Steel plate Thickness

[LowcountryData]

Hello all,

We are currently designing a 65' vessel and are having a hard time getting the recommended thicknesses needed before we can submit out plans to a Marine Surveyor.

We have asked the major builders ... particularly Bruce Roberts, but without a purchase of their plans we have been basically turned away.

We need thicknesses for the following areas and any others you might think of;

Areas & Currently suggested thicknesses are;
keel = 3/8"
bottom hull = 1/4"
side hull = 3/16"
ribs = 1/4"
topside deck = 3/16"
stringers = 1/4"

I see many posts in here referring to "mm" does anyone have a conversion table handy???<LOL>

These we have aquired from several sources, the surveyor will not do any recommendations due to insurace reasons, so we respect that. But he did recommend this site so here we are.

Our vessel most closely resembles a NY65 or a Voyager 65, that was why we wanted to get Bruce Roberts input but alas 5700$ to get the answers we want didn't seem reasonable at all.

Any help or advice would be greatly appreciated,

Thanks in advance,

[8knots]

Low Country:
Get on amazon.com and order Dave Gerr's book "The elements of boat strength" It will walk you through all the math of developing a scantling # for your hull then figure step by step every componet of your hull. Even a simpelton like me figured it out It is the best $24.00 you will could spend in my opinion! Your numbers seem in line off the top of my head. But you will come to understand that your ribs for eg, will have 4 figures you will need. the rib will resemble a "T" the rib itself will have width and thickness figures then the top or inside of the "T" will have a width and thickness thus 4 figures. all are derived from your SN (scantling number) that he explains in detail how to mathmaticly obtain from a small group of numbers describing your hull. A few evenings and some paper,the book and calculator will give you what you require! Good luck!
8Knots

[8knots]

http://www.amazon.com/exec/obidos/tg...lance&n=507846

This is the link- Click on the "look inside" and go to the table of contents. You will see a list of all the formulas. He does a good job of describing construction method too!
8Knots

[gonzo]

You need more than just thicknesses. The design of gussets, frames, knees, beams, etc. is just as important. Each design requires a particular way of building and reinforncing the structure. Bruce Robert's price is not expensive considering the time and liability. If you have a hard time converting metric to standard, it's going to be hard to understand Gerr's or any other engineering book. $5,700 is a tiny percentage of the boat's cost. Also, any mistakes will make your labor and materials worthless. The plate thickness is the least of the complications of the design. Have you considered what the weld schedule will be?

[Stephen Ditmore]

I endorse what's been said. There are several approaches to metal boat design. A boat without much internal framing will require a thicker skin than one with closely spaced frames. A frame spacing of 24" is typical for commercial steel vessels.

i think it is best to get a proper and complete set of clasification rules as the scantlings are dependent on lots of factors. this will also alow you to optimize the desig (plate thickness/ frame spacing etc.). in my experience the ABS has rules that alow reasonable "light" scantlings for sailing vessels, ABS rules ( guide for clasing offshore raicing vessels 1994 (?? not quite sure aboutthe title??).
The ABS will give more freedom of choosing a construction methode and you will probably end up with a lighter design.

Please be aware that local reinforcement (mast/ stays etc) are not included in the formulas but more a less to "surveyors satisfaction".

most often for steel sailing yacht i see platethickness of 4 mm for the hull, as this results in a lighter construction, frame spacing will be approximately 400...450 mm.

I hope this will help.

[8knots]

Gonz0's point of $5700 for plans is childsplay in the big picture of constructing a 65' vessel. You will loose that much in dropped washers, welding rod left out in the rain, miscut plate because you only had 3 cups of coffee rather than 4 and all the other pitfalls that WILL happen in the construction of your boat! Thats why they cost 2 Million from a custom builder. Steve is right on the many methods of construction. I have Bruce's "Metal Boats" It was my first book on metal boats. Worth the money anyday! He does go into construction method as does Gerr. After 24 years of study I will still take my numbers to a real N/A to confirm I am not missing something. In my opinion boat design is a combination of......Math, Gut feeling, and previous experience. Those in the field will have a firm handle on all of them and the fee's they must charge are warented by the many sleepless nights they endure trying to produce the best product they can. A reputable designer will work hard for you because the design is an extension of themself, there name, and the firms reputation. For the record Gerr's book outlines all formula's in both Imperial and metric.
Thanks for the soapbox 8Knots

[mmd]

As a professional designer, I can't help but agree with 8knots' choice in having numbers checked by another qualified designer, and Gonzo's viewpoint on the cost of design services as a percentage of the overall constructions costs. To risk being unnecessarily dramatic, consider the problem in this light: Will the warm feeling of saving a few grand in design costs comfort you when you are in the middle of an offshore passage with the kiddies bunked down for the night, and as you are checking the latest weatherfax you realize that you will not be able to outrun that storm front on your tail before you reach the nearest safe port. Are you really confident in those structural calculations that you made those many months ago? After careful & serious consideration of that question if you are not comfortable, call a designer with some experience in steel construction. A design check by a pro is good insurance and not really that expensive in the larger scheme of things. Your life may depend on it.

[SuperPiper]

Because of the discussions on this thread, I have ordered Gerr's book. As 8knots suggested, I read the first 2 chapters on-line.

I have a mini-pocket-cruiser. With each glass project I wonder: did I apply enough layers? did I extend the tabbing far enough along the hull or bulkhead? is the core thickness correct?

And, IMHO, $5700 is a lot of money.

[gonzo]

If $5700 is a lot of money, then building a 65 footer is way out of your budget. I also think that prospective buyers are sometimes too eager to dismiss the amount of work a proper desing takes. Three weeks of my time is worth every penny of $5700. Also, I am liable for mistakes.

[rjmac]

Ditto....Ditto..... If you are uncomfortable with $5700, 65ft is out of your range....., you need to be realistic, and not meant to be rude.

If you don't know how to calculate structure you may want to rethink doing your own design.

Do you know how to calculate stability?

Do you know how to calculate powering?

Also note that Gerr's book is really only for understanding strength, not for actually doing it, especially for such a large boat. In actual design practice, the internal structure and its spacing is a trade for plating thickness - more closely spaced frames = thinner plate and vice versa. However, closely spaced frames tend to have more labor, so it is a trade requiring some knowledge. Gerr just suggests a standard thickness and spacing which might not be right for a given project. Also, Gerr's book has no official standing, so a given surveyor/underwriter may not accept it. Only class rules or ISO rules have the necessary buy-in from all stakeholders to establish a real standard.

[gonzo]

Gerr's and other books that give scantligs and construction techniques have to be checked against whatever rules apply. It takes knowledge and experience to decide which way to go. For example, a rule may call for more closely spaced frames; this may allow thinner plating. Another rule may specify fireproof resins in the engineroom; they have different characteristics than regular epoxy and are not compatible with Dynel.

I think that most of us around here (at the forum) we are in the idea that we can help each other and find interesting information all of excellent topics related to boats but when it comes to this kind of "i'm building a 65' boat but...i don't know what scantlings use and $5700 for set of drawings is too much!....please, FORGET IT! is not worthy to keep having posts toward this, please leave alone this post and let's help people that really value the work and responsability that is to design a boat, and help the ones that need some advice.

Glad to be here in the forum and be able to help.

[gonzo]

Take it easy "guest". The forum is open to all questions about boats. Lowcountrydata is trying to get information and is welcome to it.