Re: Bob Perry's take on Wolfenzee's dream boat
Brent and I have debated this around the web probably for at least a decade. This is from some of the earlier discussions on this topic.
Build time and cost: While it is true that you can tack weld a steel hull very quickly using an 'origami' technique, if you compare the overall build time with welding, finishing and constructing an interior to an equal level of finish, in prior analysis that have been posted previously on other sites where we have debated this in the past, other techniques require similar cost and time to build, which is especially true since steel prices have ratcheted up relative to other materials.
If time and money are the prime determinants, in the size boats that we are taking about, then stitch and glue sheet plywood sheathed in epoxy and glass inside and out would easily beat steel on cost (and on strength if of equal weight). The time is greatly shortened on either Orgami boats or on plywood boats with accurate cutting patterns for the interior bulkheads and hull panels.
The Steel vs. Fiberglass hammer argument:
This is a favorite of the steel guys which says steel is better than glass because a steel hammer would damage a glass boat.
Again, I will refer to my previous analysis on this one. Start with the hammers, to begin with we need to compare hammers of equal weight and weight distribution. In other words, for example, to maintain that weight distribution, we need to compare say a 20 oz framing hammer made of steel to an fiberglass hammer of equal weight and weight distribution. The fiberglass hammer would have a head nearly 2 feet long and 3 inches in diameter. If we use the laminates that I have advocated in the past, I would use the vinylester resin typically used in bullet resistant military and crash helmets and a kevlar laminate in the actual impact areas. The impact resistance of that hammer would be several times greater than the steel hammer.
Then we need to look at the steel and glass that we are beating up with these hammers. In a past analysis that I posted on the Origami website, I had calculated that a fiberglass panel able to stand up to a 20 oz framing hammer would be somewhere between 3/16" and a 1/4" thick if the panel size was limited to around 2 feet span. If we compare that panel to a steel panel of an equal weight steel, the steel would be just a tick thinner than 5/100's of an inch (.05"), in other words something slightly thinner than the thickness of steel sheet metal used for body panels on a modern automobile. I'll take the equal weight fiberglass hull and steel hammer any day over the 20 oz. fiberglass hammer beating on an automobile body panel.
It comes down to the same thing here as well. Again we are talking about equal weight boats of steel, fiberglass and engineered laminate over cold molded plywood.
Lets start with the problem at hand namely the equal weight part of this sentence. If we compare the relative density of the materials involved, they are as follows: Steel= 7.85, Fiberglass= 1.92, and cold molded construction= .45 (3/4" port orford red cedar strip plank with two diagonal layers of 1/4" port orford red cedar veneers and a final longitudinal layer of douglas fir with an exterior laminate of vinylester resin and kevlar with minimal non-directional glass), So if we start out with a 1/2" thick fiberglass hull, the comparable weight steel hull would be something less than an 1/8" thick (roughly 3 MM), and a cold molded hull would be roughly 2 1/8" thick. And when the numbers are run, the fiberglass hull would have slightly more than 4 times the bending strength and roughly double the impact resistance. The cold molded hull would have nearly 11 times the bending strength, and somewhere between 3 and 4 times the impact resistance of steel.
Again, in a demolition derby, I will take the other materials over steel any day, especially when you consider how little steel would be left out of 1/8" plating after a decade of rust.
And as you noted the last time I posted these numbers on another website, if I remember correctly, your hulls are typically 1/4" and 5/16" plate. If we compare a 5/16th steel plate, to equal weight fiberglass and cold-molded hull panels, the fiberglass hull would be nearly 2 inches thick and the cold-molded hull would be 5 inches thick. The strength ratios remain the same.
I come back to my original contention, that of all of the materials that one can build a boat, on a pound for pound basis, steel is one of the weakest materials to build a boat, and if maintained in an equal fashion to the other materials, over the life of the boat, according to all studies that I have seen, a steel boat is one of the highest lifecycle maintenance forms of construction that one can chose.
But in the end, little of that matters, in sailing we make choices based on our goals, fears, and sailing venues. For some steel make sense. For most, there is little logic to owning a steel boat. The above was intended to illustrate the relative strength of materials by weight. I chose to use panel thickness as clearest way to illustrate basis of my comments on the relative strength of materials by weight. In the example, the greater thicknesses of fiberglass and cold-molded construction result in strengths that are substantially higher than comparable weight steel.
But as sometimes noted, no one would build a boat a boat this size with panels as thick as those in my example. But if you reduce the panel thickness and the strength of the panels equal to steel, you end up with a hull thickness that is closer to normal practice. In that case, you can still achieve equal strength to steel, but a very significant reduction in weight. And that is my primary point.
I don't disagree with Brent’s argument that "The truth is that steel puts a great deal of strength and toughness into a compact package” but I add that this strength comes at the cost of significant weight. In fact, more or less that is my key point. I raise this point in reference to someone considering custom building a boat with concerns towards the relative strength of the material being chosen.
The steel guys like to ask questions like; "Why don't they make icebreakers out of fibreglass or wood?" but to answer that question, until the early 1950's icebreakers were typically sheathed in Ironwood. Since then specialized steels have become the norm. As I have mentioned in prior discussions, steel really comes into its own as a vessel gets larger. When you talk about a vessel the size of an icebreaker, the compactness of steel becomes a significant advantage. Also Commercial vessels tend to be short lived compared to yachts. Beyond that, when you talk about an icebreaker, high weight is an advantage rather than a disadvantage.
Lastly, I am in agreement with statements in other discussions that, "Steel is certainly not for everyone, but neither is fiberglass, nor cold-molded wood." That is essentially the same point that I was making in my conclusion, "In any event, in sailing we make choices based on our goals, fears, and sailing venues. For some steel make sense. For most, there is little logic to owning a steel boat."
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay and part-time purveyor of marine supplies