opinions on gas vs diesel...need a little help

hi all, i'm not looking for the age old debate on gas vs diesel. i've found plenty of that info to keep myself busy for while. i'm just wondering if anyone here runs gas motors. i'm looking at aft cabin vessels in the 34-38' range and find a lot more gas available than diesel. i'm not looking for a fast vessel and would spend my time at cruising 8-10 knots anyway. i am an ex auto mechanic and am very familiar with gas motors......almost no diesel experience. im assuming that not all diesel boat owners started out with boat loads of diesel knowledge.
those with diesel motors that didn't have experience with them before, did you find the learning curve with diesels hard to adjust to?
anyone with a vessel of that size with gas motors, do you keep track of what your average gph rate is?

thanks for any thoughts all

This subject has been debated (and Master Debated) many times here. I would first suggest a little nosing around with the search function and get back to us. There is not right answer and no easy answer. One person's pie is another ones pickle. What's right for me is wrong for you. I started with tons of mechanical experience but no diesel. It took a while, but you catch on quickly.

Just a suggestion.

I share your background as far as tons of experience with automotive and no diesel. I run a single gas in my Owens 27 and no idea of fuel burn. Basically it's a non issue for me. Diesel is obviously safer as anyone who can understand flash points can figure out but there's no reason to avoid gas IMO. The threads here document safety concerns but there's also tons of threads about under loaded Diesel engines and stratosphere high repair/replacement costs.

Pay your money and make your choices but if I found the "right boat" I'd buy it diesel or gas. I know this much, I can buy a hell of a lot of gas for the price difference in your size range.

As Tom mentioned - Go into the search mode and ask questions... there are many answers. As Craig clearly implies - be it gas or diesel is not a make or break point. I add... it's the overall condition of the decades old boat that means purchase or walk away!

Happy Boat Search Daze! - Art

There is no great learning curve. Many of us went from gas car engines to diesel boat engines, to me they are simpler, requiring no spark to ignite fuel.
For me the main issue is safety: leaked liquid gasoline can become a gas which sinks into bilges, and can ignite from a spark. Being in an enclosed area explosion is possible, perhaps likely.There will be better technical explanations than mine, but that`s the effect. I`ve seen what can happen and would not have gas engines, but views differ, as you see. Your expertise would help you maintain fuel systems to exclude leaks, and I think EFI engines have less leakage (excluding older Jaguar ones). Plenty of gas engined boats operate in safely.
Fuel is less of a cost in boat ownership than it may initially appear. Good luck with your search.

Greg

Working on a diesel shouldn't be a problem. The naturally apspirated diesel in many trawlers is a work of simplicity compared to the modern gas car engine. Your background gives you a great leg up compared to me or many of the boaters I know.

I spent 35 years behind a desk where the only motor was in the pencil sharpener. Look at me now, on many occasions in the engine room with a wrench in my hand and the body contorted, longing for the desk/air conditioned office/comfortable chair.

Marty

Either gas or diesel can be economical. With only 200 hours of use a year GAS usually wins when maint is part of the equation.

The problem is displacement boats are really cheap to power because of their modest speed.

Usually the Sq RT of the LWL (water line length) is about the sweet spot.

A 34 -38 ft boat would run 6K (7mph) on only minor fuel gas or diesel.

Running at 8 to 10K will burn about 300% - 400% more fuel per hour.

SPEED of your cruising will set your fuel budget far more than gas or diesel.

Loads of trawler folks have learned to plan their days ay a 6K cruising speed , perhaps you could scale back your Desirements?

Diesel comes into play at operating hours that almost never happen for cruisers , a couple of thousand a year , and cont HP requirements that are above the output for a gas engine , 250HP+ 24/7

Big old gassers are cheap , use your experience to get the low speed range as efficient as you can , and enjoy $3.00 spark plugs instead of $100 .EA injector rebuilds and $1000 ea new ones.

No turbo , pre or after cooler is required and low power operation does no harm to a gas engine.

If you're looking to cruise economically the biggest difference between gas and diesel is maintenance costs. A raw water pump on a Cummins 6BT is $800 and an impeller is $130.

Fuel mileage and fuel costs in the gas vs diesel argument are insignificant at the normal 100 hours a year most recreational boaters use their boats as compared to all the other costs of ownership.

Diesel is safer and not as worrisome with CO either. But not many people die of gas explosions or CO issues. But with gas it's something you must educate yourself about.

Diesel boats cost lots more and the engines will last a life time if cared for properly. Most are not cared for properly and probably last about 1.5 times as long as gas. I can't quote any statistics but just my experience.

That being said, a low power normally aspirated non turbo Perkins or Lehman which many folks on TF have, have very good experience with them. The problem diesels are those with high output, 250 HP and above, required to achieve planning speeds.

For us the choice of diesel was based mostly on fuel economy, and thus range on a tank. We cruise BC and SE Alaska, and we carry only 110 gal of diesel, so range before having to stop again at a fuel dock is a prime consideration.

We run 400-500 hours most summers, and have 5,553 hours in 15 years so far on a high-rpm Volvo KAD44P electronic diesel, which also runs like a top at 1300-1400 rpm. We initially traveled at 17-18 knots most of the time, but have been doing only 6 knots 95+% of the time the last 10 years or so. Our fuel economy (mpg) is 3X better at 6 knots than at 17-18. Our boat is only a 26-footer so 6 knots is our max economical cruising speed. In your larger boat, you could do 7 knots, but not 8-10, if you want decent fuel economy.

With this much use and the need for substantial range, the initial cost of diesel has been a most worthwhile investment for us. Maintenance/repair costs have not been a significant issue, far less than our fuel costs, even at the economical slower speed. I do take good care of the power plant, and have made sure it is propped correctly and used correctly (just as important as maintenance).

Getting up to speed on marine diesels takes some work. One way is to join and follow boatdiesel.com. You can read for free, but to search and see pics you need to join- $25/yr.

There are three things that they preach on that site, the first two of which are applicable to gassers.

1. Prop your engine so that it will reach rated rpm +100 in gear.

2. Make sure that your exhaust system is high enough above the waterline to keep seawater out of your turbo and engine, typically a minimum of 12". Make sure that the injection elbow drains downhill.

3. Cruise at about 400 rpm off of top (more or less for some engines) for best engine life.

In my experience once you start demanding more than 150 hp (15 gph roughly) continuously for a 5-6 liter gasser or 200 hp (20 gph) for an 8 liter one then you are in the 1000 hour engine life range. So above 200 hp you probably should go with a diesel, no matter what your annual hour usage is. A rule of thumb is that you will hit the above numbers at about 3,000 to 3,500 rpm for a gasser. So in other words if you have to cruise at higher than 3,500 rpm, consider a diesel.

At or below those numbers gassers make sense up to about 200 hours per year usage in balancing fuel cost vs the diesel's higher capital cost.

David

I run twin gas with a 10 kw gas genset. I only have 230 hours on the Crusaders, 8.1. They are 425 hp, I generally run at 27-3200 rpm and burn about 20 gph total. At 1800 rpm, 7 kts, I burn 7 gph total. Running at 4200 I can burn 28 gph. There is a direct connection to the throttles and where the tack crosses the fuel gauge Next boat will be a trawler with SMALLER hp diesels for the different type of cruising we will be doing but for now, gas works great.

thank you all for the great input. we are definitely going to be into the trawler/cruiser lifestyle so 6-7 knots vs 8-10 doesn't bother me at all. i have considered the benefit of having the power if we want/need it. i did not realize that running diesels at low rpm's was detrimental to the motor. i am finding out more and more everyday i come to this site.

thank you much
the miller family

gmillandfam said:

. i did not realize that running diesels at low rpm's was detrimental to the motor. i am finding out more and more everyday i come to this site.

thank you much
the miller family

Click to expand...

I did not realize it either, it is a myth. Most of us run our diesels at low (whatever that is) RPMs. This subject has hundreds of posts and even so keeps cropping up like a bad penny.

Believe a diesel's problems are with no load (running in neutral). My owner's manual says not to run in neutral over five minutes at a time (more than enough time to cast off all lines). This seems inconsistent with land-based engines as in trucks and locomotives.

The learning curve is not difficult, and once you understand the basic principles of filter changes, bleeding the system you have "most" of it covered. The cooling side is similar to an inboard gas setup.

My personal belief is, if you plan on using the boat in a higher demand situations (long distances, open water) then diesel is a clear choice, if you like local cruising, maybe one vacation during the summer, the gas setup is very cost effective. Just match the boat/power to the intended mission.

I did not realize it either, it is a myth. Most of us run our diesels at low (whatever that is) RPMs. This subject has hundreds of posts and even so keeps cropping up like a bad penny.

The problem exists , tho for most it can not be seen.

When an industrial 650 hp engine is operated on a real working trawler at say 40 hp , just running hyd ,while the nets are being tended there can be service problems.

When a tractor/taxi rated 120 hp engine is operated at 40 hp forever there is less hassles.

For most a good diesel will last 6000-8000 hours or more.
Sure we have all heard of the 30,000hr hospital generators and 10-12,000 pump setups , but this is a different special service Very unlike a boat with 200 or so hours a year.

Many trawler engines do not have 3000-4000 hours after 20 years , so 30% loss of service life from possible under loading would never be noticed .

If it burned 15% more fuel would a 3-4-5th owner notice that its now 3 GPH instead of 2.3 or 2.5?
ADD a extra quart of oil between changes , no big deal.
White (lost compression ) smoke longer on warmup? no big deal.

The inability to find parts would be a bigger hassle.