Gas vs. Diesel torque comparison

[Chuck Bates]

I decided to do a foot pounds of torque comparison (hp x 5252 divided by rpm. explained in way too much detail at: http://www.motorsanddrives.com/cowern/motorterms7.html) between gas and Volvo diesel sterndrives. Below links show what I found. Interesting......

3.0 & 4.3 vs. D3-130 & 160A
http://thehulltruth.com/photos/show-...4&photoid=7426

5.0 & 5.7 vs. D4-210 & 260A
http://thehulltruth.com/photos/show-...4&photoid=7427

8.1 vs. D6-310 & 360A
http://thehulltruth.com/photos/show-...4&photoid=7428

All
http://thehulltruth.com/photos/show-...4&photoid=7429

Diesel certainly isn't for everyone. Size of boat, amount of use, type of use (waterskiing, cruising, fishing), fuel availability, etc. all determine what works best for the individual.

Some advantages Diesel power has over gas:
- resale value
- dependability
- diesel vapours are less combustible
- gas engines pose a carbon monoxide hazard
- lower fuel consumption and fuel cost
- greater range
- longer life expectancy

Some advantages Gas power has over diesel:
- fuel barges more readily available
- less initial cost
- more gas mechanics available
- lighter

I'm sure there are more advantages and disadvantages that you can share with us......?

Those traditional values have limited value when they are applied to specific boat uses. offshore racers, drag boats, runabouts, ski and wakeboard boats, jet drives, wood boat restorations, turbine powered yachts and a few others. For slow, packed with people and furniture party boats,- they are the best,- if you do not mind their strong odors. They also leave a film on all surfaces of the boat if your exhaust rolls over you. Neither is better or worse. You pick what fills your needs best.

[PowerTech]

gas is for the devil. and in the very common 200 to 300 HP range they are not lighter eather.

[FAST FRED]

Diesel engines suffer far more from the abuse of unuse.

A not properly pickeled diesel can be trash in under a year ,

the gassers dont seem to have similar hassles.

Maint on diesels is more expensive , we use gallons as the measure not quarts on oil changes.

FAST FRED

[DiverDown]

Gas is not lighter??

Helped a friend take a Cummins from a Dodge with an 800 pound engine hoist,thinking it would be enough.The engine raised an inch before the lifting arm bent.

A 225 hp Cummins is 1000 pounds dry,and a 300 hp Deere almost 1500 pounds.

Small block V8s are around 550 pounds with cast heads/exhaust,and big blocks weigh very little more.

Never in a pleasure boat-Mazda rotary is 300 pounds.

Whatever works best for you.

[Chuck Bates]

True, most diesels are heavier than gas. However, the times they-are-a-changing.

Volvo D3-160 diesel with dp drive 728 lbs.
Volvo 4.3gxi gas with dp drive 916 lbs.

I heard the D3 will be available at 190hp in late 2005. If so, it will then be able to compete, performance-wise, with the 5.0 270hp gas engine.

[DiverDown]

Volvo site: D7 237 hp with ZF trans is 1670 pounds.The 270 hp gas with drive is 984 pounds...700 pounds less.Diesel engine costs many times more.Whatever.

Don't get me wrong,I like the new common rail diesels and their quietness and efficiency is long overdue.

But as 99% of boats spend 99% + of their time either at the dock,anchored out,or stored away(not running) the efficiency of the diesel (and your hard earned cash) is wasted.
Then the maintenance problems crop up with the diesel.Like Fast Fred says,they can go off quickly and if they burn out if lightly loaded too often.

IMHO unless you use a vessel a lot,actually do more than coastal cruise,or have something large, gas may be better.

I talked a friend out of getting diesel in his new boat,he saved $$$$$ on the engine and saves tons on maintenance:he puts on 80 hours a year.

[PowerTech]

Yea good points for gas.About being lighter i was thinking of a 6LP yanmar verse a fresh water cooled 454 crusader.The yanmar seemed lighter.We always repower gas with yanmar because the high RPM lets us use the old shafts and they just about drop rite in.The deere is a whole nother animal. You can rarely even fit one under the hatch of a gas boat as tall as they are.We have only done 2 that had gas with the deere and we used the 4045T 150 H.P. and them little things run.

[DiverDown]

Deere makes fine engines all right.If run all the time can get 20,000 no problem.But...
over the years,have spent much time poking around on yachtworld.com. Countless times have seen low hour rebuilt diesels. They just rot away.

Interesting read, just found:

http://www.yachtsurvey.com/GasDiesel.htm

[Chuck Bates]

Diverdown,
Please see my original thread above. Click on http://thehulltruth.com/photos/show...64&photoid=7427

You can not compare diesel hp to gas hp. Foot pounds of torque is a better way to compare the two. To get this figure: hp x rpm divided by 5252. The D7 270hp is a work horse engine and is not comparible to the 270hp gas engine. The more comparible Volvo diesel engine is the D4-210. Granted it is a heavy engine 1420 lbs.

Diesel is certainly not for everyone. I heard that anything under 100 hrs per year would not make it worthwhile. However a friend of mine has an Eaglecraft 33' commuter boat with a single D6-350 (which will out perform an 8.1 420hp) that burns 10 US gals per hr at 28.5 knots cruising. The gas engine would be lucky to get 4 gph! I talked to a gentleman who has a charter fishing boat on Vancouver Island that figures to save $12,000 worth of fuel in 1 year when he converts from his twin 4.3lt. gas to twin D3-160 engines. This more than pays for the difference in between the two.

I don't know where you are located in Canada but the flowers are blooming here in Vancouver and we've already been boating for a month 8 months a year boating weather gives us plenty of time to enjoy our boats. Boating in Florida even more so.

I question your statement about the diesels rotting away. Obviously the owners are not keeping up on their maintenance. If these same boats had gas engines in them, do you think they'd be in any different shape

To each his own.

[DiverDown]

Gear the gas a little lower and get the same shaft torque.

BTW I love diesels too,drive a TDI VW.

Your friend's D6-350 burns 10gph,but the gas burns 4..misprint? 40?

Gas:the rebuild cost would be a small fraction of a diesel.

Desolation is only 80 miles away.
To circumnavigate Vancouver Island is +/- 550 miles.
Vancouver to Prince Rupert is a bit more.

Go to PR and back would be 1200 or so miles..
At 10 knots that would be 120 hours.
At 20 knots- 60 hours.
What percentage of Vancouver boats do this (or twice at 20 knots)equivalent every year,to make it worth the diesel? Very,very few.

I'm realistic enough to realize that I don't need a long range vessel.Can spend all my life up the coast and never see it all.

I'm in Van as well.Sold boat,putting money to work towards something else.Too bad they only come in diesel

[PowerTech]

Rite on man, I am sure we all know there is no comparing them by H.P..I don't even try to or care to.Just rip the ugly old heap out slap in some diesel And let the prop guy sweat the B.S.

[tom kane]

Now this is a very interesting thread,thanks a lot.