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Old 08-22-2015, 05:33 PM   #21
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Marinas providing only one type of fuel will provide gasoline in contrast to diesel. My local marina sells more gasoline than diesel. I often purchase diesel from a marina four hours away which dispenses a relatively high volume of (thus fresher?) diesel and at a lower price. (Good excuse for an overnight trip.)
Locally here in Maine I find just the opposite. Our marina only sells diesel. Most fuel docks only sell diesel. I am aware of only two docks with gas out of 8 local fuel docks. That is likely because we have a pretty big commercial boat fleet locally that is almost 100% diesel powered.
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Old 08-22-2015, 06:30 PM   #22
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Modern diesels are much lighter than older engines. For example, a 110 hp Yanmar diesel weighs 505 lbs not the 900 lbs B&B mentions. A 150 hp yanmar comes in at 565 lbs. Weights from Yanmar engine spec sheets on line. Similarly Volvo's 110 and 150 hp engines weigh in at 665 lbs. There are, of course, heavier engines such as the ~120 hp John Deere engines which weight around 1,000 lbs. Those engines are more suitable for a passage maker or commercial boat than most recreational boats.

Locally almost all new boats are built with diesel engines from about 25 feet up.

As far as safety goes, a modern fuel injected gas engine is much safer than a carbureted engine since there need be no exposure of volatile gasoline to air inside the boat. Gas is inherently more explosive than diesel, so diesel is still safer to have on board. The energy density of gas is about 2/3 that of diesel so to produce the same horsepower, a gas engine will burn about 50% more fuel per hour. So you will need to carry 50% more gas to get the same range that a diesel boat has.

The only advantages I see for gas is that the engine is quieter than a similar output diesel and gas engines are cheaper. However, diesel engines last longer, so the cost is offset a bit there.
I was comparing an identical Rib with a Yanmar Diesel vs. a Weber Gas. I realize other factors might have skewed the numbers some.

You said, "Locally almost all new boats are built with diesel engines from about 25 feet up." I have no doubt that's true for the area of Maine you're in. However, it's not in general. The majority of 25-40' boats being built are gas powered.

The majority of boat users do not use their boats in the same manner you do. There are pluses and minuses to both diesel and gas. Now the OP used the term for a gas trawler and I'm not getting into what a trawler is. However, that implies to me that he does intend to go rather slow and that is something a diesel tends to be the better choice for. But I wouldn't pass over the perfect boat that I could afford, simply because it's gas.
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Old 08-22-2015, 06:44 PM   #23
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Well my statement about the local boats reflects our local builders (Hinckley, Ellis, John Williams, Wilbur, Atlantic, Lyman Morse, Hogdon, etc.). Of course they are not building to a price point. I wasn't talking about lobster boats.
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Old 08-22-2015, 10:52 PM   #24
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If it helps, I was provided a fuel consumption curve from a looper on the Mainship yahoo Group. He graphed from his floscan an average of 2 mpg @ 6 mph alternating engines. Twins got about 1 mpg @ 15 mph. This was in a Mainship 36DC running twin 350 Crusaders.

A mid 30's boat with small blocks, in pretty good condition, can be had for a song and a hand shake. Not to mention you're not changing 8-10 filters and 6 gallons of oil every 50 hrs with twin diesels

I'm going to look at a gas powered Mainship tomorrow. If I'm honest with myself and my plans for the boat, gas is probably the best thing for my use. . .unless I get something huge
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Old 08-22-2015, 11:40 PM   #25
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A couple of things come to mind:

Diesels are happiest at about 80% of max loading and they have a comparatively narrow power band. On smaller boats the variability of the load is a higher percentage of the overall boat weight so the load on the engine will vary much more. Also the variability in the operating speed will take a toll.

Diesels are not to good for people who wants boats that go fast. Most gas boat owners spend most of the boat operating time at near WOT or near idle.

A lot of the torque of a diesel engine comes from the mass of the moving parts. As manufacturers move to smaller and smaller diesel engines using turbo/super charging to maintain the same horsepower, the torque advantage of a diesel will be reduced.

The same turbo/supercharging will put a lot more stress on a modern engine compared to a normally aspirated one from 50 years ago that is still going strong. Also the reduction in shear mechanical size of the component parts will reduce their overall life. Yes, you can have a diesel engine from the 40s or 50s that is still going strong. I doubt that your turbocharged Yanmar 315 hp engine will still be running 60 years from now (assuming petro fuels are still available).

The owner of a gas engine boat is able to do more of the engine maintenance himself or find someone that can. In some places diesel mechanics are hard to come by and are often a lot more expensive than the equivalent gas mechanic. People with large boats (40'+) are probably more able and more willing to pay someone else to do the dirty work on their boats.

For boats that want to go fast, a gas engine will have a higher top rpm. Since there is only a fixed gear ratio to the prop a higher engine rpm will gear a higher prop rpm. A gas engine in a boat will have a red line of about 6000 rpm. I doubt any diesel will red line at more than half of that.

For a given physical size you will get a lot more horsepower out of a gas engine compared to a diesel.

A diesel engine produces maximum torque at a lower rpm than a gas engine. You might be able to get the same amount of torque out of a gas engine but it will occur much higher in the rpm range.

The price of diesel fuel needs to be more than about 20% higher than gasoline before gasoline becomes the cheaper fuel due to the difference in energy available in the fuel.

Gasoline is more highly refined than diesel fuel and is probably a more consistent product.

When starting to look at boats I was convinced that diesels were the better choice for the size of boat I was considering. I have since revised my opinion.

It seems that in North America gas engines are preferred for recreational boats. In other parts of the world, diesel engines are often the choice.
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Old 08-23-2015, 06:54 AM   #26
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A couple of things come to mind:

Diesels are happiest at about 80% of max loading and they have a comparatively narrow power band.
Please provide data to support that statement.

Quote:
Diesels are not to good for people who wants boats that go fast.
Ever looked at offshore race boats? SEATEK engines? Isotta Fraschini?

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A lot of the torque of a diesel engine comes from the mass of the moving parts. As manufacturers move to smaller and smaller diesel engines using turbo/super charging to maintain the same horsepower, the torque advantage of a diesel will be reduced.
Nonsense. A diesel produces torque as a result of higher cylinder pressure and comparatively longer stroke among other factors. The flywheel effect created by moving parts is not part of the power equation, moving parts take power to start moving and keep moving, they don't make power because they are moving.

Dear readers, please be very careful about the many diesel engine myths that breed on boating sites. Do your own research, it is easy and much more useful.
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Old 08-23-2015, 07:32 AM   #27
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I was more intrigued with this statement....

"Gasoline is more highly refined than diesel fuel and is probably a more consistent product."

My diesel doesn't want to comment, but it is "happy" with the diesel I give it....
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Old 08-23-2015, 09:59 AM   #28
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For newbie or semi-newbie boat purchasing folks. The following is a simple guide line. Much personal research should also be accomplished about engines in any boat. If purchasing a used craft - I suggest, expert marine mechanic guidance/survey of all engines aboard.

IMO

Both diesel and gasoline engines have their place in "pleasure" boating.

Each has its own draw backs as well as its pluses. Each needs to be carefully added into the host of "compromises" that every boat demands its owner to consider. In boats below 40' gas engines could be a good choice... so could diesel... depending on many factors. Boats over 40' basically require diesel... for many reasons.

Another important item regarding either type engine is the brand... some are way better than others. If boat is used then maintenance/care provided by PO becomes a big deal maker or breaker on any brand. Some newer engine models of either type fuel are better than the same maker's older models... some are not. Then there is transmissions and drive line to consider - that's a whole other very large sector to delve into.

Survey, Survey, Survey... personally and via hired experts is the name of the game when purchasing a used boat.

And - - > DON"T fall in love with any boat until after you have cut the best deal possible and you then own it "lock-stock-and-barrel". Reason for this: So you can walk away from any deal that shows signs of future boat problems. This suggestion can eliminate a lot of costs, efforts, and heart ache in future times.

Happy Engine-Choice Daze! - Art
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Old 08-23-2015, 11:34 AM   #29
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And - - > DON"T fall in love with any boat until after you have cut the best deal possible and you then own it "lock-stock-and-barrel". Reason for this: So you can walk away from any deal that shows signs of future boat problems. This suggestion can eliminate a lot of costs, efforts, and heart ache in future times.

Happy Engine-Choice Daze! - Art
The art of negotiation is being willing to walk away. Known as the Kenny Rogers theory-Know when to hold them and know when to fold them.
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Old 08-23-2015, 12:44 PM   #30
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As much as I want to be 1 and done with boats (meaning buying the right one the first time) I know that won't happen. Being 29, a wife and 2 boys, the boat will be different than the boat we want to take on the loop trip. I still want to fish and I need a swim platform for the boys. We'll do overnight trips through out the bay, but not as often as when we empty nest.

The buying of the boat doesn't bother me, it's the costs that come with owning a boat that keeps me from pulling the trigger right now. A compromise of speed and fuel burn will be a must I know.
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Old 08-23-2015, 12:46 PM   #31
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And - - > DON"T fall in love with any boat until after you have cut the best deal possible and you then own it "lock-stock-and-barrel". Reason for this: So you can walk away from any deal that shows signs of future boat problems. This suggestion can eliminate a lot of costs, efforts, and heart ache in future times.

Happy Engine-Choice Daze! - Art
Yes, this I will say, it is hard, especially if you love boats in general. And the fact that all boats are future problems in the waiting regardless
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Old 08-23-2015, 12:48 PM   #32
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The buying of the boat doesn't bother me, it's the costs that come with owning a boat that keeps me from pulling the trigger right now.
Same. . .that's why I live on mine! At least the costs can be justified since it's your home
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Old 08-23-2015, 12:51 PM   #33
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I will say, it is hard, especially if you love boats in general.

No, it's easy.

Never never never fall in love with a boat you do not already own.
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Old 08-23-2015, 12:55 PM   #34
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Old saying about boats...

"Every portion of a boat in moving toward breakdown 24/7."

You just need to keep/have all boat portions in best condition possible and be ready to fix whatever may occur.
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Old 08-23-2015, 01:00 PM   #35
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The one thing that keeps people from hiring me as a boat broker is my favorite saying for the young and still with family about boat purchases...


Fall in love with a boat...then buy the next model smaller as you will never use it as much as you think you will.
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Old 08-23-2015, 03:43 PM   #36
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Yea my wife isnt down for living on a boat full time, already asked!
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Old 08-24-2015, 11:14 AM   #37
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A good Diesel engine, well maintained and not overloaded, should give you around 5,000 hours before needing a rebuild. Gasses are more like 1,000 hours. Gross generalizations, of course.

How to overload a diesel? Overpropping is commonly cited. Running the engine over 80% of wide open throttle. Not cooling down the running engine before shutting it down (if your turbos were engaged). Not bringing it up to temperature before opening up the speeds. Ironically, you can also under load a diesel. Excessive idling with no load and running at slow speeds can promote carbon buildup.
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Old 08-24-2015, 11:38 AM   #38
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A good Diesel engine, well maintained and not overloaded, should give you around 5,000 hours before needing a rebuild. Gasses are more like 1,000 hours. Gross generalizations, of course.

How to overload a diesel? Overpropping is commonly cited. Running the engine over 80% of wide open throttle. Not cooling down the running engine before shutting it down (if your turbos were engaged). Not bringing it up to temperature before opening up the speeds. Ironically, you can also under load a diesel. Excessive idling with no load and running at slow speeds can promote carbon buildup.
Rob - 1000 hrs for a gasser is low unless it's a high hp, high performance model and it's consistently abused at too high rpm with lacking maintenance.

Gasser's with regular %age hp to cid when used intelligently and well maintained can reach into the 3 to 4K hr zone before rebuild or replacement becomes required.

Of course... some well utilized diesels can last way over 5K hours too.
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Old 08-24-2015, 11:51 AM   #39
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A good Diesel engine, well maintained and not overloaded, should give you around 5,000 hours before needing a rebuild. Gasses are more like 1,000 hours. Gross generalizations, of course.

How to overload a diesel? Overpropping is commonly cited. Running the engine over 80% of wide open throttle. Not cooling down the running engine before shutting it down (if your turbos were engaged). Not bringing it up to temperature before opening up the speeds. Ironically, you can also under load a diesel. Excessive idling with no load and running at slow speeds can promote carbon buildup.
The carbed, electronic ignition 454 gasser in my assistance boat is passing 5000 hours any time now (13 years of grueling service) with no signs of slowing down.

It has hundreds of hours of over temp and over pressure on it....towing and ungrounding are not good for any engine if misused...

It gets minimal maintenance beyond oil changes.

A lot of low power, idling issues of diesels aren't universal...just with those that HAVE those issues...and that is dependent on if you follow manufacturer recommendations to blow out/burn off the carbon. Also is the myth of of overpropping...it is the misuse of it...not the technique itself.
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Old 08-24-2015, 11:59 AM   #40
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A good Diesel engine, well maintained and not overloaded, should give you around 5,000 hours before needing a rebuild.
A 5,000 hour time between overhauls (TBO) is extremely low for the typical diesel thats used in recreational boats. In fact I would say abnormally low. As in the operator isn't using it and maintaining it properly. The ancient Ford Lehman 120 is said to be (by people like Bob Smith who was involved in Lehman's marinization program back in the day) a 12,000 to 14,000 hour engine in recreational boat service if operated within its ideal parameters and serviced and maintained properly.

In constant and properly serviced industrial use the FL120 has gone more than 25,000 hours before needing an overhaul. A friend in Hawaii who runs a small fleet of 70' longliners all of which use Volvo diesels told me he gets very pissed off if he gets less than a 30,000 hour TBO with the engines in his boats.

Now an engine will need plenty of maintenance and repair during that time, particularly with its ancilliary components like pumps and whatnot.

Perhaps the newer-generation, higher speed, lighter weight diesels have a shorter TBO rhan the older ones, I don't know. But a TBO of only 5,000 hours woud in my opinion negate the whole reason and value of the very high cost of using this type of engine in the first place.
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