laminating large pieces of ply

[JeffM]

Any advice on laminating large pieces of ply?  I am building a cabin for the Beatrice Ann (actually Mark 3 or 4), using the 4mm okume I have on hand.  The cabin roof will be laminated mainly of 2 sheets, approx 4X6.  They

[Hirilonde]

For the most part I agree with Ray.  I have used small brads through 1" squares of thin ply scraps.  Basically the same idea as his staples through cloth.  Definitely use a notched trowel.  It assures an even coating with complete coverage.  I would however try using 2 complete layers, as in simply 2 sheets as you proposed.  This assumes the curve is a simple one, and not compound curve (curved in 2 or more directions).  The result will then be a curved piece of plywood, which will be quite stiff on its own, and fully structural in both directions (athwartship and fore'n'aft).  Try bending your ply, whichever method you choose dry over your frame first to see what you will be up against before wetting it all out with epoxy.  Better to know what you are up against before smearing goo all over the place. 

You might even want to make a mock up on your boat out of cardboard before starting.  Sometimes things don't look quite as you visualize them. This way you can better visualize it all, and tweak your camber before committing to the materials. 

[Charlie Jones]

Actually for what he is doing, the dry wall screws into backing pieces sounds like the best idea. That way he gets pressure from both sides. Like clamps.

But I'd sure go along with the notched trowel. You don't want gaps in there which the stripes would (or could) cause. Wet out both sides too, so you don't have dry places.

Start screwing down from the center line and move outward- the air will easily escape then

[Hirilonde]

Wet out both sides too, so you don't have dry places.

Absolutely, all gluing, bonding, bedding, etc. should  be done that way.  Helps avoid bubbles and voids too.

[JeffM]

Thanks, all!  Wonderful advice.  The strip laminating idea that Ray described has gotten me thinking, though:  I want the ply doubled for strength and stiffness, but wonder if I couldn't achieve this adequately (and more lightly and cheaply) by gluing thin ribs to the underside of the roof.  I don't expect to walk on this roof, but it would be good if it could stand my weight in a pinch.  The ply is going on with the grain and bend both athwartship, so I could lay in strips fore-and-aft, across the ply grain.  Hmmm....  If I do go with doubled ply, I'll definitely do it in one piece, though, starting by laying the 2nd piece flat, and gradually screwing it down from centerline outwards as you recommend.

[Charlie Jones]

When Graham built Southern Skimmer he used a single piece of ply for the cabin top- he put the stringers, etc that brace it, on the OUTSIDE, running fore and aft.

[wkisting]

Jeff, I think I'd go with the reinforced single ply idea... Just add some stringers for stiffness. Your cabin will be a removable kind, right? If so, you probably won't be walking on it anyhow, so it just needs to be strong enough to support the weight of someone who might fall or lurch against it while going forward. I think a single ply roof with moderate reinforcement will more than suit that.... easier, lighter, cheaper, less adverse effect to stability, etc.

Looking forward to seeing the results.

[Hirilonde]

When Graham built Southern Skimmer he used a single piece of ply for the cabin top- he put the stringers, etc that brace it, on the OUTSIDE, running fore and aft.

What thickness ply did Graham use though?  And what was the spacing of the stringers?  Jeff is talking 4 mm ply.  Two layers would still be under 3/8".

[Charlie Jones]

I stand corrected. I just got off the phone with Graham and Skimmers cabin is two layers. Two layers of 1/8th inch, making the entire cabin 1/4 inch thick.

Here's a couple of pics where you can  see the entire cabin top and then the ends of the exterior stringers. They double as hand rails.

The young lady is Graham's grand daughter.

[JeffM]

I guess I'm kinda guessing here on strength.  The cabin will be nominally removable (mainly because I fear making permanent drastic changes to Graham's design), but I intend on leaving it in place long-term.  One of my biggest problems with my current wood-and-cloth top is the set-up time, so I want a top that can easily withstand highway winds.  I would also like it not to collapse under my weight, but I don't picture myself climbing on it regularly.  Finally, I'd like it to help me out in a knockdown: no water flooding into the cabin, bouyancy up high so it doesn't turtle and is maybe easier to right. 

Here's my plan have so far: the vertical cabin sides (laminated to 8mm) are bolted around the outside of the coaming.  The roof stitches and glues to the sides.  The back of the cabin slopes from the aft edge of the thwart up to its highest point just forward of the forward edge of the thwart.  The main hatch coincides with the wide port floorboard, and extends over the cb trunk to give sitting headroom with the hatch open.  (It also allows room for the mizzenmast.)  All of this is very like my current wood-and-cloth top, but the new roof will be curved rather than flat--which should help in windage, visibility and strength.  http://www.messing-about.com/forums/index.php?topic=5687.0  Instead of a slot top (which turned out to be a bit impractical to use), I will have a main hatch and forward hatch, separated by a 14

[Hirilonde]

Finally, I'd like it to help me out in a knockdown: no water flooding into the cabin, bouyancy up high so it doesn't turtle and is maybe easier to right. 

I kind of doubt it will do any of this.  If it is really watertight, the hardest part of this being your companionway and the temporary joints to the boat it will slow water down getting in when capsized, but doubtfully stop it.  Getting your combing joint tight enough to not leak from spray and rain will be a challenge.  I don't think it will help at all to prevent turtling or in righting. 

I am not saying you shouldn't do the project as you are planning.  I just think your expectations are a bit high.

[JeffM]

Dave, keeping spray and rain out is pretty easy: the sides come down outside the coaming.  (The cloth roof works this way now.)  As far as keeping green water out, because I don't plan to take the cabin off, I will be caulking the coaming joint.  Similarly, the aft cabin bulkheads will have a caulked connection to cleats inside the sides and on the seats.  This leaves the companionway and hatch.  For now I will close the companionway with cloth the same way I do now for privacy, warmth, bugs.  (Are conventional washboards much impediment to water?)  The hatch is a worry: because it is offset to port, a portside knockdown will at least put the hatch edge in reach of waves, and could even put it under.  I am somewhat hopeful, given that in my capsize test (admittedly with an empty boat) the water never rose to the edge of the seats.  Since the sole is continuous the whole length of the boat, any water that does enter through the cockpit would slosh end to end when I righted, but I don't see that as a big issue.  In any event, it would be an improvement over the cloth sides: I began to fear that my kids could get trapped in there if it collapsed in a capsize.  And I would like to make it to Nantucket this coming season!

[Charlie Jones]

Two things-

First, I wouldn't actually use caulk around the edges. Not if you wish to remove it part of the time. I'd use a harder stick on foam tape, perhaps like the stuff they use under pick up toppers,  and just compress that between the surfaces.

Secondly- why go to the trouble of building a sliding hatch at all for something that small? Again, on Skimmer, Graham has a solid cabin top with a cloth part snapped over the opening. May use twist locks- can't recall. MUCH simpler to keep dry inside that way, without the slide. You could install a small commercial hatch up front for ventilation.

Also- I'm curious if you have talked to Graham at all about the project. He's really easy to work with and could well have some sketches or ideas that would help you out. I'd sure at least explain what you are doing to him for his input.

[Hirilonde]

Also- I'm curious if you have talked to Graham at all about the project. He's really easy to work with and could well have some sketches or ideas that would help you out. I'd sure at least explain what you are doing to him for his input.

Yup, that's what I would do next.  Lots of good ideas floating around, why not add "the man" to your list of resources?

[JeffM]

The foam is an idea, Charlie.  I described the project to Graham when I ordered epoxy from him, so he knows about as much as I've put in these posts.  I didn't ask for drawings, though.  He it was who pointed out the importance of caulking if I wanted the top to have any value in a knockdown.  As far as hatches go, Charlie, I recall that Southern Skimmer has no opening in the roof for the main hatch.  I need to be able to stand in the hatchway--not least because the waters I sail can be crowded and privacy hard to come by.  And I need not only to keep rain and spray out, but trailer on the highway, as well.  I have a hard time imagining a soft top secure enough.  And at my height of 6'2", the entire value of a cabin is much diminished if I can't ever sit upright.

[Charlie Jones]

;D ;D

Ok- big difference between your 6'2" and my 5'8" Or Laura's 5'2"

But I didn't mean a soft top- I just meant over the opening going into the cabin- where drop boards would go.

From what I read now, I'd build a sliding hatch also.

[Hirilonde]

Under what circumstances would you want to be sitting under cover?  Would a cockpit awning/tent that tied into the cabin when at anchor meet your needs?  This would make the hard top much more simple, hence waterproof and stronger.  It would be easier to build as well, though maybe you are looking forward to a challenge.  You would still be able to get out of the weather while sailing, 'cept the helmsman.  You would still have the permanent dry space for gear while sailing.  So many compromises, where does one draw the line?

I'm 5'8' and my wife is 5'1", easier for me too  ;D

[JeffM]

I prefer to challenge myself sailing rather than building!  A cockpit tent is a good idea for prolonged wet weather, but doesn't solve a crucial problem: ever tried to use the head in 44" of vertical height?  That's the absolute maximum I'll have under the hatch at the highest point.  To make matters worse, my back does not put up with sustained bending over.

[paul_stewart]

Very cool project, Jeff.   Some kind of cabin on the CS20 is a great idea;  "how to do it" is the big puzzle.   About all I have to offer is encouragement.  Go Jeff !

I'm glad to hear that anyone of us is pushing the limits of the envelope and trying new ideas for the CS20.  Designing shelter on the CS20 is a fascinating puzzle.   So may pros and cons.  Decisions, decisions, decisions.     Fortunately, you know what you want in terms of function.  The pop-top design you built is really cool.  Very creative and well executed.  Windows, snaps, flexibility, hatches.  But I can understand downsides such as extra set-up time, etc., as you mentioned.

I hope Graham will eventually add one of his cabin designs as an option in the CS20 plans.  I'm sure his cabin design would be outstanding.  But I know that regardless of the design specifics,  the functionality of a cabin on the CS20 is wonderful.  We absolutely love all the many benefits of the permanent hardshell cabin we built on the 'Dawn Patrol'. 

My to-do list still includes some finish work in our cabin.  Still puzzling out some of the small details.

By the way, we did not really expect to be able to put any weight on the cabin roof.  But we have come to realize that it is actually very strong. Stand on it, sit on it.   No worries.  We treat it well and I would never jump up and down on top of it, nor even stand on it unnecessarily,  but in terms of ordinary activities when sailing and trailering its strength is just fine. 

Sounds like you are thinking of a semi-permanent removable hardtop.  I have to say that listening to your descriptions, it sounds like you really want a permanent cabin but may be hesitating to commit to that.  It sounds like the only reason you would remove the "removable / semi-permanent cabin" would be because you decide you don't like the design.   Is that true?  ....after you built it,  if you were really happy with a particular hardshell design and the way it looked and functioned, then you'd probably never remove it?

For your consideration I would offer the suggestion that there probably is some 'permanent cabin' design (that only you can discover) that you will love once it is constructed.   I'm thinking you could do some full-size exploratory mock-ups using cardboard walls, for example, to aid in the discovery process. 

Ken Potts recently let me have a very brief peek at his copy of plans for the EC22,  and the "cabin plans" page was a treat to see.  (Well yes, -all- the pages were at risk of being drooled upon.)   I expect there would be some similarities between those EC22 cabin plans and hypothetical CS20 cabin plans.   Of course the EC22 is a distinctly different boat,  but even so it might be possible for you to rescale, adapt, and use that "cabin" page of the EC22 plans as the essential basis for an adaptation to the CS20   --could provide ideas for construction strategy in any case.

You might discover a plan that is perfect but seems to involve more work (e.g., extra bulkhead separating sole of the cockpit from the sole of the cabin).  But maybe not more work in the long-run if going in that direction is actually a shortcut to where you're eventually headed.   

   

I hope this is encouraging.  Trying new ideas and modifications is one of the very best things about wooden boats.   A CS20 cabin is a good idea.   How to do it is a puzzle.    Enjoy ! 

--Paul

     

[PAR]

When bonding two large sheets of plywood The biggest issue is trapping air, creating voids. A common solution is to drill lot of holes and what I do when I repair transoms, which is usually three layers of 1/2" ply.

On curved surfaces like a deck or cabin roof, you can make the curve work for you. Spread on your goo with a notched trowel, but wedge open the top piece so it only touches down the axis of the radius. On a deck or cabin top this would be the centerline. I typically use some small diameter dowels.

Screw it down along the center line first, starting in the middle and working progressively toward each edge(front to back), alternating back and forth. Next move the support outboard and do another line of screws, again alternating side to side and front to back. Air has no choice but to escape as the ply is "rolled" into position in the goo. The screwing sequence is important to prevent puckers and voids. Some like to use a spiral pattern, but I prefer to use a single line along the axis which forces the ply to go where you want.

If you're torturing the plywood to some degree then you have to figure out where the "stretched" portions are and use two or more axis lines in these areas. A spiral screw pattern works best in these locations, working from the center out.

A light weight, removable cabin could be made from foam and fabric set in goo or foam and thin ply bonded with goo. 1" foam and 1/8" plywood (each side will make a surprisingly strong cabin, that doesn't weight much at all.

Sealing it down and having secure dogs to keet in place would be a must. The truck bed liner tape works well so does the foam tubular gasket used in automotive weather stripping (can be had on a roll too). If the cabin has tapered sides from front to back in plan view you could use a simple wedge shaped lap, with matching "receiver" or the coming. As you put it on, sliding it aft will naturally tighten it down. A couple of hatch dogs or even tool box latches will secure it well enough.

As for companionways, the fewer openings in the cabin top the better in a capsize. On a CS-17 or 20, the top of a cabin would barely be in the water, though the sides would surely be. I'd focus on the coming joints being water tight and keep openings in the top to a minimum.