To improve sailboat performance with the wind as a finite source of energy, Bob Johnstone knew that stronger, stiffer, and lighter high-tech construction with a low VCG worked wonders. Typically, powerboat builders didn't care: They just built boats heavy and cheap, then added more horsepower. This left the door wide open for some sailors to create MJM Yachts as the first seriously built motoryacht with strong/light high-tech epoxy composite construction that utilized a post-cure process. The net result was a faster, lighter motoryacht that had impressive fuel-efficiency. "Twice the Fun, Half the Fuel" became MJM's mantra. As the technical editor of Soundings commented, "MJMs are built like the Boeing Dreamliner. They could last 100 years!" When setting out to build the world's most capable motoryacht, the vision was clear and ambitious. These new yachts would not only need to be fast and fuel-efficient, they had to be far more comfortable and stable, a step beyond anything available on the market. This meant advanced design and engineering, an innovative manufacturing process, and tougher, more expensive materials. This quality of construction is one of the fundamentals that set MJM Yachts apart as the finest in its class.


This is a semi-transparent CAD image of an MJM Yachts 50z showing all major equipment, layouts, and interior spaces.

Advanced Design

With the concept in mind, the next challenge was design. Who had the best eye in the business for drawing a pretty boat? To answer this, MJM founder Bob Johnston turned to highly acclaimed naval architect Doug Zurn, of Zurn Yacht Design. Using the latest computer-aided design (CAD) software, the design began to take shape. After beauty comes safety at sea, which means structural strength.

MJM yachts are designed to exceed small craft structural requirements for ISO Certified Category A Ocean. This is the International Organization for Standardization's most stringent design category. It is defined as the "category of boats considered suitable for seas of up to 7 meters (23 feet) significant wave height and winds of Beaufort Force 9 (41-47 knots) or less." In fact, the only two Downeast style yachts of any size Certified Category A Ocean are the MJM 40z and 50z. There is a comforting peace of mind and confidence gained from knowing that your boat is the best built and has the safest design possible.

Only then are creature comforts addressed: side access doors, flush main deck, an open pilothouse with 360-degree views, and the spacious great room below decks. The CAD software allows the design team to work on ergonomics and properly position all equipment and sub-systems. Being able to visualize and manipulate in a virtual environment how components and equipment will fit into a space and interact with other equipment and the crew allows for perfecting a design prior to actual manufacturing.


In this image amidships of a 50z, you see placement of the Seakeeper gyrostabilizer under the ladder,
the air-conditioning system forward of that, and the inverter/charger in blue.

 


Here is a look at a screen shot from the computer-aided design process.
The different colors represent different structural core density based on loads and stresses.

Advanced Engineering

Building a performance yacht like an MJM takes a great deal of planning and engineering to predict stresses and loads placed upon all structures. Here computations for weight, vertical center of gravity and hull shape interact to determine materials to be used to deal with forces impacting the yacht. The combination of design, engineering, materials and processes determine the final outcome, and is why an MJM is so stable, fast and fuel-efficient. A key part of the design is MJM’s improved deep-V hull shape, which influences speed, stability and handling. Other factors include buoyancy and bow shape, which on an MJM serve to eliminate a delayed response to the wheel, bow steer, or burying the bow in large following seas, not to mention helping to keep guests dry. A low center of gravity and narrow beam with chine flats redirect wave and wake energy outward and downward to dampen roll in a seaway. The narrower hull shape slices through waves instead of slamming or having each small wave create a mini collision and jolting the crew. These are just a few of the key engineering points that differentiate an MJM.


This is a look at the Corecell stringer system, with the different colors representing various densities.
This structure will be encapsulated with Eglass and epoxy in the hull, creating a unitized structure.

Superior Materials

In real estate it’s all about location, location, location; in performance yachts you can say it’s all about materials, materials, materials. Each MJM yacht is constructed from superior materials selected specifically for weight, strength, stress loads, and function. Minimizing weight is essential in a performance yacht, but you can’t do that without increasing strength and stiffness. For this reason, Master Builder Mark Lindsay and his Boston BoatWorks (BBW) were enlisted as MJM’s licensed building partner. Mark had over 30 years of high-tech boat building experience using advanced composite materials building America’s Cup, World Championship, and Olympic racing sailboats.

Epoxy, though far more expensive than traditional polyester and vinylester resins, is a much better adhesive that is 25% stronger and has greater flexural strength for longer life. Another advantage is the more tightly linked molecular structure that makes it almost impervious to osmotic blistering. In fact, the prescribed cure for boats suffering from bottom-blistering is the application of a new outer layer with epoxy resin.


This hull laminate shows a Kevlar/Eglass hybrid outer skin that uses stitched biaxial Eglass, along with a 1-inch Corecell SAN (styrene acrylonitrile) closed-cell foam core, all layered with pre-preg PRO-SET Epoxy (38% by weight), then vacuum-bagged at up to 14.7 psi and high-temperature post-cured at 145 degrees F.

The choice of Corecell is also based on strength-to-weight factors and is used to core the entire hull, deck, and superstructure. The combination of the Corecell and Kevlar in the outer skin creates a structure similar to a continuous I-beam that is stiff, strong and light. The engineering dictates what density of coring should be placed in various areas of the hull and deck. Each panel is pre-cut and numbered for installation.


Professional Boatbuilder Magazine wonders why all builders don’t use this wet impregnator system  of high-pressure rollers to saturate fiberglass material, and at the same time squeeze out excess resin, before the cloth material is put into the mold.
Other builders use either the traditionally cheap method of laying sheets of cloth in the mold, spraying copious amounts of resin on it, then hand-rolling; or laying dry glass sheets in the hull, bagging it, then infusing a diluted resin by vacuum. 

The process on MJMs results in a stronger 60:40 glass-to-resin ratio, rather than the reverse. Resin is glue and should be minimized.

Advanced Composite Construction

These materials are then utilized in a revolutionary process in the hull and deck molds. The inside of the mold is coated with a premium epoxy-compatible gelcoat. Then the outer skin is a wetted, epoxy-impregnated Kevlar/E-Glass cloth that is unrolled to go the full length of the boat. This results in strands of fiberglass going from bow to stern instead of being chopped up or sectionalized in short pieces. The Kevlar provides added impact resistance, which is what it does in bulletproof vests. Next comes the waterproof Corecell structural foam and finally the inner skin of E-Glass. There is no wood in the structure of an MJM. The hull grid with foam-cored stringers and bulkhead landings are then installed and encapsulated in a fiberglass laminate.

The next step is to bag the hull and grid with a plastic sheet. The edges are sealed and vacuum lines installed before pulling a vacuum, which compresses the laminate with a force of approximately 2,000 pounds per square foot. This process ensures there are no air voids and ensures a unitized, lightweight, and strong structure.

The last step in the lamination process is to post-cure the molded parts for 24 hours. This process allows epoxy to cure at a better molecular level than polyester and vinylester resins which on other boats continue to cure over the first year with the potential for serious print-through.


A look at the two large curing ovens at Boston BoatWorks. Each hull and deck is post-cured for 24 hours at 145 degrees F.

Epoxy-built MJMs are stronger, lighter, and longer-lasting. With hull and deck structures comprising up to 25% of a boat's total weight, you can understand why MJMs are in most cases many thousands of pounds lighter than similar-sized boats. But it doesn’t end there. Greater hull and deck weight requires more horsepower to reach acceptable cruising speeds. This means larger, heavier engines to get the boat going. Larger engines burn more fuel. That means bigger fuel tanks for reasonable range. It’s a vicious circle. MJM has taken an industry leadership role to reverse that circle and become "The World Leader in Fuel-Efficient Powerboats”.

Owner benefits are huge: better response at the wheel and more fun to drive; more speed per horsepower applied and a chance to take advantage of weather windows; and a lower center of gravity for more comfortable motion at sea. Soundings Technical Editor Eric Sorensen commented, "When it comes to the lifespan of today’s best-built boats…What’s to fail on an MJM? It’s an oven, post-cured epoxy boat. It’s as well-built as a Dreamliner, as far as I can see. There’s no reason that a boat like that couldn’t be here in 100 years.” Maybe 200 years, he later added.

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