N C Bjerg windows and refurbishment

Once again, I am getting more enquiries about these windows and how to refurbish them, particularly from owners of older Hallberg Rassy yachts. So it's time for another short article on the subject.

Who?

N C Bjerg was a Danish manufacturer of marine windows and featured on several Scandinavian yachts prior to 1997. In 1997 they went bust and the assets were bought by Norwegian based ERTEC who took over the plant and set up a new business, ERTEC DK. Since 1997 ERTEC DK has been producing replacements in small numbers using a slightly modified frame section. They did inherit a large number of patterns so in theory can replicate many of the windows previously manufactured under the N C Bjerg brand.

ERTEC DK is however a small operation so lead times can be many months, though our contact there (Sam Shad - ertec@ertec.dk) is excellent.

Sounds great but...

The issue, other than lead times and possibly price is that they have now stopped production of the seals used with these windows. One, that which is used between the flange and hull is not an issue as this can be substituted with bedding compound (eg GZ butyl tape). The other, used to seal the pane within the frame on fixed units is frankly unusable as a refurb option anyway as we will see.

Why these frames make for painful refurbishment...

The original frame section has an 'L' shaped channel. The frame is bent in one piece with a single split line fixed with a single fishplate (alloy insert). Imagining the frame laid outer face down, the tail of the 'L' now points upward. The unsymmetrical pre-cut seal (which has a 'U' section and fits around the glazing pane - normally acrylic) is fitted around the pane and then this is dropped into the frame. The (now) upper side of the seal has an inward bead which will form a neat fillet on the inside of the window after installation.

Next, the tail of the 'L' is mechanically rolled over to for the 'U' channel. This clearly can't be undone during refurbishment!

When the window is installed the inner ring (alloy) fastens to the outer frame (against the face that has been rolled with the inner edge butting up to the aforementioned 'bead' on the rubber seal.

When uninstalling this inner ring is removed and you will then normally be able to see a line of small indentations on the face of the outer frame showing where the rolling has taken place.

Refurbishment process

It's not pretty and as you will see is even more difficult for smaller frames. Basically we cut away the rubber seal to make the pane as loose as possible in the (outer) frame. We then release the fishplate and distort the frame (ie open it up) sufficient to release the pane.

We then clean up the rolled channel, cut new acrylic and put this back in the frame. We then close up the frame, refasten the fishplate and reseal the acrylic with silicone in place of what was previously rubber.

Clearly silicone does not provide the 'bead', but if possible we will attempt to cut this element from the original rubber seal so that it can be placed again between the frame flange and inner ring.

The good news is that the silicone will provide a better seal than rubber so should give many years of service once done.