Port hole ventilation


Every boat will benefit from better ventilation, it’s one of the things few boat builders consider. Opening port holes are great but must be closed if it’s raining or if you leave the boat. Here’s a simple solution which allows the ports to be left open in all weathers whilst still admitting light.

The first thing I did was make a cardboard template to test the validity of  the idea then I used 3mm thick lexan. Lexan (polycarbonate) is excellent to work with and has good anti scratch and UV properties. A jigsaw and a sharp blade is all you need to cut the Lexan. To clean up the edges, a small block  plane is perfect.

Two upright supports were made with three slots at an angle of 45 degrees.  The slots in the uprights and the horizontal pieces are only cut halfway. The pieces slot together and it is pretty solid even without gluing. The slats work perfectly at deflecting the heaviest rain but water will find its way in at the top of the port hole so to stop this a small strip of self adhesive neoprene is stuck to the top edge of the assembly.
Now we have a nice flow of air in all weathers and we can still look out of the porthole. The cost was nothing as I had the lexan and neoprene kicking  about. I made two, one for the galley and one for the heads and they took  about 3 hours to make. A perfect Sunday afternoon project!


VHB tape from 3M for bonding acrylic windows


Teak companionway doors on ‘Doolittle’ with lexan glass held in with VHB tape.

If you don’t like making holes or using messy sealants perhaps what you need is VHB tape by 3M. You might think that this is a new technology but 3M have been selling it for over 25 years and now offer a bewildering choice for hundreds of different applications, from joining aeroplane wings to building entire houses. It is a double sided sticky tape made from acrylic foam and using it is simplicity itself. Ensure the surfaces are clean, lay the tape, peel off the backing paper and bring the two surfaces together. The bond increases the longer it is in place.

It seems unaffected by UV or heat and works so well and is so easy to apply you think there must be a catch. Well of course there is. You guessed it, the only thing wrong with VHB tape is the price but when one considers how long and messy it usually is bonding windows with runny sealants, the time saved easily outweighs the cost issue. The finished result is very tidy and there is no cleaning up to do afterwards at all.


Trying to work out which tape to use to bond polycarbonate plastic to wood wasn’t easy as there are almost 40 products to choose from but in the end I worked out that their Multi-Purpose conformable Acrylic was the best choice as it bonds most materials. VHB needs to be applied in temperatures above 15 degs C but they also make a special tape for low temperature applications down to 0 deg C which is what I chose.


Because the tape is grey, it matches the aged teak well and becomes almost invisible.

It is available in black, white, grey and even clear versions in widths from ¼” to 1”. I planned to leave the teak untreated so I chose grey tape in the hope that it would not be seen once the wood had aged. The roll I bought was 1.55mm thick and 1/2” wide with the 3M code of 4957F. This was the perfect width for attaching the windows and it was easily able to follow the curve in the woodwork without kinking.


View of the inside of the doors showing how neat the VHB is.

The windows have been in place for 4 years and the tape shows no signs of letting go it’s tenacious grip and the doors are still as water tight as ever. I applied a couple of coats of varnish and let it dry well before I stuck down the tape but I suspect it would have worked just as well had I stuck it to the bare wood. I just hope I never have to replace the glass as I have no idea how I will get it out without breaking the doors!

If you want to know all the technical details and choices available, click here

Still more info from 3M, click here

And finally, a very silly video showing the remarkable properties of 3M VHB tapes over conventional mechanical fastenings.