The GIANT Performance Catamaran Build/Refit Thread

[Chotu]

Originally Posted by GRIT

I used lexan on our last boat's dodger, and pilot house. I'm not a fan. It turns milky long before plexi starts to craze, and I'm pretty sure it has a higher rate of thermal expansion than does plexiglass. At least it seemed that way.

I checked with several cat manufacturers, and they all use plexi for their windows. I'd suggest you try plexi, it comes with a 20 year warranty against crazing, it's cheaper, and nearly as easy to shape as lexan. Cuts with a jigsaw, using a plexiglass blade, sands well, and is easier for silicone to stick to.

I used dow 795 too, though I'm not overly impressed. It's letting go in places.

Cheers.
Paul.

Yes, that’s correct about the thermal expansion being less.

Good data point on the Dow 795 letting go too.

I may give plexiglass a try too.

Honestly, I’m not sure what to go with at this point, but I do feel that a mechanical sealing system will work better than any of these miracle goop in a tube solutions.

I don’t want to be stuck redoing the windows every couple years when the goop fails.

So if I can stop water from leaking in by mechanical means (upside down U channel along the top), Im really leaning toward that.

Then I can put in weather stripping near the U channel to keep the window pressed tight to keep it from rattling or leaking air/water.

No more adhesives. And I can just slide the material in and out of the U channel tracks if I need to replace it.

This way it won’t matter what the thermal expansion is. It’s free to move.

If I do this, I can also go back to continuous 8’ sections using a 4x8 sheet. I had only reduced them down to 4 x 4 to try to slow the thermal expansion issues. Less leaks if the windows are all one piece and they look better that way too.

[Chotu]

Grit: For reference, what thickness acrylic did you go with?

[LittleWing77]

I dunno Chotu. Could you stick with the glass you liked, but trade off in something really light elsewhere...?

[Chotu]

Originally Posted by LittleWing77

I dunno Chotu. Could you stick with the glass you liked, but trade off in something really light elsewhere...?

No, you were right originally. I’m really thankful for your post waking me up.

I’ve made too many deals with the weight devil in the name of comfort already. Air conditioning, dishwasher, clothes washing machine, apartment size refrigerator.

I have to keep focusing on the “every pound counts” mantra that made the boat what it is to date. I just have to devise a better system to hold the sheets of whatever plastic in place.

[GRIT]

Thanks Bob for the information regards 995, I'll look it up.

Chotu, we used 12mm plexiglass (bought from Atkins and Hoyle, a marine hatch manufacturer) on most of the boat, with 10mm in the aft cockpit windows, and doors. Largest windows are about 6 feet x 40 inches.

I like your idea, regards preventing leaks by design, rather than sealant.

Cheers, and good luck.

Paul.

[Chotu]

Some weight math:

1/2” acrylic plexiglass 4x8 sheet 91 lbs
1/4” tempered safety glass with 3m ballistic film 4 x 8 sheet 104 lbs
1/4” polycarbonate 4x8 sheet 49 lbs

1/4 polycarbonate seems ok to me based on its resilience. It’s in there now and I can’t see breaking it with a sledge hammer. It bends and bounces back.

1/2” acrylic is based on grit’s specs. I assume it has to go up in thickness to account for its more brittle nature.

1/4” glass is kind of breakable but with the ballistic film it can’t come apart when broken and remains watertight.

Thoughts?

[Manateeman]

We have good size pilot house windows 2x3 plus a pocket slide door. We felt our best chance to survive a polar bear on deck would be to use laminated glass set into the pilot house structure. We hired a professional glass company who did skyscrapers in Boston and made Mylar pattens. They set the glass in a Sitka product..not sure which. All the forward windows are fine, but two of the port side windows have delaminating issues at the bottom edge. It’s ok with me, it looks like frost in New England. I spoke at length with the USA rep for one of the largest laminated glass factories in Europe. They have seen the problem in places like Florida and are working on a solution...he advised me to wait. There was speculation too much solvent was used which softened the plastic.
Laminated glass is very strong...it’s heavy but nothing else plastic gives you the crystal clear view. The future is in high tech films.
We have 316 stainless storm panels for hurricanes to prevent scratches not for strength. I think our frosty edge was the result of Sitka and The Sitka prep solvent. The guys thought they were doing the right thing because it said marine. The pocket door was set in a stainless u channel and the last side was TIG welded at the miter with the glass in it but loose. Tiny welds with a lot of cool down. Not a procedure I’d recommend for the faint of heart.
As soon as I get rid of my worthless Bomar ocean hatches, I’ll have a polar bear proof boat. Nothing prevents nail scratches. I’m thinking tempered glass with the new high tech film might give you what you need. You could prevent the total blow out with a thinner interior Lexan piece and the film on the outside piece would protect against uv damage. Tempered glass won’t stop polar bears occording to my friends in Norway who have some eye opening videos.
They do shy away from mirror foil windows but if they smell food...
Happy trails to you
Captain Mark and his “Orcas are our bad ass buddies” manatees

[CarlF]

Steve Dashew went with glass. Used Sikaflex. Weight wasn’t a major concern.

It’s worth noting that the USCG has pretty much stopped using mechanical framing on their patrol boats. I believe the reason is that when hit by a wave frames flex and the glass pops out. So you have to over engineer the frames adding a lot of weight - not to mention pretty ugly. Glued windows won’t pop out. .Also frames (and any bolts through the window) create stress risers that cause cracks to form

https://setsail.com/glazing/

[Chotu]

Originally Posted by CarlF

Steve Dashew went with glass. Used Sikaflex. Weight wasn’t a major concern.

It’s worth noting that the USCG has pretty much stopped using mechanical framing on their patrol boats. I believe the reason is that when hit by a wave frames flex and the glass pops out. So you have to over engineer the frames adding a lot of weight - not to mention pretty ugly. Glued windows won’t pop out. .Also frames (and any bolts through the window) create stress risers that cause cracks to form

https://setsail.com/glazing/

I’m sure weight wasn’t an issue at all in an 83’ monohull. This is a different boat. Please make note of the very first post in this thread. It details the boat and design philosophy.

Which frames are you talking about, specifically, that flex? The ones that act as a flange and sit inside a cutout?

I’m talking about putting a 1” piece of U channel on the outside of the deckhouse. Epoxied to the deckhouse. So to flex, either the deckhouse is breaking, the channel is ripping off with fiberglass and exposing my core, or the aluminum itself is ripping apart. Hard to see that happening.

[Thumbs Up]

Direct bonded glazing is pretty much the norm on new boats these days. Done correctly there should be no problem. The window should have a flit strip around it which is a coating around the perimeter to keep the uv from damaging the adhesive. (car windshields have it) Should have proper bond line configuration (not double sided tape). The bonded glazing should be leak tested and only then can you apply the "beauty bead". I don't see why you would have to ruin the look with the U channel. By epoxying this channel you break your #1 rule. How would you glaze the window in place and epoxy the channel on at the same time? Aren't your windows already set back into a rebate (looks like they are. Would the channel set into that rebate as well?

[Chotu]

Originally Posted by Thumbs Up

Direct bonded glazing is pretty much the norm on new boats these days. Done correctly there should be no problem. The window should have a flit strip around it which is a coating around the perimeter to keep the uv from damaging the adhesive. (car windshields have it) Should have proper bond line configuration (not double sided tape). The bonded glazing should be leak tested and only then can you apply the "beauty bead". I don't see why you would have to ruin the look with the U channel. By epoxying this channel you break your #1 rule. How would you glaze the window in place and epoxy the channel on at the same time? Aren't your windows already set back into a rebate (looks like they are. Would the channel set into that rebate as well?

This is my fifth or sixth time now doing these windows. That’s why I’m kind of done with the direct bonded glazing. It doesn’t work. Not in the long run. Not in Florida. At least not with the materials 3M suggested I use and large sheets of polycarbonate

In the pictures, you can see the flit strip.

VHB tape has been touted forever on these forums, and as something that holds skyscraper windows in. It was supposed to hold these windows.

I realize I would be breaking my number one rule by having someone epoxy those U channels into place. The work would be done outside, so I wouldn’t have to be exposed to it.

I used to have wooden u channels when I first launched. Temporary things. Things I thought would last a bit longer. However, they rotted. They were held in place by hotmelt poly urethane glue. Even coated with epoxy they rotted. They worked great. They held the Lexan in place and allowed for expansion and contraction.

In order to put the window into the U-channel, you just bend it. You stick it in the bottom, bend it, and then stick it in the top. No problem. Instead of glazing, I would use waterproof seal. Rubber. So the window presses against that. Something of that nature.

There is no rebate at all. The windows sit on top of the deck house. External to the cut outs. In fact, it looks pretty cool. It looks like one entire piece of glass wrapping around the entire boat. One giant window.

[sailingchiro]

On our 37' lagoon, we have massive windows that are fairly thick, 3/8" or slightly thicker. It is fastened on alot of 795 between the window and fiberglass as well as the screws in the corners. The 795 is around the window as well. Of course they leak some but couldn't imagine them coming out. It seems they over lap the fiberglass about 2 1/2". Some have taken them out but all complained of the task. I plan on sanding and polishing instead of replacing.
I believe the amount of 795 between the glass and fiberglass allows for the expansion instead of the sealant around the window.

[Matt Johnson]

I wonder if you're actually having issues with the thin polycarbonate being spanned over too great of an area. The flexing may be what's causing the leak not thermal expansion. The answer could be as simple as thicker plastic or switch to stiffer acrylic.



Matt

[Cadence]

just don’t know the best way to secure the aluminum U channel to the deckhouse. Adhesives would be best. Maybe epoxy just this once and have my girlfriend do it?

That’s my initial plan.
Liquid nails.

[Chotu]

Originally Posted by Cadence

just don’t know the best way to secure the aluminum U channel to the deckhouse. Adhesives would be best. Maybe epoxy just this once and have my girlfriend do it?

That’s my initial plan.
Liquid nails.

Really??? That would be amazing if it would hold up through the sun and rain and little bits of thermal expansion.

Anyone second this suggestion?