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POWERBOAT
DESIGNS
MOLOKA’I STRAIT 72
for voyaging
Built
by:
MOLOKA'I
STRAIT MARINE
Sales:
Annapolis, MD
Tel: (410) 315-8156
The first MOLOKA’I STRAIT 72, lengthened to 75', was launched in June 2006 and is undergoing seatrials. More construction photos and running photos are at the bottom of the page.
Painting by Joe Comeau
PARTICULARS
Loa
72’ 0”
Lwl
60’ 0”
B
22’0” hull 23’ 4” rubrails
D
7’ 0”
Displ.
266,000 lbs. at Dwl242,000 lbs. mid-cruise
Block Coefficient
0.42
Prismatic Coefficient
0.60
Lbs./inch immersion
5,523 lbs/in
Displ./Length ratio
474 mid-cruise displ.
A/B area ratio
2.31
Installed power
2 x Cummins 8.3 liter diesel, 350 HP @ 2500 RPM
Speed
11.0 knots, maximum 9.0 knots, average cruise
Speed/length ratio 1.2 cruise
Range 4,500 miles @ 8 knots
Fuel capacity 6,620 gal
Water capacity 1,072 gal
Black water & gray water capacity 310 gal each
Specifications subject to change
Designed and fabricated for serious voyaging and living aboard, the MOLOKA’I STRAIT 72 hull is constructed of A36 marine-grade steel. The deck house is built in 5000 and 6000 series marine grade aluminum. Moloka’i Strait Marine (MSM) is seeking serious buyers for the first few vessels. Owner participation throughout the entire design and construction process is welcomed and encouraged to truly customize each handcrafted yacht.
GENESIS OF THE DESIGN
In April 2002, Moloka’i Strait Marine (formerly Moloka’i Strait Marine) commissioned Sponberg Yacht Design Inc. (SYDI) with the design of the MOLOKA’I STRAIT 72, a steel and aluminum expeditionary motoryacht which was to be a larger sister to the MOLOKA’I STRAIT 65. With the early success of the 65s under construction, MSM determined it was time to begin the third boat in the Moloka’i Strait design series. The 72 has all of the amenities of her smaller sister and then some, but it will still be easy to handle and operate for single-couple owners. Owners that desire a permanent crew will welcome the self-contained crew suite forward. The second design in the Moloka’i series, the MOLOKA’I STRAIT 58, is currently in development.
The MOLOKA’I STRAIT design style is inspired by the Romsdal fishing trawlers of Romsdal, Norway. This type of design is characterized by a relatively clear foredeck, a superstructure set amidships to aft, and a rounded (what we call "cruiser") stern. We have incorporated a bulbous bow into the design to reduce resistance.
HULLFORM
The hull is a heavy displacement type with a bulbous bow and cruiser stern. Long range cruising speed is 8 knots (anticipated range 4,500 miles) with a maximum speed of 11.0 knots. Range at 8.5 knots is projected to be 3,700 miles, and at 9 knots, 3,000 miles. The hullform is designed for generous interior volume with standing headroom in the engine room.
The bow and bulb shape are derived from the MOLOKA’I STRAIT 65. Many trawlers suffer from uncomfortable pitching and heeling. The pitching (almost like hobby-horsing) on many other boats of similar size seems to come from the fairly straight, wall-sided shapes of the bows. When such boats get into significant waves, there is little bow shape to dampen the motion. The wall-sided bows sink readily without absorbing much energy. As on her smaller sister, I put generous flair into the bow plating on the MOLOKA’I STRAIT 72, so that as it pitches down, the bow’s submerging volume increases more quickly than on a wall-sided bow, thereby absorbing more of the pitching energy.
The MOLOKA’I STRAIT 72 also has a Nabla-style bulb, like the 65, which is characterized by being V-shaped on its bottom surface and flatly rounded on its top. The V-shaped bottom cleaves the on-coming waves without slamming, and then as the bow pulls up on the return motion, the higher drag of the rounded top of the bulb slows the bow's lift. The resulting difference in speed between the bow sinking and returning is the damping effect of the bulb. Pitching motion bleeds out quickly, making for a very comfortable ride. Bulb proportions are critically important. A bulbous bow is designed primarily to reduce the wave-making resistance of the hullform which means you can reach the design speed with less horsepower. Resistance is reduced because the bulb produces a wave that is opposite to the normal bow wave.
The round-bilge hullform makes for gentle rolling motion (as opposed to quicker, snappier motion of a chined hullform). Naiad active stabilizers provide roll control. Therefore, we expect the motion of this boat to be exceedingly comfortable, compared to other designs on the market.
ACCOMMODATIONS
General. The MOLOKA’I STRAIT 72 is a four-deck boat with fly bridge, pilot deck, main deck, and below-deck accommodations. ‘Tween deck spacing is 7’ 6” for generous headroom throughout which leaves sufficient space for easy installation of plumbing, electrical, and HVAC services. Five watertight bulkheads divide the hull into 6 watertight compartments: anchor locker, crew cabin and bulb, guest cabin, master stateroom, engine room, and lazarette.
Below deck. The fore peak houses twin anchor lockers, and the 16” diameter Naiad bow thruster is installed in the bulb. The anchors and Nick Jackson 2500-lb. boat crane are mounted on a peak deck over the anchor lockers. A scuttle immediately behind the peak deck and under the crane provides private access to the guest/crew suite at the forward end of the accommodation. Going down the scuttle, at the bottom of the ladder, is the kitchenette that is fitted with two-burner stove, microwave, sink, and refrigerator. Access through the fore peak bulkhead is by two watertight hatches, one each into either side of the anchor locker. The bulb is open to the space underneath the crew cabin sole.
Stepping aft is a small passageway with doors that close off the kitchenette and the guest/crew cabin from the rest of the accommodation for complete privacy. The cabin has a queen-size double bed with ensuite head. To port of the guest/crew cabin is an exercise room that can be fitted with any manner of exercise equipment such as a treadmill, rowing machine or weights.
Going through the watertight bulkhead door and stepping down to the next lower level is the guest space with two cabins, one each port and starboard. The larger cabin to starboard has a queen-size double bed and ensuite head. The smaller cabin to port has over/under twin berths and an ensuite head. Just aft of the cabins are a laundry to port and the main stairway to starboard. Next to the laundry is a watertight door to the master stateroom, a suite occupying the full hull width. Fitted with a king-size double bed, it has generous closet space, a large ensuite head with Jacuzzi tub, and a complete entertainment center. The head, entertainment center, and hanging lockers separate the master stateroom from the engine room for particularly quiet living.
Next to the hanging locker, going through a watertight door, is the entryway into the engine room. The main engines have generous service room between them, and they have dry exhaust routed up the funnel. The 32 KW main generator is to port just behind the 965-gallon day tank, and the smaller 16 KW light-duty generator is opposite to starboard and aft. Both generators are equipped with wet exhaust. A workbench is located against the forward engine room bulkhead to starboard.
The aft engine room bulkhead has two exits, one a watertight hatch through to the lazarette, and the other a main entryway up to the cockpit on the main deck.
Main deck. The aft engine room entrance comes through a console built onto the back of the main deck house. It is also fitted with a sink and stowage. Immediately to port of the centerline is the Dutch-door access into the main saloon, and outboard of that is a stairway to the pilot deck. A flush-fit watertight hatch in the main deck provides access down into to the lazarette.
The main saloon has an L-shaped settee and table with two chairs situated to starboard, and a wet bar, wine rack, and entertainment center to port. On centerline forward is a fireplace that exhausts into the funnel. To port of the funnel is a day head, and opposite to starboard is a short settee and coffee table. All of this space is carpeted.
Forward of the main saloon is the main entrance and stairway on starboard with the galley to port. Stairs lead down to below-deck spaces and up to the pilot house. A wet locker nests into the stairway’s elbow. The galley is all-electric with 4-burner range/oven, large refrigerator and freezer, double sink, dishwasher, and trash compactor. On the forward side of the galley counter is a 4-seat snack bar, and at the starboard end, a dumbwaiter up to the pilot house. Coin-dot rubber flooring covers the main deck across the width of the galley/main entrance area.
At the forward end of the main deck accommodation is the fully-carpeted dining room, set up for easy entertaining. A large dining table is situated to port, and a wrap-around buffet to starboard provides generous serving and storage. Access into utility spaces forward is through decorative cabinetry doors that are situated under the tall windows in the forward end of the deck house.
The fore deck is large enough to house two boats such as an 18’ runabout to port and a smaller RIB to starboard. Between the boats is a ladder that leads up to the pilot house.
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Pilot deck. The wrap-around Portuguese walk leads to entrances into the pilot house port and starboard. A large console includes the ship’s primary helm, chart table, and electrical panels for AC and DC service. Twin Stidd helm chairs provide considerable comfort and visibility for two on watch through five large front windows. An L-shaped settee surrounds the port aft corner of the helm area, and the stairway leads down to the main deck. The dumbwaiter is built into the joinery between the settee and the ship’s office located in the port aft corner of the pilot house. The office is fitted with a single pedestal desk and filing cabinet, plus a sofa with pull-out double bed. Floor-to-ceiling bookshelves are situated near the entrance to the office.
Opposite the office is a small head for the on-watch. Next to the funnel is a locker that is underneath the stairway that leads up to the fly bridge from the aft pilot deck. The joiner bulkheads separating both the head and the office from the helm area are each fitted with joiner window panels situated in line with the aft windows so that the on-watch can see directly aft.
The aft stairway from the cockpit comes up to the pilot deck , and there is generous room up here for outside deck furniture. A bimini top can cover most of this area.
Fly bridge. The stairs from the pilot deck lead to the large fly bridge that is equipped with a secondary helm and two helm chairs. Complete controls for the main engines and bow thruster are situated to starboard. To port is a large L-shaped settee with table and galley facilities: two- burner hot plate, sink, and small refrigerator. A bimini top can cover most of the fly bridge area.
The mast is built onto the front side of the funnel and can be customized to the owner’s preference for electronics. The inside of the mast is also the chimney vent for the main accommodation ventilation system. The funnel holds the main engine and fireplace exhausts.
Power: The MOLOKA’I STRAIT 72 is powered with twin Cummins 6CTA8.3M (350C), in-line 6-cylinder, 8.3 liter, marine diesel engines turning at 2,500 RPM through Twin Disc integral V-drive gears at 2.5/1 reduction. Caterpillar is reworking their engine line, discontinuing some models and bringing new ones on line. We anticipate that their new C-9, 9 liter marine diesel will be a good fit. Propellers will be about 36” diameter on 2¾” diameter Aquamet 22 stainless steel shafts running through protective skegs that also support the twin double-plate rudders. Also included in the drive trains are Aquadrive thrust bearings and CV shafts to reduce shaft noise and vibration and allow the engines and gears to be more softly mounted.
Generator power will be by the two gensets, the larger one a 32 KW Northern Lights generator for 110 VAC, 60 Hz main house service. The smaller one will be a 16 KW Northern Lights generator for light-duty service.
Tanks: The main fuel storage tanks are located in the hull bottom with a total capacity of 5,655 gallons. A day tank of 965 gallons in the engine room brings the total fuel capacity to 6,620 gallons. Fresh water, gray water, and black water independent stainless steel tanks are located under the guest cabins. Total fresh water capacity is about 1072 gallons, and a 600 gal/day water maker is also provided. Gray water and black water tanks are each about 310 gallons.
METALS AND STRUCTURE
The hull is designed for steel construction, framed longitudinally, onto which is built an aluminum deck house. The two metals are connected by a Detacouple, which is an aluminum/steel strip that is explosively clad together, much like how our dimes and quarters are made. Detacouple was invented by DuPont over 30 years ago, and is now made by Dynamic Materials Corporation. The steel side of the strip is welded to the main deck, and the deck house is welded to the aluminum side of the strip.
The hull, main deck, and bulkhead plating is ¼” thick A36 marine grade mild steel. The main deck and the bulkheads are framed on 16½” centers, with the main deck longitudinal frames being steel flatbar, and those for the watertight bulkheads being angle bar. The hull longitudinal frames are NC-cut steel flats spaced on 18” centers. Hull and deck longitudinal frames are supported by NC-cut transverse ring frames spaced on 36” centers and fitted with flatbar T-flanges. The ends of the hull have ½” thick centerline plates, and additional deep longitudinal girders support the hull, form the engine foundations, and provide integral structure to the bottom fuel tanks.
The deck house is also longitudinally framed with transverse web frames on frame spacings similar to that on the hull. All web frames and bulkheads are NC cut, longitudinal frames and other girders are flatbar and structural shapes. Plating is ¼” thick 5083 aluminum, and all structural shapes are 6061 aluminum.
More construction photos from St. Augustine, Florida, where construction continued through 2004-2006:
Bow shot with new anchor pockets installed.
Stern view showing new swim platform that adds three feet to the length of the boat, which now makes it the MOLOKA’I STRAIT 7
5.
The first vessel is named Hercules.
M/Y Hercules in the Intracoastal Waterway on the way to the ocean for seatrials.
M/Y Hercules going out the St. Augustine inlet, riding quite well.
The flare in the bow does a nice job of keeping the spray away.
A final view of M/Y Hercules on the way back into port.
For sales information, you can go online to Moloka'i Strait Marine at http://www.molokaistrait.com
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