Types of drives and their short description
- Traditional propeller drive on shaft – simple construction and high reliability, for speeds below 30kn, and also for big and heavy vessels. The drive is tolerant of high load differences and it works well in difficult conditions. It is cheap to maintain and the cheapest to purchase.
- Stern drive – Z – type transmissions for built-in engines (Bravo 1, Brawo 2, Brawo 3, Volvo): a complex construction; high failure frequency and prone to damage due to inappropriate use and maintenance (seals, oil). This drive may not be used to operate in the shallows. It may be used for vessels with little load, below 8m, including single configuration. Z-type drive works well in vessels operating at lower speeds, up to 25 kn. High manoeuvrability in double configuration. KONRAD type drive (the most reliable on the market) is dedicated to commercial (loaded) use. As far as purchase price is concerned, the cost of transmission is comparable to SDS, more expensive than the drive integrated with outboard engines and cheaper than water jet. The drive is expensive in operation and it requires specialised knowledge to operate.
- Outboard – the most popular drive integrated with outboard engine suspended on transom; compact construction facilitates deck arrangement; simple installation. It works well for vessels up to 12m and speed up to 40kn. It may operate in the shallows, but it is sensitive to damage. It is used only with petrol engines and is sensitive to damage due to wrong use (flooding, too strong shocks). It is quite cheap to purchase due to its integration with the engine; however, its life is short, which may make it expensive to use (the cost may be higher than the purchase price) if it is frequently operated (over 100h a year).
- Surface Drive – this drive works best for vessels over 8m, speed over 30kn and double configuration. It has high manoeuvrability and may operate in the shallows (beaching) and it dirty water. The construction is simple and reliable, to be used in fast motor boats (including leisure ones) and also in patrol, racing, special purpose vessels, RIB. It may be used with diesel and petrol engines; it requires a separate gearbox for transmission reduction and operating the gears: forwards, neutral, reverse. The key issue for the right use of the drive is its appropriate configuration – suited for the specific vessel. The purchase price is comparable to stern drive, or it is lower (Konrad), and the operation cost is low.
- Water Jet drive. It is dedicated to vessels where using a traditional propeller would be dangerous – Rescue boats, dive boats. It may operate in the shallows, but without the beaching option – drawing sand into the dredge box means an expensive failure. The drive is sensitive to water pollution; its structure is complicated and prone to failures. Repair and servicing require qualified personnel. Manoeuvrability is poor at low speeds; it may be used up to the speed of 45kn. It is necessary to over dimension the power of drive units due to considerable power drops on drive (20-30%). The purchase price is comparable to SD for small propellers, and over the double cost for the bigger ones.