Tartan 3500 Swim Platform Actuator Repair
The Tartan 3500, 4100, and 4600 all shared the same electric swim
platform actuator system, so this article can apply to all models so
equipped.
Purpose: To replace stripped actuator gearing in the linear actuator of the
swim platform (the units are no longer available). The linear actuator is a
DC motor and a gear head that holds a straight rack against a small pinion
gear (see diagram below). I also moved it to a position of better mechanical
advantage so as to reduce the load on the motor and its gears when raising
and lowering the platform, but I later calculated (and got a reference from
T3500 Intuition) the low amp draw and realize that this is not really
required.
SIDE
SECTION/
VIEW
transom
pla
tf o
rm
sw
im
section of hull,
approximate
rack, shown
extended and
retracted
platform bracket
actuator new
position
swim platform
actuator old
position
old actuator
position holes
& rack slot
shown in green
actuator, new
position, seen
through hull
step
top of
swim
platform
platform
bracket
swim platform
bottom step
transom
de
r
tr
an
so
m
limit switch
un
platform hinge
point
VIEW
FROM AFT
recess for platform
limit switch
up
Sketch of swim platform
layout on 'Catcher' (#131)
showing original actuator
position in green dotted lines,
and new, raised position
in black solid lines
Tartan 3500 Swim Platform Actuator Repair
Causes: The linear actuator stopped lifting my swim platform, a problem I
have heard of from several other owners of T3500’s. The motor turned, but
the swim platform did not move. I believe that the system should never be
subject to any additional weight on the platform unless it is completely
down and supported by its guy wires. I have to suppose that ignoring this
constraint is what happened on my boat.
Technique: Tartan has diagrams and instructions available to replace this
electrical system with pulleys and line, but I prefer the original electric
control and it is the repair of this that I detail here.
The actuator assembly is a motor and a gearbox with a pinion gear driving a
captured rack back and forth to raise or
lower the swim platform. It is very simple to
disengage and remove from the hull. The
rack is attached to the swim platform’s
bracket with a clevis pin. The motor/
gearboxs attached to the inside of the
hull’s transom by three 1/4-20 machine
screws, lock washers and nuts. Access to
these latter is through the two hatches
above the transom, aft of the wheel. You
need to be a slim person to maneuver
easily in the space available back there,
but it is really quite uncluttered. You can
remove the manual bilge pump from the
Inside the transom showing the
port side by undoing the 4 screws in the
three actuator attachment bolts
access plate in the cockpit; this gives more
and the rack aperture
room. You will also need someone on the
Tartan 3500 Swim Platform Actuator Repair
outside to turn/hold the screws
(Phillips screwdriver), kneeling on
the swim platform, while you are on
the inside of the hull holding the
nuts with a wrench and prepared to
hold the actuator when it is
released.
Laura in the aft lazarette hatch
The Hatchmasters model 39B actuator used on my boat was rated at 500
lbs. Tartan used this unit on “hundreds” of boats. The manufacturing
company went out of business in 2001 but was taken over by a new
company that took the name ‘Hatchmasters’. Phone: 815.336.2034 Fax:
815.336.2112. Address: 21856 Quinn Road Sterling, Illinois http://
hatchmasters.net/
19" rack 16 pitch
view from aft
only one assembly
screw shown for
clarity
outer
pinion/rack
enclosure
inner
enclosed
passageway for
rack
view from port side
shaft cover
mounting
lugs
drive pinion
16 pitch 16T
mounting
lugs
gear box
Company label
motor
1-1/2" 1/4-20 socket
pan head ss machine
screws threaded into
the inner enclosure
Tartan 3500 Swim Platform Actuator Repair
The actuator consists of a 12 VDC motor, a gearbox head (with the
mounting lugs) with a pinion gear and a solid plastic two piece enclosure
around the pinion which constrains the actuator’s rack into engaging the
pinion. The pinion gear is held onto the shaft with a roll pin. My gear was
stripped (gear
teeth missing)
for about 1/4 of
its circumference
and I ordered a
new one (with a
16 pitch (the 20
pitch original is
no longer
available) and so
a new 16 pitch
rack to match as
well) from
Hatchmasters
($80 in 2011, including the shipping). The rack is held onto the pinion by the
two piece solid plastic enclosure which is fastened together by three 1/4-20
ss FH machine screws. Reassembly took about a minute. I greased the rack
(it has to slide in that enclosure) and the pinion gear. Positioning of the
rack is not particularly important, since the normally-closed limit switches
are opened only by the opening or closing platform reaching its limits and
then staying there, and so pressing the limit switch.
Mechanical Advantage: I wanted to move my actuator upwards to increase
the mechanical advantage between the actuator, the attachment point and
the hinge point on the swim platform. However, I now realize that the amp
Tartan 3500 Swim Platform Actuator Repair
draw is so small (because of the low actuation speed)that this is not
necessary. I was able to re-drill the three attachment holes 3.25” higher
before the actuator’s rack enclosure bumped into the underside of the
fiberglass step above it. I enlarged the aperture for the rack a similar
amount upwards too. I did this by drilling 1/4” holes on the inside edge of a
pencil line of my intended cut and sawing between them all with a coarse
keyhole saw. I smoothed the rough edges of this sawed cut with a stone
wheel on a Dremel tool. I cut a small piece of 1/2” thick polyurethane
modeling board to fit in the now unused lower portion of this cutout and
epoxied it in position after painting it a gloss white to match the hull (sort
of). I sealed the edges of the cutout with epoxy too.
Calculations: The optional change in the elevation of the actuator changes
the angle of pull on the bracket on the swim platform. Its fairly apparent
that if we pull on this bracket on the hinged platform, to pull inline with the
platform, even if you are beyond the hinge point, you would not move it
because you have no mechanical advantage. Once you start to pull from
above and somewhere towards the hinge point, you begin to be able to
move the platform. The original arrangement gave an angle of pull that
started at roughly 9° off the horizontal where the initial and hardest pull
happens. Moving the actuator up 3-1/4” changes this initial angle to about
20° off the horizontal. The difference in the pounds force required to lift
the swim platform from the original actuator position (856 lbsF or 3,800
Newtons) to the new position (525 lbsF, 2,335 Newtons) is significant but the
amp draw is pretty small to begin with (see below). The actuator is rated at
500 lbs force.
Power used: What this means in terms of power used, is always in
proportion to the time it takes to do the work. It takes 23 seconds to raise
my platform and 20 seconds to lower it. The actuator is only moving the
Tartan 3500 Swim Platform Actuator Repair
rack about 0.25m (10 inches). I watt = I newton/meter/sec. To get a result in
watts I have to multiply the Newtons by 0.25 because of the shortened
‘stroke’ and divide by 23 because of the time it takes to perform the work.
So now my 3,800 Newtons has become 41.3 watts. At 12 VDC (Ohms law:
amps=volts/watts) I have 0.29 amps required at 100% efficiency. I am
guessing we’ll get a lot less than that, so I expect about an amp.
On ‘Intuition’ (ex ‘JetLag’) T3500 #115, Don’s swim platform, still all original,
the actuator barely pulls half an amp even at the start of the pull, so I can’t
think it is under-powered even in the original, mechanically-challenged,
position. From this, maybe the actuator has a 50% efficiency.
With the new position of
installation and in reseating (and spraying with
8;8<*%2-&!#/%)
VZLWFKDW¶RII·
corrosion protection) all
$2*+%,-+-)#
./+/#*0(/#"13
the spade connections on
2.!#4%&+*$2
the DPDT operating switch
!"#$!#%&
(which were another cause
'%()*+%,-+-)#
of non-operability) the
./+/#*0(/#"1
56*789********)-:!#/,current draw on lifting the
2%0/#/,-0
swim platform with the
actuator is now just less than 4 amps on Catcher (as measured at the DC
panel) indicating excessive friction or binding. When I loosened the screws
on the pinion/rack enclosure, the draw fell to less than an amp.
!"#$%#&'()*'*+,(-*%,'%.
Limit Switches: The down movement limit switch is centered, just below the
closed platform and opened by what resembles an acorn nut on the lower
edge of the platform when it rotates into position against the transom. The
up movement limit switch is within the pocket the platform nests into
Tartan 3500 Swim Platform Actuator Repair
Showing the lower limit switch
and the upper one
(upper starboard side) and is opened by the surface of the platform
hitting it.
The operation switch on the boat’s transom is a momentary
on-forwards, off, on-reverse, so the motor stops when you take your
finger off the switch and cannot go further, whether up of down, when the
platform has reached position and opened the limit switch.
Summary: the removal, repair and re-installation is very easy. Don’t put
ANY weight on the platform until it is all the way down, resting on its guy
wires.
© Philip Roberts 2012 Palo Alto, CA
©©˙∆˚¬∆˙ƒ¥©∫