The elements of boat strength

@DogCavalry, I suppose we have been in different hemispheres of the same world, that of shipbuilding. I have always been paid to obtain the minimum weight structure that the shipyard was able to build. And the other hemisphere, for me, is as valid as mine.

 

Oh yes. A light structure, faster and more economical with the same installed power. Better fuel efficiency. You are a professional, working at the light end. Gerr's book has no use for you. If you were building a harbour tug, in a region where there is often ice in the harbour, you would not be interested in light. But you would still be a professional, not working in the area on the sorts of boat Gerr's book is meant for.

 

@DogCavalry , although I understand well what you mean, and I think you are partly right, I must explain that I have calculated structures for several tugs and I have calculated structures for ships to navigate on ice (I have even calculated that of a ship to carry liquefied gases at very low temperatures) and always, always, I have tried to calculate the structure with the philosophy that I indicated before. A structure, at least that is what I think, should not be made more or less resistant than it should be. By "it should be" I mean as required b y the regulations, safety criteria, navigability, etc., that the SOR indicates for the project.

 

Ah yes. Designed to meet the sor, and realistic loads and stresses. But not wasteful.

Anyway, I don't think a professional has any legitimate complaints to make about Gerr's work. It makes average boats to average scantlings. A pro doesn't need it. An amateur won't be designing a boat that is so extreme that Gerr doesn't work.

 

Another reason for minimizing scantling sizes is to minimize material costs. Steel, aluminum, fiberglass, carbon fiber, wood, etc which is not needed for strength, stiffness or durability is unnecessary cost.

 

That is certainly true @DCockey , although material costs are a pretty small percentage of the total. Extra weight means extra fuel consumption, which matters more in a commercial vessel.

 

Well, that in my world does not usually happen either, if by material we mean everything that is not direct workmanship.
Reducing the weight not only normally reduces labor and can reduce the cost of materials but, for the same displacement, increases the payload, which is what the shipowner prefers.

 

Actually, Gerr's rules give similar scantlings to Herresoff's rules on traditional construction.