Yamaha is responsible for a lot of the 10,000 outboards sold in New Zealand annually.
Today’s primary power source for boats 5m to 10m is outboard or sterndrive. Which one suits you and why? We look at the pros and cons of both platforms.
Most modern cruisers and family boats are powered by sterndrive or outboard propulsion. In New Zealand, the outboard rules with over 95% of all trailer boats 4-9m powered by an outboard. Most of the remaining 5% comprises diesel sterndrive, followed by petrol sterndrive and jet. However, diesel and electric outboards are starting to make inroads into the mix, albeit small at the moment.
While today there are three primary types of marine engine — outboard, sterndrive and inboard, not so 65 years ago when trailer boating was in its infancy. Let’s take a look at the advantages, and most popular applications, for each propulsion system.
INBOARD DOMINANCE
Inboard power is the classic, original marine propulsion system. A petrol or diesel engine is located within the boat, and power is transferred to the propeller by a shaft that passes through the bottom of the hull. A separate rudder steers the boat.
At one time, almost any trailer boat in the 5m to 8m range had inboard power. In the early years of pleasure boating, a converted car engine offered enough horsepower to move even midsize runabouts. Interestingly, with very few exceptions, petrol inboard engines today are still marinised car engines.
Marinisation was a big business after WW2 as the recreational boating market started to take off. Trailer boats were in their infancy, and the outboard revolution had not yet started. By the mid-1950s, we started to see specialist marinisation companies in New Zealand, with Augustin, the market leader. They made everything from struts, rudders and shafts to props and fully marinised engines. They even designed and built the boats to put their gear into. Petrol engines like the Ford 10, Watermota, based on a four-cyl Ford Prefect engine, Graymarine, 4cyl, 6cyl & V8s, Chrysler 6 cyl or Dodge V8s were widely used, as were small diesel engines from Penta, Morris, Graymarine and Universal.
At that time, outboards were only low horsepower, around 25hp maximum and unsuitable to power the larger and heavier plywood trailer boats and small cruisers. Alloy boats hardly existed, and fibreglass was in its infancy. Sterndrives were also starting to be used, with Kiwi company France Craft designing one of the few local units. Others to follow were Melhop, Perkins Z Drive, and Argonaut, all of which faded into history once MerCruiser and Volvo Penta entered the country and started their worldwide domination.
A full-page advert in a 1955 Seaspray magazine for Carl Augustin Plans detailed nine boats from 12ft through to 20ft, and all were only optioned with petrol inboards. The Augustin 20ft Overlander was powered with a Ferguson tractor engine, an adaption of the Standard Vanguard, which developed 26hp @ 2500 rpm. Â
That began to change in the late 1950s / early 1960s as outboard motors became more powerful, plus the sterndrive power train was gaining some following. Outboards had grown to 100hp, and sterndrives boosted 225hp engine packages in 1963.
Today, inboard power remains most popular for specialised tow sports boats, such as Nautique, Malibu and Mastercraft. It offers several advantages for tow sports. The engine makes a lot of torque, and the prop is always in undisturbed water under the boat, both of which help pull water skiers and boarders quickly up on the plane and hold well against the strain of the tow line.
An inboard can also provide power without creating excessive turbulence behind the boat, allowing builders of specialised wake sports boats to shape the hull to create the most desired wake for skiing, boarding or surfing.
However, when it comes to conventional trailer boats, the inboard with a shaft drive is ancient history regarding drivelines. The only exception is perhaps the jet unit which sees an inboard engine attached to a short shaft coupled to the jet unit. World leaders in jet propulsion are certainly New Zealand’s own Hamilton Jet. While jetboats are the king of the rivers, they have never really gained much of a following when it comes to offshore boating. However, rumours are that Hamilton Marine is developing a new range of fibreglass jet boats to tackle the conventional ”outboard” market in 2023.Â
Perhaps the most significant advantage of an inboard is rarely discussed – the props are well under the boat, and there is little chance of a severe accident. Obviously, the same principle applies to a jet installation. This vital detail has kept sterndrives and outboards out of the wake surfing business until recently.
Both Volvo and Mercury have introduced forward-facing lower units that put the props about .66 cm forward of where they would be otherwise. With the props no longer exposed, regular bow riders are now used for wake surfing.
While some mid-range cruisers are available with inboard petrol engines, they are quickly being supplanted by the large outboard engines or diesel sterndrives, and they seem to be bound for extinction.
STERNDRIVE CHANGES
In 1948, Mercury Marine engineer Charlie Strang mated an aluminium car racing engine to the lower unit of an outboard motor, creating a marine propulsion system more powerful than the outboard motors available at the time. During the 1950s, he and fellow engineer Jim Wynne worked at Mercury under founder Carl Kiekhaefer. The latter was initially dismissive of and opposed to a technology that would later capture 80% of the market. In 1959 Wynne left Kiekhaefer and, in less than 90 days, developed his own stern drive, which he subsequently patented.
The first commercial introduction of sterndrives was the Volvo Penta “Aquamatic” at the 1959 New York Motor Boat Show. Kiekhaefer introduced a MerCruiser outdrive in 1961 at the Chicago Boat Show. By 1962, around 20 manufacturers produced sterndrives, including several Kiwi designs. The petrol sterndrive engine was introduced as a power system that combined the torque of an inboard engine with an outboard’s steerable and trimmable drive capability.Â
Over the last half-century, Volvo Penta has continued developing the Aquamatic, adding diesel power options to its lineup in 1977. In 1982, Volvo Penta debuted the DuoProp drive, which offers greater bite, enhanced tracking and manoeuvrability, and improved steering. And most recently, Volvo Penta launched a line of composite stern drives specifically for saltwater use.
It took Mercury Marine 24 years to sell its first million sterndrive units, but only ten years to reach the second million in 1955. Today they are the largest supplier of petrol sterndrives in the world.
Today, petrol sterndrive engines range from around 200 to over 1000 hp. While petrol sterndrives are not so popular as a power option in New Zealand anymore for trailer boats, there is still a small market. It is estimated that around 50-60 petrol sterndrive packages are sold annually, shared between Mercury Marine’s Mercruiser and Volvo Penta’s Aquamatic.
While the number of stern drive boats compared to outboard-powered boats, especially up to around 10m, is small, there is still a cult following. Wayne Patten, MD of Volpower, New Zealand importers and distributors for Volvo Penta, says;
” Our smallest 200hp V6 has been a consistent seller for the smaller trailer boat market, and some of our larger models find their way into production or custom boats and repowers”.
Dean Harris, MD for Mercury Marine, says they have a couple of regular production builders that still install the smaller engines, such as the 4.5 and 6.5 Mercruisers, and supply a steady market in repower.
Interestingly while the installation costs of a sterndrive compared to an outboard are much higher, the initial unit costs are not. A Volvo Penta V6 300hp petrol sterndrive retails for around $46,000, compared to a Mercury 300hp V8 outboard at $51,000.
Single-prop sterndrives are matched up primarily with inline 4, V-6 engines. Dual-prop drives such as the MerCruiser Bravo Three and Volvo Penta Duoprop are typically paired with larger V-6 & V-8s ranging from 300 to 440 hp and are used for pushing heavier cruisers and day boats.
In New Zealand, the peak for petrol sterndrives was around the mid-2000s, when the world sales figures were around 75,000 sterndrives of all sizes. That global number has fallen considerably to less than 10,000. There are many reasons for this, but possibly none more so than the rapid advancement of the outboard. Also, at the same time, 4-stroke outboard engines got rid of the 2-stroke smell, smoke, and temperamental behaviour. And, they were much more fuel-efficient than the old 2-stroke and approached sterndrive engines in terms of fuel consumption. Today, there is little difference between the two.
DIESEL REVOLUTION
Since its introduction in 1959, Volvo Penta has continued to develop the sterndrive concept – not least through the introduction in 1977 of the classic MD40 series of diesel engines. Until then, the Aquamatic sterndrive was primarily combined with gasoline engines. With the MD40 series and new drives, Volvo Penta developed a powerful diesel package that took the boating world by storm.
Diesel power, combined with Aquamatic sterndrive, created a new market on which Volvo Penta has been the undisputed leader since that time.
In 1982 Volvo Penta introduced the Duoprop, an Aquamatic sterndrive with double, counter-rotating propellers. The Duoprop represented a significant development, with fantastic performance, sure grip in the water and improved steering. It is the diesel Duoprop range of D3, D4 and D6 engine platforms that are finding their way into Kiwi boats. Volvo Penta has the industry’s most comprehensive engine programme for drives, comprising both diesel and gasoline engines.Â
Total diesel sterndrive sales in New Zealand for all brands is around 225 units.
OUTBOARD REVOLUTION
There was a paradigm shift in trailer boat powerboats in the early ’60s with the advent of the larger horsepower outboards. Very quickly, the traditional inboard with a shaft drive and rudder disappeared in favour of the lighter and easier to install outboard. Designers like Frank Pelin, Richard Hartley and others started turning out specialist outboard-powered boat designs.
When the first of the V6 outboards were released in the mid 1970s, such as the Mercury V6 Black Max and the Johnson & Evinrude V6 Jumbos, the flood gates opened for larger trailer boats. Suddenly there was a perfect engine platform for 6-7m boats and performance runabouts. Since then, the development of the outboard has been stratospheric, from the smokey 2-stroke to highly efficient 4-strokes with everything from superchargers and turbochargers to direct injection and fuel management. Today that has been extended to diesel and electric outboards that are starting to put a whole new dimension on the simple outboard. Who would have ever imagined a V12, 600hp outboard would be available as a standard production engine. Mercury certainly did.
Originally intended only to power small fishing boats and runabouts, outboard engines have become more powerful and have often replaced inboard and sterndrive engines on larger cabin cruisers, day boats and high-performance boats. Today, with the advent of 300hp plus, V6/V8 & V12 outboards, these engines are being put on boats 15m and larger and are replacing diesel inboard engines. The number of outboards an owner can put on the transom is only dictated by the available beam.
While Kiwis are familiar with single, twin and the occasional triple outboard rig, in the US, three is considered a starting point on some boats. Four, five and yes, even six engines are not uncommon on some of the biggest centre console and sport fishing boats in the US.,
When combined, the multi-outboard package can make more power than the biggest pair of sterndrive engines available, resulting in performance that was once unimaginable. Today’s outboards are more efficient, powerful, and feature-laden than the motors offered just a few years ago. All reasons why outboards have become more popular on more types of boats.
Outboard engines are the only propulsion systems designed from scratch for marine use. Because the entire outboard engine is located outside the boat, more of the cockpit can be devoted to seating or gear storage, live bait tanks and other features in the space a sterndrive or the inboard engine would occupy. Another reason outboard power has always been a popular choice for fishing boats.
The key trade-off for outboard power on family boats is that the motor intrudes on the swim platform. With sterndrive or inboard power, the boat can be designed with a flat, full-width platform that many prefer for swimming and lounging. But lately, imaginative designers are creating a swim/staging area ahead of the outboards and behind the seating area that effectively gives occupants access to the water from either side of the boat.
Outboard sales in New Zealand are currently around 10,000 units annually.
WHICH BRAND TO BUY?
The type of engine you buy will largely be dictated by the application of the boat you buy. In many cases, the dealer will dictate your engine as the boat/motor/trailer package comes as one. If buying new, it is prudent to purchase the entire rig from one place. Today there are not the outboard choices that there once were. A vast majority of outboard brands have gone, even the once giant of them all, OMC. Today the four big players are Mercury, Yamaha, Honda and Suzuki. Technically all four are exceptional, and each offers a sweet selling point that the others don’t have. One thing that is common amongst all brands is reliability. Your purchase may simply hinge on brand loyalty. Other brands such as Tohatsu and Parsun, are also popular, especially in the smaller to the mid-range sector.
Regarding petrol sterndrives, the choice is reasonably straightforward; Mercury Marine’s Mercruiser or Volvo Penta’s Aquamatic. There are other brands on the market, although the company’s engine brand is generally matched up to a Mercruiser drive. Examples of this are Hyundai, FNM, Iveco, Steyr and Lombardini.
One exception is Yanmar which offers its own engine and drive packages. Yanmar’s 8LV is a light-weight, twin turbo V8 producing 320hp or 370-hp and can only be used with the ZT drive. The 4LV common rail engines a from 150 to 250 mhp with the Yanmar ZT370 sterndrive.
