plating thickness?

I'm wondering if anyone can help me with a starting point for determining thickness of keel plating, bottom and topsides, frame spacing, frame thickness and stringers for a steel 52m sailing yacht (masthead sloop).

I would greatly appreciate an opinion on this, and would be happy to provide any other information that might help.

Rich

 

I just downloaded the latest ABS rules, so I'll start going through that tonight. I'd still appreciate any estimates or opinions.

Thanks again,

Rich

 

Are you referring to the Guide for Building and Classing Offshore Racing Yachts ? If so, where did you get it?

 

Soren,

You can purchase the Guide from ABS by going to www.eagle.org (the ABS website), go to "Rules & Guides", and then to "Special Service". You'll see it listed there, publication #37.

Eric

 

Thanks - I didn't know that ABS have made their rules available for download.

 

Hopefully you are a student and have not begun to comprehend the enormity of your project.

Reading ABS or the MCA Rules for boats of this class is not for amateurs especially if this is a first project.

Try something which will be a little more manageable -- like something between 12 and 15 meters -- There are many well designed boats whose arrangements and even lines you can use to begin to visualize your project.

A vessel of the size you are contemplating puts you into the 170ft range and this is bigger than most gold-platers out there.

Good Luck anyway --

 

As far as I am aware, you cannot download the ABS rules. You can order them online, and they will mail them to you.

Eric

 

Thanks for the reality check, but I'll keep at it with the 52m, I've been working on it for far too long to quit now. I downloaded the ABS rules for steel vessels and have been working through the calculations given for minimum thicknesses.

Yes, I am a student, and I also realise the size of the project. It's a challenge, but I have not come across anything yet that I haven't been able to cope with through research and the help of others.

Thanks for the input guys!

Rich

 

Well, I downloaded them from the website. If you look, you will find them as pdf's.

Rich..

 

http://www.eagle.org/rules/downloads/37-ORY.PDF
This is the 1994 edition with the changes in the next pdf file

 

Rlackey;

Good project, but it's a big one. I'm assuming we are looking at something along the lines of the Dubois Tiara? In engineering the structure of a 52m sloop keeping the water out is a minor problem.

In the ABS steel vessel rules you will find a section on Global or Longitudinal Strength. This looks at the overall stiffness of your hull, but only in dealing with the hogging/sagging of the hull from waves, as your average motor ship. With a large sailing vessel you must add to this the bending loads induced by the rig. The mast step pushing down in the center of the boat and the headstay and backstay bending the ends upwards. In a modern sloop this global rig loads will be far larger than the wave loads on the hull. Principles of Yacht Design has some information on how to approach this problem.

This is not covered in the ABS steel ship rules, but it may at least be acknowledged in the Rules for offshore yachts. (Which only cover vessels to 100') The ABS Rule will keep the water out but will not deal with the sailing vessel loads.

After the global loads are considered, you next need to worry about the various point loads induced by the rig and appendages. The largest of these will be the mast step compression. Then the tension from the various shrouds and stays. Also the loads from the keel and the skeg/rudder. Draft is always a major problem with large sailing yachts and you will have some form of adjustable appendage. This alone cane be a major engineering task.

Sailing Yacht Design, Theory & Practice is a useful reference as well.

All the best, Tad

 

Actually, no one can run such a design without the experience on smaller boats. Second, as far as I remember, ABS sailing yacht rules cover boats up to 24 m. For such a big boat LY2 code from MCA is appropriate.

 

Thanks Tad,

I have a few good books on the subject that outline the considerations you mentioned. The most helpful has been "Principles of Yacht Design" which has been my bible since the beginning of this project. I am looking to the ABS rules as a starting point for structural calculations, but I have realized already that it falls short of covering everything I need to take into account.

I am not sure how much my design might share with the Dubois Tiara, probably not much apart from it's size. I started from scratch and designed the radius chine hull to meet certain performance and stability criteria that I outlined for myself in the design brief at the start of the project. The hull itself took 34 revisions to finally meet those requirements, but I have no idea how similar or different my hull is from the Tiara.

Mine has the following basic specifications:

LOA: 52m
LWL: 42m
Beam: 10.4m
Draft: 2.35m (Canoe Hull... no keel finalised yet but approx 5.0 - 6.0m)
Displacement: 422888.4kg (422.8884 tonnes)
Prismatic Coefficient: 0.56

Looking at the Tiara specs from the website:

LOA: 54.27m
LWL: 44.6m
Beam: 11m
Draft: 5.2m
Displacement: 449 tonnes

Judging from those, it's probably similar at least in proportions. According to the frictional and residual resistance calculations for my hull she should be pretty quick too.

My layout and above waterline aesthetic is entirely different though, the Tiara is very modern, mine is neo-retro, intended to be a modern interpretation of a 1920's - 1930's style inside and out.

Alik, thanks for putting me onto the MCA code. I knew that the ABS rules for offshore racing yachts would not cover a design of this size so I have been refering to the ABS Rules for Steel Vessels (and I downloaded the 2005 rules by the way, not the 1994 as far as I know), and these would be fine for a power yacht, but have only really given me a rough idea of where to start for a sailing yacht.

A starting point is all I was looking for though, I have enough reference materials to be able to perform all the additional loading calculations from the rig and so forth, but what I need is help in applying the results of these calculations to actual structural members and dimensions.

I would still appreciate anyone else's advice, apart from "you should start with something smaller first"... while probably being true, I have far too much invested into this design now and being told this does me no good whatsoever on this project. I'm a dreamer, I dream big, it's what I do.

So if anyone would be kind enough to overlook how rediculous it might seem that a student would consider taking on such a project and actually give me some practical help, I would love to hear it.

Seriously though, I have yet to read anything in the ABS rules that was not sufficiently self explanatory to be of immediate use and assistance to me so I have a hard time believing it is written in some secret code that only the seasoned and experienced professional designers can comprehend.

The fact is that with the modern 3D design and analysis tools, combined with a love for design and a honest understanding of the science, mathematics and physics involved perhaps it is not as complicated an undertaking as it once was even a few years ago.

While it is true that such a design could be handled much more quickly and efficiently by an experienced professional designer, there is no reason at all to think that after however long it takes me to finish this design (months... years, I started in 2000), it cannot be just as well thought out, innovative, strong and seaworthy as any other 52m sailing yacht, designed and manufactured by anyone else.

This project has been an amazing journey for me, I have learned more than I ever expected when I started, and I am still only at the beginning.

So maybe cut me some slack, I joined this forum to learn from you and perhaps speed up the design process on this yacht. I'm pretty stubborn about this one and I'm a bull headed perfectionist, so if something is wrong on a particular aspect of my work, I start all over again until it's right, no matter how long it takes, and this is how I learn.

Thank you all for your input so far though!

Rich

 

Rich,

Now you get to the fun part of engineering and design. You know the loads of the various parts, and if you look in catalogs for rigging parts and their materials, you know how strong and stiff the parts are. You have to match up the hardware with the loads with an appropriate safety factor. The safety factors will vary depending on nature of the problem and the part involved. You don't want a safety factor of 1.0, obviously, and only in racing boats such as the America's Cup would you shoot for safety factors between 1.0 and 2.0. Generally, you can pick safety factors between 3.0 and 4.0. I have always felt that if you have to pick a safety factor greater than 5.0, you don't know enough about the problem to make an intelligent decision.

If you have to design parts that are not off-the-shelf items, such as chainplates, for example, you have to design them yourself. Again, you know the loads and you know the strength and stiffness of materials. You have only to create the geometry of the part so that it can withstand all the loads, AND be easy to build.

Good luck.

Eric

 

Rich,

Good for you, hang in there.

The point I meant to emphasize above with all the global loading discussion was the importance of the longitudinal deck structure. Good structural continuity, some deep longitudinal girders, and hopefully a single deck level from stem to stern will deal with the rig bending loads.

Look closely at any information available on every boat that is even remotely similar to what you are doing. Figure out why things were done the way they were. Study the Perinis and output from various yards in NZ and Europe.

There is nothing magical about mega-sailor hull form, they are just small boats scaled up and made narrower to reduce stability. Thus the larger hull will be proportionately deeper. Retro can be a problem as it usually means lower freeboard, watch you don't run out of stability too soon. You can find lots of profile drawings of big boats, compare those with published weights and beam. Also, do not believe the published weights, big boats can float 6" deep without anyone noticing. (don't ask me how I know this)

Note that the 5.2m draft for Tiara is board up, she draws over 8m with it down. See your Principals for guidance in adequate lateral area, then compare those figures with any drawings you can find.

All the best, Tad