Best resource for learning to calculate scantlings

[TANSL]

It does not scale up linearly. That would increase the volume and weight by 2.4. The stress of the parts would increase by the same ratio. However, the strength of materials remains the same. It requires all new calculations.

Well, honestly, I don't see this relationship as directly proportional to displacement. There's a design pressure that depends on full-load displacement raised to the power of 0.33, but there's no direct relationship. You have to add some summand and apply some correction factors. I'm also thinking about the bulkhead scantlings, which don't depend at all on displacement. But, well, maybe I'm wrong.

 

[gonzo]

You are wrong. Read the OP's post. He is increasing all scantlings by a multiplier

 

[TANSL]

The stress of the parts would increase by the same ratio.

No, @gonzo, I'm not wrong. What I'm saying is completely accurate. What's completely incorrect is what you say in this sentence.

 

[Sgf]

What books would you recommend for learning to calculate scantlings for a new design. More engineering and less this is what we've always done.
I'm interested in larger (30-60ft ish) skin on frame boats particularly sailing multihulls.
Trial and error is much better made paper and pencil on a desk than on wood and canvas on the open sea(at least if you are the test pilot)

Many people say it can't be done because of the high torsion loads, but we built skin on frame bombers in the second world war which were built to handle major torsion and dynamic loads so it would seem possible.

Have you heard of the Palindrome? 30ft SOF proa

Proa File | Palindrome: skin-on-frame proa for the R2AK https://proafile.com/multihull-boats/article/palindrome-sof-proa-for-the-r2ak

 

[BMP]

That is interesting, have they actually taken it anywhere?

 

[Sgf]

I think he went some way on it as from a couple of articles I read he cruised up the coast of usa to go to a race and stopped off working along the way. I believe someone else has it now, it was some time ago that I looked into it

 

[Sgf]

Also ISO 12215-5 has scantlings calcs in I think and 12215-7 (Determination of loads for multihulls
and of their local scantlings using 12215-5) may be of interest

 

[TANSL]

I wouldn't tell anyone I was going to learn how to calculate scantlings using ISO, because at least the scantling standards are the least educational thing ever written. You need to know how to calculate scantlings to understand and use these standards correctly. But, fortunately or unfortunately, for small boats it's the best (or least bad) thing available.
I have several texts that attempt to teach, with the help of specialized software, how to perform calculations using ISO 12215. Although the texts cover the basics of elasticity (beam and thin plate theory), the user should have some background in these topics before starting to work.

 

[jehardiman]

I wouldn't tell anyone I was going to learn how to calculate scantlings using ISO, because at least the scantling standards are the least educational thing ever written.

What TANSL states is correct. Scantling guides (ISO or Class Society) exist only for two reasons: First, they give the minimum requirements to satisfy governmental and/or insurance risk moderation. Second, they make it easy for for an inspector to verify compliance for given actual design. Compliance with Scantling guides (ISO or Class Society) does not guarantee that the hull strength is suitable for the vessels intended purpose, only that it minimizes presumed risk.

 

[Cymen]

I think you're looking for Elements of Boat Strength by Dave Gerr. I didn't read it yet but did read an article about why he wrote the book. That article is here:

https://www.gerrmarine.com/ELEMENTS_OF_BOAT_STRENGTH/BoatStrengthIBEX.pdf

That article has some basic examples and rules of thumb that seem to be the kind of thing you're looking for. I realize this was posted some time ago but I'm searching for strength threads here and having recently read the above...

Edit: Oops, I can't delete this. I shouldn't post when I'm tired as I misread the first post. You want the opposite of the above.

 

[gonzo]

What TANSL states is correct. Scantling guides (ISO or Class Society) exist only for two reasons: First, they give the minimum requirements to satisfy governmental and/or insurance risk moderation. Second, they make it easy for for an inspector to verify compliance for given actual design. Compliance with Scantling guides (ISO or Class Society) does not guarantee that the hull strength is suitable for the vessels intended purpose, only that it minimizes presumed risk.

The OP is talking about boats of 30 to 60 feet. Class societies in general adress ships. At that size Gerr's calculations work well for designs that are not completely outside the norm.

 

[TANSL]

Any designer, regardless of their field, even of ships, strives to create a design that not just "works well," but one that functions as well as possible. That can't be achieved with mere old-fashioned methods. Let's give the task of design the dignity it deserves.
Even a small boat deserves to have the best possible scantling.