Marine vs automotive / truck motor

What differences (in general) are there between automotive and marine motors ?

I notice that marine motors have big exhaust manifolds and usually some funny tanks hanging off them

what is the purpose of this stuff and what else is changed?

I assume the governor is changed 

I know nothing about boats at all except me and boats are best kept apart as a general rule


Paul 

Paul, most marine engines have water cooled manifolds, hence their large size. The engines themselves are usually fresh water cooled, which is turn cooled via heat exchangers cooled by "raw water" from under the boat.
Yes, they often have governors set differently and therefore have reduced HP output.

My own experiences mucking about in boats for a while now. The governor is usually set to run within a narrow power band but higher rpm in most instances.
Most boats require a wet exhaust, usually only trawlers used dry exhaust stacks so the engine needs to either run raw sea water for cooling or freshwater cooling keels (external cooling pipes alongside the keel)
Our last boat was seawater cooled and pumped the surrounding water through a skin fitting via the engine driven pump, circulating the water around the block, then dumping it into a wet exhaust muffler and back out over the stern. Simple but hard on the engine, due to high corrosion aspect.
Ex trawler before we rebuilt to a liveaboard was originally a dry exhaust system but changed it over to freshwater cooling.

The engine has a closed system like a road going vehicle, the water is pumped around the block again by an engine driven water pump allowing it to travel down through the hull to long copper / SS piping.and circulated back up around the engine. .
The engine also needs a header tank fitted slightly above the engine with this system to act like a radiator top tank. 
The exhaust is seawater cooled needing a second engine driven pump to draw in the outside exhaust cooling water injected ideally just before the muffler.
Fresh air piping to the diesel is also a major factor.

Thanks wee allis

So is it as simple as unbolting manifolds and the water cooling stuff and changing the governor

I really know nothing about marine stuff

Paul

And then, there are industrial engines such as generator engines where the governor is designed to hold a single engine speed regardless of the load.

eg:  a Generator should hold a speed which is a multiple of the AC power frequency and the number of windings in the alternator. (typically, 1500 rpm in Aust which converts back to 50hz)

A mate n I fitted a 3 cylinder Daihatsu engine into a small jet boat to be a licensed fishing boat for mullet season. It was a simple conversion to marinise it using what looked lije an oversized yabby pump. Engine coolant ran tgrough small tubes in tge yabby pump body which in turn ocean water was pumped up via the jet system thriugh tge pump n back out.