Repowering Considerations

As time and miles pass, even the best-built and best-equipped cruising boats succumb to wear. Onboard equipment like rigging, sails, pumps, and other gear eventually require renewal. Unfortunately, there also comes a time when the auxiliary engine may need replacement as well. 

Although most small, well-cared-for diesels can have an average lifespan of around 10,000 hours, there may come a time to think about replacement prior to that. Not all motors have been well cared for through their lives. Rust, corrosion, poor maintenance and general abuse can shorten an engine’s life. As years pass, replacement parts can become harder and harder to source as well. Even the biggest manufacturers will not continue to produce replacement parts forever. This can result in even simple repairs becoming difficult and expensive. 

For many sailors, there comes the day that an engine replacement makes sense. Deciding on a new diesel, however, is not without its challenges. There are myriad considerations when thinking about a replacement engine. Size, horsepower, weight, and serviceability are all important elements. Brand alone should not be a limiting factor but has to be considered as well. Most dealers will want to sell you the engine brand they carry, which may or may not be the best fit for your boat. 

Before beginning the search for a new diesel, think about what things are important to your needs. Many older boats were often built with smaller engines than would be considered in today’s boats. Smaller engines were less expensive, keeping the build cost of the boat down. Also 20 to 30 years ago, the horsepower-to-weight ratios were lower. If you’ve decided on a replacement, it may be a good time to consider adding some additional horsepower to your vessel. Not only will you have reserve power, but you will also have the power to drive accessories such as high output alternators, watermakers, and refrigerators. The trick is not to add too much horsepower or you will be wasting money on power that cannot be used. Keep in mind displacement hulls have limits and adding more HP may not always be beneficial. Generally, I don’t suggest increasing more than 10 horsepower or so as any more will be wasted. Keep in mind most diesels like to be run at approximately 80% load for peak efficacy.

Size matters and not just in horsepower but in physical dimensions as well. Many boat builders are loath to provide space for the engine as this takes away space for living accommodations. Like it or not, builders often cram the engine into a tight location. This often can limit options when looking at replacement units. The good news is many modern diesels are smaller and lighter than what you may be replacing for a given horsepower. It is often possible to increase horsepower while at the same time reducing weight and overall size. Almost all engine manufacturers will have engine drawings with full dimensions available online to help with finding a good fit for your application. If you are planning on additional bolt-on equipment, then you will need room for that as well. 

 

Engine mounts
Along with basic length and width, particular attention should be paid to the engine mount pattern and how this will fit with your existing installation. Although engine beds can be modified, this adds to the expense and complication of an installation. Poorly modified mounts can create problems and make an otherwise good installation a disaster. If possible, try to get a drawing for your existing engine to compare that to the drawing of new units under consideration. Don’t forget to pay attention to the shaft coupling position as this can alter not only forward and aft positions but height up and down as well. Even if the new engine appears to be a perfect fit, if the shaft does not align with the existing coupling it could be hard to modify. 

Pay attention to serviceability of a new engine as well. Few sailboat engine compartments have the luxury of full 360 access. Make sure the unit will have the service parts such as oil filters, raw water pumps, and fuel system parts in a location where they can easily be reached for service. In some cases new access panels can be installed in the boat but this may not always be an option. Again, the engine drawings can be very helpful in planning this out, especially any bolt-on options and how they will be serviced. 

Other important areas to consider are the systems associated with the engine. This is particularly true if you are increasing horsepower. Many newer engines will be turbo charged. This means you will need more air into the engine compartment and more exhaust out. Exhaust is very important and often overlooked. Back pressure on any engine exhaust will reduce the engine’s efficiency but this is particularly important with turbocharging. Many older boats had poorly designed exhaust systems to start with, so do not assume the existing system will work with a new motor. Follow the engine manufacturer’s recommendations. A poor exhaust system could even void a new engine warranty, so care and planning are needed. Good airflow into the engine compartment is also lacking in many older installations and can also be a bit challenging to achieve. Large vents and hoses are not always easy to set up on a sailboat but will help with engine performance and keeping the engine compartment generally cooler as well. 

 

Transmission questions
Your boat’s transmission is another critical thing to think about. It may or may not be possible to use the existing transmission. It makes sense that if the motor is worn out, the transmission is likely to be close to the end of its life too. This might be the time to replace that as well. Most small engines come as a package with a transmission already installed. Make sure the reduction ratio is correct for the application. If increasing horsepower, it may be necessary to increase the propeller shaft and propeller size. This can add significantly to the overall cost of the upgrade. In some cases this may not be physically possible due to the vessel design. For many boats, increasing the propeller size can be limited due to tip clearance from the bottom of the hull. In some boats it may be impossible or cost-prohibitive due to the size and position of the shaft tube in the hull. Again, adding more horsepower may not do any good if the drive train cannot take advantage of that additional power. 

If you plan to replace an engine with a saildrive, you may be a bit more limited as to brand and engine size. It may be possible to match a different brand engine to an existing saildrive, but it is best to check this carefully. Volvo Penta will match their engines to their saildrives as well as a few Yanmar saildrives. Beta Marine can match both Volvo and Yanmar saildrives in addition to those made by Twin Disc. 

Other things to consider are the raw water supply and electrical supply. Generally, it’s not hard to increase the raw water flow to an engine, but that can increase the cost as a larger thru hull and intake strainer may be required. A larger engine may require a bit more cranking power with larger conductors. Some newer engines may have electronic controls and computers or ECMs. These units require a good power supply and can be damaged if not properly wired. It is also a good idea to have an engine-dedicated battery and electrical system separate from the boat’s electrical system.

 

Major players
Selecting an engine brand often boils down more to what best suites your needs and the dealer network depending on where you plan on cruising. The three major players in the small sailboat auxiliary engine market are Beta Marine, Yanmar, and Volvo Penta. Beta Marine and Volvo base their engines on Kubota blocks that they then marinize. Yanmar uses its own blocks. Volvo Penta uses engines essentially marinized by Perkins and sold with the Volvo color and brand name. All three are good companies with large dealer networks. Yanmar may have the largest worldwide dealer network with Volvo a close second followed by Beta Marine. There are some other players such as Westerbeke/Universal and Nanni Diesel. These are a bit more limited. Westerbeke/Universal is a good brand that focuses more on smaller engines and direct replacements for the old Universal Atomic 4 gas engine. Nanni Diesel is a large company but best known in Europe and does not have a broad market here in the US yet. Like the other companies, it also uses Kubota blocks for most of its small motors. 

Beta Marine US is best known for replacement engines rather than new OEM motors. Beta’s engines are marinized in the UK by Beta Marine UK. It developed the replacement market many years ago and has been a reliable source of aftermarket engines with a good customer service department. Beta may not be the least expensive option, but it offers services other companies do not, such as custom equipment mounts and custom motor mounts. For an additional fee, a customer can provide dimensions of existing engine beds and shaft placement and Beta Marine will make mounts to fit. This can save a lot of time and provide for a better installation. Beta Marine uses several different transmissions and can supply several brands or match an existing transmission. This adds more flexibility to your choices. 

Yanmar is one of the few companies to use its own blocks for all its engines. Many of its small engines are direct replacements for its older units, which can save a lot of work. Its smaller engines are designed for tractors and industrial use and have been marinized for marine use. Yanmar is one of the first companies to have a small auxiliary that uses the newer common rail technology. It now offers engines 40 HP and up using common rail fuel injection. Common rail can increase efficiency and help reduce emissions. The drawback to common rail is that these systems are not as easy to service and are not generally user serviceable. Yanmar also uses its own Kanzaki transmissions and saildrives, making them a true one stop shop for engine service and parts. 

Volvo Penta has been around for a long time and has a strong dealer network throughout the world. Many of its engines can be a direct drop-in replacement for its older motors, making them a good choice should you be replacing an older Volvo. Most of its smaller engines use a Kubota block which is marinized by Perkins. Volvo also uses its own transmissions and saildrives, making parts and service sourcing straightforward. 

 

Seeking out a pro
Most engine replacements are not going to be a do-it-yourself job. Selecting a yard or technician to do the work can be as important as selecting the right engine. If you have a mechanic you have worked with before and feel comfortable with, this might be your best option. Otherwise, it is best to get feedback from previous customers. Many mechanics will push to sell the engine they are a dealer for, even if that may not be best for your needs. It pays to do your own research and at least know the important questions to ask when talking to mechanics. Even the best engine will not operate correctly if poorly installed. 

When selecting a mechanic or yard, make sure they have all the skills and equipment needed to do the job. An engine replacement can require not just mechanical skills but electrical, plumbing and in some cases fiberglass skills. If possible, get references and try to see some of the work they have done.  

Finally, don’t forget that when the old engine is out is a great time to clean up and paint the engine compartment. You might also want to consider replacing other old components such as water heaters, old wiring, and possibly even fuel tanks that could not otherwise be easily accessed with the engine in place. If the engine compartment is not painted but has a factory gel coat finish, I strongly recommend freshening up with a new coat of gelcoat rather than paint. Gelcoat is more resistant to heat and chemicals and is easy to clean where paint can chip and peel with time. Either way, a new clean engine compartment will complement the new motor. 

As you can see, there is more to selecting a replacement engine than simply selecting brand and horsepower. Any motor replacement is not going to be inexpensive but will add value to your vessel as well as giving peace of mind when the power is needed most. Careful selection and a good installation will save money in the long run and keep the older boat sailing on for many years.  n

Contributing editor Wayne Canning is a surveyor and a marine writer based in Florida. 

Categories: Engines and Propulsion