Naval Architecture for Dummies

[fritz3000g]

I've been reading David Parker's 200-page rant about sailboat design (aka Ocean Voyaging), and have run into a bunch of words that I don't know the meaning of and can't find in the naval architecture glossary I downloaded.

Can anyone enlighten me about what he's ranting about (paragraphs from different parts of the book, comments by me in italics):



Shapes of cruising yachts vary from the extreme of Slocum's Spray, which was bluff-bowed with little deadrise, and which had a narrow flat run aft, to modern designs with fine bows, arc bottoms, and broad flat runs aft, sometimes with bustles or kickers.

[A combination] I have found to be good for beating in rough seas, as the bow has no flare to suddenly catch the boat as she creams into a wave... Such boats usually have a rather flat, straight afterbody and relatively hard bilges.

She is of extremely light displacement and has a modern pendulum fin keel and a spade rudder....Hulls of her form lie to steadily and self-steer as well as or better than their long-keeled cousins. (what could self-steer better than a long keel?)

The bow should not be too v-shaped, but should be slightly rounded. (A rounded bow? I've never seen anything like this. Seems like it would just push water. What am I missing?)

The narrow, deep craft with relatively slack bilges and a high ballast ratio will not be stiff initially, but as she heels she becomes more and more resistant to her press of sail.

Another common design characteristic on so-called cruising yachts is that nautical monstrosity, the clipper bow. While the fiddle head and trailboards of the traditional clipper bow are without doubt beautiful on a clipper ship, they are ridiculous on a yacht under sixty or so feet in length. A true clipper bow has hollowed waterlines below the load waterline and considerable flare above.

Any bow with too much flare and hollow underwater entry will [hobbyhorse] if the yacht has a lot of rocker to her underbody and is too beamy and short.

When underway, the narrow run associated with the sharp stern raises a tremendous quarter wave and actually causes the following seas to break far sooner than does a well-designed transom or counter-stern... I personally favor the rather straight run aft from the midsection in order to provide a flatter quarter wave.

[J Stevenson]

Here is a useful list of books on yacht design:
https://www.marineinsight.com/naval-arc ... ht-design/

I personnally suggest #4.

[fritz3000g]

Thanks I ordered it!

[Tod Mills]

bolt font words are the ones you are unfamiliar with?

[fritz3000g]

Correct.

[Ben Miller]

A hard vs. a slack bilge is one that I have trouble remembering. A quick internet search to refresh my memory confirms that a "hard" bilge is a term associated with a flat bottom and vertical sides. Think of a modern fin keel planing sailboat. Slack bilges are what you see on the more sloping, wineglass style of hull. There's a pretty good diagram showing the different styles at this page: https://www.aoki.us/zen24/performance/292/

The bow should not be too v-shaped, but should be slightly rounded. (A rounded bow? I've never seen anything like this. Seems like it would just push water. What am I missing?)

I'd assume that the author is talking about the profile where the two sides come together at the bottom, not about the front of the bow. Although certain boats do have non-pointy bows. For example.

[fritz3000g]

A quick internet search to refresh my memory confirms that a "hard" bilge is a term associated with a flat bottom and vertical sides. Think of a modern fin keel planing sailboat. Slack bilges are what you see on the more sloping, wineglass style of hull.

I'd assume that the author is talking about the profile where the two sides come together at the bottom, not about the front of the bow.

Thanks this makes sense, and is really helpful!

The link you sent looks like it's trying to promote the "moderate" hull form. CDs seem to me somewhere between moderate and wineglass (slack bilge) hull forms, as you can see here:

[Cathy Monaghan]

Take a look at this article, I think it may help you with at least some of those terms:

https://goodoldboat.com/is-your-boat-stable/