Can I make a steel boat unsinkable & self righting?

[Byrd88]

Forwarning I am new to this & not very knowledgable, hence I have joined to seek your guidance... so be gentle. I am interested in making a steel boat unsinkable, like an ETAP, I know about the 2 compound foam used, but have noticed that it is used primarily in fiberglass or aluminum boats. Is it feasible or possible to have the same effect in a heavier steel boat? Also I'd like to make it self righting like a coast guard boat, but I'm not sure if they use floatation bags or how to go about that. I have noticed in my search that it is almost impossible to find such bags, except for kayaks... Any suggestions? Any help is greatly appreciated.

[Submarine Tom]

Yes, if you know how to do it.

-Tom

[Byrd88]

Ok... would you by chance have any knowledge you'd like to expand on???

[Submarine Tom]

More than space allows (thanks for asking).

I believe the ball is in your court my friend.

You have some research to do.

Check out the Canadian and USA Coast Guard 47 foot life boats.

They have inverted instability and positive buoyancy.

Good luck.

-Tom

[Ike]

Sure, Why not?

Self righting is a little more difficult than unsinkable. Unsinkable just requires enough flotation in sealed compartments to support the boat, its equipment, and passengers, while the boat is flooded with water. On smaller boats this is done with sealed flotation chambers, on larger boats with watertight bulkheads, doors and hatches.

Self righting is much harder. Self righting means the boat has to always have a positive righting righting moment even when it is upside down. This depends on the center of gravity, center of buoyancy and the metacentric height. There's not enough room here to give you a course in how to do that. You need to study some books on naval architecture or hire an NA to do the design. Here's a very brief page on stability, http://newboatbuilders.com/docs/stability.pdf

[daiquiri]

What size of the boat are you talking about?

[Byrd88]

Thank you Ike... Would you recommend Bruce's e-books for $60 or do you have any suggestions?? As for your question D... I'm looking at 40 to 50 ft. Any help or suggestions on your end?

[marshmat]

Byrd,

A good starting point would be a modern boat design textbook such as Larsson & Eliasson "Principles of Yacht Design". There are of course many others that are also quite good.

Once you've spent a bit of quality time with such a book, and have worked through some of the example calculations and exercises, I think you'll have a good idea of how it will all come together and where to go for more specific knowledge relating to your application.

I'm pretty sure you'll find that a (nearly) unsinkable, self-righting craft can indeed be built in steel, albeit with some compromises- restricted and compartmentalized interior space, a deckhouse shape that may not be aesthetically or aerodynamically appealing, etc.

[hoytedow]

The "unsinkable" Titanic self-righted when it hit the bottom.

[Byrd88]

Thank you for the book suggestion Marsh... I did actually come by that recently in my research online, I just didn't want to purchase anything until I had a few recommendations as to which direction I should take. Thank you again...

And Hoyt... are you trying to tell me something. ;-)

[hoytedow]

Well...You can make it water-resistant, but not water-proof. You can make it sink-resistant, but not sink-proof. Un-sinkable is a very strong term.

[Byrd88]

I agree that nothing is for certain, especially until truly tested, but I'm going to try my best to acheive the closest dependable design possible... and people with your knowledge are definitely my starting point... and quite possibly my ending point after a book or two. ;-)

[hoytedow]

I am unworthy.

[Byrd88]

You're silly... Thanks again for the kick in the butt on the reality check.

[daiquiri]

Byrd, too bad you don't speak italian (right?)...
If you did, I would recommend you a book "La mia barca sicura" (My safe boat - http://www.hoepli.it/libro/la-mia-ba...9788888389691), written by this guy, Ernesto Tross, who has had an unusual idea.

He has started by collecting and analysing available statistical data about boat accidents worldwide. Then he elaborated a set of strategies aimed at counter-fighting the main origins of accidents which came out of that analysis.

Finally, he transformed his ideas of safety into a design and ultimately into a boat. It is an ugly boat by any non-military standard, but definitely safer than average.
This is a page with some pics of that sailing caterpillar: http://www.cantierino.it/AGALLERIA/orsobianco/a.html

As soon as I find some free time, I'll try to translate the main guidelines from the book, which have led him to those unusual design choices.

Cheers