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A 50' Sailing Landing Craft (LCU-J)..!
Sailing Perspective | Far Aft View | Far Forward View
Side View Aft | Side View ForwardCopyright 2016 Michael Kasten
General Concept
This concept design has been based on a request for a Junk Rigged Landing Craft of around 50 feet LOA. A seemingly strange request, but a concept that makes ultimate sense, especially for service in a location with relatively undeveloped infrastructure, and a need to move cargo on the water... The unusual side of this request is that it had to be capable under sail, with a preference for free standing masts, and a Chinese Junk rig...
Okay then...! with the middle used up for cargo, and the requirement for free access to drive aboard via the forward ramp, it was obviously out of the question to place the masts on center, as is most often done. We chose instead to make use of an increasingly common "biplane" rig, as shown in the above image. With the middle of the vessel being essentially a huge cockpit, that left only the region below the well-deck, and the buoyant bulwarks as the primary WT envelope.
We elected in favor of buoyant enclosed bulwarks because they contribute greatly to stability under sail, especially in rough conditions. The well deck inner bulwark faces are vertical, and straight fore and aft. This allows the inner bulwark faces to function as structural girders, and to provide ample utility spaces outboard.
Well-documented studies have shown that even if a green-sea floods the well deck, if there is sufficient buoyancy in the bulwarks, that will be a survivable event. A further rationale for having substantial enclosed bulwarks is that they allow sufficient lateral strength for the cantilevered free-standing un-stayed masts.
I was at first puzzled as to how to model such a craft, until I realized that I already HAD created a suitable model AND had already tested it... The Pram..! The Pram has the perfect hull form, with a transom at each end, a flat bottom, an excellent shape for sailing, and had already been modeled with buoyant WT bulwarks. Extra good..! It just had to become much larger!
The model for the 50' Junk Rigged Landing Craft was then established, first at 45 feet, then expanded to include a more comfortable pilot house / cabin at the aft end. We have taken to calling it an "LCU-J" after the military naming conventions, i.e. "Landing Craft, Utility - Junk Rigged" which I'm quite certain the military, nor anyone else for that matter, has ever considered...!
50' LCU-J - Click for Larger ImageSeaworthiness
Landing craft have a very tough job to do, and must often so so in compromised conditions within the surf zone whilst coming and going from the beach. In order to design these craft so that they are suited to the near shore environment, and to safely transport cargo through unprotected open waters, considerable very well funded research has been done in order to establish their best proportions.
The best study done to date on this subject is a 436 page research paper by Peter Hayes of the University of New South Wales from 2014. It is a summary of actual LCM / LCU in-use stability findings, a review the existing stability standards for Landing Craft, and documents many exhaustive tank tests aimed at deriving a more robust stability standard for Landing Craft.
As a result of Mr. Hayes' research, there is no question whatsoever that buoyant bulwarks are a requirement for survivability in compromised conditions. Landing Craft with simple plate bulwarks often capsized at roll angles of around 35 degrees or less, and did not survive green sea boarding events. Landing craft with buoyant bulwarks however were often stable well beyond 60 degree roll angles.
But that’s the case when assessing them on a ‘static’ basis. When looked at dynamically, the plate bulwark LC’s are extremely vulnerable in a green sea boarding situation, where the buoyant bulwark LC’s have a vastly greater survivability, i.e. much less likelihood of capsize because they are able to shed water and remain in a viable trim condition, and depending on the configuration of the bulwarks (height / width / buoyancy) a flooded-well green sea boarding event is easily survivable
Click for Larger ImageHull Form
Given that this kind of craft has considerably more beam than would a typical yacht, the initial righting moment is outstanding, providing for extremely stiff sailing without much depth of keel. A pair of long straight skegs provide very good tracking, and a pair of rudders provide excellent control. With this very shoal keel configuration, a pair of centerboards will be used in order to provide the necessary 'bite' for sailing to windward.
The shape we have here is derived directly from my Pram design. Interestingly it is very similar to the sailing scows of years past. Sailing scows have a reputation for being fast under sail, provided they have a graceful hull form and adequate sail area. Having been graced with a shapely and water-friendly hull form, this vessel will perform as well or better. The flat bottom and faceted hull shape will be quite simple to build, therefore in terms of speed per dollar the performance should be very rewarding.
Particulars are:
- Length Overall - 50'
- Maximum Beam - 20.5'
- WL Length - 35'
- Draft Light - 12 inches
- Draft Loaded - 18 inches
- Displacement at DWL - 11.3 Long Tons
- Loaded Displacement - 20 Long Tons
Sailing Rig
As a cargo vessel, the biplane junk rig keeps the masts clear of the hold nicely. Aesthetically this seems to provide just the right dose of tradition, while also providing excellent performance in an easily handled rig. In order to make good use of modern materials, the spars will be fabricated using welded aluminum pipe. The battens will be wood, and will be located on both sides of each sail, sandwiching the sail in between. The junk sail materials will be Dacron, and a cambered sail cut will be used. Target sail area is between 1,300 and 1,500 square feet.
50' LCU-J - Click for Larger Image
The Layout
Station spacing is 28 inches. Frame spacing would probably be half that. Using the 28 inch module, three stations make a perfect bunk length, two make a decent galley and head, etc. With that in mind, the layout seemed to naturally fit...
The cabin trunk is just under 11.66 feet long x 12’ wide in the middle Total length inside the cabin is around 14 feet x a width of nearly 20 feet at the forward end. The interior sole is at the same level as the exterior well deck sole. Bulkheads divide the spaces as follows, starting aft…
THE CABIN…
- A partial bulkhead at the forward end of the cabin forms the aft end of the well deck
- Extending forward two stations forward of that bulkhead below each of the side decks outboard of the well deck are a pair of large ‘quarter’ berths.
- The berths extend into the cabin by one station length, so the berths take up a small piece of each forward corner in the cabin.
- In between the berths, on center facing forward, is the helm.
- On center aft, a companionway ladder enters the cabin from the aft deck.
- Outboard to starb'd in the aft corner is a head / shower.
- Opposite that on the port side, a large galley.
- To starb'd, forward the head is a chart / nav / radio table / desk.
- To port, forward of the galley there is a dinette.
- Water tanks are arranged in the center below the aft house sole, or could possibly be located outboard, making room for stores below the CL sole.
This layout is not at all too tight, nor is it overly spacious. Each of the berths are large enough to function as a double, so two couples can be accommodated.
FORWARD… By studying the image above which shows the stations and locations of the bulkheads, the following layout can be understood best...
- Forward of the two 'quarter' berths is a space on each side below the side decks and outboard of the well deck that is four stations in length.
- In that location twin CB trunks will be arranged, and will make use of the well deck inner bulwarks as the inboard faces of the CB trunks.
- In that space are the mast steps and partners, the CB trunks, and a large space outboard of the trunks. That will ideally be used for a large fuel tank, one per side. Plus being in the middle lengthwise, there will be no adverse trim effects whether full or empty.
- Forward of that is another four station space on each side which is the ideal location for a pair of engine rooms…! Easy access will be provided by a hatch from above when the well deck is occupied, and there will be outstanding access through WT doors facing into the well deck for maintenance.
- Twin (long) shafts will drive a pair of shoal draft propellers far aft, to be housed within nozzles both for efficiency and for protection of the props in shallow water.
- Forward of the engine rooms on each side is a forepeak that will provided an ample storage / bosun’s locker space, and will also be used for the anchor gear.
- Anchoring equipment will be a vertical rope capstan / chain gypsy on each side, with the rode coming aboard through hawse pipes, thus allowing the anchors to be nested against the lower topsides right forward.
- The best arrangement for the rudders is to simply use a hinge at the forward end, with a steering arrangement like the sailing scows used, i.e. a tether to the aft edge of the rudder, leading to steering ropes.
This is not a “luxury” layout, however it is very adequate for two couples to work the vessel. And certainly the well deck can take a travel trailer aboard or any other modular camping / housing unit for that matter.
Cargo...!
At 50’ on deck length, the well deck is 31.2 feet in length by 9.5 feet in width. This is able to handle a large dual-wheel Ford F-450 Stretch with relative ease. The well deck will also easily take a standard 20 or 30 foot container.
If heavy cargo is roughly centered at the mast location fore and aft, there is perfect trim. Lighter cargo can go forward of that. If a large Dually Ford F-450 were loaded with its front end pointing aft, the trim would also turn out nicely. If the truck itself were loaded, then it would produce the most neutral trim to back it in.
Summary
This is just how the working sailors of the past would have adapted such a vessel to its new purpose, i.e. that of a safe, easily built craft. Fast cruising, windward ability, seaworthiness, simplicity of construction, ruggedness, and a reasonable cost to build and maintain... these have been the primary goals of the design. At least in my view, those goals have been met nicely.
For more information, please inquire.
50' Sailing Cargo LCU - Click for Larger ImageSailing Perspective | Far Aft View | Far Forward View
Side View Aft | Side View Forward
Please see the AVAILABLE BOAT PLANS web page.
Home | Intro | Our Design Process | Stock Design Info | Motor Yacht Designs | Sailing Yacht Designs | Prototype Designs
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