Seamanship – using the trim tabs
Setting the trim tabs
If I wish to cruise the boat at higher speed
I will slowly open the throttle(s) and at
about 8 or 9 knots will run both rocker
switches bows-down for 3 or 4 seconds. As
the boat accelerates to my cruising speed I
press the front of both rocker switches for
a second at a time about every 5 seconds.
Once the engine is running at my cruising
rpm I observe the boat speed for 10
seconds or so. I then operate the tabs for
one second (either up or down), wait 10
seconds and see if the speed has increased
or decreased. If the speed has increased
I run the tabs bows-down for another
second and monitor the speed. I keep
adjusting the tabs to achieve the
maximum boat speed at that rpm.
Now, observe where the horizon cuts
across the pulpit and use this as your
reference for the future. Just accelerate the
boat using the tabs to put the horizon in
the correct place on the pulpit. Fine-tune
the tabs by observing the boat speed.
If there is any heel, use the tabs
asymmetrically, a little at a time, to
remove the heel. You may have to
fine-tune the tabs again (using both
switches together) to get best boat speed.
If you have a head or following sea, you
may need to adjust the tabs from their
optimum position to avoid burying the
bow. If you are forced to cross a bar with
breakers, then you will need to slow down
and trim more bows-up, or go somewhere
else! Remember that the slower you go,
the less effective the rudder.
In normal conditions, as following
waves overtake the boat its speed will
increase and the bow will drop as the
stern rises – don’t touch the tab switches,
it will all come back to normal. When
motoring into a head sea, the bow will
rise and the speed will drop, again:
leave the tab switches alone and
normal speed will resume.When you moor up
Retract the tabs so that marine growth
on the rams does not destroy the seals
next time they are retracted. This should
become an automatic habit: put it in
your ‘shut-down check list’.Planing hulls
Although the trim of a faster planing
boat will be different, be it shaft or stern
drive, you still need to get the boat on
the plane by trimming the bow down as
you accelerate. You then need to adjust
the trim for best speed as before. In the
case of stern drives, you will be trimming
the drives themselves, as well as the tabs
if they are fitted, but the procedure is
the same.Automatic trim tabs
If you don’t wish to be involved in the
operation of the trim tabs manually, you
can leave it all to an automatic system.
This sets the tabs once it has been
calibrated, although you can use the tabsmanually if you wish. When off the
plane, it remains in a standby condition.
Osmotech (www.osmotech.co.uk/
acs-by-mente-marine) are the importers
of the ACS (Attitude Control System)
produced by Mente Marine (www.
mente-marine.com/acs-products/acs-rp).
You’ll need to contact Osmotech for the
price, but it would seem to be in the
region of £500 plus fitting.
Automatic trim tabs won’t find the best
setting for you, though: you still have to
find and calibrate the best trim for your
particular cruising speed on the day. At
that point, select ‘auto’ and it will then
maintain and remember that trim
attitude. If you change the boat’s load
or want a different cruising speed,
you’ll have to find the best trim again,
recalibrate and then reselect auto, so
you’ll still need to be able to set the
boat up properly in the first place.An automatic
trim tab
control from
Mente MarinePat ManleyPosition of the pulpit at six knots, tabs fully up