Fastening Plywood Sheathing

Hard spots are created when the elasticity decreases dramatically across the panel. This happens any time a structural member is in direct contact with the panel (plywood) regardless of how it's attached (assuming it's a solid attachment, glue or fasteners) This is anticipated and negated to some degree during the design process. Pre loading the panel (bending it over frames, molds, bulkheads, ribs, stringers, battens, etc.) hardens the panel a great amount (dependant on panel curvature) which helps support the panel shape in areas that are not directly supported by a load bearing member. Proper dimensioning (scantlings) also plays an important role as well.

Bent frames (ribs) are found in light weight craft with round bilge hull forms. They become impracticable after the boat gets over about 25'. Some examples of bent frames can be found in vessels over this size, but are commonly mixed with sawn frames too. Typically, you'll see bent frames with every third frame sawn in larger hulls, maybe every other frame, depending on boat size and intended service. Sawn frames are usually used in chined hull forms and are required to be larger and heavier in dimension to supply the same functions. Sawn frames are usually spaced much farther apart then bent and require heavier planking stock (because of the frame spacing). Once over the practical size for a single bent stick, double triple and quadruple bent frames (like a laminate) have been employed, though the effort is had to justify, when a sawn frame can serve.

The planks I installed were on an old (50's) multi chine, well burdened (fat and deep bellied) cruising sailboat. These garboards were attached to the rabbit with screws, also screwed to the seam batten (like a stringer, but directly behind the seam) and the sawn frames which were on 24" centers. It also had bent 2 frames between each sawn frame, which backed up the batten. It was a 26' boat and reasonably light in construction. The topside strakes were 3/8", the sawn frames about 2 1/2" x 4/4ths and the bent frames around 3/4" square. All the frames were oak, the planking 5 ply Douglas fur. You don't see much of this type of construction anymore, but it was common for many generations, both in solid and plywood planking. This is traditional plywood over frame construction. There are many different types of traditional plywood construction, but one thing always remains. This is the need for a structural grid to support the planking and hold the boat shape. Other forms of plywood construction may not require all this internal structure. This is also true of some solid wood and wood composite construction types. These methods rely on different principles to gain longitudinal and athwartship strength.

Some of these other methods are glued lapstrake, tape and seam, cold molded, strip plank and wooden composite. There are different types of methods for a few of these other types (an example would be molding over strip plank, or wooden skins over a man made core, etc.) Because of the differing engineering concepts involved in the methods utilized, it's difficult to categorize planking fastening, but it is necessary in traditional construction, even to the frames (bent or sawn).

Nero, strip planked hulls have a great deal more stiffness then conventional, conically developed plywood hulls. There are a few types of strip planking, but most all have very limited internal framing. This is gained by the heavy hull layup (I have trouble calling 1 inch square strips planking) which requires lots of adhesive and usually skinning. Yes, you'll have a localized hard point at bulkheads and the like (I assume this is what you meant), but it's not something to worry about. Most strip hulls are quite tough, easily proven by the lack of internal bracing necessary to hold the boat's shape. Strip planking isn't the lightest method to wooden hull construction, but can be a deal maker for the backyard builder. So, don't worry about he hard points, just stick to the plans as best as you can, your cat will be fine.

 

Thank you Par.

 

par ..you have waffled on there as usual ,however I must say as far as I am concerned frames are frames ribs are ribs planks are planks and plywood is er well plywood .the original question was about fastening plywood to frames, the things that are not ribs!!! my answer was definately not to and i stick to that ,in fact in a properly constructed ,moderately heavy boat the stringers will stand proud of the FRAMES and so therefore it will not be possible to fasten to said frames ,so that takes care of that .
In regard to the coracle you are playing with ,I would like to see that after you have driven in umpteen thousand screws ,talk about hard spots .by the way who stops all the screws,bet you haven"t a little electric thingy to do that ....cheers hartley

 

There are several types of frames, constructed in several different fashions, ring (sometimes called web), truss, laminated, sawn (doubled or other wise), bent (steamed or other wise), just to name a few. They can be employed in different ways, as well as mixed, such as a work boat using longitudinal frames in the fore and aft sections with transverse frames in the middle, where the extra space saved by this method can be placed in the hold.

Stringers can be "let" into a frame (some frame types lend themselves better to this than others) or bent around. Plywood hung on the sides of a boat surely is planking (I don't think many folks have difficulty with this), a garboard is a garboard, be it solid mahogany or a 1088 sheet that has a few scarfs along it's length, such as the ones I installed and you questioned. Maybe it's just syntax, but I'm reasonably comfortable with the names of most boat pieces.

Just because you are unfamiliar with a particular type or method makes it no less valid, it's just something you're less then accustomed too. So, unless you've been lurking about for some time, unwilling, or unable to contribute (7 total posts, with nearly have in this thread alone), I can't see how you can generalize my posts as "waffled on there as usual". Maybe it's goes toward the plywood, hung off the sides of many thousands of boats, that is something other then the vessel's planking, thingie . . .

 

Didn't really understand hartley's comments.

Par, your expertise, wisdom, and well written posts are excellent.

 

You forgot enligtning (well, to me)

Andre

 

Slightly confused here...


This post and provided evidence speaks for itself. The construction of these small craft evolved from cedar planking with butt joints, to scarfed plywood planking, in lapstrake and single sheet plywood.. They incorporated several fastening technigues, and have stood the test of time. All of his boats spanned several decades of building, and used for over fifty years, and yes had zero bedding compound between any piece of wood, and yes proper fitting parts, ribs being fitted to the laps as shown along the sides.

In the lap seams he used clinch nails, and evolved to small ring shank nails along the seams. Every side plank was fastened to the ribs, and in the smaller boats he built, used no longituals only frames. In the larger ones, since he still used 3/8 plywood, he used longituals and fastened the bottom with screws and even small machine screws with nuts in the foward section in the extreme stressed areas of the bottom bow. He used silicone bronze hardware to screw every piece to the ribs and frames.





http://www.simmonsseaskiff.com/

Story behind these boats

http://www.simmonsseaskiff.com/History/index.htm









In many of the new lapstake hulls, I know in this country are being built with only epoxy glue along the seam line incorporating in the building process a homemade lap clamp across the seams between the frames and ribs till the glue sets up, in construction of hulls simular to this example.




And yes I am reproducing the boat, simply because of the love of these hulls, and because the plywood did give up after going through two generations of family use, kids and mud abuse.

 

Looks like you're running along nice there Mike. The Simmons skiffs are great boats, much loved, in the this part of the world at least, a fine sea boat.

You're perfectly correct in that boat construction evolves, just like everything else. We developed newer methods, materials, techniques, some better, the ones that aren't, don't last long. There are many ways to skin a cat (or boat).

According to Hartley, those aren't ribs (first picture), those are frames, though there are no stringers (oh, no) and the plywood isn't planking, it's the stuff that holds out the wet, or something yet decided apparently.

 

Here is an example of the lap clamps I left out, no fasteners, no nothing except fasteners at the /////............... [insert ]]. Par, while I am limited in many areas and come across to others as a bit thick, this past week, I just skake it off and continue on .

 

I like that long workbench, accessable from both sides, a place for all those lumpy power tools, movable. I think it would be easier to just build one like that than to clean off the ones I have! Sam

 

I think one of the problems here is a lack of understanding regarding small runabout craft ,which have been built by every method imaginable to the type I am talking about ,which are heavily built craft ,which have to last and have "to stand up to it",constructed with hardwood frames and hardwood stringers ,my comments still stand
With regard to pars comments about me "lurking" on this site ,does he consider that he only has the right to post here and not be questioned about his views .When I first stumbled on this site recently ,quite frankly I was appalled at the sarcastic and sneering comments posted to people which were seeking information ,those people were entitled to be answered in a courteous manner and not with a holier than thou attitude ,I am merely "taking the wind out your sails " so to speak and I will continue to do so ,lastly I think it is a national trait of ours not to be blinded by Bull S...t
cheers for now

 

I see, you're either british, canadian, or mainland european, then?




Just kidding.

 

No Danishbagger just an average Aussie trying to take the "mickey" out of some self important people ,I guess you might find the same traits in your lovely Queen Mary.Denmark and Australia have something now,good luck..............cheers

 

Humble apologies Danishbagger I meant Princess Mary not Queen Mary ,perhaps one day eh ,hope I haven't strained relations with our two countries .Put it down to old age (72) and approaching senility,I try to keep young by taking the mickey out of you know who.....cheers.

 

He he, good - I thought for a moment there that you were saying that it was an american trait, lol

Actually, I don't think she _can_ become queen. Prince Henri is still a prince. Then again, wth do I know about the royals!?

Discussion is good thing, we all learn from it. I like that, but – there is no "but"

Welcome to, from one newbie on these boards to another. "Lurker", he he.

Andre