Power & Tech­nol­ogy

Su­per clean and ef­fi­cient, com­mon-rail diesels look to shake things up in a de­mand­ing, white-hot out­board mar­ket.

Power & Motor Yacht - - IN THIS ISSUE - By Jeff Moser

Two out­fits from across the pond en­ter the white-hot out­board mar­ket with ef­fi­cient, torquey diesels.

De­mand for high-horse­power out­boards has never been greater. And the lat­est-gen mo­tors have an­swered the bell: They’re more pow­er­ful, re­li­able, en­vi­ron­men­tally friendly and won’t work as hard to keep a faster cruise speed.

They’ll get you there quicker, but that in­crease in horse­power means you’ll burn more fuel. Could a diesel out­board be an ef­fi­cient power op­tion? A few com­pa­nies from across the pond are bet­ting on it.

Re­cently, I got on board a 21-foot High­field 660 RIB with a 150-hp OXE diesel out­board on its tran­som, the first oil-burn­ing out­board to meet EPA Tier 3 emis­sions stan­dards in the U.S. OXE’s par­ent com­pany, the Swe­den-based Cimco Ma­rine claims it’s 55 per­cent more fuel ef­fi­cient than a 150-hp gas out­board—an eye-open­ing state­ment.

The first thing I no­ticed was the size. The cowl­ing is wider than a com­pa­ra­bly pow­ered out­board be­cause the diesel is mounted hor­i­zon­tally, not ver­ti­cally. Also un­like gas out­boards, it uti­lizes a belt-drive sys­tem re­port­edly more durable than bevel gears and al­lows for the diesel’s in­creased torque to be trans­ferred more ef­fi­ciently to the prop.

I ran some num­bers and came away im­pressed. The 2.0L turbo is def­i­nitely torquey. I had Chris Pon­nwitz, mar­ket­ing spe­cial­ist for OXE dis­trib­u­tor Mack Boring fire­wall the throt­tles and the RIB was on plane in less than five sec­onds on its way to 32 knots in 15. It’s also stingy on fuel: At an op­ti­mum cruise of 3250 rpm, the boat ran at 24 knots and burned a mi­nus­cule 5.9 gph, good for a 294-mile range.

Don’t ex­pect a clam­orous pow­er­plant, ei­ther. I mea­sured 73 deci­bels at the helm and 78 at the tran­som at idle. (The wind and wa­ter ob­vi­ated a true read­ing at higher speeds, as the RIB is an open boat.)

OXE has big plans for its out­boards. The 150- and 200-hp mod­els are here and there are plans to fill out its of­fer­ings with mod­els from 125- to 300-hp.

Like OXE, Eng­land’s Cox Pow­er­train be­gan the de­vel­op­ment of its diesel out­board with the NATO Sin­gle-Fuel Di­rec­tive in mind: The idea is to have one source of fuel for all types of wa­ter- and land-based craft. While the con­cept is aimed pri­mar­ily at the mil­i­tary sec­tor, it’s a po­ten­tial gain for su­pery­acht ten­ders and other ac­com­pa­ny­ing ves­sels to match the fuel of the mother ship.

Cox pre­miered its pre-pro­duc­tion (full EPA cer­ti­fi­ca­tion is im­mi­nent, and pro­duc­tion is slated for mid-2019) twin-turbo, 300-hp model at last year’s Ft. Laud­erdale In­ter­na­tional Boat Show with a twin setup on a 34-foot In­trepid. Like OXE, the claims are im­pres­sive: 25 per­cent bet­ter range and 100 per­cent higher torque ver­sus its 300-hp gas coun­ter­part.

There are a few caveats: weight and price. The OXE out­board tips the scales at 770 pounds and will sell for about $46,000; that’s an av­er­age of 300 pounds heav­ier and about three times the cost of a gas out­board. The av­er­age weight for a 300-hp gas out­board is 551 pounds and Cox’s V8 is 826 pounds; at $50,000, it’s roughly dou­ble the price.

A diesel out­board could po­ten­tially re­coup these costs over the en­gine’s life­span: Both claim their en­gines have a longer run life than their gas com­peti­tors based on the su­pe­rior dura­bil­ity of diesels. And ser­vice in­ter­vals are fur­ther apart. One thing is cer­tain—you’ll burn less fuel.

Time will tell if a diesel out­board can take mar­ket share from the tra­di­tional out­board sec­tor. I sus­pect the en­gines can have a big im­pact with out­fits like the Coast Guard, in com­mer­cial ap­pli­ca­tions or for recre­ational boaters who run the heck out of their boats. Week­end war­riors will never make up the cost.

We plan on run­ning the diesel out­boards head-to-head with their gaso­line coun­ter­parts to get some real com­par­isons on fuel burn, cruise, top speed and other stats. Look for the re­sults in an up­com­ing is­sue or in our sis­ter pub­li­ca­tion Out­board mag­a­zine ( out­board­mag.com).

Both the OXE (shown) and Cox diesel out­boards can be matched to sin­gle-lever and joy­stick con­trol.

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