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Bertram31.com General Bulletin Board
Re: Glassing bulk heads / Hard spots *PIC*
Posted By: Capt Partick McCrary In Response To: Re: Glassing bulk heads / Hard spots (CMP)
Date: Sunday, 11 December 2005, at 2:30 p.m.
Ian, sides of hull only... Hard to the bottom below the chine.
Mark,
There should be no hard spot on the side of a hull between the transom corner & the point of the bow. A hull flexes, contracts and expands. Any hard line, especially a vertical bulkhead will cause undue stress to the hull along that line.
The shorter the hard line, the more concentrated the stress.
There are several ways to buffer a bulkhead from the hull & the most common technique is to leave a small space that is bridged by tabbing. The bulkhead is just as firmly held in place, but the flex of the hull is transmitted through the tabbing bridge.
If the bulkhead is hard bonded to the hull side, the natural flex of the hull is stopped at that point & maginifies the stress. At the very least, this will cause paint or gelcoat cracking. At the worst, delamination and shearing of the glass fibers ultimately opening the door to hull failure.
On Jim K's boat I suggested 5200 & still do. It would effect a good bond yet be flexible enough not to cause stress failures to occur.
Another technique is fill the gap with a rigid foam such as 4 lb density Airex, Klegecell, or Divinycell. Still tabbing with a soft radius to bridge the space.
I can walk down any given marina dock an identify every fiberglass boat that has bulkheads hard bonded to the hull sides & is more than a couple if years old...
Don't take my word for it, ask Sonny Hines, Ommie Tillet, or any naval architect.
Br,
Patrick
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