Sadler 29 electric repower: motor, battery and cable sizing

The Sadler 29 is a 8.7 m monohull with a 6.96 m waterline and 3,719 kg displacement. From those figures, the configurator's sizing model puts an electric conversion at 6 kW and 19 kWh on a 48 V system.

Boat data: sailboatdata.com — Sadler 29, checked 23 October 2026

Motor power

6 kW

4.1 kW needed at 5 kn

Battery pack

19 kWh

2 h at full rating, with reserve

DC design current

208 A @ 48 V

cabling burden: moderate

Range on that pack

10 nm

at 5 kn

Open the Sadler 29 in the configurator Compare motors for 6 kW

The boat

Length: 8.66 m
Waterline length: 6.96 m
Beam: 2.9 m
Displacement: 3,719 kg
Hull: Fin keel, transom-hung rudder
Designer: David Sadler
Builder: Sadler Yachts (UK)
Built: 1981–1988
Number built: 400
Original engine: Bukh (model and power not listed)

Power needed by speed

Speed	Shaft power
3 kn	1.1 kW
4 kn	2.2 kW
5 kncruise target	4.1 kW
6 kn	7.4 kW
6.4 knhull speed	9.2 kW

The configurator's power-per-tonne heuristic, not a tank test — real boats vary by about ±25% with hull form, fouling, sea state and propeller. Near hull speed the power climbs steeply.

48 V or 96 V

48 V systemconfigurator's choice

208 A

design DC current · cabling burden moderate · 70 mm² for a short run

96 V system

116 A

design DC current · cabling burden easy · 35 mm² for a short run

Motor lines that cover 6 kW at 48 V

Oceanvolt

SD saildrives (SD6 – SD15)

Saildrive · 6–12 kW continuous · 48 V

Oceanvolt

AXC shaft drives (AXC12 – AXC36)

Shaft drive · 12–36 kW continuous · 48 V modules

Torqeedo

Cruise 12.0 FP (fixed pod)

Pod drive · 12 kW · 48 V

From our motor comparison, matched by power and system voltage only — check drive type and fit with the maker.

What these numbers assume

The published displacement. Your boat loaded for cruising is heavier — use your own figure in the configurator.
Cruise target of 5 kn, which is 75% of the 6.4 kn hull speed.
A shaft drive (assumed — the source doesn't say; a saildrive adds about 4%).
A pack sized for 2 hours at the motor's full rating, 15% reserve and 80% usable depth of discharge.

Sadler 29

Common questions

How many kW does a Sadler 29 need for electric propulsion?+

About 4.1 kW to hold 5 knots — 75% of its 6.4-knot hull speed — so the configurator suggests a 6 kW motor. Power rises steeply above that: about 9.2 kW at hull speed. These are estimates from the boat's published waterline length and displacement; real boats vary by roughly ±25%.

What size battery does a Sadler 29 need?+

The configurator sizes about 19 kWh of LiFePO4 for 2 hours at the motor's full 6 kW rating, with a 15% reserve and 80% usable depth of discharge — about 10 nautical miles at 5 knots. Cruising below full power stretches that.

Should a Sadler 29 use 48 V or 96 V?+

At 6 kW the design DC current is about 208 A at 48 V (cabling burden: moderate) and about 116 A at 96 V (easy). The configurator picks 48 V for this boat: it stays on 48 V unless the 48 V current reaches its "very heavy" level.