Corrosion surveys were performed on the S/V Adventuress twice in 1998, both in the water and on the hard. The first was in the water March 21, 1998, and the second when the vessel was hauled out, December 3, 1998. The first survey site was with the vessel tied up at the USCG dock in the Port of Port Townsend, Washington, in salt water, on a dry day. The survey when hauled out was also in Port Townsend, at the Port facilities, while deck rebuilding work was being performed . Observations were made at both sites, electrical systems examined, resistance readings between metals taken, and tests to obtain corrosion data were taken when the vessel was in the water. These in the water corrosion measurements were underwater metal "free potentials", a reliable indicator of the condition of the underwater metals, using as an electrode Mil Spec A-1800-J zinc. The resistance readings were taken between the underwater metals in order to determine if there were any bonding connections to through hull fittings or electrical system connections to hull fittings, both done when in the water and when hauled.

As a way to organize this report, observations made first of underwater metal free potentials will be examined one at a time, with a discussion directly following each metal location. Conclusions and recommendation will follow. Attache is a list of the free potential readings found throughout the vessel, please refer to this list when going through this section of the report.

Rudder shaft-The reference electrode was placed in the water and the voltage taken at the bronze rudder post coming up in the steering box as the first free potential test made. A reading of 738 mV is generally indicative of bronze, perhaps a bit low due to some iron or zinc attached, as bronze alone reads about 780 mV average, in seawater. After the vessel was hauled, it was correctly assumed there was a bronze rudder shaft, a length of 4.25" OD x 3/8" wall tube, and there was some small 3" disc zincs attached to the rudder shaft tab plates. There were also some strengthening straps, not in contact with the rudder post itself, with their own zincs. There are four bronze drawbolts internally holding the rudder planks together. A drawing of the rudder, keel, and propeller areas is provided for reference, and attached to this report.

Note that the rudder strengthening straps have four pound streamlined zincs bolted to them, an excessive amount of zinc area for the limited bronze surface area of these isolated straps alone. Already the surrounding wood is soft and has lost it's bottom paint from wood fibers deteriorating. This is the problem with excessive zinc, it increases the voltage differential between the metals to the point that the voltage flowing through the wood causes a electro- chemical reaction with the wood lignin, altering the PH of the wood. As the wood becomes more base, it's fibers deteriorate, leaving a white powder behind, sodium hydroxide, often seen on wood boats around rudder shafts and fastenings. This deterioration is commonly called "wood delignification". It is critical on wood vessels to have about the right amount of zinc area to bronze area. Too much zinc attached to low reactive bronze, and wood delignification results in the vicinity. Not enough zinc attached to bronze, and the bronze corrodes away, although very slowly.

It is interesting to note from a shipbuilding standpoint that the bronze rudder shaft itself is not continuous all the way to the bottom gudgeon, but is only carried to the first bearing, so that in an unfortunate grounding or damage situation where the lower portion of the wooden rudder is carried away, the shaft will likely not be bent, and will leave that part of the hopefully undamaged rudder blade intact to steer by. Further the middle and lower bearings are turning on the wood rudder core bushed with steel, without any metallic shafting running through the center. Note also that the lower inner bushing is loose on the wood center, and is wearing into the wood.

Bow stem iron- a reading of 578 mV was taken, and the steel stem does not reach the water, but it is close to it in the splash zone, and is mounted to very damp wood, so it is effectively underwater. The reading is high for the mild steel, as the paint was scraped away to confirm the metal type, with two explanations. One, the collection of rigging attached to it is varied, galvanized wire, bronze wire, and stainless steel wire, some which may raise the potential if wet from rain or waves coming over the bow, which was not the case. Then there is the very likely case of there being bronze spikes holding the steel stem iron to the wood stem, but the spikes were inaccessible to determine this. Looking carefully at the juncture of the steel to the stem wood, there was no bulging or softening of the wood at this point, the usual site of damage if too much zinc was mounted on the steel, or bronze spikes were used on this big surface of steel. There isn't any zinc on this part, but as it is usually out of the water, and well painted, it is probably fine without any zinc.

Keel bolt in engine room-between main and genset a keel bolt is accessible, and a reading of 159 mV was taken representing the keel, as hopefully these bolts still are tightly connected directly to the keel. This reading indicates iorn or steel with quite a lot of zinc attatched, or passivated iorn with some zinc attatched. When hauled out there was an iorn keel, with about four square feet of zinc connected to it underwater. Inside the engine room, there were a number of wires attatched to this keel bolt, one running to the sideband radio as a counterpoise ground, and one going to the main engine block. In order to see if there was any stray currents flowing, the wires were removed, and the keel bolt/keel free potential dropped to 132 mV when the engine "bonding" wire was removed. The current was measured to be zero so there were no stray currents from electrical leakage at this time, however it is difficult to avoid problems when attaching different systems to keels.

Without the engine wire the free potential went down, to the keel's actual free potential, indicating the engine wire connects to a higher free potential metal, drawing up the keel potential. The engine is connected to the shaft and bronze propeller, a bronze through hull fitting, and the DC electrical system negative through the engine starter. So with the engine wire connected, a higher free potential metal is sacrificing the keel to protect itself. It may also be connected to the AC electrical system grounding conductor ( usually called the "ground" or "green" conductor ) which may or may not be connected to the shorepower grounding conductor. On vessels of this type the grounded conductor ( usually called the " neutral" or "white" conductor ) is not connected to the grounding conductor (ground) unless the vessel is on ship's genset power with no connection to shore. Keel or underwater metal "bonding systems" may also be used, besides for radio counterpoise, as paths to ground for lightning protection systems, for the galvanic protection of metals, and for electrical system saftey grounds.

The USCG says wood hulled vessels may connect AC shore power grounding conductors (ground), at only one point, to the vessels bonding system (or keel). This existing engine wire may be part of the AC grounding, or part of the 120 DC safety ground system, check carefully.

Through hull engine raw water-a reading of 776 mV indicates bronze freely corroding, not tied to anything. This is actually good on a wood vessel, as bonding all the through hulls togeather and attatching one big zinc will lead to "wood electrolysis" around the fittings if that zinc is too large, something often done. It is currently much more inexpensive to replace corroded through hull fittings every 50 years than it is to replace planks eaten out from wood delignification.

Through hull to port of engine room, outboard-a reading of 775 mV is also good, a normal reading for bronze through hulls alone. There is only a insulating hose connected to this fitting.

Through hull to port of engine room, inboard-a reading of 158 mV indicates this through hull is tied to something besides bronze, a lower free potential metal. Investigation revealed that the bronze piping attached to this valve led to a pump, which was connected to the main engine, which was connected to the keel. Thus this particular bronze through hull is being protected by the iron keel, and there is a major (775 mV - 158 mV = 617 mV) difference, very high, enough to cause wood delignification. Looking closely at the through hull to wood contact point, soft wood and white powder can be seen, a sure sign of wood delignification.

Foremast steel step-although not in water exterior of the hull, bilge water connects this sheet steel fabricated and galvanized fitting sufficiently to get a reading of 427 mV. This is a normal reading for steel with a little galvanizing zinc still on it. It also appeared to be painted with epoxy, further reducing the surface area available to react with the water and corrode.

Mainmast steel step-this galvanized fabrication appeared almost new, with shiny galvanization, and had a reading of 159 mV. This is a much lower reading than the other mast step. With a new coat of galvanization, almost only the zinc galvanization is exposed to the water, except for a small amount of steel where bolts may have scraped off some of the coating. So this fitting reads practically like a piece of zinc alone, with a very close reading to the mil-spec zinc electrode. Potentially, if this piece of galvanized steel were mounted directly on a wooden surface, and if a large amount of galvanizing were scraped off first, the wood may deteriorate from wood delignification. But careful shipwrights have used Irish felt under the fabrication to isolate and prevent this.

Hull stringer bolts starboard of foremast step- a reading of these sufficiently wet bolts showed them at 477 mV, freely corroding raw steel. This is to be expected from rather old looking bolts, probably from the last refastening many years ago. All the galvanization has sacrificed off. There is some wood delignification on the surface, very old and inactive, but the wood below the surface is still relatively firm and hard, and in good condition. This condition is usually found around galvanized bolts, from the zinc coating being chewed off when the nut is tightened, and the now raw steel drawing on the zinc coating to protect itself, setting up a voltage differential high enough to get wood delignification started. But eventually the zinc is used up, and the process stops.

Sister rib bolts, typical-at 476 mV, they are the same as the hull stringer bolts in appearance and condition of the wood.

Hull stringer bolts near main mast- at 479 mV, they are also similar to the other hull stringer bolts throughout the vessel. Some sodium hydroxide is present here.

Steel floor under main mast-reading 324 mV, this is still a well protected steel fabrication ,with some zinc left on it. Well protected means a free potential of 100 to 200 mV lower than the individual metal's free potential. See the free potentials listed on the "Voltage differentials for metals" list attached at the end of this report.

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Propeller shaft-scraping the shaft revealed it to be made out of steel, and a reading of 154 mV shows that there is a large amount of zinc attached, assuming a bronze propeller. Haul out revealed a large 4.5 inch by 5 inch diameter shaft nut zinc and a bronze 44D x 41P three blade propeller. This number is a little low, showing excessive zinc, but is not much of a problem for the wood hull if the shaft is isolated from the hull, which it is by the cutlass bearing being made out of dielectric material, and the shaft log being in alignment, dielectrically floating the shaft on the packing. However the transmission gears conduct to the engine, which conducts to the DC negative. Should the shaft get bent or misaligned, scraping the bronze, the low potential shaft would cause wood delignification around the high potential bronze shaft log. This condition may have happened in the past, as some very small old signs of this problem can be seen, but the wood is in good condition now, with good alignment of the shaft log.

Close examination of the hauled out boat showed that there were many different metals mounted underwater. Please see the underwater metals drawing attached at the end of this report. From the bow working aft, starting with the stem iron, it is isolated, and goes down and wraps the stem wood. It is hopefully fastened with galvanized spikes or galvanized screws. As there is always wet wood, there may be a wood delignification problems if a low potential steel shoe is attached with a higher potential bronze fastenings.

Next now below the waterline, there is a stainless steel fabricated bracket for the bobstay, bolted or lagged into the stem wood. As this is under the water the stainless steel bolts will be subject to pitting, crevice corrosion, and stress corrosion cracking. Principally, the fasteners will develop pit corrosion where the metal is inside the wood from oxygen depletion cells developing. Stainless steels underwater, if made out of the typical 316L alloy, and not an exotic alloy, will also loose strength. It was noted that one of the bolts was missing.

Wrapping the forefoot wood, and under the bobstay bracket, is a bronze sheet protecting the wood. It is not a problem that the bronze touches the stainless, as they both have about the same free potential, ( see "voltage differentials" chart ). This bronze is isolated from the above steel by a 5 foot gap.

Down below the bronze wrap, there is a steel strake strip mounted along the edge of the forefoot, with a four pound zinc attached. This steel strip was unable to be measured when in the water, but it had the appearance of rusting away a fair amount. This steel is also touching the higher potential bronze wrap, raising the steels potential, corroding away the steel, yet with the lower potential zinc pulling down the steel's potential, it is trying to lower it and protecting it. Depending on the area ratios and the metal alloy's reactivity, and without getting an in the water free potential test of this combination, it is hard to say which metal is corroding away. Probably the zinc is corroding the most, being the lowest free potential.

There is a gap of an inch from this strip to the iron keel, sufficiently isolating these two elements. The keel itself is cast iron, approximately 27"x17"x37 feet, painted with bottom paint only. It has about a one-thirty-second inch coating of hard iorn oxide. There are four almost totally wasted 6"x12" zincs, two to each side, mounted aft, brazed to the lower rudder gudgeons straps. The lowest rudder gudgeon strap is through bolted to the keel without any felt underneath, connecting the zincs, and the bronze straps, to the keel. This is providing some zinc to lower the keel's free potential, but also raising the keel potential a little with the higher potential bronze connection along with it. There is a 4"x6" zinc mounted to the keel alone about a foot forward of this strap on the starboard side. Overall, there is enough active zinc, in combination with the hard iorn oxide layer on the keel, to bring the keel's potential down to the measured 135 mV reading. There is a small amount of thin perforated bronze tape attatched to the lower gudgeon mounting wood, apparently old innterconecting conductor, no longer connected.

It is of further interest in shipbuilding metholds, that there are two blocks of lead cleanly inserted into the keel wood just foreward of the propeller arpeture by about two feet. These are flush to the surface, about 10"x28"x17" thick, isolated from anything in the vicinity. They may cover over the afternmost keel bolt nuts where the keel bolts cannot pass through the shaft tunnel.

There are two 6"x12"x1" thick zincs mounted above and below the cutlass bearing housing, sliced to conform to the curvature of the propeller aperature, and tied to the cutlass bearing housing by wires. These zincs are rather large in total surface area for the 10"x11" bronze cutlass bearing housing's surface area. Bronze, being a low reactivity metal, only needs about 1sq. inch of zinc surface area for every 100 sq. inches of bronze surface area to bring the free potential of the bronze down to the nessisary, and maximum for a wood vessel, free potential of 150 mV lower than bronze. Bronze is not a very active metal, requiring little additional electrons to stop it's corrosion. Zinc is very active, having lots of electrons to give.

There are bronze deadwood stiffeners on each side of the shaft tunnel, isolated and throughbolted. Also, there is another set of bronze stiffeners aft of the propeller apeture, also isolated and through bolted. Generally, bronze shapes like this will last 50 years without zincs attatched, although 100 or more years could be obtained if just the right amount of zinc were always connected. But once again, on a wood boat too much zinc tied to bronze is a hazard to the wood, and it is easyer to replace a visibly deteriorated bronze fitting, than the underlying wood. Next to the aft stiffener straps are a nice strong set of port and starboard bronze rudder stops, through bolted the aft keel stem, and isolated.

Once again we are back at the rudder plank stiffening straps, which are isolated on the wood of the rudder, and have a four pound zinc attatched to each strap. Above these there is the rudder shaft, with the welded on tabs that connect the shaft to the rudder planks and small button zincs bolted to the tabs. This completes the full circle of the vessel and it's underwater metals, bringing us back to the surface, rising up along with our bubbles, up through the rudder shaft tube, back onto the deck.

CONCLUSIONS

Overall the wood hull of the S/V Adventuress is in excellent condition, and there is hardly any damage from wood delignification or corroding metals. There are a few problems to address, and the zinc layout should be adjusted before replacing the zincs again.

RECOMMENDATIONS

Remove the current streamlined zincs from the rudder plank stiffener straps. Replace with one half of a 2" button zinc per strap. Use a longer strap mounting bolt , or drill and tap the strap, bolting the small zinc on with a bronze bolt or stainless bolt. Use a little waterproof grease or silicone grease under the zinc to keep water out of the bolted connection juncture.

Epoxy the lower rudder inner bearing in place on the wood center shaft, after first determining that the rudder swings true, and does not need the slop it has to keep from binding.

Check the bow stem iron covering wrap sheet to hull juncture for signs of wood softness or paint lift, possibly due to wood delignification. Replace bronze fastenings with lightly galvanized screws or spikes if there is problem.

Run a #6 AWG tinned cable from the case of the 120 volt DC/ 120 volt AC switchboard to the keel bolt on the engine room. Bond also with #6 cable the incoming shore power grounding (ground or green) wire to the DC/AC switchboard case. This will provide a good AC and DC safety ground. Be aware that the possibility exists that with this shore ground to keel connection, any rare but possible stray shore power ground currents may flow to the keel, causing the keel to suffer stray current corrosion damage. A UL listed 50 Amp galvanic isolator can be installed in this shore power grounded wire to block low voltage stray currents at dockside. Also, any shipboard 120 DC leakage to ground may corrode the keel. A milliamp meter in this AC/DC switchboard case to keel bolt wire can prevent problems by monitoring this leakage to determine if there is a current flow, yet still allow the safety of a keel ground.

Install a two pole circuit breaker in the sideband radio, to disconnect the radio's power ground when not in use, to prevent any DC negative current from reaching the keel through the sideband's case counterpoise cable or any other way than through the AC/DC switchboard ground path, except when the radio is on. Run a tinned #6 cable from the sideband's case counterpoise ground to the keel bolt in the engine room. Abandon all other wires to the keel bolt. The existing radio ground wire may be sufficient.

Isolate the through hull to port of the engine room from the engine. Use a schedule 40 PVC coupling, or a short piece of hose. Test with an ohm meter to be sure when done.

Remove the propeller shaft brushes, and cut back any wires attached to them, The prop and shaft will be okay on their own, and these brushes usually do not work effectively.

Treat all signs of wood delignification with white vinegar to increase the acidity of the wood, and stop the reactions. Boric acid is also used for this as a wood preservative. Apply on a yearly schedule. Note in the engineer's log the appearance and location of each problem spot, for continued observation and monitoring by changes in ship's personnel, if necessary. Test the free potential of all underwater metals yearly, and keep a log to determine if there is the proper amount of zinc in place on any fitting that it is advantageous to have zinc protecting. Test all through hulls for sufficient strength yearly with a hammer in a non-destructive way, preferably when hauled out. Replace through hulls every 50 years.

Replace the bobstay bracket bolts with bronze bolts of sufficient size to handle the design load. Cary them through the stem wood to the interior of the vessel if possible. The stainless steel bracket should be okay as it is exposed to oxygen on the surface.

Cut the steel forefoot strip between the keel and the bronze forefoot wood wrapping sheet clear of the bronze by ½ inch, to isolate these parts.

Remove the four old plate zincs from the lower rudder gudgeons with a grinder to the welds. Remove the old thin perforated strapping. Add two 6"x 12"x 1" or ½" zinc plates to the each side of the keel, preferably by drilling the keel and tapping in plain steel studs on layout for zincs. These may be mounted aft on the keel, as the ions released can travel all the way to the bow without a problem. If zincs with "weld on" tabs are purchased, the tabs may be simply drilled for spacer nuts and bolts, permitting easy replacement by divers. Be sure to use a little waterproof grease or silicone grease on the mounting points to keep water and corrosion out of the conductive juncture point.

Remove the two zinc plates from the cutlass bearing housing. The housing is sufficiently strong and thick enough to not need zinc protection, yet the deadwood is very costly replace if problems develop. The cutlass mounting studs can easily strip from wood delignification. A small zinc could be attatched, but the thickness of this fitting is sufficient to last another 90 years without anything.

Add a small ½ of a 2" button zinc to each piece of rudder gudgeon strapping, the stiffener plates fore and aft, and on the rudder stops, on one side only. Drilling and tapping a hole works best for a small mounting bolt here.

Paint the keel and steel strips with epoxy to reduce zinc consumption, but this is not nessisary at this time.

Look at the rudder shaft packing assembly on the interior of the hull when accessible and check for wood delignification.

All of these recommendation can be performed at any time. None are important to the safe operations of the vessel, except that adequate AC and DC system grounding be maintained.

Thank you for the opportunity to provide this information for Sound Experience, and the schooner Adventuress.

Sincerely,

John Munroe

Ocean Currents Marine Electric

DISCLAIMER

The parties understand and agree that unless otherwise agreed to in writing, Ocean Currents Marine Electric is not responsible for inaccuracies in any report, or for any errors in judgement, omissions, or negligence of Ocean Currents Marine Electric or any of its agents arising from this transaction. Ocean Currents Marine Electric is not responsible for any incidental, special, or consequential damage of any kind, in reliance on, arising from, or in connection with use of any report arising from this transaction. This contract represents the complete agreement between the undersigned parties.

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