91. Circuit
Protection
In the 12 volt system, circuit protection was relatively simple. AWG 8
cables lead from the battery to the ammeter and on to the ignition switch, via an A series single
toggle circuit breaker rated to 50
amps. The downstream devices all work off the distribution panel which
is fused on each circuit, except for the navigation lights, horn and
bilge pump, which are all protected by in-line 5 amp glass fuses. In
other words, the circuit breaker is rated at about twice the maximum
load it will be expected to carry, and the cable is rated at well over
three times the expected load. The same applies to the devices, all
protected by wiring rated well above the load, and by conservatively
sized fuses.
The A series breaker (left), and the T class fuse block
and fuse (right) taken from the Blue Sea website.
In the drive system, the Perm motor can sit happily on 110 amps input,
but I am advised that the controller should be limited to an 80 amp
output to save excessive draw on the batteries. So it would be tempting
to use a 150 amp circuit breaker in this circuit. But there aren't any
commonly available ones which handle 48 volts. Those that do are often
provided with considerable delay mechanisms so that they do not trip on
current inrush, associated with such things as winch or starter motor
use.
Most of the high current
fuses are similarly restricted to voltages less than 48, with the
exception of the T class fuses which can handle 160 volts (at a price,
of course), and have the advantage of very rapid action and high
safety margins, with an interrupt rating of 20,000 amps.
So, what exactly are we trying to protect here? The controller will
have its own fuse, which will be in the vicinity of 300 to 400 amps
because that is the short burst current of which it will be capable,
even though it will be set lower for constant use. That then leaves
only the cable and the contactor, if there is one, which need
protecting. AWG 2 cable of the type I am using is rated to about 200
amps, so the breaker needs to open before then, but not so
instantaneously that it becomes annoying. A delay would be reasonable,
such as occurs in an anchor winch for example.
There is a series of breakers which can do the job in this case, the
Carling C series breakers can be rated for 100 amps, with trip current
of 135, and a voltage of 65 volts. Provided the contactor fits in with
this profile the Carling would be perfect for the job.
So, the drive system circuit will be as follows:
Battery positive
AWG 2 red cable
Battery switch
AWG 2 red cable
Circuit breaker 100 amp, 65 volt
AWG 2 red cable
Ammeter shunt
AWG 2 red cable
Main contactor
AWG 2 red cable
Controller with fuse
AWG 2 red cable
Motor
AWG 2 black cable
Controller
AWG 2 black cable
Battery negative
Depending on the controller chosen there may need to be a reversing
contactor in there too.
The smaller 8 gauge cable of the 12 volt system enters right
and joins the small circuit breaker, then leads on to the small
ammeter. The battery selector switch is wired with 2 gauge, and its
common outlet leads to the big circuit breaker, and then
on to the shunt for the big ammeter.
The 12 volt system is as follows:
Battery positive
AWG 8 red cable
Circuit breaker 50 amp, 12 volt
AWG 2 red cable
Ammeter 50 amps
AWG 8 red cable
Positive bus
AWG 16 red wire
Unswitched devices plus ignition switch
AWG 16 coloured wires
Distribution panel
Switched devices
AWG 16 black wire
Negative bus
AWG 8 black cable
Battery negative
All circuits are closed, (ie. nothing returns via the engine block to
earth), and there is no separate ground circuit. If the boat were to be
recharged from an AC source while still in the water I would think
about adding a common grounding point, but that would involve bonding
all the through hull fittings, zincs, shaft etc. As it will only be
recharged on the trailer I think it is unnecessary. Mind you, if the
eventual decision is to take the 48 volt option, that will mean that a
qualified marine engineer will have to sign off on the installation,
and that might mean that all the bells and whistles have to be
included. 36 volts is sounding good to me.
Top of Page
92. Lagging the Cockpit
One of the important principles in electrically
powered boats is the preservation of lightness. Electric motors are
already at a disadvantage because of the weight of batteries that have
to be carried, (although this is offset to a degree by the much lighter
weight of the motor than a diesel engine). But in order to get the best
performance from the motor, the load has to be as light as possible
too.
I have been concerned for some time by the increasing mass of the boat,
and have begun to think that 24 volts will not deliver enough power for
her, so in considering cockpit lagging I want to avoid any heavy
timbers at all costs. The use of a light weight wood like Obeche is
appealing, but it is not readily available here. Western Red cedar
could work well, but so could hoop pine, which is used in this country
for the manufacture of marine ply. It is very pale, like Obeche, light
and moderately durable. Huon pine would be ideal, but it is all but
extinct now, and very expensive.
Whatever is chosen, the use of solid timber for the lagging means that
there would have to be expansion gaps, and all the work that that
involves, but the thought occurred to me that strips of hoop pine ply
could be used, provided that they were hardwood edged. There would then
be no problem from expansion, no problem dimensioning lumber to the 10
mm. thickness required, and no waste from resawing. Furthermore, the
use of a contrasting edging, such as mahogany would give a striking
look to the cockpit, which could be echoed by the use of contrasting
strips for the decking.
There is, of course, the slow and tedious business of edging the ply
strips, but while that is progressing I can get on with my Bugatti. So,
hoop pine it is. The beading has to be altered a bit from the original
plan, so as not to expose the deeper ply layers. Only the mahogany is
beaded, and it is shiplapped to keep the strips aligned properly.
The laying begins at the forward edge of the rear seat. The first
strake is laid at a slight angle to the perpendicular, leaning back a
little to give a racier look to the cockpit, remembering, however, that
the greater the rake angle the less space will be left on the sole for
feet, etc., especially at the forward end.
Because it is ply being
used, the strips can be glued to the frame, not screwed, but that means
that each piece has to be laid sequentially, giving time for the glue
to set before moving the clamp on the hold the next piece. If you are
in a hurry you could use screws.
The cleat on the sole to which the bottom end of the lagging strips
attaches is not in position yet. I want nearly all the strips to be
lined up to get a fair line for the cleat, but before the strips can be
cut to length there has to be an approximation of the cleat position
available to work from. It does not matter if the lagging is a little
bit short, as it will be covered by kickboards anyway.
93. Glove Boxes and Speaker
Boxes
The opening for the rear glove
box is in the lagging strip just in front of the seat. Because it is so
wide the relatively stable mahogany is suited to being used for that
strip in the traditional boats, whereas the lighter timbers used for
the rest of the lagging might split if they were used in such
dimensions. To reproduce the look of the mahogany I am using some
myself, and behind it there has to be a box to house the contents.
The bottom of the box sits happily on top of the intermediate
longitudinal stringer, and a cleat is added to its forward end to
attach the vertical. It is left open behind so that all the space next
to the seat behind the lagging can be used, but if the back of that
space proves to be unreachable it may have to be shortened.
The base and front wall of the glovebox are suspended on the
stringer.
The mahogany strip is fitted over the top and the lagging continues
forwards.
The next lagging strip is really
the last one which can be fitted without some landing point on the sole
being defined. The bottom ends of the lagging strips are beginning to
splay away from each other, making cutting and fitting more difficult.
So a piece of Oregon is cut to length and forced into a fair curve with
the use of spacers. This can be left for a few days while the other
side of the boat is lagged up to that level. Then it can be screwed and
glued to the sole panel.
Before moving too far ahead though, there has to be some provision for
the speaker box which will open in the mahogany strip below the
stringer, and holes of the appropriate size have to be cut in the
mahogany as well.
In order to get orifices the same shape and size on both sides I will
make up a router template and cut them with a template following bit.
The cleat for the bottom of the lagging is bent into shape.
Sprung battens hold the cleat down while the glue dries.
With the cleat fixed to the sole panel it is time to tame the lagging
strips. They are screwed to the carling and the sole cleat. That allows
the triangular gap behind the mahogany strip to be filled as well.
All strips are parallel. The apparent sun ray pattern seen
here is an
artefact of the focal length of the camera lens. A piece
of scrap hardwood here represents the kickboard which will eventually
go along
the sole.
I am not concerned about the
mahogany and the strip behind it not meeting perfectly. Later, when the
fiddle for the seat is added, it will push the mahogany into its
correct position. But before it does, I am taking the opportunity of
installing a pair of courtesy lights on the front of the seat, where
they will be concealed under the fiddle.
Concealed courtesy light on the rear seat...
and the light it provides.
With the seat cushion-retaining fiddle.
From this point forwards another sole cleat is needed. It is important
to continue the curve established by the strips already in place, so a
batten is used to establish a fair continuation of their line on the
sole.
The dark coloured batten marks the position for the next
cleat.
The second cleat is held in the marked line, and glued down.
The lagging now continues past
the old bulkhead D remnant and into the driver's compartment.
The forward glove box cover will
soon have to be placed, but it will be by trial and error to find its
best location in relation to the driver's seat. I think it probably
needs to come in about here:
Another day, another lagging strip. Here is the forward glove box cover.
With the completion of the starboard lagging, the port side is begun,
and an impression can be gained of the eventual look of the cockpit.
The speaker boxes
are, by necessity, limited in scope. There is very little room behind
the baffle to house even the hardware, let alone any cabinetry. So I
make an enclosure using the hull side as its back, and I pack the
cavity with acoustic felt lining. The baffle is attached behind the
sole cleat and intermediate stringer, so that the mahogany cover can
obscure the Ninja weaponry which passes for a grill on these speakers.
A
plain aperture mesh will fill the hole in the cover to return the
system to a more conservative appearance.
The port forward speaker pair housed in their baffle.
There is not much room back there behind the stringer.
By the way, I have found a tool which makes these circular cut-outs a
bit quicker. The maximum diameter is 5 inches, but if you take the
spurs off and invert them, and then turn their holders around you can
get quite a bit more. However, it is really poorly made, of low quality
steel, and will go dull quickly. It is also one of the most dangerous
tools I have ever used, and is only suitable for a drill press,
although the packaging does not say so. I suspect that it is made in
China, or one of the numerous other sources of gadgetry rubbish, and
after I have used it to cut the four holes in the speaker baffles, I
intend to throw it away, as I did with the last one I owned. Trying to
sharpen this pig iron would be pointless.
The "take your life in your hands" hole cutter.
If you survive the hole cutter
you should end up with a baffle which fits neatly into the space
between the sole cleat and the stringer, to be covered by the mahogany
plank.
Port side forward and stern and driver's
side forward speaker boxes.
94. Lagging the Dash
Bulkhead
Using the same edged lagging
strips as were used for the cockpit sides, the dash bulkhead can be
covered between the central console and the sides. The starboard side
of the bulkhead presents a slight obstruction to that, as there are
bolt heads sticking out of it which are helping to hold the helm
mounting box in place. They could probably be removed, now that the box
has been epoxied onto the bulkhead, but I feel safer with them still
there. There are also four smaller screws locking the steering column
holding block onto the bulkhead, but this has been epoxied to the
bulkhead over its entire surface, so they can be dispensed with.
The bolt heads are about 3 mm. deep, and they are sitting on top of 1
mm. washers. So there has to be a 4 mm. rebate cut into the back of the
lagging to accommodate them. That cannot be cut with a forstner bit
because of the central spur which would penetrate the front surface. A
router will be needed.
The bolts for the helm mounting box.
Further complication comes from the angle at which the steering
column penetrates the bulkhead. This angle has to be reproduced
precisely in the lagging to avoid unsightly gaps, although some sort of
decorative escutcheon may go there later. Also, the placement of the
lagging strips in relation to the column needs consideration. It will
be necessary to have one strip closing in on the column from each side
and meeting its partner from the other side in the midline. The strips
are 110 mm. wide. The column is
centred 137 mm. from the edge of the central console, so the first
strip beside the console will have to be cut down to 82 mm. wide. That
will look better than starting
with
a full width one next to the console and
having
the
column penetrate its neighbouring strip eccentrically.
Finally, how does one attach these strips to the dash bulkhead? They
are too thin to be screwed in from behind, and there is no way to clamp
them while glue is drying. The solution is contact adhesive, preferably
marine grade. Bostik 1431 is suitable, and should be readily available
here. But you get no second chance with an industrial grade contact
adhesive, so all the strips will have to be cut and fitted first ready
for that permanent grip. Prior to that they can be held temporarily
with double sided tape, and that will have to be used on the outer
strips, which will be meeting the side lagging at odd angles and
lengths.
A
small piece of mahogany edged ply is introduced under the dash console.
The edging has been bevelled upwards so that the shaft seal hatch can
be lifted. This created a continuity for the ply lagging on the
bulkhead outside the dash console, although it will only ever be seen
when the door which is to cover these switches is opened.
Taken prior to the
cover plates for the circuit breakers
being fitted.
With left over pieces of lagging I can begin to cover the rear seat
support as well. This will give a uniformity to the cockpit without
adding a significant amount of weight.
While I am waiting for glue to dry on the
edge banding of these lagging strips, I can finish off some odd jobs,
such as covering the circuit boards in the motor compartment.
With most of the work behind the
dash now completed, it is time to finish the joinery for the console
itself. A piece of 350 mm. wide mahogany is split down the longitudinal
middle, so that I can put it through my thicknesser, and then glued
back together again. The bottom of it is used for the door over the
lower two compartments, while the upper portion will have a cut-out and
will act as a frame for the visible instruments.
Only time will tell whether this door will be stable enough not to
warp. If
it does it may need to be replaced with a standard panel and frame door
later. It still needs 5 mm. cut off its bottom, to allow for the
carpet, and its edges need to be rounded to make them more touch
friendly, but this is fundamentally it. A magnetic catch holds it
closed, and a small chromed handle finishes it off.
What a pity it is that is is impossible to
get good quality hardware
for jobs like this. You can get good hinges in brass, with a lot of
effort, but never in stainless steel or chrome The hinges I installed
here had to have sloping mortices cut (deeper at the pin end than at
its opposite) because the leaves of the hinge are not half the
thickness of the pin. They are thin and scratched bits of beaten metal
which testify to false advertising from the company which makes them,
and
refers to them on the packet as "superior quality". Even the steel is
only 304, so how do they justify such an outrageous claim? The first
job of a quality butt hinge it to have the sum of the thicknesses of
the leaves exactly the same as the thickness of the pin side. Then you
can use a router to cut the mortices, and have the leaves line up
perfectly flush with the timber. As it is, installing these ones by
hand
with the sloping mortices took half a day! Superior quality my arse.
The upper section of the console has the frame around the instruments.
In order to rout out a suitably shaped window I make up a template
based on the dimensions of the window, minus 8.5 mm. all around, which
is the measurement of the distance from the far end of the router bit
to the template, when the copying ring is engaged.
The template for the frame window.
I had intended that
this template would serve as a template for the glove box openings as
well, but it will be too big for them. I could cut it down a bit more,
and use a larger copying ring for the dash frame and a smaller one for
the glove boxes, but I think a more suitable shape can be found for the
boxes. I might just use this for the dash, and make another for the
boxes.
The template, the cut and the finished frame.
The last piece of the dash console to go in will be the cap, which will
cover the small gap between the bulkhead and the top of the template
through which the instruments are suspended. The gap has been useful,
because it transmits the wires for the forward cockpit lights and for
the spotlight from the distribution panel to the cockpit. But now it
has to be closed to insulate the cockpit from the sound of the motor
compartment, and perhaps some of its heat too. A narrow strip of
mahogany with two fenestrations in it for the wires will sit on top of
the side frames of the console, and its front surface will be covered
by the instrument frame. The only complicating factor is the hand wheel
for the spotlight which may be too tightly impacted by these
structures, but that will have to wait until the light is actually
fitted over the full deck.
The frame is screwed in from behind, and is held in position
by the clamp while the screw positions are marked.
I had not intended to
have a two tone dashboard, but it does look quite natty in a 1930's
style. However, the mahogany will darken in time and would look out of
place, being darker than the pine, but lighter than the Cetol coated
wood. So I will put a finish on it.
This completes the dashboard, so the next step is continuing the
lagging from the side to the dash bulkhead, starting at the steering
column.
Here is where you thank
yourself for not rushing in the glue up the subdeck. Now, I can unscrew
a section of it to allow the dash bulkhead lagging to stick up above
the level of the top frame, and thereby making scribing and fitting a
lot easier.
Two lagging strips poke up above the top of the bulkhead.
The two strips are
shiplapped for joining and placed on the drill press together to cut
the hole for the steering column. The hole is placed a fraction higher
than it should eventually be, because the strips are not yet routed to
accommodate the bolt heads which will lie under them. When they are,
they will sit a little further forward, and hence a little lower
towards the sole, and any gap will be taken up. Then their tops will be
scribed.
But first, the gap between the
dash console and the inner lagging strip has to be filled with a
partial strip. Only then will the inner side of the left hand one,
above, be guaranteed to be parallel to the console.
Fitting the lateral strips is even more demanding than the inner ones,
because not only do they have a diagonal cut on them to meet the side,
but they also have to be notched to fit under the deck stringers. So
progress is slow with trial and error fitting. Eventually the starboard
side is complete and the work moves to the port, which is a bit
quicker because there is no steering column.
Starboard side dash
lagging is cut and fitted.
While waiting for
glue to dry I have started to put the finish on the sole panels.
At this point I
cannot do any more lagging until I finish the port side, as the dash
strips butt up against the side ones. Behind the port lagging is the
exit point for the bilge pump hose, so I have to bite the bullet and
drill a hole into the hull side for the through hull fitting. It seems
that everybody who builds a boat feels some trepidation at the point
when they have to cut a hole in the hull, and this episode is no
different, even though I have already done so with the shaft. The
fitting is a stainless steel flange with a tightening nut, and a
backing board is necessary for it. It seems like a sensible idea to
attach the board to the hull, and then drill the hole through both, so
it is back to the epoxy.
The through-hull for the bilge pump. It is placed where it
can be reached from the glovebox on that side.
As far as I can go with the dash lagging until the side is finished.
While I have it mixed I might as well go about
fixing some of the floating fittings, such as all the electrical
conduit joints, and a lot of the forward deck stringers, which are just
sitting in their mortices at the moment. Clearly, a lot of the boat
will have to be dismantled for all that, so I will make that a job to
continue intermittently through
next month. In the meantime I can go about the laborious task of
applying finish to all the lagging and the rear seat, as well as the
sole, and that will take up most of the rest of this month, and into
next as well.
Top of Page
95. Completing the Subdeck
Before
getting too far advanced with cutting subdeck panels, I want to make
sure that the stringers they will be sitting on are permanently fixed
in position. Sequentially, the foredeck stringers are detached from the
windscreen and glued down, and left to set overnight.
A lateral forward deck stringers are glued in.
After the clamps are removed,
and the excess glue is planed off, the joints seem to be perfectly
tight, but, because it is epoxy which is being used it is important for
some of them to have a space for the glue line. This particularly
applies to the forward-most joint where the stringer is laid into the
inner lamination of the sheer clamp. Here, there is no support for the
stringer apart from its wedged fit into the clamp. At the other joints
the stringer is supported underneath by the bulkhead top frames, and
the joints there are very tight. At the clamp, plenty of epoxy is
packed around the joint with the stringer, resulting in a very solid
complex. All this will be further strengthened by the addition of the
subdeck, which will be glued on top of it.
The stringer/sheer clamp joint, showing the epoxy filled gap.
Here, all the
stringers and beams are glued down, ready for the subdeck to be laid.
The ply is first
attached along the stringers which support the hatch structures, and
the outline of the sheer is transferred to its underneath surface for
cutting. Once cut, it is easier to handle, and can be screwed down to
the boat. Again, I will avoid gluing it yet, just in case I need to
remove it; but with the two outer panels screwed in, the shape of the
foredeck becomes obvious.
A section of subdeck being added...
and screwed down to gunwale, stringers and beams.
The same on the other side.
With the hatches put
back there is a gap between them and the subdeck panel. This is because
the panels are cut to share the stringers with other panels, but the
hatches do not need to share. These gaps will be filled with scrap
strips of ply. That is easier than cutting one piece for an exact fit,
and will not affect the integrity of the deck at all.
One annoyance which will affect the deck, however, is the fact that
extra ply had to be purchased for this section, and it has proven to be
a bit thicker than the previous batch. Both are supposed to be 6 mm.,
but the new one is nearer 7. It is probably meant to be 1/4 inch. This
creates steps which will have to be
smoothed over where the old meets the new. Unfortunately, the plans for
this
boat have underestimated the ply requirements by as much as 6 sheets
all together, and very little has been wasted. That is a pity, because
if all the ply had been ordered in a single batch this discrepancy
would not have occurred.
In the end I found some more sheets of the original brand and continued
with the subdeck at uniform thickness. The rear deck required just two
more pieces to seal it, and they were no trouble. Fitting these panels
makes the deck really come to life, and it is an exciting moment when
you can stand back and admire the lines of the boat in their full
complexity.
The second last panel of rear subdeck fits in front of the
hatch.
The last is added, and the rear deck is sealed.
Top of
Page
96. The Choice of Finish
The finish I am using on the mahogany dashboard is
Sikkens Cetol Marine. It is an oil based varnish/stain which has an
orange tint because of the iron pigments it contains to block UV rays.
This helps deepen the colour of the rather pale Fijian
mahogany, and is useful for that. It is very easy to apply, and has a
long flow time, so much so that the instructions advise against sanding
between coats, or only very lightly. Provided that the surface
preparation has been adequate then, it has clear advantages against the
heavier building finishes which do need sanding. Cetol is also easy to
touch up again with an overcoat each year. It has a satin lustre, which
I prefer to the rather too yachty-looking high gloss finishes, and, in
fact, it is one of only two satin finishes I can find which
rate themselves as
exterior grade. (The other is Bondall Monocel Marine Varnish). Despite
the fact that the cockpit is theoretically "interior", is will get full
sun exposure, which is what does the damage.
The lack of sanding between coats may be good for film build, but it
does not take account of dust which may get caught in the wet varnish.
There are 24 hour drying times for the stuff. So, it is doubly
important to do the job in as dust-free an environment as possible.
With these small removable parts that is practical, but my garage is
hardly dust-free, and when the fixed parts have to be finished they may
well need a light sanding between coats. I'll just add an extra coat,
as the company recommends. The satin lustre makes slight imperfections
less noticeable, but in any
case, if you want a gloss finish you just put a layer of Cetol Marine
Gloss over the top of the satin stuff, so there is plenty of time to
change my mind later.
Here, the template panel for the instruments has had two
coats
of Cetol. Fijian mahogany is not nearly as dark as Brazilian, but each
coat
makes it a bit darker. It will never get to match the steering
wheel though.
However, the look of orange tint on pale wood is a different matter, so
the hoop pine of the lagging is going to need another product. Cetol
also comes in "Light", and this may be the best option, but I have not
been able to locate it in Australia. If necessary I can use Monocel,
but that will
mean using Cetol on the mahogany strips and Monocel on the ply. What a
pain! In addition, the Monocel is a true varnish, which needs at least
5 coats to confer any degree of UV protection, so you begin to get that
plasticised look on the wood.
Nevertheless, it is preferable to the deep orange tint you would get on
the pale pine. Once there is a coat or two of the Cetol on the edge
strips I will just cover the whole lot with Monocel.
A single lagging strip has been coated with the Cetol/Monocel
combination.
There is still some yellowing of the pine, but not the deep orange
you get with Cetol.
For the sole, where I do not
want the carpet to be slipping around, I am using Deks Olje #1
matte finish. It is a completely flat finish, which can be glossed up
with a coat of #2 , but I will leave it flat. It is dead easy to use,
and, being a wipe off product, does not mind a bit of dust either.
A portion of the sole with Deks Olje finish.
Deks Olje
finish does not stay that dark. As it dries it lightens and leaves the
panels with a soft, silky lustre with an accentuated grain pattern. It
is almost a pity to cover it with carpet! But, then again, it is only
meranti, and I have learned a healthy disrespect for that particular
timber.
97. The
Throttle System and Controller
Electric motors depend on the
motor controller for their input, and the controller, in turn, depends
on a potentiometer to instruct it in its output. The potentiometer (or
"pot box") can be controlled by a conventional control lever, the sort
which would normally be connected to a throttle. Only a single lever is
required, and it can be discretely located on the side of the cockpit.
Depending on the type of motor controller used, it
may be necessary to
have a reversing contactor in the system, and it is possible to connect
the control lever with two cables, one to move the pot box, and the
other to activate the reversing contactor. Some controllers mange the
reversing process without a reversing contactor, but they still need a
switch to change from forward to reverse rotation.
Fortunately, however, there is a
simple solution offered by Solarboat,
which
incorporates a lever and potbox all in one, and one which acts
like a joystick, producing forward motion with a nudge forwards and
reverse with a pull backwards. It communicates with the controller via
a Cat 5e computer networking cable.
The
Solarboat
"wig-wag" type of throttle for twin engines(left), and single engines
(right) shown with a 49 mm. lens cap.
This mechanism can
be adapted to work with any handle via a pushrod system, and it does
away with the need for a separate cable to activate the reversing
switch, by the simple device of knocking off some of the teeth from the
plastic cog wheel. Where they are missing, a spring loaded lever
can move and activate the switch, and where they are present the lever
moves back and deactivates it. It is, however, quite delicate compared
with the traditional control levers, and needs a light touch so as not
to damage it. There is a slight detent position when the switch begins
to disengage, and the position is at slow ahead. If a stiff external
lever is used the instructions warn that the detent may be missed and
the throttle may be damaged by being forced past its stops.
Whichever mechanism is chosen,
it is clear that the cabling or wiring must run
through the space behind the cockpit lagging, and through the dash
bulkhead. So, before the lagging is completed in the driver's section
of the boat the throttle system has to be in place.
The throttle I have is based on a 5K ohm potentiometer. At highest
resistance it is actually 4.45K ohms, and 0 at minimum. The controller for which
this is set up is a Sevcon Millipak 4Q, and the unit will be
calibrated to see anything over 3.5K ohms as an instruction to produce
zero output to the motor. This ensures that there is a "neutral"
position available on the lever which is not so sensitive that any
slight deviation in the lever's position results in either forward or
backward output.
For those with an interest in the electronics of the controller I
include the manual in Acrobat reader format, here: Sevcon
Millipak. Part
of
the reason for choosing this controller is its ability to operate
without a reversing contactor, which allows me to use the wig-wag type
of throttle, and does away with extra switches. But it has numerous
other advantages, namely its small size and its enormous
configurability. Mind you, the calibrator for it is nearly as expensive
as some of the cheaper controllers, and the software program which
allows you to do the same thing with a PC instead, is just as
expensive. When you look at the Alltrax controllers, and note that
their software is free, you realise that the Sevcon is really very
pricey. Luckily, Solarboat will do all the configuration for me, so I
won't need to purchase the extras.
On the subject of contactors, there does need to be a main line
contactor used with the Sevcon, and it is possible to use a 24 volt
coil, no matter what the voltage of the battery system, as the
controller has the capacity to chop the input voltage so that it
averages 24 volts. I had actually been thinking of getting a 12
volt coil and connecting it through the existing ignition switch on the
house battery system, rather than put another switch into the drive
system, but this particular controller will not allow that. It
activates the contactor itself!
That seems odd, that a controller would switch on its own power supply,
but it is part of the safety mechanism that the controller employs. If
conditions are not deemed safe to start up, it won't. So the keyed
switch, if there is one, will merely activate a part of the controller,
which then allows a current through the coil of the contactor, which
then
closes, and sends full power back to the controller to be fed through
to the motor. So, I need a 24 volt coil or higher, which means that it
will not work on my 12 volt key switch. See the wiring diagram for the
controller and contactor here.
Instead of installing a second key switch I could wire the existing one
to the DC converter, so that the switch activates the main batteries,
the dc converter, and the 12 volt, converter-dependent system all in
one. But that would mean that in order, for example, to listen to the
stereo when the boat is not moving, I would have either to have the
main batteries on, or to have wired the stereo independently to a
back-up battery, bypassing the switch. At the moment it is wired to the
back-up battery via the switch. More critically, I could not keep the
refrigerator running without drawing down on the main batteries,
although I admit that if the back-up battery were run down by the
accessories the DC converter would try to recharge the back-up at the
expense of the main batteries as soon as they were turned on. (Since
the back-up battery supplies 85 amp hours, or over 1000 watt hours, it
seems unlikely that it would significantly reduce the main battery
reserve, which will be either 6 or 8 times that amount, fully charged.
But it is possible, and it could only be prevented by disconnecting the
converter from the back-up battery). However, probably the best reason
not to have the accessories dependent on the main batteries being
switched on, is that it would be easy to nudge the throttle handle
accidentally and throw the boat into motion. Only a separately switched
accessory power supply can prevent that.
Another solution: I could use the circuit breaker or the battery
selector
switch as the main on/off mechanism, and do away with the second keyed
switch altogether.
Finally, I mention this just to dismiss it: as a little indulgence I
have installed a remote controlled relay to turn on the cockpit
lighting from a pocket switch. This is to assist in boarding the boat
at night, say from a restaurant jetty, without someone having to get in
first in the dark to turn on the lights. Now it is theoretically
possible to use a remote switch for the main drive system, but there
are two reasons why I would not. Firstly, these remotes operate on
small batteries in the pocket unit, which are liable to flatten at the
most inconvenient time. Secondly, they are made in China, so are liable
to fall apart at the most inconvenient time.
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Problems
shows higher
resolution shots as well.
