Ideas Factory/ the foundry

29 on the go · 3 materials
nothing here is finished

Notte Blu running at speed across a calm sea at sunset, three-quarter side view, with a headland and hills behind. A long, low hull in gloss deep navy-teal with a thin sand-gold line along the sheer and a sculpted crease on the hull side. A thin dark window slot sits low on the forward hull side. The flush foredeck carries a sand leather sunpad with two small flush skylights, two separate smoked-glass deflectors stand ahead of the low cockpit, and sand leather seating wraps the stern, with vents on the aft deck and spray trailing from the hull. Close to the brief. Off brief: the bow is raked and rounded rather than near-vertical, and the skylights sit in the sunpad rather than forward of it.

← the floorNotte Blu/parts·if / 066

Engines and drivetrain

Twin Volvo Penta D6 diesels at 440 hp through V-drives to shafts and props, for an estimated 44 to 48 knots.

The card

parts 04 of 07

Engines and drivetrain

parts 04 of 07idea_066

The notes

rendered

Recommendation: twin Volvo Penta D6 diesels at 440 hp each (880 hp total), driving through V-drive gearboxes to conventional shafts and props. The sculpted tail rules out sterndrives and outboards, since both need a flat transom. V-drives put the engines right aft under the cockpit, keeping the cabin clear.

weight estimate

Approximate, ready to go to sea.

Item kg
Hull, deck and framing (ply, epoxy, glass) 2,000
Twin engines and gearboxes 1,560
Shafts, props, rudders, steering 200
Fuel, 600 L diesel 500
Fresh water, 150 L, plus tanks 250
Interior fit-out 500
Electrics and batteries 250
Deck gear and misc 350
Crew, 6 people 480
Total about 6,100

power needed for 40+ knots

Using Crouch's planing formula with a sport-boat constant of 180 to 190, this hull needs roughly 600 to 750 hp total for 40 knots. Twin 440s give a margin, with an estimated top speed of 44 to 48 knots. Treat this as a concept estimate; a naval architect must confirm it.

V (knots) = C ÷ √(weight in lb ÷ hp)

diesel options

Engine Power Weight each Notes
Volvo Penta D6 (recommended) 440 hp (480 available) about 625 to 720 kg by version 5.5 L in-line 6; strongest UK dealer support
Yanmar 8LV370 370 hp 435 kg without gearbox V8, much lighter; mainly sold for sterndrives, so confirm a shaft or V-drive package
Cummins QSB6.7 up to 550 hp about 658 kg 6.7 L; most power, similar weight to the Volvo

fuel and range

Approximate. Diesels burn roughly 0.2 L per hp per hour at full load. At a 35 knot cruise the pair would use around 140 L/h, giving about 4 hours or 150 nautical miles from 600 L, before reserve.

layout

  • Engines side by side under the cockpit floor, aft of the rear bench
  • V-drives turn the drive back under the engines; shafts exit the hull bottom at a shallow angle
  • Twin props with spade rudders behind them, tucked under the tail
  • Fuel tanks amidships, low, either side of the keel, to keep the centre of gravity forward
  • Engine room vented through the aft-deck vents, with a fire suppression system and a watertight bulkhead to the cabin

The Volvo Penta D6-440 data sheet lists 625 kg dry for the bobtail engine (that sheet is for the waterjet version).

The drawings

1 sheet
Side cutaway, bow on the left. The raised V-berth with drawers under, the hanging locker, the galley with the wet room opposite in the dashed 6 ft 3 in zone, and the steps down from the hatch to the sunken floor. Two watertight bulkheads close off the fuel tanks amidships and the engine room aft, where the twin diesels sit under the cockpit with V-drives turning the shafts back to the props and rudders under the tail. Engine vents on the aft deck and the platform at the stern.
01 · Side cutaway