Engine break-in

You are correct sir. A can of worms is putting it mildly.

Varying RPM is good. WOT is fine too but limit it to 10-15 seconds. Don't be afraid to hammer it either for short bursts. After an hour or two, drive it like you stole it.

on top of what was mentioned I would like to add. Change your oil.
Even though initial break in was done and oil was changed before you probably took delivery. Its important to keep good clean oil in it. Some break in and assembly lube could still be running through the system after those first couple to dozen uses depending on hours of use.
I feel it is Important to flush that out after the fact and start fresh.

Joe,

That is a wonderful description of how to break in a marine engine. I've never seen it so perfectly spelled out....from oil type, to rationale (all about those flat tapped camshafts). We ought to make that a "sticky".

I've been breaking in engines of all kinds using Dino oil before switching to full synthetic since learning of a similar routine from a power plant course instructor in A&P school many years ago. This instructor, an engineer with a doctorate in mechanical engineering (didn't even know there was such a degree) did consulting work for a major lubricant OEM and helped convince the FAA to extend major mechanical overhaul service intervals for flight training schools where engines were operated on synthetic motor oils-- reducing operating costs significantly for these schools at a time when aviation fuel was doubling in cost. We as students participated in the study and got to witness first-hand the differences between a single viscosity Dino oil as compared to full synthetic under a simulated, 2000 hour engine cycle test that was supposed to duplicate the typical touch-and-go thermal and load cycling environment. We were able to witness measurable differences in engine component wear.

One really interesting exercise we did after the tests were complete--- we performed an ignition timing experiment to simulate the way way too much advance causes engine failure. We discovered what was clearly already known--that the preignition causes huge connecting rod loads that cause the bearing inserts in the crankshaft journals to "bow" inwards, then turn in their journals, blocking the oil passageways, melting them into puddles in the crankcase before game over and catastrophic failure of the rod journal.

Modern Moly faced piston rings break in easily if the engine is honed properly.
By a professional, not with a drill driven hand held hone. The hand hones do more damage than help.
I worked with several Dyno owners. They say the blow by on a new engine usually seals up after one dyno pull.   These are not jam it to full throttle dyno pulls but they take it up easy to 3,000 and then roll on the throttle till wide open RPM is reached and back off quickly but not jerking back on the throttle.
Less stress internally this way.   These guys built over 1,500 engines a month and have to warranty them so I trust this type break in.   Your boat in the water will act exactly like a dyno pull.   Very similar loading of the engine. I would back off once top RPM is reached, no reason to keep hammering. It will break in and work very well for you.
If you chose to run the old technology Cast Iron faced piston rings the multiple acceleration technique may be necessary.
The Moly Technology has been world class since 1990 and is much kinder to your cylinder walls for a much extended life of your block. There are no negatives, I would run Moly Rings in any gas engine today if possible.
On a new engine Heat is your biggest killer, watch the gauges closely and don't let it get hot for any reason. If it is getting hot find the solution before proceeding.
Not usually an issue with boats as you have constant cooling water available.
In Fel-Pro's engineering labs we tested detonation pressure in engines.
Detonation happens when you run too low of octane or too much timing.
A Chevy 350 bone stock making about 290 HP at wide open throttle was making just over 600 pounds cylinder pressure running at its rated RPM for max horsepower with 36 degrees timing.
By advancing the timing 2 degrees to 38 total timing the cylinder pressure jumped to 900 PSI and then to over 3,000 PSI as the cylinder temps went up due to excess timing and detonation started. This type pressure can stretch the head bolts and allow the explosion to blow between cylinders burning out your head gasket.
Detonation happens when cylinder temps rise, as temperature goes up parts of the head or piston may start to glow red, this glowing red metal will act like a spark plug and set off your explosion but it does it prior to your spark plug igniting. Cylinder temps are not the same as water temp, you can overheat a cylinder without running high water temps. So one flame front starts due to the hot spot exploding the fuel air mix much prior to the spark plug igniting. This early explosion in a cylinder happens as the piston is still coming up with 7 other pistons pushing it. The piston pushing up against the early explosion creates excessive pressure in that cylinder.   Sometimes this can happen with two flame fronts colliding if the spark plug ignites your fuel mix on one side and a hot spot ignites the fuel on the other side the burn can start swirling in the chamber and it creates a torch effect that can melt a hole right through the piston or even between cylinders.
At anything much over 600 PSI your internal parts are in danger. At 3,000 PSI you will be stretching head bolts, blowing gaskets, fracturing piston rings and pounding out rod bearings. In severe cases of detonation I have seen pistons fracture.
Good reason to always make sure your timing is set at a safe number for your engine.
The safe number is unique for every engine.
A older GM stock 350 will usually accept 34-36 degrees on regular fuel.
Put newer GM Vortec heads on that same engine and it will like a much lower number like 28 degrees timing.   The head design affects how fast the fuel burns.
If you add compression on your overhaul make sure your timing curve and fuel match the new engines compression. It may need an upgrade from regular fuel to premium fuel. You may even have to richen the fuel supply to match your new compression.
Just a few things to think about. When a buddy says to advance the timing to add a little more pop think twice about it, do some reading and know what a safe timing is for your engine and set up.
A lean burn can cause all the above also, an intake manifold gasket not sealing properly is one cause. Usually if you have strong vacuum at idle you can rule this out.
Sorry to be so wordy but new engines are a lot of fun as long as you work within known boundaries. Hope this helps.

Edit: I should have noted, the timing numbers quoted are full advance timing numbers.
Rev your engine to 3,500 RPM and see what your timing is. At this RPM you measure what is known as Total Timing or All In timing. This is your important number to avoid engine damage. Your initial timing setting at idle is not nearly as important as what happens at 3,500 RPM. Timing lights are available to allow you to check timing at high RPM. If your distributor is rusty or the internal springs are broken or weak you might need to fix or replace your distributor to have both a good idle quality and a safe High RPM Timing setting.
Known as Set Back Timing lights.

If your at 1.5 hours use and all is good I know what I would do. Throw out a Rope and yell hit it. Once your winds die down.
Thanks for you kind works I admit to having experience inside an engine but very little outside the engine so this forum has helped me more than I have been able to help the forum. This is a great place to work through keeping these boats on the water.

Those Pictures are priceless. Thanks
Your comments are very accurate also.
I knew a guy that upgraded his Camaro from a 327 to a small block 400.
Increased compression from 9:1 327 to 10.5:1 in the 400.
Took about 6 mos for him to get the car on the road again.
Did his cam break in then proceeded to take it for his first test drive.
He stomped on the throttle to feel his new engine and on his first stab of the throttle broke piston rings in 3 cylinders with detonation.   He still had regular grade 6 mos old fuel in his tank had a little too much timing and the results were a total overhaul on his brand new engine. His might have gone 20 seconds before failure.