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In my efforts to reconstruct my 1948 CC 17' Deluxe according to the
"Book of Dannenberg" I have come across a few places where I have been
confident enough to branch out on my own in an effort to improve the
finished product..
Close-up
Showing Groomed notch
and Pkg Glnd Clearance
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Mr. D. uses as a general rule of thumb, to rebuild just as it was; to
replicate in other words. Of course, the Master Himself offers
numerous "better ways" not the least of which is the plywood
innerbottom with 5200 between it and the outer planks. A huge step
fwd. in longevity for the boat. There are other examples.
I, as a neophyte can see ways to improve things and generally, stronger
is better. Once you have one of these beauties stripped down to the
bones so to speak, replacement of structure and planks are the main
events. Structure is stem, gripe, keel, chines, frames, shear shelf,
and the transom which in reality is a structural bulkhead; the only one
in my boat. Let's take a closer look.
The transom structure for this boat is made up of a bottom bow, cheek
frames, gussetts (vertical and horizontal), a top bow and deck beam,
three vertical members (transom stakes) and one and 2/3rds seam
battens. Planking is of course added and therein lies much strength.
Look at Figures 1 & 2 and follow along. These figures are very busy
but there is a lot going on here.
Other than the pounding the bottom takes (which is substantial), the
other area of amplified abuse is the very back of the boat from forces
generated by the prop, strut, rudder and possibly 400 lbs. of fuel in
the immediate vicinity! Rack, rack, rack goes the transom as we turn.
Back to the structure. The lower corner of the cheek frame is through
bolted to the chine at an angle and the horizontal corner created by
the chine and the lower transom bow is reinforced with a gusset,
through bolted to the chine and the lower transom bow. Captured
between this horizontal gusset and the lower transom bow is a vertical
gusset plate that is then screwed to the fwd. face of the cheek frame.
This creates a rigid, reinforced corner in three dimensions; fore and
aft, up and down and athwartships. There is no glue used on any of
these mating surfaces originally. Fasteners are 1/4 -20 brass carriage
bolts and of course the ubiquitous brass screws. The aforementioned
vertical gussett plates were limited in height by the exhaust pipe to
port, about 6 inches. The stbd. side matched for symetry so the same
part number could be put on either side. This was a production boat,
afterall.
The tops of the cheek frames are joined by the transom top bow which is
screwed (two big screws on each side) into the end grain of the cheek
frames. A curved deck beam is then screwed to the top of the transom
top bow (screws from underneath to reduce interference from deck
screws, I'm sure). A cleat, screwed to the fwd. face of the cheek
frame even with it's top surface supports the shear shelf and joins the
transom to the rest of the upper part of the boat.
Fuel Tank Blocking Access
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Between top and bottom transom bows there are three vertical members;
one central 2 x 4 member and one lesser member to each side that act as
spacers and simply hold the seam battens and planks in place. They are
at least through bolted to the tail ends of the stringers at the
bottom. The tops of course are end grain screwed through the top bow.
The center member is key here as it does several things. As expected,
it is joined to the upper and lower transom bows by large, long screws
through the bows and into the end grain. Firstly, it was a piece of
structure for the transom and secondly, screwed to it's base is a brass
casting that supports the rudder weight and acts as a secondary journal
bearing for the top of the rudder shaft. The stuffing box is just
below it and is an integral part of the main rudder shaft bearing
bolted to the keel. This latter unit is quite typical for many
installations I suspect.
Taken as a whole, the transom has the small vertical gussets, the
planking and all those end grain screws to keep it geometrically and
dimentionally stable. So it appeared to me that this center beam was
pretty important to things staying together over the life of the boat
yet it appeared to be a weak link if racking occurred or rudder shaft
torque was excessive. What to do?
Lifting Yoke Bolted in Place
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When disassembled, the whole transom structure was trash with two
exceptions. The lower, horizontal gussets were perfect and made of
heavy oak; reuseable. The cheek frames were complex in geometry that
combined tumblehome and hull taper in two planes plus connecting the
chines and bottom bow. They were checked, riddled with screw holes but
solid, thick oak and no rot; reuseable with some help!
Studying the scene brought to mind several obvious flaws. 1. End grain
screws for strength have got to go; 2. the cheek frames needed help; 3.
more rigidity to resist racking had to be incorporated; 4. the brass
rudder support/journal device needed additional help to resist rudder
shaft torque; 5. the top bow and accompanying deck beam needed a better
fastening scheme.
Lifting Yoke Foot Cut Off
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I started with the cheek frames while the hull was upside down as they
were an integral part of new chines, new bottom bow and the whole new
bottom. They were still held in place by transom planking and side
planks. I made new, heavy duty, vertical gussetts twice as high with a
hole for the exhaust pipe to port and after installing the new inner
chines and bottom bow, and using nearly every clamp I owned, bolted in
the old lower horizontal gussets. Almost a perfect fit to the original
compound angles of the gussetts! I was on the right track. Squaring
was done by measuring the diagonals as best I could; clamped it all
down and glued (5200), screwed and bolted it all together. I then
finished the bottom as access was no longer needed to these corners.
Needless to say all components old and new were coated with CPES and
screw holes filled.
After the boat was upright and checked for plumb and square and true, I
milled all new structural parts and steam bent the new upper bow and
deck support beam from oak as I had done the bottom bow. I had left
the center support in place for dimensional replication. Attaching the
top bow was a challenge I agonized over for some time. The problem was
compounded by lack of dimensions on the plan for determining the angle
of the transom relative to what? Ultimately I decided the transom was
at right angles to the waterline and the upper bow coincided with the
lower one. Easy to say, hard to do and I'm not sure yet if I got it
right but it looks good.
Old Vertical and Horizontal Gussetts
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The upper bow had some spring back so it had to be braced in the middle
and clamped fwd. at the ends to keep the curve. I then through
bolted the outboard ends through the tops of the cheek frames at an
angle! The clamps pulling fwd. and the center brace pushing back had
to remain in place until the shear shelfs were in and structure added.
The shear shelfs were then installed and attached to new cleats on the
cheek frames bringing them level to the top of the new top bow. Keep
in mind that it is the shear shelf that is fastened to the tops of all
the frames and the stem. Once attached to the transom, you have
completed the circle, so to speak. Temporary cross braces remained in
place athwartships between key frames to assure dimentional stability.
The clamps holding the cheek frames fwd. could now be removed but I
kept a brace in the middle for assurance. It was subsequently removed
when I found less the 1/16 of an inch change when removed. Now I was
ready to tackel the new center support piece. I initially installed
the new piece using long screws through the top and bottom bows into
the end grain. Then I milled a new piece that overlapped the center
piece top and bottom allowing me to screw it to the top and bottom bows
and the new center structural piece. Now nothing would move up or down
as the screws were in shear and not just hanging on to end grain. The
deck support beam was then through bolted to the top bow in four places
and screwed at the very ends.
Rudder Soppurt Casting
Drilled for Thru Bolting
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The plot thickens. I knew the aft lifting yoke went between and was
bolted to the main longitudinals (stringers) clear at the back. What I
didn't realize was that it had "feet" on it that went under the
longitudinals and in quick order I found out there was no way to
install this piece after the innerbottom was installed without bending
it which I did not want to do. I'll have to re-read Mr. D's book and
see if this was brought out; probably was and I missed it. Considering
the yoke is bolted to each stringer with two, 1/2" bolts (4 bolts
total), I whacked off the feet eliminating the "belt and suspenders"
approach and proceeded with the installation.
When properly aligned with a future hole in the deck for the lifting
ring, the yoke stood about 3/16" off the new laminated center structual
support. This was too easy. A shim, drill two holes, counter sink the
carriage bolt heads and tighten her down. We now had a rigid triangle
joining the center structural support, stringers and bottom bow
(stringers are through bolted to the bottom bow). By virtue of the new
lamination on the center support we really have two rigid triangles
that include the top bow which is now through bolted to the cheek
frames. Combining the larger vertical plate gussetts with the rigid
triangles of the lifting yoke gives us a really rigid, rack resistant
transom structure. The picture gives you some idea of the finished
structure.
All that was left to do was install the rudder bearing with packing
gland, the rudder, the steering arm and the rudder support/bearing
casting. See the pictures.
The rudder bearing/packing gland assy. bolted in easily. I pushed the
rudder up through it and held it there with a bungee cord while I
"groomed" (a small notch and some shims) the rudder support/bearing
casting, the repacked packing gland, the new thrust washer and steering
arm into their respective positions. I added a new brass thrust washer
under the steering arm where wear was noticed. This required a slight
elongation of the keyway in the rudder stock drive square so that the
steering arm clamping bolt would pass through
Side View All Bolted Up
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The rudder support/bearing casting needed to be securely fastened to
the center post. To accomplish this, I used two through bolts and one
screw on each side to secure it in place. Originally there had been
only two screws per side. I had to drill two holes and modify the
piece slightly to eliminate sloped surfaces for nuts, bolts and screws
to seat evenly on. When all was tightened down, including the packing
nut and lock nut, there was no binding and the rudder arm moved easily
but firmly against the tightened packing. Add to this center support
the battens and planking and it will be very torque and rack resistant.
It is important to note that the rudder bearing/support casting be
located high enough on the rudder stock to allow backing off the
packing nut in order to add packing or repack. Of real concern here is
how in the world do you repack this packing gland once the transom
planks are installed? The engine and fuel tank appear to block access
completely. Hmmm; better get it right the first time.
Transom Overview
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So there you have it. A better transom and rudder assy. rebuild. Is
all this added rigidity needed? Well, I really don't know but it was
easy and the cost in time and man hours was minimal. Though arguable,
it sure can't hurt and adds confidence to your restoration. Time will
tell.
It was great fun figuring all this out and I hope the Figures and
pictures make sense out of all the words. I have subsequently fit up
the deck support srtucture to a true centerline and it looks like I got
it right.
END
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