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  #11  
Old 10-12-2006
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Stephen-
If I were enlarging the doorway...and the doorway is simply cut into a 1/2" plywood sheet?
I'd suspect the sheet isn't "very" loadbearing and framing out the new doorway (or the whole sheet) probably would carry any extra load. One of the options, if it is a doorway with rounded corners, would be to use wood veneer and glue lamination and build it up into an "oval" (rounded rectangle) to fit the new doorway, turning it into a trim molding and structural support all in one. (No but joints, no ends, no stress concentrations from them.)

Or, maybe just replace the bulkhead with heavier material to compensate for the bigger hole in it.
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  #12  
Old 10-12-2006
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Does the existing opening go all the way to the underdeck surface or is there part of the bulkhead over the top of the door ? If there is then you could almost certainly increase the size of the opening but.....Curves are stronger than straights so it would be preferable to have the new opening with curved top plus I'd look at increasing the thickness of whats left (around the opening) which can be achieved by laminating another thickness of plywood to the existing. Even so, I'd still ask a naval architect or shipwright to advise before you start a hacking.
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  #13  
Old 10-13-2006
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I am inclined to think that even if the renovations were done very well they will make it much harder to sell the boat when the time comes.
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  #14  
Old 10-13-2006
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Quote:
Originally Posted by chefmango1
...In home construction when you poke a hole in a wall you add headers, however in this bulkhead partition there is no additional or beefed up bracing. Thus my question should be more correctly can I increase the size of the doorway by 10-20 or 30 percent. I posted the question because maybe there is someone out there who has done something along the same lines. As far as resale value goes I'm not that concerned because just as you customize your house or car it can turn out for the better, after all these things are boats, not precious antiques. Calls to Beneteau by the way were not helpful.
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Stephen,

If you query this forum enough you may get the answer that you think that you need for your project. Down the road when it's time for resale a good surveyor and some potential buyers will spot structural alterations, even if they are not disclosed ahead of time. Then if the buyer is not scared off right away they will start asking questions such as "What marine architect was used for the re-design ?". Surely you do not intend to tell them "User X on sailnet.com said it was ok". So the bottom line is that you need to employ the services of a marine architect before making any structural changes just for future resale, let alone for the safety of the good souls on board.

As to the market value of a high production vessel such as a Beneteau. that is fairly straightforward to determine from the high volume of resales. But if one makes significant layout changes, the market value becomes much more of a free variable, with brokers and surveyors challenged to determine it. Without a qualified architect involved, the determined value will surely go down. I can see a future buyer's survey report for his insurance company even killing the deal at whatever price. Going without insurance is not an option these days for almost anyone in a marina even if they decide to self-insure.

I do wish you luck as you proceed and hope that you consider the kind of advice that this project mandates.
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  #15  
Old 10-13-2006
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I am really surprised that Beneteau was not helpful. I have had to contact them about a variety of things and have been amazed at how thorough and helpful they have been.

Anyway, to the problem at hand. Primary bulkheads act as a diaphram that move loads from one portion of the hull to another. They typically handle very large loads overall loads but because of their large cross sectional area, these large overall loads only result in comparatively small unit stresses (i.e. pounds per sqare inch) in tension, compression and sheer.

As you cut away an area of a bulkhead you decrease its cross sectional area. As cross sectional area decreases, unit areas increase propotionately. A 20% larger opening may actually reduce the cross sectional area in one axis by far more than 20% and it make also very dramatically decrease the ability of the bulkhead to take compressive loads without buckling. (Buckling in controlled by a ratio of small cross sectional dimension of compressive member relative to its unbraced length, small increases in length can result in big opportunities for buckling when the depth of the member is only 1/2")

There are ways of providing additional cross sectional areas and additional resistance to buckling where these loads are being concentrated and to then distribute thse loads back into the surrounding bulkhead. These methods consist of of reinforcing the bulkhead and tabbing by doubling the bulkhead, adding an epoxy/ glass overlay, or adding rigid frames at openings.

Home construction is somewhat different than marine construction since the torsional loads generally are quite small compared to the vertical loads. In normal home construction, we typically count on sheathing and drywall membranes to provide sufficient lateral resistance. Boats are closer to a waterfront home with lots of glass, where diagonal bracing, sheer walls and rigid frames are introduced to address lateral loads and where headers alone are not sufficient.

Respectfully,
Jeff
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Old 10-13-2006
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Quote:
Originally Posted by Jeff_H
...
...Boats are closer to a waterfront home with lots of glass, where diagonal bracing, sheer walls and rigid frames are introduced to address lateral loads and where headers alone are not sufficient.

Respectfully,
Jeff
I would add that it's also like the home is in an earthquake zone..
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  #17  
Old 10-13-2006
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Neal and others have offered some very wise advice. It would pay to do more research into this proposal.

In my opinion, there is an inequity by stating installing a partition header in a house is analogous with altering a structural bulkhead in a sailboat. I'm only a humble building architect, but I at least know, that modifying a boat's bulkhead requires the knowledge of a marine architect. Marine engineering is a unique science, especially with sailboats, due to the increased lateral forces generated through heeling & from the rig above.

Simply installing a "beam" or "header" in a bulkhead may not suffice in carrying loads dispersed by either creating a new opening, or enlarging an existing opening. Is the bulkhead in compression as a result of deck-stepped spars? Is it used to resist the chainplate tension of stays or shrouds? Are other fittings, such as cleats or winches attached to the bulkhead? What function does the bulkhead serve in resisting shear, or resistance of vessel displacement loads from below? I would tread carefully if I were you.

Edit - I submitted this reply before seeing Jeff's post - he's the resident "marine architect" here and is respected by most.
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Last edited by TrueBlue; 10-13-2006 at 03:27 PM.
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  #18  
Old 10-16-2006
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This thread has probably already canvassed a too-wide range of opinions, but speaking as a reasonably experienced boatbuilder, I'd suggest that if you can add bracing then incrreasing the aperture of the door by 15-20% should not be that critical. However, it would be foolish to incease without the extra bracing. This opinion is largely based on the construction (as drawn) of the double-skinned main (mast) bulkhead in my catamaran, where there are sizable openings into the two forward cabins, also smaller openings above the dinette into some storage spaces, but around each and inside the outer skins there is a "web" of WRC beams.

Consider epoxy-bonding similar beams around the enlarged openings - in you case, make them decorative too.

Hope this helps

Alan
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  #19  
Old 10-17-2006
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Based on discussions I've had with Beneteau USA and the Chicago Beneteau dealer (specifically regarding the 36.7 model not a First 345), removing a bulkhead is not recommended. If in doubt it's probably better to leave it the way the boat was designed. Besides, squeezing through a small doorway in the cabin of a boat is part of the charm
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  #20  
Old 10-18-2006
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Wouldnt it just be easier to buy a new boat with the layout you like. I dont get all this customizing
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