How much weaker are crazed hatches

tudorsailor

tudorsailor

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The Lewmar hatches on my 2001 boat are of course all crazed. The cosmetic effect does not bother me but are they much weaker and could they give way if stepped upon?

The yacht lives in the Med and I do not have hatch covers.

TudorSailor
 
By default you should direct your deck operations to try and avoid treading directly on hatches anyway.
I'd guess badly crazed hatches have reduced strength to the tune of approximately 20% - 30%.
Don't come moaning to me if you put your foot through one of them though.
 
Look on it as a benefit. Our boat is also in the Med and when the sun shines on the crazed main hatch it's diffused over a wide angle and the whole saloon area is brightened up.

More seriously, when we bought our boat the surveyor said there's no problem with mechanical strength with crazing. I guess there is a limit somewhere but ours are 10/12mm thick and the crazing is probably only on the surface.
 
tudorsailor said:
The Lewmar hatches on my 2001 boat are of course all crazed. The cosmetic effect does not bother me but are they much weaker and could they give way if stepped upon?

The yacht lives in the Med and I do not have hatch covers.

TudorSailor
Click to expand...

After 16 years of UK sun I changed the acrylic in two Lewmar hatches that were very crazed. After removal i put the glazing between two strips of wood on the floor and jumped on the middle. Repeated this many times. I could not break it!

Www.solocoastalsailing.co.uk
 
When my boat was being surveyed I asked the surveyor about the front crazed Lewmar hatch. He said that he had in the past recommended replacement. However he took a crazed hatch home which had been replaced and tried to break it with a sledge hammer. He failed. My hatch did a further 10 years and I replaced it this year mainly due to it leaking
and the need to replace the internal ply liner.
 
ditchcrawler said:
When my boat was being surveyed I asked the surveyor about the front crazed Lewmar hatch. He said that he had in the past recommended replacement. However he took a crazed hatch home which had been replaced and tried to break it with a sledge hammer. He failed. My hatch did a further 10 years and I replaced it this year mainly due to it leaking and the need to replace the internal ply liner.
Click to expand...

I've heard many similar anecdotes. Equally, crazing can often be polished out (albeit laboriously), which suggests the penetration of the crazing is often not deep.

On the other hand, when we bought our present boat six years ago, I determined to replace the crazed topside windows, mainly on the basis that the installation was ugly. I doing so I accidentally dropped one of the windows perhaps three metres onto the hard standing. It shattered to bits. I'll never know precisely what it was made from, but it certainly gave me pause...
 
I renewed the crazed windows on my previous boat, 6mm Perspex. I tried to break them and the only way I managed to was to clamp the Perspex in a large engineers vice and swing at it with a large lump hammer! So I'm not too worried about my crazed hatches on my present boat, but I have made a cover for the forehatch to slow down further crazing.
 
My old 6mm perspex windows ( circa 1972 - replaced 2005 ) were not crazed particulary - but had seen better days, My test with a hammer re-assured me It was worth replacing - they shattered very easily ! Maybe a uv thing. I replaced with 6mm polycarbonate.
 
If Acylic shatters "easily" then probably someone has allowed acetone to come in contact with it which will cause microscopic cracks.
Otherwise crazing maybe ugly but is harmless.
I don't mind crazing as it prevents deck walkers (when rafted) from peering into the cabin.
 
Thanks for all the replies. I think I will live with the hatches as they are...............

I was wondering what the difference was between acrylic and perspex. Turns out perspex is the brand name for acrylic. Acrylic is polymethyl methacrylate - which is also the "cement" I use to implant a joint replacement.

In my world we are taught that PMMA is plastic, so like a golf tee. If hit hard and fast its brittle and breaks, as does a golf tee, Slowly applied force allows plastic deformation and creep. So one can bend a golf tee if gentle slow force applied. Having creep for a joint replacement is a good thing!

I wonder if all I was taught about PMMA was true!

TudorSailor/Surgeon
 
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I don't know how germane this is but in the early 80s I was involved in some research on motorcycle helmets and it was discovered that polycarbonate helmets suffered from significant UV degradation which led to poor impact resistance. Now perhaps they have come up with variants that resist UV degradation but it would be something I would look into before using polycarbonate on hatches.
 
The alternative to Perspex/acrylic is lexan, which is the best known brand name for Polycarbonate. Even stronger than acrylic - allegedly bullet proof - but more easily scratched than perspex. Arguably better choice if you want ultimate strength or making a large poorly supported panel such as washboards. However I have used it for windows as well.
 
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