Rebuild or Replace?

By Adam Paull

Fishermen's News October 2011

The fishing season has begun. Your boat, your gear and your crew are in place for the peak of the season. Then that engine you were hoping to get one more season out of decides to let go.

What is it going to cost you?

If you are unfortunate enough to have a catastrophic engine failure, you can expect to miss a minimum of one to two weeks while you await your repower. You can also anticipate a disgruntled crew concerned about not making money, overtime for the shop doing the work to get you going again, and airfare costs (nearly $2 per pound) to fly an engine from Seattle to Alaska. It all adds up to a difficult situation that would have been a lot cheaper with some off-season attention.

This may sound like a doomsday scenario, but these types of failures occur every year.

Your boat is your business, so the financials of when and how to repower your vessel are important business considerations. When contemplating a repower, start by answering three questions:

• What is the history of your current engine(s)?
• How long do you expect your current engine(s) to provide reliable service?
• How much would unplanned downtime cost your business?
Now let’s assume you want to avoid a doomsday scenario like the one detailed above, and that you are weighing the decision to rebuild your current engine or replace it with a new engine.

Rebuild Current Engine
Rebuilding can seem to be the more frugal of the two options. It can be a good option, but only if you have a good starting point: a newer-technology engine that can be rebuilt to factory specifications with factory parts and dealer support. This option enables you to keep a familiar engine that works with all existing vessel systems.

However, there are many questions associated with rebuilding, such as:

Are parts readily available? Many service parts for older engines are nonexistent, and the quality of aftermarket parts can be questionable.

Can you rebuild back to factory specifications with new liners and pistons?

What is labor going to cost to remove, rebuild and replace?

Is a warranty available on the rebuilt engine or parts? If done incorrectly, rebuilt engines generally do not last as long as new engines.

The bottom line is that rebuilding your engine can be an acceptable option as long as you have a good starting point, take the time to restore the engine to factory specifications with factory parts, and weigh the performance and efficiency tradeoffs.

Install A New Engine
A rebuilt engine may be appealing and may appear to be the more economical solution. You probably favor your old engine, it likely does not have electronics, and you know what to expect.

However, when you compare a rebuilt engine to a new engine, you may find that a brand new replacement engine could easily pay for itself when you factor in the fuel cost savings, reliability (uptime) and electronic features.

Let’s examine the benefits of installing a new engine.

Cost
A brand-new engine may seem costly, but consider these ways to offset and minimize the expense:

Factor in fuel efficiency gains that new technology offers. New electronically controlled engines have features and controls that allow the factory to better calibrate and optimize for performance and fuel efficiency. Some John Deere customers have reported up to a 33 percent improvement in fuel efficiency with a new engine compared to their old engine. That kind of fuel economy gain is not possible with an older, rebuilt engine, and fuel cost savings can really add up over a few seasons.

Obtain funding assistance. Alaska, Oregon, and California have programs to help with offsetting some of the cost of upgrading your engine. New engines generally qualify easily for these types of programs, which are established to improve fuel efficiency and/or emissions.

Sell your old engine. Some customers have been able to make good money selling the engine being replaced.

Long-Term Reliability and Uptime
What is your productivity worth? Before new engines start production, they have gone through extensive product validation and verification (PV&V) processes to ensure that customers receive the reliability and uptime they expect. These processes get more elaborate with each engine development program to ensure that a new engine is better than its predecessor. Many marine engine components have endured the same strenuous testing as the manufacturer’s agricultural tractors and construction equipment. These types of PV&V processes make certain that you will get the best long-term reliability and uptime.

What about the electronics? Electronics on diesel engines are not new, and the electronics incorporated into new engines have undergone the same strenuous testing. Not only do these electronics offer precision controls for optimal fuel delivery – often increasing both power and fuel economy – they also provide engine protections to prevent catastrophic damage. These protections can prevent an unplanned engine swap in the middle of your prime fishing season. Additionally, when the engine requires maintenance, electronics enable precision troubleshooting to facilitate diagnostics and a quick return to normal operation. Older engines do not have such features.

Dealer support and parts availability are additional reliability and uptime considerations. If you have a problem, it is important to consider the ability to obtain parts and support. With a new engine, dealer support and service parts are generally more readily available.

New Engine Specification
Adding power costs money, while a replacement engine of similar power to your old engine can save work. Careful specification of your engine could result in significant savings.

Increasing horsepower will likely require costly upgrades to gears, coolers, exhaust, and other systems with – depending on hull form – the potential for a minimal improvement to vessel performance. However, manufacturers such as John Deere offer single circuit keel cooled ratings that are very similar to ratings of engines being replaced. A horsepower-for-horsepower exchange may allow the reuse of the exhaust system, transmission and keel cooler. Additionally, the existing controls can typically be reused with the addition of an electronic throttle position sensor. You could achieve significant savings by reusing many of the old engine systems rather than upgrading parts of the propulsion system – a requirement when significant horsepower is added to the boat.

To ensure that you get the best return on your new engine investment with increased productivity and uptime, the engine and engine systems must be specified appropriately. Let’s take a closer look at two replacement scenarios: horsepower-for-horsepower and higher horsepower.

Horsepower-for-Horsepower
Swapping in a new, equivalent-horsepower engine can be an economical solution. You can reap the benefits of the new engine’s reliability and fuel efficiency while having the opportunity to reuse many of the existing vessel systems. These are significant factors when comparing the return on investment of a horsepower-for-horsepower replacement with that of a higher-horsepower swap. Even if you need to replace or rework a few components, you can still achieve significant savings.

In a horsepower-to-horsepower engine swap, one of the important factors to avoid overlooking is rated engine RPM (rated engine speed). Rated engine speed is roughly defined by the manufacturer as the highest engine speed at which power is observed and effectively utilized for the specific rating for which the engine is programmed. Generally, this is the horsepower of the engine, and the maximum speed governor is typically set around 40 rpm above this speed. This is where all power is not created equal.

Mathematically, Power = Torque x Engine Speed. What this means is an equivalent-power engine at a higher rated speed has lower torque. In simple terms, torque is the force that makes things turn, so at the same rated power the lower rated speed will have more torque and better vessel response, especially when maneuvering and operating at low speed.

This fundamental torque effect continues in lower engine speeds as well. With today’s electronic engines, low speed torque capacity is limited primarily by the air system. This is because a good turbocharger match at high speed is a poor turbocharger match at low speed. Therefore, when comparing low speed torque capacity for equivalent rated power, the lower rated speed will have a higher torque capacity.

This is a critical point to consider, as the rated engine speed is fundamental to the gear and propeller match. For fishing and other commercial applications, torque curve capacity and torque rise provide the ability to haul a load. Suffice it to say a 300-HP at 3200 RPM engine will not provide the torque of a 300-HP at 2200 RPM engine.

Higher Horsepower
Now let’s assume you want to increase the performance of your fishing vessel. Not only will you need an increase in power, you will also need to consider changing out engine systems such as the keel cooler and exhaust system along with your propeller and gear.

Also remember that the extra power means your engine will need more cold air below deck for your engine to breathe. This is probably one of the most overlooked considerations – and it is one that can have serious implications for long-term performance and efficiency.

Most often, a little more performance can cost a lot more money. Weigh your productivity gains against the cost of the performance improvements. Depending on your specific scenario, it may not be worth the extra expense.

Other Considerations
The engine is the heart of your vessel; it provides the motive force. Therefore, it is important that all components work well together. Consider your hull type, vessel weight, gear, prop, engine and engine systems together as a package. When looking to size your propeller, gear and engine together, it is critical to do so correctly. This most often requires visits to your dealer and prop shop or naval architect.

Marine engines are calibrated and components are designed to run on a prop curve. For reliability and performance, it is important that the marine gear and propeller are sized appropriately with the vessel hull type and weight to run on this prop curve. This comes into play when the manufacturer specifies an application requirement to achieve rated engine speed or higher when loaded at wide-open throttle (WOT). This is crucial because if the vessel can achieve rated speed or higher at WOT, it essentially ensures that it is running along the prop curve. The higher above rated speed you are able to achieve, the more margin you have for a payload.

If you are not able to achieve rated speed or higher at WOT, it means you are running on the torque curve, which if sustained can be detrimental to a marine engine. As the engine is designed and calibrated to run on the prop curve, this is where it performs best and where you can expect the most life. On the torque curve, firing pressures and temperatures can get much higher and continuous exposure will negatively impact engine life and durability. For these reasons, it is critical to ensure that your vessel is able to achieve rated engine speed at WOT under continuous operating conditions.

After the work is completed, the best way to make certain that you get the most out of your new engine is through a proper sea trial with your marine engine dealer. This testing process confirms that all the vessel systems are sized appropriately and meet the engine manufacturer’s guidelines. These guidelines have been developed over time with many hours of real world and lab testing to ensure the maximum life and performance of your engine.

All things considered, your specific needs and circumstances will determine the best repower solution. Your propulsion and generator engines are your livelihood. Take the time to ensure that you don’t miss an opportunity, and that you get the best return on your investment. Talk to your local dealer and distributor and weigh performance with short- and long-term expenses to determine which solution is right for you.

Adam Paull is a Senior Engineer of Marine & OEM Engine Programs for John Deere Power Systems.