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Old 08-22-2015, 03:59 AM   #1
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Gas vs. Diesel

Just wondering if there's a unicorn out there.

Is there such thing as an economical gas trawler? Something that's over 30' with a couple of cabins.

I see newer boats that are really nice, but are gas that are the same price as older diesel trawlers. Just wondering what other people think.
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Old 08-22-2015, 04:04 AM   #2
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Read up on Tollycrafts. A number of their cabin cruiser models, some of them pretty good sized, were gas powered from the manufacturer. Some of them were later converted to diesel by their owners, some remain gas to this day. Art of this forum can probably provide more information on Tollycraft's use of gas engines.
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Old 08-22-2015, 10:40 AM   #3
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The only downside to gas is it's eagerness to burn or explode so if one can get around that why would anyone want a diesel engine w it's propensity to vibrate, stink, make lots of noise, cost lots of money and be excessively heavy?
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Old 08-22-2015, 10:52 AM   #4
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Diesels are much more forgiving I've had gas motors in boats before and they are way more maintenance and prone to break downs. The only upside is the cost of replacement.
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Old 08-22-2015, 11:09 AM   #5
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Originally Posted by manyboats View Post
The only downside to gas is it's eagerness to burn or explode so if one can get around that why would anyone want a diesel engine w it's propensity to vibrate, stink, make lots of noise, cost lots of money and be excessively heavy?
I don't know, that's why I asked lol. All my tugs and ships have been diesel so there must be something to it!
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Old 08-22-2015, 11:13 AM   #6
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Another aspect for using a diesel engine is the fact that one gallon of diesel is used to produce 18 horsepower vs a gasoline engine uses one gallon to produce only 10 horsepower. Simple math tells me that a boat with a diesel engine will be more economical in the long run plus with the fact that gasoline is highly flammable makes diesel power an easy choice for me.
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Old 08-22-2015, 11:29 AM   #7
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If boat is not going to log lots of miles, gas engines are fine. If you are going to long trips, high fuel costs are going to aggravate you. Gasoline on docks is for some reason much more pricey than diesel, and you burn more too.

Two safety concerns: Explosive fuel. And gas engines make LOTS more CO than diesels. Both issues can be handled, but risks remain.
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Old 08-22-2015, 11:35 AM   #8
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The choice was easy for me as low hours of usage and familiarity made going gas the obvious choice. About 36' or so would be my limit though. Beyond that diesel is the king IMO.

The additional cost of gasoline is quite small and not noticeable on a sub 200 hour per year boat.
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Old 08-22-2015, 11:54 AM   #9
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I knew/know two couples who own Tollycraft 37'. Nice boats. They are both gas and they love them. They knew going in about gas vs diesel and both are knowledgeable boat owners.


They do not plane them often. Normally run the vessel as a slow boat but can run faster when they have to get somewhere.

They will still burn more fuel than the same boat with diesels run at the same vessel speed.

There are many others with gassers who I've talked to and of course I owned two of them.

The catch they looked at is the premium for a diesel equipped boat vs a gas equipped boat would pay for the extra fuel use and mtce. for many, many years.
In fact one couple figure the premium for diesel engines would never likely be made up.

They made this choice some years ago so things may have changed somewhat but if you are willing to not run hard the fuel cost vs the purchase premium may well be worthwhile.

For comparison I was aboard a beautiful 37 Tolly with 3208 Cats tracking a problem. It was a TIGHT squeeze, very tight, and I'm not sure the outboard sides could be reached, certainly not easily, nor by me. Diesels are often physically larger, HP for HP, so be aware of access as you WILL have to deal with it sometime. V8 are worse and the 3208 are often found in vessels of this vintage, good engine, but wide.

The concern of safety, gas vs diesel, is valid but too many people look at gas as an invitation to a blow up which is simply NOT TRUE unless the owner is , or almost so, completey oblivious to deteriorating conditions and developing problems.

Gas engines do need more awareness and less fooling around about fuel system mtce., engine mtce., and safety procedures so that must be taken into account.

One more thing is range. For the same tankage and boat speed a diesel will give 20%-40% greater range.

So if you can live with the trade off , as many do, then gas should be acceptable alternative.

I'll hazard a guess and if you expect to run less than about 100- 150hr a years then the trade offs will be worthwhile looking into.
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Old 08-22-2015, 12:11 PM   #10
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Wonder if there is a difference in insurance rates for gas/diesel in same boat?
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Old 08-22-2015, 12:56 PM   #11
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Quote:
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Wonder if there is a difference in insurance rates for gas/diesel in same boat?
I'll defer to any of the insurance guys here...but in the discussions with insurance companies in the past I would say yes generally but depending on the boat, the operator and the safety equipment...it may not be much or any at all...

Bigger boats need horsepower to go fast or push a heavy load....at a certain size gas just doesn't cut it....it sure has grown in the last several decades...but in the mid forties and semi-displacement or planing hull....gas is a rarity.

My boat and cruising style..I only need 50hp or so....gas has crossed my mind if I ever have to repower.
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Old 08-22-2015, 01:04 PM   #12
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The vast majority of most boats on lakes are gas. The vast majority of most boats below 35' are gas. So clearly there is a place for it. Now, determining where that is and isn't may be more difficult.

The first thing I did was look at the largest seller of boats in the 30-50' range, Sea Ray. They use gas engines with stern drives up through their Sundancer 370 and start using diesel with straight drives and/or zeus pods on their Sundancer 410 and larger.

I do think the drive you're coupling to has a role to play. Stern drives predominate under 40' and straight drives and pods above.

For the average user of a boat in the under 40' range, gas will be less expensive, not just to purchase but over the life of their usage. On a Sundancer 370, a Yanmar Diesel adds $34,000 to the price of the boat or about 8% of the base price. However, on stern drives they're now offering options such as Axius and Sea Core so the diesel is only $7,500 over the most expensive outboard.

The diesel in the above case, however, will underperform the gas engine, so it's not the appropriate choice for the majority of purchasers of that boat. It would perhaps be a great choice for a trawler like purchaser though who intended to use the boat mostly at lower speeds.

I have a rather simple example of the effect of diesel on a small boat's performance by using an extreme case. Williams makes a 445 tender, so just over 14'. With a 100 hp gas engine it has a WOT of 42 knots. With a 100 hp diesel it has a WOT of 32 knots. Why? The single diesel engine adds 900 pounds of weight, taking the weight of the boat from 950 lbs to 1850 lbs. So the weight difference is an issue. It becomes less so as the size of the boat increases and as the owner is less concerned with getting top speeds.

At the time many of these older boats were built there was another issue. Diesel fuel cost much more per gallon than gas. Now, on the waterway, it's reversed due to most non-marine gas containing ethanol. Non ethanol gas right now runs 60 to 90 cents per gallon more than diesel. So the economics have turned dramatically. Now you're talking savings on fuel usage and price with diesel.

The average boat on a lake is used less than 100 hours a year. At that usage there is no reason not to go with gas engines. Fuel consumption doesn't matter. Weight and purchase price do. Also space within the boat. Inboard outboards take far less space inside.

Now for coastal usage there's one more issue. Historically, stern drives didn't survive salt water well. This has been greatly improved with things like Seacore, but a straight shaft can still handle the conditions better.

If I was a light to moderate user and found the boat I liked with gas engines, they passed the survey with flying colors, then I wouldn't hesitate to buy it. I ran nothing but gas engines from the time I was 13 until I was 43. I only knew there were diesel boats peripherally. If the boat is what I want and does what I want then gas it up.
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Old 08-22-2015, 01:16 PM   #13
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You are showing your age...as late as 2000, diesel was half the price of gas.

Where I am, regular ethanol is still cheaper than diesel.

My example always was..my last boat model, a 37 Silverton was 99% a gasser when looking for a used one

The PO ordered it from the factory with 3208 Cats. The boat was nearly 3000 pounds heavier and about 4 knots slower top end and 2 knots slower at cruise.

But, the Cats got 2x the mileage over gasser and the price of diesel was 1/2 that of regular gas in 1999. So my fuel costs were 1/4 that of gasser on a sportfish where 200-300 gallon fuel burn a day was not uncommon.

My last fill up when I retired and left Annapolis in June of 1999, I paid 68 cents a gallon for diesel with the Boat US discount.

Fortunately gasser have gotten way more reliable and efficient from those days...they are also pretty safe with a mediocum of maintenance.
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Old 08-22-2015, 02:15 PM   #14
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You are showing your age...as late as 2000, diesel was half the price of gas.

Where I am, regular ethanol is still cheaper than diesel.

My example always was..my last boat model, a 37 Silverton was 99% a gasser when looking for a used one

The PO ordered it from the factory with 3208 Cats. The boat was nearly 3000 pounds heavier and about 4 knots slower top end and 2 knots slower at cruise.

But, the Cats got 2x the mileage over gasser and the price of diesel was 1/2 that of regular gas in 1999. So my fuel costs were 1/4 that of gasser on a sportfish where 200-300 gallon fuel burn a day was not uncommon.

My last fill up when I retired and left Annapolis in June of 1999, I paid 68 cents a gallon for diesel with the Boat US discount.

Fortunately gasser have gotten way more reliable and efficient from those days...they are also pretty safe with a mediocum of maintenance.
Well I was actually going from what may be a very bad memory on that subject. The only diesel I saw was on the road and thought it was higher at one time. Have no idea what years and can't find any table to substantiate or disprove it. I never actually purchased diesel until 2012 and since then only on the water.

I'll trust your memory on that.

I'm talking boat use as to today's prices and Diesel is much cheaper in our area than non-ethanol. The average price of diesel at marinas in Fort Lauderdale is about $2.70 with delivery as low as $2.22. Non-ethanol gas which is all that's offered in 95% of the area is $3.80 with a low of $3.50. I did find one delivery for ethanol gas at $2.55. Their ethanol gas was $3.55.

So on the water in Fort Lauderdale today I can get diesel for a low of $2.22, non-ethanol gas for $2.55 and ethanol gas for $3.50.

As to the road, I did read today where diesel was lower than gas for the first time since 2004. In Fort Lauderdale, Diesel is $2.67 on the road and gas is $2.35 today per Gas Buddy.
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Old 08-22-2015, 02:37 PM   #15
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Old 08-22-2015, 03:12 PM   #16
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BandB wrote;
"I do think the drive you're coupling to has a role to play. Stern drives predominate under 40' and straight drives and pods above."

Two diesels and/or large diesels coupled to stern drives would make a very stern heavy boat.
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Old 08-22-2015, 03:26 PM   #17
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Hum, maybe gas would be better for now. I want to do some cruising up and down the Chesapeake Bay and even down to New Bern, NC, but as of now it won't be that often.

Though there's a Krogan in Baltimore I've been watching along with a few older trawlers that could work. I showed my wife what The Loop was and she said she wants to do it.
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Old 08-22-2015, 04:11 PM   #18
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The vast majority of most boats on lakes are gas. The vast majority of most boats below 35' are gas. So clearly there is a place for it. Now, determining where that is and isn't may be more difficult.

The first thing I did was look at the largest seller of boats in the 30-50' range, Sea Ray. They use gas engines with stern drives up through their Sundancer 370 and start using diesel with straight drives and/or zeus pods on their Sundancer 410 and larger.

I do think the drive you're coupling to has a role to play. Stern drives predominate under 40' and straight drives and pods above.

For the average user of a boat in the under 40' range, gas will be less expensive, not just to purchase but over the life of their usage. On a Sundancer 370, a Yanmar Diesel adds $34,000 to the price of the boat or about 8% of the base price. However, on stern drives they're now offering options such as Axius and Sea Core so the diesel is only $7,500 over the most expensive outboard.

The diesel in the above case, however, will underperform the gas engine, so it's not the appropriate choice for the majority of purchasers of that boat. It would perhaps be a great choice for a trawler like purchaser though who intended to use the boat mostly at lower speeds.

I have a rather simple example of the effect of diesel on a small boat's performance by using an extreme case. Williams makes a 445 tender, so just over 14'. With a 100 hp gas engine it has a WOT of 42 knots. With a 100 hp diesel it has a WOT of 32 knots. Why? The single diesel engine adds 900 pounds of weight, taking the weight of the boat from 950 lbs to 1850 lbs. So the weight difference is an issue. It becomes less so as the size of the boat increases and as the owner is less concerned with getting top speeds.

At the time many of these older boats were built there was another issue. Diesel fuel cost much more per gallon than gas. Now, on the waterway, it's reversed due to most non-marine gas containing ethanol. Non ethanol gas right now runs 60 to 90 cents per gallon more than diesel. So the economics have turned dramatically. Now you're talking savings on fuel usage and price with diesel.

The average boat on a lake is used less than 100 hours a year. At that usage there is no reason not to go with gas engines. Fuel consumption doesn't matter. Weight and purchase price do. Also space within the boat. Inboard outboards take far less space inside.

Now for coastal usage there's one more issue. Historically, stern drives didn't survive salt water well. This has been greatly improved with things like Seacore, but a straight shaft can still handle the conditions better.

If I was a light to moderate user and found the boat I liked with gas engines, they passed the survey with flying colors, then I wouldn't hesitate to buy it. I ran nothing but gas engines from the time I was 13 until I was 43. I only knew there were diesel boats peripherally. If the boat is what I want and does what I want then gas it up.
Nobody has mentioned torque, so I will. Diesel engines produce a lot more torque than gas engines, especially at low rpm. You can't use a transmission to vary the torque/speed relationship on a boat, like you can on a car. So when you need a lot of torque to manuever a big boat at low speeds (think docking), a diesel engine has advantages. And with the higher torque, a diesel engine will produce its power at lower rpm, perhaps resulting in longer life.
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Old 08-22-2015, 05:27 PM   #19
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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.)
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Old 08-22-2015, 05:30 PM   #20
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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.
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