How to check if Hatteras Extension was done right?

Considering purchasing a 63' Hatteras that has been extended to a 70'. I've asked for info/paperwork on where the extension was done, but not received yet.

How can I tell if the extension has been done properly without pulling it out of the water?

Most notably, if the propulsion was extended or not.

 

We do a lot of stretches on commercial boats. We always assume that a stretch is good if the installers took the time to stretch all the systems. Rule of thumb for us up here is over 10% stretch of original length and keels need to be stretched or they get a little squirrely. Probably less of an issue with big twins. Keep in mind these are not scientific rules but rather observations from fisherman. Anecdotal, but we have stretched infinitely more boats in the last 20 years than made new so it's a widely adapted process.

Running joke here is if the stretch is still attached it was a good stretch. Main problems I've seen has come from the systems installation. Saw a failure of one this last winter, but not from a structural standpoint. Boat had been stretched years prior but the aft section only produced buoyancy. They had not stretched pumps and free water from a leaky hatch began to slosh in the open stern and over she went.

Not a fault of the extension itself but rather taking a shortcut.

 

Is she a motor yacht or a sportsfisherman type of Hatteras?
Do you have any photos that you can post of this vessel please?

With difficulty, even if it has been hauled out, especially if the fibreglassed area in way of where the extension is attached to the original hull is now hiding behind furnishings or linings.
However as @comfisherman has wisely pointed out above 'if the stretch is still attached it was a good stretch' - and it is not now likely to 'fall off' in a hurry.

Extending / modifying the propulsion / running gear would be an expensive undertaking, as the alignment of the engines would change, and they would require longer shafts, intermediate shaft bearings, new shaft support brackets, and new stern tubes would have to be fitted (while cutting out / glassing over the locations of the old stern tubes).
New rudder stock tubes would also have to be fitted further aft.
It is possible that the rudders and propellers are still in the original location - although an extension of 7' is quite a lot, and it would certainly be 'better' in all respects move the propellers and rudders 7' further aft as well.
It should be possible to tell from looking inside the vessel to see if the propulsion and steering gear has been extended further aft as well?

The photo below is of a Buddy Davis sportsfisherman here that was 'stretched' almost 20 years ago, because her owner wanted to have a larger fishing cockpit.
She was only lengthened by about 3' - 4', but the owner still moved the rudders and propellers further aft as well - it was a big job.

 

Wondering why a rearmost prop and rudder?
Why not props in the middle of a hull, pulling rather than pushing at the back which tilts the boat bow high up in the air burying the stern in the water and so then you need planes to level the hull

And frequently when steering boat, I never use the rudders, I just change speed and prop directions of engines. I can spin on a dime in a harbor without touching the rudders. I think mid hull props would be the best thing for my boat.

Perhaps rear most props were originally done that way long ago as was the easiest way to setup engines in boats, and it just carried on that way over time.

 

There certainly are advantages in doing this - there are many 'tractor tug' designs that have their propulsion units amidships or even up forward.
Here is a neat little 25' tractor tug - if you google 'tractor tug' you will find many more.
Tug – Mini Tractor Tug – Hockema Group https://hockema.com/projects/tugs/mini-tractor/

 

Because that results in a lower propulsive efficiency due to the prop acting in a region with increased fluid velocity related to the hull velocity. In addition, you get reduced leverage from whatever course-control arrangements applied. But, as always in marine engineering, there are special applications, where the balance is biased towards the unorthodox. However, that is not ground for the assumption that today's propulsion systems in general are based on negligence.....

 

On the single engine boats they don't track as well with the prop farther forward. Some of the coastal crabbers actually prefer the location for spinning on the gear, granted they don't travel long distances.

 

How about the large container ships the props are not placed entirely in the water, but right at the surface. This is done for efficiency reasons. Must be a lot of turbulence then.
SPINNING SHIP PROPELLER Compilation 2022 (Full Speed) (youtube.com)

I actually remember in mid 1960's a terrifying experience as a little kid in my dad's small sail boat and this huge container ship and its spinning prop and we were getting closer and closer. The prop was mounted up high and I could see the blade spinning. I was scared we would get sucked. Somehow we got too close. I think it was Narraganset bay in Cape Cod, we were out in the shipping channel.

I was also scared of those large lighted shipping channel markers floating in water. I imagined the boat sinking and having to try to hang on to them