Results 1 to 19 of 19

Thread: Cold molded with soft wood in between.

  1. #1
    Join Date
    Apr 2016
    Location
    Kuala Lumpur, Malaysia
    Posts
    164

    Default Cold molded with soft wood in between.

    While rereading Ian Nicholson's Boatbuilding book, he mention that it is possible to use lighter wood in inner layer while use harder and stronger wood for outer layer.
    I wondered if it is possible to use something as light as balsa inside a 2 layer cold molded building or using it sandwich in between if it is 3 layer?
    I have not heard something like this been done.

  2. #2
    Join Date
    Sep 2010
    Location
    Bainbridge Island WA
    Posts
    2,025

    Default Re: Cold molded with soft wood in between.

    There are countless fiberglass boats built as you describe suffering from wet, rotting balsa cores. Or foam in the same wet condition.
    Steve

    Boats, like whiskey, are all good.
    R.D Culler

  3. #3
    Join Date
    Dec 2003
    Location
    Portland, Oregon
    Posts
    39,649

    Default Re: Cold molded with soft wood in between.

    What Stromborg alludes to is a common building technique. Composite construction. He's talking about a core of balsa and skins of polyester-based FRP. The core in that case is designed to add beam strength by separating the webs (fiberglass skins) as much as possible, while not adding any more weight than absolutely necessary. A similar composite more often used by the d.i.y. boatbuilding crowd is a non-durable plywood core with expoxy-based FRP skins.

    But the principle is the same and so are the issues. Choosing such construction makes it imperative that one seals out moisture. Keeping scrapes touched up quickly. Using an oversized annulus of epoxy at each fastener. Keeping the bedding for all hardware sound and effective. Etc. A fair amount of repair work that Harbor Woodworks does stems from the fact that entropy never sleeps, and not everyone understands how assiduous they need to be about these issues.

    The rigidity benefits gained by such a 'cored composite' approach are manifest. So are the dangers and challenges.

    So what I'd suggest, if you decide to mix species in the way you specify is to use the lighter weight material at the core, but make sure it's a durable (rot-resistant) species. Western Red Cedar is one example. Truthfully, though, I'd do some calculations to see if what I imagine to be small weight gain is worth the hassle of adding another species to the mix.

    And... on a more general note... I'd suggest you read the boatbuilding with epoxy 'bible'. West System has kindly offered this book, which used to cost $30, as well as lots of other good info, as a free download. It has the answers to most of the questions you've asked, written more carefully than we here are likely to manage in ad hoc response. If you can't find the answers you seek, come on back and seek here.

    http://www.westsystem.com/the-gougeo...-construction/

    http://www.westsystem.com/instruction-2/
    Last edited by David G; 06-27-2017 at 09:35 AM.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  4. #4
    Join Date
    Apr 2016
    Location
    Kuala Lumpur, Malaysia
    Posts
    164

    Default Re: Cold molded with soft wood in between.

    I see, there is no absolute way of settling water ingress.
    I just read it was mention in passing in Ian Nicholson's book, and I understand that most cold molded are done either with ply or cedar, rarely a composite of different woods.

    While foam core is used in GRP boats, was it possible on the other hand to use foam core in cold molded?
    There won't have problems with rotting in this case.

  5. #5
    Join Date
    Dec 2003
    Location
    Portland, Oregon
    Posts
    39,649

    Default Re: Cold molded with soft wood in between.

    Quote Originally Posted by Wckoek View Post
    I see, there is no absolute way of settling water ingress.
    I just read it was mention in passing in Ian Nicholson's book, and I understand that most cold molded are done either with ply or cedar, rarely a composite of different woods.

    While foam core is used in GRP boats, was it possible on the other hand to use foam core in cold molded?
    There won't have problems with rotting in this case.
    Again I suggest: read the book.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  6. #6
    Join Date
    Jan 2016
    Location
    Bolton, Massachusetts, USA
    Posts
    72

    Default Re: Cold molded with soft wood in between.

    End grain balsa is a wonderful (structural) core material. It's problematic, as others have mentioned, if it gets wet. There are great examples of boats with both wet and dry cores. It's not always easy to know which is which. I used endgrain balsa to stiffen some deck sections of my kayak. (Instead of additional layers of plywood and glass as the plans called for.) It's wonderful to work with. The WWII Mosquito Bomber used it sandwiched between layers of thin plywood. Unfortunately, the adhesive technology of the day doomed those aircraft to a short life. The deckhouse of the new DDG-1000 (Zumwalt) destroyer uses endgrain balsa between carbon cloth/vinyl ester skins. Interestingly, ships 2 and 3 are both using metal for the deckhouses(aluminum, I think).

    Good luck,

  7. #7
    Join Date
    Jan 2004
    Location
    Norwich,United Kingdom
    Posts
    4,694

    Default Re: Cold molded with soft wood in between.

    You might theoretically use foam core with a cold moulded hull.The challenge would be to find away to wrap the foam round a compound curved surface and bond it to the previous layer.If I had to do it and was able to take the time I think I would make every effort to seal the mould and early layers so that a vacuum bag could be applied and I would run a test to be sure it worked before mixing any glue.No doubt the foam would have to be applied as "panels" or "planks" and they would need to be clearly identified for location as they were dry fitted and it might need battens to stop them sliding out of position and maybe double as an infill at sheer height.If I was convinced the foam would stay in place,I would round up two or three helpers and spread the glue,tape or pin the foam in place and add my vacuum bag.After a successful cure I would add the outer skin and again vacuum it against the foam,probably in sections until the layer is complete.I would then expect to add another layer on the opposing diagonal and after fairing possibly a skin of 200 gsm glass.

  8. #8
    Join Date
    Apr 2016
    Location
    Kuala Lumpur, Malaysia
    Posts
    164

    Default Re: Cold molded with soft wood in between.

    Quote Originally Posted by John Meachen View Post
    You might theoretically use foam core with a cold moulded hull.The challenge would be to find away to wrap the foam round a compound curved surface and bond it to the previous layer.If I had to do it and was able to take the time I think I would make every effort to seal the mould and early layers so that a vacuum bag could be applied and I would run a test to be sure it worked before mixing any glue.No doubt the foam would have to be applied as "panels" or "planks" and they would need to be clearly identified for location as they were dry fitted and it might need battens to stop them sliding out of position and maybe double as an infill at sheer height.If I was convinced the foam would stay in place,I would round up two or three helpers and spread the glue,tape or pin the foam in place and add my vacuum bag.After a successful cure I would add the outer skin and again vacuum it against the foam,probably in sections until the layer is complete.I would then expect to add another layer on the opposing diagonal and after fairing possibly a skin of 200 gsm glass.
    It's very tedious, more so than resin infusion, vacuum bag with fiberglass or carbon fiber.
    I just thought it is realistic to build a lightweight one off hull by just directly cold molded a layer on top of foam core.
    But it seemed realistic to apply it on deckhouse or other components without much curve.

  9. #9
    Join Date
    Jan 2005
    Location
    Deepest Darkest Wales
    Posts
    17,962

    Default Re: Cold molded with soft wood in between.

    The engineering of stiff and strong panels by the use of a comparatively lightweight core between two skins of stronger material is not new - how light, how thick and how strong is a matter for calculation - from memory I.N. covers this in at least one of his books.

    The O.P. makes NO mention of foam - he asked about the putative use of balsa (A TIMBER) as a mid layer in a cold moulded hull.

    Similarly nobody suggested the use of end grain balsa in a cold moulded hull.

    Nicolson is a very experienced sailor, naval architect and boat builder - brief biog.

    If you have any doubts about the technique - why not ask the man directly.

    https://www.iims.org.uk/iims-members.../ian-nicolson/
    Someday, I'm going to settle down and be a grumpy old man.

  10. #10
    Join Date
    Apr 2016
    Location
    Kuala Lumpur, Malaysia
    Posts
    164

    Default Re: Cold molded with soft wood in between.

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    The engineering of stiff and strong panels by the use of a comparatively lightweight core between two skins of stronger material is not new - how light, how thick and how strong is a matter for calculation - from memory I.N. covers this in at least one of his books.

    The O.P. makes NO mention of foam - he asked about the putative use of balsa (A TIMBER) as a mid layer in a cold moulded hull.

    Similarly nobody suggested the use of end grain balsa in a cold moulded hull.

    Nicolson is a very experienced sailor, naval architect and boat builder - brief biog.

    If you have any doubts about the technique - why not ask the man directly.

    https://www.iims.org.uk/iims-members.../ian-nicolson/
    Yes, the book I have in question is his "Cold-moulded and Strip-planked Wood Boat Building" which is mention it is possible to use a lighter and softer layer of wood sandwich between harder layers, but he didn't explain it further but he do provide a table of weight, strength and evaluation of different species of wood.

    He didn't mention the use of balsa in the book, but maybe I should make it clearer initially I thought since Lindsay Lord uses balsa with fiberglass encapsulated, the problem is that the boat is designed to flex, how about using it with wood ala cold molded instead?
    And if foam panels can be applied in this way as well?

    Most people cold mold or strip plank with either cedar, spruce or cypress, I have not heard of people mixing different species of wood in the build.

    Balsa does seemed to offer very good strength for its weight. Of course there is the issue of rot as well.

  11. #11
    Join Date
    Apr 2016
    Location
    Kuala Lumpur, Malaysia
    Posts
    164

    Default Re: Cold molded with soft wood in between.

    Ian Nicholson must have been 89 now, I checked online.
    Not sure if I can ask him directly.

  12. #12
    Join Date
    Jan 2004
    Location
    Norwich,United Kingdom
    Posts
    4,694

    Default Re: Cold molded with soft wood in between.

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    The engineering of stiff and strong panels by the use of a comparatively lightweight core between two skins of stronger material is not new - how light, how thick and how strong is a matter for calculation - from memory I.N. covers this in at least one of his books.

    The O.P. makes NO mention of foam - he asked about the putative use of balsa (A TIMBER) as a mid layer in a cold moulded hull.

    Similarly nobody suggested the use of end grain balsa in a cold moulded hull.

    Nicolson is a very experienced sailor, naval architect and boat builder - brief biog.

    If you have any doubts about the technique - why not ask the man directly.

    https://www.iims.org.uk/iims-members.../ian-nicolson/


    Actually,the OP brought up the use of foam in post #4.I knew of a local powerboat racer who was keen to investigate the possibilities of a foam cored ply structure,it didn't get very far along the path of development for reasons which weren't technical but matrimonial.

  13. #13
    Join Date
    Nov 2001
    Location
    Seattle
    Posts
    21,388

    Default Re: Cold molded with soft wood in between.

    The book came out 20 years ago, and we have more experience with this type of construction that we had at the time. Why not use something like Western red cedar for all the layers? It's light, and the sheer strength would be the same all the way through, so it would not be as prone to delamination.

  14. #14
    Join Date
    Apr 2016
    Location
    Kuala Lumpur, Malaysia
    Posts
    164

    Default Re: Cold molded with soft wood in between.

    Quote Originally Posted by johnw View Post
    The book came out 20 years ago, and we have more experience with this type of construction that we had at the time. Why not use something like Western red cedar for all the layers? It's light, and the sheer strength would be the same all the way through, so it would not be as prone to delamination.
    I was thinking that it would be possible to use stronger and harder wood for outer layers without the weight penalty, but then why it isn't been used, I hope it's as simple as delaminates rather than people are just conservative to try the method.

  15. #15
    Join Date
    Oct 2001
    Location
    Flattop Islands
    Posts
    2,155

    Default Re: Cold molded with soft wood in between.

    If properly engineered there's no reason not to use balsa or foam as a core with denser wood skins. Schooner Creek Boats have done a lot of cold-molded hulls with foam cores, very successfully. I imagine the problems arise in actually using the sheets of square-cut end-grain balsa. The reason for using balsa would be to save weight and expense (balsa is cheaper than good foam). If you are building a lightweight hull the inner skin will be thin, how do you support it while constructing the hull? You're going to have to build a complete male or female mold. Then to get good strength and bonding you'll need two diagonal layers inside and out. So you need to plank the hull 5 times! Fairing and filling as you go. Plus building a sixth hull in the form of a mold which will be thrown away. This burns up tons of time and adds weight in the form of filler, and expense. Vs one layer of strip planks over simple sawn molds, it's a no-brainer which is easier, quicker, and less expensive. Plus the strip planked (cedar) hull will have far better impact resistance at the cost of some slight increase in weight.
    ___________________________________
    Tad
    cogge ketch Blackfish
    cat ketch Ratty
    http://www.tadroberts.ca
    http://blog.tadroberts.ca/
    http://www.passagemakerlite.com

  16. #16
    Join Date
    Dec 2003
    Location
    Portland, Oregon
    Posts
    39,649

    Default Re: Cold molded with soft wood in between.

    Quote Originally Posted by Wckoek View Post
    I was thinking that it would be possible to use stronger and harder wood for outer layers without the weight penalty, but then why it isn't been used, I hope it's as simple as delaminates rather than people are just conservative to try the method.
    People have already tried the method. And most methods you could dream up. And every method has its strengths & drawbacks. Your OP says that your interest in using a lighter species for the center layer stems from the weight issue.

    What I tried to get across in post #3 is that I doubt you would save much weight by going with even the lightest of species for 1/3 of the planking. And the weight savings from using balsa (rot-prone) instead of something like western red cedar (durable) would be even less.

    But since we're talking theoreticals... there's another issue: a lighter hull is not always a good thing. While you might gain an easier hull to launch, retrieve, and manhandle on the beach... too much lightness can cause a hull to perform differently, and potentially worse, than the designer intended.

    I understand why baltek or other sorts of balsa cores... or open-cell foam... are used. It's cheap, uniform, and well-suited to fast production applications. Lots of boats out there with such cores. And you can decide for yourself whether such a cost savings makes sense when weighed against the potential rot issues. But I wouldn't choose such a route if it was a boat I cared about. I've repaired tool many of them... so I'm a bit jaded, I guess. Esp. since there are easy options for not much more money.
    Last edited by David G; 06-29-2017 at 10:00 AM.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  17. #17
    Join Date
    Apr 2016
    Location
    Kuala Lumpur, Malaysia
    Posts
    164

    Default Re: Cold molded with soft wood in between.

    Quote Originally Posted by TR View Post
    If properly engineered there's no reason not to use balsa or foam as a core with denser wood skins. Schooner Creek Boats have done a lot of cold-molded hulls with foam cores, very successfully. I imagine the problems arise in actually using the sheets of square-cut end-grain balsa. The reason for using balsa would be to save weight and expense (balsa is cheaper than good foam). If you are building a lightweight hull the inner skin will be thin, how do you support it while constructing the hull? You're going to have to build a complete male or female mold. Then to get good strength and bonding you'll need two diagonal layers inside and out. So you need to plank the hull 5 times! Fairing and filling as you go. Plus building a sixth hull in the form of a mold which will be thrown away. This burns up tons of time and adds weight in the form of filler, and expense. Vs one layer of strip planks over simple sawn molds, it's a no-brainer which is easier, quicker, and less expensive. Plus the strip planked (cedar) hull will have far better impact resistance at the cost of some slight increase in weight.
    I guess the reason to do so is purely to build a lightweight race boat without the need for vacuum bagging and resin infusion.
    I get it why the process isn't common used when it's so labor intensive, but maybe is a good alternative for lightweight, strong hull other than GRP and Carbon Fiber with foam core.

  18. #18
    Join Date
    Apr 2016
    Location
    Kuala Lumpur, Malaysia
    Posts
    164

    Default Re: Cold molded with soft wood in between.

    Quote Originally Posted by David G View Post
    People have already tried the method. And most methods you could dream up. And every method has its strengths & drawbacks. Your OP says that your interest in using a lighter species for the center layer stems from the weight issue.

    What I tried to get across in post #3 is that I doubt you would save much weight by going with even the lightest of species for 1/3 of the planking. And the weight savings from using balsa (rot-prone) instead of something like western red cedar (durable) would be even less.

    But since we're talking theoreticals... there's another issue: a lighter hull is not always a good thing. While you might gain an easier hull to launch, retrieve, and manhandle on the beach... too much lightness can cause a hull to perform differently, and potentially worse, than the designer intended.

    I understand why baltek or other sorts of balsa cores... or open-cell foam... are used. It's cheap, uniform, and well-suited to fast production applications. Lots of boats out there with such cores. And you can decide for yourself whether such a cost savings makes sense when weighed against the potential rot issues. But I wouldn't choose such a route if it was a boat I cared about. I've repaired tool many of them... so I'm a bit jaded, I guess. Esp. since there are easy options for not much more money.
    I see, for a more durable boat, maybe sandwich a cedar is a better choice, but even then why not go directly for a easier route by going strip plank with cedar all the way.

  19. #19
    Join Date
    Dec 2003
    Location
    Portland, Oregon
    Posts
    39,649

    Default Re: Cold molded with soft wood in between.

    Quote Originally Posted by Wckoek View Post
    I see, for a more durable boat, maybe sandwich a cedar is a better choice, but even then why not go directly for a easier route by going strip plank with cedar all the way.
    The most common reason for mixing species is that one wants either the toughness of a heavier species on the outside of the hull... or the looks, as the intent is to finish 'bright'. One reason for choosing cold-molding over strip-planking is that slightly more curvaceous shapes can be managed more easily. Otherwise... nothing wrong with the all-cedar strip-plank route.

    It would help - me at least - if you would specify a design. I find myself losing patience rather quickly with all the open-ended theoretical palaver. The answer to most such queries is: 'sure you could, but would it make sense in your particular instance'.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •