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Discussion Starter · #1 ·
I have read a number of offshore cruising books that recommend a minimum half-inch lexan for roof hatches. The Bomar and Lewmar websites offer no information on how thick their lexan is for a given hatch size, unless I missed it. Can someone please provide a link for this information if available.

Also, what about tempered safety glass? How do the Ultra II hatches soldd here at the Sailnet store compare to the lexan ones?

My main concern is the hatch lens strength/durability and longevity, rather than how convenient it might be to operate, tho that is also a concern.

Can a nicro solar fan be mounted in a tempered glass lens. I'm guessing no.

I notice the Bomar hatches have one crossbar on their smaller hatches and two on their bigger ones. Is this because their lexan is thinner than Bomar's?

There are some hatches that have 316 ss frames over aluminum bases. Is there any advantage to this. Seems this might be a corrosion issue.
 

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Acrylic is what most use..

Here are some quotes from Tony D'andrea who is the Acrylic & Polycarb guru in the marine industry. He is the Nigel Calder of portlights and hatches and owns the largest hatch warranty & repair facility in the world.

Bomar claims they use Lexan but then reinforces the hatch with cross bars to prevent foreshortening and cave ins.

Atkins & Hoyle and Goiot make some beautiful & BOMB proof stuff if you want to pay for it & both use cast Acrylic.

There's more here than you probably need to know but it's good info.



Tony on Acrylic vs. Polycarbonate:



"Consider the Following:

  • All major hatch, portlight and window manufacturers use Acrylic in offshore / bluewater marine products.
  • Acrylic is more scratch resistant than standard (9034) polycarbonate.
  • Acrylic is significantly more durable when exposed to Ultra Violet radiation (sunlight).
  • Acrylic is less expensive than Polycarbonate.
Don't misunderstand my preference for acrylic. I buy, use and sell a significant amount of both products and each has its application. In my humble opinion Acrylic is more durable, versatile and cost effective in the hands of a skilled craftsman than polycarbonate.

Additional considerations may include polycarbonate with UV and scratch resistant coatings. While these products are heavily promoted by several manufacturers and carry 5, 10 even 15 year warranties the following information has been reported in "real life"applications:
  • Polycarbonate is impact resistant. When its new it is almost impossible to break.
  • Small quantities (less than a 4 by 8) in gauges over 1/8th inch are difficult to to find in the uv/scratch resistant grades.
  • Colors are limited. Only two standards (gray and bronze). Try and find anything thicker than 1/4 in UV/ scratch resistant!
  • Polycarbonate foreshortens when subject to static or dynamic loads. What this means is if you replace your hatch lens with polycarb, seal it and then step on it the ductile material will deflect (bow) in the center. One of two things may happen. 1st you will surely break the watertight seal, 2nd you may end up with a leg in your galley.
  • As for the warranty: The original owner is warranted against failure subject to the material being submitted to the distributor for evaluation with the original invoice subject to actual replacement cost at the time of purchase. I guess this means they sell you a new square of material and apply the old payment to the new cost. How about the labor to fabricate the part, install it and sealant? Why take the chance?
Polycarbonate is a great material, The US Air force uses it for fighter canopies! I sell Polycarb to the USCG and US Navy. Remember they don't mind using it because we are paying to replace it every three years.
Both Acrylic and Polycarbonate have specific uses and installation requirements.

Cast Acrylic (of a specific thickness) is in accordance with CE and ABYC guidelines, and installed on virtually all of the big blue water sail boats produced on both sides of the pond. Polycarbonate is commonly used as a replacement due to its ease of fabrication and incredible initial strength. The USCG and USN require Polycarbonate on their vessels but they also have a PM cycle of 36 to 42 months for change out. My Tax dollars at work...

Due to its ductility Polycarbonate it is more challenging to install. I have seen Sika Flex 295UV with primer and Dow 795 both mentioned. I use and recommend both. Dont go over 4 ft continuous length with a fixed portlight. Remember the coefficiant of thermal expansion for Acrylic and Polycarbonate is in the neiborhood of .000039 per inch per degree F. That means an 8ft plastic port will expand and contract up to 1/2 of an inch from the coldest day in Feb to the hottest day in summer. WOW!! Compartmentalize the job. It will be easier to install and less prone to leaks.

Never ever bolt a plastic portlight in place. Screws are fine to hold a lens till the adhesive cures. Take them out asap and fill the holes with the afformentioned products. Both of these products are rated at 700 + percent elongation before tear.
Strong flexible and UV resistant.

Been to a boat show lately? Seen any screws? Glass is good so long as your boat does not twist or torque. Show me a fiberglass boat that does not twist and I will show you a cocktail barge tied to the dock.
"

Tony on Sealants:

"I hear the question as to which sealant to use when bonding Acrylic, or Polycarbonate to aluminum, stainless or FRP over and over and over.....
Well here goes... The only three adhesives I would consider using are Sika Flex 295 UV with the primer, GE SG-4000, and Dow 795. Using the correct adhesive is only 1/2 the battle. Do not apply the sealants below 50 degrees F. The temperature must maintain at least 50F during the entire 21 day cure cycle. Cut this corner and your finished before you start. Preparation of the bond area is also very/ very important. DO NOT TOUCH THE BOND AREA WITH YOUR BARE HANDS! Contamination from the dirt and skin oils will make a solid cure impossible. You may clean the FRP and metal with acetone to prep the area but if you touch the Lexan or Plexi with harsh solvents you will ruin the portlight. A 50/50 mix of isopropal alcohol and distilled water will work well to clean the plastic if needed. Remember that clean enough is not clean enough."
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I have Atkins and Hoyle hatches on both my boats, but fixed 1/2 inch through-bolted Lexan for the pilothouse sides and the fixed coach house portlights. I have tempered glass in the A&H opening ports (5) and in the three forward "windscreens" in the pilothouse and will have tempered glass in the opening 10 inch Newfound Metals circular portlights I am planning to install in the pilothouse in place of the fixed Lexan I have now.

There is a reason and a logic behind each material in each location, and I feel quite happy with those decisions and choices.
 

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Discussion Starter · #4 · (Edited)
Thank you Valiente and Maine Sail, much appreciated.

I visited Tony D'andrea's website and unfortunately there doesn't appear to be any information there that would assist a person in selecting a new hatch, other than his advise to choose Acrylic over polycarbonate. And since, according to him, all major hatch manufacturers use Acrylic, it's a moot point, tho Bomar uses Lexan according to their marketing literature. :confused:

The Atkins and Hoyle XR Offshore Hatch offers the option of either 3/8" (0.95 cm) thick acrylic or support bars. I can't really compare this product to others because I scanned the websites for Bomar, Hood, Nibo, Gebo, Moolight, Goiot, Vetus, Taylor, Man Ship, and Lewmar Marine and so far I see NO INFORMATION about acrylic thickness or support bars. In fact, they don't offer much information at all, other than measurements and a little photo. So I'm back to square one.
 

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For what

For what it's worth I sailed a Shannon in the Perfect storm and we got beat to hell. The boat had acrylic hatches that I doubt were 1/2" and had no failures.

Our current boat has cruised 30k plus miles with Goiot hatches. One is 24 X 24 with no support bars and 3/8" casat acrylic. Zero issues. I just swapped the acrylic this season after 30 years of service with zero leaks and zero failures despite many, many, many off shore miles.

Call Tony he will be glad to fill you in on what you should look for and also may tell you who's hatches he thinks highly of, if you ask..
 

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For what it's worth I sailed a Shannon in the Perfect storm and we got beat to hell. The boat had acrylic hatches that I doubt were 1/2" and had no failures.

Our current boat has cruised 30k plus miles with Goiot hatches. One is 24 X 24 with no support bars and 3/8" casat acrylic. Zero issues. I just swapped the acrylic this season after 30 years of service with zero leaks and zero failures despite many, many, many off shore miles.
Someone at my club threw out a 21 inch square Goiot hatch in good condition excepting that the acrylic had a crack in it. I scooped it, and will replace the acrylic and repurpose the hatch to go into my forward collision bulkhead (above the waterline) as a way to get into the forepeak without going on deck from the saloon, plus a way to air out that area.

The collision bulkhead has limber holes that would normally remain plugged on passage with rubber stoppers.

Yes, it will look a trifle odd to have a clear deck hatch in the "wall" of the saloon, but as far as I'm concerned, it will solve a number of problems, will save me $1,500-$2,000 from the sort of "submarine hatch" one might normally find, will get air and light into a dark part of the boat, and will allow us to carry long items in the main salon that might be torn off the deck in bad weather, like whisker poles or our Portabote.

I intend on having this hatch close to the "ceiling" of the saloon, and if I've got water in the forepeak within 22 inches of the underside of the deck, having a hatch there is the last of my worries.
 

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Discussion Starter · #8 ·
If you are looking for hatches that will not shatter, look past Lewmar,I have several in my office that are in no less than 4 pieces.
Are these the Lewmar "Ocean" hatches or the low profile ones? It is my understanding that most, if not all, low profile hatches use 1/4" Acrylic or Lexan. This is too bad because these low profile hatches take less of a wave hit. A low-profile cast aluminum model with a half-inch lens combined with one or more cross bars would be a good product.
 

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Discussion Starter · #9 ·
...I scooped it, and will replace the acrylic and repurpose the hatch to go into my forward collision bulkhead (above the waterline) as a way to get into the forepeak without going on deck from the saloon, plus a way to air out that area.

The collision bulkhead has limber holes that would normally remain plugged on passage with rubber stoppers.
I guess you don't really need a watertight collision bulkhead, since your boat is steel.
 

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Discussion Starter · #10 ·
For what it's worth I sailed a Shannon in the Perfect storm and we got beat to hell. The boat had acrylic hatches that I doubt were 1/2" and had no failures.

Our current boat has cruised 30k plus miles with Goiot hatches. One is 24 X 24 with no support bars and 3/8" casat acrylic. Zero issues. I just swapped the acrylic this season after 30 years of service with zero leaks and zero failures despite many, many, many off shore miles.
Yes, I personally don't know of any boat losses due to a deck hatch shattering. Nevertheless, logic dictates that a smaller hatch with a thicker lens will take more of a pounding and probably has increased longevity over a large hatch with a thin lens. The thicker lens, it seems to me, will have a larger bonding area, will flex less, and therefore be less likely to break down along the seal and leak.

The marketing material used by hatch manufacturers makes it pretty clear that the top priority by far is how easy they are to prop open with one hand. A testament to the modern boater mentality.
 

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I guess you don't really need a watertight collision bulkhead, since your boat is steel.
Oh, no, I do, but if the bulkhead is watertight to within two feet of the deck, I don't lose a lot. A regular doggable hatch is likely fine for that, as tearing up a serious hole in the first seven feet of the boat would probably mean abandoning ship anyway, just in a more orderly fashion or with the option of "sitting tight".

The boat has two other half-height bulkheads either end of the engine bay.
 
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