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Thread: Converting from carvel planking to strip planking/cold molded

  1. #1
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    Question Converting from carvel planking to strip planking/cold molded

    This is a fairly straight forward question...for plans that call for carvel plank construcition...specifically Fenwick William's designs from WB...how do you build them via strip planking/or cold molding? Do you keep the frames (sawn and laminated) and simply strip plank them? How do you determine the thickness of the planking?

  2. #2
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    You could just simply strip plank over the carvel structure with planking of the same thickness as the original carvel planks, but it would be a bit heavier than necessary. Strip/cold mold construction is stronger than traditional carvel construction, so the internal structure and planking thickness can usually be reduced in size slightly. To determine how much lighter, one has to calculate the scantlings for the particular vessel, paying attention to method of construction (laminated frames or solid wood?) and wood species. The most accessible source of information on this is Dave Gerr's book, "The Elements of Boat Strength", available from our sponsors.

    The lighter structure and planking will make for a lighter boat, which, if unrecognized, will result in the boat floating higher on her lines and therefore affecting the stability characteristics. However, when converting older designs to this form of construction, the addition of the creature comforts of today that were not yet dreamed of when the boat was designed; such as space heaters, hot & cold running water, holding tanks, stereos, electronic navigational gizmos, etc.; usually evens the weights out. One must be aware of changes being made in the centre of gravity as well, so that no surprises are discovered too late in the roll period of the boat.

    If you are uncomfortable with the responsibility of determining all of these important bits of data, consult your friendly neighbourhood professional boat designer (one who is experienced in wood-composite construction). He/she should be able to do the conversion calculations and weight calculations for you for only a tiny fraction of the cost of the vessel. A small price to pay for confidence in the information, right?
    Last edited by mmd; 07-17-2006 at 11:13 AM.
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  3. #3
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    Question

    Does this work with any carvel design? Would it work as well with a particularly heavy boat, like "Blue Moon"? Would it be possible to reduce the number or size of frames?

  4. #4
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    What MMD said.....On Gilmers Blue Moon I think several have already been built this way..I saw one just before launch a number of years ago that Mr. Gilmer was inspecting before launch...as I recall, the stem, backbone assembly was all laminated fir, the transom and 8 or 9 frames were laminated to the original dimensions, then strip planked at the required original planking less 1/4 inch, then 2 layers of 1/8th inch veneer, then covered with epoxy/glass...and she sat less than 1/2 inch high before anything was added...
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  5. #5
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    The following was a pretty good thread on this subject if it is still available.

    http://www.woodenboat-ubb.com/vbulle...ad.php?t=11036

    RB

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  7. #7
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    It seems the mold structure (frames) would have to be removed to facilitate glassing the hull interior. How necassary is glassing the hull interior?

  8. #8
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    Here's the modern version of that old thread:

    http://www.woodenboatvb.com/www/vbul...ad.php?t=11036

  9. #9
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    MMD took the time to put in a very good post, and I think his first sentence basically tells it all, just simply strip plank with the same instead of carvel plank..all else the same....

    Timothy B - haven't seen you around much lately, been wondering if you where o. k. I know you and me have been strong advocates of the traditional strip plank method. I think we both have done a lot of research in to the various strip planked methods..
    I am in the process of putting up a 32 ft. long building, and when it is done, shortly, I will start the weston farmers piute, a 25 ft. launch.
    I am going to change the planking from board and batten to strip.
    Going to pull my panty hose up and do the traditional square strips, with no glue or seam sealers, cloth or anything other then wood to wood, with bronze nails and bolts. Back to the basics.....

  10. #10
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    As a "petit bureaucrat" I suppose you expect to see things done properly. Get a NA, or at least a Designer to do the calculations. MMD comes to mind, for instance. You'd not likely be sorry.

  11. #11
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    Quote Originally Posted by Andrew
    It seems the mold structure (frames) would have to be removed to facilitate glassing the hull interior. How necassary is glassing the hull interior?
    The ribs can be left out all together if you glass the inside and outside of the hull - and someone has done the calcs to work out the thickness of planking and the amount of glass.
    ______________________

    Ribs are there partially to stop the planking from splitting or moving apart (ie they take the loads that are crossgrain to the planking.

    The glass does the same job as it will have some (sometimes all if using unidirectional cloth in one method) running across the grain.
    ______________________

    The other purpose of the ribs is to provide bending stifness in the hull side.

    If you glass both sides the glass itself forms a composite beam with the cedar as a core. In the same way as a foam cored boat or a surfboard gets its bending strength - two faces of glass with a core keeping them apart - the foam can be very weak - you can crumble it with your hands - but with the glass there you can drop off very big waves with no problems.
    _____________________

    It is important though to know how much glass on both sides and how thick the core needs to be.

    If it is too little - the boat will break - and you lose the whole value of the boat.

    If it is too much you end up spending too much money on materials and/or the boat is heavier than needed.
    ____________________

    Another factor with this sort of construction is that the internal fitout also provides a huge amount of stiffness/strength.

    Bunk tops and faces, cockpit seat tops and faces (and their internal divisions), galley, cupboards etc are all structurally bonded to the hull providing a series of very large beams and boxes that support the skin.

    So it all works together as a unit.

    Thats how we did the catboat http://www.storerboatplans.com/DavidCatboat/davidcatboat.html and many others over the years.
    ___________________

    With the glassless strip planking mentioned above the cross grain loads are carried partly by the ribs and partly by the edge nailing or dowelling. I don't know much about that construction apart from that.

    Best Regards
    Michael Storer
    Last edited by Boatmik; 04-24-2007 at 05:22 PM.

  12. #12
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    Quote Originally Posted by RonW
    MMD took the time to put in a very good post, and I think his first sentence basically tells it all, just simply strip plank with the same instead of carvel plank..all else the same....

    Timothy B - haven't seen you around much lately, been wondering if you where o. k. I know you and me have been strong advocates of the traditional strip plank method. I think we both have done a lot of research in to the various strip planked methods..
    Hey! Yeah, I have been away but ok I've had to put the boat plans on hold for awhile after an initial flurry! The house has taken precedence.

    I am indeed a strong supporter of the 'Traditional Strip Plank' method of building, and not just for amateur builders (tho they get the most benefit from it). Pulsifer Hamptons are made this way and he does an amazing job of it. As far as what to put between the strips, I still believe that a compromise is in order. If you really want to go old time, you would paint them with thickened paint (oil paint) before nailing them up. Maybe you would even put a thin strip of muslin to help with the seal. Personally, I might try using cheap, industrial polyurethane that had been formulated for sealing concrete.. but putting it on thinly. Essentially, if you want to get the thing done before you die of starvation, you could be a bit more 'sloppy' about the joins this way. We all know that 90% is good enough and that last 10% costs just as much as the first 90% did. As one very accomplished artisan has said "Better is the enemy of Good". Of course he also said "Don't do anything half arsed" so I wouldn't go the route of the complete wood butcher ;-)

    At the end of the day, this sort of construction is extremely strong, tight and durable. If you do it on a traditional carvel framing scheme the darn boat will be bulletproof, and in fact you could be -really- sloppy and just strip her up loose-like and cover her over with Xynole (I wouldn't, but I'm somewhere inbetween a butcher and a perfectionist . Some might say it would be too heavy, but hey.. I dare anyone to complain about that when they get into a 2 day hurricane off of Florida! Heck, with strip planking like this you could strip it with thinner wood and glue up 1/4" or whatever ply over her diagonally and have a poor man's cold molded boat. Talk about strong! And nowhere do you have to be concerned about perfect accuracy of spiling, things popping loose, or even too much about wood quality.

    Quote Originally Posted by RonW
    I am in the process of putting up a 32 ft. long building, and when it is done, shortly, I will start the weston farmers piute, a 25 ft. launch.
    I am going to change the planking from board and batten to strip.
    Going to pull my panty hose up and do the traditional square strips, with no glue or seam sealers, cloth or anything other then wood to wood, with bronze nails and bolts. Back to the basics.....
    Good luck and good on ya! :-) Make sure you are using dimensionally stable softwood for the planking!
    Last edited by TimothyB; 07-24-2006 at 10:27 AM.

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