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Thread: cabin construction advice needed

  1. #36
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    Default Re: cabin construction advice needed

    Deck beams are normally the same thickness for their entire length. The mechanical layout seen above in #12 is an elliptical arc. If you conthinue the layout you will find that the ends become much steeper as the arc grows in length. Those who wish to have a turtle back form can use this layout method but it can look a bit odd if not done correctly. One other thing that should be considered is that this layout form must be made for each beam as just cutting the ends off will not work for making a shorter beam as doing that will create a hollow in the center line of the deck house or deck when viewed in the sheer plan. So, be sure to draw each pattern to a chalk line or batten down the centerline of the deck house. Deck houses normally do not have sheer in the centerline unless it is pre-planned by the N.A. or designer. Also note that a well drawn deck house should have it's coach roof disappearing at the stem head if an extended line is projected down the center of the house to the bow. This is one way to insure that you will avoid a common mistake made by Jerry Builders who creat deck houses that often resemble a comfort station mounted on a raft!
    Jay

  2. #37
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    Default Re: cabin construction advice needed

    I have a question regarding drawing the arc for the cabin camber: how is the arc measured in order to divide it into 4 equal parts?
    incidentally, im drawing out my camber to 6 1/2" in 6'. this will give me the headroom I want with lower cabin sides.
    Last edited by Bernadette; 07-20-2020 at 06:15 AM.

  3. #38
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    Default Re: cabin construction advice needed

    Quote Originally Posted by Bernadette View Post
    I have a question regarding drawing the arc for the cabin camber: how is the arc measured in order to divide it into 4 equal parts?
    incidentally, im drawing out my camber to 6 1/2" in 6'. this will give me the headroom I want with lower cabin sides.
    Are you asking about how to divide the ark IAW Post 9?
    I would use a pair of dividers to guess, and then work in by trial and a=error.
    Or you could use a compass and swing arcs like this
    Camber (2).jpg
    It really is quite difficult to build an ugly wooden boat.

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  4. #39
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    Default Re: cabin construction advice needed

    I remember Tom Colvin wrote that in his opinion, really good sitting headroom was far more important than standing headroom. Argued that there was "lots of standing headroom on deck" (), and that comfort in a boat which was going to be used either for living or for long passages really depended on having good and functional spaces to sit and to work below.

    In his view, standing headroom was something of a luxury in small-ish vessels (and even some designs of larger ones), and shouldn't be permitted to expand enough to compromise the functionality of the decks, or raise the center of gravity of the vessel unduly. Where it wasn't gonna be possible very easily (often partly achieved by lowering the sole somehow), best to ensure good sitting headroom instead.
    If I use the word "God," I sure don't mean an old man in the sky who just loves the occasional goat sacrifice. - Anne Lamott

  5. #40
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    Default Re: cabin construction advice needed

    You can do it like this:

    Screenshot 2020-07-20 at 13.13.25.pngDraw the line AE. Draw a perpendicular from the centre of AE to cut the arc at C. Draw lines CA and CE. Draw a perpendicular from the centre of CA to cut the arc at B. Draw a perpendicular from the centre of CE to cut the arc at D.

    This works for any number of even divisions. An odd number is rather more difficult!

    Cheers -- George
    Last edited by debenriver; 07-20-2020 at 12:36 PM.
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  6. #41
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    Default Re: cabin construction advice needed

    Thanks Nick, Tom & George. I will admit it had me stumped and despite trying a number of methods, I just couldn't get it right!
    The cabin sole is atop the floors so not possible to lower anymore. I think in a 30' of the size I am building: one might or would expect to have some standing headroom, albeit limited in some respects. I think I'll end up with headroom (for a 5/10" husband ) at least for half the length of the cabin. I'll be pleased with that arrangement. I'm still essentially experimenting with overall dimensions.

  7. #42
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    Default Re: cabin construction advice needed

    Nick and I are essentially constructing the same thing by different methods. Nick's is simpler and more accurate more easily, because it only requires a compass, whereas mine requires a rule and a square!

    I think at 30' standing headroom is very sensible. You will never see an odd extra inch or so on the coachroof coamings or camber in practice. And when heeled at sea a decent camber is good to stand on to windward. And you'll not be swearing when you bang your head on a beam for the fifty-ninth time ....

    Boats are to enjoy using and being on – not a purist spectator sport. My view anyway.

    Cheers -- George
    To be truly free to live, one must be free to think and speak.

    A C Grayling

  8. #43
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    Default Re: cabin construction advice needed

    George, I redrew my camber batton today (using your method).
    It looks good. So thanks for the help.
    I did a mock up today with the new camber and overall head heights...I will end up with 6' under the beam in the center portion of the cabin. I don't know how far forward I can take this height as I haven't yet decided on the height at the forward end of the cabin. And Im anticipating the furniture/fit out will preclude any need to move too far outboard whilst below so any loss of headroom there won't be an issue.
    I have decided on a cabin side height of 19 1/2" at the aft end so Im happy with that. I was aiming for 18" but the compromise in head height wont detract at all.
    Last edited by Bernadette; 07-21-2020 at 06:09 AM.

  9. #44
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    Default Re: cabin construction advice needed

    Hey All,

    Wow. . . this thread has been "sent from heaven" and timely as well.

    We too are about to embark on building a cabin for our 20' LOA, 8' Beam flat bottomed ply on frame boat. From what we've read on this thread, our initial concept for the cabin seems feasible, but more than that - the "how to" and ideas we've found here is invaluable.

    A heartfelt thank you to all that participated in this thread from an old guy doing his first boat!

    Stay safe, stay healthy.

    J.

  10. #45
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    Smile Re: cabin construction advice needed

    Quote Originally Posted by Bernadette View Post
    George, I redrew my camber batton today (using your method).
    It looks good. So thanks for the help.
    I did a mock up today with the new camber and overall head heights...I will end up with 6' under the beam in the center portion of the cabin. I don't know how far forward I can take this height as I haven't yet decided on the height at the forward end of the cabin. And Im anticipating the furniture/fit out will preclude any need to move too far outboard whilst below so any loss of headroom there won't be an issue.
    I have decided on a cabin side height of 19 1/2" at the aft end so Im happy with that. I was aiming for 18" but the compromise in head height wont detract at all.
    I'm really glad it's working out well
    To be truly free to live, one must be free to think and speak.

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  11. #46
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    Default Re: cabin construction advice needed

    a further question: this time to do with laminating the beams.

    my laminating jig is the revised 6 1/2" camber over 6 ' and Ive done two so far but neither are holding their shape when cured. they are 'flattening out' by about 17mm (apologies for the use of both metric and imperial measures. I generally use both when building).

    anyhow, im currently laminating beams using 4 lengths of 15mm thickness.

    to maintain the correct camber/curvature I was thinking of dressing my laminations down to say 9mm and using 6 laminations to keep the desired beam depth.

    does anyone have thoughts on this (i.e. will six thinner laminations hold the desired shape?)

  12. #47
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    Default Re: cabin construction advice needed

    I usually recommend a minimum of seven laminates to avoid springback. For a 60mm laminated beam, I would use 10 off 6mm laminates.

    Cheers -- George
    To be truly free to live, one must be free to think and speak.

    A C Grayling

  13. #48
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    Default Re: cabin construction advice needed

    Thanks George.
    Heck! but thats a lot of laminations...

    I hate to appear picky or ungrateful for the advice, but is there any scientific formulae or law that does actually stipulate just how many laminations are required for a particular job? Is there a body of knowledge on this I can read about? I ask because Im planning on building the tiller/s (always build a spare!) with multiple laminations and wanted to build in the curves rather than cutting through a laminated block of timber for the shape.

    anyhow, tomorrow I'll dress down my stock and trial thinner laminations for the cabin beams. All this mucking around with the cabin has put me back time wise but Im happy with the results im getting.

  14. #49
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    Default Re: cabin construction advice needed

    Bernadette, I’ve used Gougeon’s formula with some success for laminating beams. Works well on the ones I did. You can use metric too, I used mm.

    y = x/n2
    y= the amount of springback
    x= the amount of deflection
    n= the number of plies

    thus with four plies(n) the spring back (y) will be 1/16” if the amount of deflection(x) is 1”

  15. #50
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    Default Re: cabin construction advice needed

    Thanks Andrew.
    Your response reminded me that I actually have Gougeons' book in my own library...found the formula on page 94!

    I wonder if I can get away with using the current camber form/jig ive been using rather than creating a new one with increased curvature to compensate for springback?
    tomorrow I'll be glueing up a beam using an increased number of laminations so will try this first then proceed from there. sort of don't want to have to build another form.
    Last edited by Bernadette; 07-27-2020 at 05:56 AM.

  16. #51
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    Default Re: cabin construction advice needed

    If you work the Gougeon formula with 7 laminates and 6½" (165mm) deflection

    y = 165/7² = 3mm which is probably acceptable. Which is sort of why I never use less than 7 laminates on any design, and normally more.

    With 10 laminations:

    y = 165/10² = 1.65mm which is really pretty much imperceptible. I would use your existing jig with 10 off 6mm laminates.

    I have never found that making a form with more curve than you want, to counter possible springback, to be a very satisfactory way to go, as the results are not very predictable.

    In practice it isn't difficult to use 10 laminations, nor particularly time consuming, when you take the job as a whole – accurate result – no springback – good to go straight off the jig every time – etc. And you get a stronger beam – so you can if you wish, reduce the depth a little. You can do the lamination in two goes if laying all ten at once is a bit daunting.

    Most of the boats I design have laminated ring frames, so the beam sections are made from 3mm laminates like the rest of the frame – so there are often 13 to 15 laminates – most builders do those in two goes, specially to start with until they get the hang of it.

    Cheers -- George
    Last edited by debenriver; 07-27-2020 at 06:43 AM.
    To be truly free to live, one must be free to think and speak.

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  17. #52
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    Default Re: cabin construction advice needed

    I agree with George except cutting 10 lam’s at 3 mm ea wastes a lot of wood and glue. I got pretty close with the Gougeon method and if you can get all the beams at close to the right height on the Carlin then you’ll only have to do a little fairing.
    You could use same jig with packers increasing outwards.

  18. #53
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    Default Re: cabin construction advice needed

    Quote Originally Posted by Andrew Donald View Post
    I agree with George except cutting 10 lam’s at 3 mm ea wastes a lot of wood and glue. I got pretty close with the Gougeon method and if you can get all the beams at close to the right height on the Carlin then you’ll only have to do a little fairing.
    You could use same jig with packers increasing outwards.
    Well it's 10 laminations at 6mm – so not quite so bad! And, within reason, the more glue joints you have in a lamination, the stronger the beam.

    Sliced veneers (up to 3mm) are very common in the UK and Europe, so the question of timber waste is not an issue. Agreed, it does take more epoxy, but the thinner the laminate (again within reason) the more truly a wood/epoxy composite you get as the epoxy will penetrate through the timber. We used to make laminated stems for our 30' Naja class (and many larger boats) generally from 10mm Iroko – the epoxy would permeate through that thickness – not everywhere, but considerably.

    I know it's much harder here where sliced veneers are not readily available, so laminating is naturally less popular and more wasteful of material. The 15mm laminates that Bernadette currently has would split into near enough 6mm with a fine kerf saw.

    If the beams are a constant camber (6½" over 72" = 9%), which will produce a fair cabin top, then a different jig will be needed for different length beams. Which is not as bad as it sounds because each beam will be pretty much perfect and only need bevelling (if there is bevel) and the top will be fair without any further work.

    The easiest jig is, I think, made by drawing out the camber on a board (¾" particle board for example), tape polythene tightly over the board, then screw clamping blocks to the floor about every 4" - 6" or so along the camber line. Then laminate the beam inside the blocks. The laminates will usually stay in place sideways hard on the board, but you can use a couple of rebated blocks screwed down to the board to makes sure they do, if necessary. I would make the width of the laminates about ⅛"-¼" wider than the siding of the beam and then run it through the thicknesser after it had cured.

    It's a pretty quick job to draw out the next camber and reposition the clamping blocks.

    Cheers -- George

    PS - here is a typical set-up (it's part of a frame) – the builder there is using L-shaped blocks, but simple rectangular ones will do fine.

    slideImg10.jpg
    Last edited by debenriver; 07-27-2020 at 08:40 AM.
    To be truly free to live, one must be free to think and speak.

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  19. #54
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    Default Re: cabin construction advice needed

    Beam lamination has been progressing: using 7 laminations of 8 mm. This has resulted in only a small amount of springback (around 1/8"). so im happy with this and have been moving along with this set up. I have made my beams somewhat smaller in part due to preserve my timber stock.

    a further question with respect to the line of the cabin (not the center line but rather the line at the cabins sides): it's traditional to keep the cabin height the same for and aft but im wondering about lowering the height at the forward end somewhat...any thoughts? the reasoning I guess is to avoid a boxy appearance, and tp keep head height at the aft end of the cabin.

  20. #55
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    Default Re: cabin construction advice needed

    I sometimes design cabin sides that are not parallel to the waterline. Both straight and curved in profile.

    It sort of depends on the sheer and the crop (camber) of the decks. Because the sheer is rising as you move forward, the actual physical height of the cabin sides will decrease even with them parallel to the waterline, so they will look smaller anyway. And because the cabin is getting narrower, the camber will be less in actual terms, even though the same %, so the centreline will also tend to run lower as you move forward. If the cabin runs aft of the widest beam (and the sidedecks are parallel to the sheer), then the centreline will also drop a little aft of the widest point.

    If you wish, you can drop the line of the top edge of the cabin coamings in the profile view, relative to the waterline, as you go forward and this can often look quite nice. Also viewed in the profile view, the top edge of the coamings doesn't have to be a straight line – it can have sheer or reverse sheer. All can look good in the right circumstances. And as long as you stick to a constant camber % and make the actual camber of each beam the same % of its length, you will end up with a fair and reasonably developable cabin top – at least developable enough to lay ply on without a problem.

    But I wouldn't, personally, sacrifice too much headroom, just for the sake of dropping the top of the coamings a little, because with the rise in the sheer, their actual height is going to decrease anyway, so they will look as if the total height is getting smaller as you move forward. You don't really see the centreline, except on a drawing, because the coachroof top is a surface and the centreline is not a hard edge like the top of the coamings – so I wouldn't worry too much about that.

    Also, if you are worried about the cabin looking "boxy", you can slope the front coaming rather than make it vertical. I sometimes run the front coaming at a shallow enough angle to put a deck access hatch in. That way the coachroof tends to run into the foredeck, rather than ending abruptly. A disadvantage is that a well sloped front doesn't break up a sea landing on the foredeck in the same way as a vertical one does – so under some circumstances the boat can be wetter at sea.

    I think when you come down to it, it all depends on the style of the boat.

    George
    To be truly free to live, one must be free to think and speak.

    A C Grayling

  21. #56
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    Default Re: cabin construction advice needed

    I was concerned about boxiness too so leaned the sides in 5 degrees and curved the windshields.

    Beams were simply laminated over a temporary ridge pole and a couple of temporary carlins so we are using different approaches to that but here you can see the effect of the 5 degree leaning.

    Also, my upper cabin edge is straight and pitched forward some and the lower one is pitched forward more and curved. That meant that the ply had to be tortured in on the lower one but it was just as easy as the straight one.

    You can read more about it on pages 9 and 10 here...http://forum.woodenboat.com/showthre...y-build/page10





    Curved windshield.


  22. #57
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    Default Re: cabin construction advice needed

    I know it's hard in the shed, but have you made a mock up to see how you think it will look and feel, inside and out?

  23. #58
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    Default Re: cabin construction advice needed

    Quote Originally Posted by Thad View Post
    I know it's hard in the shed, but have you made a mock up to see how you think it will look and feel, inside and out?
    yes it is incredibly hard in the shed with little room to get a perspective of the whole arrangement.

  24. #59
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    Default Re: cabin construction advice needed

    Quote Originally Posted by debenriver View Post
    I sometimes design cabin sides that are not parallel to the waterline. Both straight and curved in profile.

    It sort of depends on the sheer and the crop (camber) of the decks. Because the sheer is rising as you move forward, the actual physical height of the cabin sides will decrease even with them parallel to the waterline, so they will look smaller anyway. And because the cabin is getting narrower, the camber will be less in actual terms, even though the same %, so the centreline will also tend to run lower as you move forward. If the cabin runs aft of the widest beam (and the sidedecks are parallel to the sheer), then the centreline will also drop a little aft of the widest point.

    If you wish, you can drop the line of the top edge of the cabin coamings in the profile view, relative to the waterline, as you go forward and this can often look quite nice. Also viewed in the profile view, the top edge of the coamings doesn't have to be a straight line – it can have sheer or reverse sheer. All can look good in the right circumstances. And as long as you stick to a constant camber % and make the actual camber of each beam the same % of its length, you will end up with a fair and reasonably developable cabin top – at least developable enough to lay ply on without a problem.

    But I wouldn't, personally, sacrifice too much headroom, just for the sake of dropping the top of the coamings a little, because with the rise in the sheer, their actual height is going to decrease anyway, so they will look as if the total height is getting smaller as you move forward. You don't really see the centreline, except on a drawing, because the coachroof top is a surface and the centreline is not a hard edge like the top of the coamings – so I wouldn't worry too much about that.

    Also, if you are worried about the cabin looking "boxy", you can slope the front coaming rather than make it vertical. I sometimes run the front coaming at a shallow enough angle to put a deck access hatch in. That way the coachroof tends to run into the foredeck, rather than ending abruptly. A disadvantage is that a well sloped front doesn't break up a sea landing on the foredeck in the same way as a vertical one does – so under some circumstances the boat can be wetter at sea.

    I think when you come down to it, it all depends on the style of the boat.

    George
    hello George, yes Im using the same camber over the entire cabin and I have dropped the coaming as it moves forward (in a straight line - no sweeping as drawn in the plans for the boat). just now my dimensions escape me but its subtle change in height relative to the waterline. Honestly, Im stressing I think I may have gone too far with this and will need to reassess before proceeding.

  25. #60
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    Default Re: cabin construction advice needed

    You can over-think this! And you can't usually get back far enough or to the right height to see it properly in the building shed.

    An inch here or there in the height won't make a big difference visually once the boat is in the water as you will be seeing the whole thing as a collection of 3-dimensional surfaces, rather than a 2-dimensional drawing. And mostly (hopefully) you will be aboard the boat rather than looking at it from afar anyway!

    Probably, I would simply keep the top of the coamings parallel to the waterline as this most always looks OK and not stress about it any more... But if you have already dropped the front end, then that will likely look OK too!

    Cheers -- George
    To be truly free to live, one must be free to think and speak.

    A C Grayling

  26. #61
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    Default Re: cabin construction advice needed

    hello George,
    somewhere along the time line I do believe I was overthinking all of this! I went back on Monday and took measurements and got the level and straightedge out again...to my satisfaction I have run the cabin top parallel to the waterline.
    I'll be posting photos up soon...as soon a is can figure out whats happening with the computer (its not accepting uploads form my phone just now).

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