Type a line (B1 0 P -3 T -5 S -2 B2 -1 in 0.01 mm) or fill in the fields: the line and the fields stay in step.
Several cylinders: separate them with a semicolon, or write cyl 1, cyl 2 before each.
Enter the dial gauge readings taken between the crank webs as the engine is turned, B1 and B2 either side of bottom dead centre, P at port, T at the top and S at starboard, and the calculator gives the vertical and horizontal deflection in your unit and in mm. For several cylinders it draws a table and a chart of the vertical deflection and shows which cylinders are over the limit you enter. It shows the working with your numbers, and gives a line you can copy or add to a request.
No limits are built in, neither maker limits nor rules of thumb: compare with the engine maker’s deflection limits for the condition, engine hot or cold, ship loaded or in ballast. The calculator does not work out the alignment or the main bearing loads, and reads no meaning into the sign of a deflection beyond the convention it states.
At bottom dead centre the connecting rod would foul the gauge, so two readings are taken next to it, one either side: B1 and B2. The bottom reading is their mean, B = (B1 + B2) / 2. With B1 0 and B2 -1 (in 0.01 mm), B = -0.5.
The top reading less the bottom one. With T -5: -5 - (-0.5) = -4.5, or -0.045 mm. For several cylinders the vertical deflections go into the table and the chart, with the limit entered.
The starboard reading less the port one: with S -2 and P -3 it is -2 - (-3) = 1, or 0.010 mm. Conventions vary: some record sheets write P - S, the same figure with the opposite sign, so use the one in the engine maker’s record sheet.
| Quantity | Relation | Note |
|---|---|---|
| Bottom reading B | B = (B1 + B2) / 2 | two readings either side of bottom dead centre, where the connecting rod is in the way; one bottom reading is used as it is |
| Vertical deflection | T - B | the top reading less the bottom one |
| Horizontal deflection | S - P | the starboard reading less the port one; some record sheets write P - S, the same figure with the opposite sign |
| Five figures without letters | B1, P, T, S, B2 | the order in which the calculator reads them |
| Units | 0.01 mm; 1 in = 25.4 mm | the dial gauge reads in 0.01 mm; figures without a unit are read in 0.01 mm |
| Limit | a figure, in its own unit or in the unit of the readings | the size of each deflection is compared with it; no limits are built in |
The readings are taken with the sign the gauge shows. What a positive deflection means, the webs opening or closing, depends on how the gauge is set and read, and conventions vary between record sheets, so the calculator reads no meaning into the sign: check it against the sign convention of the engine maker’s deflection record sheet.
The method, five readings per crank with two of them either side of bottom dead centre because the connecting rod is in the way there, the bottom reading as their mean, the vertical deflection as the top reading less the bottom one and the horizontal deflection as the starboard reading less the port one, is described in independent marine engine inspection and maintenance references. They also say that the deflection limits are the engine maker’s, and that the engine temperature, the loading and the draughts are recorded with each set. Sign conventions vary between engines and record sheets, and some write the horizontal difference as P - S, so the calculator states its own convention. The dial gauge division of 0.01 mm and 1 in = 25.4 mm (exact) follow unit references and gauge descriptions.
In two differences. The bottom reading is the mean of the two readings taken either side of bottom dead centre, B = (B1 + B2) / 2. The vertical deflection is T - B, the top reading less the bottom; the horizontal deflection is S - P, the starboard reading less the port one. With B1 0, P -3, T -5, S -2 and B2 -1 in 0.01 mm: B = (0 + (-1)) / 2 = -0.5, the vertical deflection is -5 - (-0.5) = -4.5, or -0.045 mm, and the horizontal deflection is -2 - (-3) = 1, or 0.010 mm.
Because the connecting rod is in the way: at bottom dead centre it would foul the gauge, so the reading is not taken there but just either side of it, as B1 and B2 (or bottom port and bottom starboard). Their mean stands for the bottom reading. With one bottom reading the calculator uses it as it is.
That depends on how the gauge is set and read, and conventions vary between engines and record sheets: what a positive figure means (the webs opening or closing) is set by the convention in use, and some record sheets write the horizontal deflection as P - S, which gives the same figure with the opposite sign. The calculator takes each reading with the sign the gauge shows and states its convention, T - B and S - P. Read the result with the sign convention of the engine maker’s deflection record sheet.
With the engine maker’s deflection limits for the condition in which the readings were taken: engine hot or cold, ship loaded or in ballast. The calculator has no limits built in, neither maker limits nor a rule of thumb. Enter the limit in the line as a figure with its unit (limit 0.15 mm), or in the limit field in the unit of the readings, and it shows which cylinders are over it, comparing the size of each deflection with the limit. A limit given as a fraction of the stroke is not taken: enter it in mm.
Because the readings change with it. References on taking deflections ask for the engine temperature (hot or cold), the loading and the draughts to be recorded with each set, and readings taken in different conditions are not compared with each other. The condition field puts that note into the result and the line, so the set can be compared with the previous one and with the maker’s limits for the same condition.
The readings with their positions (B1 0 P -3 T -5 S -2 B2 -1), also bottom port and bottom starboard (BP, BS) for the two bottom readings; five figures per cylinder without letters, read as B1, P, T, S, B2; several cylinders separated by a semicolon, a new line, cyl 1, cyl 2 or 1), 2); or a series of vertical deflections (6 cylinders vertical -5 3 2 -1 4 -6). Units: 0.01 mm, the dial gauge division, which is taken when no unit is written; mm; inch, at 25.4 mm. Words such as hot, cold, loaded or ballast in the line go into the condition. On the Russian page Russian position letters are read too.
The calculator gives the deflections from your readings. When main bearing shells or other parts for the crankshaft alignment are needed, send the line from the calculator with the engine details and a photograph of the nameplate, and Vessel Core checks the details before an offer goes back.
