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The Gavin needs little or no maintenance (either version), but
there are certain things that should be checked periodically. We
highly recommend that you read and understand this manual fully to
ensure the proper functionality, performance and longevity of your
When all is well with your Gavin Scooter, the motor should NEVER
get hot, it should never leak through the seal, and it should never
need any kind of servicing whatsoever. These are continuous duty
electric motors and are highly efficient.
Any and all questions on your Gavin Scooter should be directed
to George Irvine. George has extensive experience
and makes use of that knowledge base. What takes him seconds to
figure out and minutes to fix, could take the uninitiated days. He
also likes to see how they are doing from time to time and can
easily spot developing problems and correct them. He has all the
parts and special tools to perform any type of job on these, and he
likes doing it.
Access Port Plug
Be sure the access port plug is all the way down before use, or it
could leak hydrogen. If the fittings get disturbed for some reason,
they could back out of their threaded slots slightly and leak. This
has not yet happened, but some people must tinker with things, so
be aware that these are threaded through the lid and must be held
firm from the top when tightening the bolts.
Batteries can be quite frustrating. They will test perfectly and
then fail for no apparent reason. They can not tolerate heat. Do
not store them in your car or in a hot place. 110 degrees F is all
it takes to kill them. They otherwise should get 200 cycles, but we
throw ours away after less than 100, or if the burn test falls more
than 5 minutes short of optimal.
If you get bad ones from us, we can have our supplier ship new
ones right to you. It's best to get them locally so you can take
them in and exchange them. This saves weight in shipping, which
costs more and may damage the scooter.
The other thing to remember is that all batteries off gas - even
Ni-Cads. Never leave your scooter sealed or pull the trigger out of
the water. If you leave it sealed, it may blow up and that can be
extremely dangerous and cause serious injury.
You will need a 24V Battery Charger to charge your scooter
batteries. Sears has one with 12 and 25 volt settings, gel cell
settings, fast, normal or maintain charge settings, an analog
ammeter, 2,10 or 20 max amp settings, etc., and it is in a proper
case for good ventilation and costs about $80 in the automotive
section. The Interactor charger does not offer settings, therefore
allowing no control of the charge process, and is overpriced at
$110. Xenotronics has a high quality charger for about $400, but
the Sears charger is more than adequate.
With the Sears charger, you must be sure the "gel" switch
setting is in the right place or it will put out too much and give
you all kinds of bad signals, not to mention improper charging.
They also give bad signals if the connection is not perfect.
Make sure your charging port plugs are not getting loose or
Brownies has some chargers they found that seem to work. We
ordered one but have not tried it.
To check to see if the batteries are charged if you are not sure
that the charger is telling the truth, put your multimeter on amp
dc and move the non com plug to the amp slot and then clip it in
between one side of the circuit (you will need to jumper the other
side) and turn on the charger. If it will not take current and the
charger is reading voltage, then it is charged. You can check the
charger for volts first and then the battery, then the amps, and
then the resting voltage of the battery.
The connections from the battery are gold and should never cause a
problem. They are two-part connectors that hold the fitting
without pulling the wire - use the handplugs to disconnect. Inside
they have set screws holding the wire, which is tinned with silver
to go against the gold fitting. At the other ends are merely high
temp connectors, crimped and soldered. The charging port is a
simple Radio Shack connector. The wire is all boat cable, #10.
The battery packs need to have their bulkheads spaced properly. The
upper bulkhead needs to be such that the lid can go all the way
down without the O-ring. The nose cone has inserts in it to hold
the top of the battery rods in position so the pack will not move.
You can put a piece of foam in there as well. We do that to keep
pressure on the nose cone when the O-ring is out. See the FAQ page
for more information on balancing your scooter and battery
packs and spacing.
The blades will eventually wear out and the scooter slow down a
little. This is because the holes that are used to control the
pitch wallow out. New blades are 27 per set. It takes a while to
wear them out. I have not personally worn any out, but my hard core
divers have. If there is any other change in performance, sound, or
speed, send us the motor immediately, without passing "go". It is
either perfect, or it is not. If not, we fix it.
The body O-rings are number 375. They sometimes appear "cracked" on
the outside - ignore this. You may never have to replace these, but
they cost about a buck if you do.
We have been testing clutches and have found that there is no set
number of washers that work for any given combination of Arnold
Jackson clutch and motor. The shafts are different on different
motors. The step in the clutches is different for different
clutches. What has to be done is that you have to add enough
washers to clear to top of the shaft, but just barely. The clutch
needs to slip easily; it needs to slip as soon as it touches
anything but water. There is no number of thick washers that will
work. You can check the thickness of the washers with a micrometer.
They need to be .024. The .032 washers are too stiff. Just one too
many washers will not allow the clutch to slip. The .032 are for
the Mako clutch, which slips far more easily and will wear out upon
repeated slippage, whereas the Arnold Jackson clutch is designed to
slip any number of times. The replacement Mako clutch costs about 4
bucks. The replacement Arnold Jackson clutch costs about $120.
CHECK YOUR CLUTCH TO MAKE SURE IT WILL SLIP PROPERLY
You must first check this on the bench with the relay bypassed or
it will fry the relay if the clutch does not slip.
- Open the lid
- Disconnect the positive lead from the motor to the relay,
jumper that leads to the battery.
- Put a jumper on the gold pin in the black socket on the motor
- Hold the prop and touch the black jumper to the battery.
It should slip instantly. If it grabs, start removing washers until
it does not grab.
If you are a weenie, and if you have one of my rewinds, you are
not going to like it if it does not slip - consider yourself
If it does slip properly, or after you have put the washers so that
it slips properly, you are now safe to put it back together and put
it in the water to test again.
- Make sure it will hold with full pitch and with fully charged
Grab it underwater and make it slip and be sure it will
Sometimes it will ride on top of the plate and you just bump the
trigger a couple of times to get it to reseat. I keep mine so that
they nearly slip all the time, and anything that got into the prop,
like cave line, would instantly slip the clutch. To give you and
idea of how it should be set, you should be able to stick any
body part in there with no worries. The Mako needs to be kept
more tight and not slipped intentionally.
Do not add back in more than one washer at a time or you will
lock it up and fry it. The other thing that happens, and this
happened to me, is that if you stall the motor just right, it will
arc on the brushboard and then the whole motor needs to be taken
apart. To avoid this disaster, do your first testing on the bench
where just touching the lead to the battery momentarily is all you
do the first time. I was trying to see what would break and I found
out. It was interesting when I took the motor apart - it was dated
1988. It took me 14 years to have to take it apart.
If you do not have the right washers, you need to get them from
Arnold Jackson, or otherwise all of you get together and designate
somebody to order them and distribute them, or get them from
whomever you got the Arnold Jackson clutch from. While you are at
it, throw away the Arnold Jackson screws and put in 8-32 1 1/4" pan
head Phillips screws.
The latches are sometimes difficult or time consuming to get made,
so don't break them. If you do break them, however, George Irvine
will send you more. Leave the latches closed as the only time they
like to break off or rip out is when they are open. Closed, the
strikes will straighten out before you can sheer those screws, even
in the PVC body. If you mess up the latch holes, you can drill them
all the way through and use a 3/8" ## 6-32 machine screw and some
silicone to hold you over until a new body can be made. Bill Gavin
used to run them through like that, but it is not necessary for
strength, and leaves open that quick fix option if you do mangle
one. The other option for quick fix is to hot air melt the PVC and
put the screw back in. That can also be done with the HDPE parts.
If you do mangle any part, like if you wreck your car or something,
send it in to be welded back together - either version.
When checking connections under the motor lid, be sure to not try
to tighten them without holding both sides of the fitting (remember
they are threaded, and tightening the gold nuts will turn the gold
fitting the other way unless held.) Make sure these fittings are
tight so there is no intermittence in the scooter. If there is,
this is the problem.
Learn how to use a multimeter. Get one from Radio Shack (if you
don't have one, don't tell anyone because that falls into the "too
stupid to dive" category). I am sure you have all seen Pina
checking her backup lights with one before every dive, along with
her primary light and her scooter. The continuity function will
tell you if your reed switch is working, the ohms will tell you if
your relay is welded, the amps will tell you if you motor is
drawing the right amount of current and hence has no problems, and
the volts... you guessed it, will tell you the resting voltage of
your batteries which you will know is what it should be or not. We
need to not be sending me back scooters that need a two dollar
part. We need to find out what is really wrong and then figure out
what to do about it.
If the relay mechanically sticks, well that is an odd one. If it
fries in the on position, this means it took a severe current shock
and that means the motor is broken. Do not keep replacing it and
blowing it. Check it with the meter - relay for ohms, motor for
current, etc. If it the thing just won't work, we get out the meter
and start with the reed. Then check the relay, (which you can hear
click) and then apply current directly to the motor. If the motor
won't run, it needs to be rebuilt. It lost its brush board or the
wires to it. If the relay clicks, the motor will run, but not
through the relay, there is a broken solder joint and you must
re-solder the five points on the back of the board. If the relay
won't click or is stuck on but the reed and motor are ok, then the
relay needs to be replaced. De-solder it from the board and replace
it. The reed comes from any Radio Shack, the relay from any
The nose o-ring should be left out when not in use to reduce risk
of hydrogen buildup if the batteries offgas. The ring should not be
put in within an hour of charging. When you get out of the water,
take out the ring. What happens is that if hydrogen comes out of
the battery through its vents, as it does when charging or really
at any time it wants to where the reaction gets behind, it builds
pressure in the sealed scooter and could possible find its way past
the double O-ring seal on the motor compartment lid.
O-Rings - Motor
The O-rings in the motor compartment are numbers 252 and 256 for
the HDPE and 252 and 256 for the PVC version, or both can be 256 on
the PVC version for a tighter fit for the double seal. These are
the only rings you should ever grease (silicone - but do not use
spray or hydrocarbon sprays as the propellant could ignite later
when you start the motor), but the main thing is to be sure the
O-rings are "alive" and not "dead" (not flat or losing their
resilience). and that there is nothing on them that would cause
them to leak.
Be sure the lid is all the way down before use. When putting the
lid on, it must go down evenly and not extrude the ring anyplace -
you must feel no springing action at all. It is easier to get it
all the way down if you remove the port plug first, and then put
the plug back in after the lid is secure. On the HDPE version, the
fit is even tighter so it is harder to get the lid in all the way.
This is critical, so be sure it is in and sealed.
You should periodically check this compartment with a vacuum hand pump to be sure of its
integrity. You should remove the access port plug after dives and
hold the tail upside down to check for water and to observe any
other problems. The motor should NEVER get hot. If it does, there
is a problem. If the motor gets hot, it will expand the air and
push the lid off. To help ensure that the motor does not get hot,
observe the following:
- DO NOT spray any conductive lubricant into the motor
- DO - Dive a streamlined gear configuration and maintain proper
body position to keep from giving the scooter too much drag for the
Check the motor temperature from time to time when using the
scooter by touching the tail cone. If there is a problem, send in
the motor. Do not run it into the dirt. Do not get lazy and blow
these things up. Do not leave the nose O-ring in when not in use,
transporting or otherwise after use and never seal it after
charging without waiting at least 30 minutes to an hour.
To check the compartment for water after diving, it is best to
merely remove the testing port and check for water, instead of
removing the lid. Every time you remove the lid, it stresses all
the connections unnecessarily. If you do remove the lid, be sure to
keep one hand on top of the motor compartment lid when releasing
the snaps. The lid that has the relay under it. If you allow the
lid to pop up it will pull on the wires from the motor.
The reed switch may be one of two types but we usually choose the
Radio Shack window switch because it is widely available in most
countries, even though there is no reason for one to break unless
you bang it on something with the scooter apart. If you do replace
it, use the same fittings and be sure to sand off the little flange
so it will fit in its hole. The other type of reed switch is one
that is threaded into the tail section. This type of reed switch
you must get from me, but that is no problem. This one lets you
adjust the trigger by turning the reed.
The relay is a 30 amp relay on a custom-made board. For
replacements, either get them from me in one piece or de-solder the
relay and put on one just like it - the part number is on the
relay. Some relays are just faulty and can mechanically stick, but
usually if there is a relay problem it is really a motor problem
that needs to be fixed. Any motor problems need to be sent to
George Irvine for repair or replacement at no cost. Just take out
the motor by removing the four screws and send it to us in a double
box that is well padded so the tail cone does not get damaged.
Scooter - Body Position
The body should be held in a flat position with the neck tilted
back to see and the feet at body level or higher. If you are at any
angle, you are inefficient and will be slower. If your feet are
pointed down, you will be much slower and under unnecessary stress.
You should be able to operate and steer the scooter with one finger
if it and you are properly balanced and positioned. JJ and I ride
these things for 6-7 hours straight with no fatigue of any kind.
That is what you are shooting for no matter how long your dive is.
You should never be fighting the scooter, and length makes no
difference. Pina rides a Magnum Gavin in Manatee with no problem
what so ever, and she is 5'3", 110.
Improper riding of the scooter merely makes it draw too much
current. My motors are set to 57 pounds thrust with a static draw
of 16 amps (that is what the burn times are based on and the
battery condition tests (see the WKPP page for burn testing
details). If you are a good diver, you should draw a lot less
than 16 amps. Speed adjustments allow the team to all move
Salt Water Diving
Any scooter used in salt water needs to be rinsed in fresh water
afterwards. Don't let it sit, as the salt water will leave salt
crystals which will then react with the metal parts and get into
the surface of the motor seal. The way a seal works is by a
molecule layer of water across its face, not because the material
has some magic properties. We use ceramic seals which will not
rust, but will be scored if left with salt on them or around them.
To break in these seals and start the process, we use a drop of
motor oil, but once the scooter is put together, it is not a good
idea to disturb this device.
A rinse in fresh water after diving, followed by a spray of CRC
or WD40 around the area of the seal, will do a lot to prevent any
problems. You do not have to take the props and clutch off, merely
use the little tube that comes with these cans to spray under the
clutch and into that area. The idea is to prevent the cone around
the seal from reacting with the salt and eating away. Eventually
this process will leave the seal unable to hold at its edges, even
if the two seal plates are not damaged. Then the whole motor cone
has to be replaced, which is extremely time consuming.
An easy way to rinse a scooter is to put it in a fill bin and
run it a few seconds (with the pitch turned down). You can also use
a hose and force water in under the clutch.
Most of the snap rings are stainless steel, but even that will
rust out and let the seal spring loose, which will push back the
clutch plate from the shear pin and allow the whole prop assembly
to unscrew. Once in a while that ring needs to be replaced. It is
just under the clutch plate. The snap ring under the seal is hard
steel. That ring needs to be in place or the shaft will have play
in it, causing the seal to leak when you first put the scooter in
the water. There should be no play in your shaft; if there is, that
ring needs to be replaced, which means removing the seal all the
way. The bottom part comes out with an O-ring pick - this does not
hurt it at all. Check your prop set before putting the scooter in
the water and push the whole thing inward to be sure the seal is
shut. Otherwise they will leak a little when you first put them in
before the pressure closes the seal. That is where all the leaks
actually happen - right at the surface when you first put them in
Seal and Clutch Assembly