Diesels vs Gas Engine - Pros and Cons

SeadawgVB said:
This (above, bolded by me) I should have pointed out as well. If the seas come up a bit to where you are climbing then surfing, then the gas motors suffer due to lack of torque.
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Yes! this is the first thing i noticed in rough conditions and this is not a small thing. When you add in autopilot you are just watching the waves go by as you ride them out. The bulk of your time is then spent watching your gauges, chart plotter etc. Much more relaxing ride for sure.
 
Irie308 said:
Yes! this is the first thing i noticed in rough conditions and this is not a small thing. When you add in autopilot you are just watching the waves go by as you ride them out. The bulk of your time is then spent watching your gauges, chart plotter etc. Much more relaxing ride for sure.
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I switched from a single gas to a single diesel boat this year. Note that the boats are quite different and and the design has some factor: 27 ft 7500 lb, 8.5 ft beam gas outdrive vs. 34 ft. 16000 lb 12 ft beam shaft drive diesel. Some observations that may have already been mentioned:
  • Operation in "weather". It hadn't occurred to me until reading this post, but it's right. In heavier seas with gas, I was constantly working the throttle. Diesel: Throttle work approaches zero so far. Set it and go. If seas build a little I just backed the throttle off a little bit.
  • Getting on plane. Gas: A real process. Tabs down, drive down, Apply full throttle, plow water, start to come on plane, tabs up, slowly bring drive up, on plane. Diesel: Apply throttle. Accelerates. Turbo kicks in. Get knocked back in seat. On plane. Seriously, the acceleration from the diesel is stunning. I'm at 28 MPH in the time my old boat was just getting on plane, and barely feel it.
  • Docking. The torque from the diesel and the resulting large prop is can turn is impressive. With the old boat I left it in gear basically the entire time I was entering or exiting the slip. With the new diesel I bump it in and out of gear. The prop moves so much water it's incredible. In some ways it moves so fast at low speeds it's annoying. I'd imagine in a twin configuration the steering response would be seriously impressive.
  • Maintenance. So far the diesel seems like it's the easier of the two for regular maintenance. There are no spark plugs, no cool fuel filters. It seems like basically just change the filters and keep the fuel clean. Now, there is the matter of servicing the aftercooler, but that also seems pretty straight forward. Winterization seems dead simple per the Cummins tech that did a walk through with me. I feel more comfortable doing diesel maintenance vs. gas due to the non-explosive nature of the fuel, and that the engine parts are much more accessible. Also, gas engines do wear out an need a rebuild. With care, the diesel should run many thousands of hours.
  • Fuel. Less expensive then gas. Far better fuel economy for a given weight. No issues with CO when running either the main or the genny. (I get virtually NO diesel odor - modern emissions!)

Having now had a diesel boat for a few months, given 2 larger boats of the same type, in similar condition, and similar prices, I'd pick the diesel.
 
marks737 said:
Diesel all the way. Much more economical, more reliable, more torque, safer no CO worries, cheaper fuel. Rock steady power, just set it and forget it. No RPM variations in rough water. Easy to maintain, just take care of them preventatively.
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That's usually how I'd describe my boats performance, with an occasional exception. Weekend before last I had 2-3' following seas on some long stretched out swells. There were a couple times climbing the swells, up, up, up, that I dropped from 23 to 18 knots before I started going downhill again.

It was interesting, I've never been on swells like that before, never been on the ocean. I'd look around and you couldn't really see them but you knew you were climbing. Maybe if there was another boat running out there far enough away I could have seen him going down into the troughs.

Now that I'm thinking about it, my speed was changing but I don't remember looking at engine rpm but you could definitely hear them working harder.
 
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Guys,

Can't thank you enough. I loved my Mercs and treated them like one of my kids but I think it's time to step it up. I do have the fear of the unknown SeaDawg. Zach312 totally agree on the CO2, as a Dad of 3 you have love not worry about that or filling up at the pump. JVM225 part of the struggle was around the maintenance...I watched a video on replacing the fuel filters - very different than the simply spin on filters but I think I can handle it. The 19 quarts of oil in each engine seems insane to me...I wondered why they sold oil in 5 gallon buckets. The other thing that sold me was FreightDog's Engine picture - great picture.

I will let you know how I make out! I really appreciate all the advise!

Steve
 
stevediarchangel said:
Guys,

Can't thank you enough. I loved my Mercs and treated them like one of my kids but I think it's time to step it up. I do have the fear of the unknown SeaDawg. Zach312 totally agree on the CO2, as a Dad of 3 you have love not worry about that or filling up at the pump. JVM225 part of the struggle was around the maintenance...I watched a video on replacing the fuel filters - very different than the simply spin on filters but I think I can handle it. The 19 quarts of oil in each engine seems insane to me...I wondered why they sold oil in 5 gallon buckets. The other thing that sold me was FreightDog's Engine picture - great picture.

I will let you know how I make out! I really appreciate all the advise!

Steve
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I was really scared of diesels because of the unknown too but it’s worth it. The skill level for routine maintenance and replacement of things that go on the engines like belts, hoses or possibly a starter or alternator if that should ever come up is no different on a Diesel than on a Gasser.
Plenty of info on required maintenance intervals around too.
If it came down to it, taking the motor apart and putting it together is still just turning wrenches.
For me, the fear is in the inability to diagnose a problem if one should arise because I’ve never had a diesel or dealt with turbos before.
But from what I can see so far they don’t break too often if properly maintained. Plus it’s nice to eliminate ignition items from the maintenance or potential failure list. I think those are the things that give the most trouble on properly maintained gas motors anyway.
 
stevediarchangel said:
The 19 quarts of oil in each engine seems insane to me...I wondered why they sold oil in 5 gallon buckets.

I will let you know how I make out! I really appreciate all the advise!

Steve
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Yeah, the oil volume is something. Costco has oil in sale now. I just picked up 2 3 gallon cases. I would not go with the 5 gallon pails. Everything I’ve heard is they are a pain to deal with.
 
b_arrington said:
Yeah, the oil volume is something. Costco has oil in sale now. I just picked up 2 3 gallon cases. I would not go with the 5 gallon pails. Everything I’ve heard is they are a pain to deal with.
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My 3126 Caterpillars take 6 1/2 gallons each. Thirteen gallons for the motors and another gallon for the generator. I buy one gallon jugs of Rotella. I find them easier to handle and although I’m sure pumping oil back in through the Reverso pump is fine I prefer to fill the old fashioned way.
 
  • We just came back from a long weekend in Portland (about 70 nm from home). The ride up was at 20 knots with a burn rate of 10 gph per engine. The ride up was smooth with a slight 5 knot crosswind. Travel time three and a half hours. The return trip was a little different with 3-4 foot seas and a 9 knot headwind. We didn’t stuff the nose but came close a couple times. However, again 20 knots, 10 gph per engine, and three and a half hours. Off course this morning was spent washing salt spray off of the pilot house roof and antennas.
  • So, no question in my mind that diesels are the better long haul choice. Also did I mention that diesel is roughly 30 to 50 cents per gallon lower than gas. I also noticed that there is no coaxing the boat up on plane, just push the handles forward and it goes.
H
 
JVM225 said:
My 3126 Caterpillars take 6 1/2 gallons each. Thirteen gallons for the motors and another gallon for the generator. I buy one gallon jugs of Rotella. I find them easier to handle and although I’m sure pumping oil back in through the Reverso pump is fine I prefer to fill the old fashioned way.
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Ok I don’t feel so bad now. My Cummins’ total capacity is 4.3 gallons. Oil pan high capacity is 3.25 gallons. And only one propulsion engine.
 
b_arrington said:
Ok I don’t feel so bad now. My Cummins’ total capacity is 4.3 gallons. Oil pan high capacity is 3.25 gallons. And only one propulsion engine.
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I saw that sale at Costco, but it is only on Multi Grade Rotella. My engines use straight 30 weight and I usually get my Rotella at Walmart for about $14.00 a gallon.
 
JVM225 said:
I saw that sale at Costco, but it is only on Multi Grade Rotella. My engines use straight 30 weight and I usually get my Rotella at Walmart for about $14.00 a gallon.
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Yes, it was on 15w-40. That's the spec for the main and genny. With the sale it worked out to about $10 per gallon.
 
JVM225 said:
I saw that sale at Costco, but it is only on Multi Grade Rotella. My engines use straight 30 weight and I usually get my Rotella at Walmart for about $14.00 a gallon.
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I am on Long Island too. Do you run the Rotella t1 sae 30 or 40??? Asking because a friend was advising me not to run 30..had a long winded answer that conflicted with what I thought I knew. ..previous owner was running 15-40 but I’ve read enough to understand not to use the multi viscosity in these 3126.
 
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kvduff said:
Do you run the Rotella t1 sae 30 or 40??? Asking because a friend was advising me not to run 30..had a long winded answer that conflicted with what I thought I knew. ..previous owner was running 15-40 but I’ve read enough to understand not to use the multi viscosity in these 3126.
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30w here in the Seattle/Tacoma area... I keep an eye out for the local auto stores, Walmart etc, for oil specials. This season it was Advanced Auto Parts with Rotella for $12/gallon. I like the 5 gallon buckets myself, but when gallon jugs are on sale I am a gallon jug guy!!
 
kvduff said:
I am on Long Island too. Do you run the Rotella t1 sae 30 or 40??? Asking because a friend was advising me not to run 30..had a long winded answer that conflicted with what I thought I knew. ..previous owner was running 15-40 but I’ve read enough to understand not to use the multi viscosity in these 3126.
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I am sure Frank W will answer but my understanding is the Rotella SAE 30 matches all of the Cat specs.
 
midexp said:
I have a 400 Sundancer with gassers. It pops up on plane instantly. Not quite sure what you mean by coasting. Certainly isn't the case with mine.
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Coaxing. It sounds foreign to us because of how well gasser 400DA's plane-out. It just depends on the boat. A friend of mine bought a 32 express with small blocks and v-drives last week. It's a nice boat, but it doesn't plane well and falls back off easily.

Even when a diesel boat is under-powered, and or course that happens, it doesn't feel as bad because of the turbos. At the point in the 32 last week when I was making sure the throttles were all the way up and the tabs all the way down and all I could do was hope and wait for the that boat to get off her ass, even an under-powered diesel boat would be enjoying literal "boost".
 
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