Gebo Hatch refurbishment and Covers

In 2024 the GEBO hatches were completely refurbished with new acrylic lenses, seals and and hardware, and were provided with Sumbrella covers to protect them from future UV damage.

While the 20-year old GEBO hatches were fully operational and leak-free, they were showing signs of age, with crazed plexiglass and UV-degraded hardware. The plan was to prepare the lenses in my shop in Toronto, order the hardware from The Netherlands, and the DOW 795 glazing silicone from the USA, and ship the lot to the boat for installation.  While visiting the boat I had photographed the hatches, documented the hardware required, and measured the glazing.

Fortunately GEBO still exists, and this style of hatch is still in production. Parts are available and Gebo's communication was excellent.    Here is the factory literature: https://www.gebo.com/wp-content/uploads/2019/08/Standard-Deckhatches-without-flange.pdf

Fabricating new Acrylic lenses

When I was at the boat, I measured the glazing dimensions accurately but I did not note the corner radii.  It appeared at first that the hatches used by Alubat might have been the off-the-shelf items listed below, so I reached out to GEBO to see if they had dimensioned drawings available.  They did not, but were able to provide the glazing dimensions and corner radii of the current, standard hatches.  This meant that I could make blanks in the shop at home, but had to drill the holes for the hardware at the boat.  

The overall dimensions are consistent with current production hatches, with the exception of the largest hatches where I measured glazing 7mm wider than the standard item.   Unfortunately the larger hatches futher differ from standard items with a 40mm corner radius vs the 60mm radius on the current standard hatch.  The 2001 OVNI hatches use the smaller 40mm radius for all hatches hatches   Best to confirm the glazing dimensions, corner radius, and hole placement using the actual hatches installed - assume nothing!  See the table below containing my measured dimensions and their 2023 standard hatch dimensions.

The acrylic is specified by GEBO as 10mm thick for all 8 of the deck hatches supplied on the OVNI 435.  This thickness is not available in North America, where 3/8" is the rough equivalent.   GEBO describes the colour as "Grey tinted" and the colour code for dark grey tint that I've used previously is # 2074.   3/8" acrylic, 2074 tint is stocked here at Plastic World in Toronto, where a 4'X4' half-sheet currently (June 2023) costs C$234.  This is enough to re-glaze all of the GEBO hatches on the 435.

The acrylic was cut to size on the tablesaw.   A template was made for the corner radii per the guidance provided by GEBO,   and the corners traced with a fine pencil, cut on the bandsaw, and sanded to the pencil line.  The plastic scraper’s V-Notch was used to relieve all sharp edges.   This all would have been much more difficult to do at the boat.

The plexiglass dimesions were correct except for the corner-radius issue noted above, and it required only light sanding to achieve an adequate perimeter gap for the sealant.   There was sufficient material in the half-sheet to make a spare large hatch replacement.  Replacement lenses for the 3 larger deck hatches, two cabin top and 4 cabin side resulted in a 35lb bundle to be shipped. 

Replacing the hardware

 Gebo specifies its hardware based on the glazing thickness, (10mm or 15mm) which is in this case 10mm.  All hardware is available as of 2023. The handles are an equal mix of left and right handed, with the small, cabin side hatches intended to be operated with one's left hand.  Thoughtful.

Required parts and spares:

The GEBO hardware requires two 6mm blind holes (for anti-rotation pins) and a 14mm through hole for the handle.   You will require one of their special wrenches to access the hinge nuts.  (included in the hinge repair kit)  Order extra external handles and hinge caps.  

I took a chance and ordered the very high quality bug screens for the mid-sized cabin top hatches, and they fit perfectly.    I really should get some screens for the small hatches.

Dow 795

Great stuff and the only silicone I would use on a boat.  Ensure the material is fresh - it will not cure if it is past its shelf life!

How to remove and reinstall the glazing

By first slicing the silicone from above, then gently inserting a thin, flexible, putty knife between the frame and the plastic lens from below, and patiently working it around the entire perimeter, the acrylic lens can  be parted, intact, from the frame.   It will then serve as a perfect template for  the replacement.   See blog post here for more specifics.    If you know of a good way to remove cured silicone please share.    

Mark took two full days to refurbish the hatches, and they are now as new.  Thanks Mark!

Having replaced all of the plexiglass and much of the hardware in the Gebo hatches, it made little sense to leave them exposed to equatorial sunlight for months while Sakura basks on the hard.   

Repurposing a tired sail cover and following the Sailrite YouTube video, some basic drawstring hatch covers were made.   It was a good basic sewing project, and an even better use of a worn sail cover. 

The dimensions (in inches) specified in that video are as follows:

• Rectangular cabin-top hatches:   24 3/4 diag, 18 1/2 hinge side, 22 long side
• Forward deck hatch:  30 3/4 diag, 25 1/2 hinge side, 24 other side
• Small hatches:  14 1/4 diag,  13 3/4  hinge side, 12 1/4 other side

Trapping the drawstring cord in the gasket can permit water ingress, and I am not confident that the barrel fastener will remain secure over time. (I knotted the rope to prevent it moving).  I think a better approach mnight be shock cord of the correct length to snap onto the hatch after it is closed.  update:  The covers have remained in place.  No problem.

While this approach seems adequate, IMO there’s a better design in this most excellent book.

Canvas for Cruisers: The Complete Guide

by Julie M. Gifford