Originally Posted by Edo Kazumichi
Another question. Glass can be easily repaired but what about being holed? Certainly steel is better protection against that. What about those uncharted rocks and submerged cargo containers? Then again, do we really travel at speeds high enough that a collision with these things would sent us to the bottom?
On the question of speed, the total weight would not slow us down since it is drag, not mass, that we are working against. And drag is just a function of wetted surface area. If my Newtonian mechanics is correct the only thing that will suffer from weight is acceleration.
Kevlar or spectra reinforced laminates are exceptionally difficult to hole...so if holing is a big concern of yours, have several layers of kevlar added to the boat's skin. A thick solid laminate hull is remarkably difficult to hole from impact. Abrasion is a different story and steel hulls are far more abrasion resistant.
Also, some steels are poorly made and can have structural defects, like the ones used on the Titanic, and fail catastrophically under impact, shattering instead of bending... This is exceptionally rare now-a-days, but might be an issue in a four-decade old boat.
Corrosion is a far bigger issue than collision as a general rule. It is ongoing and ever present, and a much bigger issue with a steel hull than a GRP one.
Uncharted rocks aren't that much of a problem on the open ocean, as the ocean is far deeper and wider than your boat... it is only near shore that it is a problem, and that can be handled for the most part by keeping an appropriate watch.
Keeping a proper watch will also help avoid semi-submerged shipping containers, which are not as big a hazard as many make them out to be. Consider this... Most containers have to be knocked off of a ship's deck before hitting the water. The height of the deck is often eighty or more feet from the water. The chance of the container landing in the water with out any damage is relatively small. Once holed, the containers will tend to sink, as most goods either absorb water or are denser than water.
Even a low-speed collision has the potential to send your boat to the bottom. IMHO, you're better off in a boat that is easier to maneuver and has less inertia working against you. Generally, the boats that are easier to maneuver and have less total mass, are also a bit faster in design. YMMV. What good is seeing the shipping container, if your boat is unable to dodge it?
The total mass of the boat does work against you. The inertia of the boat and the drag caused by the hull both have to be overcome before the boat can be accelerated. A heavy steel boat, like the one you're describing, has enough mass that in the light winds that are very common, you'd be very lucky to get moving at 3 knots. The boat is also limited by hull speed, which in the case of a 36' boat is only about nine knots, and with a boat that heavy, you'll be lucky make five.
Unlike what most people think, light air is far more common than heavy air on the open ocean. Most of the bluewater sailors I know tell me the most important thing for good passagemaking ability is good light air performance—either by getting the right light air sails or by boat design.
There are a few places that I would probably rather sail in a metal ship, rather than a GRP one. The extreme latitudes, where ice and icebergs are common is probably the only one I can think of. The coast lines in these areas also tends to be far more rocky than in more temperate climes. The colder water is less of a problem with respect to corrosion as well.
Just my $.02 worth.