Choosing Engines

The choice of engines was a bit confusing at first, as the 55hp standard engines offered by Outremer seemed a bit small. They also offer a 75hp engine as an option, so I had to do some research to determine which was best for us. We decided to go with Volvo D2-75hp engines for Wildling. Here’s why:

First of all, it’s great that Outremer is comfortable recommending 55hp engines for a 59 foot boat. This further confirms the performance of the 5X design, in that it can be effectively propelled by a 55hp power plant. Contrast this with our previous 47 foot Catana, which had 50hp Volvo engines, and that Catana is installing 110hp engines in their new 59 foot catamaran.

In order to make the decision, we had to determine the selection criteria that were important to us:

  1. Weight and hydrodynamic performance of the hulls – heavy and less efficient designs need larger engines
  2. Windage – larger hulls have more wind force against them and require more powerful engines
  3. Manufacturer and reliability of the engine model – For our purposes we considered Yanmar and Volvo and both normally aspirated and turbo-charged engine models
  4. Ease of maintenance
  5. Access to trained service technicians in our intended cruising grounds
  6. Weight of the engines
  7. Fuel efficiency
  8. Engine load / RPM at cruising speed
  9. Ability to handle extreme situations – overcoming high wind and current, handling difficult bar crossings, docking in windy conditions
Volvo D2-75

Volvo D2-75hp with Saildrive – We are installing two of these on Wildling


There are many opinions on which of the two major marine engine manufacturers is best. Some folks hate Volvo and swear by Yanmar and vice versa. We had Volvos on our last boat, and they were fine for us. They were pretty easy to work on and very reliable, although the cost of parts was high. When I talked with Outremer about the reasons they had chosen Volvo, it had to do with the level of after sales service and warranty repairs in the Mediterranean cruising area. They had some bad experiences with Yanmar, and have had much better service from Volvo, so that drove their choice. Since I didn’t have too much of a bias either way, I decided to stick with Outremer’s recommendation of Volvo.


When I did the test sail on the 5X Addiction, I was able to experience the performance of the Volvo D2-55hp engines that Outremer provides as standard. They did a fine job, and pushed the boat along at 8-9 knots at around 2200 rpm, with hardly any vibration from the 3 blade folding propellers. I’m sure that the 55hp option would be good enough in most cases, but I was a bit worried about how well they would do in more extreme conditions.

The 5X is a big boat, and when pushing into large seas, against high winds and strong currents, it felt to me that the extra power of the 75hp option would be a better choice. We also have some difficult bar crossings on the east coast of Australia, so having some extra power to keep in front of the breaking waves, when coming across the bars could give some safety margin. That was my assumption, but I had to study the performance data for each engine to validate it.


The big advantage of the 75hp Volvo engine is that it is actually the exact same engine as the 55hp, except it is fitted with a turbocharger, a more robust saildrive leg and a 4 blade (higher torque) propeller. This adds 20kg per engine, which isn’t much given the large increase in power and torque. From an operation and maintenance point of view there’s not really any difference between the two engines, so it comes down to the reliability of the turbocharger.


Based on the research I did, it seems that modern turbocharged diesel engines are very reliable. It’s also reassuring to know that each of the boats competing in the Volvo Ocean Race is equipped with a D2-75 Volvo engine as the sole source of power generation and emergency propulsion. Given the power benefits of the turbo it seems the extra complexity is worth the risk.


Because the D2-75 produces more power and torque at lower revs, it will be under a lot less stress than the D2-55, which will lead to less noise and vibration when running, and the ability to power larger alternators for rapidly recharging the lithium battery bank.

It’s a well known fact that running marine diesel engines at low load is not good for them, but in talking to the engine experts, I found that by keeping the engine high on the torque curve and at 1,800 rpm and above when running for extended periods, they will do fine.

Here are the performance curves for the two engines, which show a big difference in engine load under cruising conditions:

The Volvo D2-55 engine produces maximum torque at

The Volvo D2-55 engine produces 28hp and 135Nm of toque at 2,400 RPM, which is also the maximum RPM recommended by Volvo for continuous operation

 VOLVO D2-75 Performance curves

The addition of a turbocharger on the D2-75 provides a significant torque boost

The addition of a turbocharger on the D2-75 provides 35% more torque at much lower RPM, and a 25% power increase at maximum cruising revs

The D2-75 engine develops peak torque at 1,800 rpm. When fitted with a high torque, 4 blade folding propeller, this engine will provide the same level of performance as the D2-55 at much lower revs. This equates to less stress on the engine, less noise, less vibration, less heat and essentially the same fuel consumption as the D2-55. In addition to these benefits, the D2-75 has extra power available when needed in difficult conditions. All of these factors added up to the D2-75 being our preferred engine choice for the 5X.


The ideal location for engines on a catamaran from a performance and motion perspective is at the center of the vessel in each hull. This makes a big difference in the motion of the boat at sea. Less motion = higher efficiency = more speed (and comfort). The other great thing about placing the engines in the center, is that you can install a shaft drive instead of a saildrive.

The shaft drive system is more reliable and much easier to maintain than a saildrive

The shaft drive system is more reliable and much easier to maintain than a saildrive, but it requires that the engines are placed forward in the vessel to make room for the shaft.

Saildrives are complicated to maintain, as they require the boat to be pulled out of the water every one to two years to service the seals that prevent seawater entering the gear case. They will also corrode if careful attention isn’t paid to preventing electrolysis.

Saildrive on Outremer 49

Saildrive on an Outremer 51. The vertical drive leg allows the engines to be placed further towards the back of the vessel. Note the sacrificial skegs that protect the drive legs from impact. A nice safety feature!

When going over the 5X design with Outremer, we had a good deal of discussion about the engine placement and drives. They were quite willing to move the engines forward and install shaft drives for us, but in the end it came down to Robin’s decision!

The big compromise with shaft drives in Catamarans is the engines have to be mounted further forward, which places them either under the aft bunks or under the companionway floor. Compare this to the saildrive option which places the engines in nice, big engine rooms at the aft ends of the boat, that are completely isolated from the living areas.

Center mounted engines are great for perrformance, but are disruptive to life aboard the boat when the are being serviced.

Center mounted engines are great for performance, but are difficult to work on and disruptive to life aboard when they are being serviced.

Pulling our beds apart every time I need to work on the engines is a pain for me, and a non-starter for Robin! We were also concerned about the extra heat and diesel smells that are hard to avoid when the engines are located inside the living areas of the boat.

The 5X with saildrives locates the engines at the aft ends of the boat with lots of access. It's a compromise, but I think it's a good choice.

The 5X with saildrives locates the engines at the aft ends of the boat in dedicated engine rooms with plenty of access. It’s a compromise, but I think it’s a good choice.

12 thoughts on “Choosing Engines

    • It sure is cool! And since you helped me with the Volvo engines on Zangezi, you already know how to maintain these new ones! We just have to find our way around the new engine rooms, but that should be fun! 🙂

  1. Doug, did you ever consider something like this?
    I was doing some research on large cats and found your site and the moonwave gunboat site. Gunboats seem like overkill to me, but the 5x is well outside my price range as well. I’m just trying to find out how many moonwave systems are being installed or looked at/rejected.

    I look forward to following your blog on your 5x. I can at least fantasize about owning one in the future 🙂


    • Hi James, I did consider a hybrid drive system, and while I like the technology and approach, it turned out to not be a good fit for our needs on Wildling. I have three main issues with them:

      1. Weight – The hybrid systems require a diesel generator to provide autonomy, since the electric motors will only run a few hours on the propulsion battery. Although the motors weigh less than a diesel engine, when you add the generator, the weight goes up close to the diesel engine weight. Then you have to add the propulsion batteries, and then the solar array, which is 5 times the size and weight of the array we have on Wildling. The heavier array requires a heavier, redesigned davit system to carry it, so weight increases again. The result of all this, is that you get electric drives, but at best without any weight savings, and at worst, with a considerable weight increase.

      2. Complexity – Adding the additional diesel generator and charging systems, regen-propellers, solar panels, electrical distribution and control systems and electric motor cooling systems. Takes up storage on the boat, and adds a lot more maintenance and complexity over the simple Volvo engine and alternator setup that we will have on Wildling. When things go wrong, and they will, how do you troubleshoot them? Who will repair them in remote locations? How easy will it be to get spare parts?

      3. Performance – I would like to see a lot more data on the drag generated by the propellers in recharging mode before I would be comfortable installing a hybrid drive system on a performance cruising catamaran like the 5X.

      So for me, while I really do like the concept, I just can’t get comfortable with applying it onboard Wildling. Perhaps if we had a larger electrical budget, and were installing a generator anyway, it might be more appealing, but since that isn’t the case, I decided against hybrid electric drives.

  2. Hi Doug, Thanks for the detailed blog postings. I sail extensively in the West coast of France where there are huge tides. I note that the sail drives have a sacrificial skeg but if it possible for Outremers to take the ground on a flat beach or is that only going to be achieved with keels? Many thanks!

    • Hi Tom, Outremer designed the mini keels to provide protection for the saildrive legs and propellers, so they have made a trade off between protection and strength. The goal is for the keel to be destroyed without damaging the hull or the saildrive if you hit something, so they aren’t strong enough to take the weight of the boat. That said, the factory is very accommodating of custom requests when they build each boat, so if you needed reinforced keels they could maybe do that for you.

  3. Hi Doug,
    I did a bit of research on Electric Drives for Yachts, Serial Hybrid came out the worst in Cost, Weight, Reliability and Complexity, Parallel Hybrid is the better option for Yachts but none of these systems pay off unless they regenerate power! if they don’t do that you’re far better off sticking with Diesels and your Watt & Sea Hydro. No Electric systems suppliers are advertising regeneration facts and i know of many that have been disappointed with their ability to regenerate, one supplier (no brand names) showed a nice video of their unit making 400watts @6knots in a tank test, in the real world a guy was making just 60watts @7knts with the same unit! that video was interestingly pulled from the site, I’d say the Prop, motor and controller were optimized just for that test (smoke and mirrors), I have been personally told from a supplier not to get a particular brand as a customer they the sold to was so unimpressed he ripped them out and went back to Diesels! Problem is a Motor designed to propel will never regen to well, just like a Generator is designed to regen wont propel to well if at all? (watt & sea have two totally different types for Hydro and Propelling).
    I like you like the concept, but they need to start showing real regen figures, and real world results, I just haven’t seen that yet?

    • Hi Mal,
      Thanks for posting your research and thoughts on electric drives. I was at the multihull show in La Grande Motte, yesterday and looked at the latest E-Drive engines. They really are an awesome concept, but just not practical for a boat like ours. The best case right now is a big solar array and lithium battery bank and a generator to supplement as needed, so you would possibly burn less fuel over time, but it still doesn’t solve the weight, cost, complexity issues.

      • Nor the safety issue, i wouldn’t want an electric motor tripping out to protect itself when you need full power in a storm or emergency situation, that’s another reason i prefer Parallel Hybrid, but to save a bit of fuel you need to spend so much for the system, It doesn’t make economic scene, only do it i guess if you want to limit your dependence on fossil fuels and we already do that now, we sail:)

  4. Hi Doug,
    Thanks so much for the time and effort of making your fine videos! They are wonderfully instructive and will be a major help in the design and outfitting of our Royal Cape Catamaran e.g. with 110hp Volvo Penta V-drives as the very best powering compromise. The continuous line electric winch headsail furling system you have is fantastic, and we will try to reproduce.

    Rob C.

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