Tips on how to make surface-mounted windows look good?

[Dellquay13]

The answer is a method that's easy and simple to do and doesn't leak.

That's probably going to be replacing like for like using new Perspex bedded down on Scapa tape. I'd avoid painting or sticking anything around the border just in case that causes any reaction with paint solvents or adhesive affecting the Perspex.

The Hadlow Marine website is full of useful info.

I too used Scapa tape from Hadlow. I chose black the first time on a previous boat, as that matched lots of stuff aboard. On the current boat I chose grey. It looks like a trim through the windows. It was super fast and mess free. Goes without saying that they don’t leak (but there you go I just said it…)

 

[dovekie]

Hello,

I have a cobra 850 and want to replace the windows as the existing acrylic has faded and yellowed. The windows currently are surface mounted, screwed straight onto the hull.

I have investigated having frames made for them, as I hate how they look. However, all practical considerations (ease of installation / maintenance, cost, not having to have frames made, etc.) point to just replacing like-for-like with a new piece of acrylic.

I don't want to make my life 10x harder than it needs to be for the sake of aesthetic so as a compromise, I thought I'd reach out to see if there are any tips on how to get the most out of surface-mounted windows?

Thank you,
Eddie

In case anyone wants to see what I'm working with:

IMG-20250422-185238 hosted at ImgBB

May I echo Neeves (and others) point about needing sufficient thickness of sealant - apologies if you know all this. The window and the coachroof will not expand and contract identically with changes in temperature. So they move in shear relative to one another. 6mm of sealant can accommodate much more sheer than 1mm. We have had window seals fail because of too thin a sealant bond.

 

[robert.lowe2311]

Use trim or molding to frame them, paint to match the wall or create contrast, and add curtains or blinds to blend them into the room’s style.

 

[KevinV]

Use trim or molding to frame them, paint to match the wall or create contrast, and add curtains or blinds to blend them into the room’s style.

You're obviously bonkers enough to fit in just fine - welcome to the forum!

What is your opinion on pelmets, and gold cord tie-backs with tassels?

 

[bluerm166]

Suggest that when/if your plastics supplier advises a thicker acrylic ( because he hasn't got the right thickness in stock,believes in belt and braces) you increase the length of the fixing screws accordingly.
This historically wasn't done on our boat when the original 8mm was over the years increased to 10mm on port and 12mm on starboard so there was never much hope of keeping the water out.

 

[ducked]

May I echo Neeves (and others) point about needing sufficient thickness of sealant - apologies if you know all this. The window and the coachroof will not expand and contract identically with changes in temperature. So they move in shear relative to one another. 6mm of sealant can accommodate much more sheer than 1mm. We have had window seals fail because of too thin a sealant bond.

6mm of sealant sounds like an awful lot.

If the windows are frameless, which is pretty much an OP condition, they will be quite proud of the surface, catching rain and, in extremis, potentially subject to wave or rope damage and taking divots out of shins. The sealant (depending on the sealant) might also tend sag out of the joint, and the existing screws may be too short.

 

[LiftyK]

This is a great idea, thank you. We used tape to seal the stick on windows. It worked really well but ;left while fibreglass visible inside the window area. Painting the acrylic would fix that.

 

[yatnus]

If you’re keeping the same screw-through method, you can cover the screws with black caps or even make a black vinyl border around the edge makes it look more deliberate.

 

[RunAgroundHard]

... I don't want to make my life 10x harder than it needs to be for the sake of aesthetic so as a compromise, I thought I'd reach out to see if there are any tips on how to get the most out of surface-mounted windows? ...

IMG-20250422-185238 hosted at ImgBB

I agree that plastic windows stuck straight onto the hull are not the most aesthetic looking windows. In your shoes, after getting the new windows cut I would fill all the holes in the hull with an epoxy mix so I was not worried about aligning old holes in hull with new holes in window. I would not glue the window on as it is a temporary measure at best and likely glued on in less than optimum conditions.

On the new window, fit Scapa 3507 bedding tape, 3mm thick, around the inside edge of the new window, cut to be the same width as the window to GRP width. The tape is superior to mastic seal and very easy to work with. I would buy some half round bar and carefully cut to fit the new window, likely I would use play or balsa strips the same width as the half round to make templates first, before cutting the half round bar. Drill the half round bar at an appropriate centre spacing for the new screws and counter sink the holes because I would use counter sunk dome heads in stainless. Fit the window to the hull and then use duck tape strips to temporarily hold frame and window to the GRP. Drill the GRP and then coat the stainless steel screw with Duralec or Teff Gell (Teff Gell is better). Wipe of excess Teff Gell / Duralex while still wet, align screw heads for neatness.

Personally that is not 10 times harder and you will have a neat windows. Even if you don't use the aluminium half round bar, use the tape. I am coming on 7 years now with my tape and frames and not a drop of water has come through and still robust.

All the best.


Scapa 3507 bedding tapes
Aluminium Half Round Bar
Self Tapping Counter Sunk Dome Head Screws
Duralec or Teff Gell

 

[MontyMariner]

Agree use tinted either grey or bronze and maybe a dark sealant rather than white.

Yes, I would use a Black sealant which would make it look like a frame.

 

[D1bram]

I replaced the framed (but very knackered) windows on my boat with surface Perspex (or acrylic). They are a dark smoke, look very tinted from the outside but hardly at all from inside.

I used single sided Scapa tape, there's no mess with this method and the windows can be simply unbolted in the future should you need to for any reason.

I'd probably prefer to have had nice new frames, but the cost would have been prohibitive.

 

[TSB240]

Hello,

I have a cobra 850 and want to replace the windows as the existing acrylic has faded and yellowed. The windows currently are surface mounted, screwed straight onto the hull.

I have investigated having frames made for them, as I hate how they look. However, all practical considerations (ease of installation / maintenance, cost, not having to have frames made, etc.) point to just replacing like-for-like with a new piece of acrylic.

I don't want to make my life 10x harder than it needs to be for the sake of aesthetic so as a compromise, I thought I'd reach out to see if there are any tips on how to get the most out of surface-mounted windows?

Thank you,
Eddie

In case anyone wants to see what I'm working with:

IMG-20250422-185238 hosted at ImgBB

I have just fitted some new Perspex windows on my Hard top project.

If you use perspex they must be bonded in with a UV resistant sika 295. Don't use screws and scapa tape , silicone, or double sided sellotape!

The procedure is to trial fit your perspex.
Mark the interior of the perspex with the outline of the opening.
Mark the exterior oitline of your window on the cabin. ADD masking tape to this allowing fir a small finishing bead. Trim with a sharp knife around the corners.
The perspex is normally covered with a thin protective sheet on both sides.
Additional masking tape does no harm.
Mask up right to the edge of the perspex on the external side.
The interior masking and film can then be lightly scored where marked and removed.

Sand with 120 grit on the inside only of the perspex.

Clean with rubbing alcohol NOT Acetone.

Acetone will cause premature cracking and crazing of Perspex or Acrylic glass.

Spray this with an acrylic paint of your choice.(Plasticote). I used black but you can use any colour you like to form a nice scratch proof frame to the window as it is on the inside.
This then has to be lightly sanded down and a Sika 209D primer applied to both perspex and opening to ensure a good bond with Sika 295 UV.

I cut the nozzle right back on the sika plastic nozzle. This allows a single generous bead of 295 uv sealant that will cover about 20- 25 mm of sealed area when slightly compressed.

Smooth any excess of sealant with a gloved finger, wet wipes are essential for removing it from areas you don't want it. If you use plenty of masking tape either side of the sealant it must be removed whilst the sealant is semi flexible and hasn't gone off. I usually wait about an hour.

I finally finished off the edges with a small finishing bead and a wet teaspoon. I used some cream CT1 sealant from toolstation to completely hide any remaining black of the 209D primer or sika 295UV

Sounds like a lot of work but I am just doing as they originally did in the bendytoy factory!

Do it right and you won't get any annoying leaks or windows falling out.

 

[RunAgroundHard]

… Don't use screws and scapa tape …!

Curious as to why not. Mine are still sealed with Scapa and have been tested in heavy sea and lashing rain multiple times, over 5 years.

 

[TSB240]

Curious as to why not. Mine are still sealed with Scapa and have been tested in heavy sea and lashing rain multiple times, over 5 years.

No holes to dril in Perspex.
No holes drilled in boat.

My screen lasted 22 years until crazing got annoying with no leaks.
Come back in another 15!

Clean look.

 

[wallacebob]

This fella makes a very neat job of it: