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Thread: To frame or not to frame.
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11th April 2012, 09:39 PM #1Intermediate Member
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To frame or not to frame.
Hi.
I am in the throws of constructing a clinker plywood 16 foot( 4.8 mt) Putt Putt with a twin cylinder Chapman motor. I have the boat fully lofted thanks to the video I purchased from Queensland boat builder Alan Graham. I have the moulds made and timber for the keel.
The reason for this post is that upon purchasing the book written by renowned boat builder Iain Oughtred on clinker plywood construction he states,"Some builders may like to build a traditional boat for the challenge of doing it the old fashioned way. For most purposes however, the substitution of plywood and glue for solid planks,frames and rivets is well worth consideration" unquote.
I would like to agree with him as this can save a lot of work. The boat would turn out as lofted but not having frames(ribs).
My main concern here is that without frames and with an engine within, would that cause distorsion and eventual fatigue to the boat. I know that internal seating and bulkheads help.
Waiting for your thoughts. Cheers Dan
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11th April 2012 09:39 PM # ADSGoogle Adsense Advertisement
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14th April 2012, 02:45 PM #2
Converting a set of plans from a traditional build to a glued lap build isn't as simple as using plywood for the planking and tossing the frames out. A glued lapstrake build will still have structural elements, just not as many as the traditional lapstrake build. Some things remain the same, such as engine beds, possably some stringers, maybe some bulkheads and furniture too.
Call Mr. Graham and see if he's familiar with glued lapstrake and what he thinks about the conversion. Don't be surprised if he scoffs at the idea, as some take great offense at "alterations" to their work. Don't take it personally, just move on. Most any set of plans can be converted, given some education, a book or two, some study or you can pay to have the plans converted. I do this a few times a year and it's not that costly really.
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15th April 2012, 07:50 PM #3Intermediate Member
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Thanks Par.
In my thread I did neglect to mention that the boat Alan designed and built is epoxy glued, but still retains the frames. In order to keep a traditional look. I am thinking if no frames are needed then I don't need the ribbands. Without having to use these, I can trace out the station moulds which I have made, onto 12mm plywood and construct the boat on a strongback upside down. Thinking of my poor back.
Cheers Dan.
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16th April 2012, 03:44 PM #4
You'll still have to address the athwartship loads some how. Can you post a picture of the construction plan?
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18th April 2012, 10:19 PM #5Intermediate Member
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Hi, Par.
Unable to download from a playing dvd so I have done the next best thing,I think? Paused the disc then took a photograph off the screen . Hope it will give you an idea of the boat. Now lets see if I am able to send them. Thanks for your assistance.
Cheers Dan
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22nd April 2012, 01:05 PM #6
Dan,
Follow Allan's Plans, the frames give the hull the right look and can be laminated in after the hull is turned , depending on their thickness you could laminate them from 2-3 layers of 4mm ply .
everything in a boat is there for a reason , be VERY CAREFUL before you leave a structural member out.
Jeff
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28th September 2012, 07:45 AM #7New Member
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Hi Dan. It’s been a while and you may have finished the build by now. If you are still quivering on the brink here’s my thoughts.
From what I understand substituting plywood for solid wood planking as Iain Oughtred suggests is not really applicable as this boat is already planked in plywood with epoxy-glued seams. So what you are proposing is to eliminate structural elements of the design. In a traditional design ribs and/or frames provide the cross-grain strength that solid planking lacks but as pic 3 shows, the floors rest on the ribs which help distribute loads into the boat's skin, as well as greatly increasing hull stiffness. The ribbands also contribute to hull stiffness as well as making the plank fitting and assembly easier, and are needed anyway in the building mold to guide plank cutting and support plank edges during beveling and gluing. It’s probably more trouble to prevent them becoming glued!
The frames and ribbands are not there just for a trad appearance. This boat has the look of being designed for minimum weight, with light planking stiffened by light frames and ribbands. If you are serious about eliminating these the planking will need to be beefier IMHO. That will take more knowhow than I possess. Another thought - the more flexible hull would likely be noisier, acting like a drum when the engine is running.
of course, the floors, engine bearers, thwarts etc are non-negotiable!
I don’t agree with Jeff about using laminated plywood for the ribs, BTW. Laminated ribs are fine IMHO but solid wood would be far stronger and stiffer as well as lighter for a given cross-section than ply, since nearly half of ply’s grain is going the wrong way to do any good. I haven't done much steaming but it's a lot less work than laminating: the only reason I laminate ribs is if they are critical to defining hull shape during construction, since a laminated member will hold it's shape indefinitely.
Hope you're going to show pics of the process!
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