Moby Duck Haul Out, Diesel Duck underwater hull design and related discussion


it has been five years since my last haul out for bottom maintenance.  That might seem like a long time.  It is not.  I clean the bottom of the boat myself.  This has many advantages.  First, all underwater parts of the boat get a personal detailed inspection.  The piece of mind I get from this before embarking on a voyage is invaluable.  I don't understand how someone could entrust their safety in someone else's hands.  I inspect the shaft.  I am looking for any shaft corrosion and wear in the cutlass bearing.  By turning the shaft to see how smoothly it turns and seeing if there is any side to side movement I can head off any future problems.  I inspect the prop.  The five blade feathering prop I have is much more complex than the normal four blade fixed prop Seahorse installs.  It likes to be kept clean and exercised (blades opened and closed repeatedly) monthly.  In the picture my prop just has some hard growth on it making it appear dirty.  The 6 month greasing schedule must be followed to the letter.  It is pretty simple with the removal of a small grease port on the hub.  This port is then replaced with a grease nipple.  The hub is then pumped full of grease with a standard grease gun until it begins to overflow.  This is easy to do underwater.  Yes, this prop has additional maintenance requirements but the advantages FAR outweigh this.  George Buehler, the designer of Diesel Ducks, told me that a deep full keel boat should have a prop with an odd number of blades.  The rational behind this is that with a four blade prop two blades at a time will be behind the keel with each revolution.  As you can see in the picture of my five blade prop, with each revolution of the prop only one blade will be behind the keel at a time leaving FOUR blades in clear water versus two for the standard four blade prop.  You can imagine what a difference this makes in efficiency and thrust/power with four blades in clear water with each revolution versus two.  Another advantage is with my much larger sail area then most Ducks and with the drag of a big prop completely eliminated by the fully feathering feature of my prop, I can really sail.  I love telling the story of how when fishing on my three week voyage to Southern California from Hawaii we put the engine in neutral to reel in a fish.  The sails were up at the time for steadying purposes with the wind hitting us about 30 degrees off the bow and with the swell and current directly on the nose.  A strong gust of wind slowly spun us around pointing us back in the direction of Hawaii again.  The wind caught the sails filling them completely and with the wind now behind us and the swell and the current now pushing us we were headed back to Hawaii under sail only with the engine in neutral at 6 knots.  Moby Duck would have no problem crossing the Pacific under sail only in the trade wind belt going the right direction.  Unlike what I did.  Plus, with the prop efficiency and large amount of sail area when I am motorsailing I am only burning a little over a gallon an hour at 6 knots.  With my 2000 gallons of fuel I have over 12000 mile range under power.  An additional advantage of my prop is the ability to easily change the blade pitch while the boat is in the water.  You rarely change the prop pitch but it is nice to know you can if there is a problem and you need less load on the engine.  

Back to my explanation of why you should clean the bottom of the boat yourself.  When I clean the bottom I use at the most a plastic scraper very lightly.  For the first two years of the bottom paint's life, when its growth killing properties are at their peak, I will use only a coarse rag to wipe the bottom clean.  The vast majority of boat owners use a commercial service.  Their divers will use a metal scraper to quickly and most efficiently clean the bottom.  They could care less what this will cost you in the long run only concerned with cleaning a set amount boats in a given amount of time.  With each swipe of the sharp metal scraper they remove a very thin layer of bottom paint greatly accelerating the time between haul outs.  There is another problem with this.  On, steel boats like Moby Duck the welds on the steel hull plates below the water line are not ground flat and faired.  They stick up about an 1/8 of an inch above the flat hull plating.  The rational for this is that no one will see them underwater and why not leave them thicker and stronger.  So, if you are not careful when scraping the bottom, after a short period of time a metal scraper with sharp edges will scrape both the bottom paint and the primer off of the welds.  Almost all of the boats in my marina are in a one year to 1.5 year haul out schedule.  When cleaning the bottom I carefully inspect every square inch of the bottom looking for potential problems.  The haul out confirmed that my bottom care procedure works with NO corrosion issues whatsoever.  If you look at the picture of the hull zinc you can see what a weld on the underwater part of the hull looks like.

Another reason my bottom paint has lasted five years is the quality of the paint.  Due to environmental regulations the type of paint I used is not legal in the USA.  The Philippines has no such regulations.  I used an extremely hard oil based epoxy two part primer that is used on commercial ships that have extended haul out schedules.  In addition, I used a two part hard epoxy bottom paint.  There are two types of bottom paint – ablative and hard.  The ablative bottom paint is meant to wear away as you use the boat taking the growth with it.  Again, the downside of this is greatly decreasing your time between haul outs versus a hard bottom paint.  During this haul out I wanted to match as closely as I could what I applied in the Phillipines but without breaking any California/USA environmental regulations.  I contacted the AkzoNobel Interlux paint representative.  He told me that the only way to repeat the performance of those highly toxic but extremely durable paint I bought in the Philippines would be with by extremely careful preparation of the bottom,  many additional coats of paint then what would be normally used and additional drying times.  Most shipyards will paint and launch in the same day.  A very good shipyard gave me a quote of $4500 to do the bottom including hauling, launching, power washing, light sanding and the cost of the paint and application.  Their labor rate is $115 an hour.  I ended up doing it myself for $7000 and doing it "right".  "Right" means completely sealing the bottom again with multiple coats of a two part epoxy primer specifically Interlux 2000 and then multiple coats of Interlux Ultra hard bottom paint with additional drying time and sanding.   Many more than what is normally done.  The additional money was spent on paint versus what the shipyard quoted me.  Top of the line bottom paint these days is almost $300 a gallon.  I used 10 gallons.  When the boat was initially hauled out of the water the shipyard manager was shocked at how well the bottom looked after 5 years.  The bottom paint was almost completely intact.  I proceeded to sand the bottom paint removing any loose flakes and abrading the service.  The primer and bottom paint were then applied with extended drying times between coats.  I gave the boat an extra 2 days on the hard just to make sure everything was dry.  The shipyard charges $175 a day just to have the boat out of the water in their shipyard.  To give you an idea of what the shipyard will normally do is that the paint specs allow reimmersion after only 8 hours of drying with the paint still soft to touch.

After paint I proceeded to replace the hull, prop and thruster zincs.  The hull of the Duck is overzinced so the other zincs have very little to do and last a long time.  Each of the 16 hull zincs was replaced with a top quality Martyr brand 17 pound flat zinc.  All of the thru hulls were greased and exercised.  The Duck has a commercial sea chest system.  That means there is only one below waterline thru hull.  For comparison, my friend's Nordhavn 43 has 13.  It is really nice that when I leave the boat that I just close the one thru hull and have eliminated any potential problems with regards to water entering the hull through a bad hose or valve.

I have included a picture of my stern thruster and water sports platform.  Note how the platform is welded to the hull in six different places.  Overbuilt.  It had no problem supporting my 850lb Sea Doo across the Pacific Ocean.  When the Sea Doo is removed it makes a perfect place to use for entering the water with heavy scuba diving equipment.  In addition, I will store my dinghy there allowing easy deployment and retrieval.  I can do this with either the 1000lb rated hydraulic davit or with the rope and pulley system on the dual davits.  If you are cruising in poorer parts of the world it is imperative that you have an easy system for your dinghy.  Everywhere I went in Mexico, Central and South America and various places in SE Asia there was always some cruiser who left his dinghy in the water and it disappeared overnight.  The stern thruster makes any docking situation easy.  Being able to move the boat sideways by simultaneously using the bow and stern thruster or kick the stern around with the stern thruster in a single screw, very heavy boat like the Duck is invaluable.  The good news is that the Duck is so heavy and with the deep keel it takes a lot of current and wind to move it around as you approach your berth.  The bad news is that once it starts moving it takes a lot of power to stop it or maneuver it.  Along with the 360 degree view from the flybridge, where you want to be when docking, the bow and stern thruster take the stress out of leaving and entering a berth.  In the flybridge picture you will note the bow and stern thruster control right next to the helm. 

There is another picture of the keel cooler.  You have to look closely at the picture with guy remotely controlling the travel lift.  Look carefully at the keel and you will see a large tube welded to the surface of it.  This is another system found mostly on commercial boats.  The coolant leaves the engine goes through the keel cooler and radiates the heat into the sea water and then reenters the engine.  This way, no saltwater ever enters your engine.  Normally there will be a seawater intake thru hull and another seawater exhaust thru hull with the seawater running through a heat exchanger on the engine using an engine mounted pump.  There are multiple zincs in that system that require constant maintenance to avoid corrosion in the internal passages of your engine.

Happy to be ready for another 5 years of trouble free use of the boat!  I get a good laugh when people tell me that steel boats are a maintenance nightmare compared to fiberglass boats.  The first thing they think of is rust issues.  The epoxy coatings available today completely seal the steel with no chance of corrosion.  The coatings are so durable you can hit them with a hammer and they don't crack off.  Sanding is very difficult.  There was absolutely no sign of any type of corrosion on any portions of my hull.