July '07
47. The Bilge Runners
48. Consideration of the
Windscreen
49. The Motor Mounts
The point has been reached when I want to
fillet the sole to the hull,
before completing the lagging, so I cannot delay any more the
attachment of the bilge runners to the hull bottom. As well as being
epoxy glued onto the bottom, they are fixed with through-hull screws at
100 mm. centres. As they are averaging 5 metres in length, that means
about 200 screws! I think that electric screwdriver was one of the best
tools I ever bought.
At 5 metres it is unlikely that a single length of timber can be found,
but that is what I thought about the Jarrah for the keel. If it is not
available I will have to scarf the runners from shorter lengths. The
plan calls for dimensions of 18 mm. x 30 mm., so in theory all four
could be cut from the same 150 mm. boards, provided they are straight
enough. Even if they are not, there should be enough persuasion with
all those screws to straighten out even the most recalcitrant warp.
The fixation schedule will be as follows: align the runners in their
approximate location to check for position over the unpainted surface
strips on the hull bottom, and, once satisfied, drill the first screw
hole up through the hull at the stern to land between the outer and
inner transoms. Marking 100 mm. points forward of that hole, but
avoiding obstructions like bulkheads and floors, drill the rest of the
holes up as far as the point where the runners terminate at the bow
end. Clamp the runner to the hull at the transom and drill down into it
from within the boat, and drive home the first screw to pull it tightly
up to the hull. If the unattached end is supported well it may be
possible to continue drilling and screwing like this until the entire
runner is dry fitted. If a helper is available it will speed things up
considerably. The bottom paint of the hull should now be protected from
epoxy by running masking tape strips alongside the runners. Unscrew the
runners. Coat the hull strips and runners with some unthickened
resin, and then some thickened, and re-attach to the hull. Clean up any
squeeze out of epoxy, and, once it has stopped oozing, remove the
masking tape.
However, before beginning with the runners I have to revisit the
floors, and glue them down, now that the sole is lifted again. As each
longitudinal floor is glued in, I add shims to the rear half of the
matrix to raise it all the 3 mm. by which it is lower than the front
half.
The shims are started on the outside of
the floor matrix, and held in by brads while the epoxy sets.
After the outer
longitudinal floor has set the procedure is repeated
for the inner one, adding the next set of shims.
I am also
taking the opportunity to reinforce some of the floor timbers. The
occasional knot has appeared in this wood, despite it being classified
as clear grade, so I am gluing pieces of ply to the affected segments.
They are topped with a hardwood edge, like the sole segments, so as not
to expose a cut end of ply, but only where the sole will be able to be
lifted.
Ply reinforcement of a floor
segment (left), and a finish for the underneath of a sole segment
(right).
At
the same time as these tasks are being done I am using up any spare
resin to finish the under-surface of the sole segments before they are
permanently attached to the floors.
Weights hold down a springy
longitudinal floor, and a clamp straightens a shim.
The occasional
cosmetic procedure can be done too. Here, the rather jagged hole in the
dash bulkhead, which allows passage of the shaft, is improved by a
better looking cover. I will hardly ever be seen, except when the
shaft seal hatch is opened, but I like the look of it anyway. In
addition, the reinforcing strips are being positioned on some of the
floors, and on the port side bulkhead D remnant.
After a coat of resin on the
covering strips.
As it happened, the
only piece of spotted gum I could get my hands on was 300 mm.x 38 mm.,
two and a half metres long. That is enough to get eight strips cut off
the width to be planed down to 30 x 18, with a bit left over. They will
have to be scarfed, but as the runners are going to be glued to the
hull there is no need for an over-generous scarf length. (In fact, they
could equally well be butted I suspect). The board is already face
planed on both sides, but there is still rough cut wood in the middle
of one of the faces. Nevertheless, it is straight enough to be able to
joint
an edge. My planer will only handle 200 mm. in the thicknessing
function, so I propose to cut the board down the centre of its length
as a first step. The weight of the board makes it necessary to set up
some rollers to help the feed, and a ripping blade on the table saw is
an absolute necessity.
The runner develops
a lot of bow when it is cut off the board, but I don't think that will
cause any real problem. The inner runners, nearest to the keel, are
longer than the outer ones, and will need two scarf joints each,
whereas the outer ones can get away with only one.
The question of preventing splintering of the ply arises with the
placement of screws through the hull, and a method I have devised from
working alone is to first use a very small drill bit to make a pilot
hole, then drill part way through the ply from one direction, and
change position to complete the hole from the other side. In this case
I begin from outside the hull, then move to the inside. All of the
screw holes need to be sealed with epoxy before being used, and a
little extra epoxy bog is kept at hand to force down the hole when the
runner is finally being screwed and glued on.
The first scarf joint for the
bilge
runners.
After final dimensioning the
runners are clamped together
in pairs to "discipline" their bow and warp, and hopefully make it
easier to attach them to the hull.
Discipline, but no bondage.
After drilling
the holes up through the hull, the stern end of the first runner was
attached with a single screw in the transom's hollow.
With a helper
drilling down into the runner while I held it fast to the hull, we were
gradually able to fix its whole length. There is something I would do
differently, however, if I had the chance: the forward termination of
the runner is at an arbitrary position somewhere under the motor
compartment. I would choose the terminate it about 300 mm. abaft
where it ends now, because the flare of the hull at this point is quite
significant, meaning that there has to be a lot of twist in the runner.
So much so, in fact, that I had to devise a clamp to hold its position
against the hull, as the screws alone were not sufficient.
Sliding wedges clamp the
forward end of the runner to the hull.
This is not as
easy as I imagined it would be, and it took the best part of half a day
to screw this one runner onto the hull. Now, the hull has to be masked
off with tape, and the runner has to be removed again in order to have
its epoxy applied, and then the whole thing starts over. But at the end
of the day I have a set of screws and washers running down the bilge
plotting the location of the runner underneath.
The second runner
proves a little easier with the experience gained from the first, and
by the end of a second day there were two runners attached to the hull
and the next two ready to go on as well. However, a lack of foresight
when making the cradle for the boat in its upright position has
necessitated a little diversion. The course of the outer runners goes
straight through one of the uprights of the cradle, as can be seen
below. So I have to chip out enough of the top to the offending member
to allow passage for the runner before I can start to attach these
outer ones to the hull.
There is
something unsettling about lying underneath a boat and cutting through
one of its supports, a bit like sitting on a branch of a tree to cut it
off. Nevertheless, all went well, and soon enough there were three,
then four runners on the hull.
As there will
be a few days before I glue the runners on, I have left the masking
tape off for the time being, so that there is no danger of it pulling
off the paint when it is removed.
The time spent
"training" the runner to the shape of the hull is well worth it. When
the time comes to glue it on it is not nearly as resistant to twisting
as it was before, and it proved to be possible to do the job single
handed. I had been worried that to do so would see the epoxy go off
before I had finished, but it went smoothly. The few minor gaps left
after the training of the runner were easily filled with the epoxy,
which formed a comb-like network up through the hull via the screw
holes. Nothing will ever move this runner off this hull, short of their
total destruction.
A minor gap at the front end of one of the runners, showing the
epoxy bridge.
Top of Page
48. Consideration
of the
Windscreen
I have come to regard the
windscreen of the slipper launch as the pivotal factor in its
appearance. The Andrews look, incorporating the backward rake, the
flared side frame, and the exaggerated V shape seems to achieve so much
of the essence of boat design of the period, that to make a boat
without
these features is to destroy its elusive elegance. Even the other
slipper launches of the time, made up by some of Andrews' competitors,
such as Hobbs, seem to lose the thread because of the pedestrian
treatment of their windscreen. Just look at this sad gathering:
From an extended
coaming on a boat which
looks like but is not a slipper launch, to the big ugly
metal framed
ones which are, while the traditional
Andrews example (53) nestles
subtly
in the background.
...and
poor old
Goebbels has no balls at
all.
Now, here
is the classic look:
I have expanded my
thoughts on the importance of the windscreen in the Problems
page under the heading "Windscreen
and Drivers' Seat".
From a practical point of view, the lateral screen frame must meet the
coaming at its front, so it must lie parallel to the hull side there,
as the coaming does. It must be the same height above the deck as the
coaming is, plus any finial on top, and it must be thick enough to
house the windscreen glass with a groove. Looking at the pictures
closely shows that the frame piece does not actually form a rebate with
the coaming, but rather joins it in a butt joint. On this point one
really ought to
deviate from the Andrews design. To quote from Fred P. Bingham in
his book 'Boat Joinery and Cabinetmaking Simplified', on the subject of
the forward corners of cabins and cockpits, "a simple solution would be
to butt the sides against the end with a cleat in the corner. This is
lubberly construction. It is unsightly, prone to rot, and seen on cheap
boats. The proper method is to construct a pair of rabbited corner
posts to receive the cabin sides and front piece." Now, I don't want to
be regarded as a lubber, so
I had better look into the corner posts.
The lateral windscreen frame
butts up against the inside of the coaming.
The length of
the side frame
matches the width of
the
coaming, which brings it well below deck level, and it must be so
angled that the bottom windscreen frame, which joins onto the lateral,
will pass
forwards and upwards to meet its fellow in the midline, all the time
maintaining a uniform reveal over the top of the deck, which is
generally about twice the width of the quarter-round fillet which
softens its transition to the deck.
This means that
the top edge of the bottom frame must be slightly curved to follow the
camber of the deck, which is easy enough. But it also means that the
joint between the bottom frames and the central post of the windscreen
is more difficult. Assuming that the glass is flat, the rake of
the central post must be the same as that of the lateral frames, and
therefore a very specific angle of cut will be needed on the edges of
the central post, and the ends of the bottom frames in order for this
to occur.
Specifically, because the bottom frames are rising from outside to
inside, roughly following the inclination of the deck camber, and
moving forward from outside to inside, they meet the centre post with
compound angles. They can be angled across their width to meet a
straight centre post, or the centre post can be tapered to meet them if
they are left square ended.
Furthermore, if the centre post is truly flat, then the ends of the
bottom frames will have to be bevelled to meet it. Alternatively, if
the centre post is V-shaped it can join the bottom frames with square
ends. It is difficult to get a good view of the centre posts, but at
least some of them appear to have a sharp V angle visible on their
front surfaces.
The above three photos show sharp
angulation on the front of the window frame centre posts.
With this evidence
I
can now plan the joinery of the window frame. But before it is actually
built I will have to cantilever the central foredeck stringer back into
the cockpit a little way to support the windscreen frame. That in turn
means that I will have to make allowance for the hatch in the foredeck,
and that means that the engine compartment is soon going to become very
awkward to enter. So before much more is done it is time to put in the
motor mounts.
Top of Page
In January '07 I
added
a floor timber to the forward face of the dash bulkhead to act as a
support for the sole in the foot wells, if they became necessary. It
was
only screwed and not glued into place, so that the hole for the
propeller shaft could be bored through the bulkhead and both floors
simultaneously; so, the forward floor can still be removed if it
proves
to be unnecessary. But it adds strength to the hull and bulkhead area
where the (reverse) thrust of the motor will act, so I intend to leave
it. The first job with installing the motor mounts then is to glue in
the floor.
Since the beginning of this year I have decided to redesign the cockpit
and bring the
driver's seating back to allow for a retropositioned windscreen. As a
result, the footwells seem to be irrelevant, and may well be replaced
by a foot board in the driver's compartment.
The original intention with the motor mount was to locate it between
the footwells, but now an alternative arrangement needs to be devised.
For the diesel engine version of the boat, engine beds were proposed to
stretch between bulkheads C and B. I need a structure which will hold
the motor in a plane at right angles to the shaft, and which will be
strong enough to transmit the thrust of the motor safely to the hull.
Something built up on engine beds is a possibility, but so too would be
a device like this one:
This mounting device
is attached to a Lynch motor. The longitudinal
bars can be screwed down to engine beds directly, avoiding the
necessity of building a dedicated frame for the motor. The beds
themselves are hardwood which is filleted onto the bulkheads and bolted
and epoxied through the hull, which is needed to absorb the vibration
of a diesel engine. With the much more civilised behaviour of electric
motors it may be possible to avoid the through-hull fittings, settling
instead for epoxy filleting. The varying angle on the bottom of the
beds has to be cut to meet the hull bottom, which is changing direction
quite rapidly in this part of the boat; and the top of the beds has to
be cut to parallel the shaft at the correct height. But thereafter, the
thrust of the motor is transmitted directly to the bulkheads and hull
bottom.
On the other hand
aluminium, fibreglass
or ply baffles can be used in a similar way, attached to the existing
engine beds or bulkheads. On the right is one of the examples from
Solarboat, which
is here up against an athwartships wooden beam. This arrangement has
the advantage of protecting the motor from any spray of bilge water
thrown up by the sprocket on the shaft. Naturally, having gone to the
trouble of employing a packless shaft seal, I will be very disappointed
if there is any water in the bilge, but I would not like a shorting
motor to add to my disillusionment if such were to be the case.
While the baffle shown right is simple enough to install, it does
require the shaft to lie at a predetermined angle with the waterline
(and, therefore, with the bulkheads). Otherwise some sort of wedging is
necessary to make allowances. As my shaft is not at such an angle, it
seemed just as easy to manufacture some motor bearers and a home made
baffle to suit. The midline of the shaft was projected onto bulkhead B
by a laser sitting on the shaft itself. Points on bulkhead B and the
floor in front of bulkhead C, which corresponded with the top of the
shaft were then plotted, and two bearers were fitted between
them. Of necessity the bearers were now lying parallel to the shaft.
A laser finds the projected
top of the propeller shaft on bulkhead B, and two motor bearers are
trial fitted.
At
this stage the bearers are not contacting the hull, and it might be
possible to leave that arrangement, but, despite the relatively well
mannered behaviour of the electric motor, I will feel happier if there
is a good grip from the bearers onto both bulkheads and the hull; so
the ultimate aim
is
to fill in the gap between the bottom of the existing bearers and the
hull.
The distance between the bearers is 290 mm., which is the width of the
pre-fabricated baffles. My baffle, which I had envisaged to be made of
two layers of 9 mm.
ply glued together, was to fit into slots cut into the inside of the
bearers at right angles to their long axis, and the thrust would be
supported by triangular gussets both in front of and behind the
baffle, sitting on top of the bearers. The lack of an athwartships
member against which the baffle bears,
such as the shown in the picture of the motor
assembly above, will allow very
generous access to the sprockets and drive belt from the front, and to
the motor from behind.
However, on taking possession of a motor and sprocket on loan from Solarboat, in order to use them as
templates for the manufacture of my baffle, it became obvious that my
plan was not going to succeed: the gap between the front of the thrust
bearing and the back of the sprocket is only 15 mm., so an 18 mm. ply
baffle is out of the question. I briefly entertained the idea of
cutting a raceway groove in one of the layers of ply, to allow passage
for the sprockets and belt, but the need to countersink screw holes
into the remaining attenuated layer for the mounting of the thrust
bearing housing dealt a final blow to the plan. It would have been too
tenuous a thickness of ply left to take the thrust of the shaft, even
if it would have been sufficient to take the torque of the motor.
Instead, I decided to have a polyethylene baffle made up to size,
which could be only 10 mm. thick and just as strong as is needed.
Drawing for the baffle, and the real
thing.
In the meantime,
while I am
waiting for glue to dry I bide my time
with odd jobs. Here
I have just put a limber hole through the base of the dash bulkhead,
and have reinforced it with fibreglass. You can see the peel ply over
the area.
I am doing that
now because I am about to glue the floor timber to the
forward side of the dash bulkhead, before fixing the motor bearers in.
Once the floor is glued in it would be awkward to put a limber hole in
underneath it. Just as I covered the hole in the bulkhead for the
propeller shaft on the cockpit side, so too shall I for the motor
compartment side. The motor mounts will bear against this piece of ply
rather than the soft Oregon of which the floor is made, and a similar
arrangement is to be employed on the stern side of bulkhead B.
Gluing the cover plate onto
the floor in front of the dash bulkhead.
After
the cover plate is dry the bearers are put back into position and
hardwood fillets are cut to shape to accommodate them and prevent them
from twisting out. The same is then repeated with the ply
buffer in front and two more fillets.
The
motor bearers
riding on
the plywood baffle at bulkhead C, then the first fillets are bolted in.
The bearers do not touch the hull at this stage, so the
fillets are
registered by the alignment of their tops with
the tops of the bearers.
At the front end of
the bearers, at bulkhead B, their position is held by wedges, as the
ply buffer is not yet attached to the bulkhead.
The next lot of
fillets, for the front end, will not be as straight forward as the rear
ones, because they will have to fit around the epoxy fillets between
the hull and the bulkhead. In addition, because there are no floors
attached to this bulkhead I will need a pair of backing blocks on the
other (forward) side to accept the bolts.
The forward set of motor mount
fillets (left), and the view on the other side of the bulkhead.
In order to fill in the gap underneath these bearers strips of scrap
are mounted on their sides, and the hull shape is scribed onto them.
They are cut to shape, refitted and then clamped to the bearers. With
the bearers now removed and inverted all that has to be done is shape
some filling strips to fit between the pieces of scrap, laminate them
together,
and bond them to the bottom of the bearers. The bearers can now slotted
to accept the motor baffle and replaced, then
trimmed if necessary to sit properly on the hull, and epoxy glued to
it. Further fixation points can be made by screwing through the fillets
into the bearers front and rear.
The scribed ply sides being
fitted to a mount.
The laminated motor mount prior to shaping and after.
The shaped bearers are dropped back into position ready for
grooving to
accept the motor baffle.
While this was
being
done, I took the opportunity of drilling limber holes through the
bottom of bulkhead B, between the fuel compartment and the motor
compartment. Because of the longitudinal girder it is not possible to
use a single central hole, so two are put in, one on either side of it.
Limber holes in bulkhead B,
seen from the fuel compartment (left), and the motor compartment
(right). The bolts for the
motor mount fillets are left long here, as
the backing blocks have not yet been fitted.
So it is time to acquire the thrust bearing. The housing grooves for
the baffle will be a lot easier to cut off the boat, so I will not glue
them in until that is done. After it is, the bearers can be epoxy
filleted to the hull bottom to help absorb the thrust of the motor, and
those fillets will also be glass reinforced.
Until then, it is time to move on to the next phase of the
construction, which takes me forward into the fuel compartment and
beyond, to begin preparations for the foredeck structures.
Forward to August '07
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Problems
shows higher
resolution shots as well.
