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Old 15-09-2005, 10:34   #1
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solar vents

i noticed on a boat similar to mine they have a solar vent in their forward hatch - old style bomar with tinted plexi - already have a leak to repair at caulking between plexi and alum frame.
can these vents be added retro ? whats involved ?
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Old 15-09-2005, 11:56   #2
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Use a good sharp hole saw to create the correct sized opening in the polycarbonate/plexiglass hatchlight. Drill as slowly as possible.
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Old 15-09-2005, 13:47   #3
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well gord - we both know there is no such thing as a "sharp" hole saw, but i get the drift. i won't use the one that has trimmed buried nails. hard plexi likes to crack and i do have some tricks to reduce risk. should things go ugly, it this the same product i will find at a glass/glazing business on land ? am i correct that the caulk that bonds plexi to frame is silicon ? west marine sells several solar vents - cheapest one is by (or sold under the name) bomar. i don't want cheap. the others seem to presume i will go thru cabin and may extend down too far. they do not mention hatch installation. any more info ?
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Old 15-09-2005, 14:09   #4
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Most have a drill bit center and circular blade. Just drill from both sides a bit to start the hole from each side. Use a variable speed drill and just drill as slow as you can. The saw gets hot if you go too fast and makes a molten mess. Drill on a flat surface if you can so the plexi is braced well.

With new stuff you drill with the prtective paper cover still on.

A Dremmle hole saw is also nice too.
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Old 15-09-2005, 14:33   #5
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To cut Old Perspex, A hole saw will work OK. Firstly, drill the centre hole, without the hole saw blade attached. Then with blade fitted, start by cutting the surface from underneath first. Don't go too far. Then come back to the otherside and apply water to the surface as a cooling and lubricating agent. A small amount of disnwasign liquid helps as a wetting agent. Slowly work through, without applying to much pressure. Once the hole has been cut, run around the edge with some fine sandpaper to "stress relief" the cut edge.
Ensure the hole is slightly bigger than the unit going into it to allow for heat expansion. As for sealing, Don't use a sealant at all. The unit will or should come with a seal. If it doesn't, go by some thin seal strip with sticky side, from the hardware store. Ensure this covers all bolt holes.
Ensure bolt holes in the perspex are bigger than the bolts. Do not use a tight fit and ensure no pressure is on any or between any to bolts. It is also a good idea to use a countersink to "V " the edge of the bolt hole to relieve stress.
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Old 15-09-2005, 15:27   #6
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wheels - your detailing is perfect, including all the tricks. very nice. what is "perspex" ? nz brand of plexi ? i still wonder if, although i am coming to conclude, the plexi is just plexi - buy it at any glass shop. caulking question is not at vent, but rather where plexi meets hatch frame. i already have a leak in the corner, so i think i will remove the plexi, (gives me more control for vent project) and then replace (old plexi is pretty scratched up) or reinstall with what looks to be black silicon, similar to automotive caulk used at windshield replacement. aluminum is not easy to stick to, so i wondered if there is a better choice. i do not know marine products as well as i know residential construction. the plexi will shrink and grow with temp change so the caulking must allow for expand / contract. the other question is who makes the best solar vent that can be installed thru a thin hatch and not stick down into the cabin. paul - dremmel would be perfect tool for rounding corners of new piece of plexi to scribe to frame (i would make template rather than freehand) and also to ease edge of cutout to relieve stress and risk of cracking later. you guys are good, but didn't answer my poorly worded questions. capt. lar
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Old 15-09-2005, 18:42   #7
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capt. lar,

Perspex is an English way of saying "Plexiglass". Apologies to our NZ friends who have moved on from the colonial days. My in-laws live in Torbay.
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Old 15-09-2005, 20:55   #8
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Wheels, just to clarify, you are not suggesting using counter sunk, or "flat head" screw are you? The counter sunk holes with a pan head screw will work, (although I have never heard of using the counter sink that way). If you use counter sunk screws, it will crack the plexi or lexan around all of the screws.
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Old 16-09-2005, 01:41   #9
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Thanks for the ask for clarification there Kai Nui. I can see where a misunderstanding could arise. So to be clearer, the countersink is a very small usage of the device. Just enough to shave the edges of the holl, nothing else. Certainly not deep enough to fit a counter sunk screw head.
Here in NZ, "Perspex" which I think yes, is also called "Plexiglass" (I think from the term of Plastic Flexible Glass) is an Acrylic sheeting. Lexan is the "bullet" proof material that I think is called "Polycarbinate". (Correct me if I am wrong on that one.) Lexan although stronger, is very prone to fine scratching on it's surface. Perspex is not as strong to impacts as Lexan, but has a very good surface that will not scratch easily. Both materials will easily fracture along itself if stressed in a specific way. The most common failure is due to bolt holes being to small and little room for a sheet to expand. teh stress built up eventually causes the sheet to fail.
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Old 16-09-2005, 01:47   #10
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Oh and I forgot to add capt. Lar, sealants to use would be an "MS Silicon sealant" or use a Urathane sealant with it's required primer. Sikaflex is often talked about. There are a few others as well. For the aluminium, you MUST use a primer. But also read the product literature for use on Aluminium, as an etcher may need to be applied first. If doen correctly, these adhesive sealants are all that are required. No other fastner is needed. I know of some portholes in bow's of some big boats that those adhesives are all that hold the window in.
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Old 16-09-2005, 03:58   #11
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Hatchlight Bedding

Silicone:
Depending on the Frame material, you’ll have to choose between a Neutral Cure or Acetoxy Cure Silicone(*1). “MS” products (Modified Silicone, usually silicone/polyurethane), such as Boat Life “Life-Seal” etc., have also been used successfully.

*1 Acetoxy cure products release acetic acid during curing, which can attack the underlying substrate material. This can cause corrosion of certain metals and prevent the proper adhesion of the silicone. However, on other materials, the acid can etch the surface slightly and increase the adhesion. Aluminum is one such material. Copper and zinc, however, are corroded by the acid. Thus brass and galvanized steel should not be used with silicones which release acid. Dissimilar metals can form electrolytic couples and corrode severely underneath a covering of acetic acid releasing silicone.
Assume that Silicone sealants are corrosive, unless labeled (or you know) otherwise. Silicones do not generally adhere well to all other plastics (polycarbonate, plexiglass, et al), nor do other sealants adhere to a silicone contaminated surface (*2). Use silicone sealants compatible with polycarbonate such as: Dow-Corning #999-A with Primer, or GE Silglaze N Gesil N (Always check compatibility to polycarbonates before using elastomeric adhesives)
*2 A damaged seam sealed with polysulfide or polyurethane, for example, can be repaired with the same material once the damaged material has been sanded or cut away. On the contrary, when replacing a fitting bedded in silicone, all of the old material should be removed, the mating surfaces cleaned, and the part should be completely rebedded in fresh material.


Expansion:
Polycarbonate and black anodized aluminum will (thermally) expand and contract at about the same rate. Allow for movement of about 1/32"/per ft. of material, over a 70 degree temperature swing. Dark polycarbonates may expand slightly more than bare natural aluminum. It is also important that the frame offers sufficient edge engagement to hold the sheet secure (not TOO much expansion gap).

Polysulfides & Polyurethanes should NOT be used with most (*4) plastics:
Polysulfides should not be used for bedding/sealing PVC, acrylic (Plexiglas), ABS, or polycarbonate (Lexan) plastics, because the solvents in polysulfides can leach the plasticizer from these plastics and cause them to harden and crack.
The prohibition against the use of polyurethanes for bedding thermoplastic fittings is the same as for polysulfides, but interestingly, the problem is exactly the opposite. Solvents, leaching from some plastics, can react with polyurethanes and cause a failure of the adhesive sealant compound.
Plastic fittings made of epoxy, nylon, or Delrin, can be safely bedded with the poly's.

Fungicides & UV Protection:
Household silicones contain a fungicide (anti-mildew agent) that rapidly turns yellow when exposed to ultraviolet rays. The higher-priced “marine” silicones also contain a fungicide, but employ UV-screening agents to prevent yellowing.

Countersinking:
Plastic glazing should NOT be countersunk (even slightly, for gasketting purposes); which can lead to edge cracking & failure.
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Old 16-09-2005, 06:29   #12
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thanks gord - thats what i call detailed info. good to go. thanks to all for input. capt. lar
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Old 16-09-2005, 09:17   #13
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Suffering from Sealant Confusion? ~ by Scott Thurston, March 2000
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Old 16-09-2005, 10:04   #14
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It may be the damp atmosphere in winter, but the solar vents have a very bad track record in UK. Great while they last, but guaranteed for a year and broken in 1 year and 1 day.
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Old 16-09-2005, 13:16   #15
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The small 3" or 4" diameter power vents are inadequate to satisfy the entire ventilation requirements of even the smallest boat. They can, however, provide some excellent supplementary direct spot ventilation - especially as required in sleeping accommodations & (othwerwise) enclosed compartments.

I installed a couple of 3" Nicro (Marinco) Day-Night Solar Vents (#N20503S), c/w NiCad batteries on “Southbound” in 1992. I used 1 as a F/A supply (V-Berth hatch, blowing directly on my face - very welcome), and 1 as an exhaust (Head).

While the fans & solar cells worked great (for what they are), the back-up batteries didn’t last more than a year. I replaced the originals (once) with the same sad result. Ten years later, the fans still produced decent ventilation (± 12 cfm) during the daylight hours.
I don’t know if the newer units are still eating batteries, or if the newer Ni-MH batteries might survive longer.
BTW: I recall that you have to remove the “dead” battery, to get the units to run on daylight solar power.

Were I to do it over, I’d probably use the hard wired 4" Combination Solar/12V Vent (#N20704COS) producing about 18 cfm.

See also Nicro’s ”Boater's Guide To Cabin Ventilation” at: http://marinco.securesites.net/docs/...vent_guide.pdf
and
“Ventilation” (Keeping your boat dry for livability and longevity) ~ By Joe Parker
http://www.marinershardware.com/InfoVent.php
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