Home |
Search |
Today's Posts |
|
#2
posted to rec.boats
|
|||
|
|||
Yanmar Offers a Turbo Diesel Outboard
On Thu, 12 Oct 2017 20:22:05 -0400, wrote:
On Thu, 12 Oct 2017 23:58:29 -0000 (UTC), Bill wrote: wrote: On Thu, 12 Oct 2017 14:59:28 -0400, "Mr. Luddite" wrote: On 10/12/2017 2:13 PM, Bill wrote: wrote: On Thu, 12 Oct 2017 12:13:08 -0400, wrote: On Thu, 12 Oct 2017 11:17:07 -0400, wrote: Here's a real world example of the diesel vs gas engine trade off. Our old Bertram 33 had a 320 gallon fuel tank which seems like a lot but it had 454 gas engines which burned 35 gallons per hour. Cruising speed barely reached 18 knots on a good day. Doing the math, you come up with a safe fuel range of less than 140 miles, not enough for offshore canyon fishing in the NY area. Converting to diesel engines, the burn rate drops to about 20 gallons per hour, and cruising speed climbs to 23 knots or so, for a fuel range of around 300 miles. That's a big difference in the capability of the boat and has nothing to do with the price of fuel or reliability. That must be one heavy sommich if 2 454s only get you 18 MPH. The guy around the corner has a 36 (Donzi I think) with 2 250s on it that will cruise in the 30s burning a combined 25-30 GPH or so (a whole lot more at WOT tho) === A Bertram 33 is a much different boat than a Donzi: Heavier close to 20,000 lbs; Beamier; Windage from a full flybridge with enclosure; Full cruising interior. It would do 25 kts wide open with half fuel but I was concientious about keeping the RPMs at no more than 3200 or 3300. The whole point of my comparison excercise was to show that increased fuel range with diesel is often the deciding factor as opposed to fuel cost savings. I do understand the diesel thing. My buddy used to captain a bigger Bertie with 2 6-71s in it for a rich guy (46 or 50 sumpin?). Nice boat. Winter at Pier 66 and summer in Annapolis. He gave it all up for IBM and a family. There were IBM guys who said they would have just swapped jobs ;-) My friend has a 39’ Luhrs. Twin Cummins. They are heavier than a gas engine, but I bet not that much more than a 454. Unlike a 6-71. I was curious so I looked it up. A fully dressed 454 with cast iron heads weighs 685 lbs from the factory. A Cummins 5.9L diesel by comparison is 1200 lbs or 515 lbs heavier. Twins would mean a weight difference of over 1,000 lbs. That's quite a bit, even for a 39' boat. Major difference is: The 454 develops 450-500 lb-ft of torque at 3200 RPM (depending on year) while the diesel Cummins develops peak torque of 610 lb-ft at 1600 RPM The extra torque probably comes from the longer stroke in the diesel. (4.0" vs 4.75") They make gasoline engines "square" or even over bore to reduce the reciprocating forces of a longer stroke for a given displacement It lets them run at higher RPMs. Surprised me the difference in weight. A lot of the short stroke in gas engines is to reduce ring speed. A long stroke and high RPM and the speed of the rings becomes pretty astronomical. Lots of the fuel mileage comes from the BTU’s in a gallon of diesel vs. a gallon of gas. BTU is pretty much equivalent per pound of fuel, but diesel weighs more than gas per gallon. I supposed I was to know that after all of the generator talk and the BTUs of Diesel, gasoline and propane. Harry did. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Turbo Diesel Outboards | General | |||
Fuel/Oil slick from exhaust of Turbo Diesel | General | |||
Volvo vs Yanmar diesel | Cruising | |||
need help with Yanmar YSB12 diesel | ASA | |||
WTB: Yanmar D36 diesel outboard | General |