Mercury Diesel Sterndrive test ride
 

I got a ride today on a 2012 Chaparral 19' deck boat/bow rider powered by a 150 hp 2.0L turbo diesel sterndrive. This boat was just repowered after having "sunk" on the trailer last year. (plug in, lots of rain, dead battery).

Old power was a 3.0L 135hp EFI. I can't speak directly to the performance with the old motor, but the brief ride today was interesting. New power was a reported $23K installed including a new fuel tank. (This was almost $6K more than was quoted prior to install)

Old 135hp gas motor (as reported by owner):
Top Speed - 42 mph
Cruise speed - 25 mph
Fuel consumption at cruise - 5.5 gph
Fuel consumption at 80% power - 8.5 gph (about 35 mph)
Time to plane - "about" 4 seconds

New 150hp diesel motor (observed with Smart Gauges):
Top Speed - 48 mph
Cruise speed - 24 mph
Fuel consumption at cruise - 2.9 gph
Fuel consumption at 75% power - 6.7 gph (about 35-36 mph)
Fuel consumption at WOT (3950 rpm) - 7.9 gph
Time to plane - 4.5 seconds.

It falls off plane at about 17 mph now, He never noticed what if did before. New power plant is about 115-120 lbs heavier than the old, according to the owner.

That's 8.3 mpg at cruise, a 65% increase in economy, and still better than 6 mpg at WOT! New motor has power steering (not ordered, but installed and charged by the dealer in P'cola anyway, an extra $900)

Because of the Diamond 4 Prop, I think with changing the prop he can get better planing performance with the right SS prop.

I noticed it is VERY quiet, even at 75% power. We were able to talk without trying to shout over the engine noise. WOT is still noisy, though.

One thing: Even with the diesel, it still didn't ride like a SeaCraft. It still rode like a Chaparral. :\
And Choctawhatchee Bay was really rough today. :(

How much does the diesel package weigh? (Total of engine & Outdrive) Would two of them fit in a 23' I/O set up?

Don't know about 2 of the 150HP but one of these will fit nicely:https://mercurymarine-gsdesign1.netd..._370_tier3.pdf
It is a twin turbo 4.2L 370 HP VWMarine engine with a Merc label. Brake Specific Fuel Consumption is about 40% of what it is for a small block chevy and it weighs about the same. I'm pretty sure it costs a good bit more though...

Cost is the big factor considering diesel power when compared to any gas set up OB or IO. On commercial boats that put 1k+ hours a year on the power it can make financial sense to go with diesel as the amount of fuel used over time will offset the increase in cost. That said, most recreational users will never use the amount of fuel over time to offset the overall cost difference between the two.

Overall fuel cost is a lot less of a factor for us here in the US than for motors in the Med where a lot of boats come with these small automotive diesels. Regular gas for a car on the motorway is still between $4.50 and $6.50 a gallon in Spain, France, the Netherlands and Italy. As of this spring, low sulphur road diesels was about 78% of the cost of gas on the street in France. That little VW, even with the suprise price increase still went for about two times what a new Yamaha F150 would go for with its controls I suspect. if you were paying those kinds of prices, how long would it take you to make up money if you were burning less than 60% of the fuel at cruise fuel that cost 80% as much?

Each is about 115 lbs more than the 140/3.0L with the alpha one drive. As for size, it's a bit bigger, especially in height, 3" longer, 4" wider, and 9" taller than current the current 3.0, and just 4" taller than the pre-1992 carb'd 3.0L

32"L x 30"W x 30"H, compared to 29 x 26 x 21".

Oh, yeah, it's about 2.5x the price, not counting the changes necessary to your on-board fuel system. Complete package; motor, transmission, transom group and drive is over $20K USD installed.

But if you use the boat a lot, and plan on keeping it for 20+ years....

Interesting. That is less than I thought it would be if the price includes the outdrive. I thought that low $20K price was just for the "bobtail" engine. If the 230/260hp 3 liter V6 with the Bravo setup if priced proportionally to the 150/170 2 liter package, then maybe it becomes a bit more attractive option in situations where folks are converting slightly larger I/0 boats to bracketed 6 cylinder 4stroke outboards.

the 370hp V8 with a Bravo XR drive is about 45k. Same width as the v6 just a little longer.

I had heard that low to mid 40's number for the 4.2 liter engine, but once again was not aware it included the beefed up Bravo drive which is a pretty big ticket item on its own. That is somewhat encouraging. The test numbers that I have seen for the 370hp have been in the 10-10.5 gph range at the economy cruise speed of 3000 rpm and around 20-21 at WOT of 4200. That's about 2/3 the fuel burn of a 300 Verado. If the 265 hp 3 liter in in the low $30K range, how much more is that than the MSRP for a new 4.2 liter Yamaha Outboard with the fly by wire setup?

Even if the cost was a wash, which I am doubtful, the extra weight and reduced performance at cruise and top end would be a deal breaker for me. The slowest I cruise is 24 knots and on a good day 28-30.

Personally I love diesel power but not on small boats. I've seen them on 23' boats and other than fuel economy they just are not very impressive.