Pilot house roof camber.

Discussion in 'Boat Design' started by FAST FRED, Nov 19, 2010.

  1. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Existing,
     

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  2. apex1

    apex1 Guest

    Thats our way of doing it, yes.

    It seems I misunderstood hiding as being bury them under the panel.

    Regards
    Richard
     
  3. cthippo
    Joined: Sep 2010
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    cthippo Senior Member

    OK, see, that's a design flaw right there :p

    Large timbers definitely seem like overkill for this, especially when large span trusses for buildings are built almost exclusively with 2x4s.
     
  4. alan white
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    alan white Senior Member

    Solid sawn frames as applied here, aren't nearly as strong as laminated frames. The problem is at the sides when the crown is somewhat pronounced, where the grain runs at an angle to the run of the beam. The wood isn't necessarily wasted if sawn (rather than laminated) ----you can edge glue your wide stock and keep cutting curves so that your last underside cut becomes your next top cut. However, laminated beams can be smaller (across ten feet, if you space beams at 16", sawn beams might be 4" tall but laminated beams might be only 3" tall). The lammed roof won't be more rigid. However it will be more resiliant, and less subject to cracking and splitting.
    Also, laminated beams will self-fair while sawn beams will have to be carefully faired with a belt sander or your favorite tool.
     
  5. Landlubber
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    Landlubber Senior Member

    ..that design of boat you can run constant camber framing, so much easier to build too.
     
  6. PAR
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    PAR Yacht Designer/Builder

    I agree with lubber, you don't need much for this type of roof, though sawn beams are inherently weak compared to every other technique. They also tend to be heavy for the same strength. It should be noted that repair and maintenance may require one or two persons on that roof at some point. A system that can tolerate this abuse would be a wise choice.
     
  7. FAST FRED
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    In working out the pattern for the roof beams I came across a great idea.

    Since there must be a large roof hatch to remove the engine,

    Ian Nicolson "Customize your Boat" suggests the hatch be athwartship , rather than fore and aft.

    As the departing engine will be on a crane hook anyway , rotating it 90 deg is child's play.

    Only one beam needs to be removable , rather than boxing and cutting 4 or more .

    Thought I would pass on this interesting idea , if anyone else needs a simple cure or an easier modification .

    FF
     
  8. michael pierzga
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    michael pierzga Senior Member

    Hard to say since I cant see your layout, but athwartships is logical. The front end and rear end of a wheelhouse are fragile...windows, doors...the sides of the house are robust and naturally stiff for and aft. might as well transfer the pop top roof load to the sides and use the roof framing as a natural guide for a hatch. Also when for and aft how would you keep the roof structure from sagging without additional structure ? Athwartships needs very little structure. Im looking at the cabin house access hatch on a very well built boat right now and it is athwartships.
     
  9. Commuter Boats
    Joined: Oct 2006
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    Commuter Boats Commuter Boats

    IMO As work boats these boats have a very good reputation but when converted the pleasure craft it's easy to get the C/G to high.
    I'm a fiberglass guy and I like foam cores a lot....
    You mentioned that it would have a fiberglass skin so you're probably not afraid of that product, I would advocate for a thick (1.5 in) foam core with relatively light fiberglass skins.
    The structure would likely be lighter than plywood construction and could be made lower with the same headroom by eliminating the beams, further contributing to stability.

    A few years ago a client purchased a 25-year-old, 35 foot lobster hull (Duffy I think) that was being retired from the livelihood of commercial crabbing. The boat had a rotten plywood cabin and an engine that had recently been rebuilt. He came to me for a cabin and dictated a floor plan and head room.
    What I produced is somewhat of an ugly duckling I know but I feel as though I did as well as I could with what I had to work with. The hull was produced with two different shear lines, work boat and pleasure boat with the workboats shear nearly 5 inches lower than the pleasure boats. If in what I produced the shear was 5 inches higher, the balance would be much better. The salon / pilothouse deck is just 4 inches above the valve cover of a Cat 3208 and I provided 6'3" of head room with a roof thickness of just over 2 inches with headliner, glass, foam, glass, so there was no room for me to lower the profile.
    I built a mold for the hardtop out of chipboard and tinfoil, laid-up the top skin, with an inch and a half upward turned flange ( 1.5 oz mat, a 12 in. 24 oz roving around the perimeter, .75 0z mat, 24 oz roving, 3/4 mat, ).After the top skin was completed, I formed up the cabin sides and doghouse, laid up the outer skin of the cabin before I laid two layers of .75 inch foam ( H 60) and bottom skin of mat, roving, mat. A little extra reinforcing was used above where the aft bulkhead would land and where electronics would be hung. At that point the hardtop was done and the rest of the cabin was cored and finished out. The mold was stripped, the cabin was turned right side up and nearly finished before I remove it from my shop and transported it to the boat. If I remember correctly the entire structure weighed just over 300 pounds.

    A long drawn out story to say that you should consider composite construction, it can be lighter, better insulating, requires no consideration for a hatch at this time as it would be simple to cut whatever is necessary when the time comes and then glass the cut out back in, and it can have a lower profile for the same headroom.
     

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  10. tom28571
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    tom28571 Senior Member

    Commuter, That is a very nice looking job. I echo the function advantages of an insulated and lightweight cabintop. I would go with a ply/foam/ply torsionbox construction myself but the end result is nearly the same.
     
  11. mark775

    mark775 Guest

    Commuter, I'm not going to say anything about the looks - I've done some here, as well and given constraints, it is difficult to make something that pleases you and the client's pocketbook. We've got a guy that builds like you here, http://www.slothboats.com/index.html . Where are you in Southeast? - I'll tell our guys that go down there for Sitka Sound, Kah Shakes or trolling about you when they crash their boats or blow an engine or whatever.
    On the thought of increasing headroom yet minimizing visual height, I've thought of a solid laminate of carbon fiber for the cabintop of my similar boat. (Well, a carbon fiber laminate with a decorative laminate of wood on the under side) It has worked fine with balsa cored glass since '79, but I'm getting a crick in my neck! Thoughts on what kind of laminate schedual?
    I agree with an earlier poster about drawing pictures, thinking about what looks right, etc. The laminated beam idea is sound and I think that Fred's cabin is going to be plenty strong - what looks right is the most important, now.
    You know, I went to great lengths to foam insulate parts of my boat at which I could get and didn't notice a difference (I was 1" Balsa core FRP and added 1/2" of blue board). I feel that there is enough glass and open ventilation anyway that if one has enough insulation that it is not sweating, it is enough and not worth the reduced headroom (get a bigger heater). Plywood is strong, light, and a pretty good insulator. I'm just not that big on foam but up high on the boat is a good place for it, I guess.
     
  12. apex1

    apex1 Guest

    Fully concur, and a bit easier to make also.
     
  13. Submarine Tom

    Submarine Tom Previous Member

    I didn't mention this earlier (Post #11), but it now seems relevant: On top of the 2 1/4' (56mm) spruce beams I made was 1/4" (6mm) ply, 2" (50mm) R-12 foam, 1/4" ply topped with Fiberglas (cloth) and gelcoat (black). For better visibilty, the beams could easily be hidden inside with the foam sheets. I preferred to have mine show. It made for a more insulative roof and with an oversized strip of mahogany along the bottom, quite decorative.

    -Tom
     
  14. Commuter Boats
    Joined: Oct 2006
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    Commuter Boats Commuter Boats

    As far as them being easier to make I think it's a wash in light of the fact the standard size panels don't work. The gentleman has already seen the value of a fiberglass skin on the exposed surface to minimize maintenance and because the fiberglass skin and the plywood don't complement each other particularly well, the structure is already overweight. It's been my experience that most plywood structures onboard boats gaining weight with age and the foam fiberglass structure although not immune is less likely to be adversely affected by its environment.
     

  15. tom28571
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    tom28571 Senior Member

    Its probably a matter of what we are most familiar and proficient with. For me, it takes a lot of fiberglass to equal the strength and stiffness of a ply panel. I do question the claim of weight gain. That has not been my experience when both plywood and fiberglass are equally protected.
     
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