CONFESSIONS OF A BOAT CREATOR by Bob Johnstone
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| 50z at 40 knots - Turning Water into Steam |
I was concerned about installing triple IPS 600s in the 50z because it seemed logical that 3 engines would
use 50% more fuel than 2 engines. MJM’s mantra has been “Twice the Fun, Half the
Fuel”. Wouldn’t this be undermining a key reason for MJM success? Our designer, Doug
Zurn, and the engineers from Volvo Penta straightened me out, “Bob, fuel efficiency is a function of
horsepower applied to overcome the drag of pushing a particular boat through the water at a given
speed. So, it doesn’t matter whether it’s 1, 2, or 3 engines, the same amount of HP is required to get that
hull going. So, 3 engines will each be working less than 2 engines.” But, I wasn’t buying that theory at
displacement speeds under 9 knots, where the major part of boat hours are spent in harbors, watching
races, on the ICW, etc.. Seemed 3 engines would be just humming there, not very productively, when 2
would more than do the job. They had no answer for that. Our most experienced dealer thought triple engines were a bad idea because his customers never
cruised over 25 knots. Of course, there weren’t many boats around that could, so that hindsight was a
safe 20:20 but his son said, “Go for it, Bob.”
PERFORMANCE EXCITES
Whether is it was blasting around the harbor in a Sunfish sailboat or a low freeboard Boston Whaler as a kid, those amazing moments launched most of us into the world of boating as a lifetime pursuit. Trouble is, as our boats got bigger, the thrill of driving the early sportscar like craft was being lost... along with that feeling of being one with wind, boat and waves. Restoring that joy of driving and performance was the motivation in creating J Boats, Inc., which is the leading performance brand of sailboats and where we’re going with MJM Yachts. So it didn’t take much encouragement from the more youthful of our MJM dealers to brighten the vision of having a 50z that outperformed the Sabre 48, Hinckley Talaria 48 and East Bay 50 by 10 knots, with the same 50 gph fuel burn at 35 knots others got at 25 knots, while keeping a lower profile, flush decks and side doors at floating dock height. We were off and running.
VOILA! 3 ARE BETTER THAN 2
Of the 11 MJM 50z’s ordered to date, 9 have been triples. Only 2 have ordered twins. One for shoal cruising on the Chesapeake and Bahamas and the other due to a ledge in front of his dock in Marblehead harbor. The 50z with twins draws only 2 feet 10 inches which is less than a 40z, because the drives are mounted further up and outboard under the hull on the deadrise. And, fuel efficiency of triples is marginally better at slow harbor speeds on a heavier boat than with twins. No one forecast this. My explanation from sailing days is that 3 sets of props blowing bubbles under the back end of the hull do a better job than 2 sets of props or even a single prop in helping the boat break loose from the drag of the water. Sailors were always brainstorming schemes to win races, like pumping liquid ivory soap through the head’s overboard discharge to lubricate the hull.
PERFORMANCE EXCITES
Whether is it was blasting around the harbor in a Sunfish sailboat or a low freeboard Boston Whaler as a kid, those amazing moments launched most of us into the world of boating as a lifetime pursuit. Trouble is, as our boats got bigger, the thrill of driving the early sportscar like craft was being lost... along with that feeling of being one with wind, boat and waves. Restoring that joy of driving and performance was the motivation in creating J Boats, Inc., which is the leading performance brand of sailboats and where we’re going with MJM Yachts. So it didn’t take much encouragement from the more youthful of our MJM dealers to brighten the vision of having a 50z that outperformed the Sabre 48, Hinckley Talaria 48 and East Bay 50 by 10 knots, with the same 50 gph fuel burn at 35 knots others got at 25 knots, while keeping a lower profile, flush decks and side doors at floating dock height. We were off and running.
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| Volvo Penta Triple IPS 600 (3x435 HP) D6 Diesels |
Of the 11 MJM 50z’s ordered to date, 9 have been triples. Only 2 have ordered twins. One for shoal cruising on the Chesapeake and Bahamas and the other due to a ledge in front of his dock in Marblehead harbor. The 50z with twins draws only 2 feet 10 inches which is less than a 40z, because the drives are mounted further up and outboard under the hull on the deadrise. And, fuel efficiency of triples is marginally better at slow harbor speeds on a heavier boat than with twins. No one forecast this. My explanation from sailing days is that 3 sets of props blowing bubbles under the back end of the hull do a better job than 2 sets of props or even a single prop in helping the boat break loose from the drag of the water. Sailors were always brainstorming schemes to win races, like pumping liquid ivory soap through the head’s overboard discharge to lubricate the hull.
