Questions on power systems

[Waylon]

Hello! I’m looking to buy my first trawler. I am getting myself up to speed on the engines available on most trawler’s.

My basic understanding is gasoline vs diesel engines show diesel get better efficiency overall, agree?

I see some helm stations with twins but only one set of levers. How do these work? Are the levers like an outboard controller where you shift and accelerate with the same lever?

I also prefer a fast cruiser for the ability to move closer to 18-20 knots if needed and the ability to slow cruise too for more efficient cruising. My question is with boats like Carvers (not trawlers) and Silvertons, even with twin diesel engines are not going to be as efficient as a fast trawler- how great is the difference?

Lastly- I know in the I/O world of engines there are some unreliable ones to avoid (Cobra outdrives for example). Are there any less favorable diesel engines that I should be skeptical of?

Many thanks!!

 

[Hippocampus]

Diesel has a higher energy density.that means greater range with the same volume of fuel. It doesn’t have the same risk of fire or explosion. It isn’t as volital so less smell if some is spilled. It’s doesn’t need blowers before and after fueling so faster fuel stops. It only needs compression, air and fuel to run so no ignition system. Engines tend to last longer and can be rebuilt to original spec. Many have replaceable sleeves.
For a trawler diesel makes more sense for many reasons. That’s why petrol trawlers cost less.
The fewer big holes you have in a boat the less risk of sinking. The fewer big leaks the slower you will sink. I/O are another maintenance point and another risk point. It maybe difficult to address a I/O leak adequately.

 

[lwarden]

Welcome!
You will probably generate a lot of opinions with these questions, but I'll take a shot a a couple of them.

Boats with a single level per engine are like an outboard as you guessed, where they move to the first detent and engage forward or reverse and then from there add throttle. These are often fly by wire, especially if you see the lever is somewhat shorter and built by or ZF/Mathers and Glendinning.

I'll leave the slower trawler engine selection to others on this forum who have more experience with sub-planing speeds, but I'll throw in my 2c on planing engine choices....
Diesel is more efficient than gas and generally more reliable. Older mechanical diesels are simple and don't suffer from ignition-related issues or many challenges with gasoline fuel injection or carburetor problems. Diesel is also safer if there is a fuel leak.

In terms of engine preferences for a planing hull, I would suggest this order: Cummins, Yanmar, CAT, Volvo. Each engine manufacturer had good and not-so-good engines so doing some research is required. The sub-planing choices include the above engines as well as Ford Lehman, Perkins, John Deere and other more obscure engines like Gardener.

In order for the group here to help you it would be helpful to share your intended usage of the boat you are looking for.

 

[DavidM]

Answers:

1. Diesel engines use 20% less fuel than gassers, partially due to higher energy content of diesel but also inherent efficiency turning fuel into horsepower.

2. Single lever controls handle both shifting and throttle. I like them. Others don’t.

3. Hull type does make a big difference at low speeds. Pure displacement hulls are the most efficient, semi displacement use 25-50% more fuel and planing hulls maybe 100%. All at low speeds of course.

4. At high speeds you want more of a planning hull, well duh.

5. I/Os have about as long a life as the gas engine that drives them. There are few if any diesel I/Os.

6. Most boaters don’t like Volvos due to higher parts cost but to me it doesn’t make much difference. Cummins and Yanmar’s have most of the diesel boating market.

David

 

[Waylon]

Great info - thanks very much. My plan to either do a liveaboard scenario in the Jacksonville, Florida area with plans to do 3-4 day long trips during the month. So comfort is key and so is fuel efficiency.

What is the consensus on turbo diesels?

Do most boats this size provide some sort of MPG? I know they claim GPH but that really doesn't show the efficiency per mile.

 

[DavidM]

All marine engine manufacturers publish hp vs rpm vs fuel consumption curves at and with a virtual prop. Few boat builders publish curves for their boats.

Turbo diesels are the way to go for speeds in the teens.

David

 

[rgano]

I have been around the waterfront for almost a half dozen decades, and I have never seen a gasoline powered trawler. I have never seen an I/O powered trawler.

When I wanted the solid comforts of a reliable vessel, I bought a heavy displacement hull with a couple of Ford-Lehman naturally aspirated engines. When I got tired of the eight-knot limit of a 42-foot displacement hull, I got a lightly constructed hull with a turbo-charged Yanmar. I could never afford a trawler sized vessel (36-50 feet in my humble opinion) with a four or less foot draft so you can confidently go where you'd like on the eastern seaboard with the enormous engine power required to push it at the speeds you are suggesting. There will be compromises in the lightness of the hull construction to go fast, and you will be faced with running a thoroughbred diesel at pony speeds about which much has been written here.

There was a monstrous big difference between a Carver and my Grand Banks "trawler." Step aboard one and then the other - you won't even have to enter the boat to know what I am talking about - it's "heft." This topic could also relate to whether you are more about the journey (trawler) or the destination (something other than a trawler). That was the transition I made when I downsized.