Fin Stabilizers
Top left: In this arrangement, a hydraulic pump assembly bolted to a transmission power takeoff provides the most reliable form
of hydraulic interface with the vessel’s engine. Above right: A stabilizer actuator installed on a new vessel shows the heavy,
glassed-in backing plate beneath the assembly. Above left: Once common, crankshaft-driven hydraulic pumps are now rarely
installed, except on vessels that lack a transmission power takeoff port. In order to work reliably, this setup must be precisely
aligned to the engine and rigidly supported, typically by the engine rather than the vessel’s hull.
arrangement was the most challenging part of a stabilizer
pump installation.
While many of these installations are still going strong,
provided they are properly aligned, thankfully there is
now a better, more reliable, and less expensive option.
Many diesel engines and nearly all transmissions are now
available with a power takeoff (PTO) port. This enables
the hydraulic pump to be rotated directly from a gear
within the engine or transmission, which eliminates
the need for couplings, belts, and sensitive alignment
adjustments. Given the choice, particularly in retrofits
to older vessels, gear-driven PTOs are by far preferable
to crankshaft-driven, flexible coupling hydraulic pump
installations. For vessels that lack a PTO drive, it often
makes sense to install a new, rebuilt, or modified
transmission that includes a PTO port rather than drive
the pump from the crankshaft, even if it will cost more in
the short run.
There are a number of caveats where hydraulic pumps
are concerned, and one is particularly relevant for the
boat owner. Although it’s a rare occurrence, if the
hydraulic pump fails catastrophically or if the system
develops a major fluid leak (the hydraulic fluid is the
pump’s lubricant), the pump may seize, which could lead
to transmission damage or engine damage/shutdown.
Remember: the pump is running off a gear inside the
engine or transmission, and if the pump stops, this gear
will either stop or break. You can prepare for this
possibility by having a blanking plate (simply a flat piece
of steel or aluminum and a gasket) made for the pump’s
