How do the most popular forms of inboard drives compare? Here’s a closer look at each drive system’s unique characteristics…and which may be the perfect match for your needs.
Similar to outboard powered boats, propellers have long proven a reliable, effective means to propel inboard boats through the water as well. However, the drive systems that a majority of recreational boats utilize to transfer power from the onboard engine to the propeller have proven a little more diverse. Particularly when watersports are a key component of your on-water activity – and of course, many water sport and wake surf boats eliminate the propeller entirely through the use of jet drive systems.
Sterndrives (or outdrives) have long proven popular, as they are incredibly versatile and keep a clean, obstruction-free transom. V-Drives are a twist on the traditional “ski boat” inboard, and boast a hardcore wake sports heritage without the cockpit-clogging mid-engine. The new kid on the block – Volvo Penta’s Forward Drive – attempts to combine the best attributes of both, offering the versatility inherent in the sterndrive with the wake-surf-friendly prop location touted by the V-Drive. Jet drives (or jet-powered) offer a shallower draft and pose less of a danger to wake surfers, water skiers and swimmers in the water.
So how can boaters and wake sports enthusiasts use the characteristics of these three propulsion systems to best fit their boating lifestyles? Let’s examine each drive’s physical design to see how it affects the system’s ultimate performance on the water.
Sometimes referred to as “inboard/outboards” (or I/O for short) due to the fact that they combine an inboard engine with an outer drive unit similar to an outboard motor, sterndrives connect the engine driveshaft to the sterndrive unit via a flexible U-joint at the transom. Power is then redirected via a set of gears downward through a driveshaft within the housing before once again redirected 90-degrees aft through an additional set of gears that spin the propshaft. A clutch allows the propshaft to spin in both forward or reverse direction, or disengage entirely when in neutral.
Volvo Penta’s Forward Drive is essentially just a twist on the sterndrive concept. The difference is that the propshaft runs forward, rather than rearward, at the bottom of the drive unit. This enables dual propellers to be mounted at the front of the drive, tucking props safely underneath the hull and allowing Forward Drive to be a viable alternative for the fast-growing wakesurf market. Conventional sterndrives, with the prop located well aft of the transom, are not safe to use for the sport due to the rider’s close proximity to the propeller.
Above: Volvo Penta’s Forward Drive. Photo: Volvo Penta.
Unlike sterndrive and Forward Drive, V-Drive, as its name implies, features a V-shaped driveline and no drive mounted to the transom. The engine is positioned 180-degrees from its usual orientation so that the driveshaft runs forward. That driveshaft then connects with a gearbox located below the cockpit floor, and power redirected back toward the stern and at a downward angle via a propshaft that exits through the hull and features a fixed-position propeller well forward of the boat’s transom.
Above: 2021 Sanger V215 SX wake boat with V-drive. Photo: Sanger Boats via Gone Fishin Marine in Dixon, CA.
Jet drives (or jet-powered) boats mate the inboard engine to a jet pump which draws in water from the intake at the bottom of the hull and expels a high-powered water stream from the nozzle on the stern of the boat to propel it forward. Since there is no propeller to hit the ground, they can get into shallower water and are also safer for watersports and swimmers since there is no dangerous moving propeller behind the boat.
Influence On Handling
As you might expect, the physics behind each drive system — and the resulting influence on handling — is notably different.
As both sterndrive and Forward Drive place propeller and rudder on the same movable drive unit, they pivot in unison based on the driver’s actions at the steering wheel. The result is known as “vectored thrust,” as the propeller’s thrust is able to be directed in the direction the captain wants the boat to go. A V-drive’s propeller, in contrast, is locked in a fix position and thrust directed straight back. A separate movable rudder, located in that prop’s slipstream, is what influences the boat’s direction, again based on the driver’s input at the steering wheel.
While both produce impressive handling results when moving forward, the V-Drive typically proves more agile as the rudder, freed from the bulk of a sterndrive’s housing, can pivot throughout a much greater range (as much as 110 degrees). By comparison, stern and Forward Drive units typically swing through roughly a 70-degree arc. Most V-Drives also feature additional tracking fins under the hull, forward of the propeller. The placement of each drive also changes the hull’s pivot point, with the V-drive’s pivot point far more centered under the hull, a Forward Drive’s more aft, and the sterndrive the furthest aft of the three.
Jet drive boats can be harder to steer than the other drive systems listed here and the wake they produce is often more turbulent. Additionally, waterborne debris can get sucked into jet drives more easily, which can lead to vibrations and issues with propulsion, steering and handling. Furthermore sterndrives tend to handle rough water better than jet boats and can be trimmed to adjust to water conditions, whereas jet drives cannot.
Hull Design And Drive System
The hull design typically used with each individual drive also plays a role. Both sterndrive and Forward Drive boats commonly feature a deeper vee, resulting in a steeper banking characteristic in aggressive turns at speed. Most V-Drive hulls, in contrast, feature less deadrise and typically turn flatter.
The true separation between sterndrive-based and V-Drive systems is found in reverse. Even at slower speeds, the vectored thrust produced by sterndrive and Forward Drive provide relatively predictable, nimble handling in any direction, a clear advantage whether backing off the trailer, away from the dock or navigating tight confines. As a V-Drive has minimal water flow passing across the rudder at low speeds, control in reverse is mostly influenced by prop rotation and torque, the directional force created by the propeller.
The typical V-Drive will pull well in one direction when in reverse but have little directional pull in the other. Experienced V-Drive captains will learn to use prop torque to their advantage when backing in the boat’s favored direction and a bump into forward and a turn of the wheel to reset the boat’s angle should they need to back in the weaker direction. Given this characteristic, many V-Drive manufacturers have begun to add optional thrusters or pivoting fins just forward of the propeller to improve backing performance.
As to performance, expect comparably-powered boats equipped with each drive system to excel in some aspects and perform less strongly in others.
Pure top speed favors the sterndrive and Forward Drive. As both can be trimmed, running angles can be increased and the hull’s wetted surface reduced. A V-Drive simply has far more hull in the water and runs at a lower angle.
Acceleration, however, favors the V-Drive. Due to the downward angle of the driveshaft, V-drives direct thrust not just aft but at a negative angle, allowing them to quickly leverage the hull onto plane. By comparison, sterndrive and Forward Drive, even in the fully submersed position, direct their thrust almost straight back, causing the bow to raise higher as the boat climbs out of the water before planing atop the surface. Sterndrives and Forward Drives also have to overcome the weight and bulk of the drives themselves, located far aft on the transom. The shallower deadrise of most V-Drive-equipped hulls also play a role.
As to fuel economy, drive systems are similar at slow speeds, but sterndrive and Forward Drive both typically prove superior to V-Drive at higher speeds. Again, trim plays a role, with the trimmable drives able to dramatically reduce their wetted surface. Jet boats are fastest off the starting line but they generally lack on fuel efficiency and top speed.
X Factors: Trim, Draft, Positioning
Both sterndrive and Forward Drive units can be trimmed, or even raised partially out of the water. Trimming the drive raises the boat’s running angle at planing speeds, improving top-end speed or adjusting the ride to compensate for rough water conditions or changing passenger loads. Shallow water is also a consideration. Sterndrives fare best in these conditions, as the drive can be raised to considerably lessen the boat’s draft. While Forward Drive can also be raised in low water conditions, the forward location of the props lessens the advantage. The fixed position of V-Drive hardware makes it impossible to trim. Overall draft is often notably less compared to a sterndrive-style unit in its fully lowered position, but the sterndrive unit can be raised significantly higher.
Should you strike an underwater object with significant force, both sterndrive and Forward Drive are designed to kick up and lessen damage. That said, the “hook” shape of Forward Drive could potentially prove more problematic should it catch on an obstacle. V-drive hardware is the shallowest of the three while running, but it’s fixed nature is likely prone to the most damage in the event of an underwater strike.
Both sterndrive and Forward Drive outlet exhaust through the base of the drive far below the waterline, lessening noise and fumes.
While each drive system has its own strengths and weaknesses, how — and where — an owner plans to use them will likely be the deciding factor on which system proves best.
For the hardcore wake sports enthusiast, a V-drive remains the gold standard. Low-end power, key for getting a heavily loaded boat up to speed, is superior and the wake V-drive-equipped boats produce unmatched for size and shape. V-drive manufacturers have also had the advantage of years of developing wake-enhancing devices perfectly matched to their hulls. V-drives, however, aren’t the best match for those that want blistering top speed, frequently boat in rougher water conditions, or have worries about sliding up to the sandbar or striking underwater objects.
Sterndrives are the jack of all trades, producing solid performance whether skiing and wakeboarding or just cruising with friends. They can’t rival a V-drive’s wake performance for the hardcore wakeboarding enthusiast, but they can handle a larger variety of water conditions, get superior gas mileage compared to V-drives at top speeds, and can be trimmed to have the lowest draft of any of the three drive alternatives. The one glaring drawack? They absolutely cannot be used for wakesurfing. The prop is simply too exposed.
Forward Drive, as it was designed to do, bridges the gap between V-drive and sterndrive. It features all the just-mentioned benefits of a sterndrive, but as it relocates the props forward, allows your crew to safely wake surf at a solid, recreational level. That drive, however, can sit quite low, an issue that requires care not only when running in shallow or debris-prone waters, but also when trailering.
The best choice for you? How you plan to play — and the characteristics of your playground — will likely provide the answer.