Eric,
On the Lagoon 410's port yanmar I saw being worked on, the pump impeller can be replaced with no trouble, sure.
But what happened is that one of the screws for the impeller plate weeped a little over time and it went on undetected long enough to cause the screw to corrode and become frozen in the pump housing.
It sheared off in the pump housing when the owner tried to remove the screw/plate and fix the weeping.
There was not enough clearance at all to deal with that type of sheared-off screw task, so the pump had to be pulled.
It is a gear-driven pump on that engine, and so you need enough clearance to unbolt it from the engine block and slide it far enough forward for the oil side and gear drive to escape the block.
There is not nearly enough forward clearance to do that and the engine had to be unbolted and lifted a little and moved sideways.
And while the seawater pump itself is not a part that needs to be serviced/replaced often, it is clearly a wear item nonetheless.
The seawater pump's rear seal that prevents seawater from entering the engine oil is a wear item, as is the cam in the seawater section of the pump (that the impeller rides on).
In areas with extremely silty water, the impeller-wear surfaces in the pump can wear even more so and eventually reduce the pump's volume, etc.
The issue is not really the seawater pump anyway.
The issue is that be it the starter, alternator, seawater pump, injectors, high pressure pump, freshwater pump, hoses, oil and temp sensors, heat exchanger, manifolds or
whatever . . . the issue is that if it is bolted to an engine block, it may and probably will need some servicing, or removal, or replacement during the entire life of the engine.
You would surely like to think that NONE of those bolt-on-component exchanges/servicings would require moving the engine!
Right?
But . . . welcome to the wonderful world of boating!
These types of complications are the norm, not the exception on boats . . . monohulls with engines shoehorned into very tight compartments with blind spots, catamarans with engines stuffed under the bunks, powerboats that often have engines with very difficult access too . . . it is an accepted design in most boats, really.
I have been in a LOT of very challenging engine compartments in my decades of boating life. It's nothing new.
Try setting the points and timing on a Chris Craft aft cabin cruiser with 454 gas engines . . . with only about eight inches of clearance over the entire engine area . . . YIKES!
That said, the point is that it was
phenominal in the catamaran boating industry when the Lagoon 380 broke new ground and came up with engine access that is pretty much exactly like a 55 Chevy with a 289.
You can climb in there with the engine and literally sleep with it there is so much room.
Everything is simple, in plain sight, and each and every nut and bolt can be "got at" and inspected in bright sunlight and/or serviced in bright sunlight instantly and with not one obstruction in your way while you get the job done instead of wrestle access.
Will all of my gearhead experience over my lifetime, I KNEW what I was looking at when I saw the 380's new style design. It brought tears of joy to my eyes!
It's like the "priceless" commercials.
Very nice used Lagoon 380: $299,000;
Fuel and full provisions to head out: $300;
Owning a boat that allows you to work on the engines with no trouble whatsoever:
priceless.
All the best,
Buddy