Repair and Maintenance of a Drascombe Lugger

Fitting an Inspection Hatch

The impetus for this project came from the desire to remove two plastic cleats bolted into sealed buoyancy areas beneath the aft end of the decks. The cleats tended to catch on clothing as well as getting in the way when sleeping (camping) on the floorboards. There was no access to these buoyancy areas and I consequently had no idea as to if they were sealed empty tanks or else filled with foam buoyancy. I decided that the answer was to install two circular plastic inspection hatches. A step by step guide to installing one of the hatches is described.

The Location of the Cleats

Location of cleat and bulkheads, port side Cleat to be Removed

This picture shows the port side deck next to the lazarette. The black cleat was bolted in place and the white lines show the approximate position of internal bulkheads (under the side deck), which made it impossible to get a spanner inside to unbolt the cleat. I decided that the only easy way to remove the cleat was to install an inspection hatch in the front side of the side bench. This would also provide an opportunity to inspect the nature of the buoyancy; was it an empty cavity or was it filled with foam?

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What size of Inspection Hatch?

A GRP panel into which a circular screw hatch is to be fitted should be reasonably flat as a curve will distort the hatch frame when it is bolted in place, preventing the hatch cover from being screwed into place. The more curved the panel is then the smaller the hatch will have to be to avoid distortion. I decided that the curve on the Lugger deck-panel was slight enough to allow an 8 inch diameter hatch to be fitted (10¼ inches overall diameter including the frame).

Materials & Tools

Materials & Tools

For fitting this 8" hatch I needed: 1. A free-mounted hacksaw blade (or pad-saw), 2. 7 mm spanner & 3. screwdriver (to secure the nuts & bolts holding the hatch frame in position), 4. 10" (250 mm) half-round file, 5. hand-operated twist drill (with ¼" ¹⁄8" & 4mm bits), 6. a miniature power drill (e.g. a Dremel) with a ¹⁄16" bit, 7. compass & pencil, 8. inspection hatch frame (with '0' ring seal), 9. inspection hatch cover (screws into inspection hatch frame), 10. eight M4 16 mm countersunk stainless machine screws, eight M4 stainless nuts, eight M4 stainless washers, 11. Silicone sealant (to ensure a waterproof seal between the hatch frame and the GRP panel). A steel tape measure (not shown).

The 8 inch diameter inspection hatch I used was made by Barton part number 40081 (black), 40080 (white), or 40082 (clear). Note that the kit as supplied does not include the stainless fixing screws, washers & nuts which have to be purchased separately.

Installation Instructions

position of the hatch, port side Positioning the Hatch

I decided to position the hatch midway between the lazarette and the first hatch opening in the deck moulding, and midway between the top of the floorboards and the top of the side deck. The exact measurements are shown in the photograph.

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Template for the cut-out hole Template for the Cut-out Hole

Once the centrepoint of the hatch was marked on the GRP panel, a compass & pencil were used to scribe the cut-out circle which for this hatch frame had a radius of 4¼ inches.

An inner circle of radius 4¹⁄ 8 inches was then drawn & used as a guide to drill a series of interlocking ¼" holes into the GRP panel. This is explained in more detail below.

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Drawing the cut-out circle Drawing the cut-out circle on the GRP Panel

A compass and pencil were used to draw the 8½" diameter cut-out hole for the circular hatch frame.

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Drawing the inner (drill-guide) circle Drawing the inner (drill-guide) circle on the GRP Panel

This picture shows the inner circle of radius 4¹⁄8 within the outer cut-out circle, both drawn by compass & pencil. The inner circle was the guide for drilling a series of interlocking ¼" holes, the first stage in making the cut-out.

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Drilling the pilot holes Drilling the Holes in the GRP Panel

I decided that the best way of doing this would be to initially drill small pilot holes. A small ¹⁄16" drill bit can be centred more accurately on the pencil guide line than can the larger ¼" bit. Drilling pilot holes may take more time but ensures a more accurate final cut-out.

A miniature power drill (a Dremel), was used to drill the pilot holes of ¹⁄16" diameter right round the inner circle. The spacing between the centre of each hole was roughly ¼" but this is not critical as long as each hole is centred, as accurately as possible, on the pencil guide line. These holes then acted as a guide for the larger ¼" drill.

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Drilling the ¼" holes Drilling the ¼" holes in the GRP Panel

Once all the pilot holes were drilled, they were enlarged using a ¼" drill (either using a hand drill, my preferred method, or a power-drill). Any of the pilot holes which were out of alignment (which would have caused the ¼" hole to go over the outer cut-out line), or too close together were either omitted or drilled out using a smaller ¹⁄8" drill bit.

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Drilling Completed Drilling Completed

This photograph shows all the ¹⁄16" pilot holes that could be, drilled out to a diameter of ¼" (or, failing that, ¹⁄8").

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Cutting out with a Hacksaw Cutting out with a Hacksaw

A mounted hacksaw blade was used to cut through the residual GRP between the holes. This was a fairly quick job but the glass fibres quickly blunted the hacksaw blade which was discarded once the cut had been completed.

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Rough cut-out completed Rough cut-out completed

After cutting through the residual GRP between the holes using a hacksaw, the circular GRP cut-out fell on to the floorboards revealing blocks of polystyrene foam packed into the buoyancy cavity. This foam, together with the cleat, must have been fixed to the deck moulding during the manufacture of the boat, before the deck was finally attached to the hull and the foam & cleat sealed in by the two bulkheads.

The polystyrene blocks had to be removed before further progress could be made. This was achieved by using the hacksaw to cut them into small enough pieces to remove through the cut-out aperture. Once this had been done the final shaping of the cut-out could be carried out.

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Smoothing with a half-round file Final Smoothing with a Half-round File

After removing the polystyrene foam buoyancy (to be replaced with polythene milk bottles), the final shaping & smoothing of the cut-out was achieved using a half-round file (as shown), to cut back to the cut-out line.

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The Completed Cut-out The Completed Cut-out

The completed cut-out in the GRP panel, ready for the fitting of the inspection hatch frame. At this stage it was possible to inspect the interior of the buoyancy chamber which revealed that it was not airtight and could not easily be made so. It was now possible to insert a spanner and unbolt the cleat.

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Drilling the fixing holes Drilling the fixing holes

The black plastic hatch frame was temporarily fitted into the cut-out in the GRP panel. The bolt holes in the frame were used as a template to drill the corresponding 4mm diameter fixing holes in the GRP panel. After drilling each hole, an M4 machine screw was inserted through the frame and GRP, and lightly secured in place with a nut to hold the frame rigidly in position whilst the other holes were drilled.

At this stage the plastic cleat had been successfully unbolted & removed.

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Drilling the fixing holes Completed Fixing Holes

The hatch frame was unbolted & removed to reveal the eight 4 mm fixing holes drilled in the GRP panel.

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Applying Silicone Sealant to the Frame Applying Silicone Sealant to the Frame

A bead of silicone sealant was applied all the way round the inside corner of the hatch frame prior to final installation.

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Completed Hatch Installation Completed Hatch Installation

The hatch frame was inserted into the cut-out in the GRP panel and bolted in place (using eight stainless M4 machine screws, washers & nuts). Sealed polythene 2.27 litre (4 pint) milk bottles were inserted through the hatch to replace the original polystyrene foam buoyancy. The bolt holes of the removed cleat were also filled and made good with matching gelcoat. Finally, the 8 " diameter hatch cover was screwed into place with the 'O' ring fitted for a watertight seal. Project completed!

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Project started and completed, June 2006