Prop tuning and grease.

There is a lot of passion on this forum, would not worry about it too much. You do not want a quiet board room meeting, with only pc opinions and polite smiles that don't mount to a hill of beans!

So for your existing shaft propeller set-up, assuming the yard cleaned/checked the shafts and you had the props tuned to ISO Class S with a propeller scan/readout to verify you can:

Check the initial fit with prussian blue die (usually called Dykem, found in any real machine shop).
Lap the props onto the shaft, if needed.
Re-check with blue die, should remove 90% + or re-lap.
Once you have removed 90%+ of blue dye, assembly the Class S props and you are good to go.

Do all SoCal boatyards do this as standard practice - I doubt it, they will charge extra. If they do not know what you are talking about, make a note of it and get a new yard the next time around.

Yes, this is the precision all-out method/process. You can get by with less if you are not the perfectionist like many on this forum tend to be.

But one hint - for a powerboat, the drive train is everything. Every revolution, every rpm it is working for YOU. The best money spent on a powerboat is on the drive train first, in my humble opinion, as you get a return on your investment every rpm!

There are proper ways of doing a job in order to protect your investment and the continued economical use of your boat. There will always be some guy who will tell you he has gotten away some shortcut for years. What some mechanic and a boat driver do at some sandlot boatyard usually falls into the "shade tree" class of maintenance and repairs.

There is only one proper way to check a propeller for fit and that is with bluing. It isn't high tech, it isn't expensive, it doesn't take long and it is not wasting time or money just because the prop is being fitted to a small recreational boat. I honestly cannot understand why anyone would argue against doing the job right.

All the arguments against checking for fit before grinding the prop and shaft away are just more boatyard mythology passed on by poorly qualified and untrained people. If a prop was fitted correctly in the first place then unless there has been damage or rework done on the shaft taper or the prop taper then no, it probably doesn't need to be lapped again but it should be checked. After all it only adds a few minutes to the job. But, if a new prop is fitted to the old shaft or the old prop is fitted to a new shaft then it must be test fitted with bluing and examined for fit. Like I said earlier, gooping on a blob of grinding compound just because Bubba has done it that way for years and got away with it should not be good enough for your investment, no matter how small compared to some other boat or what Bubba claims is "good enough" for your boat.

Arguing that small boats don't need or deserve the same attention to detail and professional service as a megayacht is a disservice to all who come here for reliable advice and information.

Yes, I manage,maintain, and Captain a LLoydship. I'm bringing it back from Nassau on Wednesday. The owners FT Capt/crew from his larger yacht ran it over there and did the trip with him for a few weeks, but the Captain had to fly down to St. Thomas to unload his 3rd yacht which is shipping over from Italy. As for the Viking, there's one for sale on yachtworld right now with an ask of $899k, 2004 65'.

I certaintly would check the shafts too if someone ground up a set of props. Proper terminology for "magnetic particle check" of the shafts is called Magnafluxing. A process that has been used for decades now mainly was done for checking cylinder heads and engine blocks.

Grinding the prop and shaft away??? You'd have to spend eternity turning the propellor by hand with valve grinding compound to grind the prop and shaft away. I'm not disagreeing with you that using the Dyteck dye is not the absolute best way to do it, but in the real world just doesn't get done very often on 100'< yachts. BTW, it should absolutely be lapped every single time you drop the props and put them back on. You're going to get a little corrosion and crap in between the prop and shaft after a while. Even if it's a very very mild lapping just to clean up the surfaces.

If you've personally lapped props before, you can tell pretty easily if you've gotten them lapped properly without even using dye just by looking at the scoring marks on the shaft and prop....you can easily eyeball it and see if everything has been evenly scoured and if there are any low/high spots by the grinding marks.....

You can look at the image below and see that shaft has been lapped pretty darn good by the even grinding of the entire area of the shaft where the hub sits on. It's around 90-92% I would guess. There's one small area about an inch from the start of the taper where there are a few very minor high spots where the s/s looks just a touch darker.....

https://1969chriscraftroamer46.files.wordpress.com/2014/10/dscf6134.jpg

to the OP, if you do use the Prussian blue dye, Napa sells it along with valve grinding compound. Use the Prussian blue dye (it's blue dye mixed with grease, so it stays put) very sparingly and put a very light coat on the shaft, then put prop on spin it 1-2 revolutions and pull the prop off and see what you have.

On the smaller props on most yachts under 100', you can physically see what you got and what you didn't get with the valve grinding compound. Look at the picture in the link I posted of the lapped shaft that I posted, you'll see any spots that weren't equally scored with the valve grinding compound. Look about an inch back from where the taper starts, you'll see several lines that are a darker color, those are high spots, but a very very small area, then the rest of it is all uniformly mated and scored with the compound. You can see high spots and low spots by the color and pattern in the stainless or bronze, if it all has made even contact with the propellor hub or it hasn't. You really don't need the dye, if you have an experienced eye. On the very large props it's not as easy to tell so therefore you use the dye.

It's sort of like an experienced painter. They don't need to measure how much reducer they put in the paint they're mixing, they do it all by how it runs off of the stirring stick they are mixing the paint with.

I posted that post in case the OP does want to get the dye and wants to do it himself without making a huge mess.

Ah yes ... Google is the grease that says "I knew that all along."

Magnaflux is a trademark for a magnetic particle inspection process and hardware. The proper terminology for the process is "magnetic particle inspection." Google the hardware required and let us know how it works and if there are any limitations that might

And with regard to using MPI for small boat shafting, I think a bit more time with Google will tell you something about what properties of the material being tested are important to successful crack detection. A bit more time on Google might enlighten you about the properties of the material most commonly used to make the shafts used on small boats.

And while you have Google open, take a look at "dye penetrant inspection."