Scantling Spreadsheet

I know this has previously been discussed but not resolved.

Has anyone got access to or written a basic spreadsheet to calculate plate thickness, scantlings for hard chine alloy boats up to say 10m in length and 40 knots max speed that complies with ABS/ISO etc.

This would naturally be on a "No Care / No Responsibility" basis,but would be so helpfull for us amature designers to determine displacement etc.

It was previously sugested that a collaboritive effort could be benificial to many.

 

That is by far a toooooooo broad attempt to get a proper response.
How long is a string? Are there spreadsheets?

 

Perhaps you'll have to do like the rest of us...read the rules. Then make your own in excel...just takes a bit of time. (Maybe a one day, if you're not familair with the rules or excel). Once done...saves lots of endless grunt work. But they key thing, as you read the rules and write your own spread sheet, you'll understand the rules and their limitations.
Far better than just 'borrowing one'.

 

Agree with Ad Hoc, read the rule books.. then create own exceel sheet according to ur own requirements.. it will be easier to understand each term of the rule books.

 

I agree also with Ad Hoc but I'll make one remark and one suggestion;

The remark is that happily in metal (steel and alloy) ISO, Det Norske Veritas (DNV) and others arrive to the practically same results. So you do not need to read all the existing rules of the world. I have the suspicion (and since a long time) that some organisms and countries make rules for the pleasure of making rules (Italy was specialist of the fact).

In GRP and sandwich it's not the same thing; maybe it's changed, but the lone good set of scantlings in small boats was that used by DNV, the worst being the Lloyds. Maybe ISO has made a goot of rules set with no overkill scantlings.

The suggestion is you have to check your results comparing it with some existing, lightest and successfull boats.
Some will believe I'm payed by Mr Gerr but it's worth to compare your results with those obtained by the "Gerr's structural cooking recipe" (I call it like that because it's so deceptively simple) when it's possible.
Until now I'll have always gotten consistent results by the Gerr's structural cooking recipe, and the more sophisticated methods I use. The Gerr's is on the heavy side, and it's easy to understand why (liability).

But using your own sheet will permit to refine. In small common boats I find useless to go to FEM and other complicated niceties, where you can make easily big mistakes. Only useful in special boats or big ships. I call in my personal vocabulary the use of overweight means of engineering: mental ************.

 

Ad Hoc, you are a real Master, if you write ISO 12215-5 to excel in one day and at first shot!

My deep obeisance,
Terho

 

terhohalme
No..i was just brought up in a shipyard environment where time=money. One learns very quickly to focus on what is important and what is "oooh, that's nice..interesting but doesn't answer the orginal Q". Having your boss/shopfloor telling you're holding up production teaches you things that books and university cannot! That's where you either sink or swim.

 

Ad Hoc, sure that's obvious.

For a quick check, Gerr's book "The Elements of Boat Strength" is fine.

 

terhohalme

I must admit, I've never seen or or heard of this book. I've been doing structural calc's from first principals for so long now, it is second nature and "obvious" to me. But I do appreciate that this is not so for many people. For me to do a midship section of say a 40m catamaran, takes me about 10mins. Whereas when i first started some 20years ago, took me all week!

PS
Just did a quick google search for the book. It does state the limitations of the book very well, viz:
1)Standard monohulls
2)Boats between 10 and 120 feet
3)Max speed 45knots.

Goes on to say "To determine scantlings for larger or smaller vessels, for multihulls, and for higher speed craft, builders must do a detailed engineering analysis of consult a qualified naval architect or marine engineer."

So, its ok for basic run about day/monohull boats really.

 

Yes the Gerr's book is very good for ordinary boats within its limits. I think that Gerr did a very nice job (and an excellent intellectual work). Good and well working simplification is a tough task.

Not very nice for for some so called structural engineers who used to convince naive customers that the scantlings of a 30 feet/25 knots monohull was a very hard job, asking years of training with a total mastering of differential and matricial calculus. So very expensive. And I'm half kidding...

I'm retired now, and my main occupation is to admire my garden, so I do not follow closely the last developments. However I asked a friend of mine to send me a PDF of the ISO 12215-5 (I have not any use of it and I wouldn't spend any money to buy it) to have my own non authorized opinion, I've just read it in diagonal.

I have not dug it, nor made calculations but I felt a warning signal (you know: the red light flashing in the left side of the brain) for using it in composites. Just instinct. That seems inconsistent specially in sandwiches. There are things I do not like it at all. For example the criteria of buckling bother me.

I would use it in "advanced" composites with the most extreme caution and with at least 2 other methods to triple check it. Maybe I'm wrong, but I have no confidence in this rule in composites. I warned my friend and counseled him to use the services of a good reliable engineer.

Often the norms established by organisms are useless in "exotic" composites, remember the stupidity of Lloyds rules on GRP sandwiches. I would be ashamed and retired far of the world in a cistercian monastery after publishing a such set of rules.

Metal is so simple compared to composites. And on a 10 m, 45 knots monohull which need a good safety margin it's pure cake, truly cooking recipe. Thousands of similar boats have been made, every combination have tried, some thumb rules are known.
I would make an sheet for the intellectual fun and for the pleasure of shaving a few kilos. After you see that you're using 6 different plating thicknesses and maybe the shipyard would be happier with only 3 different thicknesses to order and for making welders life simpler. And you're back to the simpler system...laughs.