SHAFT DRIVE V STERNDRIVE

How to Choose a Boat – 4 Major Drive Types Explained

One of the most common questions I get asked when someone is choosing a boat is “Should I buy this boat for X amount?” Before I can give a good answer, some basic details need to be figured out. First, you need to determine the main purpose of your boat (for example: fishing, cruising, watersports etc). Second, where you’re going to keep it. Are you going to moor it, or trailer it? Of course, the size of the boat may dictate this, but not always. Where you’re planning to store it may also affect the type of engine setup that you choose and vice versa. How do you know what type of engine and drive you should get?

Here’s a rundown of your options on how to choose a boat to help you figure out whether to moor or trailer, and what sort of engine and drive to go for.

How to Choose a Boat – Moored or Trailered?

When choosing your first boat you need to think about how you will get to it, and how to get your boat in the water.

·         Do you have a big enough car to tow it?

·         Will you have a berth or a mooring?

·         If you have a mooring, how will you get out to the boat?

·         Will you use the boat regularly enough to keep batteries charged?

·         If you have a waterfront property with a slipway, is it set up to accommodate your choice of boat and if not, what else needs to be done?

Maintenance costs vary greatly depending on whether the boat is kept permanently in the water or not.

Moored Boats

When you have a moored boat, you will need to have it slipped, cleaned and antifouled every 6-12 months. The reason for this is that over time the part of the boat in contact with water will accumulate barnacles and moss. Antifouling reduces the amount of growth, and it also becomes easier to clean off when you have a protective coating. You will also need to change corrosive anodes to stop metal parts (e.g. stern drives, shafts, propellers etc.) of your boat corroding away.

Trailer Boat

When you store your boat on either a trailer or dry-dock, you no longer need to antifoul the boat as it isn’t in contact with the water. This will minimize maintenance costs, but you will still need to consider:

·         Storage – garage, warehouse, off-street or on-street?

·         A suitable car to tow – for instance, once a boat and trailer combo weighs over 2 tonnes, you’ll need to carefully consider your tow vehicle.

How to Choose a Boat: Engine and Drive Setup

How a boat is powered and the type of transmission attached can also have a large impact on maintenance costs. Let’s look at the different drive types and review the pros and cons of each.

There are four major drive types you will come across when buying a boat:

1.      Inboard Stern drive,

2.      Inboard Shaft drive, and

3.      Outboard

4.      Pod Drive

There are other setups available, but these are less common in Australia.

Inboard Stern drive

Stern drive is a transmission and engine package, which combines outboard drive with an inboard engine. They come in all different combinations: large stern drives coupled with diesel engines or smaller ones coupled to petrol engines. They are also available from several manufacturers but the two most common brands in New Zealand, for example are Mercury and Volvo.

Inboard Shaft Drive

A boat with a shaft drive has the engine mounted inboard, with a shaft through the hull driving a propeller. Shaft drives may have the engine mounted in a few different positions, including (but not limited to) middle and rear. A rudder behind the propeller steers the vessel.

Outboard

Outboards have the engine attached to the stern, on the outside of the boat. It is a single unit, which includes the engine and transmission in the one package.

Pod Drives

Vessels fitted with pod drives have the engine mounted either in the mid or the rear of the boat, with a “pod” incorporating the transmission, propellers and outdrive straight through the bottom. A pod can steer left to right, and the two most popular brands are Volvo IPS and Cummins/Mercruiser Zues Drive.

Stern drives

When you choose to buy a boat, there are several options to consider. Typically, the main reason people buy second hand boats fitted with stern drives is because they are common, cheaper than other types and provide good handling characteristics. They allow you to trim up and down to shift the planing position, and the whole stern drive physically moves when you steer. Stern drives are a great option for a trailer boat, especially as you won’t have any barnacle growth on them. They need to be serviced yearly but are a good all-round option.

When a stern drive is used on a moored boat it becomes the less desirable option. Stern drives usually have rubber bellows that house drive components and stop water entry. These crack with age, and if you leave your boat moored over time it will grow barnacles. When the leg is turned to steer the sharp barnacles can pierce the bellows, allowing water entry. The water can then cause damage to bearings and other components and if left unattended it may even cause the boat to sink.

Another thing to be aware of is the water pickups, which cool the engine. These are mounted on the stern drive from factory. In the picture below they are covered in barnacle growth, which would cause the engine to overheat under load.

Shaft drives

Shaft drives are a much better option if you’re intending to moor the boat. Barnacles will still grow on them but there is no rubber bellows to change, as they don’t have to steer. They have shaft seals that can wear and leak over time, but don’t cost as much to maintain.

A downfall of a shaft drive is that they draw more water, so you cannot enter shallow waterways. They do need anodes fitted yearly, but so does a stern drive. As for handling, a single engine shaft drive can be more difficult to steer compared to a single engine stern drive. If you have twin engines, then shaft drives are an easier boat to manoeuvre. Twin shafts allow you to split the controls, using one engine in forward and one in reverse, spinning the boat on the spot – this works too on a stern drive but to a lesser effect.

Outboard

Outboard powered boats can sometimes have the best of both worlds with regards to maintenance costs. They are easily removed/replaced if a major repair needs to take place and can be trimmed upwards to keep them out of the water, hence not needing to be antifouled. Outboard boats also provide the handling benefits of a stern drive, in that they can be trimmed up and down and steer left and right. They offer more useable boat space, because the motor isn’t mounted inside.

The disadvantages of outboards are when you need certain weight distribution, bigger horsepower, or diesel power. Some people prefer shaft drive or inboard for fishing, so they can fish off the back too.

Pod drives

Pod drives are exclusively paired with diesel engines and provide several benefits. All pod drives are coupled to a joystick, which enables control of the boat without manually engaging gears and steering. This makes the learning curve for docking the boat much easier. Pod drives are also between 10-30% more fuel efficient than a traditional shaft drive, as they can propel the vessel with less drag. Zeus pod drives offer inbuilt trim tabs and have rear facing propellers, whereas Volvo IPS do not offer trim tabs and have forward facing propellers.

The disadvantages of pod drives are that they cost more than a regular shaft drive to maintain. They do not have rubber bellows like a traditional sterndrive but use expensive synthetic oils that need to be changed regularly, along with anodes. Pod drives are very sensitive to water entry, and certified technicians are required to work on them. This means there are less people available to fix them should you have issues in remote locations.

Summary

Drive Type	Advantages	Disadvantages
Inboard Stern Drive	HandlingBoat designPerformance	Maintenance costs when moored Reliability  Replacement   Corrosion
Inboard Shaft Drive	Maintenance when moored vs. stern driveReliabilityEngine output potential	ReplacementHandlingEfficiency (fuel)Draft required in shallow waterCorrosionPerformance
Outboard	HandlingMaintenanceReplacementBoat DesignPerformanceEfficiency (fuel)	Engine output potentialWeight distributionEngine security (theft)Fuel type (currently no diesel outboards)
Pod Drive	Ease of use (joystick control)Efficiency (fuel)Engine output potential	Draft required in shallow waterCorrosionReplacementMaintenance costsAvailability of mechanics

Basic comparison of drive types

So how do I choose a boat and what do I buy?

Everyone’s situation is different and needs to be taken into consideration. When choosing a boat, you need to assess your intended use for the boat, your storage options, your budget and your ability to maintain it.

To determine if a boat is worth taking to a survey, a service history is an essential part of this process.

Some people can be quite flexible and would be happy with any of the above options, whereas others have specific requirements.

You’ve heard the sterndrive horror stories… thousands spent on repairing transoms and other components – but how does something like this happen?

When you’re looking at a 30-35ft boat in the $80-120k price bracket, you’re likely going to run into a lot of sterndrive packages. But what does that even mean? Usually they tick all the boxes, having an immaculate interior, generator, and sometimes they’ll even have air-conditioning. So, what’s the downfall?

Sterndrives

With any sterndrive, there are several additional parts that live in the water such as bellows, universal joints, steering rods, bushes, transom assemblies and trim rams – which a shaft-drive vessel doesn’t have to worry about. Surely, you’d think that would mean they cost more, but not necessarily. A sterndrive is mass produced and very popular, meaning they cost less initially. There are going to be some trade-offs in the long term, such as maintenance as they will need to be anti-fouled, and the cleaned internally for barnacle growth. It’s also common to expect between 10-15 years out of a well-used sterndrive and transom assembly, and then it’s a matter of continual repairs or replacing it once and for all.

Sterndrives are a faster and more efficient design, as they are mounted to the rear and produce less drag. They use less fuel than a shaft-drive, and can be trimmed up in shallow waters, allowing you to beach your boat. The trim can also be adjusted whilst running to help with the correct bow angle you desire for certain conditions.

Shaft-drives

So, what about shaft-drives? Are they all bliss? To a certain degree, shaft-drives are a lot less maintenance. Now, this isn’t to say that a 15-year-old shaft-drive boat won’t need any maintenance – there are still numerous parts such as skeg bearings, rudders, bonding straps and seals that wear-out and need to be replaced. The distinct advantage is that they’re cheaper and more readily available, having a longer running life.

But what does it cost to swap one of these transom assemblies out?

Cost Comparison

Let’s do a comparison using a 15-year-old 32ft boat as an example. One boat is a shaft or V-drive, and the other is a twin sterndrive. Both boats have 500 hours, and for arguments-sake need some maintenance. From our experience, we will consider the differences in maintenance considerations at 10-15 years for both shaft-drive and sterndrive. 

	Shaft Drive	Stern Drive
Parts	Shaft & Seals  $500-700 per side (x2)	Transom Assembly  $5,000-6,500 per side (x2)
Parts	PSS Rudder Seals  $500-700 (x2)	Sterndrive & Transom Package $12,500-15,000 per side (x2)
Parts	Skeg bearings $200-400 per side (x2)	$7,000-9,000 for a new sterndrive
Parts	Bonding straps $200-300
Services	Balance props & rudders $2,000-3,000 for both sides
Total Labour	Best case: 21 Hours $2,200 Worst case: 30 Hours $3,300 Labour calculated at $110 per hour	Best case: 27 Hours $2,970 Worst case: 40 Hours $4,400 Labour calculated at $110 per hour
Total Cost	Best case: $6,690 Worst case: $10,200	Best case: $12,970 Worst case: $27,970 Worst case with new sterndrives: $34,400

Estimated costs of repairs

As you can see, the cost of repairing a sterndrive is predominately parts, but it also includes more labour, because every time you work on the transom the motor needs to be removed. Every boat will be different, and that’s why the labour amount will change. All these costs are NOT incorporating any engine work, slipping costs and days on the slipway, which can add up significantly as well. These costs will vary depending on the boat design, as some vessels may require floors and seating to be removed to gain access. It will be cheaper to get all the work done at the same time, as opposed to bit-by-bit as you will have to pay for slipping each time.

On the other side of the argument, a shaft-drive boat will usually attract a higher price, but not always. A new Sea Ray in V-Drive is $17,000 as an additional option when new. Sometimes a price of $20-40k more is asked, but this may also include a diesel. It’s near impossible to find a shaft-drive boat in the 22-28ft range and they’re usually less manoeuvrable with one engine. Owning a single sterndrive can be much more acceptable cost-wise compared to a twin sterndrive, but it will still cost more than an equivalent shaft-drive. 

Allowing all the engines to be mounted to the stern does have its design, speed and economic advantages – but they really hurt when it comes to second hand maintenance costs. Ultimately if sterndrives were not invented, we would have far fewer vessel designs.

Is shaft drive better than sterndrive?

As a comparison, shaft drive is cheaper to maintain over a long period of time when compared to sterndrives of a similar age in salt-water. As a trade-off, shaft drives are less efficient, and sterndrives provide more fuel efficiency and higher top speeds when installed in planing hulls.

Are sterndrives expensive to maintain?

As a rule of thumb, sterndrives that are moored in salt-water are the most expensive propulsion type to maintain when compared to shaft drives and outboards. This is due to the additional moving parts, limited access and regular cleaning and maintenance required.