gas vs diesel

[Graham Lorimer]

Only way to get it there without spending a fortune on shipping or road transport, also an unbelievably great summer. After going through 176 locks, some on which were only 5 meters wide, got pretty good at the boat handling side of it all.

Probably the only 400 DA to have done the trip, they are pretty rare over here.

GL

 

[dantheman]

I drove my 400DA with Cat 3116 engines for 32 days at 500 - 600 rpm down through the French canals last summer, (speed restrictions all the way) and when we finally reached open water, the slightest puff of black smoke and all was fine.

In total we did about 230 hours at that speed, and the engines always started instantly hot or cold, never ever stalled and were not affected by the experience at all. Probably the biggest downside was the additional hours on the clock, but saved about US$20,000 from the cost of shipping UK to the Med, and had a stunning summer as a bonus.

To me the choice is a no-brainer, Diesel every time

Graham

Graham,
That's great news to me, I hope to get 50 footer once they get into my price range. has anyone else done extensive idling with diesels?

 

[fwebster]

If you expect to run at idle speed, the 500DA is probably the wrong boat. You should be looking at trawlers.

Engines in pleasure boats are designed and fitted out to produce planing speed power. If Graham were planning to run his boat all the time that way, it would be better if he had 210 hp naturally aspirated 3116's instead 350hp turbocharged 3116's. The Detroit 6V72's or 92's or 3196 cats in a 500DA would be a worse fit for idling about.

I find that the pleasure engines do very well if you can get the RPM's up in the mid range where they are having to work some. My engines seem to like running at 1400-1600 RPM which gets us about 14-15 kts., and is just before the transom squats and the boat pushes a ton of water to climb up on plane.

 

[Sua Sponte]

....or 3196 cats in a 500DA would be a worse fit for idling about.

Word. You throw my boat in gear and it does a "wheelie" goes almost eight knots at idle @ ~725 RPMs. It doesn't like to go slow...I have to goose it in and out of gear when in no-wake zones.

 

[remo1950]

I think that your engines are set at too high RPM to do that. Look on the data plate and see what the idle RPM is and check to see if it does not read higher than that on your tachometer. Check each engine one at the time. I think they idle around 700 rpm but im not sure.

 

[fwebster]

No.....that is very typical behavior for larger Sea rays with high hp diesels. My boat runs at 7 kts at idle and passengers need to be sitting down or holding on when you put the boat in gear. I ran a 510DA last month with 800 hp 3406's and she ran 11 kts at idle, but had trolling valves and slow idle controls for tight spaces.

 

[320Bob]

... Engines in pleasure boats are designed and fitted out to produce planing speed power...

Frank,
Does this apply to gasoline engines also? I typically run mine around 1500 rpm which is about 8 mph since this is what the Admiral prefers. I do try to take it up to planing speed of around 3500 rpm for a few miles most times we go out but then go back to cocktail cruise speed. Is this use profile potentially detrimental to my engines in the long run?

 

[Scott1]

Is this use profile potentially detrimental to my engines in the long run?

No.

 

[timjet]

I'm going to chip in here, but bare in mind I just purchased a 35 Carver with twin Cummins diesels and have very little experience. I did however do a bit of research on the diesel/gas debate.

I learned from my research that boats under about 22000 lbs are probably more economical and cheaper to operate and maintain with a gas engine. As you get over this displacement gas engines just don't have the torque to properly move the boat so diesels are a better configuration.

Other things to consider are maintenance. A diesel is going to cost more and sometimes much more to maintain. A rebuilt gas can be installed for the cost of just a minor overhaul on a diesel. Diesel mechanics get about $100/Hr in SW Fl.
Some 1000 hr gas engine have probably seen there day as others have mentioned and a diesel will run forever if properly maintained. But my guess is that most owners don't properly maintain their diesel engines and consequently the life of their diesels can be shorten to that of a gas.

Safety: Diesel fuel is overwhelmingly safer than gas. And consider the fact that a gas generator running at night when you're asleep emitting all sorts for CO2 should give pause for concern. Safe as long as all that CO2 is channeled safely overboard.
I had a fuel leak on my stbd engine due to a damaged fuel filter. After about 3 hrs running I noticed the diesel in the bilge. I moped it up with diapers, but if this had been gas I would have called the fire dept from a very safe distance.

Fuel economy: Economy is slightly better on a diesel and so is the cost per gallon, but this savings is balanced by the higher maintenance costs of diesel, especially if you don't do most of the maintenance yourself. I replaced the raw water pump on my port Cummins diesel at a cost of $1150.
Check out dieselboat.com for all things diesel, but don't spend too much time there, it'll scare the hell out of you.

In the size range boat you are considering there is probably no definitive answer, but for me the safety of diesel heavily influenced my decision.

 

[sbw1]

I'm going to chip in here, but bare in mind I just purchased a 35 Carver with twin Cummins diesels and have very little experience. I did however do a bit of research on the diesel/gas debate.

I learned from my research that boats under about 22000 lbs are probably more economical and cheaper to operate and maintain with a gas engine. As you get over this displacement gas engines just don't have the torque to properly move the boat so diesels are a better configuration.

Other things to consider are maintenance. A diesel is going to cost more and sometimes much more to maintain. A rebuilt gas can be installed for the cost of just a minor overhaul on a diesel. Diesel mechanics get about $100/Hr in SW Fl.
Some 1000 hr gas engine have probably seen there day as others have mentioned and a diesel will run forever if properly maintained. But my guess is that most owners don't properly maintain their diesel engines and consequently the life of their diesels can be shorten to that of a gas.

Safety: Diesel fuel is overwhelmingly safer than gas. And consider the fact that a gas generator running at night when you're asleep emitting all sorts for CO2 should give pause for concern. Safe as long as all that CO2 is channeled safely overboard.
I had a fuel leak on my stbd engine due to a damaged fuel filter. After about 3 hrs running I noticed the diesel in the bilge. I moped it up with diapers, but if this had been gas I would have called the fire dept from a very safe distance.

Fuel economy: Economy is slightly better on a diesel and so is the cost per gallon, but this savings is balanced by the higher maintenance costs of diesel, especially if you don't do most of the maintenance yourself. I replaced the raw water pump on my port Cummins diesel at a cost of $1150.
Check out dieselboat.com for all things diesel, but don't spend too much time there, it'll scare the hell out of you.

In the size range boat you are considering there is probably no definitive answer, but for me the safety of diesel heavily influenced my decision.

One of the better posts on this subject. Most are not objective about this question and have knee jerk responses.

 

[Glen S]

I'll add my $0.02 for the fun of it. My 97 400 DA has the 7.4 MPI's - these are the Bluewater raw water cooled versions (great lakes boat). This summer (our first with the boat) we had a 2 week holiday and ran about 380 miles. I was getting a comfortable 200 miles per tank (330gal) running at 3200 RPM which was giving me 20 knots on the GPS. Now, I will admit to not having been on a big Sea Ray with Diesels but the 400 seems to have great performance with the gassers, and is for sure quiet and smooth. For docking, we had everything from calm to 30 knots side gusts and we managed. You do need to use some throttle in the wind but once I got used to that it has been fine. I did look originally for diesels but just could not justify the premium cost - even used. We will likely do aroud 30 - 40 hrs per year so for us the life of the big blocks should be OK (they have about 600 hours on them). Anyway, would I like to have diesels.... sure - but the 7.4's seem to work great for us.