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Building Kurbatov's 'Paltus'

Translated from the Russian ....

The attention of amateur boatbuilders is drawn to the proposed project, which has been developed from the sales materials of Honnor Marine, builder of the Drascombe series of boats. By careful study of this project, a real possibility exists for the home builder, using readily available materials.

The hull is sheathed using strips of 7mm thick waterproof plywood (1), using the 'edge-upon-edge' or clinker method. Plywood is also used in the construction of frames, onboard seats and deck. During construction, the strakes are glued together and rivetted with 3mm copper nails/rivets and copper washers at 60-80mm intervals. The double-thickness clinker overlap (which should be within the limits of 15-20 mm) serve as longitudinal stiffening stringers which makes possible the construction of a strong and rigid hull with the additional use of only five frames. Even further strength and rigidity are provided by the vertical walls and horizontal surfaces of seating and decks.

1. The '7mm waterproof plywood' to which Kurbatov refers is a special grade available in Russia. If using WBP or marine plywood, then the next size up should be used.

Another, more contemporary method of building the hull with the same "angular" contours is proposed: the strakes may be joined by clips made from copper wire, with epoxy resin and glass tape being applied to both sides of the join. The copper clips only provide a convenient method of assembly, the ultimate strength of the join being dependant upon the epoxy and glass fibre tape. One Leningrad boatbuilder has even employed synthetic thread in place of the copper wire in the construction of an 8-metre plywood yacht.

Both methods of construction are approximately equivalent in terms of labour, expense and reliability. However, many supporters of clinker construction consider that their method deflects spray and helps to moderate rolling in heavy sea. One criticism made of the 'stitch and tape' method, however, is that if the gluing of the fibreglass tape is inadequate, moisture penetration with rapid rotting of the wood may follow. Thus it is necessary to ensure that the seams are covered adequately on both sides with glass tape (using several layers - see later) and epoxy glue.

Assembly of the hull may be more conveniently performed on the construction mold in the normal position, i.e., with the keel downwards. The strakes are then applied to the previously assembled and carefully positioned transverse frames, keel, stem and transom. When constructing the mould, the dimensions of frames 2, 4, 6 and 8 (as taken from the table of offsets) must be adjusted to take into account the thickness of the external plywood skin, as the measurements given refer to the external hull surface. Within the table, measurements of the chines are considered to be that of the upper edge of the strake.

 Table of Offsets

Frame Number

 0 1 3 3 4 5 6 7 8 9 10 Tr.

Height from the Base-Line, mm

Keel 260 61 10 0 7 25 51 88 128 173 221 -
Strake 1 355 300 250 215 186 176 179 190 210 235 263 265
Strake 2 520 456 405 360 325 310 310 324 348 378 405 415
Strake 3 740 680 624 580 550 530 522 534 560 593 628 667
Sheer 965 910 864 825 792 778 762 760 760 770 780 -

Half-widths from centre-line, mm

Sheer 286 510 689 820 900 945 955 932 880 795 685 545
Strake 3 230 466 655 800 895 945 955 932 880 765 685 545
Strake 2 140 363 551 699 795 848 860 838 784 705 608 555
Strake 1 52 225 380 510 605 660 671 649 595 514 415 -

The stem and keel must be faired before attaching them to the building mould: the stem-piece should be bevelled to accommodate the bunching together of the strakes where they will join the stem. The required angle can be determined either by a lath or a length of the plywood used for the strakes.

Before cutting a strake from a plywood sheet, a full-length template should be made from low-quality plywood or hardboard. After attaching the template to the curved mould by panel-pins, the lines of the strake are extended outwards from the mould and marks made on the inside of the template. After removing the template, these marks may be joined by using a flexible lath to indicate the position of the next strake. (With the exception of the sheer-strake, an allowance of 15-20mm should be added for overlap. Then place this template onto the high-quality plywood to be used for the strake, and transfer the line by pricking-through with the point of an awl, before finally cutting-out the strake.

The first strake to be applied is the lower bottom, and is attached to the keel by 4mm x 30mm wood screws, spaced at 60 mm intervals. At the stern, the next strake will present at an abrupt angle which makes the overlap unsuitable for riveting. Here it is better to simply butt it's edge against the previous strake and secure with copper wire clips and epoxy and glassfibre tape as described above, after trimming to ensure that the strake fits snugly against the bottom strake. The adjoining edge surfaces are thoroughly cleaned, and coated with glue before rivetting.
The longitudinal clinker strakes must become flush at the stem. Thus for a distance of approximately 800 mm it is necessary to chamfer the outer edge of the strake and the lower inner edge of the next strake of the clinker join.

The strakes are temporarily attached to the mould by nails, so that when the entire hull is riveted, the moulds may be taken out and replaced by frames, with wood screws being employed to secure the skin to the frames, using the nail holes as a guide. Rather than fairing each frame so that the planking will have flat surfaces to glue and fasten to, installation of the frames may be simplified by bevelling only those frame components which make contact with the inner surface of hull (i.e. the frame battens) to provide a flat contact surface - then the plywood frame itself may be attached to those previously bevelled parts, directly into place.(2)
To further simplify this process, the hull can be pulled gently away from the mould using suitable lengths of wood. It is necessary to have previously made cut-outs in the frames for the longitudinal chines of the strakes.

2. Taking 'Frame - Station 2' as an example (see Frames diagram), cut the plywood frame with a flat (90 degree) edge. Then cut wooden battens 58 and 51, and bevel them to fit the hull curvature, before attaching them to both the hull and plywood frame with screws and glue. Then cut-out and attach batten 60. The frame is now completely installed into the hull.

The described boat uses a heavy centreboard, cut from steel plate of thickness 12 - 14 mm. It's weight is about 45 kg which, when added to the dynamic loads of landing on a sand-bar or even simply when rolling, requires a centreboard case of substantial strength. The base, knees and supporting timbers of the centreboard case should be made from oak, with the walls of the case being made from 7 - 10mm exterior plywood, the case being secured to the keel by bolts, with waterproof glue being used throughout. A second similar well, in a smaller size, is provided for a lifting rudder. Before assembly, a layer of diluted glue should be applied to the internal surfaces of both wells, as a sealing coat.

In spite of the high water resistance of exterior plywood, it's open edges require protection against the penetration of moisture. Two or three layers of fibreglass tape with a width of 25-40mm should be laid on all outer edges, with a wider overlapping layer superimposed upon these. Covering the joins using just one piece is not an option, as voids may be created along the angles, into which water will subsequently penetrate.

For rowing, the boat must be fitted with a pair of removeable transverse thwarts (with the sizes 28 x 250 x 1200 mm), which would be located above the longitudinal bank-seats and prevented from moving along the boat by simple bosses or lugs attached to boards at their leading and trailing edges. The optimum length of oars for this boat is 3300 mm. (10'10")

The unsinkability of the boat may be assured by providing hermetic sealing of compartments beneath the longitudinal bank-seats (for example between stations 4 and 6), although it would be necessary to provide hermetically-sealed inspection holes in the vertical walls of the compartments for their periodic inspection, repair and drying. Alternatively, the area beneath the bank-seats could be filled with closed-cell foam buoyancy.

Anticipating questions from readers as to what opportunities exist for the substitution of waterproof plywood by other materials, we shall answer as follows:
for the building of this boat it is possible to use a sheet glass-fiber-reinforced plastic, fiberglass laminate and even the more usual construction-grade plywood, providing that several layers of fiberglass fabric are applied on top of the skin in order to achieve the desired rigidity and durability. A thickness of GRP skin of 4-5 mm would be sufficient, especially if reinforced by ribs made from plastic foam. Even if these materials are not available, it would still be possible to build the hull from glued strip-plank laths, or even fir or pine boards, glued edge to edge.

The main-mast, mizzen and gunter spars are of continuous, round cross-section, however it is preferred that these be made from two or even four pine laths, as glued spars are more durable and there is less chance of them warping with fluctuations of humidity.

Regarding the sails and rigging of the boat: the mizzen-mast has no standing rigging - it stands in a metal mast step, and is supported by wooden partners at the top of the rudder well. The mainmast is supported by a pair of shrouds, and a forestay - which can be provided by the steel luff-wire 'bolt-rope' of the foresail if jib roller-furling is fitted. This roller-furling consists of a drum (6), attached to the tack of the jib or genoa, being freely rotating relative to it's deck fitting (10). The head of the sail is attached to the halyard by means of a swivel (2), which ensures free rotation of the foresail's luff-wire or bolt-rope without twisting the halyard. Thin synthetic rope (7) is wound on the drum, so that when it is unwound the foresail is reduced to a dense roll.
The running end of this control rope (7) is led back into the cockpit for ease of access by the helmsman.

Thus, at anchor, or at the approach to land, it is not necessary to lower the sail from it's mast. To restore the sail to it's working state, all that is required is to release the control rope, and unfurl the sail by pulling on it's sheets. Of course it is still possible to attach the foresail in the usual way, using piston-hanks or clips hooked onto the forestay.

The mizzensail-boomkin must be made detachable; for it will simplify mooring by the stern to a high quay and simplify management of the boat when sails are not being used.

Installation of the main-sheet of the "Paltus" may be the same as on the original "Drascombe Lugger", when it is possible to control the sail by means of one sheet, and during tacking it is not necessary to adjust the sheet with each turn - the sail automatically passing from side to side, although it is recommended that the sheet's cleat be positioned close to the centreline so that on both tacks the sheet length is approximately equal.

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