Fellow catamaran designer Richard Woods did some nice research on sticking windows. He contacted 3M, and this is what they replied:

Thank you for contacting 3M, the innovation company. Our VHB tapes are suitable for bonding plexiglass windows to a fiberglass boat. A similar application bonding windows in motor homes is currently utilizing VHB tape.

The VHB 5952 family may be a good choice, but we prefer tape 5962,which is the same product except thicker (62 mils thick). The extra thickness helps fill any gaps between the plexiglass (perspex) and the fiberglass to help insure a tight seal, plus the thicker tape will expand and contract more. The VHB tapes will expand lengthwise three times the thickness of the tape.

Another tape that is an option is VHB 4979F. This product is also 62mils thick. The core of the tape is gray, but the top and bottom surfaces are black (you can only see the gray at the edges).

With both products, it would be best to use Adhesion Promoter 111. Plexiglass can have a variety of coatings, such as anti-glare,anti-fog, or scratch resistant. Some coatings are a bit slick. AP111 helps insure the tape bonds well.

If the window has square corners, a small dab of sealant may be needed right at the corner seam to help make it water-tight. Our 4000UV sealant is an option.

Regards,John Dritsas-Inside IATD Product Specialist- 651-575-4270 jdritsas@mmm.com mailto:jdritsas@mmm.com

And I’m impressed how helpful 3M is,especially compared to ZipLock.  I have been specifying using Norton double stick tape for years and it is in a graphic here from a year or so ago.  I did not have a part number though so this is great.  Most of my cat windows are recessed so standing water can freeze and damage the seal.  To prevent that, I spec a UV resistant silicone sealant to be applied both inside and out as in the detail below.

One thing to keep in mind when installing windows this way is that once you place the window on the tape, its there.  You cannot try it again.  Line it up exactly right the first time.

Of course no fasteners are needed.  One good example of this is the KHSD 58′ Aolani http://www.aolani.cc/  They have about a mile of window seams and are well into their second decade.

The thickness of the tape helps dissipate the dimension delta caused by  the temperature delta.  That amount for acrylic is .00004″ per inch per degree.  So a delta of 100 degrees F and a window of 6′ would have a thermal size change of 0.288″.    That would be between two sides, so half of that at each side.  Clearly a goal in life then is to try to place windows during midrange temperature.  That will halve your dimensional delta.

It just got more stressful here. I hope everybody can wait a few more days on everything. Demanding and I think unfair customer insisting on being first in line or getting full refund. Already has most of set. I do appreciate everybody else’s patience and will keep on working late to catch up.

One more wonderful video from silent Bay.
http://vimeo.com/88110770

“There will be no shortage of crew aboard the Hughes 58 cat Li’l Explorers. Mom and Dad (in dark blue) will have these five youngsters along, plus a baby. But wait ’til you hear what they had to go through before they could begin their cruising dreams.”  Photo Latitude / Andy© 2014 Latitude 38 Publishing, LLC

“Well…Cat2Fold and I have made the big screen!!!
We’ll be featured on a Norwegian reality TV show called “Paradise Hotel”!
It should be playing within the next few months.”

such compassion.

I just got back from Midway Plywood in Lynnwood, WA.  www.midwayplywood.com/‎

They have supplied many of my plywood/epoxy projects including the two Lake Victoria ferries. I had gotten a report that the 3mm plywood (2.7mm actually) was such poor quality that it was not usable. I just bought some very good sheets, so this shipment is better. It is Seal Brand which I have used before. The price has gone up about 50% in the last 6 months to $17.95 per sheet before tax.  It is about half the price of 4mm BS-6566 plywood at Edensaw Woods. http://www.edensaw.com/

I have not D790 tested it yet.  Possibly Thain Boat has.  I’m guessing the numbers would not be as good as BS1088 but close.

I always assume that everybody knows the information in the article below but I just was brought up short, so it may be time again. A true believer over at multihull_boatbuilder forum sent me a note telling me that everytime I point out one of Derek Kelsall’s technical mistakes (and there are so many; he is big polyester fan) “people…believe in your expertise less and less”.  I did find out that he is unaware of the below and not interested in it. It won’t be the first time that true believers wished I would stop pointing out what I see. Again, because I think it is so important to having a good vessel.

There are many good reasons to use epoxy instead of polyester.
First, stretch to failure. Glass fabric has about 6% stretch to failure. So does most room-temperature epoxy, and many vinylesters. Polyester stretch to failure is, everyone? About 1%. So in tension, the glass is only loaded to about 17% of its strength before the resin matrix starts to break apart and become a necklace.

Polyester will be bonding with water throughout its life, and it will gain surprising weight from that water, while losing strength properties. If I may quote from a D570 water weight gain test, “The orthophathlic casting had more than a 2.5% weight gain after 4 days, then showed a weight loss on the 7th and 14th days. That means the polymer is being broken down, solubilized, leached out of the composite, and replaced with water.”

The biggest benefit of epoxy is that epoxy is more forgiving during construction. Get the mix ratio right and you are there. With polyester, or even vinylester, one has to vary the MEKP level and vary the N,N-DMA level, oppositely, as a function of temperature change. Or, also, vary the BPO level and again vary the N,N-DMA level oppositely, as a function of temperature. The catylist/promotors have to be done exactly right to get a good degree of cure. The catylist/promoters will have amounts of down to fractions of a percent. Those amounts must be very precise if good results are intended.
Also, if the part is stored at less than 10C it may never cure fully, even with a later post cure. Using epoxy, you can improve the laminate properties with a post cure, almost always.
Interplastic Corp. has some great papers on this, which I am quoting from. Specifically, Proper Cure of Vinyl Ester Resins and A 15-Year Study of the Effective Use of Permeation Barriers in Marine Composites to Prevent Corrosion and Blistering.
I’ve never been able to afford a temperature controlled shop, so this
matters a great deal to me.
Until someone is using a Barcol hardness tool or even better, a D790
flexural strength test to prove it, I don’t want to hear how a laminate is acceptable with any or all the above conditions off, just because the lay-up looks good.
The point is if the temperature was too cold when you did an
epoxy laminate, you could bring it up to close to 100% cure later.
If you, for example, do a polyester laminate at 15C with 1% BPO and 0.3% N,N-DMA, you will have only an 80% cure and it probably cannot ever be improved.
That same formulation however will give 96% cure at 25C.

Most room temperature cure epoxies post-cure at around 65C to 70C. Static properties increase with the cure, and so does toughness against impacts. Epoxy can accrue the benefits of a post cure but polyester and most vinylester  will not be improved by a post-cure.  You got what you got.

Blisters are also a huge issue. With polyester, especially with orthophthalic resin, as Terry McCabe of Interplastic said, “Its not if it will form blisters, but when.” The useful paper again is “A 15 Year Study of the Effective Use of Permeation Barriers in Marine Composites to Prevent Corrosion and Blistering“. Aand again, Interplastic.

Shelf life is another issue. The useful shelf life of epoxy resin is years. Hardner has a shorter shelf life though it is still good for years. Both vinylester and polyester components have a shelf live of just months. If your project gets interrupted, that can cost you if you did a bulk-buy to save money.

  In an issue of Multihulls Magazine, Tom Pawlak notes several other shortcomings of not using epoxy resin, including excess shrinking of the part. That is more significant than simply the parts not fitting. Excessive shrinking sets up what is called residual stress within the part. That is stress between the various layers that are oriented different directions. The result will be earlier failure under less load.

In conclusion, both epoxy and vinylester are much preferred to polyester. Structurally, epoxy and vinylester are close in properties. Epoxy however is much easier to work with, and is much more forgiving.

 I have had this KHSD 42 here before, but I really like this picture.  CM construction.  And on Face a video.  https://www.facebook.com/photo.php?v=10200858081254047

Several people have visited with Brian on C2F recently.
See http://members5.boardhost.com/lamanzanilla/msg/1391418285.html

and this from Dr. Peter; “BTW, I spent a day last week on Cat2fold, in La Manzanilla, Mex. Now owned by a Brian Charette,. He cruises it on the Pacific side of Mexico and puts it on dry land in San Carlos, Mex, in the summer while he builds straw-bale houses in Wyoming and Idaho. One of the reasons he chose the boat was that he could fit in the boat- he is 6 foot 7,
blonde, rasta hair, very hip, 42 years old, lady-killer kind of dude.
Has two kids 8 and 11 who cruised with him for a month this year. Their
top speed was 18 knots surfing under bare poles. We did about 11 during
the day in about 18 ambient wind. It has to be the easiest smoothest rig
to run around with. I was so happy to give it a whirl because that is
the configuration I think I would end up with, paired to a big outboard,
once I get really old. So I thought you would appreciate an update on
one of your really original boats!”