Lewmar Hatch Crazed Finish Repair

[Celestialsailor]

Originally Posted by travellerw

I very much disagree with the posts here. The crazing is on the outside layer of the Acrylic and is no more than 1mm deep (yes it looks deeper).

If you are willing to do the work, you can bring them back to factory look. Its exactly like polishing and sanding gelcoat. Start with 220 grit WET and sand. Use water and light to determine when you have sanded low enough to remove the crazing (careful, 220 will remove material fast). Then move to 400, 600, 800, 1200, 1500 and polishing compound. What do you have to loose? This process is used in the airline industry all the time!

I had a C80 chartplotter that looked exactly like you hatch. I was able to polish all the crazing out and the screen looks like new now (although the anti-glare coating is gone).

This is pure silliness. 1mm deep is .040". You would have 100 hours in it, only to remove 20% of the material (average sized hatches are generally 1/4") and have it a wavy finish. I'm a Toolmaker by trade and I can tell you it takes a lot of experience to polish a surface flat within even .005".
In turn it takes me less than 3 hours to remove the old plastic glaze, clean the silicon off, mask it and reseal it and clean up. New acrylic is inexpensive and a plastics shop and make a perfect fit from your old one.
I also doubt the airline industry does this sanding. Those planes are under the strictest safety guidelines.

[travellerw]

Ken...

What size hatches are those.. I was just surfing Defender and it turns out the replacements acrylic is not that much. Depending on the size, it looks like between $180-$250USD.

Of course you will probably pay more in the Med.

[Kenomac]

45cm x 33cm approx. I'll check Defender.com

Thanks

[travellerw]

Originally Posted by Celestialsailor

This is pure silliness. 1mm deep is .040". You would have 100 hours in it, only to remove 20% of the material (average sized hatches are generally 1/4") and have it a wavy finish. I'm a Toolmaker by trade and I can tell you it takes a lot of experience to polish a surface flat within even .005".
In turn it takes me less than 3 hours to remove the old plastic glaze, clean the silicon off, mask it and reseal it and clean up. New acrylic is inexpensive and a plastics shop and make a perfect fit from your old one.
I also doubt the airline industry does this sanding. Those planes are under the strictest safety guidelines.

Yup you are right about the depth.. 1mm would be very extreme. The crazing in the OPs picture is probably 8-10 thou or so.

You are wrong about the airline industry and a quick google search would have proved that. Here is a link (there are tons more, including youtube vids).
Ron Kilber's Logbook - Care and Repair of Acrylic Aircraft Windows

I used to own a plastics company (signs and laser cutting). We sanded and polished acrylics and polycarbonate all the time. I really wished I still owned even 1 laser cutter as I could cut new acrylics for my boat for next to nothing.

The fact is, sometimes its easier to repair something when cruising than buying new. That way you don't have to deal with shipping, customs and other logistics. These can be substantial hurdles depending on where you are (Mexico sucks).

[travellerw]

Originally Posted by Kenomac

45cm x 33cm approx. I'll check Defender.com

Thanks

Sounds like a 20 sized hatch.. You can also contact Lewmar directly and they will sell you the replacement acrylic. I have phoned them a few times and their service has been fantastic.

[Kenomac]

I'll go out and try polishing one tomorrow morning. The crazing is so shallow, I can't even feel any roughness in the outer finish. I'd do it right now except that it's gotten quite windy outside.

I'm just going to tape it off to protect the anodized finish and polish it like I would the hull. It can't end up being any worse? Right?

[donradcliffe]

I replaced 5 hatch lenses in Brisbane, and the local plastic company cut the acrylic replacements in one day, for a total cost of $200 Australian. Its not worth trying to polish them, especially if you have to remove the lenses to do it.

[Nineteen]

Originally Posted by Celestialsailor

I also doubt the airline industry does this sanding. Those planes are under the strictest safety guidelines.

Hi
Dont take this the wrong way but the airline industry uses this process all the time - particularly with cabin windows.

We also use it on windscreens with acrylic inner or outer panes that get scratched.

Of course it depends on the depth and the remaining thickness is measured ultrasonicaly to confirm it is within limits.

It is quicker and much cheaper than replacing a windscreen and we get up to 3 goes out of a cabin window.

Cheers
Tom

[Cheechako]

Originally Posted by Nineteen

Hi
Dont take this the wrong way but the airline industry uses this process all the time - particularly with cabin windows.

We also use it on windscreens with acrylic inner or outer panes that get scratched.

Of course it depends on the depth and the remaining thickness is measured ultrasonicaly to confirm it is within limits.

It is quicker and much cheaper than replacing a windscreen and we get up to 3 goes out of a cabin window.

Cheers
Tom

Yep, as I mentioned earlier, my ex son in law owns an FAA certified facility that does these windows, even does the front cockpit windows. Yes there are a lot of requirements, like minimum thickness etc, but it's done all the time. He actually polished some hatches for me years ago. But they were not crazed like that, just kind of pitted and not clear.

[Paul L]

Originally Posted by Kenomac

I'll go out and try polishing one tomorrow morning. The crazing is so shallow, I can't even feel any roughness in the outer finish. I'd do it right now except that it's gotten quite windy outside.

I'm just going to tape it off to protect the anodized finish and polish it like I would the hull. It can't end up being any worse? Right?

Did you try resurfacing the lenses? Did it work?

[Kenomac]

Originally Posted by Paul L

Did you try resurfacing the lenses? Did it work?

I lost interest and will simply replace the hatch covers someday when the project moves to the top of the list.