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Half-ton ST-28. Yacht project for self-construction

Half-ton ST-28. Yacht project for self-construction The project of a half-ton class yacht, offered to the attention of readers, was developed by the author in the student design bureau Ocean of the Leningrad Shipbuilding Institute.

Judging by the applications and letters, there is an urgent need to build along with cruising and racing vessels of other types yachts of minimal dimensions capable of participating in long sea races and at the same time not burdensome in daily operation. In our opinion, the best variant of a vessel that meets such requirements is a half-ton; even a small team of yachtsmen can carry out the construction of such a yacht with the involvement of the simplest technological equipment and available materials.

Currently, the half-ton is the smallest of the yachts allowed to participate in major domestic sea races such as the Baltic and Black Sea Cups. At the same time, it is already a fairly spacious and comfortable vessel, on which the equipment necessary for yachts of the 2nd category of navigation, for example, an inflatable life raft, can be placed without much damage to the crew's amenities and general architecture. It is also important that for a half-ton, sufficiently effective sails can be sewn from dacron, whereas for larger yachts, sails made of stronger and less deformable dacron under load are needed, which, unfortunately, is in short supply.

The half-ton yacht ST-28 was designed with the expectation of the possibility of industrial production, but without the use of any extreme solutions or innovations. We believed that the project should not grow old for quite a long time, usually spent on mastering the construction of a new yacht, so we tried to apply stable trends in the design of cruising and racing yachts, and not fashion trends.

Basic data of the half-ton ST-28
Longest length, m 8,74
KVL length, m 7,25
Maximum width, m 3,15
KVL width, m 2,34
Draft, m 1,70
Displacement, t 2,55
False frame weight, t 1,080
Measured sail area, m² 43,3
IOR racing score, m 6,6

The yacht is designed for medium and fresh winds and, as the analysis of the comparative characteristics of the best yachts of the half-ton class shows, is quite competitive. With a relatively long length of the KVL, the ST-28 has a small displacement; due to this, the L/D 1/3 and S/D indicators are obtained high. The values of L/B and Rfk/D lie in the range of average values.

Theoretical drawing of the yacht ST-28

Theoretical drawing of the yacht
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Table of ordinates of the theoretical drawing

Table of ordinates of the theoretical drawing

General location longitudinal section and plan
General location of the yacht
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1 inflatable life raft PSN-6M (lightweight version); 2 plug-in payol; 3 consumable fuel tank with a capacity of 10 liters; 4 self-draining fiberglass cockpit; 5 soundproof engine casing with a step; 6 shelves for books and manuals; 7 navigator's table; 8 navigation instruments; 9 table with folding lid; 10 under-mast pillars; 11 upper berth; 12 forelock; 13 anchor niche; 14 muffler with exhaust pipe; 15 disconnecting clutch with lowering V-belt transmission; 16 auxiliary engine; 17 sofa bed; 18 toilet bowl; 19 sails; 20 fresh water tanks with a capacity of 35 liters; 21 navigator's seat; 22 battery; 23 berth; 24 removable shield; 25 boom-sheet shoulder strap; 26 waterproof bulkhead; 27 gas cylinders; 28 lockers; 29 a sheet winch; 30 a block of staysail-sheets with a pogo; 31 a cabinet for storm clothing; 32 a shelf for dishes; 33 a gas stove; 34 a sink; 35 a rack for fixing shrouds; 36 a cabinet for shore clothing; 37 a closet door; also closes the vhok in the forepeak; 38 shoe boxes; 39 anchor niche cover; 40 payoles, BFS plywood, δ=8.

The internal layout of the yacht and its supply comply with the restrictions imposed by the Rules of Classification, Construction and Measurement of sports yachts on vessels participating in category 2 races.

The main workplace during the race the self-draining cockpit is functionally divided into two parts by a ledge on the payole and a boom-sheet overrun. The aft part of the cockpit is convenient for the helmsman to work both on tacking and on passing courses. The floor is raised here. There is a life raft under it, which, when the yacht is submerged in the water, should, having raised the payol, float up and open itself. The forward lower part of the cockpit is designed to work effectively with the sheets and braces of two sailors without compromising the view for the helmsman.

On both sides of the cockpit are the covers of the afterpipe, in which gas cylinders, buckets, mops, mooring ends, etc. are stored. Armor and emergency pyrotechnics are reinforced on the inside of the covers. The afterpeak is separated from the rest of the yacht by a watertight bulkhead.

The entrance inside the yacht is central with a sliding cap. The role of the step is played by a removable soundproof engine casing.

The project provides for the installation of an air-cooled carburetor gasoline engine UD-25 with a capacity of 8 hp at 3000 rpm. The engine of this type has a mass of 52 kg and dimensions of 530x455x565. It is possible to use a starter generator G250-G1 (from the Volga car) with a relay regulator PP350 or PP362. Unfortunately, today it is impossible to offer a more acceptable version of the power plant due to the lack of stationary boat engines in mass production.

The relative position of the engine and shaft allows you to place a V-belt transmission that lowers the rotational speed to 1000-1500 rpm on the screw, and a friction-type disconnecting clutch. Near the engine (under the cockpit) there is a consumable fuel tank with a capacity of 10 liters with the output of the float level gauge pointer on the bottom of the cockpit.

To the left of the entrance there is a rather large navigator's table and shelves for navigation aids, navigational instruments, etc. The navigator's table panel is a pencil case for maps, which has the ability to recline to the front bulkhead.

To the right of the entrance there is a galley with a two-burner gas stove, sink, shelves and cabinets for dishes and food. The main elements of the galley are assembled using standard products available for sale (polyethylene sinks, a waste bucket, etc.). In the rear of the galley, a closet for storm clothing and life jackets is made in a niche. If it is necessary to dry the clothes, the engine casing panel can be removed, warm air from the engine cooling system will flow into the compartment. In addition, the use of a gas heater of the GIIBA type is provided.

The layout of the mess is traditional. There are four beds here. The upper bunks in the lowered position form the backs of the lower sofas. Behind the sofas at the sides there are niches for personal belongings.

The forepeak stores sails in nets and coils of cables. There is also a toilet (outrigger bucket); it can be placed under the folding shelves, which will allow you to fully use the volume of the forepeak to accommodate a racing set of sails. In the cruising version, additional sleeping places can be equipped in this compartment.

Drinking water tanks are located under the sofas in the cabin. This arrangement of variable cargo near the center of gravity of the yacht allows you to receive and consume significant reserves of water without changing its landing, and also makes it possible to reduce the total moment of inertia of the masses relative to the yacht's center of gravity.

The design of the hull and the technology of its construction are designed for the manufacture of the vessel by teams of yachtsmen with a relatively modest production base. A number of yacht components are designed in several variants; any of them can be chosen by the builder based on their capabilities.

The design scheme of the half-ton yacht hull set

Constructive scheme of the yacht hull set
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Considering that wood remains the most accessible material for an amateur shipbuilder and at the same time allows you to get sufficiently high weight indicators, the article provides two design options for a wooden hull. The main elements of the set were selected in accordance with the Rules of classification, construction and measurement; in cases of deviation from these Rules, the strength of the structure was checked by appropriate calculations. Frames, tie bars, keel, staves and beams are laminated: the outer layers are made of oak or ash, the inner ones are made of pine. This design, with almost the same strength as in the version with bent oak frames made of solid wood, allows you to slightly reduce the weight of the case and the consumption of scarce materials. Builders get the opportunity to use short-sized lumber of small cross-sections and reduced grade. The consumption of fasteners made of non-ferrous metals is reduced. The drying process of wood harvested for the manufacture of a set is accelerated (thin boards dry much faster than bars).

Of course, it is also possible to use bent oak frames instead of glued ones. Glued beams can be replaced with solid pine sections of 35x55 on reinforced frames and 30x40 on the rest.

Sheathing can be performed according to one of the following options.

Yacht hull design variant 1. Pine rack-and-pinion sheathing on VIAM-B3 glue or ED20 type resins and PO-300, painted with pale red nails. The thickness of the skin in the central part of the yacht is 18 mm; to the extremities, a reduction in thickness to 15 mm is allowed.

2. The skin is typed, as in the first variant, from glued pine slats of much smaller thickness (8 mm) and then pasted crosswise (at an angle of 45-60 to DP) from side to side in two layers with strips of 3 mm plywood FBS or BP-A. Each layer is pressed to the pine lining with ordinary nails (for example, 1.5x25) on flies.

It is possible to sheathe the case with a 10 mm pine board and paste over the top with a couple of layers of BPS or BP-A plywood with a thickness of 3 mm.

When using bakelized plywood, it is better to use epoxy resins as glue; the surface of the plywood in the places of gluing should be sanded so that the surface layer of bakelite is completely removed.

Diagonal plywood pasting in two layers significantly increases the rigidity and strength of the case, its water resistance, resistance to fluctuations in humidity and temperature.

Deck decking and deckhouse can be made of 8 mm bakelized or water-resistant plywood of the BPS-1 brand.

The mast, made of pipe (aluminum-magnesium alloy), is installed on the deck. The hinged design of the spur provides the possibility of fine-tuning (centering) and filling up the mast. If necessary, two people can put the mast on the ST-28. The design of the swinging top of the mast allows, by wrapping the turnbuckle of the afterstay, to simultaneously fill the forestay, without creating bending forces on the mast.

Sail pattern
Sail pattern
Measurement characteristics according to IOR rules: I=11.58m; O=3.66m; P=10.00m; E=3.06m; R=6.6m.

The boom can be made of a light-alloy profile or of a pipe with a welded lip. (see scheme, 1200x616, 92.2 Kb)

Mast construction (see the scheme, 1200x2674, 411 Kb) and its equipment are also designed with a view to manufacturing in the conditions of a yacht club workshop; elements welded to the mast are excluded if possible. Most of the parts can be mounted on a wooden mast without modification.

The axial force from the mast is transmitted through the pillars (see diagram, 1200x1495, 219 Kb ) (AMg61 pipe with a diameter of 50-80 mm) for a welded steel structure that evenly distributes the load along the keel beam and steel floras on the sides and frames. Flora and details of the support unit are cut from a 3-millimeter sheet of carbon or low-alloy steel grades VStZsp2, VStZGsp2, 09G2, 10G2X1D or 10XSND.

A welded fin keel is provided (see diagram, 1200x1495, 219 Kb) in the form of a box made of steel sheets 6-8 mm thick, into which 860 kg of lead must be poured. Before pouring, it is recommended to either bury the box in the sand (and tamp it around), or put temporary stiffeners on potholders outside the box. On the finished fin, the welds are cleaned, the entire surface is sandblasted or cleaned with metal brushes, primed with lead meerkat on drying oil and painted with pentaphthalic paint in the desired color. Voids in the fin formed as a result of lead shrinkage must be filled with Portland cement. The fin is attached to the hull of the yacht with 14 screws 2M16x90. The wedge-shaped shape of the fin with a moderate narrowing (η=2.0) and a small relative thickness (C=7-12%) allows us to hope for a higher value of its hydrodynamic quality than, for example, the keel of the yacht Carter-30.

In parallel with the preparation for the publication of these materials, more accurate calculations of the polar diagrams of the yacht were carried out using computers. According to the results of calculations, it can be recommended to reduce the lengths of the root and end chords of the fin cross section indicated in the drawings to 1300 and 600 mm, respectively, to increase the maximum thickness (along the inner surface of the metal hull) of the profile to 100 mm along the entire height of the fin. In this case, the position of the trailing edge of the fin relative to the body should be shifted by 50 mm to the nose.

The steering wheel pen is made of PVC-2 or PS-1 foam, followed by pasting with seven to eight layers of fiberglass on polyester resin. In the drawings (see diagram here, 1973x1770, 333 KB) shows a variant of the pipe baller Ø68x8 (stainless steel X18N10T). However, the baller can also be made from a rod with a diameter of 54 mm (X18N10T), 60 mm (VStZsp), 40 mm (VTZ-1 alloy) or from a pipe of 47x5 or 60x3 of VT3-1 alloy.

Half-ton housing ST-28 made of fiberglass
The body of the half-ton ST-28 is made of fiberglass.

If the baller is replaced, the ordinates of the rudder root section profile shown in the drawing must be changed to the appropriate scale. The recommended dimensions of the baller meet the requirements of the Rules for cantilever balance rudders.

Currently, a fiberglass version of the yacht is under construction of the hull. Briefly, the following can be said about him. The body is molded from fiberglass based on fiberglass TZHS-0,56-0 on resin NPS-609-21M. The thickness of the side is 6 mm, the bottom is 10 mm, the deck is 4 mm. When fixing a transverse set on the side and deck of 400 mm, the cross-section of U-shaped cross-links is 20x40, which meets the relevant norms of the Rules for the Classification and Construction of yachts made of fiberglass by English Lloyd.

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