Boating and Sailing.pdf - Moja ladja

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Part 2: The Basics of Operation
Time to Trim Out
Trim out (push the top of the trim button) when the boat is on plane and you want to go
faster. This causes the lower unit to tilt away from the transom. Trimming out raises the
bow and rocks the boat back onto the aft third of the bottom, the surface designed for
most efficient high-speed running in a planing hull.
Boater-ese
Negative trim is when
the lower unit of an outdrive is
tilted in toward the transom.
Positive trim is when the lower
unit of an outdrive is tilted away
from the transom.
With the bow forced upward
by trimming out the twin
outboards, this Monza can
get anglers offshore in a
hurry.
(Photo credit: Haber & Quinn)
This reduces what engineers call the wetted surface,
the section of bottom in contact with the water, and
consequently cuts drag and improves speed and fuel
economy.
In the extremes, as in high-performance bass boats and
racing boats, the front half of the boat is actually out of
the water. On family boats, the front may just touch the
surface, but it’s not plowing along as it would under
zero or negative trim.
It Ain’t Flipper—Stop Your Boat from Porpoising
The higher you trim the bow, the faster the boat will go until you overtrim, at which
point the prop and speed can’t support the bow and it falls off, or drops the bow back to
the surface.
This creates fore-and-aft rocking called porpoising. In the extremes, it’s a bit like riding a
bucking horse. You stop it by trimming in a bit, or by giving more throttle, because the
faster you go, the more weight the combination of engine power, prop, and hull design
can support.