Are all boat engine compartments designed to completely replace an engine? Or does fiberglass need to be cutout on some models? If so, would I constact the manufacturer to determine? Or are there some engines like Detroit diesels that are designed never to be removed from the engine compartment?
On boats and ships you do what you need to do to get to what you need to get to. Most smaller boats will allow you to remove a motor by lifting floor panels and doors, but on many if not most larger boats you cut out the side of the hull and slide them out there.
Sounds very expensive. What percentage of 40-60 foot boats would you estimate don’t need to have fiberglass cut due to inadequate access to remove an engine? How does a crane work to remove an engine horizontally out of the hull?
Most boats in that size range will have them removed through the deck. No cranes, just a motor hoist, leverage and a lot of muscle. But understand that whole motors are seldom taken out except for a complete rebuild or replacement. In that case getting the motor out and in is just one part of a very expensive job. When motors are taken out via the hull the hole is cut, a forklift comes over, picks up the motor and takes it out or they're pulled out on a track. Here's a video of a motor being pulled from a 32' Carver:
Detroits aren't designed to never be removed. In their heyday they were often removed to do a complete rebuild because it's faster and easier to work in a shop. Most boats can change a engine without cutting holes. Sometimes the engine needs some parts removed. On steel boats and ships it's more common to cut holes.
Unless the block is cracked, say through freezing, the Detroits can be rebuilt without removing them as they have cylinder liners. Depending on installation you may have to lift them a little to get to bottom end of it all.
On most boats the engines can come up without major surgery. Usually the builder has designed hatches which can be opened up for the engines to come up. Sometimes though because of the layout there may be cabinetry above that need to be taken out. It all depends. As others have mentioned, in most cases engines can be rebuilt “in frame” without removing the block from the boat
Lots of threads on this on this site if you do a search. Also some good YouTube videos . Just search Repower.
Everything comes down to size, right? Just came across an article about this very subject: https://jalopnik.com/the-fascinating-way-the-u-s-coast-guard-replaces-a-shi-1845745216
Generic questions, generic answers: no, not ALL engine compartments are designed for engine replacement - not easily, anyway. And yes, some fiberglass cutting can be necessary. I'm aware of boats where cutting a hole in both the internal saloon floor and the flybridge deck was easier than any other alternative. But the point is, why are you asking? If you are interested in a particular boat in need of repowering, you are likely to get more accurate, specific answers here without even asking the manufacturer. Alternatively, if you just would like to avoid boats where this process is very hard, the first thing you should look for is the engines placement. In many V-drive boats, engine removal is just a matter of lifting a large hatch in the cockpit. Some go even further, having such hatch hinged, therefore easy to open also for better engines access regardless of their removal. Pretty sure I wouldn't chose any boat for that reason alone, though.
Coming to think of it, this photo explains what I meant better than a thousand words, as they say. And by sheer coincidence, the engines are DD...