A ship's chart indicating compass deflection due to ship's iron.

Related Terms


Crankshaft deflection is the difference between the crankshaft webs depending on the position of the crank pin, usually in opposite positions: BDC - TDC and Port - Stbd.

For the purpose of measuring the crankshaft webs deflection, on the inner side of the web recesses should be staked at a distance from the axis of the crank neck equal to: (S + d) / 2, where S is the piston stroke, d is the crank diameter.

A rakemark with a dial gauge with a precision of 0.01 mm to be inserted into these recesses.

Deflections usually measured in 4 positions of the crankshaft every 90 °.

Deflection considered positive and is marked with a plus A sign if the divergence of the cranks' cheeks when the crank neck is located at TDC is larger than when it is at BDC.

Deflection considered negative and is marked with a minus sign if the divergence of the crank cheeks when the crank neck is in the BDC.

If deflection is positive, the crankshaft lowered and this determines the divergence of the webs, i.e. the bearings surfaces are lowered relative to the crankshaft axis, and therefore worn more than others.

With a negative deflection, the crankshaft is raised and the bearings surfaces are located above the others.

Thus, to align the axis of the crankshaft with a positive deflection, main bearings surfaces to be raised, i.e. new ones more thick to be installed, and with a negative deflection, the main bearings surfaces to be lowered, i.e. thinner shells to be installed.

The positive deflection to be eliminated to align the crankshaft axis. These achieved by replacing one or two bearings.

The deflections limits indicated by the maker in the technical documentation for each engine.


  1. The displacement of an electron beam from its straight-line path by an electrostatic or electromagnetic field.
  2. Shape change or reduction in the diameter of a conduit, produced without fracturing the material.
  3. Elastic movement or sinking of a loaded structural member, particularly of the mid-span of a beam.


An ammeter of only moderate accuracy in which the current to be measured passes through a small coil, distorting the field of a circular permanent magnet, and an iron vane aligns itself with the axis of the distorted field, the deflection being roughly proportional to the current.


A pressure-plate anemometer consisting of a plate which is free to swing about a horizontal axis in its own plane above its center of gravity; the angular deflection of the plate is a function of the wind speed; this instrument is not used for station measurements because of the false reading which results when the frequency of the wind gusts and the natural frequency of the swinging plate coincide.


[ENG ACOUS] A microphone in which the motion of a membrane is detected using a light beam reflected from it, either with the aid of an interferometer or by detecting the deflection of the beam.


A voltmeter in which the current, produced when the voltage to be measured is applied across a known resistance, is sent through coils pivoted in the magnetic field of permanent magnets, and the resulting torque on the coils is balanced by control springs so that the deflection of a pointer attached to the coils is proportional to the current.


A pyrheliometer of the bimetallic type used to measure the intensity of direct solar radiation; the radiation is measured in terms of the angular deflection of a blackened bimetallic strip which is exposed to the direct solar beams.


A formal identity between the differential equation and boundary conditions for a stress function for torsion of an elastic prismatic bar, and those for the deflection of a uniformly stretched membrane with the same boundary as the cross section of the bar, subjected to a uniform pressure.


If a load applied at one point A of an elastic structure results in a given deflection at another point B, then the same load applied at B will result in the same deflection at A.


A beam of cantilever design, firmly anchored at one end and with a large deflection under a load. Also known as flat spring.

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