Two deck hatches can carry the same nominal size and still require different canvas covers. A raised aluminium frame, a nearly flush lid and a projecting hinge do not create the same shape for fabric to follow. When ordering a hatch cover compatible with a Lewmar hatch, the size number is only one part of the identification.
The practical aim is to describe the hatch that is actually installed on the boat. Boat model information is useful background, but it does not confirm that every hatch is original or that a previous owner has not fitted a different series.
Identify the series before comparing dimensions
Look for the manufacturer's identification markings and photograph them clearly. Also take a view from above and a low side view showing the frame height. If you believe the hatch is Ocean, Low Profile, Medium Profile or a Flush series, treat that as a starting identification to be checked against the installed unit.
Lewmar publishes separate product information for its ranges. Use the relevant manufacturer drawing when one is available. An online listing with only a size number is not enough to establish that a cover pattern is interchangeable across those ranges.
Measure the outside, not just the deck opening
A hatch specification can include both an outside frame dimension and a cut-out dimension. The cut-out describes the opening required in the deck; it does not necessarily describe the fabric's outer boundary. For a slip-over cover, measure the external envelope of the parts the cover must enclose.
Record the overall length and width, the frame or lid height above the surrounding deck, and any overhanging edges. Mark where each measurement starts and ends. On a rectangular hatch, identify the fore-and-aft direction so that the hinge position is not accidentally rotated by 90 degrees.
Report inches and centimetres where helpful, keeping one set as the original measurement. For example, 20 inches is 50.8 cm. Do not round several intermediate conversions and then expect them to match a close-fitting pattern.
Corner shape changes the perimeter
A fabric panel drawn with tight corners can pull diagonally over a hatch with generous curves. A panel with overly rounded corners may leave material bunching near the edges. Equal maximum length and width therefore do not prove that two hatches need the same pattern.
If you cannot measure the corner radius reliably, send a straight-on photograph with a ruler in the same plane as the lid. For a difficult shape, a full-size paper tracing can be more useful than a guessed radius. Label the tracing, mark the hinge side and verify its scale before sending it.
Show hinges, handles and nearby deck hardware
Hinges may project beyond the frame or sit higher than the surface the cover rests on. External handles, vents and other fittings can also alter the local height. Photograph these features individually and include a wider view to show their orientation.
Nearby grabrails, lines or a coachroof edge can limit how a cover is fitted and removed. A deep skirt that looks suitable on an isolated drawing may be awkward beside an obstruction. Specify whether the cover is intended for a closed hatch only, and remove it when needed to preserve hatch operation and emergency access.
Decide what the cover is meant to cover
Some owners want the fabric to cover the acrylic lid while leaving most of the frame visible. Others want the skirt to extend around the raised frame. These are different finished shapes. Discuss the lower edge, fastening method and removal routine before comparing prices.
Do not tighten elastic or a drawcord so aggressively that the fabric pulls on a handle or leaves a heavily loaded point over a hinge. In windy conditions, fit and retention matter, but the solution should follow the installed hatch geometry. Salt deposits and dirt trapped under a cover should also be removed using care methods suitable for the hatch surface.
A sensible way to combine hatch sizes
If a boat has several hatches, group them only after comparing the complete external shape. Start with series and nominal size, then compare outer length, width, height, corner profile and hinge projections. A shared cover pattern is a design decision to verify, not an automatic consequence of matching size labels.
Number the hatches on a simple deck sketch and attach the corresponding measurements and photographs. This prevents a forward hatch measurement being paired with a cabin-top photograph. It also makes a small batch of custom covers easier to review before sewing.
Preparing a hatch cover request
Send the series or identification code, outside measurements, low side photographs, corner information, hinge orientation and the intended skirt depth. Tell us whether the boat remains at an exposed berth or is stored under shelter, and how often the covers will be removed.
Sailboat Cover can use that information to discuss a custom pattern and fastening arrangement. References to Lewmar identify the hatch application; they do not mean that our independently made covers are manufactured or endorsed by Lewmar.
Further reading: Lewmar Low Profile Hatch product information.
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