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A better powerboat is born of performance sailing designs.




You’d think after founding the world’s leading performance sailboat company, J/Boats, Inc., creating nearly 14,000 sailboats in some 40 countries with dozens of  “Boat of the Year” awards, Bob Johnstone would have been ready to retire from boat building.  But, after he surprised his wife Mary, with a Dyer 29 powerboat on their 40th wedding anniversary to continue their life-long shared adventure on the water, the seed of a second boat company was planted.


MJM stands for Mary Johnstone’s Motorboat and the “Z” is to honor designer Doug Zurn who has a number of power and sailboat designs to his credit. First off the line was the MJM 34z, which was followed by four more models with the MJM 50z flagship introduced in 2014. There’s something about the DNA of sailboats applied to powerboats that has led to a very functional, seaworthy and beautiful outcome.


The MJM 50z in some ways is closer to being representative of a Maine lobster boat than other so called Downeast designs. Witness the flush deck from wheel to transom and spacious open layout. Eliminate the starboard aft corner post and install a hoist outboard of the helm and you’re there!  But, the MJM 50z goes way beyond a lobster boat in terms of comfort: side access doors at floating dock height, a full-length Bimini over the cockpit and HVAC all-weather boating with either sliding glass or roll-up Strataglass sides to create an entertaining space comparable to the upper fly bridge deck of a 100-foot motor yacht. Besides aesthetics, the layout is all about ease of movement and security at sea. There are only 3-steps down from bridge to the spacious Great Cabin below and stainless handrails everywhere… no scary flybridge ladders.


Johnstone brought his ‘best performing brand’ marketing strategy and sailing experience to the project.  The boats had to be fast, fun, easy to handle and fuel-efficient. He knew the only way to get there was through advanced composite construction… something no other powerboat company was doing.  This meant a pre-preg, epoxy, vacuum-set and oven post-cured Kevlar, Eglass and Corecell laminate for a stronger, lighter, longer lasting yacht with a lower vertical center of gravity for better stability. When combined with a 3.5 length: beam ratio (vs. the typical 2.7-3.0 ratio), a more sophisticated deep-V, with sharp entry and Carolina bow flare, this Eco-Smart design requires less horsepower to overcome drag, therefore uses less fuel.


In fact, the MJM 50z is one of only two Downeast designs of any length available from any builder to be certified ISO Category A “Ocean” for safety and seaworthiness, the other being the MJM Yachts 40z. You’d think that would be enough of an edge.  But, no!  Johnstone is thinking of maximizing owner experience, not just beating up on the competition… although he seems to enjoy that, also.  He took a giant step to further maximize guest comfort by making the MJM 50z as steady as a sailboat in ocean waves. 50z became the first powerboat worldwide to come equipped with a Seakeeper gyrostabilizer as standard equipment. The 950 lb. gyro takes about 35 minutes to spin up to 9,000 rpm to eliminate 93% of the roll whether underway, at anchor or in a marina with shorepower

Step Aboard

The MJM 50z looks elegantly sleek at the dock and it only gets better once aboard. The aft transom has built-in seating. Additionally, two movable chairs are tucked in on either side, creating a five-across settee when underway.  Six are accommodated for meals when side chairs are pulled out to face the table. To starboard is an additional aft-facing double seat and across is a serving bar that includes a fridge or icemaker and an optional grill. You can lounge in open air and enjoy the sun, or hide from the elements under the full coverage of the yacht Bimini.


Twin Volvo Penta 435 HP D6 diesel pod drives with IPS joystick docking and DPS station keeping are standard. But, it seems that Johnstone has found some kindred spirits. 18 of the initial 20 buyers have opted for the triple engines for a top speed of 40 knots and cruising speed of 35 knots…10 knots faster than the competition. No surprise where that came from!  At 35 knots, she’s burning 50 gallons/hour, which is what others burn at 25 knots.  Pull back to conventional cruising speeds of 21 knots and she’s getting an unprecedented 1.0 NMPG.


Moving forward, you step under the hardtop into an all-weather area, which brings the outdoors in. You are surrounded by unobstructed 360-degree sightlines.  Yet at night, with drop down privacy curtains the space magically converts to a private, climate-controlled (A/C is standard) sleeping cabin for three. The extra wide pilot and co-pilot seats provide the safety of 2+ sets of eyes and offer as many as four people the joy of sharing navigation and adventures afloat.


A U-shaped dinette is located aft of the double Stidd helm chair. Opposite to port is a settee behind the wide Stidd co-piloting seat.  Under each settee is cavernous and lockable storage, each capable of hiding two full-size bicycles where they won’t rust or be stolen. A center deck hatch houses the Seakeeper gyro and optional side-by-side Miele washer and dryer.


Forward of the helm are two of the new Raymarine gS165 multifunction displays, a large designated depth display and autopilot control. Volvo Penta EVC engine panel, trim tab control, IPS joystick and spotlight control are on the lower surface. A VHF radio is conveniently mounted on the overhead to starboard within earshot. The nicely varnished 24” destroyer wheel will make sailors feel very much at home and in control as they maneuver the boat with finger tip ease.  The Luxury of Effortless Driving.


Because few people are left-handed, I questioned the positioning of the joystick at the center of the dash and to the left of the wheel. Johnstone demonstrated that in the most difficult move, which is trying to swivel around, looking aft when backing into a slip: the joystick is perfectly located for a right-hander. Left-handers can stand on centerline, facing aft, and have an even better perspective.

Inviting Interior
Three steps lead down to the interior, which is almost like not going below because it’s wide open with a view to either side and plenty of light from about 50% more opening ports and hatches than you’ll find on any other boat. To port is a full galley with two-drawer refrigeration, two-burner ceramic cooktop, microwave/convection oven, deep sink, and a Corian countertop with workspace for two people without getting in each other’s way.


To starboard are a large L-shaped settee and a hi/lo electric table that lowers to make a double berth. Privacy for this innovative, multi-use cabin comes either in the form of a heavy Pullman curtain or a cleverly designed removable hard wall with panels that stow out of sight when not in use. The spacious guest head with glass enclosed shower serves those sleeping here and on the bridgedeck… or becomes the luxury of a his or her head with just a couple aboard.


The large master stateroom, “Flag Country” in naval terms, is like none other on a powerboat of this size. Along with the largest, most comfortable berth in boating that is 68” across and 78” long, there are two hanging lockers, a “Stressless-Type” easy chair, a dressing table/workstation and an Ultraleather pouf that doubles as desk chair, footstool, and supplementary guest/dining chair (two are provided) anywhere in the boat. I’m not one to sit below when there’s such a great bridge deck above, but that chair and a good book will be tempting.  All this and two overhead deck hatches… one right over the forward half of the berth, so you can watch the stars at night, not feel claustrophobic or pop up at night to adjust the anchor line without getting out of bed or roaming the dew covered deck in your skivvies.  Standard finish is classic Herreshoff sailing yacht elegance: cherry trimmed antique white panels with cherry slatted hull sidings. On the MJM 50z,  “down below” isn’t that “down” or “below”.


With triple Volvo Penta engines, only the outer two engines are rotating in the joystick IPS docking or DPS station keeping mode, yet the 50z can be operated at very slow speeds with just the center engine.  Or if anticipating the need to navigate a soft, pluff mud shoal (2’10” deep rather than 3’10”), the center engine could be turned off and very slowly dragged through the mud by the outer two. What seems illogical isn’t.  Sea trials of the standard 50z with twins demonstrate that triples, even with more weight, are more fuel-efficient.  That’s because the total horsepower needed to overcome resistance at a given speed, whether one, two or three engines, doesn’t change.  Fuel burn, a function of horsepower applied, doesn’t change.  Twin engines need more RPM each than triples at a given speed. What is mind-blowing, but explained by racing sailboat experience: Triples are more efficient than twins at displacement speeds under 10 knots. Johnstone’s explanation (Volvo Penta didn’t have one) is that prop wash from 3 engines is better distributed across the width of the hull’s underbody than with one or two engines… more effectively releasing the hull from the grip of the water. On a racing sailboat, he made it a practice to eliminate any radius between bottom and transom…  keep a sharp razor edge, so the water breaks away clean without turbulence and resultant drag.


In open water, our test boat took predictably comfortable and even turns at high speed and sliced through the waves with barely a shudder. In a light, early morning breeze of 5-8 knots and one-foot chop, we carved figure of eights to make waves to test the ride and the Seakeeper’s effectiveness. Coming broadside into three-foot peaks, we rolled, but a bit less than you’d expect from most powerboats. Then we repeated, but this time with the Seakeeper gyro engaged. I couldn’t hear it with the engines running. The boat immediately settled down, even when broadside to the waves.  The Seakeeper is like being anchored to a rock.  No herky-jerky response to a wave.  The boat just doesn’t move.  It’s like there are no waves. Nice.

Johnstone isn’t the only one to set his sights on the growing Baby Boomer population that may be done with hoisting sails. However, in case you think the MJM line of motor yachts is just for retiring sailors, think again. The East Coast-born styling will impress even those who have never set foot aboard a sailboat and will also tempt anyone moving down from larger trawler yachts. “This boat lets people downsize with dignity,” says Johnstone. “They give up very little spacious living and gain the ability to run a fun boat alone if necessary, and with friends and family whenever they want. It’s spur-of-the-moment easy.”


Old sailors never die; they just keep on boating with bigger engines. With the MJM 50z, other aging salts (of the non-professional variety) can make a dignified transition and still be able to defend this amalgam of sail and power over cocktails at the yacht club.  If Johnstone can do it, everyone has permission. As this National Sailing Hall of Fame inductee says, “I thought I’d be the last one to ever own a powerboat.”


LOA: 55'3"
Beam: 15’0”
Air Height: 10’6”
Draft: 2’10” Twin IPS 600, 3’10" Triple IPS 600
Displacement: 32,850 lbs. Half Load
Fuel: 520 gallons
Water:  170 gallons
Propulsion:  3x435 hp Volvo Penta IPS 600
Price w/Triples: $2,045,000 Base