Window replacement recommendations please, for Hunter 212

[JimInPB]

I’m getting ready to replace the windows on a Hunter 212 & I was hoping to get some feedback from others that have replaced windows on sailboats before. I am particularly interested in hearing how Dow 795 has held up long term & hearing if anyone has recommendations for mounting systems that might be even better than 795. I’m looking to do things once & do them right.

I already received good information on another thread that I posted to the other day, but this is starting to get pretty far off topic from the original purpose of that thread, so I thought that it would be better for me to start a new thread, rather than hijack that one off into the wilderness. The other thread can be found here -

https://forums.sailboatowners.com/index.php?threads/good-deal-or-not-for-hunter-212.173955/page-2

Thanks already to Crazy Dave Condon & Mike Rottenborn, who already provided useful information on the previous thread.

I am also interested in finding out what window material is preferred for the windows themselves. At this time, I am considering either the more rigid Acrylic (aka Plexiglas, aka Lucite) or the more impact resistant polycarbonate (aka Lexan). I have yet to find any information on how the thermal expansion rates of these two materials compares to the expansion rate of the ACP (plastic) hull. I have also not yet decided if I want to add metal trim &/or screws to mechanically retain the new windows. I plan to go to a local plastic fabricator to have the new windows cut & bent to fit the contours of the hull. Replacement windows are not an off-the-shelf item from the OEM.

Any wisdom that is born of past experience is welcomed & appreciated.

Thanks,
Jim

 

[Mark Maulden]

My experience: My boat is 37 yrs old. Bought it six yrs ago with half the (original) windows cracked. The mfgr used Dow 700 37 yrs ago and that seal was still very good. I decided to have the yard replace windows as I'm not the best with sealants etc. They recommended the new technology stuff called Sika 295. A year later, the windows flopped out onto the deck. The yard owner surmised that the installer did not use the required primer. They cleaned things up and rebedded. Fast forward to now and one window leaks severely. This means the peripheral seal and the flat surface seal is compromised. Looking at the periphery seal, it is basically crumbling out and is also starting on other windows. The boat will be hauled in a few weeks for an engine transplant and the Beta dealer is also a wooden boat shipright. He stated he has seen numerous Sika 295 failures. So he said he'd help with new windows and we both agreed that Dow 795 is the right stuff. Do not use Sika!! 700 has 500% elasticity rating and i think 795 is close to that..

 

[JimInPB]

One of my main concerns is that the manufacturer rates 795 as a building sealant, & not a marine product.
http://www.bondedmaterials.net/assets/data/dow_corning_795.pdf
Does anybody have a couple of years on a 795 install that can tell me how it's holding up??

 

[jssailem]

Jim
Dow 795 is identified as a "Structural Glazing Sealant"
The special properties make it excellent for a boat.

FEATURES

•  Meets ASTM C1184 for Structural Silicone Sealant
•  Meets ASTM C719 Class 50 High movement capability +/-50% in well designed weatherseal joint
•  Excellent adhesion to a wide range of substrates including glass, anodized and coated aluminum profiles
•  Non corrosive cure system
  
  BENEFITS:

•  Ease of use – all-temperature gunnability and easy tooling
•  The cured product exhibits excellent weathering characteristics, and a high resistance to ultra-violet radiation, heat and humidity.
•  High ultimate tensile strength which makes it suitable for structural bonding applications
•  Excellent mechanical properties
  

 

[Crazy Dave Condon]

Dow 795, use it. Anything else you are wasting your time. Just be careful that the lexan and deck do not touch one another. It is time tested and used by everyone.

 

[agprice22]

I have replaced the windows and hatches in several boats. I cut my own 1/4", dark smoked plexi for the job. I drilled holes larger than the screws for the windows . I bedded them all with 795. I traced the inner opening and cut away the mask. I lightly scuffed the revealed plexi with sandpaper til it was uniformly matte. I applied 795 to the windows and screwed them to the boat. I used 795 to seal any remaining gaps along the edges.
You can remove the screws and caulk the holes or leave the screws.
Beware along the lower edges of the windows. The aft and inward slants combined in the cabin top will cause water to leak into the cabin there. Be sure those areas are well sealed.
If you have large, over hanging areas of plexi with no opening behind, you can paint them black and just caulk around the edge.

On the boats I have redone, the 795 was actually still quite rubbery and even gooey, leaving black adhesive smeared on my knife. I would call that a successful adhesive after nearly 30 years on one boat and 12 on another.

 

[MikeRottenborn]

Jim,

Tinted polycarbonate windows would be a nice upgrade to the Hunter 212 if you could have them bent to the countour of the original windows. Acrylic can also be bent but it may cracked if it comes into contact with alcohol, especially if the edges were flame treated.

Please keep me posted on what you end up doing here since I might be interested in a new set of windows someday as well.

Thanks,
Mike

 

[JimInPB]

Thank you for all the helpful replies. First hand reports of long-term success with 795 were what I was hoping for. The reports of other things that did not work well were also very useful to me. The advice about scuffing the plexi was an interesting read as well.

I used Acrylic for the windshield on my center console power boat. I mounted that on rubber stand offs with bolts inside. That mounting system worked well for that application, but that was an application that did not involve a water tight seal. That windshield has 90⁰ bends that were about 5 thickness’ in radius. I have not had any issues with cracking in the 2-3 years since I installed it. That plastic was cut & bent to spec by a local fabricator. I am considering changing to polycarbonate in this application only for the added impact resistance. I take sailboat windows seriously because in heavy seas, a broken window is a potential source to take on significantly more water than a bilge pump can handle. It may be overkill on this boat. I’m going to think about it for a while before making a decision.

My one remaining concern with the Dow 795 is this passage from the spec sheet –

Meets ASTM C719 Class 50 High movement capability +/-50% in well designed weatherseal joint

I need to find out what their definition of a well designed joint is. I’ll have to do some digging on that one. There is probably a range of clearance heights & bead widths that needs to be respected.

I’ll post my results when the project comes together.

Thanks for all the great feedback,
Jim

 

[agprice22]

Design is probably far from being a concern where there is an inch or two overlap of the window over the cabin. This adhesive is used to glue massive plates of glass to the sides of skyscrapers! It is used as a joint filler. Our uses are child's play to Dow 795!