Help, Please

[Neophyte]

I'm an non marine designer looking for some elementary books to allow me to learn some layman level info regarding stability, buoyancy, and self-righting.

Any suggestions would be appreciated.

[Skippy]

Here's some general info. You might have to poke around a little to find that specific topic.

Ted Brewer's online primer on yacht design
Books
More books

More specifically for multihulls, John Shuttleworth's article

[Neophyte]

I'll look into these. I sincerely appreciate your help.

[mackid068]

Oh, fellow neophyte, self righting features are common amongst SOLAS (safety of life at sea treaty) approved totally enclosed lifeboats. search SOLAS totally enclosed lifeboat online. Also, look at ovatek.com.

[Mikey]

The Nature of Boats by Dave Gerr is amusing and good reading, explains things in a good way using simple language. Not specifically about stability, contains quite a lot more than that.

Mikey

[jfblouin]

Do you look for a self-righting hull design of for a self-righting system like on RIB?

[Neophyte]

Thank you gentlemen, for your suggestions. I am already looking into them.

The question as to type of "hull" I'm interested in, impels me to confess that my interest lies not in your traditional arena but in applying marine design basics to the construction of wooden duck decoys. They are, after all, specialized small watercraft intended to lie at anchor.

Suffice it to say that I've been making them for years without completely understanding the physics behind them, following the tried and true designs of the past.

There are those who feel that a self-righting capability is important for a decoy, even vital. They argue that a decoy should be capable of recovering from a capsize should they be overturned by wind or wave action or if it lands in an overturned position while being "set out" by being thrown into position. This group typically achieves a self-righting capability by adding more and more ballast to an applied keel until they succeed.

I am of the dissenting group who feels that form stability is far more important than self-righting and, also, that the "add more weight" methodology disproportionately increases transport weight and displacement offsetting any benefits gained.

I find their logic faulty as:

1. when the water is rough enough to overturn a stable decoy, I don't plan to be there.
2. ducks won't land in water that rough, and
3. I don't know of anyone who sets our decoys by throwing them.

I make my decoys with a broad flat bottom with maximum beam forward to reduce drag.

Solely to satiate my curiosity, I wanted to learn more about the forces in play and the tradeoffs that must be considered, hence the question.

Again, I appreciate your willingness to help out.

[mackid068]

Hunting decoys, huh? Ballast them with mushroom anchors or whatever light anchor is most suitable. Regarding the self righting, fill the top part with buoyant foam and make the bottom weighted.

[Neophyte]

Regarding the self righting, fill the top part with buoyant foam and make the bottom weighted.

There are a lot of modern decoy carvers who do just that. However, like the traditional wooden boat people, I'm a traditional wooden decoy carver. I continue to use a drawknife and shaving horse while others use modern motor tools.

If I was seeking increased production... or even efficiency, I might consider "modern" tools and materials; but, I find enjoyment in doing things the old way.

As for anchors, in the case of decoys the analogy to boating is a complete one. Mushrooms are fine in a sandy bottom... grapnel types work well in rocky ground... and sometimes dead weight (Navy type) anchors are the best solution. (Although, I'll confess that I generally limit scope on my decoys to 3:1.)

[mackid068]

So that's a no on the modern materials. Old ways are often fun. Do you have a picture of one of your decoys? For self righting ability, weighting it is good and to prevent turtling (flipping and staying there), keep the center of gravity low, at least, that's the rule for boats.

[Neophyte]

[quote=mackid068] Do you have a picture of one of your decoys? QUOTE]

As you're from CT, here's a black duck,. Black ducks are/were the most frequently hunted marsh ducks in your area, particularly along the Housatonic.

The thumbnail doesn't look so hot; but if you click on it, it will clear up.

[lewisboats]

Functional Art.... Impressive!

Steve

[Neophyte]

Thank you, sir, for your kind assessment.

The tradeoffs of art and function is one half of the attraction for me. The other half is tradition. Many decoy carvers concentrate on the art and neglect the function. Indeed, I suspect that some of them have no experience with functional decoys at all.

[mackid068]

Enough with the thank you sirs. Nice and polite, but unneeded. We're all equals here, regardless of knowledge. Its a pretty looking duck.

[Neophyte]

Originally Posted by mackid068

Enough with the thank you sirs. Nice and polite, but unneeded. We're all equals here, regardless of knowledge.

I assure you that the courtesies are just that... not obsequiousness. They are a product of my rural southern upbringing.

Even though I am in my 60's, I say "thank you, sir" to my grandson when I owe him a "thank you." I say the same to my younger co-workers and would do the same for anyone.

... one of those cultural things.