Some thoughts on vessel engineering

[sailingdog]

Very true... but carbon fiber, properly engineered, can help with highly loaded areas on boats. The key is properly engineering it.

About 20 years ago, when they first came out with carbon fiber bicycle frames for racing bicycles, a common failure would occur after a very mild crash. The frame would get scratched in the mild crash and then, under the stresses of racing, the frame would shear at the stress point caused by the scratches. Until the bicycle frame designers learned that carbon fiber is very strong in one direction only... they had a pretty steep learning curve.

Still, carbon fiber is a far better stiffening material for most of the types of loads seen on a deck than is Kevlar. Kevlar is great for making laminates that are highly puncture or tear resistant, but it doesn't have any stiffness to speak of—you just can't push on a rope.

There was a whole rash of fiberglass rudder stock failures on high tech boats a few years (maybe decades, it's all kind of blurring together) ago. The stocks were too flexible so they added a layer of carbon fiber to stiffen them up. However, the carbon fiber layer wasn't strong enough to fully take the load. It was stiff enough, however, that it would become fully stressed before the fiberglass stock and bent enough to take any real load. As a result, the carbon fiber would fracture. The result was like that little scratch you put on a glass tube or sheet to snap it cleanly in two. Rudders that might have just flexed snapped off and drifted away.

 

[Ross]

I added fiberglass and Airex core from the turn of the bilge to the cabin top because I felt that there was a little too much bounce in the deck when I walked on it. On a thirty foot boat I added about 175 pounds of chopped strand mat and about 75 pounds of 24 ounce woven roving and probably 400 pounds of resin. But doors stay shut, dishes stay in the racks, books stay on the shelves. My rudder is supported on both ends and I have no fear of it breaking off. My keel is integral with the hull and the ballast is encapsulated.
As I have said I am a carpenter and if a structure isn't stiff enough then you can reduce the spacing between frames or increase the thickness of the skins or both. You can select stronger material or better methods.

 

[Todd Smith]

I guess my engineering assumption would be that the sea can break my boat no matter how strong I make it.

Depends on what part of the boat you are talking about. I haven't heard too many accounts where the actual hull was broken on a cruising boat in an ocean passage, except by impact with some floating object.

Windows, hatches, thru hulls, steering, rig. Those things seem to get broken. Oh and the crew.

Todd