Messing about in boats since 1975. Online Since 1997.
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120' Cargo Yacht'
Side View | Aft View | Forward ViewCopyright 2016 Michael Kasten
General Concept
Based on a request for a cargo carrying motor yacht of 120 feet on deck (36.5 meters) I developed the prototype shown here.
The single chine shape has many advantages... primarily that of being quite simple to build in metal, therefore requiring considerably less labor.
Particulars of the 120' Cargo Yacht are:
- Length on Deck - 120'
- Beam on Deck - 32'
- WL Length - 102.7'
- Draft - just under 10' at the rudder heel
- Displacement at DWL - 277 Long Tons
The 120’ Cargo Yacht has a carrying capacity of approximately 44 long tons. Maximum load amounts to around 16% of the light ship displacement. The 120’ Cargo Yacht has an average capacity of 4.9 long tons per inch of immersion. Thus the cargo capacity of 44 tons assumes 9 inches of immersion at maximum loading. When light, the Displacement to Length ratio is 256. When loaded the D/L is 275, therefore still a fairly light displacement vessel even when loaded.
Although a relatively light vessel, the calculated Relative Motion Comfort Index is around 94 in the half load condition. That is with the expectation of scoring in the mid-thirties or greater... In other words, a very sea-kindly shape.
I have assumed there will be twin engines for the sake of redundancy, therefore twin skegs and twin rudders. The speed potential of the hull is just under 15 knots. To achieve top speed, twin diesels of approximately 750 hp each would be required. To travel at that speed is quite wasteful of fuel, and for economical passage making, the most efficient speed under power will be kept below around 11.5 knots. Assuming 10,000 US Gallons of fuel, with a 15% reserve for generator use, per the Beebe algorithm the range should be as follows:
- At 14 knots - 1,300 NM
- At 13 knots - 1,800 NM
- At 12 knots - 2,500 NM
- At 11 knots - 3,500 NM
- At 10 knots - 4,500 NM
It is very apparent that one might well choose the lower end of those speeds. 10 knots is after all fairly brisk, and would only require the power of one engine. If arranged with diesel electric propulsion, then one generator could power both motors, with plenty of power in reserve for house loads. When full speed is required, the second generator is brought online. For time in harbor, a night-time pony gen would be ideal.
120' Cargo Skipjack - Click for Larger ImageLayout Options
At 120’ on deck length, the vessel is able to have a cargo hatch of 27’ length by around 16’ width. The hold that I have modeled is 45’ in length, 13 feet in height and roughly 28’ width. The hold will easily take four 20’ extra height containers.
Since the cargo hold must be amidships for the best balance under load, there is a deck house aft having 7.5 feet of interior headroom. In the deck house the bridge is right forward, with room for a large galley / saloon / lounge / dining room aft. Below the bridge and right aft of the cargo hold is the engine room, with bulk fuel tanks on each side. Additional tanks are below the cargo hold sole, and water / waste tanks are below the sole forward.
Aft of the engine room, below the deck house, the space is perfect for use as a large owner's suite, complete with walk-in closet and large head / shower. Forward of the cargo hold, there is room for two crew cabins with a crew galley, mess, and ship’s laundry. Below the crew cabins is a large shop and bosun's locker.
As an alternate concept for the aft accommodations, they could be used for a luxury guest suite, and the owner and mate would have the forward accommodations. In this way, the guests would essentially pay the fuel bill, while the cargo earns the vessel's keep. Alternately, certainly the cargo hold could be transformed into four or more ultra deluxe suites for charters if that were to be the preferred use.
Summary
Fast cruising, extreme seaworthiness, simplicity of construction, ruggedness, and a reasonable cost to build and maintain... these have been the primary goals of the design. I think those goals have been very well met.
For more information, please inquire.
120' Cargo yacht - Click for Larger Image
Please see the AVAILABLE BOAT PLANS web page.
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