Learning scantling part 1: general arrangement. Naval Architects please help

[magwas]

This is my second attempt to learn scantling through the forum. This time I try to slowly dig into the matter, hopefully now I will be able to ask small enough questions to be easily answered. I am counting on experienced members to help with my adventure, and I hope it will be useful for others trying to learn the art of boat design. If you are also in my shoes, I encurage you to comment: ask your questions, and show the need to architects and designers for their insight.

I understand that the first step is to have some general arrangement.



Now I have figured out, that the situation is more complex than that. See Learning scantling, step 0: design flow



I have created two boats as examples which can be worked on. I created them with FreeShip, and attached them here as both FreeShip fbm and autocad dxf files and jpg pictures.
First question:

Q1: Are the attached plans qualify as "general arrangement"?

A1: No, the General Arrangement plan details every part of the ship, not just the structural ones.the Aussie requirements of a General Arrangement are here:
http://www.dpi.wa.gov.au/mediafiles/mar_cv_info_030.pdf
"""
General Arrangement (GA) drawing(s) must show the following:
· Profile of the vessel (both port and starboard sides if they are significantly different).
· Plan of each deck.
· Table of vessel principal particulars indicating the vessels dimensions to be used for
scantling calculations, namely:
- USL Class (e.g.; 2B)
- Overall length, (m)
- Measured length, (m)
- Moulded beam, (m)
- Displacement for scantling calculations (at deepest operational draft), (t)
- Waterline length at scantling displacement, (m)
- Waterline beam at scantling displacement, (m)
- Hull draft at scantling displacement, (m)
- Vessel speed at scantling displacement, (kts)
- Number of passengers and crew
· Bulkhead locations. Watertight bulkheads are to be labelled and watertight doors to
shown.
· Frame locations and spacings.
· Access ways, steps and ladders.
· Bulwarks and railings. Minimum height and spacing of bulwark and rails to be noted in
the drawing.
· All spaces to be labelled indicating their use.
· The location and sill/coaming height of all hatches, doors and removable panels.
· Seats, Berths, Toilets.
· Navigation lights.
· Freeing ports.
· Location of all ventilation grills and closing devices.
· Deck machinery (windlass, fishing gear etc.).
· Fixed buoyancy and ballast.
· Escapes.
· All tanks.
· Anchor and chain lockers.
· Liferafts and floating off buoyancy.
"""

Q2: I have choosen mast and keel size and position randomly. Is it okay for a general arrangement, or should I start with sizing them?

A2: see Learning scantling, step 0: design flow

The reason for these two boats:
Ultimately I want to build - as I guess many others - a bluewater trimaran. As I m not brave enough to start with that, here is the sequence I am thinking about:
- First a small 3m canoe. This is the small one. I have actually built its model, and I am confident that I can build the real one. I know it does not really needs much scantling, but:
- After that another one. Then put on some rigging on them to have a sailing catamaran. Now this is the point where I think some scantling work is due. Well, maybe for that I could just copy the sizes from a well known design, but I want to be able to come up with a soundly engineered solution.
- When I see that the above works, start the trimaran. The middle hull will look something like the bigger one attached (not a deep keel though). I had put this design here to have a design which is actually within the applicability limits of the scantling rules.

I plan to use the Germanisher LLoyd scantling rules as they are at http://www.gl-group.com/infoServices...h/abschn01.pdf

At this stage Freeship can tell a lot of numbers about the boat, mainly hidrostatics. I am somewhat at a loss with them, because I do not have reference numbers. I understand, that metacentric height shows initial stability, and I guess that number will be important to watch when designing the keel for the sailboat. So the question is:

Q3: Is there a rule of thumb regarding how much should transverse metacentric height be for a sailing monohull?

A3: A3: It is in the scantling rules. In the GL rules it is in I-3-3, section 5, C, 1.2 see http://www.gl-group.com/infoServices...h/abschn05.pdf

Ladies and gentlemen, our next issue will be concerned with keel design.

[magwas]

I have changed the tri plan in the meantime. Now it not leaks, and checks okay.

My questions are still the same:

Q1: Are the attached plans qualify as "general arrangement"?

Q2: I have choosen mast and keel size and position randomly. Is it okay for a general arrangement, or should I start with sizing them?

Q3: Is there a rule of thumb regarding how much should transverse metacentric height be for a sailing monohull?

[SamSam]

I would think a soundly engineered solution would start with what you are going for, a trimaran, rather than building two separate sorts of craft and then cobbling them together, ending up with a questionable, clunky boat.

I don't have any knowledge to impart to you, but I would think general arrangement would include the size of the boat, the use of the boat-blue water daytrips or blue water cruising, the length of trips and how much crew, and what materials you want to use. Probably other stuff, too.

I don't believe anyone is going to want to teach you boat design and construction but they will probably help you learn by telling you of various books or websites and answering some questions. You can do a lot for yourself by learning how to use the search functions. There are two of them, you can search the whole boat design site or you can search within each forum, such as multihulls, stability, boatbuilding, etc.

Here's a search for 'scantlings' in the whole site which gives very broad results....
http://www.boatdesign.net/forums/sea...archid=1636038

or here is the same search in 'multihulls' which is closer to what you want, but still has a pile of information....
http://www.boatdesign.net/forums/sea...archid=1636041

[magwas]

You did not undertood me. My goal is not to figure out how to scantle these particular boats. I want to learn how to scantle, so I can engineer my own boats. These boats just serve as example.

Yes, I could buy books on the subject, and yes I have made these searches.
But I prefer free information, which can be easily shared. I think that a profession is mature only when information necessary to conduct it is readily available.

About material and goals:
I want to build from plywood, but also want to be able to calculate scantlings from steel.
The small boat is for confined waters, one person. The big one is blue water, 5 persons.

[PAR]

To be blunt, there are no free rides when it comes to engineering the scantlings for a vessel, especially a blue water yacht. Do the calculations, understand the products, physical limitations of the materials, comprehend the dynamics, concepts, principles, etc., etc., etc. To suggest anything less is asking for a free ride and you'll find most of use will find this insulting. Considering the "profession" is hundreds of years old, I think it's reached maturity, though clearly you haven't, if you expect a free pass on understanding necessary concepts and principles aspects, of the tasks you must perform.

[SamSam]

I see my links don't work today. Strange.

I understood you well enough.

I know you're going to say "well he would say that" but please think very seriously before designing and building your own 50ft catamaran. I had been sailing for 20 years, spent 3 years at college studying yacht design, made two Atlantic crossings and worked for both Derek Kelsall and James Wharram before I felt confident to design and build my first catamaran.

I assume you have designed and built other things. Like the house you live in. That is a pretty trivial design exercise really. After all it is only a rectangular box that doesn't move. It doesn't even have to float. And clearly it is really easy to build, especially in wood.

A car is also easy, even the big car makers buy in engines, wheels etc. Maybe you've designed and built your own airplane. Again relatively easy for you have to have some one inspect your work before you can fly.

With a boat you're on your own.

Ever wondered why so few yacht designers actually sail their own boats?? Nigel Irens once told me he doesn't like to sail his own designs any more - they are too frightening. And I know what he means. People always doubt their own work don't they? Beating to windward in a rising gale with your family on board is not the time to have doubts about your design/building ability.

If I was to design a 50ft cat I'd be looking at about 2000 hours to produce a full set of plans. You would take longer. Remember that a computer and CAD software is only a glorified pencil. There is no button on my keyboard that says "50ft cat press here"

Then it would take say 20,000 hours to build. And about AUD200,000 in materials

That is a lot of money and probably 10% of your life gone to waste if it doesn't work out.

You say you own a Hobie 18. So here's an idea. Why not make a central hull and convert the Hobie into a 20ft trimaran?? You could do it in a winter for the cost of say 12 sheets of plywood. Then if it works out (and you liked designing and building it) try a bigger boat.

But to answer your original question. You will find a lot on hull shapes, daggerboards, rigs etc on my website (on the Articles pages and also in the FAQ's). There aren't very many multihull design books around, and most of those are dated. The best general book on yacht design is indeed Rolf Eliasson's. He is a very successful yacht designer and the book is up to date.

Have you considered enrolling in the Westlawn Yacht Design course??

Sorry to be so negative, but it is for your own (and also for your family) good!

Richard Woods of Woods Designs

www.sailingcatamarans.com

No one wants to nurse you through something that takes many years. Everybody has got to make a living. If they are teaching yacht design, they want to get paid, if they're doing something else for a living, they don't have time to teach you all they know, and they are still learning also.

Your questions...
Q1: Are the attached plans qualify as "general arrangement"?

Q2: I have choosen mast and keel size and position randomly. Is it okay for a general arrangement, or should I start with sizing them?

Q3: Is there a rule of thumb regarding how much should transverse metacentric height be for a sailing monohull?

Free answers...
A1: About all it tells us is that it's a boat.

A2: All it does is tell us it's a sailboat, it does nothing whatsoever to help design and engineer the boat.

A3: Yes, there is a rule of thumb.

The GM must equal or exceed the minimum required GM for that ship for the duration of the forthcoming voyage. This is to ensure that the ship has adequate stability.

http://en.wikipedia.org/wiki/Metacentric_height

The rest is compromise. What sort of action or movement you want the boat to have at rest and underway depends on what shape and weight the hull is and how the shape and weight is distributed around the boat. It also depends on what forces are acting upon the boat, not the least of which are the size, shape, weight and location of the keel and sail.

I know you don't want to search but you're going to have to. You want it all free, it's all out there if you search.

Book on designing and building a Catamaran

[gonzo]

If you want to start small, how about trying to understand a beam? Start by a box and an I beam.

[magwas]

I have IT background.
In my profession if someone pops up and asks questions, we either answer it, or tell them how to proceed to be able to ask meaningful questions which can be answered.
If someone wants to learn, we help them. We point them to sources of information, readily available on the net.

I am asking three questions. I believe they are simple enough so that they can be answered without much effort. I did not ask you to do my homework for me. I did not ask you to magically transfer knowledge directly to my head. I did not just pop up and asked questions which can be answered with a little googling.

And yes, I can deal with an I beam. Maybe I am not confident with my result, and when I do the actual computations, I might show them to you, and ask you to check it by asking specific questions about specific steps. And I do expect an answer, because in all other fields I am familiar with, the ones who really master the profession are glad to answer such questions. They know that the young ones are not a threat, but strengthen the profession. And by answering these questions publicly will strengthen their own reputation, and help not just the one they actually answering, but all the following ones.

So my questions are (do not bother with the 3rd, I could find the answer for it):

Q1: Are the attached plans qualify as "general arrangement"?

Q2: I have choosen mast and keel size and position randomly. Is it okay for a general arrangement, or should I start with sizing them?

Q3: Is there a rule of thumb regarding how much should transverse metacentric height be for a sailing monohull?

A3: It is in the scantling rules. In the GL rules it is in I-3-3, section 5, C, 1.2 see http://www.gl-group.com/infoServices...h/abschn05.pdf

[capt vimes]

magwas
i can recommend "principles of yacht design" from larsson & elliason...

this book describes quite clearly most of your questions and the relation between all of the dimensions...
it gives you hand-on examples on how the CB and CG is calculated, how they relate to each other and where the Metacentric height comes into play...
it is quite good explained how the scantlings work and how they should be computed...

all of your questions will be answered...
BUT:
you will nevertheless NOT be able to design your own sea going yacht!

because the understanding of all the calculations, theoretical aspects of a design/construction and scantlings is by no means enough to make it SAIL in an appropriate manner... it probably will float but sailing - no!

do you know where your long.CB should be located according to your long.CG?
what happens if those two are not aligned properly?

and such information you will not find anywhere but in schools where guys study for years to learn boatbuilding/-designing... and experience of course...
i also played with the idea of designing my own yacht and read through this afore mentioned book twice... i shelfed the idea again because i could see that there is a lot more to boatbuilding but follow some calculation rules and draw some nice looking images...

i do not intend to discourage you but if you do not understand the very basic principles - it will end in disaster... and one cannot explain you all that stuff by means of an internet forum...

[SamSam]

Sorry, I can't open your files to see what you are talking about.

Maybe look at "design spiral" below...

http://www.westlawn.edu/student_cent...ure_series.asp

[dreamer]

Originally Posted by PAR

To be blunt, there are no free rides when it comes to engineering the scantlings for a vessel, especially a blue water yacht. Do the calculations, understand the products, physical limitations of the materials, comprehend the dynamics, concepts, principles, etc., etc., etc. To suggest anything less is asking for a free ride and you'll find most of use will find this insulting. Considering the "profession" is hundreds of years old, I think it's reached maturity, though clearly you haven't, if you expect a free pass on understanding necessary concepts and principles aspects, of the tasks you must perform.

Originally Posted by magwas

I have IT background...blah blah blah

you talk too much. Just ask your questions. You already blew it with the initial post. That was a poor setup and condescending as Par pointed out.

Originally Posted by capt vimes

magwas
i can recommend "principles of yacht design" from larsson & elliason...
i also played with the idea of designing my own yacht and read through this afore mentioned book twice... i shelfed the idea again because i could see that there is a lot more to boatbuilding but follow some calculation rules and draw some nice looking images...

i do not intend to discourage you but if you do not understand the very basic principles - it will end in disaster... and one cannot explain you all that stuff by means of an internet forum...

I started with this book too, but after reading many other texts came to the conclusion that 'Principles of Yacht Design' wasn't a good book to start with. I didn't find that it builds a good foundation. Maybe I'll come back to it after reading some of the other texts I have in my collection.

I work in IT too and just like in IT, when someone doesn't know how to ask a question properly, helping them is difficult.

[capt vimes]

Originally Posted by dreamer

I started with this book too, but after reading many other texts came to the conclusion that 'Principles of Yacht Design' wasn't a good book to start with. I didn't find that it builds a good foundation. Maybe I'll come back to it after reading some of the other texts I have in my collection.

hmm... for me it was just the right thing because it gives a good overview of the principles... as stated in the title...
sure enough one book cannot cover every single detail of boatbuilding at length, but nevertheless - at least you got an idea of what is required and how naval architects work...
it is very technical in some places which is good for me being a fully qualified structural engineer - might be harder for people to understand with no technical background...

but - and that was what i tried to comunicate to magwas - only after reading it, i realised that i am definitely not able to design a yacht for its intended purpose... sailing that is...

i know that i do know nothing...
a word from an old greek philosopher and the more you know about something the more you realise that there is even a lot more to it which you do not know...
from an uneducated viewpoint - everthing looks easy...

[PAR]

Q1: Are the attached plans qualify as "general arrangement"?

Q2: I have choosen mast and keel size and position randomly. Is it okay for a general arrangement, or should I start with sizing them?

Q3: Is there a rule of thumb regarding how much should transverse metacentric height be for a sailing monohull?

Q1, the answer is No, this is not acceptable as a "General Arrangement Plan".

Q2, though it appears this is precisely the same question as Q1, it's slightly more detailed and the answer is still No, this is not acceptable as a "General Arrangement Plan".

Q3 the simple answer is yes, there is a general rule of thumb, actually several, but this is a complicated subject and can't be generalized under rules of thumb, without complete understanding of the dynamics involved.

[dreamer]

Originally Posted by capt vimes

but - and that was what i tried to comunicate to magwas - only after reading it, i realised that i am definitely not able to design a yacht for its intended purpose...

perfect. Same here.

and I think my problem with the Larsson book was that it was the very first book I picked up. Too much at once. It is a good book, just wasn't for me at the time. Now you've convinced me I should re-vist it.

I have a handfull of favorite resources that have helped me understand the basics. This site is one of those resources. The Search function works! The other favorite resources aren't in books but come from those who are in the business of designing yachts. Yes, people are willing to answer questions if you approach them respectfully and with a genuine interest to learn.

[terhohalme]

If "principles" is too hart, try "Nature of Boats" by Dave Gerr (soft cover). It IS a very good guidance to boats.