Hull Form Design - Doing better than a floating brick

Pinned post for Q&A :)

Everyone who's disappointed we didn't get the 84-hour version of this video raise their hand. XD

Being a Marine engineering student I completely agree, that anything above the basics is mind numbingly complex .

I think we can all agree floaty log was the peak of naval design.

Everyone: Which would be better, thin and long, or short and wide? Rear-Admiral Popov: R O U N D.

Then there's all the fun you can have with SUBMERSIBLE hulls. Back when the US began playing with nuclear powered submarines, they decided to build a little experimental boat, mostly full of batteries, to do some testing of what the handling characteristics of this new hull form called a 'body of revolution' would be like. The tank tests said it should be a very efficient hull form for a sub while underwater, which was where a nuclear powered sub was expected to spend almost all it's time while on patrol. A body of revolution is one which is formed by taking a curve and rotating it about an axis. For the sort of curve you'd use for a hull shape, the result is sort of cigar shaped, and all cross sections of it are circles. So, they build this test boat and take it out to do test maneuvering to see if it does anything strange. Well, it did something strange, all right. The strange behavior was named the "Jesus Christ Factor," most likely due to someone saying that when it was discovered. One of the properties of a hull form that has all cross sections being circular is it has no hydro-dynamically preferred orientation in the water. They tried to pull a sharp turn (like you'd pull in combat to evade enemy anti-sub weapons) and discovered that when you turn sharply in a sub with this kind of hull form, it likes to snap-roll into a steep dive, in excess of 45 degrees down. Now, snapping into a steep dive is fine and dandy when you WANT to do that, and could make for a nifty evasion maneuver, but most of the time you don't want to evade like that. It risks you hitting the sea bed or exceeding your crush depth. fortunately, it just needed a small rudder added to the back of the conning tower to prevent the boats from doing that.

I feel insulted, my brick shaped boat floats just fine. Admittedly it isn't very fast... And it turns like, well... A brick... But other than that it works fine, sort of

The Square Cube Law: it's why a 20" shell is a lot more than four-inches scarier than a 16" shell.

2:50 The chance to show the Russian round battleships on screen was missed here.

When I was a young midshipman, we spent a month in a classroom wrestling with the concept of ship's stability. You nailed it in a matter of minutes. Well done Professor Drach.

As a naval architect with more than 45 years of experience in hull design, this was a good video for non-technical people to help them understand the complexity and compromise that goes into every ship design. On stability: roll acceleration is critical not only to equipment functionality but also to habitability. Too stiff a ship, roll period very short, and equipment, especially those located in high places can actually be broken off the ship, and people have trouble standing and moving around. On speed/power: as a gross rule of thumb for every 3 knot increase in speed, double the shaft power. This rough approximation works throughout the speed range. During my 12 years responsible for hull form at a major U.S. shipyard, it was common for us to go through dozens of iterations on the hull geometry (both commercial and naval auxiliaries ships) before we settled on one that met all of the requirements for speed, power, range, habitability, seakeeping, maneuverability, as well as sufficient volume to carry whatever was necessary to meet the mission requirements. Inevitably, the final hull was not ideal for any requirement, but always met, and often significantly exceeded, the contract specifications. Always a fun puzzle to crack!

"since we're not going to make an 84hr run time video ..." ... wait, you're not? ... where did YT put the Down vote ...

Hydrodynamics: for when thermodynamics alone is no longer depressing enough on its own

Reads title A wise Sergeant once said: For a brick, he flew she floated pretty good.

I always click fastest on Drach's nerdy engineering videos. Boilers, steel formulation and now hull form. Excellent. I can pretend it's continuing professional development if anyone asks me.

As a Naval Architect, I can say that this video is very good and covers pretty much every major concept in naval architecture (excluding all the math. There is a LOT of math). Very good summary of what naval architects think about when designing a a hull form.

Drachinifel: mentions a brick. USS Monitor enters the conversation.

Can concur, I have a shorter, fatter hull form, and I am quite slow. :)

I can't believe you didn't go at least a tiny bit into the American stern, with its surfboard like qualities that got rid of the turbulence not by narrowing the stern horizontally, but tapering it vertically. THAT is where America got her fast battleships, even though prop design then became a problem for quite a while, due to cavitation, the boatman's nightmare. But by narrowing it vertically, it made each fast battleship into a surfboard, not only not wasting its hp by burying its ass into the sea like any old displacement hull, but using that wasted hp to propel them even faster, by surfing their own wake, a phenomenon most experienced pleasure boat captains are familiar with. Transferring that concept to a battleship platform, given that almost all pleasure yachts at the time went for the traditional horizontal narrowing so the bow looked much as the stern, was indeed revolutionary. It was really only achieved 100% with the Iowas, due to length limitations on the Washingtons and South Dakotas, but not mentioning it is sort of goofy, given that all modern warship and many commercial ships use the exact same technology, just tuned up a bit. Funny you included the square stern, but not that. You do know only American Heavy Cruisers had that stern? Light cruisers had traditional round sterns, which were the beginning of the surfboard stern, although far simpler as they were so narrow. The fat battleship sterns came from this concept. But I suppose you could go on forever on this subject. Kudos for a valiant charge at a complex subject and an extremely understandable presentation. I dare say you might have saved many lives by making Sunday sailors more aware of metacentric height alone! (Their eyes glaze over when the phrase is even mentioned, even though they own a million dollar yacht!)

Currently sitting in my stateroom on the usns loyal watching this. Google the ship to see what happens when you care about sea keeping to the extreme. We barely roll at all in up to 12 ft seas... but out top speed in a sea state 0 is 6 knots