Ralston stability and trim indicator

The predecessor of the modern Loadicator and other computerized calculators was the Ralston Stability and Trim Indicator. I can still see the captain and first officer hunched over this mysterious fully analog instrument and moving the small weights over the ship’s plan which was engraved inside the box. All very impressive we thought.

The instrument consisted of an aluminium base plate upon which was engraved an outline diagram of the ship and its compartments. The plate was set in a heavy brass frame and could be balanced on suspension points in a fore-and-aft, or athwartshps direction. A mechanical calculating device is fitted to the upper part of the frame and this includes various scales for calculating the ship’s stability and trim. The instrument is housed in a mahogany case which contains two drawers for storing weights.


I have used one many years ago. We would go through the loading list to see what was practicable in the planning stages. The actual stability was always calculated longhand using a adding machine if you were lucky enough to have one.
There was one Scottish shipping company that ran a liner service to the Far East with ships with very fine lines and very tender. It was normal practice to stick a weight representing 50 tonnes on the funnel before preceding with the rest of the calculations.

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That’s a bit scary; our latest lightship survey has changed the regular 37T above the funnel to 113T above the funnel.
That is after the scrubber system was removed.

I like these:

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After a lengthy and exhaustive 2 minute google search I couldn’t find a pic of the first one I used, a 1960 vintage Loadmaster with big spinny knobs for each set of cargo tanks. This is the new and improved version that was on our “new” ship:

The Loadmaster was a pain to use, we didn’t carry a wide variety of products (all black oil) so we most likely had a cargo plan that closely matched our new orders, if we had to do any calculations, we did them by hand as it was usually easier than the Loadmaster. When we got our first computer onboard (1985, IBM XT) I wrote a loading spreadsheet with Lotus 123, if I started loading and went to lunch, it was almost ready to go by the time I got back.

With a crude tanker like the W. Alton Jones there wasn’t much need for a Ralston. In Mena al Ahmadi we were topped off in 12 hours to the mark and that was it, unloading in Philadelphia took 24 hours.

It was a different story on a product tanker I sailed on, with all kinds of different special oils like tallow which had to be heated, also very expensive sewing machine oil! Cargo planning was in that case important and then the Ralston was useful in dividing the different parcels over the 33 tanks.

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On a tanker very similar to your picture we used a Kelvin Hughes instrument for bending moments and sheer forces. I only used a Ralston with a general cargo ship. The loadmaster that Mr Cavo described with the knobs I used on a handy sized bulk carrier. The loading calculator I used on a container vessel was massive, time consuming and expensive. The next ship had a piece of rubbish with a thermal printer.
I then found myself in the fortunate position to recommend a PC based system that was class approved and became standardised throughout the fleet.

When I sailed on an ATB in the mid 80s, the mates used to calculate the upcoming cargo (usually different grades of gasoline and diesel) by hand. After about a year, we got one of those Compaq PCs with a loading program on it. Saved those guys hours of number crunching. I used it to keep my resume updated. . . . oh, and my yard list, too.


Those drug store loads were a pain. Especially to discharge them and keep an even keel for multiple discharge ports. Started as a tankerman in my teens, all calculations by hand/paper. 3 different grades of gas and kerosene and diesel thrown in the pile. By the early 80’s or so those loading programs on the computers were a great relief, By the time they came out, I was Captain and and working on much bigger shit. A multiple load/discharge tankerman was much more valuable than a straight load dude with one discharge port.

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