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steel hulls?
On Sun, 9 Mar 2008 07:43:23 -0400, "Roger Long"
wrote: Aluminum is not theoretically as strong but aluminum boats tend to deform and stay watertight in accidents where steel will fracture. For equal weight Al and steel are equal in strength. Considering weldability and panal stiffness aluminum is better because it is thicker. Note that the alloys used for boatbuilding are not the strongest available in either material. In the case of aluminum, the usual alloys do not need paint, Every fifty year old al boat I know has been out in the weather without paint and no sign of corrosion. Most aluminum commercial boats, for example Alaskan fishing boats are left unpainted in salt water and don't corrode. My 22 foot cuddy is bare Al, and I wouldn't consider any other material. You are correct about the fact that steel will tear in cases where aluminum will just get a big dent. Think shipping container. 10 000 a year get washed off the boxboats, Casady |
steel hulls? adding armor to FG hulls
Red wrote:
OTOH if you're thinking of an object piercing the hull like an ice pick, having the Kevlar layer on the outside might not make much difference. In any event, having it on the outside is better than nothing. Fresh Breezes- Doug King ------ Actually I was just pondering this as there are frequent stories about the various partially submerged objects such as shipping containers sinking boats. Since I am getting closer to buying a boat, I wondered if there wasn't something that could be done to at least reasonably increase protection from said objects. I realize you aren't going to make it bullet proof, but any amount of improvement without too much tradeoff in weight, etc, may be worth it. Peace of mind sort of thing. Thanks. Red Had a friend that put in many, many thousands of miles with at least 7 round trips between New Zealand and Victoria BC. In that time he hit one container and one sleeping whale. This was in a homebuilt 33' steel cutter. Both hits in the South Pacific. The container left a good dent in the bow and the whale bent the rudder. I guess what I'm trying to say is the chances of hitting something large enough to cause serious damage is very slight and then probably wouldn't be catastropic G |
steel hulls? adding armor to FG hulls
On Mon, 10 Mar 2008 22:27:50 -0500, Red wrote:
OTOH if you're thinking of an object piercing the hull like an ice pick, having the Kevlar layer on the outside might not make much difference. In any event, having it on the outside is better than nothing. Fresh Breezes- Doug King ------ Actually I was just pondering this as there are frequent stories about the various partially submerged objects such as shipping containers sinking boats. Since I am getting closer to buying a boat, I wondered if there wasn't something that could be done to at least reasonably increase protection from said objects. I realize you aren't going to make it bullet proof, but any amount of improvement without too much tradeoff in weight, etc, may be worth it. Peace of mind sort of thing. Thanks. Red Perhaps the first thing wold be to research the subject to determine how many fiberglass/steel/aluminum/wooden yachts are sunk annually. Once the frequency is determined it should be easy to assess the appropriate action. as an example, airplanes crash nearly every year but few passengers carry a parachute as part of their carry-on luggage... Bruce-in-Bangkok (correct email address for reply) |
steel hulls? adding armor to FG hulls
On Tue, 11 Mar 2008 04:43:42 +0000, Gordon wrote:
Red wrote: OTOH if you're thinking of an object piercing the hull like an ice pick, having the Kevlar layer on the outside might not make much difference. In any event, having it on the outside is better than nothing. Fresh Breezes- Doug King ------ Actually I was just pondering this as there are frequent stories about the various partially submerged objects such as shipping containers sinking boats. Since I am getting closer to buying a boat, I wondered if there wasn't something that could be done to at least reasonably increase protection from said objects. I realize you aren't going to make it bullet proof, but any amount of improvement without too much tradeoff in weight, etc, may be worth it. Peace of mind sort of thing. Thanks. Red Had a friend that put in many, many thousands of miles with at least 7 round trips between New Zealand and Victoria BC. In that time he hit one container and one sleeping whale. This was in a homebuilt 33' steel cutter. Both hits in the South Pacific. The container left a good dent in the bow and the whale bent the rudder. I guess what I'm trying to say is the chances of hitting something large enough to cause serious damage is very slight and then probably wouldn't be catastropic G That is somewhere around 45,000 N.M. so if he hit two objects in that distance it averages one object every 22,000 miles. How many people will cruise that distance in their whole life. Bruce-in-Bangkok (correct email address for reply) |
steel hulls? adding armor to FG hulls
" wrote:
Amen. But, having been tangentially involved in a completely disastrous attempt to bond Kevlar (tm) fabric to PVC foam with epoxy I strongly advise getting advise from the fabric provider before bonding. A Method that worked very well with both epoxy and polyester with stitched glass didn't fly with Kevlar (literally as the structure was a wing for an ultra-lite). I wonder why. Incompatible binder in the cloth? One issue with both carbon fiber & aramids (you're right, Kevlar is a trademarked brand name) is that the cloth is much lighter than conventional fiberglass... duh, that's a big reason to use it... but it also means that the cloth tends to float up out of the resin. The best way to bond it is to vacuum bag it, or use pre-preg, but it can be laid up like conventional FG once you know to not pour on more resin when it looks dry. Or you can use thickening/bonding agents mixed into the resin, that holds it in place better anyway. I used peel ply, with no vacuum bagging, over a carbon fiber & Kevlar lay-up with very good results. .... And, yeah, you're right, the stuff goes all fuzzy if you look at it funny and it kills scissors. Carbon is less of a pain to work with but you can't use it to armor existing hulls. It would help add compression srength as an outside layer. I dunno if it would help with impact resistance. The yield curve for carbon fiber (also called graphite) is almost straight, the stuff tends to fracture and people think of it as brittle. Of course, it takes about 10x more force than steel can withstand, but we're so used to seeing stuff bend before it breaks that it's counterintuitive that material which *doesn't bend* and suddenly snaps is really strong. And it also doesn't lend itself to "soft failure" modes. DSK |
steel hulls?
(Richard Casady) wrote:
For equal weight Al and steel are equal in strength. The "rule of thumb" I recall is that aluminum is half as strong as steel, and 1/3 the weight of steel. For equally strong structures, aluminum will be about 25% lighter than steel. DSK |
steel hulls? adding armor to FG hulls
Gordon wrote:
Had a friend that put in many, many thousands of miles with at least 7 round trips between New Zealand and Victoria BC. In that time he hit one container and one sleeping whale. This was in a homebuilt 33' steel cutter. Both hits in the South Pacific. I wonder what time frame this was? I think shipping losses of containers is much higher in the late 1990s ~early 2000s although they say it's tapering off now. I also wonder what happened to the whale. The container left a good dent in the bow and the whale bent the rudder. I guess what I'm trying to say is the chances of hitting something large enough to cause serious damage is very slight and then probably wouldn't be catastropic In a steel boat ;) Bruce in Bangkok wrote: That is somewhere around 45,000 N.M. so if he hit two objects in that distance it averages one object every 22,000 miles. How many people will cruise that distance in their whole life. Lots and lots and lots. Not so many do that many open-sea miles. But look at the odds another way... if you had a revolver with 1,000 chambers, and "only" one chamber had a live round.... would you spin the chamber, put it to your head, and pull the trigger? Just for fun? If the odds are low, but consequences very serious, then it's worth a little work and study to avoid that BANG. Of course, YMMV DSK |
steel hulls? adding armor to FG hulls
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steel hulls? adding armor to FG hulls
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steel hulls? adding armor to FG hulls
"Bruce in Bangkok" wrote in message ... That is somewhere around 45,000 N.M. so if he hit two objects in that distance it averages one object every 22,000 miles. How many people will cruise that distance in their whole life. Certainly not you, sir! Pretty hard to get that kind of mileage under your keel sitting at the Bangkok dock. Wilbur Hubbard |
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