The hull is solid glass with fiberglass over plywood for the decks. Good luck
A hammer, possibly not with a steel head, banged on the deck will thwack or thwock, no thwocks are wanted, only sharp sounds. Any muted sounds that don't require removal of headliner etc. warrant a sigh of relief. Thwocks and worse yet, thuds, weren't part of the original build.
Re: Diesel, is there a way to get a good sample? Perhaps a hose to the bottom of the tank that would be sealed so the fuel could be sampled top to bottom.
First, the listing is incorrect on the engines, those are Cummins VT370s, 370hp.
They are very good engines but getting parts is becoming more difficult. Need to use a little creativity in locating parts sometimes. Same for the transmissions as they are Capitols.
As far as the fuel tanks, I would not attempt to start anything on them before verifying what is in the bottom of the tanks. To pull a fuel sample, I would suggest using a large syringe 100CC or larger and a length of tubing with a weight on the end. Drop it into the tank and see what is on the bottom.
Since you have a bladder tank, you do have the ability to rig up a fuel polisher and transfer the polished fuel to the bladder tank. If you have clean fuel, no water, then you can start getting the engines working. Biggest issue is that you do not want to run water through the injectors.
I would also make sure that the engines are not seized. Try to bar them over by hand. Should rotate a full 720deg without issue. If you can't go twice around, something is stuck in the valve train/ injector linkage. Same thing on the generator.
How bad is the marine growth on the hull? Likely you will need to get the thru-hulls opened up. You will also likely need to replace the impellers on all of the sea water pumps and clean the sea strainers.
I would suggest to crawl down in the bilge and inspect the thr-hull backing blocks. They are probably getting soft from rot due to the age of the boat. Not that you can do anything about them without a haul out, but you will know of impending issues and maybe some temporary remediation to keep the hull afloat.
Also make sure that the bilge pumps are fully operational. That means that the float switches work and that the pumps can actually pump and discharge water overboard. You will also going to need to check the exhaust system hoses, especially at the stern where they connect to the fiberglass exhaust pipe. These tend to deteriorate and a failure will sink your boat before you even know what is happening.
Good Afternoon Dominic and Ron:
The horsepower quoted on the broker's spec sheet is correct. Starting with the 1966 and ending with the 1969 model years, the 47' Commander was offered as an alternative to the Detroit Diesel 8V53N, the Cummins V8 300-M engines rated at 280 shaft horsepower @3000 RPM, with a brake horsepower rating of 300 HP at the same RPM. The VT8 370-M, rated at 370 Brake Horsepower, 350 Shaft Horsepower, was introduced on the 47 in 1970 year of which I strongly believe that Dick Morland's boat was the first one to have them installed. The VT8 became standard on the 47 for the 1972 model year and stayed as such for the rest of the production run until 1977. Speed difference was at cruise, 15kts @2600 RPM for the V8 powered versions and 17kts for the VT8 equipped boats. Both blocks were identical with a displacement of 785 cubic inches with the exception being that the VT8 had a single dry turbocharger, and had Capitol marine gears while the V8 had Twin Disc MG 506 marine gears.
Interestingly, the Detroit Diesel powered 47 vs the Cummins V8 powered 47 was that they were pretty similar at cruise at 2600 RPM with the Cummins powered one slightly faster at WOT. Reason was that the Cummins engines spun 200 RPMS faster at WOT over the Detroits (2800 vs 3000). Most probably the Cummins engine version was probably more fuel efficient and quieter at all speeds being that they were 4 cycle engines vs the 2 cycle Detroits. Both versions used the very same Twin Disc gears at 1.97:1 reduction, running on 1.5" shafts, swinging 23" x 21" x 4 wheels. As a comparison, the later VT8 versions were running with Capitol Marine Gears at 2:47:1 reduction, running 1.75" SS shafts, swinging 27"x28"x4 wheels while having a sharper shaft down angle. Hope this helps in clarifying the engine issue.
Minor point of clarification, the decks are not plywood cored, the entire boat is solid fiberglass. The only wood anywhere is trim at the toe tail and railings, and in that model year, also in the hard top over the aft deck. They quickly had problems with it and switched to a solid fiberglass hard top in 1970. You won't have issues with rotten coring on this boat other than perhaps in the hard top. Jim Rivas above has proven to be an invaluable source of information in maintaining my boat, definitely make friends with him.
the all fiberglass hardtop was introduced for the 1969 model year. The wood extended hardtop was only used for the 1968 model year.