reasons not to use high-performance diesels

ALL diesels are most efficient when working hard.

The hassle with a high performance diesel rated at sat 200hp then operated at 100 is the efficiency will suck.

For longest service a simple rule of thumb is to operate at 80% of rated power at 90% of rated RPM..

So If you needed 100hp about 120 hp would work fine for long range cruising.

But some folks want "extra" power for slogging into 20 ft waves or high speed for a "dash" to shore to beat weather.

Probably a 1-in 100 need that costs fuel and reduces engine service life for the life of the engine.

 

Let's look at a BSFC map and check. Hmm, this 90 HP car engine is MOST efficient in the 40-50HP (50%) range. And that's at 40% of max rpm. Extra credit if you look up the wear map for a typical diesel.

http://ecomodder.com/wiki/index.php/File:ALH_BSFC_map_with_power_hyperbolae.png

 

Jonr is right there, when it comes to efficiency. If you take a look at a BSFC chart of a typical diesel engine, you will see that the best efficiency is obtained when the engine is working somewhere around 50% of max RPM and 80% of max load (at that RPM).

I agree that for the longest service life of the engine and it's components, it might be necessary to run the engine at somewhat higher RPMs, between 70-80% of the maximum. But that can be overcome by a careful engineering. My diesel car has a recommended cruise RPM around 1600-1700, and hence has been (presumably) designed to minimize wear on moving and loaded parts in that RPM range.

Cheers

 

The problem is that the propeller and engine power curves are always very different. The curves should cross at the engine's maximum HP and rated RPM. However, that unloads the engine at mid range.

 

PAR;
the boat i will be building is an old 18' runabout (Hacker). I dont intend to turn it into some high speed missile. I just want to be sure it gets up to plane and behave the way it was designed to. My main concern is to have enough torque/power but also not to end up with a huge dinosaur as an engine.

CDK,
Thanks for clearing that up. Have you had any experience with the engines from PSA?
The one i'm thinking about using is the 2.2 HDI biturbo because it can be very cheap and i have easy access to the neccessary tools to rebuilt it and remapping the ECU.

 

Dissipating heat is a problem when using a standard automobile engine.

Vetus used to sell marinized PSA diesels.


You might have a look.

 

Michael,
i allready had a look at Vetus for parts but thanks for the tip anyway, i took a second look and now noticed they have 2L-common rail engines which is basically what i'm after.
I'm bracing myself for the price...

 

- - Frosty's boat has Yanmar - which are 6 cylinder Landcruiser diesels.
- - I am using tiny Nanni diesels which are Kubota with a stupidly reduced sump size (3 liters of engine oil for a "sailboat" :!: - 712cc 3 cyl engines), cruising at 7knots running at 2500rpm for 2 miles per litre of fuel - up to 3500 rpm consumption goes to 3 litres/mile for about 10 knots.
- - In SE asia the "longtails" use USED light truck engines...
- - Bill Barry-Cotter used diesels (italian) on his racewinning F1 Maritimo boats, until they banned using diesels - insisting on USA derived V8 petrol engines
- - The C10 from Robin Chamberlin designs (in my Gallery), uses a pair of marinised 50hp Kubota engine cruising at 15 knots.

It was suggested to me that I run near maximum torque and happily the propeller rotates at about 1000 rpm and 7 knots satisfied my need. Crunch your numbers and enjoy the pleasure and fun boating on the water...

 

the engine displacement may not be indicative of fuel consumption, but the part load specific fuel consumption. IOW, if the efficiency of the engine on two different size engines, putting out the same HP, is the same, they will consume the same amount of fuel.

Of course a more modern engine will be more compact and much lighter, so it will help you get on plane sooner with less power, but you have to look at the efficiency to know which one will actually consume less fuel.

You will likely get better efficiency out of the more modern engines, but you have to watch out for the complexity level as well. A lot of modern automobile engines have complex computerized fuel controllers with a lot of sensitive senors. these may not hold up very well in a marine environment, reliability is a major issue. If your car breaks down because wires are corroded or sensors fail, you are inconvenienced, if you are far from port late in the day in your boat, it could become desperate fast.

And as mentioned, you have to look at your conversion costs as well. Most car engines are not suitable for use in a boat without some significant modifications. Also, consider how much you will be using the boat in reality, if it is just for recreation and you will only be going out 10 to 12 times a year, the yearly fuel savings will be smaller than if you use it daily for work or commuting. So consider your total life-cycle costs aw well, purchase, maintenance and fuel consumption. You may be better off with marine engine in the long run, depending on the purchase and conversion costs.

 

I wish I had!
Before I bought my two VW 1.9TD engines someone offered me a pair of PSA HDI diesels with less than 50.000 km (traffic accident victims). When I sent someone over to inspect the goods, it turned out all wiring had been cut when the engines were removed, standard procedure for a scrapyard. Without the ECU, wiring harness and sensors it is very expensive to get the engines back to life again. The pricing for these items is unbelievable.

 

For folks that can live with a tiny diesel, both Kubota and Yanmar enhines are used in over the road reefer trucks.

These usually have a huge a hugely over sized oil pan (so the unit can run 10+ days with no driver input).

About $400 at the local reefer service shop ,used.

 

Lots of good info so far, thanks to everybody!
Petros, i'm aware of the electronics and their complexity. I've been involved in racing where we replace complete OEM ECU's and replace them by aftermarket units (Motec etc) but in this case the orignal ECU is very easy to modify as there is a huge market for people who want more power from their diesel cars and remapping has become as simple as rejetting carbs.
For the sensors i'm not really afraid of moist etc. In Belgium they send out spray-trucks with salt when the roads are frozen. Most cars see a lot of this salt but still get up to 300.000kms without major problems due to the salt. For a boat that will get a few hours of use in a month and only 5 months a year, this wont be a big problem i think.

CDK ; Complete cars turn up for reasonable prices (if they flip and the roof is damaged they are around 2000euro's) but if you ever have another shot at a PSA-engine, you can get the ECU reset and remapped for 500euro's if it doesn't match the engine. You can also get the code removed so it will start without the original transponder/key. If you can get your hands on the software you can run them from a pc.

 

you might also consider getting an older Diesel that has pure mechanical controls, no electrical parts at all except the starter. I once owned a '74 Mercedes 240D which had a real simple and efficient diesel with no electronics, we only paid $900US for the car and we drove it for years. It was very reliable and parts were still plentiful, though the engine is a bit heavier than the more modern ones, it would greatly simplify the installation.

 

The reason you use a modern diesel engine is its energy density.

Adapting a modern turbo charged, electronically controlled, clean burning diesel for marine use will be a challenge.

Im sure it can be done if you are clever and understand how all the modern components work .

 

Petros,
I've looked at conventional diesels too but they all seem very heavy and for anything over 100hp i will need a bigger boat i'm afraid... For a 18' runabout i dont think they will be a very good choice. I've tried to get some prices for the Mitsubishi-based direct injection engines and the VW TDI-based mercury-diesels but i'm pretty sure they will be way outside my budget.
I've only just begun to build the boat so the problem wont be very urgent for a few years but out of curiousity i dropped by the guy who does the programming in our race-team. We took a look at my car (2L HDI-engine) and it's fairly easy to disable Exhaust recirculation and exhaust convertor-sensors. (my 2 main concerns) Changing other stuff like injection-volume wasn't really complicated.
btw, i haven't mentioned this but the reason i'm so diesel minded is not just the gas-price, i just like turbo's and diesels that howl