Engine Questions - More to come...

He's talking about putting them in a Sportfish I'm pretty sure. The Sportfish guys want to cruise at 30+ knots these days. The Sportfishes can handle much larger and heavier engines then a motoryacht because they have less weight above the waterline. Its quite common for a sportfish owner to have a 3,000 lb tower put on top of the boat (between the tower itself, hardtops, electronics on the tower, rigging etc.) They're built stronger typically with a little more beam. C18's are usually put in everything from a 45' Cabo express to a 50' Egg Harbor SF. 55-60' usually have c30's or c32's or 1500 hp MAN's or 12v2000's typically and they're fine with that. I've run the 54' Hatteras SF with C30's and it run's great with them and rides amazing. They also put C32's in as small as a 52' Cabo express.

As to diesel engines:

First the caveat... I have little experience with operation and maintenance of engines or knowledge of this model vs that model...other than what is normal to driving cars or running the boat. However, I have had a lot of experience with development of technology. Including consulting on new engine concept proofs for CAT... for technology a company I was on the board of was doing the research in emission reductions etc. Now I am many years out of the test lab and am unfamiliar with this model or that but I can explain the fundamentals. But I will not use complex overly technical terms in this so everyone can understand...

This issue of fuel efficiency in this thread vs low fueling rate or power levels and injector system etc... see if this explanation helps on the issue.

Many liquid fuel rocket motors operate on hypergolic ignition. That is when the fuel and oxidizer contact each other they burn on contact without a starting spark or flame... they BURN or properly oxidize ON CONTACT.

Well it so happens diesel engines work on hypergolic ignition too. The diesel fuel when sprayed in fine droplets into the hot compressed air it ignites on contact with the air in the combustion chamber of the engine. The air is the oxidizer.

The temperature of air and the density combine with the cetane rating or ignition temperature and burning characteristic of the fuel determine the delay of ignition. I skip over this as that is a hugely complex subject and not applicable in this discussion because we are assuming good quality fuel and for this discussion lets assume the fuel is a constant and the same.

The key is the ignition and burning take place on the outside of the fuel droplet exposed to the oxidizer.

Why diesels smoke... is the fuel burns outside of the droplet in to the center of the droplet. Thus the larger the droplets are the more chance for the fuel to pyrolize or degrade outside in... burning from the surface to the center of the droplet... and that the fuel not directly touching the air is "cooked" fuel when it does burn... as it does not completely burn in the cooking process before forming a coke or soot particle. Why is the droplet only burns where it is exposed to the oxygen in the air… but the center heats up from that combustion. Noting the area on a larger droplet is less per unit mass of the droplet than on a smaller droplet so the larger the droplet is the more susceptible it is to creating soot. The soot can be burned but it has a higher input heat need to start than is possible in an engine. So it is best not to create the soot particle in the first place.

How this is done is by two basic means:
First, is by making the droplet burn in clean air so that more oxygen is around it to burn. This is done by suppling more air to the engine than it needs for chemical balanced combustion. Also, if the air swirls in the combustion chamber as the injection takes place the drops are injected into clean uncontaminated air as the injection happens over time.

Second, is by making the droplet smaller. This is done with the injector nozzle design, pressure and rate of squirting it in... to make the droplets finer.

Modern diesel injections system are all about making the droplets finer to minimize the soot production...

By more efficiently burning the fuel without coking or making soot of part of the drop the fuel efficiency goes up... in fact if the fuel was infinitely fine drops there would be no soot emission… if sufficient air were available for chemical balance and the air and fuel spray were perfectly mixed.

Now maximum power on both diesel and gas engines is produced at about 30% over the chemical balance between the fuel and air... that is rich. This is where the highest combustion temperature is also produced in an engine and where most danger of overheating pistons and valves is. Why... long explanation but it practically coincides with the practical result. At this fueling rate... diesel put out black ugly clouds of smoke because the combustion is inefficient.

Now you can figure out why... and the argument about this or that mechanical embodiment performs.