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Alan Stewart

Cockpit hatch hinges???

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Apparently I was sold a SS cockpit hinge in which the screws and the pivot rod through the hinge was not ss.  It lasted about four months.  Now that I have ground off the last of the rusted screws, I am ready to touch up gouges with thickened epoxy and put in a new set of hinges. What is B & B's suggested hinge system and hardware for those lockers? 

 

 

I think Graham has always used stainless steel piano hinge for his cockpit hatches. Piano hinge is nice because it's pretty flat, and very strong and stable. B&B purchases piano hinge from our main supplier "paxton" which is 304 stainless. Generally we feel that 304 stainless is fine for our small boats which live most of their life on trailers sometimes even under cover rather than sitting in salt water. For an ocean cruising boat going with 316 stainless would probably be worth the extra cost. 

 

Our 1-1/16" 304 stainless polished piano hinge is $28 for a 6' length and we've used it on many cockpit hatches. I've often seen stainless steel screws create rust stains on the stainless piano hinge and my guess is that the screws are not as high a quality 304 as the hinge itself. I think it's worth the extra for 316 screws in this case because the staining looks bad but I think the 304 hinge is ok. 

We usually just use pan head screws for cockpit hatches. In practice they really don't stick up too bad and they are usually behind your butt when you're sitting in the cockpit so it's just not an issue. 

 

McMaster sells 316 piano hinge for not much more. about $36 but it's unpolished. The also have polished for more like $46 on last check (all 6' lengths)

 

I'm about to need some hinge material for my own build and I really wanted to try something different. I wanted to try and save some weight but also just make it a bit easier to install especially for all of my bunk hatches in the cabin. I've known about live hinges forever because we used them on model airplanes especially RC gliders where the elevator and aileron hinges were just kevlar strips bonded into the wing core and then scored to free them. A google search for "kevlar piano hinge" shows all sorts of very expensive options most of which include carbon fiber legs with the kevlar in between. I bought a small amount of kevlar to try and make my own for use on my cabin bunk hatches and maybe even cockpit hatches but my first test was not very good. the hinge snapped after just a few dozen bends. I'm going to keep trying though but I think i should have started with some thicker kevlar and the next test I'll try to prevent epoxy from getting to the hinge line at all perhaps with some hot wax pressed into the hinge line before laying up the kevlar flat on a mold surface. I also used plain old kevlar tape so half the fibers are wasted going along the length of the hinge. I should have got some thicker bias tape which would have had all fibers across the hinge line and requiring less bending of any one fiber. I will report back on my next attempt. 

 

I would just buy some kevlar hinge (video below) but the price is ridiculous. Sure would be nice though to just glue it down and done! so maybe if you factor in all the time it takes to screw, bed, polish, drill, yada yada it's maybe 6 vs 1/2 dozen cost wise. 

 

Another option i recently saw as fiberglass or carbon piano hinge with a stainless steel rod. Here is a boatdesign thread that describes the making. https://www.boatdesign.net/threads/carbon-piano-hinges.61551/ Basically folding some glass or Carbon over a tube or rod so that you're left with a hole then cut the "teeth" for the hinge and slide in the final rod. I was thinking of trying to make it with fiberglass and then slide in a 3/32" 316 stainless tig welding rod.

 

Graham did his bunk hatches on Carlita with some aluminum piano hinge that he had left over the I believe Tom Lathrop gave him (very light and nice). After Jay used riv-nuts to attach his rub-rail to his boat Graham wanted to try something similar and he actually used pop rivets (correction he used solid aluminum rivets inserted from below and then peened closed) to attach the piano hinges to his bunk hatches. This has the advantage of being nearly flush inside and out as opposed to using screws and then having to grind all the tips off that stick through the 1/4" plywood. It worked fairly well and I don't think any have come loose. 

 

 

 

 

 

 

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9 minutes ago, Alan Stewart said:

I've often seen stainless steel screws create rust stains on the stainless piano hinge and my guess is that the screws are not as high a quality 304 as the hinge itself.

 

Stainless steel is weird, at least to common "intuition".  When it stays wet it corrodes.  Water gets into the countersink of the hardware, behind the head of the fastener and dries slowly.  During the wet period corrosion occurs, called "crevice corrosion".  It can be caused by scratches as well.  316 hardware and fasteners is the best solution, but it will still occur.  Another thing that can help is to buff the fastener heads and countersink in the hardware with a jeweler's wheel w/rouge.  We actually did this at a previous employer's shop.

 

For those who want a thorough explanation instead of my over-simplified version:  https://www.sciencedirect.com/topics/materials-science/crevice-corrosion

 

I used bronze piano hinges and screws.  They turned "patina green" and I like it.

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Update:
I have ordered some new aramid tape which is heavier weight and also bias woven to have another attempt at making a kevlar hinge. I found bias kevlar (aramid) tapes sold by a nice outfit in maryland. https://sweetcomposites.com/Seamtape.html

 

I will report back how it works out. 

 

Below is a picture of Graham's cockpit hatch piano hinge. They are 1 1/16" wide. No signs of crevice corrosion. I am sure Graham would have polished his hinges before installation. 

 

20190920_083547.thumb.jpg.d9fa253f24ce500190788284dbc1aef5.jpg

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Hi Alan,

Please let us know how these turn out.

I'd like to try if you have success (sound perfect for my front casting deck/hatch).

Another material I have considered is Innegra.

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I was looking what McMaster-Carr has for piano hinges and learned they offer it in aluminum as well. Would anodized aluminum be suitable for hinge material other than the fact using s/s fasteners can create galvanic reaction?

 

Todd

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An option you might think about is Tap Plastic's flex hinge:  a continuous hinge made of acrylic & a urethane flexing piece.  I bought some for a project & it was too stiff for what I was doing but a hatch gives you a lot more leverage.  With the acrylic leaves you'd have to carefully drill clearance holes for the fasteners - don't leave any stresses on the acrylic except the clamping force.  They claim it's UV stable but...

https://www.tapplastics.com/product/plastics/handles_hinges_latches/flex_fold_2_hinge/124

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