Inboard Drive Differences: Sterndrive, Forward, V-Drive & Jet Drive

How do the most common sorts of inboard drives compare? Here's a closer look at every driveway system's unique attributes...and which may be the perfect match for your needs.


Overview

However, the push systems a vast majority of recreational boats utilize to transport power from the search motor to the propeller have proven a little more diverse. Especially when watersports are an integral component of your on-water action -- and of course, lots of water game and aftermath surf boats remove the propeller completely through the use of jet drive systems.


Sterndrives (or outdrives) have long proven popular, since they are amazingly flexible and keep a clean, obstruction-free transom. V-Drives are a spin on the conventional "ski boat" inboard, and boast a hardcore wake sports heritage without the cockpit-clogging mid-engine. Jet compels (or jet-powered) provide a searchable draft and pose less of a danger to wake up surfers, water skiers and swimmers in the water.


Just how do boaters and wake up sports fans utilize the qualities of these three propulsion systems to best fit their boating lifestyles? Let's examine each drive's physical design to understand how it affects the system's ultimate performance on the water.

Sterndrives (Outdrives)

Occasionally referred to as "inboard/outboards" (or I/O for short) because of the simple fact that they combine a inboard engine with an outer drive unit very similar to an outboard motor, sterndrives join the motor driveshaft to the sterndrive device via a flexible U-joint at the transom. Power is then redirected via a set of gears downhill via a driveshaft within the housing before once more redirected 90-degrees aft via an additional set of gears that twist the propshaft. A clutch permits the propshaft to twist in both forward or reverse direction, or disengage completely when in neutral.


Forward Drives

The difference is that the propshaft runs ahead, rather than rearward, at the bottom of the drive unit. This enables dual propellers to be mounted at the front of the driveway, tucking props safely under the hull and allowing Forward Drive to be a feasible choice for the fast-growing wakesurf marketplace. Conventional sterndrives, with the prop located well aft of the transom, aren't safe to use for its sport due to the rider's close proximity to the propeller.

volvo-penta-forward-drive_2-938x535

Above: Volvo Penta's Forward Drive.


V-Drives

The motor is positioned 180-degrees from its typical orientation so that the driveshaft runs ahead. This driveshaft then connects with a gearbox positioned beneath the cockpit floor, and power redirected back toward the stern and at a downward angle by means of a propshaft that exits through the hull and comes with a fixed-position propeller well forward of the boat's transom.

v-drive-boat

Jet Drives

Jet drives (or jet-powered) boats mate the inboard motor to a jet pump which draws in water from the consumption at the base of the hull and expels a high-powered water flow from the nozzle on the stern of the ship to propel it forwards. As there is no propeller to strike the earth, they can get into shallower water and are also safer for watersports and swimmers as there is no dangerous moving propeller behind the boat.


Influence on Handling

As you might expect, the physics behind each push system -- and the consequent influence on handling -- is notably different.

As both sterndrive and Forward Drive place propeller and rudder on the exact same movable drive unit, they pivot in unison based on the driver's activities in the steering wheel. The result is known as"vectored thrust," as the propeller's thrust is able to be directed from the way the captain wants the ship to go. A V-drive's propeller, by comparison, is locked in a fix position and thrust directed straight back. A separate movable rudder, located in that prop's slipstream, is what affects the ship's direction, again based on the driver's input in the steering wheel.


While both create remarkable handling results when going forward, the V-Drive typically proves more agile as the rudder, freed from the bulk of a sterndrive's housing, may pivot throughout a significantly greater range (as much as 110 degrees). In contrast, stern and Forward Drive components typically swing through roughly a 70-degree arc. Most V-Drives also contain 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 a lot more focused beneath the hull, a Forward Drive's more aft, and also the sterndrive the furthest aft of those three.


Jet drive ships can be harder to steer than the other drive systems recorded here and also the aftermath they create is often more tumultuous. Additionally, waterborne debris can get sucked into jet pushes more easily, which may lead to vibrations and issues using propulsion, steering and handling. Furthermore sterndrives have a tendency to handle rough water better than jet boats and can be trimmed to adjust to water requirements, whereas jet drives can't.


Hull Design And Drive System

The hull design usually utilized with each individual drive also plays a role. The two sterndrive and Forward Drive ships commonly feature a deeper vee, resulting in a steeper banking characteristic in aggressive turns at speed. Many V-Drive hulls, by comparison, feature less deadrise and generally turn flatter.


The legitimate separation between sterndrive-based and V-Drive systems is located in reverse. At slower speeds, the vectored thrust made by sterndrive and Forward Drive provide comparatively predictable, nimble handling whatsoever, a definite benefit whether backing off the trailer, away from the pier or navigating tight confines. As a V-Drive has minimum water flow passing across the rudder at low rates, control in reverse is mostly influenced by prop spinning and torque, the more directional pressure created by the propeller.


The typical V-Drive will pull well in 1 way when in reverse but have little directional pull in the other. Experienced V-Drive captains will learn how to use prop torque for their advantage when backing in the ship's favored direction and a bump into forwards along with a twist of the wheel to reset the boat's angle should they need to back in the poorer direction. Given this characteristic, many V-Drive makers have started to add optional thrusters or pivoting fins only ahead of the propeller to enhance backing performance.


Acceleration/Speed/Fuel Economy

As to performance, expect comparably-powered ships equipped with each drive system to excel in certain aspects and execute less strongly others.


Pure top rate favors the sterndrive and Forward Drive. As both can be trimmed, running angles could be increased and the hull's wetted surface reduced. A V-Drive just has much more hull from the water also 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, letting them quickly leverage the hull onto plane. By comparison, sterndrive and Forward Drive, even in the fully submersed position, steer their thrust almost directly back, causing the bow to raise higher as the ship climbs from the water before planing beneath the surface. Sterndrives and Forward Drives also have to overcome the bulk and weight of the drives themselves, located far aft on the transom. The shallower deadrise of the majority of V-Drive-equipped hulls play a role.


As to fuel economy, push systems are similar at slow speeds, but sterndrive and Forward Drive typically prove superior to V-Drive at higher speeds. Again, trim plays a role, with all the trimmable drives able to dramatically lower their wetted surface. Jet boats are quickest off the starting line but they generally lack on fuel efficiency and top speed.


X Factors: Trim, Draft, Positioning

Both sterndrive and Forward Drive components can be trimmed, as well as raised partially from the water. Trimming the driveway raises the ship's running angle in planing speeds, enhancing top-end adjusting or speed the ride to compensate for rough water conditions or altering passenger loads. Shallow water is also a consideration. Sterndrives fare best in such conditions, as the drive can be increased to substantially lessen the ship's draft. While Forward Drive may also be raised in low water conditions, the forward location of the props lessens the advantage. In general draft is often notably less compared to some sterndrive-style unit in its fully lowered position, but the sterndrive device can be increased significantly greater.


In the event you hit an underwater object with significant force, both sterndrive and Forward Drive are all intended to kick up and lessen harm. Nevertheless, the "hook" form of Forward Drive may potentially prove more problematic should it catch on an obstruction. V-drive hardware would be the shallowest of the three while running, but it's fixed nature is likely more likely to the most damage in the case of an underwater strike.


Both sterndrive and Forward Drive outlet exhaust through the base of this driveway far below the waterline, decreasing noise and fumes.


Respective Playgrounds

While each push system has its strengths and weaknesses, how -- and where -- an owner plans to utilize them will likely be the deciding factor on which system demonstrates best.


For the hardcore wake sports enthusiast, a V-drive remains the golden standard. Low-end power, essential for getting a heavily loaded ship 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 creating wake-enhancing devices perfectly matched to their hulls. V-drives, however, aren't the best game for the ones that want blistering top speed, often boat in water requirements, or have concerns about slipping to the sandbar or striking underwater objects.


Sterndrives are the jack of all trades, making strong performance whether skiing and wakeboarding or just cruising with friends. They can not rival a V-drive's wake operation for the hardcore wakeboarding enthusiast, but they can deal with a bigger assortment of water conditions, get superior gas mileage when compared with V-drives at high speeds, and can be trimmed to possess the lowest draft of any of the three drive alternatives. The one glaring drawack? They absolutely cannot be used for wakesurfing. The prop is just too exposed.


Forward Drive, because it was developed to perform bridges the gap between V-drive and sterndrive. It includes all of the just-mentioned added benefits of a sterndrive, however also as it relocates the props forward, enables your team to safely wake surf in a sound, recreational degree. That drive, though, can sit quite low, a problem that needs care not only when conducting in shallow or debris-prone waters, but also when trailering.


The ideal choice for you? The way you intend to play -- and the qualities of your playground -- will probably provide the answer.


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