plating thickness?

[rlackey]

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

[rlackey]

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

[sorenfdk]

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?

[Eric Sponberg]

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

[sorenfdk]

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.

[webbwash]

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 --

[Eric Sponberg]

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

[rlackey]

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

[rlackey]

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

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

Rich..

[webbwash]

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

[Tad]

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

[Alik]

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.

[rlackey]

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 :D

[Eric Sponberg]

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....:D

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

[Tad]

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

[sorenfdk]

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.
Exactly. Except that people who don't know enough about the problem, also don't know that they should pick a greater safety factor.

[rlackey]

Okay! now were getting somewhere, this is all great input!

I'll post some renderings of the hull tomorrow.

Rich

[rlackey]

Here's the hull, I posted these before in a different thread. Tad, I would appreciate some opinions.

From what you have said so far I've got two problems (challenges sounds a bit better ;) ) with this design, firstly the lack of a single deck running the whole length of the hull as it has a raised deck forward and a lower deck aft. Secondly is the small freeboard at the stern, which may get pretty close to the water at a large degree of heel.

It is inspired by a 1930's style power yacht, and I loved the raised deck style but the above concerns may be good reasons why I have never seen a sailboat like this.

It has two full decks below the sheer line, and a third superstructure deck above plus the pilothouse.

Stability has also been an issue, but I may get rid of the pilothouse on the uppermost deck as this will bring the C of G a bit lower and increase stability.

This is not a self righting sailboat though! If it capsizes, it's staying that way!

However, I'm not about to give it up without a good fight. I think it could be a beautiful design with heaps of space inside and out.

Rich

Oops, I wanted to add that as you can see I haven't designed a keel yet, when I said between 5 - 6m draft, that was board up also, you are very right, it would need to be more like 8m with the board down. So much for taking her into shallow waters. I am looking into a few more exotic keel designs that may allow a shallower draft.

Before I can really calculate loading from the rig accurately I need to design it first, along with the keel, so it seems I still have a ways to go yet.

[Tad]

Rich,

Okay, cool boat.

You are the designer so you get to decide where and how to compromise. A big question is what is this boat? Is she a charter yacht, (with MCA compliance implied?) and is she a true sailing vessel or a sail assisted power boat? Why would someone want this boat, what does she do that no other currently available yacht does?

Where are the edges of "modern interpretation"? The double-ended form is lovely at low speed when it will leave no wake. But modern interpretation (for me) implies better performance and thus higher speeds under both sail and power. This form is less than ideal in that light, and I would really like to see more bearing (width) aft to damp out pitching.

Where does the mast go, behind what I assume is the pilothouse? What about sheeting and staying of the mast and sails? Is there a bowsprit? Have you taken a look at Dellenbaugh angle and deck edge immersion? What about a ketch or schooner rig?

My guess would be that the aft deck is too low. Does it have full bulwarks? I would solve the structural problems by extending the upper (boat?) deck full length. On the other hand if the existing main deck level extends full length then you only need a shear wall (diagonal tie) amidships between the upper and main deck.

Big dinghies and toy space are required on modern boats, I get those positions and any possible holes in the topsides worked out before getting too deeply into construction.

If she is to be a "real" sailing vessel I would be inclined to drop the upper house 1/2 level. This would reduce windage, lower the rig and sail centers, and perhaps give you the opportunity to have a flying bridge aft of the PH.


Tad

[rlackey]

Thanks for the input Tad,

Okay, she's a personal design that I would one day like to build just for my own use and pleasure should I ever have the financial resources to undertake construction of such a large boat. I would like to think that when refined and finished, she would be of interest to others largely due to her styling more than anything else.

I have not been designing her necessarily for any commercial purpose, or with any thought to selling the design to a third party but I intend to comply with MCA regulations regardless.

I first saw the basic design on a motor yacht, and I loved the lines, the space and the layout, but I wanted a sailing yacht not a motor yacht. The idea is that she will be a full sailing yacht, not a sail assisted motor yacht, and in fact, as with the Tiara, her mast height would also be around 60m.

Yes the mast would be directly behind the pilot house, but the more I'm looking at it, the more I think your idea is a good one in terms of dropping the upper house half level and having a flying bridge aft of the PH, I am thinking of just getting rid of the PH altogether. Dropping the upper house half level will sacrifice using that whole internal space as another full height deck, there is plenty of space though, so maybe this is a small compromise.

I suppose there is not much modern interpretation in there yet. I have played around with different designs at the stern, including a much more modern full transom that had much more width, perhaps I should revisit it. Again I like the aesthetics of the narrower stern, but I see what you are saying about how it limits performance. I'll work on it.

Yes, there will be a bowsprit, and the main deck does extend the whole length, so that does indeed help with structural rigidity.

I have also considered other rigs, I don't have my heart set on a sloop, or even on any single aspect of the design as it currently stands, it's a work in progress and you have been a great help so far!

If I am honest, if I were to build her, I would probably be retired and I would live on her and I am not sure how much open ocean cruising she would ever see, but I don't want a glorified house boat that looks like a sail boat, I want a sail boat that is fully capable of open ocean cruising at speed, and to sail well, so she needs to be designed as such.

I'll be working on the hull form some more now.

Thanks! :D :D

Rich

[rlackey]

Looking back through the 34 revisions to the hull form, the submerged portion hasn't changed dramatically at the stern even with the more modern transom, it wasn't in fact any wider than it is now, and as far as I can tell from what I have been learning in 'principles of yacht design' and looking at more modern hulls ,the below waterline form at the stern is not all that different to the modern forms, it just has a different form above the waterline, but surely this shouldn't impact anything more than aesthetics? Of course it isn't a submerged transom, but I thought this was only found on motor yachts. Perhaps the renderings don't show this well. I will post some more specific to this area though.

I will also check the hull at up to 40 deg of heel and see just how close that lower aft deck is to the water. I know I have done this before, and as far as I remember, though it is low, it wasn't submerged. If I were to add width to the stern, it would however probably become a problem.

Rich

[Tad]

Rich,

I would expect the prismatic (canoe body) to be somewhat low (.52-.53) with the double ended form. Pulling more volume into the ends will raise this to maybe .55-.56, but it means the waterlines are rather full aft, with a sharp zig towards the centerline after station 9. This is really hard to manage with the double-ended form above water. What about a clipper style fantail? It would still be a problem with the waterlines but will provide more width and volume above the water.

MCA compliance requires watertight bulkheads and a floodable length study, with minimum freeboard requirements when various compartments are flooded. Absorbing work if you can get it!

All the best, Tad

[rlackey]

Hi Tad!

Well, I know for certain that the prismatic coefficient of the canoe body is 0.56 already, this was the figure I wanted and spent a long time trying to reach it.

I really appreciate your thoughts. Thanks again!

Rich

[Tad]

Rich,

Well, that shows you what I know! I would be interested in seeing some hull lines, it's very dificult to tell much about the shape from what you posted above.

Tad

[rlackey]

Hi Tad,

I hope I haven't caused offense. I meant in no way to tell you that you don't know what you are talking about. If that came across, I apologize, I really do appreciate your help.

Of course it is almost impossible to determine such specifications from the pictures I posted, and of course my calculations could be wrong.

I'll post some lines drawings, and if you don't mind taking a look, maybe you can tell more from those.

I have dropped the upper house half level and things already look better.

Thanks,

Rich

[Tad]

Rich,

No, no offence at all. I try to take this fairly lightly, but forget to add the little grinning faces :D :D

The calculation of CP will require a first guess at your overall displacement, and that is a huge question, how realistic is it?

There are three rules for designing sucessful large boats; Watch your weights, watch you weights, and watch your weights. Things like carbon spars, composite or alloy deckhouses, and the electrical system in this size vessel can gain or lose tens of tons. It's what keeps designer's up at night. And why we can demand huge salaries :D

Take care, Tad

[JimCooper]

Rlackey

I hope this is just tilting at windfarms

Have you calced the windage on all that superstructure? Theres a lot of similar sized deep sea fishing vessels that wouldn't throw up such a lot of frontal area simply for the extra fuel you have to burn..

Your anchor load in a blow is going to be horrific. You have designed a small pretty looking ship. Take some advice Forget the sailing keel. Your're only going to sail that broad off anyway. To windward the superstructure is just one large sail constantly aback .
You'd better throw in a couple of good big donks, she'd never claw to windward in any conditions no matter what keel you gave her.

If you want a sailing vessel you need a lot of changes, any designers here are remiss if they don't tell you this.

My humble opinion
Jim

[kmorin]

rlackey, I suggest that you get Dave Gerr's book The Elements of Boat Stength (ISBN 071365287X) which uses a 'scantling number' derived from the displacment, length, breath etc; and that number is used throughout the book to calculate plate thickness, frame depth, flanges and spacing as well as most other nominal frame element's. It is very detailed and exhaustive of metal framing and design conventions are illustrated to confirm interconnections.

While the book isn't THE final solution to the application of all rules society's when applied to a specific boat, it will give you a "beginning" and that is what you'd mentioned was your current focus.

You can use the formula's in a spread sheet to work out a very reliable first draft that can be checked against the various international rules' for given members.

This method (using Dave's book) starts you right out with a conservative practicing designer's guide to sizing structural components without interperting "rules". Also you could add multipliers in whatever increment you decide to 'beef-up' any member that may require conformance to a higher standard of construction if you found that necessary.

(Full Disclosure:) I've found the results of Dave Gerr's calculations to be very satisfactory in small planing boats, but I have no experience with anything HALF the size you're contemplating.

Cheers,
kmorin

[kmorin]

rlackey, since posting I've looked at the Gerr book and used your posted dim.s for a guide, although I don't have the Depth of your Hull, just draft so I estimated about 5 meters.

For example, the bottom worked out to 14 mm plate, topside 10 to 11 mm and transom 15 to 16 mm. 9mm decks and 7 to 8mm cabin sides. 650 mm spacing for longs, which are 125 mm deep and 15 mm thick. (assuming a flat bar type for example) The bottom frames would be 436 mm deep, of 14 mm plate with a flange the same width as the ht of the frame's bottom member and a thickness of 18mm for the flange. These frames would be about 175 cm spaced using the formula in this book.

Just a quick look at the ease with which you could approximate the construction with adequate scantlings as you're likely to go around the design cycle a few more times this approximation will help in hull mass, LCG of the hull sans equipment, and other values for use in the preliminary cycles' estimations and approximations.

Cheers,
kmorin

[rlackey]

Thanks guys, I've ordered the book, and the upper superstructure is going through a major redesign. I really appreciate the help. I'll post some new renderings soon.

Rich

[Tad]

kmorin;

As it is often mentioned in this forum I've been meaning to say something about the use of Dave Gerr's book, Boat Strength, for some time.

Except for casual interest, the serious student of yacht design or naval architecture will find this book of no use. It's not intended for serious "real life" naval architects; it is intended for the interested amateur who wants to think about boat scantlings.

One of the opening statements in the book is that, "scantling rules in this book were developed by the author, to cover only, vessels between 10 and 120 feet length overall." This would seem to put it out of contention for consideration as to Rich’s project.

Another disclaimer is "The author and International Marine make no representations as to the suitability of these rules and procedures for determining the scantlings of any vessel." This, in my book, would put it out of contention for serious consideration in regards to any project.

While the author lists several out of date classification rules in his Bibliography; ABS, Lloyd’s, and US Coast Guard guidelines. He gives no indication if these were consulted in any way with regards to his suggested scantlings. All his suggestions seem to be based on the size of the vessel, (his scantling number) rather than on expected loads. He gives no indication as to how his assumed loads were arrived at or what they might consist of and what the safety factor might be. There is no mention of global or longitudinal bending loads, thus the book is useless for larger vessels.

Regardless of vessel size, if a naval architect is asked in a court of law, "how did you arrive at these scantlings?” You had better have something better to show than, "they came out of Dave Gerr's book".

I would urge you to obtain a current actual scantling rule which the authors are willing to stand behind. Have at look at the Hull Construction, Materials, and Scantling Determination chapters in Larsson & Eliasson. For small fast boats ABS high-speed craft or Lloyd's SSC rules are a good start.


All the best, Tad

[kmorin]

Tad, I was responding to an inquiry at the most preliminary level of design! I didn't think the 52m boat was at the shipyard- nor do I think Rich is at the CNC output file level of his project. ( I think he intimated it was a possible future project.)

This guided me to offer him a simple and inexpensive means to get in the "ball park". I'd say Dave's book was worth its wt in platinum for just exactly where this designer lists his project. All that was requested was a method to generate a rational number; not the final FEA for the panel stiffening webbing arrangements for his stabilizer fins' through hull.

Without previous experience, and as a formative designer coming up with realistic hull materials to estimate one's way around the preliminary design cycle precludes sucessful use of the rules based investigation. A "life time boat", I think, may have dozens of iterations perhaps 100's? In your capacity as a practicing designer, how many refining cycles do you expect from concept to water? 10? 30?

So, to respond to the original posted question within context of his circumstances; I still feel Dave's book is almost perfect for this level of Rich's project.

Of course as he progresses in his learning with the great incentive of designing the best dream yacht he can, Rich will add more and more detail, just as you do when you refine your designs. As the details are refined the numbers will come along, the rationale behind each judgement will become more informed as the overall knowledge increases with time.

However, for a 'first-around-the-cycle' -quick set of rules of thumb for initial calcs- nothing in the market place beats this simple approach- figure a common ratio "size" to other boats and pro-rate the entire scantling 'set' and frame organization to this ratio. I agree whole heatedly that its not an end-all last word design tool, but I really didn't think Rich was at that point in his design.

As to applicability and disclaimers- everyone knows that publishers have lawyers who insert phrases in commercial literature! If you printed a copy of your design contract wouldn't it have some disclaimers that your lawyer insisted was "good business?"
120' versus 150' - again all Rich asked about was how to get some START, initial guess, point of origin, something to hang his hat on.

I think most readers here realize that the design cycle works from general to detailed and if Rich ended up with light or heavy plate, frames, and decks in his prelim estimates, they'd show up as unrealistic coefficients, too light or heavy a displacement and other indications he'd erred in the preliminary assumptions.

After going around the design cycle a bit, Rich will arrive at a time when he'll have to start considering the overall structural design as opposed to a stick and frame approach, and when this comes I'd guess someone as thorough as he's showing himself to be- will either learn the needed numbers or hire it from a design office with experience in this size. (frankly, once he's at a stage of life that he can afford this yacht I feel he'd insure his investment by having ALL the calcs and overall design reviewed by NA, PE, and EE to insure it was up to Rules Standards. Feadship & Westport Ship don't offer too much in the 'owner/builder' line that I've heard about.)

I've never designed or built anything larger than the life boats or tender for this "ship" so I'm out of my depth designing it. But for certain the Gerr book will provide a simple PRELIMINARY guide to help get Rich's ideas out of his imagination and onto the drawing board with some rough beginning of scantlings' values.

Cheers,
kmorin