Marine Propulsion On Recreational Vessels

Boats come in many different shapes and sizes with varying purposes. The desired use of the boat may determine which marine propulsion method is best suited. The most common marine propulsion methods include:

• Outboard
• Sterndrive
• Shaft Drive
• Pod Drive
• Jet Drive

Fitment of bow and stern thrusters, joystick integration, second or even third helm stations and wireless controllers can be used to offer tremendous slow speed manoeuvring and a feeling of competency at the helm. We will elaborate on some of these throughout this article, discussing their uses, benefits, berthing tips, maintenance and disadvantages.

My Maiden Solo Voyage

As an apprentice mechanic, I’d been tasked to collect and return a Deltacraft for annual works. We motored over in the work boat, and I was dropped off with a “see you back at the marina”. After the pre-start checks (firing up the engine and checking the gears), I was ready to go. I throw the lines and I’m off at a blistering 6 knots back to our marina. The Deltacraft was a 20ft single screw (single propellor shaft drive) – as basic as it gets. While this seems really simple, remember this was my:

1. First time driving a single shaft, and
2. “Maiden solo voyage”.

Whilst motoring back I tried to remember all the tips I’d been given. Steer then gear, transverse thrust, only go as fast as your willing to hit something. This is fine in open water, but when you’re passing boats ranging from 100 thousand to 3 million dollars, everything starts to feel real. With the work berth in sight, up bumps the breeze, and my heart starts racing. Suddenly, I am drenched in sweat and my mind is boggled with the bosses’ “hot tips” I mentioned earlier. After a few attempts, I berthed the boat and tied up with no major issues.

Moving past my first experience and onto driving 30-70ft vessels on a daily basis with all propulsion types, learning to remain calm in potentially hairy situations, all those other tips become second nature. If my old boss ever heard a thruster from the workshop, he’d be down in a flash asking who was the Nancy who needed a thruster?! I have endless thanks to him and it certainly helped with the fundamentals at the time, however, in my opinion, if you’ve got it, use it – whatever makes you feel more comfortable at the helm.

Outboard

Outboards are the marine propulsion of choice for many smaller craft. This is due to their ease of installation, low maintenance and running costs, and varied range of power ratings. Having said that, outboards are also the choice for many ski racing and offshore fishing boats. This is due to their high performance and power to weight ratio.

Manoeuvrability is average. The term “steer before gear” comes into play when berthing or when limited space is available. Many boaters like the idea of being able to see the exact position of the motor by simply turning around. You can find outboards being fuelled by petrol (whether 2 stroke or 4 stroke), diesel and more recently electric outboards are growing in popularity for smaller craft.

Some disadvantages of an outboard engine can include limits to swim platform design and access to aft of vessel. In some cases the cost to overhaul an outboard outweighs the cost to replace.

Sterndrive

Sterndrives can be powered by diesel or petrol engines, the later being the most common. Sterndrives are found fitted to predominantly bow riders, cabin cruisers and sports cruisers up to around 40ft. Volvo Penta and MerCruiser are the most common manufacturers you’ll see, and each have various models of sterndrives. From single propeller arrangements with dog clutches (like many outboards) and in-gearcase water pumps, to twin counter rotating propellers with cone clutches and engine mounted water pumps. These are different types of sterndrives that you may come across.

This style of marine propulsion offers widespread availability and benefits from a large network of qualified trades for servicing and repairs.

The disadvantages of sterndrives are with more exposed components to saltwater and marine environment, comes the additional service cost and risk of failure. Many seals within the sterndrive sit below the water line when the vessel is at rest, over time these seals can become brittle, especially with dry stacked boats. Water entry to the gear oil (the main cause of failure) could be due to age, impact, temperature, over pressure, installation failure and the list goes on.

Another critical component is the uni-bellows, a flexible rubber boot is relied upon to protect the universal shaft. The universal shaft connects engine rotation to sterndrive, and the bellows is solely responsible for sealing water out of your boat and allows the shaft to rotate freely through all angles of sterndrive steering and trim.

Corrosion to universal shaft assemblies due to bellow leakage or failure is a big concern. Imagine this shaft rotating at 5000 RPM, flying apart and blowing a gaping hole in your transom. Your bilge pumps likely wont keep up, and it’s game over. Annual maintenance to your sterndrives including removal should be a priority.

Shaft Drive

With the exception of ski and tow sports boats, shaft drive power boats typically start around mid 30ft in single and twin installations. Generally, boats 30-40ft are petrol and 40ft and above are diesel. People often say they wouldn’t buy anything that wasn’t shaft drive and diesel. Whilst this combination is ideal, factors like vessel cost, additional coolers and saltwater servicing come into play with these higher horsepower forced induction engines.

The main benefits to shaft drive over sterndrive are the vessel layout and having less running gear in the water (meaning less points of potential failure). Shaft manoeuvrability in twin situations is exceptional. You’ll have advantage of sitting the helm forward and being able to walk the engines for berthing. This means there’s less to think about in stressful situations.

You don’t get out maintenance free though. You’ll still have serviceable items such as stern and skeg bearings, shaft seals (I have another article on types of shaft seals here) and engine weighting and alignment, which can be labour intensive to achieve optimal results.

The disadvantages to shaft drives is the cost for repair or replacement due to collision or grounding. A new shaft will need to be manufactured. Don’t fall for the “we can straighten this shaft” talk. In my experience, these solutions will temporarily fix or hide a vibration issue, and shafts tend to have a memory and overtime revert back to bent.

Propellers can be built up and balanced. Stern glands can be serviced or replaced and shaft bearings can be replaced, but all of these repairs require the vessel to be on a hard stand. For extended repairs (for example, propeller manufacture), a shaft driven vessel can easily be bunged and returned to water to save on costly hard stand fees.

Pod Drive

The most common pod drive is the Volvo Penta IPS, in twin, triple and even quad installations. The biggest benefit to IPS is the simple fact of how much fun they are to drive, the lightness steering, and the ease of manoeuvring in tight marina berthing.

IPS drives are fuel efficient, with many owners reporting they see the difference at the pump. Fitted with a responsive joystick means you’ll be able to move in any manner. These can also be calibrated to suit your docking style, and simple enough for a video game savvy child to berth better than many skippers. Features such as DPS (Dynamic Positioning System) can be added meaning the vessel can hold its position. When engaged, the skipper can assess surroundings without being bound to the helm, allowing hands free to handle lines or even get another ‘frothie’! One disadvantage to docking is that manoeuvrability is lessened in shallow water as the stern of the vessel feels to dig down.

IPS maintenance is relatively straight forward, and so is their oil/filter change and anode replacement. Much like sterndrives, they have seals that wear out overtime and live below the water. Being twin forward facing propellers, impact can pose a problem resulting in bent shafts and water ingress into the drive. Rope and fishing lines can also create issues – line cutters can be fit to reduce the likelihood of seal damage, resulting in water ingress to the drive. Once water contaminates the pod, lubrication is lessened, temperatures increase and clutch pack burnout is the result. If this occurs, it’s time to remove, strip, assess and overhaul the pods at a large expense. Lastly, they have a large amount of proprietary electronics, so if components fail they can be very expensive to replace.

Jet Drive

The most common type of jet drive recreational boats are jet skis. Aside from this, it is rare to find a jet drive in a recreational boat, although there are some some small jet boats around, for example jet tenders, and some commercial operations. Think the Sydney Harbour jet, which you will often see joyriding around the harbour on a sunny summer’s day. An advantage to a jet drive is that they can be ran where depth is an issue, as they require a very shallow draft to operate. Maintenance for jet drives is relatively simple, with regularl inspection of impellor and housing recommended. They also require lubrication of the steering components. Jet drives do have seals that can fail, and as they get older let water into the hull.

Berthing a jet drive is very different to any other type of marine propulsion. On first practice, slow speed maneuvering is compared to skating on ice. The handling characteristics of a jet require throttle to be engaged to have a reaction from the steering. This means the old saying “steer before gear” does not hold true and is the complete opposite when driving a jet.

In conclusion

Overall, each of these marine propulsion types have their own unique advantages and disadvantages. Either way, a day on the water can be much more enjoyed than at the desk or job site. Whichever driveline you have, all that matters is that you are out and about enjoying yourself on the water safely.

About the Author

Brendan is a dual certified Marine Surveyor & Engineer, who completed his trade at well respected marine engineering company based on the Hawkesbury River. After relocating his family to the Gold Coast, he joined the BoatBuy team. Brendan is an expert in his field, and completes over 200 inspections per year. Liked this article? Feel free to email me with any boating related questions you might have here. You can also contact the team at BoatBuy here.