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Layup schedule for hatch boards?


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I want to make a set of hatch boards to replace the acrylic ones, which are becoming crazed, and I was thinking composite material would be lighter & stronger for offshore.

Does anyone have an idea of what layup schedule to use?  I was thinking 3/8" Corecell A-500 for the core, with this 50/50 carbon/kevlar 5.7oz blend, for the strength & impact resistance. 

I didn't immediately find a clear answer on how much force the boards need be designed to withstand, but the companionway is roughly 23 x 24".  

 

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47 minutes ago, Salona said:

I want to make a set of hatch boards to replace the acrylic ones, which are becoming crazed, and I was thinking composite material would be lighter & stronger for offshore.

Does anyone have an idea of what layup schedule to use?  I was thinking 3/8" Corecell A-500 for the core, with this 50/50 carbon/kevlar 5.7oz blend, for the strength & impact resistance. 

I didn't immediately find a clear answer on how much force the boards need be designed to withstand, but the companionway is roughly 23 x 24".  

 

Kevlar fibers are very difficult to work with ... you will regret Kevlar 

go with carbon...  unless you need to deflect incoming bullets 

you can buy carbon in sheet form ... 1mm thick ...it works similar to g-10 

Laminate this carbon sheet skin to your chosen core 

 

High density filler the core perimeter during construction 

trim  to fit with a flush cut router and plywood template 

 

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3 minutes ago, slug zitski said:

Kevlar fibers are very difficult to work with ... you will regret Kevlar 

Yeah I've only worked w/Kevlar once, and it didn't wet out well. I've heard you need to vacuum infuse it to reliably wet it.  

But I've heard good things about the 50/50 carbon/kevlar weave, in terms of ease of lamination. This is what I'm talking about: https://compositeenvisions.com/blue-reflections-carbon-fiber-blue-kevlar-fabric-2x2-twill-3k-50-127cm-5-7oz-193gsm/

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I still think Slug has it. Whether you go with carbon plate or vacuum bag carbon to the foam, I think it still makes more sense than mixing your materials. There's another thread around here about making hatchboards from carbon and foam - I think you're overthinking the strength issue. Look for basketcase's posts on making his.

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For hatch boards I wouldn't even bother with carbon as this doesn't need the strength.  I would just use foam core and fiberglass for the parts.  I would start with a layer of 6oz on each side which should be more than enough.  If you don't have a vacuum pump lay it up with peelply,  place on some heavy plastic/tarp on a flat surface then add some heavy things to press the part down.  I would recommend doing one side at a time and having the working side be facing down so the load is more even.  The peel ply will give you a great finish without a lot of post work.

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Just to clarify - I have the equipment for vacuum bagging parts and already have a several rolls of carbon uni & 5.7oz bi-directional.  I'm just trying to get an idea of how thick the laminate should be. Offhand I was thinking 6 layers on each side is going to plenty stiff and strong, but I would prefer to engineer it to meet a particular spec if there is one for hatch boards. (The plates do look appealing, but already have the MGS epoxy and carbon fabric)

Alternatively, I could just engineer it to match the load-bearing capability of the screws holding the aluminum tracks in place, since that might end up being the limiting factor for strength.

 

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19 minutes ago, teamvmg said:

6 Layers each side!!!      Make yourself one with 2 layers of that biax each side and see if you can break it. 

Well this gets back to my original question. How much force should it withstand?  I'm not concerned about whether I can break it or not, but rather the force that a breaking wave over the stern creates.

The companionway is approx 2x2' or 4ft2.  

A very quick google search indicates that breaking wave creates between 250-6,000 lbs of force / ft, which as expected, varies considerably depending on the geometry of the object, wave height, etc...  Here's one resource, I'm sure there are more: https://core.ac.uk/download/pdf/216213484.pdf

But even assuming the low-end of this range, that's 1,000lbs of force on the hatch boards.   

So... what assumption should I use? Or is there a standard for ocean racing boats that generally suffices (e.g. should withstand XX weight)?  

 

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Where do you sail? Do you often have breaking waves hitting your companionway?

Anyway if you want to use the ABS Guide for Building and Classing Offshore Yachts the design head for cabin aft and sides is 1.98m of water.

That is 1025 kg/m3 x 1m2 x 1.98m = 2029 kg/m2 = 415 lbs/ft2. That is still a lot of force.

Do you know how to calculate a laminate based on this value however??

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Oh - yes about 2 layers of 5.7 biax will be adequate but flexy if that sort of load is applied. About 2" deflection midspan. Best practice would be cap the edges with laminate, not just dig out core and fill with bog.

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2" of deflection midspan?  Wouldn't that mean they'd pop out of the rails? Not what you'd want to happen.  Is there something wrong with 3/4" plywood? High tech here seems like a lot of work & expense for minimal results. Light foam hatchboards might also be more likely to blow overboard if they're not kept carefully below.

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13 hours ago, Zonker said:

Where do you sail? Do you often have breaking waves hitting your companionway?

Anyway if you want to use the ABS Guide for Building and Classing Offshore Yachts the design head for cabin aft and sides is 1.98m of water.

That is 1025 kg/m3 x 1m2 x 1.98m = 2029 kg/m2 = 415 lbs/ft2. That is still a lot of force.

Thanks - this is very helpful.  While we only do one offshore race a year, figure if I'm going to make new hatch boards they might as well work when you need them.  The boat came with the saloon-style double doors.  Those are great at the dock but I'm skeptical how strong they are and they tend to snag spin sheets.  

13 hours ago, Zonker said:

Do you know how to calculate a laminate based on this value however??

I hope so, though it's been at least 10 yrs... I have to find the spreadsheets I used back then - any that you can point me to?

8 hours ago, Zonker said:

They might - depends on the depth of the side channels. The original poster asked about a lighter solution...

3/4" aluminum channels. When the channels are installed, I'm guessing the weight will be close to original. 

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what about multi-wall polycarbonate?

 

https://www.interstateplastics.com/16mm-Polycarbonate-Hurricane-And-Storm-Panel-Full-Sheet-POLCECKSW.php?kitoptionpk=7245&src=adwordspla&thisisforcallrail=1&campaignid=225228743&adgroupid=37851262274&creative=153445283219&matchtype=&network=g&device=c&keyword=sheets-POLCECKSW-kits7245&gclid=EAIaIQobChMI14yGuqOm7wIVAZ2zCh2NEA2UEAQYAiABEgIstvD_BwE&

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Vectorply has their free "Vectorlam" cloud based software. It is adequate sort of.

Define a laminate (skins) + 2nd laminate (core). For skins select material = carbon and architecture = 45 double bias and search. Search will return some 6 oz which is really 5.7 oz when you click on it. I just used 2 layer of double bias but a single extra layer of uni would make it extry strong.

Then go to Tools and Analysis and pick "I beam". Tell the software your I beam is : laminate 1 skin (flange) + laminate 2 core (web) + laminate 1 skin (other flange)

Pick pin end supports, distributed load (lbs/inch, assume inch wide strip). I didn't try the "Panel" option; just the beam one.

One drawback is core thickness seems to be limited to 0.5 and 1.0 inch. I picked 0.5 for yours. In your case I'd make a sandwich of the core and keep it to a reinforced 3/8" width at the rails. But I think to reduce deflection glue in a full width extra core inboard of the rails or 2-3 transverse strips core (say 2" wide) to reduce overall panel size. 

 

image.png.dfeda6e7dc7b0b03d4882a4dc2458b51.png

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The polycarb panel is an interesting choice - but since Salona said 3/8" core I originally figured his channel width is narrower than that.

No material properties given but given the thickness it's probably a good choice. Stuff scratches easily so make a protective bag to keep them if you care about that sort of thing.

 

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And just FWIW, a 2” deflection on the center of a 24” panel get about a 0.34” change in the panel width. So in a 1/2” channel they’ll most likely stay in just fine. 

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For wave slap typical on sides of ships, a static equivalent is 550 lb/sq.ft.  That's likely way more than you need.  Maybe half of that would be plenty, and likely would break the grooves they slide into before the boards.

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I agree that high-grade plywood is hard to beat, but 6 or 9 mm with the edges built up would be nice & light. If they had to be composite, foam with hand-laminated & peel plyed skins would be bomber. I prefer honeycomb core with glass skins for drop boards because the light that comes through is great, but reinforcing the edges is challenging.

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8 hours ago, Zonker said:

more likely to break some other part of the boat if you get 550 lb/ft2

Ya probably.  So thinking of operational loads for hatchboards.. 

Case 1- a static equivalent of maybe 2 ft above the top-most edge of the top hatch board.

Case 2- inversion from rollover. head from half the freeboard at midships to the top of the hatchboards.  For typical boat maybe 4 ft of head roughly.

Case 3- big guy in a storm slams into the hatchboard.  Say 250 lbs at say 20 ft/sec? Deceleration to 0 at 0.1 sec..  (250/32.2)x(20/0.1) = 1553 lb.

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14 hours ago, Russell Brown said:

I agree that high-grade plywood is hard to beat, but 6 or 9 mm with the edges built up would be nice & light. If they had to be composite, foam with hand-laminated & peel plyed skins would be bomber. I prefer honeycomb core with glass skins for drop boards because the light that comes through is great, but reinforcing the edges is challenging.

TBH, the main reason I want them to be light, is I hate it when people drop plexiglass hatch boards. They always land corner down and it damages the cored laminate even if it doesn't show right away, just like wearing high heels on a boat.

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On 3/9/2021 at 7:54 PM, PaulK said:

2" of deflection midspan?  Wouldn't that mean they'd pop out of the rails? Not what you'd want to happen.  Is there something wrong with 3/4" plywood? High tech here seems like a lot of work & expense for minimal results. Light foam hatchboards might also be more likely to blow overboard if they're not kept carefully below.

Offshore sailing rules require that the boards are retained with a cord, even during the removal process, for this reason.

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15 hours ago, Russell Brown said:

I agree that high-grade plywood is hard to beat, but 6 or 9 mm with the edges built up would be nice & light. If they had to be composite, foam with hand-laminated & peel plyed skins would be bomber. I prefer honeycomb core with glass skins for drop boards because the light that comes through is great, but reinforcing the edges is challenging.

I just built an instrument panel using foam and clear-coat carbon, cause, well, the shitty plastic one had to go, so why not...

 

But I just used some wood strips on the edges in the laminate the same thickness as the panel. so - wood strips that fit the space, foam core, carbon fabric cause it looks cool, then clear. Took care of the edge problem. I'm going to use a piano hinge/thumbscrews to make access a bit easier. I'm in that space on a surprisingly frequent basis.

 

Gotta cut the holes tonight.

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17 hours ago, Russell Brown said:

I agree that high-grade plywood is hard to beat, but 6 or 9 mm with the edges built up would be nice & light. If they had to be composite, foam with hand-laminated & peel plyed skins would be bomber. I prefer honeycomb core with glass skins for drop boards because the light that comes through is great, but reinforcing the edges is challenging.

Actually, I really like this, same question I guess, what layup schedule?

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11 hours ago, Russell Brown said:

The light that comes through is nice. Amber-colored honeycomb. Mmmmm

Russell that looks awesome.  If you can -- what honeycomb and layup schedule?  

After seeing that I'm considering replacing an old acrylic hatch board.  I do like the light that comes in with the tinted acrylic.

I'm thinking cut 1/2 to 1" wide foam or ply outer ring/rim to shape then add honeycomb in the opening and laminate.  UV clearcoat to prevent epoxy yellowing.  Might be a fun project.

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That was 1/2" honeycomb with 3 layers of 8.9 oz "Rutan" cloth on both sides. it is not so easy to bag honeycomb as the edges want to cave in, so need sacrificial borders. The skins need to be thick enough so that the core can be routed away on the edges and packed with thickened epoxy. The turn dogs/latches/handles are made from Delrin on the router table using a template.

DSCN3011.jpeg

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On 3/14/2021 at 4:08 AM, Russell Brown said:

That was 1/2" honeycomb with 3 layers of 8.9 oz "Rutan" cloth on both sides. it is not so easy to bag honeycomb as the edges want to cave in, so need sacrificial borders. The skins need to be thick enough so that the core can be routed away on the edges and packed with thickened epoxy. The turn dogs/latches/handles are made from Delrin on the router table using a template.

DSCN3011.jpeg

Hi Russell,

For a simple rectangular shape, is there any reason not to replace those sacrificial strips with a G10/foam/wood/etc. permanent frame?  I would be tempted to cut the core slightly oversized, slather the inside of the frame with thickened epoxy, and squeeze the honeycomb in.  Not sure how good of a bond one could expect between the frame and core, but if they are both well bonded to the skins I would expect it to be okay.  I haven't worked with honeycomb cores before, though.

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On 3/13/2021 at 9:08 PM, Russell Brown said:

That was 1/2" honeycomb with 3 layers of 8.9 oz "Rutan" cloth on both sides. it is not so easy to bag honeycomb as the edges want to cave in, so need sacrificial borders. The skins need to be thick enough so that the core can be routed away on the edges and packed with thickened epoxy. The turn dogs/latches/handles are made from Delrin on the router table using a template.

DSCN3011.jpeg

Any word on the next book? Love your hatches, always found them very functional and easy to use. 

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Thanks. No date yet, but it's on the list. I have all the photos now and I think it will be quick to write. It will be rather thick, but an e-book only.

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On 3/12/2021 at 3:57 AM, Russell Brown said:

I prefer honeycomb core with glass skins for drop boards because the light that comes through is great,

Do you have some example numbers for comparison between a basic acryllic drop board versus a honeycomb one?
I am quite curious about the weight advantage. My boat(and where I sail on) aren't body weight wonders, but why not get for something a little lighter when I need to replace them eventually?

Not as nice and clear as acryllic of course, but from the pictures you posted it is still quite bright.

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As luck would have it, we broke on of our hinged companionway double-doors during a sporty race* this weekend, so this project just moved up the priority list.

*Not waves that broke it, just rail in the water w/a human wrestling w/lines in the companionway.

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