The inclining test

As I wrote previously, Cangarda's launching (or partially floating) instability really has little or nothing to do with its stability at sea. A vessel stability derives from its shape, its mass and the center of mass. The distribution of the mass is important for calculations of motions and ship strength, but for hydrostatic stability calculations, it makes no difference how it is distributed, only where its centroid, or Center of Gravity (CG), is.

It's easy to figure out a ship's weight and the longitudinal (LCG) and transverse (TCG) centroids from just observing its drafts, trim and heel. Weight as function of the volume of water of water displaced...Archimedes figured that out it two thousand years ago (Hey, Eureka!). But determining the vertical centroid, the VCG, is different and has to be determined by an inclining experiment. Here's a pretty good explanation of the process at the naval post graduate school website.

The elements of the experiment are moving precisely measured weights, precise distances transversely in the ship to cause heel, then measuring (precisely) that heel angle. This is the relationship between the heel and weight moment (weight x distance).

The weight or displacement of the ship, , is known. The transverse moments and resulting heel angles are measured. Solve for GM. From GM, and the ship hydrostatics, derive the VCG.

In theory easy, in practice...precision is everything. The standards and precision for conducting the test are in our federal regulations. A vessel must be heeled to a maximum angle between two and four degrees, the angle to be measured precisely. We commonly use a pendulums or water filled clinometers. Here's what they look like:

I say pendulums plural because three separate devices are required (and I think insisting on "pendula" is affectacious). To get the required precision, the minimum greatest deflection is six inches. To get that deflection for two degrees of heel, the pendulum length has to be 172" (4.4m). A pendulum that long on a boat on a windy day wiggles around quite a bit...it can be hard to get an accurate reading.

We're conducting the inclining experiment on the Alcatraz Flyer on April 11th. It's a very wide and stiff little ship, and to get the required minimum of two degrees of heel, we have to move thirteen tons of weight in a specified set of movements across the deck. It takes up most of the day.

More on launching instability

Oh, man. The idiot with the needle gun is out there on the rusty old Ranger again today, futilely hammering away. "Idiot! Idiot! You are accomplishing nothing except to drive me nuts!"
I'm going to go outside and scream at him.

(...three minutes later) Well, he couldn't hear me yelling, but I feel much anyway.

As I wrote yesterday, Cangarda's (ex Magedoma, ex Cangarda) near capsize is not unique in ship launching history, especially for long slender vessels like steam yachts. Here's an illustration from the London News in 1883 showing the capsize and sinking of the S/Y Daphne:

Not quite the same thing happened to the American S/Y Norma in 1884 as you can see from the Times archive:

http://query.nytimes.com/mem/archive-free/pdf?_r=1&res=9806E1D9163AEF33A25757C0A9639C94659FD7CF&oref=slogin

It simply had too many passengers on deck. It wasn't a launching instability.
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Back to Cangarda. Here is a the picture of forward moving dolly:

Note how it only supports the vessel at a single point on the bar keel. And wow, check out the tires:

Even more amazing, those were the good "road wheels", the mover changed them for even more threadbare launching wheels right before the launch.

To retrun to yesterday's theme, what does its launching instability say about Cangarda's ultimate seaworthiness? Basically, nothing. Here is a graph of its righting arm in its most adverse loading condition:

Cangarda has a great range of positive stability (> 90 degrees) but, compared to a modern motor yacht, a very little initial form stability. This means that it will be very subject to roll motion and have large roll response to relatively small waves, but is also pretty immune to full capsize due to the low center of gravity. The roll stabilizers (obviously, not original to the vessel), should give it a better ride.

Transverse stability

Cangarda...you can't get enough of it! On Friday, the owner said the filmmakers had promised to put up a dedicated Cangarda site, but I don't know if that will ever happen. In the meantime, I will attempt to bring you up to date. Thomas asked about the near capsize at launching. It is true. It happened. Here is a shocking photo:John Horton (on the rail) probably hadn't anticipated this event, and is trying to decide whether to hold on or leap free. Andrew and Jody were in the Zodiac and are backing like mad. Yeah, it looks funny now, but it was serious and could have been far worse. I just read the article you cited: http://www.ebdailynews.com/article/2007-8-25-eb-yacht. Evidently, some people, including the owner, didn't fully understand what happened. As you point out, he seemed to think that this was proof of the vessel's inherent stability. It's not.

This is classic launching instability and, until recently, has been a standard part of elementary naval architecture instruction. Today, most vessels are launched parallel to their design waterline either with a travel lift, a syncholift, or by allowing water to enter the building dock --never losing transverse stability. Years ago, most vessels were end launched (stern first) off an inclined railway or set of building ways. Launched this way, as soon as the stern floats, the ship is only supported at the bow, and would lose all transverse stability if inadequately suported. The forward poppets have to be strong enough to resist that lateral load.

If a vessel were launched perfectly straight and there were no asymmetry, then it could slide all the way to the end of the ways with no incident just as a riderless bicycle could be sent down a hill with a perfectly straight push. The farther the ship makes it down the ways, the more form stability it gains...its a race between the stabilizing and destabilizing forces. Here's a link to a video of a launching in 1907 that went wrong: http://www.youtube.com/watch?v=Mj-FIXlTPIo
The instability and the overturning moment can be calculated. Before computers that calculation was difficult and rarely done, now (with the right software) it is easy and accurate. Long, slender vessels are more prone to overturning than short, wide ones (with LCB well aft of amidships). Cangarda was launched by a very interesting and energetic housemover who had experience launching large fishing boats with the same gear and method. The gear consisted of a massive, multiwheel dolly under the stern, and a steerable dolly that supported the bow at a single point. When I told Jeff and him that Cangarda would capsize the mover said, "I was thinking about some kind of tie down, but I didn't want to eff up the guy's paint."

"Well. His paint is going to get effed up a whole lot more when he capsizes on the ways".

The mover's gear was old and primitive, and watching his crew and he move Cangarda out of the yard brought to mind a horde of ancient Egyptians hauling a giant obelisk with ropes and rollers.

To make a long story a little shorter, prior to the launch the housemover added sufficient lateral support to the bow dolly, but when the stern floated free, the rusted old dolly itself split apart. Luckily, the mover was driving the truck, and when he saw his dolly start to rip apart, had the presence of mind to push Cangarda down the ways as fast as possible, thereby preventing a disaster too heinous to contemplate.

What does this say about Cangarda's transverse stability or ability to weather a severe storm...nothing.

Loadlines

Maybe you've seen one of these on the side of a ship and wondered what it was:

It's an International Load Line "Plimsoll mark", named after Samuel Plimsoll, a 19th century British MP, who took up the cause of preventing ships sinking by overloading. The mark was adopted by international convention in 1966 and has applied to ships of all signatory nations since then. Of course, it was created to prevent greedy shipowners from overloading large commercial vessels with cargo, but it applies to any ship (other than a yacht or warship) over 79ft in length, including even small, wooden sailing ships like our Spirit of South Carolina.

Unfortunately, Spirit's load line is now slightly submerged. Today, I have to find out why.

- Was the Plimsoll mark placed in the wrong spot?

- Has the wooden structure soaked up a significant amount of water since the orginal stability calculations?

- Is someone storing gold bullion on board?

I suspect it's a combination of the first and the last...well, probably not gold bullion, but sailors are notorious packrats, and I'll wager there are random bits of chain (never know when it might be useful), tackle, tools, packets of Cheetos, etc that weren't there when the vessel was new.

I think we'll be able to fix this pretty easily by adding additional deadweight load items e.g., "crew stores", "bits of chain", "snack foods", to the stability calculations, to account for the general increase in weight, without however, exceeding some of the transverse stability requirements. Not too much, not too little.

Diesel oil

Cangarda instant update: Cangarda is taking on fuel today. The pump truck is right outside(but luckily I have my noise cancelling headset) and the +3000 gallons of diesel should take all day at acceptance rate of the vessel. (Just checked, fueling rate is ~24 gallons/minute...so a little more than two hours.)

I touched on the repowering of the Alcatraz Flyer yesterday. In the SF Bay we're very conscious about vehicle emissions. (That's why there are more Priuses here than anywhere in the world - they're powered by guilt) Replacing the Flyer's old Caterpillar 3512's with the MTU's will result in +30 gallon fuel saving per engine per hour at the operational speed. Let's say the vessel operates 1000 hours per year at the average operational power. That's an average fuel saving of ~60,000 gallons/year, which means at hundreds of thousands of dollars of fuel savings per year. Since there are ~2.78 kg of carbon per gallon of diesel, it also means 1668 metric tons of carbon won't be emitted into the atmosphere each year.

Alcatraz Clipper

Another Cangarda comment! Maybe I should start a steam yacht Cangarda blog?
Dear Thomas and other steam aficionados (nuts) who may read this, I believe Tri-Coastal Marine has been cut loose from this project (although no one has informed me one way or the other). We will update our Cangarda webpage when we get a chance. We've got many inquiries/complaints about progress with the steam plant, and I don't have any good answers. Basically, it is complicated, principally due to all the automatic combustion controls. I'll take some pictures of the engine room and post them so you can get a feel for it.

FYI, as I wrote previously, it appears to me that the project is at a standstill. Not a lot of recent activity, no sign of steam....John Horton is the only guy out there today. I'm pretty certain that Steve Cobb (captain) has left as well...at least he doesn't come around for coffee anymore.

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Ahem. To return to the (my) Naval Architect's Blog:

This morning I headed over to Bayside Boatworks in Sausalito to measure the Alcatraz Clipper. The Clipper and the Flyer are ex- Blue and Gold Fleet ferries that Alcatraz Cruises bought for the Alcatraz/Pier 39 route. They are both over thirty years old, but still good. The Clipper is up on the railway at Bayside for replating, repowering and general rehabiliation. Here's a picture from the upper deck this morning over Richardson Bay:

What view. This railway, as others, was built on the foundation of WWII Liberty ship building ways. It's a little like stumbling across the giant remains of a previous civilization.

It barely fits.

The boats are old, and the documentation is indifferent. Today we measured the deck edge, chine, profile, draft marks, and propeller shaft location. This will ensure that we have an accurate hull model for future calculations. Here are the surveyors digitizing the chine with a total station device.

Surveyor with total station device

Cangarda

A reader, yikes! Yes, there has been quite a lot of interest in Cangarda, and it is true our website is totally lame and out of date. In our defense, well umm...I think we’ve been more or less cut loose from the project so, aside from taking up 140' of dock outside the door, it’s dropped off the radar screen. Our part in its restoration was quite interesting and purely technical, but we weren't the builders, and provided no project management or any oversight. However, for all the steam aficionados, we will try and update our website to reflect its current condition, just because no one else seems to be doing it. As to its color, strange rig, etc., they were the personal choices of the owner...blame us for other stuff, but not that.

John evidently has been following Cangarda’s progress. For those who have an interest, Cangarda is/was the only existing American example from the short lived era of steam yachting. Here's our Cangarda page
She was built in my hometown of Wilmington, Delaware by the Pusey and Jones Co. in 1901. While I'm not old enough to remember Cangarda being built, I do remember the yard closing down in 1959. Here's a picture taken at the P&J dock in 1901:


As far recent photos and her current condition, it was launched in August of last year and Andrew Worm posted some of his photos here. Since then, it's been sitting at our dock with a few guys picking away at it. Is it going to sail anytime soon? (We could have steam ship pool!). My guess is...well, I better not say. They haven't "raised steam" yet -- I will post that milestone when it occurs. I'm sure the builder, Jeff Rutherford rbsinc@sbcglobal.net, can give a more up to date schedule.

More needle gun

Here's a picture of the guy with the needle gun on the old, rusty Ranger...that vessel's an argument for sending old steel ships to Pakistan. Turning it into wire coat hangers would be a higher use for the steel. Today, I felt like going out there and telling them how stupid and useless they are, but why bring them down? They feel they're being productive. (They also play that 'orrible mexican, mariachi music, with the tuba all day...does anyone actually like that stuff? I suppose it sounds okay in old Puerto Vallarta, but it doesn't travel very well.)

Let me retract what I said about old steel ships. We've been spending a lot of time on some thirty five year old ferry boats for Alcatraz Cruises and they are still great. Every day they reliably carry thousands of overweight persons (snack bar aboard!) from Pier 39 to Alcatraz Island and back. They've been upgraded and repowered (depowered from 2000 hp to 1300) and fitted with catalytic converters...this is the Bay Area, and we all drive Priuses. Funny thing, the same company runs the same boats from Manhattan to Liberty Island in NY, but they could care less about catalytic converters there...instead, all passengers have pass through airport like security.

check out our website to see what we've been up to: www.tricoastal.com

F!cking needle gun

Jeesus H. Christ! Some idiot with a needle gun has been blasting rust off an old crew boat for three straight days. He's about forty feet from my desk -- like being inside a 55 gallon drum with that fool hammering on the outside...kind of explains why I'm not being very productive.

FYI, a needle gun is hand held device, containing about twenty boron rods that jitter back and forth, powered by compressed air. The reciprocating rods bust rust off steel plate and can be pretty effective if the plate is thick enough (over 1/4"), but are useless for thin plating since it just deflects away under the blows. That moron is using it on 1/8" deck plating. All the energy is dissipated as sound, while the rust remains. This could go on for days.