Fast unique assembly method !

What's to figure out Steve? A butt joint on the garboards or topside planks in the above image is two pieces each and uses the maximum length of each panel. A puzzle joint decreases this length and adding a dog bone to it adds complexity. So, with the above garboards, instead of 4 pieces and two seams as would be with scarfs or butt joints, the puzzles and dog bones take this to 12 separate pieces of material! Yep, fine engineering . . .

 

Ah.. found one, a puzzle joint without dog bones, yes it eats some sheet length (dog bones don't) but for those cases that not max length is needed it beats the dog bone in parts to be handled and strength I think. But does it beat a scarf joint for a CNC pre cut kit..?? Both eat some sheet length and a pre cut scarf joint is vulnerable in a kit as mentioned by Steve. Your comments please..??

PT Skiff


How do you put some pressure on it in all directions while it cures..?



Kit parts assembled before gluing...

...no tabs* and wedges, just some stiches I think.

* (PS - see the last sentence of post#49 about the tabs and slots)

BTW, Troy showed a nice jig for scarf joints here in post#2 and gave some links for another one in post#23 (thanks Troy!). I think it's a nice way to build up some confidence and learning some techniques by building one of those simple jigs and make some scarf joints just to learn how to do it... And everyone can find such info nowadays...

Cheers,
Angel

(pics attached so they will stay with the thread for discusion matters)

 

Par, yes, the dogbone joint used, uses way too many parts adding uneeded complexity for no gain, a sraight butt joint with glass both sides would be easiest for both the kitset maker and the builder, followed by a puzzle joint as used on the PTskiff kit and others,followed by a real scarf. However i dont see any other added complexities built into the kit, there are no extra parts used as Teddy implied in post #36 that are only there for assembly,(that t rex backbone also forms the dart style keel) and the assembly sequence is logical, the wedged together structure will be much more rigid before filleting than a regular wired together hull, it is clearly not an original system but its not a dumb one either, his target audience is certainly not guys like us that can already build a boat, its the type of person who spends money to buy a CLC kit rather then start with a stack of plywood.
Steve.

 

Angel, yeah,thats the type of puzzle joint i was reffering to,much better than the dogbone imho, plywood is easy to scarf when you stack them staggered by the width of the scarf and use a power planer, as the gluelines give you a great visual guide to keep them straight across the panel, the thicker the plywood the easier it is to scarf as they stay flatter. On the PC skiff i think they do have small tabs that fit into slots in the planking,(no wedges though) you can see them on the floors at the bottom of the middle picture.
Steve.

 

I'm not sure what this is but I call it added complexity If that structure could be used as a jig for the next hull that would make some sense but...

 

A well designed taped seam build doesn't need a building jig, maybe a single temporary bulkhead, but that's about it. Some of these kits, including the one above are showing a fair bit of additional material, that doesn't stay in the boat once completed.

 

True. I object to spending anything that doesn't stay on the boat.

The idea at the start of the thread is clever but I worry about the potential for kinky hull syndrome with all those slots.

It is not for home builder-from-scratch types like me. However it would be simple enough for a scratch builder to drill small holes and use Spanish Windlasses to hold the hull together in the same way, provided he/she was confident about the accuracy of the panel cutting. But a few screws into the molds seems simpler ...

 

On the designers website some pictures of a build of a boat like the one this thread started with... see left bottom corner thumbs.

Here some info about puzzle joints on Duckworks.

Cheers,
Angel

 

The PT Skiff retains all its 'jigs' from what I can see of the construction method - and the internals form required strengthening as its a power boat, and water ballasted. The fact that they also provide precise alignment of the topsides is a clever bonus.

It seems well thought out and maintainable from the stuff I have read.

 

There are no additional parts that need to be removed on that cat hull, i dont know which design it is but it is not the eco 5 and does not appear to be the KD650 either as it is a symetrical hull, anyway, its not important, what it is, is a dart type hull which uses the small skeg shape that is clearly evident in the keel line to prevent leeway, in lieu of daggerboards,assymetry,minikeel etc. This is incorporated into the backbone, you could remove it and build in a daggerboard trunk if you wanted to if you want to add complexity. The top of the backbone supports the sole which appears to be glassed in providing tremendous strength, this could be left out as its not needed with the number of bulkheads but most likely the hulls would be used for storage and often there are removable sole panels to allow for better stowage so you may as well build them in. You could use less bulkheads but since you are not using stringers to break up the panel sizes and presumably they are trying to keep the plywood thickness down it would probably no be wise. The only other piece of structure is the longitudinal which is notched into the bulkheads to support the deck, if you took it out you would need to replace it with something else. If you look at the pictures Angel provided there are just as many components, just different ones.
Steve.

 

Right, it's not the ECO 5.5 which I linked. I was misled by the top of the page which says ‘‘ECO 5.5’’ and has an ECO 5.5 picture on top + everyting else on that webside which is about the K-designs ECO 5.5 (exept the 'more designs' page). The bottom of the 'kit' page says ‘‘Please note that the pics above are from an openbridgedeck sailingversion’’. But not only is the cabin gone... the bow and other things are different too. So I don't know which design it is. Strange that he takes this example to sell ECO 5.5 kits.

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Back to the build.. how does he make the fillets in there..?? OK take the deck off, but then you still can't go to bottom..

Like Teddy said, after the 65 minutes of that page the build has just begun and he has made it very difficult to complete..








http://www.youtube.com/watch?v=jn8L9oMZYbE


Filleting the inside and glass over the fillets, please how do you get in the corners beneath that floor..??

Cheers,
Angel

PS

The 65 minutes doesn't include the cutting off of all the taps, sanding them down and filling all the slots and smoothen everything up. Also the dogbone jointed panels must have been pre prepared, no way he has made and cured them in the same 65 min as he wedged up the hull kit.

(pics attached so they will stay with the thread for discusion matters)

 

The cat hull goes against tradition that the keel is mounted outside the waterproof hull.

Most boats make sure that the hull is sealed up first, then the hull is attached. Then often extra 'sacrificial' bits, deadwood, are added

The reason for this is that when the keel hits something, or you rest the boat on it, or just keep pulling it on and off the trailer, any movement in the keel doesnt jeopardise the waterproofness of the hull.

In this catamaran design, the keel goes right through to the interior with no waterproof barrier. If the plywood keel is damaged, water will migrate all the way to the inside, into the main structural members. Also, from a strength point of view, there is not the usual tension join of the hull bottom.

In small boats, there is usually a complete layer of fg cloth that spans from one side the boat to the other, and prevents the keel seam from splitting apart under tension.

In this design, any tension ( pressure from fast motoring for example) relies on the fibreglass staying attached to the central keel. From experience, it doesnt take a lot of tension to separate epoxied fibreglass from the surface of plywood - ( the plywood breaks) - where if fibreglass is a continuous sheet, it is very strong.

Primitive diagram attached to illustrate

 

Here is another thread discussing scarf vs puzzle puzzle joints.

http://www.boatdesign.net/forums/wo...tion/joining-plywood-puzzle-joints-35333.html

Looks like the fun is over on this cat once all of the wedges are inserted. Filleting and glassing the seams looks like a royal PITA.

 

This is Pars reply to one jointing option -

If thats how much someone was charging for a finger joint, he is quite correct - its a ridiculous price, but that kind of expense is not my experience.

My local furniture maker will do a very complicated and detailed dice up of a whole sheet of plywood for $40, so if I had, say six sheets of ply to merely finger-joint, then it would probably only be $20 or $30 per sheet.

Percentage wise, that still might seem a lot, but its about the same amount of labour and materials $ that it would take to scarf the sheets, and you get a way more accurate and attractive finish, and probably, a much stronger joint for 1/4" ply. Even the Payson join is a lot of trouble, and a lot more epoxy and cloth than a finger joint.

Yes, thats the first big problem for sure - the internal fillets.

 

rwatson, there is nothing wrong with the keel penetrating the hull like this,its done all the time,in fact in this case its a lot like in carvel construction where the garboard plank is rabbeted into the backbone. I doubt that that single piece of ply makes up the entire keel,it would not be strong enough so i would guess that there would be extra layers of ply each side then a nice structural fillet and glass,it will be massivly strong and leakproof. It would be nice if Claude were to come on this thread and answer some of the questions regarding the filleting and glassing issues that have been brought up. It may be that we are not seeing the kit in its enirety in the videos, i have manufactured hundreds of stitch and tape kits 30 yrs ago before cnc machines and we used solid wood parts where necessary,in the case of this cat it could (but dosnt appear to) have for example, cheeks which glue each side of the stem,with the correct bevels machined which would eliminate the need for glassing the inside of this area. On the joining of the plywood sheet subject,i looked at the other thread you linked and i think yhe only one of these machine made joints i like of all the ones ive seen is the true puzzle joint on the PT skiff because it locates the sheets in two directions, most of the others are finger joints and dont offer any advantage(to the builder) over a scarf or glass taped butt.
Steve.