Mary,
Here are two things I stole off the Internet. The first is a link to
an article about building a rudder, but it begins with some ugly
pictures of what the inside of the old rudder looked like. The second
is an article that describes what's inside a typical fiberglass rudder
and how it's constructed around a metal armature. I think it's safe
to say your Tuna rudder armature is stainless and that it's been
sitting in saturated foam for many years - probably since shortly
after launching.
Draining is a good idea. For one thing, if you catch the water and it
appears rusty-looking, the stainless steel is probably deteriorating.
But be sure to solve the leaking problem before you reinstall and
relaunch.
On my current boat the rudder post is hollow aluminum tubing and it
was originally anodized. Over the years that layer wore off and the
post appeared to be pitted where it entered the rudder top. Before a
race to Hawaii we removed the rudder and opened it up by cutting
rectangular patches out and then carved away the foam. The webbing
appeared to be okay, but there was definitely pitting around the shaft
from where it entered the rudder down a few inches.
We cut the rudder post at an angle, inserted a bolt of aluminum and
then bolted and welded it all together. Then we re-foamed and patched
the fiberglass. You can't tell it's been repaired, but knowing things
were okay and that the previously hollow post was now solid made the
race the focus and not whether the rudder was going to fall off. By
the way, we also had an emergency rudder along that would have steered
the boat just in case.
I suggest you might do a little investigation inside the rudder.
Pat Broderick, former Tuna
http://www.instructables.com/id/How-to-Build-a-Sailboat-Rudder-from-Scratch/
SOONER OR LATER owners of fiberglass sailboats become interested in
how the rudders on their boats are constructed. Usually this happens
after an owner notices there is water dribbling out of a boat’s rudder
long after it has been hauled out of the water. In the early days of
fiberglass boatbuilding, when most sailboats had full keels and
attached rudders, many rudders were still made of wood. These were
constructed in the traditional fashion and consisted of a row of
planks, often mahogany, joined end to end, usually with internal drift
pins that were fastened to the rudderstock. You never had to worry
about these rudders getting all full of water, but you did sometimes
have to worry about the planks coming loose.
Since the late 1960s, almost all fiberglass boats have been built with
fiberglass rudders. Not all glass rudders are created equal, but most
are built on the same basic principle. Most commonly, the spine of the
structure is a metal rudderstock (also sometimes called a rudderpost)
off of which sprouts a lateral armature that supports the rudder
blade. Traditionally, this armature is welded to the rudderstock and
consists of a series of lateral rods or bars, or perhaps a simple flat
plate. More recently, foil-shaped fins similar to those seen in the
frames of airplane wings have become more common. This skeletal
structure is embedded in a high-density closed-cell plastic foam core,
which is sheathed in a thin fiberglass skin. This composite foam-core
construction is relatively light with neutral buoyancy, which
significantly improves the feel of a sailboat’s helm while sailing.
Interior rudder structures
The key variable is the material from which the rudderstock and its
armature are manufactured. If metal is used, the best choice is
probably silicon bronze, but this is rarely seen anymore. Sometimes
aluminum or even titanium are used to save weight, but the most common
choice is stainless steel. We like to think of stainless steel as an
“ideal” corrosion-proof metal, but this is really only true in
limited circumstances. It does resist corrosion well when routinely
exposed to oxygen, but is subject to pitting corrosion when trapped in
a deoxygenated environment, which is just what you’ll find inside a
fiberglass-skinned rudder once its foam core is saturated with water.
Such saturation, unfortunately, is common in any rudder with a metal
stock. The joint where the stock enters the rudder blade is apt to
leak sooner or later, because the three different materials involved–
fiberglass, metal, and plastic foam–all contract and expand at
different rates as the ambient temperature changes. No matter how well
the joint is sealed when the rudder is first constructed, small gaps
through which water can intrude are inevitably created. Knowledgeable
boatowners take this for granted. They assume their rudder cores are
constantly absorbing water and so drill holes in the bottom of their
rudder blades every time they haul their boats in order to let the
moisture drain out. (A better alternative, obviously, would be for
builders to install drain plugs in the first place.)
Another problem with stainless steel in rudders has to do with its
welding characteristics. When stainless steel is welded, the carbon
and chromium in it mix to form chromium carbide. This creates two sub-
alloys–chromium carbide and chromium-depleted steel–that are different
enough in their composition to form a corrosive galvanic couple within
the weld. Insert this galvanically compromised weld inside a moist
oxygen-depleted foam-cored rudder, and it is much more likely the
rudder’s stainless-steel armature will corrode and fail. A stainless-
steel rudderstock is also apt to suffer from crevice corrosion inside
the shaft seal in the bearing where it exits the hull, as this is
another area where water is trapped and becomes stagnant and
deoxygenated.
All these problems can be ameliorated if the stainless steel inside a
rudder is high-quality 316-L alloy. This variant resists pitting
corrosion much more readily than its lesser 302- and 304-alloy
cousins. It also has a lower carbon content (thus the L designation)
and is less compromised when welded. Unfortunately, there is no easy
way to distinguish between alloys. Silicon bronze, by comparison, is
virtually corrosion proof under the same circumstances, unless it is
coupled directly to steel or aluminum.
Rudderstocks can also be fabricated from a composite laminate such as
fiberglass or carbon fiber. The great advantage of a laminate stock is
that the stock and the skin of the rudder blade can be the same
material, which means the joint where the stock enters the blade can
be permanently sealed. Also, the rudderstock can be bonded directly to
the interior surface of the skin, thus eliminating the need for
interior armature to resist twisting loads as the rudder turns back
and forth.
Laminated rudderstocks generally must be wider than metal stocks in
order to resist the transverse loads imposed on them. This means the
rudder blade must also be wider, which tends to degrade the rudder’s
hydrodynamic form. One way around this is to flatten the sides of the
stock into a trapezoid shape. This not only creates a narrower cross-
section, but also presents a much larger surface area for bonding the
stock to the skin of the rudder blade. Note, however, that a trapezoid
stock needs bearing rounds installed where the stock passes through
its rudder bearings in order for the rudder to turn properly.
Metal vs. laminate rudderstocks
In practice, unfortunately, fiberglass rudderstocks have not performed
well. Some mass-production builders have embraced them, because they
are cheaper and lighter than stainless-steel stocks, but there have
been several incidents where fiberglass stocks have failed in moderate
sailing conditions. Builders, as a result, are now more wary of them.
Carbon fiber is another story. Carbon rudderstocks have proven much
more reliable, as carbon is much stiffer and stronger. It is also much
lighter. An all-carbon rudder (i.e., a carbon stock bonded to carbon
skins wrapped around high-density foam) weighs less than half as much
as a conventional foam-filled glass rudder with a stainless-steel
stock and armature, but also costs two to three times more. Carbon
rudders therefore are normally seen only on race boats and high-
quality cruising boats.
On Oct 1, 2013, at 5:37 PM, Mary Falslev wrote:
> I managed to take my rudder off today and bring it indoors to dry
> off before assessing whether a simple repair or a replacement is in
> order. The good news is the the shaft is not compromised. There is
> a hairline crack of about two inches in length on the bottom surface
> of the rudder. I plan to open that up just enough for it to dry
> out. If it dries, then I hope it can be repaired with a fiberglass
> patch. Now it is drying out in a spare shower in the house. I
> would like to hear from anyone else who has every removed or
> replaced a rudder._______________________________________________
> Tuna mailing list
>Tuna at myfleet.org>http://myfleet.org/mailman/listinfo/tuna
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