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Gas vs diesel fuel consumption

 
 
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Old 08-20-2009, 01:17 PM   #1 (permalink)
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Gas vs diesel fuel consumption

Hi, Everyone...We are a whisper away from purchasing a pristine 2003 39ft. Silverton motor yacht, completely loaded with everything except sattellite tv. We would like to determine what fuel consumption we can realistically expect at cruising speed with gas crusader engines (400 series). Also I'd love to hear any advice or opinions you could offer regarding the pros and cons of gas vs. diesel and whether or not the much more expensive diesels are worth the investment considering we would be weekend sailors on the Connecticut River and Sound with occasional jaunts (annual vacations) to Cape Cod or North Carolina. We only have experience with a Sea Ray 32 ft motor boat so we are rather tentative in making this investment as we are newly retired. This will be our "cottage" and our last "luxury".

We are very new to boating, and so far we are loving, loving, loving it!! Any and all insider info would be sooo welcome as I'm sure we have so much to learn. We just feel that we can't rely on commission dependant sales people to honestly answer our questions. Please respond either to my e-mail or in this forum. We look forward to making new friends! LB
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Old 08-20-2009, 01:42 PM   #2 (permalink)
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Quote:
Originally Posted by llbarilla
Hi, Everyone...We are a whisper away from purchasing a pristine 2003 39ft. Silverton motor yacht, completely loaded with everything except sattellite tv. We would like to determine what fuel consumption we can realistically expect at cruising speed with gas crusader engines (400 series). Also I'd love to hear any advice or opinions you could offer regarding the pros and cons of gas vs. diesel and whether or not the much more expensive diesels are worth the investment considering we would be weekend sailors on the Connecticut River and Sound with occasional jaunts (annual vacations) to Cape Cod or North Carolina. We only have experience with a Sea Ray 32 ft motor boat so we are rather tentative in making this investment as we are newly retired. This will be our "cottage" and our last "luxury".

We are very new to boating, and so far we are loving, loving, loving it!! Any and all insider info would be sooo welcome as I'm sure we have so much to learn. We just feel that we can't rely on commission dependant sales people to honestly answer our questions. Please respond either to my e-mail or in this forum. We look forward to making new friends! LB
Welcome to YF. At 39' and especially with plans to go to NC I'd go with diesels. You'll get most of the $ back on resale and it will make resale much easier. Generally, diesels will give you much better gph. With that boat I'd guess (but only a guess) about 28gph at cruise. You'll also find diesels more reliable and the fuel more stable. You've got several good people on the Ct. River to get opinions from, Portland Marine and Essex Boatworks are 2.
For me, the cutoff point for gas is about 34' to 36'. Good luck.
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Old 08-20-2009, 03:52 PM   #3 (permalink)
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LB

I will second the diesel recommendation for a boat this size. If you were going to just short hop in the Sound, you could make a case to go with gas but going as far as NC I would say not. As NYCAP stated, you can't just calculate the fuel savings when looking at the higher cost of diesels. The resale will be much easier and at a higher price down the road.

Right now, anything that big with gas engines is not selling so unless you are getting it for a song, you are better off looking for a good deal on a boat with diesels. IMO
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Old 08-20-2009, 04:53 PM   #4 (permalink)
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Right now, anything that big with gas engines is not selling so unless you are getting it for a song, you are better off looking for a good deal on a boat with diesels. IMO
That sounds like a good reason to compare prices for equivalent boats with either powerplant. If a diesel boat sells for $225k and a gas boat sells for $150k and they are the same otherwise, I would say $75k will buy a lot of gas for the difference in pump price between diesel and gas, maybe even enough to fill the tanks for the entire period the boat is owned and used, and the interest would buy a lot of wine and cheese.

The O.P. wrote: "weekend sailors on the Connecticut River and Sound with occasional jaunts (annual vacations) to Cape Cod or North Carolina" and that doesn't sound like extended cruising to me.

I have never been a big fan of gas engines in boats but I am a big fan of cost effective boating. Resale? You get what the market says it is worth, if you got it low you have a bigger market when you decide to sell. Darn few boats are good investments so why even pretend it matters.
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Old 08-20-2009, 05:04 PM   #5 (permalink)
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if you got it low you have a bigger market when you decide to sell.
That's what's known as a value trap. Prices decline when there is low demand or a small market; low price alone does not create a larger market. If it's cheap now, it will have to be cheaper then unless we find a whole new earthful of oil and gas drops to 20˘ a gallon again.
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Old 08-20-2009, 06:33 PM   #6 (permalink)
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Quote:
Originally Posted by llbarilla
Hi, Everyone...We are a whisper away from purchasing a pristine 2003 39ft. Silverton motor yacht, completely loaded with everything except sattellite tv. We would like to determine what fuel consumption we can realistically expect at cruising speed with gas crusader engines (400 series). Also I'd love to hear any advice or opinions you could offer regarding the pros and cons of gas vs. diesel and whether or not the much more expensive diesels are worth the investment considering we would be weekend sailors on the Connecticut River and Sound with occasional jaunts (annual vacations) to Cape Cod or North Carolina. We only have experience with a Sea Ray 32 ft motor boat so we are rather tentative in making this investment as we are newly retired. This will be our "cottage" and our last "luxury".

We are very new to boating, and so far we are loving, loving, loving it!! Any and all insider info would be sooo welcome as I'm sure we have so much to learn. We just feel that we can't rely on commission dependant sales people to honestly answer our questions. Please respond either to my e-mail or in this forum. We look forward to making new friends! LB
I happen to manage one of these boats. You DO NOT want to run that boat at cruise. It does not get onto plane and only does around 14 knots at cruising speed with the gas and you're burning about 40 gph or more. It runs best around 1500-2000 rpm's burning considerably less, maybe 15-20 gph and you're still doing 9-10 knots. The boat feels very underpowered with gas if you try to push it at cruise. But at 1500-2000 rpm's it runs well.....I personally wouldn't run it at cruise as a general rule of thumb.

The diesels will be more efficient at the lower speeds, and a lot more reliable IMO. Even though the gas parts and general maintanence (oil changes etc) are cheaper. You have a lot more components to go wrong. Keep in mind the diesel boat will have a diesel generator which will burn less fuel as well. I don't know what the price difference is between one with gas and one with diesel, but if it's considerable as someone else said you can buy a lot of gas with it.

On another note, all in all it's appears to be a faily well built boat for it's price range with a lot of room inside and out and we've had relatively few issues with it. It is better suited to ICW and inland waters instead of trying to make ocean crossings with it.
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Old 09-22-2009, 01:14 AM   #7 (permalink)
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Thank you Friends!

You were all so kind to respond to my previous questions about whether or not to consider a Silverton 39' (gas engines) motor yacht. We took your advice and kept searching until we found a diesel powered 39' Silverton motor yacht. My other half just has a few more questions regarding diesel fuel consumtion. He's a retired mechanic, so forgive me for asking such technical questions as he asked me to read and post his questions word-for-word exactly as he wrote them for me.....so here goes!:


We are in the process of purchasing a 39'Silverton Motor Yacht. The boat is equipped with twin Yanmars 380HP Model 6LYASTD Diesel engines. If any of your folks can advise us on fuel consumtion we would much appreciate the info since we are planning long inter coastal cruising next summer. Please advise us re: Idle at 1500 RPM, 1800 RPM and full throttle operation gallons per hour. We would normally cruise @1800-2400 RPM. Also, what is the history for well maintained engines with regular oil and filter changes before needing overhaul? Thanks so much, you guys. We're so glad we found you! Linda
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Old 09-22-2009, 04:14 AM   #8 (permalink)
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Dear LB,

Your recent post has merged with your previous thread. PLEASE do not open new threads on the same subject.
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Old 09-22-2009, 07:17 AM   #9 (permalink)
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It's been a few years since I've run with Yanmars, but I liked them. They're high reving, fast, miserly workhourses. You find them in a lot of watertaxis. I used to run a 43 Ocean SF with them. 5 NY-Fl trips plus the owner's other use without a hiccup. If memory serves me correct we cruised at about 29 kts. and burned in the area of 23 or 27gph. The down side (from what I hear) is that they don't lend themselves to major rebuilds well, but I have no personal experience there.
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Old 09-22-2009, 09:00 AM   #10 (permalink)
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Each boat and engine combination performs a little differently so to get the max performance one needs to experiment to get peak performance. Also running at displacements speeds, less than approx 8.5 kts for your boat length you can get significantly better fuel economy. For example I run a 37' Tolly and get 3 nautical miles per gallon (total) at 1200 RPM however at 1350 RPM, I only get 1 nautical mile per gallon and only going about .5 kts faster. My point being that 1500 on a diesel of this engine/boat size may not be an efficient speed.
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Old 09-22-2009, 02:16 PM   #11 (permalink)
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Quote:
Originally Posted by llbarilla
You were all so kind to respond to my previous questions about whether or not to consider a Silverton 39' (gas engines) motor yacht. We took your advice and kept searching until we found a diesel powered 39' Silverton motor yacht. My other half just has a few more questions regarding diesel fuel consumtion. He's a retired mechanic, so forgive me for asking such technical questions as he asked me to read and post his questions word-for-word exactly as he wrote them for me.....so here goes!:


We are in the process of purchasing a 39'Silverton Motor Yacht. The boat is equipped with twin Yanmars 380HP Model 6LYASTD Diesel engines. If any of your folks can advise us on fuel consumtion we would much appreciate the info since we are planning long inter coastal cruising next summer. Please advise us re: Idle at 1500 RPM, 1800 RPM and full throttle operation gallons per hour. We would normally cruise @1800-2400 RPM. Also, what is the history for well maintained engines with regular oil and filter changes before needing overhaul? Thanks so much, you guys. We're so glad we found you! Linda
Yanmars are good engines and I believe they go about 5,000 hours. BUT, you should call your local Yanmar dealer and ask them how many hours they go. Also ask them for a fuel burn chart on that particular engine. If the engine is achieving full RPM's at WOT, the the chart should be pretty accurate. Once you have the fuel burn chart, take the boat out run it at the various rpm's and jot down your speed (from GPS) at each rpm. Then go home and calculate your gallons per mile. Fuel burn divided by boat speed.

One thing I would recommend with Yanmar's or any diesel is having at least 1 spare set of filters for both motors (fuel and oil), maybe 2 sets of fuel filters, and a spare set of impellors and belts if the engine is equipped with belts.
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