Fuel Burn on 04/05 390 Sundancer with 8.1s

Quint

New Member
Jun 11, 2007
25
Las Vegas
Boat Info
2001 240 Sundeck
Engines
6.2 MerCruiser with Bravo 3
Hey folks

Some of you will recognize me as the person who has started a quest to get a mid sized Sea Ray that's comfortable for my family of five and yet not too expensive. I originally thought I would get an 03 or 03 420 DA with diesels, but living in Nevada, I would have to get one from far afield (most likely Florida) and then have it transported overland. No doubt this would be VERY expensive.

There are a few nice 390's in California, but they all come with gas engines. I know that you diesel fans would never consider gas power for reasons of torque, fuel burn, longevity and maintenance, but even so, the Mercruiser 8.1's probably produce sufficient power to run comfortably at 20 - 25 mph.

Does anyone have direct experience of the fuel burn with the 390 DA with gas powered engines? I am looking to pay around $250 - 280K for a nice one, and I think the $50K or so that I would save would buy a heck of a lot of gasoline.

Any feedback and guidance would be much appreciated! :smt001
 
Not exactly an apples to apples comparison, but the 8.1's in my 38 Dancer will "gulp" about 40 GPH running at about 27 mph. No foul smell, no clogging filters, no loss of sleep worrying if my fuel is seperating while I sleep, no worry about carrying spare fuel filters, no fuel polishing system on my Xmas list, just grab hold, smash the throttle and run :thumbsup:
 
I think a 390 with gas engines will increasingly becoem a hard trade or resale as gas goes north of $4.
Expect no better than .6 mpg running about 24 mph.
 
HokiesFan said:
Not exactly an apples to apples comparison, but the 8.1's in my 38 Dancer will "gulp" about 40 GPH running at about 27 mph. No foul smell, no clogging filters, no loss of sleep worrying if my fuel is seperating while I sleep, no worry about carrying spare fuel filters, no fuel polishing system on my Xmas list, just grab hold, smash the throttle and run :thumbsup:

All in good fun, but it is important to keep the facts on the table for folks considering gas v. diesel on this forum. The circumstances you describe would usually be attributable to poor fuel system maintenance. With proper care (which for me means adding a maintenance dose of biocide at each fill up, changing fuel filters annually, and buying from high volume diesel retailers like Prince William) there is no reason to lose sleep over fuel filtration, fuel water separation, etc. Yes, prudent diesel captains carry spare racors and some clean diesel fuel to swap elements at sea if required....but a bad load of fuel can happen to gas or diesel boats, so prudent skippers carry spare fuel filters aboard in case Murphy comes calling, regardless of gas or diesel propulsion.
As to fuel burn, I've posted my numbers, but to cruise at 27 MPH (23.5 knots) I burn 20.5 GPH or thereabouts. As to smelly, yes, diesels smell different than gas engines. Diesels just don't pump out the same amount of CO.
I'd wager that folks who have owned both gas and diesel boats prefer the oil burners, but gas vs diesel is a decision each buyer/owner has to make based on boat size, weight, manner of use, and a host of other considerations.

regards
Skip
 
We have a 2003 380 with 8.1s and only about 180 hours on the engines and the boat works magnificently with them. The boat planes at 17-18 knots with almost no bow rise, and cruises very comfortably at 25-27 knots. My fuel burn at that speed on the computer is around .8 nautical miles per gallon, with 4-5 people on board and 3\4 fuel load. It certainly drops at WOT (which is about 36 knots) but I rarely go that fast.

Our boat is on the market (at $218,000 with slip included) in Huntington Harbor in Southern California only because the nonstop activities of our 3 teenaged kids have limited our available time to fly over from Salt Lake City, as evidenced by the low hours.

A larger boat (i.e., 42 and above) requires diesels, which I have calculated would have gotten me about 30% better mileage in our 380 but at a $50-60k premium, which as you correctly noted buys a lot of gas. The proponents of diesels in boats 40 feet and below will argue that you "get your money back" when you sell the boat. Comparing list prices with sale prices in diesel boats certainly raises the question if this is entirely true, but the most obvious point that is almost always overlooked are the opportunity costs associated with tying up that money in a non-interest bearing\non-dividend producing asset.

At the historic stock market rate of return of 10%, the earnings on $55,000 expended to buy diesels would be almost an additional $40,000 over 5 years, compounded annually. And that can really buy you a lot of gas.

Charlie
 
It may be alot of the gas vs. diesel has to do with your location in the country. I have read many posts on CSR and SRO about the lower operating costs of diesel boats. Someday I hope to have a 40 or 44DA...and constantly look (on the internet) at ones for sale in the midwest. The dealers in this area do not order lower 40' boats with diesels unless they are custom ordered....and alot of that probably has to do with the useage in our area. Since we are on land locked lakes, we normally do not do 4-6 hours cruises at cruising speeds. We may cruise for an hour and then drop anchor and relax. Of all of the boats I have looked at in the midwest...at Lake of the Ozarks and Table Rock and Grand Lake....I have not seen any 390/40 DA with diesel.....and only 1(yes one) 420/44DA with diesel.
 
cthronson said:
We have a 2003 380 with 8.1s and only about 180 hours on the engines and the boat works magnificently with them. The boat planes at 17-18 knots with almost no bow rise, and cruises very comfortably at 25-27 knots. My fuel burn at that speed on the computer is around .8 nautical miles per gallon, with 4-5 people on board and 3\4 fuel load. It certainly drops at WOT (which is about 36 knots) but I rarely go that fast.

Our boat is on the market (at $218,000 with slip included) in Huntington Harbor in Southern California only because the nonstop activities of our 3 teenaged kids have limited our available time to fly over from Salt Lake City, as evidenced by the low hours.

A larger boat (i.e., 42 and above) requires diesels, which I have calculated would have gotten me about 30% better mileage in our 380 but at a $50-60k premium, which as you correctly noted buys a lot of gas. The proponents of diesels in boats 40 feet and below will argue that you "get your money back" when you sell the boat. Comparing list prices with sale prices in diesel boats certainly raises the question if this is entirely true, but the most obvious point that is almost always overlooked are the opportunity costs associated with tying up that money in a non-interest bearing\non-dividend producing asset.

At the historic stock market rate of return of 10%, the earnings on $55,000 expended to buy diesels would be almost an additional $40,000 over 5 years, compounded annually. And that can really buy you a lot of gas.

Charlie

Charlie,
When you cruise at 25 to 27 kts, what rpm do your 8.1S engines turn at that speed? Also what is your WOT rpm @ 36 kts?
 
Cruise RPM is around 3300-3400, and WOT is aroung 4300-4400. The boat just touches 36 knots, at sea level with light chop, at WOT. It is a stable, exciting ride in a boat that size.

Charlie
 
I had a 2002 380DA with 8.1s. Traded it in at the end of last season. From memory, I would average about 30- 35 GPH.

About 3 hours ago I filled up my 410DA with CAT diesel after a few hundred miles, most on plane, and some full throttle runs and some getting on plane quickly runs. Boat was loaded with gear, fuel, water and a dinghy with motor on the swimplatform. Ran mostly in the ocean and had to traverse the NJ Inlets a total of 4 times on the tank of fuel. Averaged out the GPH about an hour ago.....17 GPH.... :grin:

The price for Gasoline was $3.37/gal. The diesel fuel was $2.35/gal.

These are REAL WORLD number comparisons....your mileage may vary...
 
I'm getting .67 MPG cruising at 24 MPH, 3600 RPM, 35/36 GPH. This is with the boat tanks full/empty, tabs down/up, 2 to 6 folks on board. I know the numbers should change, but they don't. I don't worry about it anymore. Anyway, when I plan a trip, at $3.35 - $3.50 a gallon, I spend about $5.00 a mile. On my same boat with diesels it would cost about $2.50 per mile. To make it worth the additional $50K that diesels would cost I'd have to travel 20000 miles over the course of ownership of this boat. Somehow, I just don't see me putting in that kind of mileage with my limited boating time so gas makes sense for me.
 
I've no knowledge of the 390. I, too, had a 2002 380DA with 8.1's.

My burn numbers were similar to those mentioned above. The thing that I found was that it was really sensitive to seas conditions. It didn't vary too much under different loads, but add 4 foot seas, or worse, 6 footers, and it burned about an extra 10 gph. I almost ran out coming back one time because I didn't factor in the extra burn for rough water.

Just something to keep in mind.

I'm not getting into that diesel vs gas debate. I've had both, and they both have their advantages.
 
You east coast boaters have much better prices on diesel...in Missouri (on the water) gas is around 3.55....diesel around 3.29... not as much price difference here.
 
RiverGalsMan said:
......, I spend about $5.00 a mile. On my same boat with diesels it would cost about $2.50 per mile. To make it worth the additional $50K that diesels would cost I'd have to travel 20000 miles over the course of ownership of this boat. Somehow, I just don't see me putting in that kind of mileage with my limited boating time so gas makes sense for me.

I can't argue with your numbers, however, there are more variables than just the initial cost. When it comes to reseale, especially on larger vessels, you will recoup the $50k.

If you were to take an average boatloan, over 20years on larger vesels, $50K would cost you (and this number is out of the sky) about $400-500 extra per month. Depending on how much fuel you put in your tank, you can easily make up most of that difference on every fill up. And then when you sell your diesel boat, you get the rest back....
 
osd9 said:
RiverGalsMan said:
......, I spend about $5.00 a mile. On my same boat with diesels it would cost about $2.50 per mile. To make it worth the additional $50K that diesels would cost I'd have to travel 20000 miles over the course of ownership of this boat. Somehow, I just don't see me putting in that kind of mileage with my limited boating time so gas makes sense for me.

I can't argue with your numbers, however, there are more variables than just the initial cost. When it comes to resale, especially on larger vessels, you will recoup the $50k.

If you were to take an average boatloan, over 20years on larger vesels, $50K would cost you (and this number is out of the sky) about $400-500 extra per month. Depending on how much fuel you put in your tank, you can easily make up most of that difference on every fill up. And then when you sell your diesel boat, you get the rest back..

Now don't get me wrong, I'm not bashing/praising gas or diesel...I could help argue from either side....I'm just trying to introduce a few more variables.....
 
There are a couple of areas where there's no question diesel would be nice to have.

1) Generator. Even though I've got a Kohler low CO version, it still concerns me.

2) Range. It'd be nice to be able to go 300/400 miles between fillups. In the Chesapeake it's not that major an issue, but to head up to New York or even further it certainly limits me.

Does anyone know if I can use a digital CO meter and hold it at the exhaust of the generator to see if the CO really is low? On that note, what really is low, anyway? Would this be a valid test?
 
RiverGalsMan said:
Oh, didn't mean to hijack the thread. I'll start a new one, on low CO generators, if needed.
Okay, now go straight to jail. Do not cross start. Do not collect $400. :lol:
 
Here are some real trip numbers for my boat.

NJ to Connecticut River - Full Gas and Water, 5 adults on board, it took 7 hours @ 3400 RPMs 25 MPH --- 200 Gallons.

Connecticut River to Warwick RI full Gas, Full Water, 4 Adults on Board, 5 hours, at 3400 RPM, 25 MPH 150 Gallons

Warwick to Mystic CT Full Gas, 1/2 water, fully loaded for a 10 day vacation, 3 hours at 3250 RPM's 23MPH, 72 Gallons. (Rough conditions)

I average 24-28 GPH. I use 32 GPH to estimate fuel needed for a trip.

The bottom is clean, and the props were re-conditioned.

I believe the 390DA weighs 500lbs more then the 380DA.

I travel with another 380, he runs his boat at 3800 RPM's at 31 MPH and burns quite a bit more then I do. He estimates 40-44GPH. But he does arrive a lot sooner then I do.

Hope this helps.
 
Thanks everyone. It would seem that for average conditions (load, sea conditions, cruising speed, etc) the 8.1s consume about 30 gph, doing approx 25 mph.

Lovers of the oil burners talk about torque, longevity, low fuel burn, quietness, good resale value, etc. There are many positives, and I cannot really understand why Sea Ray dealers don't order more boats with diesels. I'm thinking that for inland waterways, where the distances are relatively smaller and the thought of diesel as being "oily, dirty & smelly", the extra outlay might be hard to justify. However, all those positives are hard to ignore.

For me, it comes down to this: availability. Given that I'm buying in Las Vegas, there just aren't that many boats with diesels, unless they're 45'+ cruisers, like some Carvers and Meridian that we occasionally see.

But thanks to everyone for chiming in: there was a wealth of information of cruising speed, fuel burn, revs, distances, and what to expect. I can live with 30-ish gph for cruising at 25-ish mph. As Charlie & Larry said, you need to do a helluva lot of miles over the life of the boat to justify the cost difference.

Thanks again to everyone! :thumbsup:
 

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