4 protrudes into the opening so it can used to support the new hatch. If you have made a neat job of the top ply cutout, this piece can be reused as your center hatch. Here's a shot of the new center hatch opening. Note the cut outs for the box sections and the new insulation fitted under the new 'L' sections.

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The plywood hatches above the main engines on our boat were 'cupping' due to the heat from the diesels. To remedy this extra fore and aft sections of 1"x1" box aluminium were installed above the engines to supplement the existing inverted 'U' section. On one end the timber was chiseled out to provide an entry while additional 'U' saddles were welded to the existing 'U' section to accept the new box section (see photo 1) These were made so that everything was a press fit and could be removed in seconds. Three lengths of 1"X1" box section were also fitted across the new hatch opening to provide extra support and to prevent cupping. "Check outs" were chiseled either side of the fore and aft bearers to support the new box section. Again these were made a press fit so that they could be removed in seconds.

Aluminium 'L' section was fitted between the new grid sections so that it matched that already fitted around the engine openings.

Once this was all fitting nice, all the box sections were removed and sent to the powdercoaters. While this was being done the bearers around the openings were sanded, degreased and painted with 2 pot paint. The whole grid was then reassembled and new insulation (Accustop in our case) cut and fitted under the 'L' sections. Here's a shot of the full grid in place.

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Incidentally Accustop underlay was also used under the salon floor carpet instead of the normal rubber underlay. I never tested noise levels with a Db meter but I am sure it has quietened down the engine noise. Here's one with all the panels down.

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So the carpet and underlay is then attached to the new hatch and the job is almost complete. Remember that you will have to trim the plywood hatch just enough to alllow for a nice fit once the underlay and carpet have been rolled and stapled around the edges. Remember that you will also have to fit new sound insulation to the underside of the new center hatch. The easiest way to do this is, with the hatch down, crawl into the Tunnel Of Doom and mark the corner positions of the insulation with a pencil. Then remove the hatch and fit the insulation to your markings, for a perfect fit.

The old hatch pulls were also taken off and new hatch pulls fitted.
These are simplicity itself, and consist of a small length of nylon fabric backing tape ( the same stuff used on biminis to reinforce the stitch line) Get a piece that matches the color of your carpet and then screw it onto the center edge of the engine hatches with a washer under the screw to distribute load. Make the protruding loop just long enough to comfortably insert your index finger so you can lift the hatch. The loop can be doubled over itself and pushed into the carpet pile so that it is virtually invisible. We only fitted 2 of these, one on each of the forward engine hatches. Once you have these up all the other panels can be easily removed. That's it, job done. Added bonus...your diesel mechanic won't make excuses about how busy he is next time you phone him up to work on your motors!

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Ken

'94 4788 - "Crystal Voyager "

If you can dream it, you can do it
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