Lewmar Superhatch lens replacement

[Delancey]

I am replacing crazed acrylic lenses on my thirty year old Lewmar Superhatches.

Having removed the lenses, I can see what appears to be the Chartreuse yellow-green color of zinc chromate primer that looks like it was applied to the aluminum hatch frame prior to the silicone sealant used between the frame and lens.

The only way I can think to remove the existing silicone before completing the installation is mechanically, by sanding, which will likely breach the anodizing and require the reapplication of new primer.

Any thoughts on silicone removal and re-installation? I know some sealants require the use of primers but I have never heard of one used for silicone and I have never heard of priming required for anodized aluminum.

[Roy M]

Abrasion, abrasion, abrasion, followed by either re-anodizing, powder coating or linear polyurethane (including aluminum primer), then, it's your choice on the sealant and the lens. The primer on the anodizing may be to protect the metal from the acetic acid in the silicone. This is a good time to replace the hatch seals and, possibly, the latch seals. Or, buy new ones and sell the old ones on e-bay. What's your experience level and time worth? I'm able to do the work on my own, 35 year old Bomars, but I'm going with new hatches with Lexan. They are overheads, and the eventual dulling of the finish of the lens will merely act as a diffuser. My old hatches are simply old, the repair parts are difficult to find, and the anodize is scuffed. My time is better spent doing other things.

[Redcoat]

Go to a glass shop that replaces auto windshields . They use a primer that is applied like shoe polish. Will prime and fill those areas. Also not any silicone will work I have seen it mentioned in other posts here. Lewmar has the whole kits and vids online.

[Delancey]

Originally Posted by Roy M

Abrasion, abrasion, abrasion, followed by either re-anodizing, powder coating or linear polyurethane (including aluminum primer), then, it's your choice on the sealant and the lens. The primer on the anodizing may be to protect the metal from the acetic acid in the silicone. This is a good time to replace the hatch seals and, possibly, the latch seals. Or, buy new ones and sell the old ones on e-bay. What's your experience level and time worth? I'm able to do the work on my own, 35 year old Bomars, but I'm going with new hatches with Lexan. They are overheads, and the eventual dulling of the finish of the lens will merely act as a diffuser. My old hatches are simply old, the repair parts are difficult to find, and the anodize is scuffed. My time is better spent doing other things.

I've been designing and fabricating with most of these materials for twenty years and have access to a CNC machine I used to program and cut my parts, however not a ton of experience with the silicone removal, hence the first part of the question.

I am replacing five hatch lenses and my companionway slide, as well as the drop boards. To match the spec on the companionway slide, I am getting all of it out of a single sheet of 1/2" material. I was able to get the sheet for about $250 from a local supplier. The companionway slide will be thermoformed later.

The acrylic is cell cast, as distinct from the less expensive extruded product, and has superior optical and structural properties. I avoided Chinese product, the stuff I got was from Mexico.

Lewmar uses the same cell cast acrylic in favor of it's greater hardness and scratch resistance. Sure the Lexan is "unbreakable" (which is not true BTW, you can break it just fine) but is more expensive and if the hatch is designed properly in the first place, then the greater strength of the polycarbonate is wasted at the expense of getting scratched more easily.

Because the material spec for the original lenses was 10mm and my product was 0.475" I cut a radius shoulder around the perimeter so I would have a proper fit with the gasket. The acrylic is isotropic and hard corners produce unfavorable stresses, the radius is important to alleviate this. The handles conveniently have two plastic washers just the right thickness where removal of one will give me a good fit so I didn't shoulder the handle holes.

I figured abrasion was the way to go as far as the silicone removal goes but way hoping there might be another way. I don't mind having to use the zinc chromate primer, which I have used before with APU's, I just don't have any on hand. One more thing to get. I also have some experience with anodizing so if you have any questions I'll tell you what I know.

As far as the why goes it's partly because I can, partly because I can't bring myself to throw and bunch of perfectly good hatch frames in the tip, partly because the new hatches Lewmar makes are a different sized radius in the corners which would create a finish issue for me.

A note about Lewmar, I tried to contact them regarding the primer and found them to be supremely unhelpful. I was told the installation was "proprietary" and that I should contact Tony at Select Plastics for professional replacement. I mean I get it that Lewmar is in the business of selling hatches but butyl tape and silicone? Proprietary my ass, not even thrity years ago when the hatches were new.

I had been in touch with Tony earlier on in my research. He was very helpful and nice, unfortunately his quote was basically more than new hatches. To rich for my blood, $4k in hatches uninstalled will cost me about twenty hours labor and $350 in materials without having to remove the old flange from the deck or deal with the finish issue.

I'll post more pics late in the project, for now some of the parts cut and edges polished. There's a radius on the inside of the shoulder, the shadow kind of hides it but it's there.

[Tim R.]

I just replaced the lens only on one of my Ocean hatches(size 60). I was able to get one for about $500 shipped from Port Supply. Less than what it would cost for Select to do a replacement. I now have one to play with and hope to work out a way to replace the acrylic only. I have 5 more Ocean(size 10) series hatches that need new acrylic and hope to save some dollars.

[Redcoat]

Delancy are you making any of those for Bommar. I need one replaced but as everybody is saying it is costly. Hatch alone is $1000.00+.

[Delancey]

Originally Posted by Redcoat

Delancy are you making any of those for Bommar. I need one replaced but as everybody is saying it is costly. Hatch alone is $1000.00+.

I don't know about Bomar, only the Lewmar Superhatch ones I am working on so I can't comment on the others. Look in your area to see if you can find a plastics fabricator if you don't want to cut the piece yourself with a jig saw.

If not a plastic fabricator, try your local sign company as they often have router tables and work with acrylic regularly. If you get lucky you might find someone with a piece of drop material big enough for your single hatch otherwise you will have to pay for a whole sheet.

Unlikely you will find the cast product, I suppose the extruded type may work but it's not my first choice. If you have to machine the material down in thickness as I have done, it might not be a bad idea to have the acrylic annealed after machining. Sometimes the sign guys have ovens for thermoforming and can do that for you too.

[Delancey]

Someone messaged me about this so here is the rest of the story-

I went ahead and sanded the hatch frames down to remove the caulk followed by masking and priming with a Zinc Chromate primer. In my case a spray can type that is intended for painting outdrives. I have also used brush and spray application version.

I did this because when I removed the existing caulk I could see what appeared to me to be the brush application version that had been applied to the hatch frame originally prior to caulking. To be safe I did a test with the caulk I was using which I allowed proper curing and was satisfied.

Like anodizing, zinc chromate primer produces a stable form of surface oxidation, one that is suitable for further bonding. If you ever tried to paint bare aluminum but were disappointed it flaked off later it's because you skipped this step.

No joke- zinc chromate is POISON! follow directions and only you with proper ventilation and protection. For Real.

[Delancey]

With the hatched prepped, time to mask like a pro. Peel back the paper masking on the acrylic. Lay a utility blade flat on the paper mask and trim off the excess.

Now apply your masking tape to the exposed acrylic surface. Leave some hanging off the edge which you will trim off later with your blade using a constant downward pressure to seal the edge of the tape to the acrylic. Also helps to smooth over the tape job with a rag and some pressure.

As you are applying the tape try to imagine how it will be to remove the tape while the caulk is wet (more on this bit later) and you have gloves on your hands. It is not very easy.

Be smart and sequence your tape strips as you work your way around the piece. When you get to the end place a folded over strip as a handle underneath the last strip of tape so that with one pull you can remove all the masking.

[Delancey]

Next, install the butyl tape and mate the pieces. Start by measuring out the length of the butyl tape you need an cutting it in advance. Be careful with all of this because if your stretch out the butyl tape, you will make it smaller in section and you need to do your best to maintain tolerances if you want to do a pro job.

Again, when you place the butyl tape, do so by pushing in the tape into itself when you go around the corners rather than stretching it to fit. If you stretch it, it will become thinner, which will leave a gap or air bubble when the lens goes on.

With the tape installed in the hatch frame I placed the lens on box above the hatch frame and lifted the hatch frame up into place. Because the butyl tape is so tacky you need to really nail when you mate the two pieces together.

If you are little off you have to do over, if you get parts stuck to the tape and stretch it to get it off you need to toss the tape and reapply. Best to lift the frame up to the lens than try to drop the lens into the frame as you will find you have much more control.

Once the parts are mated you want to clamp them. In my case I used a vacuum bag but I suppose you could use weight. Clamps might not be my first choice because I think you want to have as uniform clamping pressure as possible.

[Delancey]

Unfortunately I don't have picture of the most fun part, the caulking! Mainly because It's messy and I always wear glove for that business.

In this case I used Dow 795 in black. Put it somewhere warm or in the sun. It will flow better. Since you did such a nice careful job masking, don't be shy with the product. I find it better to push rather than pull with the tip and take your time to make sure you are filling the void and not leaving behind voids.

Apply excess then remove with a continuous sweeping motion, consistent pressure, and a clean sharp spatula. Pros call this step "tooling" and when you are done pull on your handle to remove the masking tape by pulling the tape away from the joint.

If you muck it up a bit, stop! Leave it alone! Go get a beer and be happy you did a great job. Do not try and fix it, you will only make it worse. Better to remove cured silicone than to try and remove it wet, you're just going to smear it around and contaminate a larger area.

Give you hatches the proper time to cure depending on the caulk you use, in my case I think it was about a week. Enjoy!

[Delancey]

Couple final thoughts-

Cost to replace from WM was about $3,100 for my five hatches, not including shipping. Select Plastics was a little more plus had like a six or eight week lead time which just did not work for me.

My cost was $250 for the acrylic, $16 for the zinc chromate primer, and I think like $10 for the butyl tape from EBay plus about 16 hours of my time.

I decided to reuse the hatch seals. That wasn't me being cheap, that was me thinking these things are going to go in a landfill for the next 100,000 years if I throw them away, besides, the hatches don't leak at the seal so if it ain't broke don't fix it.

The seals themselves are made from a type of material called EPDM that is used for roofing. If I ever have problems with them I will let you know.

If you want I can save you a little time and give you my AutoCAD drawings, you can give these files to anybody who cuts using a CNC. PM me an email. My hatches were sized 60, 40, and 20.

[Sailorman Ed]

Delancey - excellent write-up!!
Ed

[Nicholson58]

Nice job!

I would have been tempted to use a very sharp wood chisel and carefully remove 98% of the calk & fillers and not scratch the aluminum. As long as the original bond is still good this can work.

I get plastic from McMaster Carr and TPI (Total Plastics). TPI is local and we get OEM pricing. I have access to a machine shop so the rest is easy. Occasionally, the shop discards an acrylic drop big enough to be interesting. Seldom makes it to the dumpster.

I've dealt with Select Plastics too. They are very proud of their stuff as indicated in the pricing. This is like my experience finding gr-5 titanium for my chain plates. Prices varied from 205 each to 1000. Works best if they don't know its for a boat.

[Delancey]

Originally Posted by Nicholson58

I would have been tempted to use a very sharp wood chisel and carefully remove 98% of the calk & fillers and not scratch the aluminum. As long as the original bond is still good this can work.

Aluminum Oxide Fun Fact - Aluminum oxide is of sufficient hardness to cut steel. Hence it is used as a common abrasive for sandpaper, grinding disks, and cut-off wheels.

The anodized coatings used as aluminum finishes are sort of an organized layer of aluminum oxide resultant from an electrochemical process and are very hard.

Anodizers typically use a powerful acid bath to strip previously anodized parts. Keep in mind that anodizing is just a surface treatment, so once overcome, the base material remains relatively soft.

In theory, anodizing alone should be sufficient surface prep for bonding so why my hatches had the zinc chromate before the silicone I don't know.

Maybe it wasn't silicone but some other caulk that requires a primer and maybe the primer wasn't zinc chromate, I don't know either way because the guy at Lewmar was so profoundly unhelpful.

But what I do know is that I did a adhesion test with the intended materials whereby the cured caulk itself failed before the bond between materials failed.

I probably compromised they anodized surface by sanding which is reason enough for the primer if you want to be picky. Since it tested out I went ahead even though I couldn't be assured it was spec.

Zinc Chromate primers typically are very thin, more like a chemical wash and work by reacting with the base aluminum to again, produce an organized aluminum oxide surface that resist sloughing and promotes bonding.

Last summer I saw a boat I worked on some twenty years prior. The work included painting some fabricated aluminum winch bases. Prep work included sanding and brush application of a Zspars Zinc Chromate Primer followed by topcoats with an oil enamel.

While I am sure the winch bases have received new coats of paint, I believe the original prep work remained.