Hull thickness calculation

[great white]

I admit in advance that I should leave these things to a naval architect or proven designer. With that in mind, please advise me... is there a constant or formula that will permit one (me) to figure out the proper thickness of the deck, topsides and hull for a plywood hull that will never touch bottom? I am thinking of a sort of... "if the boat is thirty feet long, the topsides should be 3/4" thick and the bottom should be 1 1/2" thick"... thing.
(Ordinarily, I WOULD leave this to a pro, but when you have zero bucks and a burning desire, you do what you can. And I promise, before I build, I will have the plans vetted by a professional. No shaky, dangerous bricks from this b'y!)

[ 04-15-2004, 06:47 PM: Message edited by: great white ]

[htom]

Skene, Elements of Yacht Design or
Gerr, Elements of Boat Strength or
...

Dave Gerr is probably the most recent, but Skene might be more useful. Not the simplest topic.

[great white]

htom, thanks. Will get copies of both ASAP. Or will try.

Roy

[Bruce Hooke]

For plywood Gerr's book (Elements of Boat Strength is the one to get. However, Skene's is also very useful for general boat design questions and provides a much better look at the overall process than Gerr does. Gerr's book is more of a reference manual.

[great white]

Bruce, thanks for the overview. I've been surfing for the last few hours, and I found several sources for both books. Not the library, unfortunately, but still, they're out there. It sounds as if you would recommend the Gerr book over the Skene book for this one area. I think that's the way I'm going to go. Thanks again.

[Aramas]

Firstly, scantlings are based on displacement rather than length. The easiest way is to find a vaguely similar design and use the same scantlings. Bolger's books are good in that respect.

[great white]

Thank you, Aramas.

[Bruce Taylor]

What are you building, GW?

[George Roberts]

Aramas ---

Scantlings can be based on displacement or the product of length, length, width, and depth, or just the cube of the length or any other set of properties that seem appropiate. Most authors tell you which they are using.

The most important aspect of scantling is the scaling of the load. Most authors do NOT tell you which they are using. Very dangerous.

[great white]

Bruce... without acces to funding right now, I am getting ready to submit a sea of ideas arranged as coherently as possible to a marine architect. I figure that the more work I do now, for free, the less work the designer will have to do later, at an hourly rate.
The long-term goal of this exercise is to get as close as possible to a design for a live-aboard retierment home for my wife and I. One of the biggest problems is that I think almost everything is a good idea.
If I approach a pro with a mish-mash, without a FIRM idea of what I want, he'll have 1) a stroke and 2) a huge bank account at the end.
Besides, I'm incredibly hands-on.
The boat should be EASY and FAST to build, as maintenance free as any boat can be, comfortable as a houseboat (with some slight travel ability) with pretty good storage. It will almost certainly stay within a mile or so of the north shore of the Great Lakes, often sitting at a remote anchorage for a month or more at a time. I am a HUGE fan of the Bolger designs, since the Sharpie style seems so quick to get closed in.
To sum up, I am a future huge fan of MAIB as a lifestyle, who has turned to planning and sketching and drawing as a means of dealing with my addiction.
Short question, long answer.

[buhmkin]

Sharpie's pretty popular amongst the nearly/just retired set. Shoal draft and potentially some headroom. My grandparents wanted an Airstream, my parents want to build a sharpie. Sign of the times, I guess.

As to the rules of scantling for plywood construction, I would gladly offer any input given that this forum is for that but I have no idea. To second Aramas, see what Bolger's done and do similar, you can't go too wrong. Check the Glen-L site, too, might be something there.

[great white]

Yeah, Bolger is a genius. His designs have given me direction, even from months ago. I started with Wharram, but the complexity of two hulls... and the cost... proved to be too much. I even e-mailed Bolger, asking about the thickness thing, but he hasn't replied.
So, failing a response from the resident genius, I throw myself on the mercies of the geniuses on the Wooden Boat Board.

[TimothyB]

Although he is a controversial guy, George Buehler sounds like his ideas are right up your alley. You won't be building a gold plater, and your grandchildren won't inherit the boat, but his designs are safe, seaworthy, easy to build and 'hell for stout'. You can get 30+ years from his designs. Even more if you do it right, but I'll let you read his views on that.

http://www.georgebuehler.com/

Add to that his book 'Backyard Boatbuilding' has a bunch of free plans with offsets.. older designs but servicable ones that have carried lots of folks around the briny blue. And his book isn't that expensive.

[Bruce Hooke]

Originally posted by great white:
Yeah, Bolger is a genius. His designs have given me direction, even from months ago. I started with Wharram, but the complexity of two hulls... and the cost... proved to be too much. I even e-mailed Bolger, asking about the thickness thing, but he hasn't replied.
So, failing a response from the resident genius, I throw myself on the mercies of the geniuses on the Wooden Boat Board.I'm not surprised that Bolger did not reply. As the responses above have shown, this is not a question that can be answered with an equation or two -- why else would there be books on the subject. HOWEVER, what you can do, and what I think most designers do, is LOOK at some similar designs by Bolger and others, check what scantlings (plywood thickness, etc.) they used, and then use the same or similar scantlings for your boat. HOWEVER, this route needs to be approached with caution -- you have to understand the parameters that are behind the plywood thickness and other scantlings so that you can accurately judge how similar your boat is to the boats you are comparing it with. For example, if you just compare based on length you will get all sorts of different answers because other parameters such as displacement really matter much more. Even boats of the same size may vary a good bit based on intended service, frame spacing and similar factors. If you want to get the plywood thickness and other aspects of the design right then you need to learn about this stuff.

I also think that it is good practice to start by developing your own numbers based on Gerr's book and similar sources and then check how your figures compare with what other designers have come up with. If they match up fairly well then you are probably on the right track. If they don't then you need to look into why.

[Bruce Hooke]

Originally posted by great white:
I admit in advance that I should leave these things to a naval architect or proven designer. With that in mind, please advise me... is there a constant or formula that will permit one (me) to figure out the proper thickness of the deck, topsides and hull for a plywood hull that will never touch bottom? I am thinking of a sort of... "if the boat is thirty feet long, the topsides should be 3/4" thick and the bottom should be 1 1/2" thick"... thing.
(Ordinarily, I WOULD leave this to a pro, but when you have zero bucks and a burning desire, you do what you can. And I promise, before I build, I will have the plans vetted by a professional. No shaky, dangerous bricks from this b'y!)IF the real reason why you don't want to pay for a design by a pro is, in fact, cost (and not just because you want to design your own boat because you feel like it -- which is fine) then I would suggest that there are two routes you might want to consider:

1. Make real sure that there is not a suitable design already available. The cost of a stock design is likely to be less than what you will spend on books just to start learning boat design.

2. If you need a truly unique design then start finding ways to earn more money doing whatever you are good at until you have enough money so that you can pay a designer.

Of course, if you just enjoy learning about boat design then go for it. After you've completed 5 or 10 designs and read 30 or 40 books about the subject, you may have something that is worth building.

Another good reason for continuing to design your own boat would be if this is basically an exercise in learning about what you are looking for so that you can better talk to a pro when you have the money.

I'm not trying to be mean -- I have taken an amateur interest in boat design for a long time -- but, I've seen too many cases where an amateur with lots of enthusiasm but not enough knowledge put lots of time and money into building something that turned out to be a real dog once it hit the water, which is a very sad situation. Remember, the design is just about the cheapest part of building most boats.

[great white]

Timothy B, thanks, I will go there immediately.
Bruce Hooke, thanks also. You seem to have put a lot of thought into things like this. I admit that part of my passion is the thought of actually putting epoxy to wood, on my own design. I am not naive enought to assume that anything I come up with is going to work for anyone else, but, as I used to build houses, ground up, I am sort of familiar with the processes and tools that would be required.
I have been surfing for several months, looking for designs that meet my (changing) criteria. The difficult thing is, there is so much good work out there, so many great ideas, that I have a hard time developing a critical assessment of them. I start thinking about how great the idea is, and I find that I am losing sleep trying to incorporate it into my boat. This is part of why I am pounding things, trying to get a handle - so that I don't drive some designer nuts because I came across a site that advocates paper mache hulls, reinforced with duct tape stringers and pop-can frames.

[great white]

Timothy B... GREAT site. George Buehler has officially replaced Wharram and Bolger on the hit parade. Of course, see the reply to Bruce Hooke... things change. But for now, his designs and philosophy are most appealing.

[FG]

I'd think about rehabing an older boat if I had that severly limited finacial resources and a hands on approach. Sounds like you've got time to look for a project if you have time to design one.

[great white]

FG, I thought about that. The thing is, I have some ideas that I want to try out, some things that I need on my boat, that I haven't seen on any of the designs... well, at least, not until I went to George Buehler's site.
In addition, my wife and I both have special needs and, frankly, I'd rather start from the ground up to meet them than work from the top down.
Thanks for the thought.

[Big Red]

Sounds like the perfect oppotunity to recommend one of my favourite sites:

Svensons (http://www.svensons.com/boat/)

There is a whole bunch of free plans from old magazines here. Maybe there are some leads here for you. Big files though, hope you've got a good connection. smile.gif

Red.

[great white]

Thanks Big Red. Lots of designs...

[Ron Williamson]

Mark Van is around here somewhere.
He designed and built something akin to what you're looking for.Try the search thingie.
R

[Hwyl]

Here is Mark's site http://markvdesigns.tripod.com/boatbuilding/

You don't say if you are looking for a motor boat or a sail boat. If yo are looking for a motor boat "Heart of Gold" is a great one. "Don't Panic"

He recently lost his Dad, he may have gone cruising, I haven't seen him post in a couple of weeks

[great white]

Funny you should mention Mark Van. I found his site a while ago, and downloaded the whole thing, pictures and all, for reference. He has, indeed, built something very much like what I want - the style, the simplcity. His site provided a lot of sleepless nights for me.
The whole sharpie thing is a great approach to what I need. Mark took the concept to a new place... at least, new to me... and nudged me toward the 'turn-of-the-century' look. I've sort of combined Mark's ideas with the Bolger Idaho and most of George Beuhler's philosophy, and wound up at a very exciting place.
While I am not rash enough to assume that I can design a boat myself, I AM rash enough to think that I can at least supervise the building of a pretty good boat that will meet my needs... once I have a clear idea of what I need.
And Mark V did, in fact, provide me with the clearest vision of that idea. Now, all I have to do is change it... <grin>

[htom]

bump
again

[ 06-19-2004, 12:50 AM: Message edited by: htom ]