the deck on my Pearson Ensign

Discussion in 'Sailboats' started by LeRi222, Apr 2, 2010.

  1. PAR
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    PAR Yacht Designer/Builder

    Had you read the previous posts Sean, you'd have found the close stringer spacing recommendations, as well as the other structural details, that would have addressed any of your concerns, before they arose.
     
  2. seasailor55
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    seasailor55 Senior Member

    Thanks for the feedback, and I apologize for the quality of the drawing. It was very clear when I drew it, but by the time I scanned it, e-mailed and saved it to my hard drive, then attached it to my post, it lost a lot of clarity.
    At any rate, it represents what I envision the boat heeled over under sail would look like from a 3/4 stern view, showing most of the deck and part of the cockpit. And yes, I think the boat does have lovely lines.

    The seats, as you mentioned, probably should be taller in proportion to their width (that is, the cockpit floor should be lower, and I believe it is). I took some measurements a while back and seem to remember the sole being 34" from the deck at the cabin bulkhead and the seat risers 14" from the deck, which would give the seats a 20" rise.

    I drew what scaled out to be a 12" crown, but on a drawing of that scale a pencil line can be +/- an inch. It could be angle of the cockpit side decks (I crowned them slightly for strength and drainage) which makes the foredeck crown look slightly less. The overall proportions were what I was trying to capture for review, as well as any glaring mistakes in the design, although it doesn't hurt to have some fun with the sail shapes and the water and I find that putting a person in a drawing usually adds some life and perspective.

    Great advice, as always, on the beam and stringer joints. As far as the deck contours, I'm sure the stringers will have to have some bow or bend in them and I'm going to try to do a fairly gentle sweep, just enough to keep it from being dead straight, with most of it toward the bow, where the crown will be slightly less, and I can flatten things out a bit. If needed, I could put the plywood in tension, or as you said "talk to it", which assuming it doesn't crack or bulge and the fasteners and epoxy keep it in place, could have a stiffening effect.

    By the way, the "horizontal" 1X2 stringers that I was referring to would be a beam shelf (probably the wrong terminology, again!). That is, I envisioned taking a 1X2 and screwing it to the underside of the 1X2 oak sheer clamp in a horizontal orientation, thereby creating, in conjunction with the sheer clamp, a wooden "L" that the beams could rest against and sit upon. This wouldn't secure them from fore and aft movement, but I suppose that the epoxy and a fastener would take care of that. Probably totally unneccessary and not worth the extra weight, expense or effort, in light of what I've heard thus far.

    Great idea on the aft deck treatment. Lose the hatch and open up the bulkhead. This would give me a place for the outboard's gas tank, etc. and still allow access to the transom and back stay chainplate. Thanks again.
     
  3. PAR
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    PAR Yacht Designer/Builder

    The idea of an "L" assemble along the sheer makes me think it'll capture dust, dirt and most importantly, moisture, just under the deck, between each beam. The sheer clamp, a hardwood 1x2, (vertically oriented) glued and screwed to the hull shell along the inside of the sheer, is all you need. Outside of this and also screwed to it will be the rub rail, which just adds more beef in this area, you don't need a horizontal oriented shelf.

    So, if the rub rail is 1" thick, the hull say a 1/4" thick and the 1x2 sheer clamp, brings a total of 2" of material along the rail at the sheer. That's enough heft to bash things pretty good and also accept fasteners and glue.

    If you'd like to avoid the sloped pockets in the sheer clamp, just notch it, very slightly, say about an 1/8" deep with a router and a flat bottom bit the same thickness as the deck beam. Just plow out this shallow groove at each point the deck beams land. When you fit the deck beams, they'll "key" into the slot, but you'll need a heavy structural fillet on each side (beam to clamp) to hold it in place, as well as the epoxy used to glue it in the shallow groove. The shallow groove just locates it where it needs to be and is slightly simpler then the sloped joint I've shown.

    You could also skip the shallow groove thing too and use just plain old wood working, such as a knee. This would be a horizontal triangular piece screwed to the beam and the sheer clamp. It seems a simple thing, but the topside angle the sheer clamp is at, has to match the slope of the deck beam in all three directions, so some fancy cutting will be needed after "picking up" the bevels with a gauge. Naturally, you'll probably want to epoxy these into place too.

    Lastly you could employ just straight "liquid joinery" techniques and use only a structural fillet on each side of the beam/clamp interface (use the 3:1 fillet radius rule). Technically, this would be okay, but I'd still be tempted to place a big old honking screw in, through the hull and sheer clamp, into the end of the beam, just to be sure it doesn't move. Call me old fashioned, even though I know the epoxy works by itself, I don't trust it all by itself except on fairly small boats.

    On the aft deck treatment, I wouldn't have but a little chunk of aft deck. On small craft (I know what I said in the last sentence of the last paragraph) I've found you need to occasionally get at the transom, to reach over, fend off, smack down boarders, etc. With an aft deck, you have to climb up on top of the thing, hope to not fall off and tend to whatever duty has demanded you get out on that dainty, sparse handhold area. Me, I'd rather walk out, lean over, grab whatever I'm after, then go back to the cockpit, reasonably upright, as I've found I'm more secure upright then on my knees. In the case of your boat, I'd curve the aft end of the cockpit, so I could get to the center of the transom in arms reach from the cockpit. It could still have the aft deck thing I know you like, but the curve will let you get closer to the transom if standing in the center of the cockpit (or kneeling on that seat). It's a personal taste thing I suspect more then anything, so do what you like, I'm just throwing around options.
     
  4. seasailor55
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    seasailor55 Senior Member

    Interesting concept. I'll try to sketch this out and see what it would look like. It would make reaching the outboard easier (unless I do a well in the aft deck, as we discussed previously). I have a couple of questions/concerns. This would put the tiller and rudder post in an open area of the cockpit away from the rear bulkhead or ring frame. How would you envision supporting top of the rudder post tube? Would you keep the rear seat and just make it longer, put a curve in the ring frame, or is there some other slick way to handle this? Also, how would you envision the rear of the coaming terminating?
    Your thoughts, please.

    By the way, you were correct about the deck crown in the drawing. It is 9", which gives 45" headroom in the cabin/deck and is, as you mentioned proportionally balanced. I tried a 12" crown using a batten today and it looked odd, sort of like the nose cone on an F-16 mounted on an Ensign hull. I'll stick with 9".
     
  5. sean9c
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    sean9c Senior Member

    I've read them all. This thread sure gets contentious. Makes one hesitant to contribute. Still think 1/4" ply is pretty thin but given enough framing will work, though it's likely to save time and effort in framing to go with a thicker ply. Also, in my experience, a 1X sheer clamp is pretty small, sure it'll work but it doesn't give you much "face" for fasteners. Laminate 2 pieces of 1X that way it's less likely to split when you put fasteners in it.
    You might look again at 12" of deck camber with 7ft of beam, that's a lot of camber. It's going to seem like you're walking on the side of a hill. Also with a sheer that flat and that much camber I think it'll look like the boat's always going downhill.
     
  6. PAR
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    PAR Yacht Designer/Builder

    This is an Ensign, not a 30' cruiser Sean. Scantlings are generally scaled to the loads and size of the yacht. Having a 2x clamp is absurd on a boat of this scale, particularly one intended for class racing. As has been posted, 9" is the choice for the crown, though 12" was debated. As for 1/4" decking, I can name at least 100 different designs of this general size and smaller, that employ 1/4" thick decking.

    The contentious nature of the thread was the result of a forum member, who's sole interest is to disrupt and insult. His participation here has been edited, though much of the collateral damage is still evident in the remaining posts.
     
  7. sean9c
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    sean9c Senior Member

    I'm not arguing so don't take it that way.
    What doesn't scale with size is that the same weight person will be jumping on the deck of this boat as a 60ft boat.
    In what class would you race a modified Ensign? I wouldn't think you'd be welcome in the Ensign class.
    Hard to figure why you'd think a sheer clamp that was net 1-1/2"X1-1/2" would be absurd (a pretty strong word). It's even less than 1-1/2" one you bevel the top to take the deck. I think the first time a fastener split the net 3/4" sheer clamp, when you got too close to the edge, you'd wish it was thicker. Back in the bad old days when Fir was cheap we used to rip 1" net stair tread material for stringers and clamps, always seemed a good compromise in size.
    The Ensign is big enough that people are going to be walking on the deck, and as I understand it the intended use of the boat is as a trainer, which tend to get more than their fair share of abuse. Using 1/4" ply just means you have to spend more time with frames and stringers. I've been talked into using 1/4" ply decks on boats this size and when it was all said and done wished I'd used thicker.
     
  8. seasailor55
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    seasailor55 Senior Member

    Well guys,

    It seems that, from the very beginning, there has been a lot of discussion regarding the thickness of the decking, but most of it appears to be centered on 3/8" vs. 1/4". I weighed a sheet 3/8" fir plywood that I had on hand, and it came out at 35 lbs. Assuming 10 sheets of plywood would be needed (decking, v-berth, bulkheads, cockpit seats), 3/8" would come out to 350 lbs. What would 10 sheets of 1/4" fir weigh, and what weight saving, as far as framing goes, could I reasonably expect to achieve by using 3/8" instead of 1/4"? If the 1/4" turns out to be a little flexible, I could probably add another beam or two under the deck stringers to stiffen it up. All in all, it makes me wonder if I shouldn't find some 1/8" and laminate a crowned 1/4" deck, which should be very light and stiff. The issues I have with this are: finding 1/8" exterior grade fir plywood, using a lot more of it, a lot more epoxy, and possibly twice as much time cutting all this out and fitting it. What about splitting the difference and using 5/16" (8mm?). Would that still take the contours of the crowned slightly sweeping deck?
     
  9. PAR
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    PAR Yacht Designer/Builder

    1/4" Okoume is 20 pounds. So, 10 sheets is 200 pounds for a 43% savings in weight over the 3/8". Even with the 5 or 6 pounds of extra framing for the lighter 1/4" deck, it's still a big savings in a part of the hull where you want to save weight.

    The 3/8" will likely not bend to the radius employed on the deck currently, though a lower crown could be used. 1/8" plywood isn't generally available as a construction grade, though is available as a marine or cabinet grade. Cabinet/furniture grades aren't suitable for boats, for several reasons.

    Hench my logic with 1/4" plywood. Look, literally hundreds (probably thousands) of small boat designs have used 1/4" plywood for decks, hulls and bulkheads. If the plywood is good quality (5 layers of veneer used, no voids, etc.) then it's remarkably strong. The heavy crown you're going to employ on the deck, also makes the plywood stronger, as do the close beam spacing. Will there be some flex? Of course there will be, but this is how if should be. The sides of your boat are solid 'glass and they flex too.

    You use what you want, but those recommending 3/8" would be very hard pressed to get the 9" crown (that's looks so darn nice too) pushed into it, not to mention the torment that will be necessary, as it's bent to the sheering sweep too. 3/8" will never do this, trust me, I've bent a lot of unwilling pieces of plywood and solid wood.

    There isn't any 5/16" plywood that I know of, without a custom order. 3/8" plywood is usually milled at 9 mm (about 23/64") actually slightly thinner, maybe 8.5 mm (about 11/32"). 1/4" plywood is usually 6 mm (about 15/64").
     
  10. seasailor55
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    seasailor55 Senior Member

    Wow,

    Didn't realize there was that much weight difference between 1/4" and 3/8". Not that this an America's Cup contender where 10ths of an ounce count, but weight above the waterline is the enemy of any sailboat. The 1/4" would also be much easier to bend, cut, and fit, and would be my preference. A 1/4" deck it shall be. I've heard designers and builders talk about using Okoume. Exactly what type of wood is it? Thanks again for the info.

    On a side note, I've put some thought into the shorter rear deck mentioned. I could lengthen the cockpit by a foot, (a plus for a good crowd) still have a decent rear deck, and be in reach of the outboard and back stay, or I could just put a nice pretty curve in the rear coaming. Either way, I would have to move the rear bulkhead aft. That would put the main traveler in the cockpit behind the rudder post, but I suppose that since I'd need something to brace the rudder post anyway, that wouldn't be much of a problem. An athwartship beam or a beefed up rear seat would take care of both issues. Hey, then I could move the cabin/foredeck bulkhead aft a foot and gain some room there! On second thought, better not!
     
  11. PAR
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    PAR Yacht Designer/Builder

    Okoume is an African hardwood, known for it's strength to weight ratio. If Meranti (commonly called lauan) was used instead of Okoume, a 1/4" sheet would be about 25 pounds which is still a 30% reduction in weight over a 3/8" sheet.

    You can move the traveler aft to the new deck location, which I like better then a tripping device, that you need to step over to get to the aft deck. On the other hand you could leave the aft deck as it is. It's difficult to get a good grasp without the boat sitting her in the yard so I can climb in with a tape measure or rig up a cardboard aft deck to see how much trouble access will really be.
     
  12. seasailor55
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    seasailor55 Senior Member

    I climbed in the boat and took a measurement from the aft cockpit bulkhead to the top of the transom and got 30". I sat on the front of the aft deck framing, and I could reach past the transom with no problem. Since the long shaft outboard's tiller folds up or down, there shouldn't be an issue controlling the engine's rpm's. Steering could be left to boat's tiller under way, or at low speeds where the boat's rudder doesn't bite well, to the outboard's swivel mount. I had this same set-up on my Alberg designed South Coast 21, (aft deck, inboard rudder, transom mounted outboard) and had no problems. At speed under power, the boat's rudder did fine. When I needed low speed maneuvering capability, I secured the boat's tiller in a neutral position, and did everything with the outboard. An outboard mounted in a well however, with limited swivel room might be an issue, unless the well was fairly large. Without the aft hatch, the rear deck would be free of obstructions, the backstay provides a handhold for steadying, and the rear deck won't have as much crown as the foredeck, as space under the deck isn't an issue. Since the boom is inboard of the rear deck, sail handling and reefing can all be done from the cockpit. I also plan on installing 1-1/2" high toe rails bow to stern along the sheer.
     
  13. sean9c
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    sean9c Senior Member

    If you choose to go with 1/4" plywood deck, or it sounds more likely 6mm if you do Okoume, I would encourage you to buy a sheet and build a little mockup of your deck. Something big enough that you can walk on and see if you think it's stiff enough. Get your biggest heavy footed friend to try it.
    Also remember that unless you camber your cockpit seats you will have to use more framing than you do in the cambered area. And the cockpit floor more framing than the seats.
     
  14. seasailor55
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    seasailor55 Senior Member

    Sean,

    I see that you are from Anacortes, Wash. There was a Save A Classic ad in the back of Wooden Boat magazine a few months back concerning William Albert Robinson's former 70' brigantine VARUA. It was in a boatyard in Anacortes, waiting for someone save it and complete a restoration in progress. Do you happen to know of this boat (ship?) and what happened to it?
     

  15. PAR
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    PAR Yacht Designer/Builder

    Sean, maybe you're right and just about every NA and marine engineer I know are just wrong. Hell they shouldn't even sell 1/4" any more . . .
     
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