WesWorld

I was designing a little landing craft for riverine police service, and thought, "Hey - what would a tender to such a thing look like?"

So I simmed one. Not that I plan on building any at this time, but I thought I'd share.

The tiny well-deck could be for amphib stuff, but I was actually thinking more in terms of repairing patrol boats far from conventional bases.

Riverboat tender laid down 1944

Displacement:
578 t light; 595 t standard; 692 t normal; 769 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
(225.87 ft / 223.10 ft) x 39.37 ft x (3.94 / 4.32 ft)
(68.85 m / 68.00 m) x 12.00 m x (1.20 / 1.32 m)

Armament:
4 - 0.59" / 15.0 mm 45.0 cal guns - 0.10lbs / 0.05kg shells, 15,000 per gun
Machine guns in deck mounts, 1944 Model
4 x Single mounts on sides, evenly spread
Weight of broadside 0 lbs / 0 kg

Armour:
- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 0.39" / 10 mm - -

Machinery:
Diesel Internal combustion generators,
Electric motors, 2 shafts, 201 shp / 150 Kw = 8.30 kts
Range 2,000 nm at 8.00 kts (Simmed as: Range 14,000nm at 8.00 kts)
Bunker at max displacement = 25 t (Simmed as: Bunker at max displacement = 174 tons)

Complement:
66 - 87

Cost:
£0.141 million / $0.566 million

Distribution of weights at normal displacement:
Armament: 0 tons, 0.0 %
- Guns: 0 tons, 0.0 %
Armour: 2 tons, 0.4 %
- Armament: 2 tons, 0.4 %
Machinery: 5 tons, 0.7 %
Hull, fittings & equipment: 348 tons, 50.3 %
Fuel, ammunition & stores: 114 tons, 16.5 %
Miscellaneous weights: 222 tons, 32.1 %
- Hull above water: 222 tons
-132 t: 20 x 6 x 1.1 m well deck aft (simmed as bunkerage)
-17 t: Gasoline, water, and other wet stores (simmed as bunkerage)
-100 t: Accommodation for 50 at 2 t per.
-25 t: Operations and work space
-25 t: Medical facilities
-10 t: Brig
-25 t: Workshop
-37 t: Weight reserve/cargo

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
4,669 lbs / 2,118 Kg = 45,335.5 x 0.6 " / 15 mm shells or 2.3 torpedoes
Stability (Unstable if below 1.00): 1.27
Metacentric height 1.9 ft / 0.6 m
Roll period: 12.0 seconds
Steadiness - As gun platform (Average = 50 %): 100 %
- Recoil effect (Restricted arc if above 1.00): 0.00
Seaboat quality (Average = 1.00): 1.36

Hull form characteristics:
Hull has low quarterdeck ,
a normal bow and a cruiser stern
Block coefficient (normal/deep): 0.700 / 0.709
Length to Beam Ratio: 5.67 : 1
'Natural speed' for length: 14.94 kts
Power going to wave formation at top speed: 18 %
Trim (Max stability = 0, Max steadiness = 100): 75
Bow angle (Positive = bow angles forward): 10.00 degrees
Stern overhang: 0.00 ft / 0.00 m
Freeboard (% = length of deck as a percentage of waterline length):
Fore end, Aft end
- Forecastle: 20.00 %, 15.75 ft / 4.80 m, 12.80 ft / 3.90 m
- Forward deck: 30.00 %, 12.80 ft / 3.90 m, 12.80 ft / 3.90 m
- Aft deck: 20.00 %, 12.80 ft / 3.90 m, 12.80 ft / 3.90 m
- Quarter deck: 30.00 %, 4.92 ft / 1.50 m, 4.92 ft / 1.50 m
- Average freeboard: 10.67 ft / 3.25 m
Ship tends to be wet forward

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 39.3 %
- Above water (accommodation/working, high = better): 260.0 %
Waterplane Area: 7,040 Square feet or 654 Square metres
Displacement factor (Displacement / loading): 294 %
Structure weight / hull surface area: 40 lbs/sq ft or 196 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0.93
- Longitudinal: 1.83
- Overall: 1.00
Excellent machinery, storage, compartmentation space
Excellent accommodation and workspace room
Ship has slow, easy roll, a good, steady gun platform
Good seaboat, rides out heavy weather easily

Interesting concept, I'm sure I've heard of something like this before, either on WW or OTL.
Got to wonder whether beaching a small craft is easier for repairs or a simple ramp on the bank?

The easier, and historical, alternative is a marine railway or patent slip.

A small craft would be floated into a suitable cradle and then winched up onto a slip to have hull work done on her and then winched back down and refloated.

If you've ever seen the movie "They Were Expendable" they show PT boats being worked on and then refloated at a rather primitive marine railway.

During WW2 the USN Seabees improvised small floating dry docks out of steel pontoons to do accomplish the same end - get the hull out of the water so that repairs and cleaning could take place.

C'mon, the tender is so much cooler...

I dunno, I've seen some cool marine railway's on the Trent-severn waterways in Northern Ontario. For riverboats its certainly a much cheaper alternative to a large single purpose tender.