Originally Posted by GalaxyGirl
There is a boat that I'm interested in. The broker says that the odometer hours don't match the dashboard hours for the engines. He says that the owner has no knowledge of what the actual hours are and the previous owner has no info either. They also don't have any information if the engines have been rebuilt or not. I thought this was strange.
I'm wondering if a mechanical inspection
can tell me if the engines are good despite having no history
or if I should not consider this boat at all because of the discrepancy and lack of info?
Can a neglected engine become a good engine with a rebuild or can a bad engine not be rebuilt at all?
Is the engine hour meter mechanically driven and the dashboard electrically driven? I know on small airplanes that the mechanical hour meter can run 70% of the actual time of flight, like doing touch and go landing practice where some is just gliding. What I would do is see if either hour meter is actually working and go with the working one if there is one.
I would be more concerned with the horsepower the engine is rated at for its displacement
. A diesel
engine of a given displacement
, which is how much air all the cylinders can take in when the engine goes around once, can have a range of horsepower ratings depending on how big the fuel
injectors are. The bigger the injector, the more horsepower; however, more power means accelerated wear, lots of cylinder wear. A compression
test will tell something about that as will engine oil
analysis on use oil
. The marine pleasure craft application has the most wear and here are the specifications for that:
These graphs are for turbocharged engines. The graph to the left is for maximum power, the one on the right for much longer engine life. Take a look at the graphs and note the gallons of diesel used per hour vs. the engine speed or revolutions per minute (RPM) when a fixed pitch propeller
is used. Very few boats have propellers that have an adjustable pitch
because of the cost, although tugboats use them because of the improved fuel economy. The graphs are a bit confusing because it shows horsepower over a range of RPM
for rated brake horsepower (BHP) and just below that rated shaft horsepower (SHP), which is with accessories, and right under that is propeller
horsepower. Propeller horsepower falls off quickly for lower RPM
because a propeller cannot absorb the power that is there. It is sort of like the tires on a car spinning on ice. Unlike ice though, increased RPM does result in better 'tire traction'.
If the same displacement engine is being used for normal marine use with longer life required, the horsepower is less than for marine pleasure craft: http://www.detroitdieselpartsdirect....1TI-Marine.pdf
. Note that there are power specifications for Continuous, Intermittent, and maximum power and the each specification has a different size injector to limit the amount of horsepower dependent on power specification.
The 12V71 engines are rebuildable. The cylinders and pistons are removed and new ones are installed along with new bearings and other items. There are engine kits that supply all the necessary parts
. Detroit parts
are less expensive than most other manufacturers. Check on ebay or even Amazon. Of course you need a mechanic to put it all together. An automotive machine shop that specializes in diesels could do the job. The 12V71 was used in 18 wheeler over the road trucks and is common. It was a very smooth running engine in a truck, but had lots of noise. This noise can bother some power boaters. Also, these Detroit 2 cycle engines do not give as much power per gallon (specific fuel consumption) as 4 cycle engines like Cummins diesels. Detroit is the only 2 cycle engine in boats. In ships there are 2 cycle engines, but these are massive, low RPM, and run on residual oils that are much heavier fuel than diesel.
The two turbocharged engines have ten times the horsepower that is needed for cruise
with a displacement hull
. One engine that is not turbocharged would be about the right size for a trawler
, a boat without a hull
that can plane. A boat that gets up on top of the water
and moves at say 18 knots is up on plane, but range is limited because these boats have to be light and too much diesel for long range cruse would weigh so much and the boat could not plane. Note that a boat that planes has a much greater fuel consumption
and limited engine life, maybe as little as 500 hours if the boat is run full power most of the time.