Quotes

American Tug Haulout tasks

Note - Weasel Words: This document was written by Jeremy Bell based on notes taken during Kurt Dilworth’s Maintenance presentation at the 2006 American Tug rendezvous at the factory in La Conner. Since I have an AT34 I listened hardest to the items that concerned that model. Any errors are the responsibility of the author and not Tomco/American Tug. Neither of us accept any responsibility if you are desperate enough to follow these instructions, please exercise all due care blah blah blah….you know how this legalese goes.

Now that more than 100 American Tugs have been launched, and in use for 5+ years, more data is available on ongoing underwater maintenance tasks. This document attempts to outline the factory and owners experiences with the underwater ‘out-of-sight’ stuff.

Figure 1: Photo of the aft underside of AT34 hull number 48, ‘Tardis’.

Propeller:

AT34s built with the 380HP engine are currently being equipped with 26LH25.5 4-bladed bronze propellers with an anti-sing trailing edge, tuned to class 1 specifications. 27LH25.5 means that the diameter is 26 inches, the pitch is 25.5 inches and the propeller rotates counter-clockwise in forward gear.

Other engine configurations use slightly different variations (the 330HP, for example has a 26LH23 4-bladed bronze prop). While the prop pitch varies based on the size of the engine, all AT34s use 26 inch 4-bladed bronze props with left-hand rotation, anti-singing trailing edge and are tuned to class 1 specifications.

AT41s have Nibral 5-bladed prop. Much bigger, but I didn’t catch the exact size. Anyone ??

The prop should be removed every second year, and inspected and repaired as needed by a competent Propeller Shop. The shaft key, keyway and threads should also be checked.

Zincs:

American Tugs are not bonded, which means that the under water metals on the boat are not connected together. Each piece of underwater metal therefore has to be separately protected by a zinc:

· Depending on the amount of clearance available on the AT34, the propeller and shaft have either a 2in Limited Clearance shaft zinc, or (as on the boat in figure 1) a Camp ‘H’ prop zinc carried on special propshaft nut. The factory replace the original slotted screw with a 5/16in X ¾ hex-head screw, so that divers can apply more leverage when installing a new zinc.

· The rudder shaft should have a 1 1/4in donut shaft zinc. Early Tugs did not have this installed at the factory. Can be installed above the rudder (as in figure 1) or below.

· The bow thruster has 2 zincs, and most of the optional stern thrusters have 1. These are part SM51180 and are proprietary to Sidepower. They can be ordered from the importer, Imtra. Boatyards will probably not carry them. You might want to get a spare screw as well – this is part SM61174.

The following is a link to the Imtra website and the page for the Sidepower zincs.

http://www.imtra.com/product/thrusters/side_power_thrusters/annual_service_items_replacement_parts/zinc_anodes/sm51180.htm

All zincs need to be replaced when they are significantly worn; after all, zincs are cheap (relatively) and underwater metal is expensive. They must all be installed with Blue Loctite to prevent loosening. If this is to be done underwater, apply the previous day, and a thin ‘skin’ will form and not wash away on installation.

The prop zinc erodes the fastest, the rudder zinc the slowest. In electrically ‘hot’ marinas (or if there are many metal boats around) the prop zinc may last as little as 3 to 6 months.

Note: If the boat is used predominately in fresh water, you may want to investigate using magnesium anodes in place of zincs.

Unprotected Underwater Metal:

Crevice corrosion was recently found on the rudder bearing support bolts of one of the first AT34s launched. These bolts provide hold the lower rudder bearing, and are usually covered in sealant or bottom paint. They are shown by the yellow circles in the photo below.

Figure 2: Rudder bearing support bolts

The 2 bolts are 3/8in diameter and 5in long, low-carbon stainless-steel, and should be removed and replaced every year. The factory is investigating the possibility of an external plate and zinc between these bolts to protect them from galvanic corrosion.

The engine (and AC if fitted) water intake covers are made of composite materials, but are held-on by SS screws. The covers should be removed and the screws replaced every year (which also means you can bottom-paint behind the covers properly). Note that these are short screws – they do not penetrate the hull. Be sure to replace these with like-sized SS screws.

Thruhulls:

These are all Forespar Marelon, an industry-accepted high-quality material. They require no maintenance other than being opened/closed once a month or so, and light external greasing with Forespar grease. They have a lifetime warrantee if not disassembled.

Incidentally, the removable white cap on the handle is sized to block the thruhull opening as an emergency ‘plug’.

Engine Zincs:

Note: This was not covered by Kurt at the seminar – but was added by the author since we were on the subject of zincs and maintenance.

The Cummins engine uses 3 pencil zincs (2 in the Aftercooler, 1 in the heat exchanger) the brass heads are normally painted Red by the engine supplier. The lower aftercooler zinc wears the fastest. Replacements are in the ‘Cruising Spares’, and can be purchased from most marine supply stores (e.g. West Marine) as Camp E-2 zincs, either as a complete bolt head/zinc assembly, or just the zinc pencil. In either case, attach the zinc to the bolt head with blue loctite and tighten them snugly – you definitely do not want these to come loose. No sealant should be used on installation as it prevents electrical contact.

Check the length of the old heat exchanger zinc: on some engines (330HP, for example) this needs to be shortened by 3/8 to 1/2in.

Bow Thruster:

Before the haul-out, go into the thruster box under the berth and check the oil level in the reservoir and inspect the clear oil supply tube. If this is milky, water is getting into the mechanism and you need to schedule a pro to inspect the bow thruster during the haulout. And bring money……

During the haul-out, the thruster zincs and propellers should be removed and inspected. Change the drive leg oil by removing the drain bolt (accessible once the propellers have been removed) and draining about 3-4 tablespoons of oil. Inspect the washer and clean or replace as needed. Top-up the reservoir with EP90 oil (probably the same grade you use in the dinghy outboard gearbox).

Bottom Paint everything (including the prop blades, but not the zincs…), check the shear pins, grease the shaft and reassemble with new zincs.

More information on annual maintenance for the thruster can be found at the following Imtra website:

http://www.imtra.com/downloadTypes/SP_Annual_Maintenance.pdf#search=%22imtra%20thruster%20maintenance%22

Bottom Paint:

Note: This was not covered by Kurt at the seminar – but was added by the based on previous email correspondence with Kurt.

The Factory used to apply Woolsey Vinelast vinyl paint, but this has now been withdrawn from sale after Petit bought-out Woolsey. Currently Petit Trinidad Pro paint is being used at the factory. Petit Technical Support recommend a light ‘scuffing’ of the vinelast paint before using Trinidad Pro or SR paint (there have been no compatibility issues on my boat after doing this a year ago). Note: even if you find some ‘on sale’ do not go back to Vinelast – its not recommended as a topcoat over Trinidad .

Jeremy Bell AT34 #48 “Tardis”

PS. How do you know if you are ready to tackle these and other boat maintenance tasks ? Take the Dave Barry ‘Real Man quiz’:

Just before leaving the planet, a race of advanced space aliens gives you a small device that cures every known disease, ends world hunger and brings everlasting peace.

Do you:

a) Take it to the President of the United States ?

b) Take it to the Secretary-General of the UN ?

c) Take it apart ?

If you answered c) – you’re ready to tackle this stuff…..