The dictionary defines “propulsion” as the act of moving or driving something forward. The word shares its root with the verb to “propel,” and the noun “propeller.” But, not every drive system that moves your yacht forward involves propellers at all!
Here is a list of the most common types of drives you may run across on today’s modern motor yachts, and the relative advantages, and disadvantages of each option.
Straight Shaft Inboard
A Straight Shaft inboard is the most common, or “traditional” drive found on today’s motor boats. On a straight shaft inboard, the engine is mounted “inside” of the boat facing the back of the boat. The engine connects to the transmission and a driveshaft that goes “straight out” of the bottom of the boat, ending in a propeller. In this type of drive, the rudder is just rear of the prop, which changes the direction of the thrust provided by the propeller, while steering the boat.
- It is relatively easy to set up and maintain, and when well maintained is very reliable.
- Its placement toward the center of the boat makes for better weight distribution, which results in a smoother ride, and greater fuel efficiency
- The direct shaft drive to the engines allows for very little power loss between the engine and the screw.
- In some configurations, on some motor yachts, a straight shaft inboard my mean compromising cabin space.
The “V-drive” inboard was designed to negate that “con” above, of the straight shaft inboard. From an engineering point of view, the V-drive is very similar to the straight drive. However, in a V-drive, the engine is placed more toward the back of the yacht, with the engine facing forward, to maximize interior space.
- You gain the aforementioned cabin space.
- By placing the motor further back you give up the smoother ride and may cause more bow rise.
- You lose the efficiency of the direct drive, and lose some power reversing the direction of the shaft to the prop.
Jet drives have become increasingly popular on smaller boats, roundabouts and tenders, but they have also been finding their way onto larger yachts as well. A jet drive does not use a propeller at all. Instead it uses an “impeller” that is inside of the boat. The impeller provides thrust out of a steerable jet nozzle similar to the engines on a personal water craft, but on a much larger scale.
- A shallower draft, since there is no external propeller.
- A smoother ride. Jet drives tend to be smoother, with much less vibrations than more traditional drives.
- A faster ride. Since the jet “thrusters” are on the back of the boat, and not the bottom, you lose the “drag” normally created by traditional running gear, which results in more speed.
- Even more interior space. Since the engines for a jet drive are placed in further towards the back of the boat, you gain even more interior space, than you do with a V-drive.
- High Maintenance – Jet drives are a lot more complicated than more traditional drives, and require more maintenance.
- Less fuel efficient than more common drives
- Less maneuverability – There is no rudder on a jet drive boat. The boat is steered by changing the direction of the jet nozzles on the back of the boat, so jet drive boats can turn sluggishly at low speeds, when there is minimal thrust.
In a way, a surface drive yacht combines the advantages of a jet drive with a more traditional drive. Like a V-drive or straight shaft, a surface drive uses a shaft attached to an external propeller. But, in this case the propeller is on a pivoting system at the back of the boat, like a jet drive, instead of under the boat as in a traditional drive. They are called surface drives because the top half of the prop is actually out of the water when the boat is underway!
- Pros and Cons – The surface drive has almost all of the advantages of a jet drive, plus they are fuel efficient, and high-performing. However, while they are the epitome of efficiency and performance, they do not achieve that status cheaply. Surface drives are expensive to install and maintain.
Pod drives are the latest and most expensive type of propulsion units available for luxury yachts. They first came on the market about 2006. Currently there are not that many manufacturers of pod drives. They are available in different configurations from each maker, but generally speaking, pod drives are available for engines around 300hp on up to about 1100hp, which means they can be found on boats anywhere from 30ft to over 100ft.
Pods are complex marvels of engineering that provide a great degree of handling and performance, with counter rotating propellers that direct the thrust and large gear housings that act as rudders, all married to a joystick system that allows the Captain to operate each pod independently. Maneuvers such as docking a large vessel, are made much easier with pod drives.
- Incredibly efficient.
- Incredibly maneuverable.
- Position Holding – Tied to a GPS a pod drive can hold your boat in one position precisely and perfectly, regardless of the ocean conditions.
- Very little noise and very little vibration.
- Very expensive to install, maintain, and operate. Pods not only have a lot of moving parts, but they also require powerful computers, which can increase the cost of purchasing and/or operating a pod drive yacht by as much as 15%
- Less qualified techs – For now, as there are fewer makers of pods, and they are still on relatively few boats, there are a limited number of shipyards, and service technicians qualified to work on them.
- Size limitations – Since current pod drives max out at 1100hp that limits the size of the boat they can drive.
Bottom Line on Drive Systems
There are different drive systems available. Which is best for you depends on how you want to use your yacht, your budget, and the needs of your boat.
Operating a motor yacht can be costly. You can reduce your expenses, and avoid costly repairs by keeping her well maintained. On Demand yachting from FYM can help. If you would like to learn more, or if you have any questions or comments about this blog post, do not hesitate to contact our Yacht Management specialists, or call us at (954) 900-9968.