390 Motor Yacht or 400 Motor Yacht with Gas

J

jmunro123

Member
Feb 2, 2008
370
Gran Bend, Great Lakes
Boat Info
2004 Sea Ray 390 Motor Yacht
Engines
8.1's
I was wondering if any of the owners of 390 or the 400 Motor Yacht with the 8.1 Gas Engines can comment on fuel economy, GPH and typical cruise speed. We had 8.1's on the 340 Dancer and while a good engine I am concerned about them on a boat of this weight. But I have also read some good things about the 8.1's so was wondering if anyone can comment.

I am looking at a 2004 390 Motor Yacht tomorrow.

Thoughts?
 
It's been my understanding that any time you get a boat above the ~35' range it should have diesels. Gassers in boats above that size will eat you up with the gas bills. Of course, you have to consider how long you're going to own the boat and how much you'll use it. If it's going to be a dock queen and not get a lot of hours it might be hard to justify the additional cost of diesels.

That boat is going to weigh around 24-26,000 lbs in running condition. That's a lot of weight to be pushing with gas engines.
 
It'll do just fine on gas, as long as you don't go anywhere...

Seriously, a MY that size with gassers isn't designed for cruising any distance. You won't get any better than .5-.6 mpg on a good day. It's going to cost well over $100 an hour to run in terms of fuel costs alone, and you won't be able to pass a fuel dock without stopping. Dockside handling will be a nightmare without a thruster, as there's a large amount of windage on a ACMY and you've got tiny wheels (because of the gas engines) trying to control the boat.

For casual, short distance cruising though no problem if you're willing to live with the downsides. For sure- if you get to the point of purchasing/ sea trial, be sure the boat is fully loaded with fuel and water and a few bodies- and that the engines still reach recommended WOT. It would be extremely easy to overprop a boat that size with gassers... resulting in engines that would never see 1000 hours.
 
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tobnpr said:
For sure- if you get to the point of purchasing/ sea trial, be sure the boat is fully loaded with fuel and water and a few bodies- and that the engines still reach recommended WOT. It would be extremely easy to overprop a boat that size with gassers... resulting in engines that would never see 1000 hours.
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tobnpr brought up a good point. If you get serious about the boat, find out from the engine manufacturer what the WOT rpm reading should be, and from the boat maker find out what the speed should be at WOT.

Run the boat at WOT for 10 minutes during the sea trial. This will tell you three very important things...
1. If the boat will not hit the WOT rpm's, it is overpropped and will not last long.
2. If the boat reaches the WOT rpm range but doesn't hit the rated speed it is underpropped.
3. By running at WOT for 10 minutes if there are any impediments to a free air flow through the engine (intake, combustion, exhaust) the exhaust temps will climb and the engine likely will overheat. This impediment to free air flow will shorten the life of the engine(s).

If the salesman won't let you run at WOT for 10 minutes, walk quickly back to your car because he may know something he's not willing to share with you.
 
I agree, 0.5 -0.6 mpg. It will be a pig on fuel. Nice boat though if you plan to stay put or do the occasional sunset cruise. You could live aboard quite comfortably.
 
The family (2 kids boy and girl ) looked at the 390MY today. It's like an express cockpit with A/C mounted on a Motor Yacht. That part of the boat is very well done, yes it looks unconventional but it is so purposeful. The inside of the boat is simply amazing and for a family its would appear to be a great boat. On our 340 we put about 50 to 60 hours per year. We like to spend more time at the club and on the water but the 340 was kind of tight on space.

When I got in the helm seat I was thinking, 'man this is a big boat' but the visibilty was very good. I thought the same thing when I first got on the seat of the 340 for the first time.

I am expecting about 34 gallons per hour at 3500 RPM and 22 MPH. So about 4 MPH slower than the 340 with about the same fuel consumption.

Do you think that makes sense on the speed and fuel consumption. I would like to have Diesel's but not sure its worth the extra money.

Any comments are welcome.
 
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jmunro123 said:
I am expecting about 34 gallons per hour at 3500 RPM and 22 MPH. So about 4 MPH slower than the 340 with about the same fuel consumption.

Do you think that makes sense on the speed and fuel consumption. I would like to have Diesel's but not sure its worth the extra money.

Any comments are welcome.
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I think you may be overly optimistic. Load her up with water, fuel, gear and add some slime to the hull. While the fuel burn of any engine is constant at a given RPM, expecting a certain velocity at that RPM is difficult. It is a heavy boat. Your displacement with full load will be just shy of 30,000#. Although the 8.1s are strong, you will be using every bit of them to motivate that displacement. My guess is that you will be cruising along at 40-50GPH at 22-24 mph. That is based on my experience of a test drive of a lighter and less beamy 36DB with the same power package.
 
What I see from listings is a 20 knot + cruise with the 450 hp Cummins.

Realistically with a loaded boat I can't see more than 16-17 kts at cruise.

If you're concerned about cruise speed, or fuel economy, gas engines are the wrong choice for you. For your usage, 50-60 hours per year the diesels would be hard to justify other than from a resale perspective. Just keep the plastic handy when you get near a fuel dock...it's gonna cost $1000 to fill the tanks- and you'll get less than 150 miles for your money.

After looking at a few online, I'll reiterate my concern about handling. That boat has a huge amount of windage- and only a 3' draft. If you purchase and go to sea trial, pick a windy day so you'll know what you're in for.
 
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Our dealer would not stock or order a MY with gas engines. Their position is out of self defense........they want the customer to have what he wants, but they definitely do not want to be forced to take a gas MY back on trade for a diesel one to keep the original owner happy when gets fed up with the $150/hour fuel bill. These boats do not sell easily or quickly.

I've delivered 2 MY's for the dealer here and they have a ride characteristic that I do not enjoy. The boats are top heavy and they will roll horribly in any beam sea.......try a narrow inlet with a beam following sea and you better have your big boy boat driver's pants on.
 
There's only five or so MY's with gas power listed on YW currently, ranging from $180-$210 asking. Interestingly, the DA's are priced higher; seems to be in line with the limited demand FW was referring to. Is $175 the asking price, or what you're thinking of offering?

It would be helpful if you could get some info on actual sales prices. Sounds like the price may be reasonable, but not a steal...

If you'd like, I can talk to the broker that's handling the sale of my boat to see if he would mind pulling up an recent "sold" prices to give you a better idea. PM me if you'd like.
 
tobnpr said:
There's only five or so MY's with gas power listed on YW currently, ranging from $180-$210 asking. Interestingly, the DA's are priced higher; seems to be in line with the limited demand FW was referring to. Is $175 the asking price, or what you're thinking of offering?
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175,000 is what I offer (and pay). There are a few on YW, one 2004 bank repo with a broken windsheild for $180,0000 in california - likely salt water boat.
 
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jmunro123 said:
175,000 is what I offer (and pay). There are a few on YW, one 2004 bank repo with a broken windsheild for $180,0000 in california - likely salt water boat.
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The one in California is now $ 159,000 with the windshield still shattered, the rest of the boat is spotless other than the pinstriping needs to be replaced.
 
jmunro, it would appear from your signature photo that you have already bought the 2004 with gas engines and now you are seeking some justification from this group that your purchase was a good one.

Let me just say one thing, and take it for what it's worth....

The wrong boat, at the best price in the world, is still the wrong boat.
 
Gofirstclass said:
jmunro, it would appear from your signature photo that you have already bought the 2004 with gas engines and now you are seeking some justification from this group that your purchase was a good one.

Let me just say one thing, and take it for what it's worth....

The wrong boat, at the best price in the world, is still the wrong boat.
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Thanks for that. That post was put up before I bought it. I have to agree the wrong boat at the best price is stll the wrong boat.

However, that does not apply to in this case. For me this is the right boat at a good price.
 
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