Caribbean 27 Diesel

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Caribbean 27 Diesel
Caribbean 27 Diesel

The word classic is applied to all sorts of things that probably don’t deserve it. However, it is the term best suited for describing the design of Caribbean open series boats. In this era of organic flowing curves and moulded glass windscreens, Caribbean dayboats manage to unify modern technology and comfort with timeless style. You could fish from one of these but the real point is to wile away your weekend leisure hours in pleasant company over lunch and swimming. The Caribbean 27 is the company’s latest model designed for this very civilised approach to boating.

The extra foot in length over the 26 is not the only new thing about this boat. Twin petrol engines turning sterndrives has always been the approach to powering this size and type of Caribbean, but a company called Nautical Marine in Sorrento, Victoria, and one of its customers thought differently.

The Alpha One sterndrives are still in place but the motive power of the twin 220hp V6 MerCruiser MPI 4.3lt petrol engines for which these drives are the standard option has been replaced with a couple of 150hp Cummins MerCruiser QSD 2.0lt diesel engines. What makes engines with less than half the displacement and less power an excellent alternative to the bigger capacity originals? In a word — turbochargers.

The swept volume of the four-cylinder QSD diesel engines may be smaller than the V6 units but using turbochargers to cram extra air into the cylinders effectively increases their capacity and provides more torque for getting the boat up and going.

At the request of Nautical Marine, Mercury has been involved in the project right from the start and technical expertise has been one of its major contributions.

Mark Barrow from Mercury said, "The propeller makes or breaks a boat. We did extensive testing with a lot of different props to find exactly the right one for this boat/engine combination. The 19in ENERTIA version we finally settled on is actually a touch slower than another we tested, but it performed better everywhere else in the rev range of the new engines." We’d have to agree. The boat is as responsive as you’d expect from a boat in this class and even in the hard turns it never showed any sign of letting go.

The faster the propeller can be turned, the faster the top speed of the boat will be. Marine petrol engines rev faster than marine diesels, so they have higher top speeds and that’s the case here. But it’s not the whole story. With the propellers that were finally chosen, the diesel equipped boat is only about 10 to 12kmh slower than it was on petrol, which is pretty good for half the original engine capacity. So, what do you get for the mild sacrifice in top speed? One more word — economy.

Top revs for the diesels are 4100rpm (compared with 4800rpm for the V6 units). Turning the motors at these revs got the boat up to 24mph (58kmh). At that speed, fuel consumption was 31.8lt/h for each engine or 63.6lt/h for both engines. However, pulling the engines back to 3000rpm saw speed drop to 24mph (38.62kmh) while fuel consumption figures dropped to just 15lt per hour for each engine. Consuming 30lt/h in total means that the contents of the 550lt tank that comes with the Caribbean 27 lasts around 30 to 35 per cent longer than it would with the original petrol engines. Not only is that better for the budget, it will also increase range and the time between fills.

The advantages offered by Cummins MerCruiser turbocharged diesel engines might make you wonder why more aren’t fitted to boats like the Caribbean 27. It’s really a matter of perception.

Some people still think of diesels as clunky, oily, smelly and smoky but current generation diesels are nothing of the sort. The Cummins MerCruiser QSD four-valve common rail injected engines seen here are pretty quiet at 3000rpm and casual conversation wasn’t a problem anywhere in the boat. It’s not much noisier at 4100rpm either and that’s exactly what you want in a day cruiser like the Caribbean 27.

None of the other perceived diesel problems were present either. In fact, International Marine (makers of the Caribbean range and others) had technical staff present on the test day. One of the things they were checking for, with some pretty sophisticated equipment, was the presence of any smoke under fairly harsh conditions. Basically, the boat was run on one engine at a time at a range of throttle settings including WOT to see if any smoke was present. There wasn’t. Neither was there any odour. Really, you wouldn’t know what was pushing the boat if you weren’t told.

The boat is very nice to drive right from the beginning. A quick flick of the key and each engine starts instantly. This is because of the VIP (Vessel Integration Panel) management system controlling each engine but the installation contributes to the pleasure of using the boat too.

Jimmy Janssen, from Nautical Marine, says they were fussy with the details of the conversion. We asked for an example and he brought up cables. "Having large radius curves means that the cable will operate more smoothly allowing finer control over the engines. This is important for an owner trying to manoeuvre the boat at a busy ramp, even though it takes more cable", Janssen explained. And the boat does have good low-speed control and manoeuvrability. With one engine in reverse, it can actually turn in almost its own length at a ramp. Finer throttle control also allows the boat to come off plane more gradually.

Closer inspection of the installation reveals more attention to detail. For instance, a good deal of rewiring was also required for the job and along with the components to which it’s connected it’s been kept up high where it’s least likely to be affected by water.

Service items have been placed in positions allowing easy access where possible. Key modifications were made to the engine mounts to get the new diesels into exactly the right position to utilise the existing sterndrives. Says Jimmy: "We could have used adaptor plates to match the existing mounting positions to the engine mounts, but that’s sloppy. Instead, we remodelled the fibreglass mounting points in the hull for a more integrated finish." Also, many mounting areas for components like the engine control modules on the inner transom have also been reinforced and gelcoated for long-term strength and to resist cracking from vibration.

Fibreglass reinforcing has also been added to strengthen the fixing points for the new fuel system fittings. The fuel system itself had to be installed in strict accordance with Cummins instructions for the system to run correctly. Return fuel from the common rail system, for instance, can’t just be dropped back into the tank. The return line has to be in exactly the correct position to ensure that cool fuel is fed to the engine. This is important because the fuel has a cooling function within the system.

On the matter of heat, the inside of the transom had to be modified to deal with the heat of the turbochargers. The turbine housings have also been fitted with heat shields. After all the modifications were complete, the transom was completely re-fibreglassed to consolidate and reseal the work. If this isn’t done an owner may not notice for a few years, but after 10 years problems would start to show.

Although the companies involved weren’t exactly sure of what the performance differences between both types of engines would be in this application until they tried it, advanced calculations showed that it would work. If not, then they wouldn’t have pressed on with the job.

The technicalities are relatively straightforward for companies like Nautical and MerCruiser, it was just a matter of finding out how long it would take, what materials would be consumed and whether it would be commercially viable. Happily, it has proved to be. Keith Davis, owner of Nautical Marine, says, "In the end, the job wasn’t much more difficult than many of the other jobs we do. It just hadn’t been done before in this style of boat with these engines, that’s all."

This was a brand-new boat, however, the client wanted considerable custom work done. All of the seating layout and upholstery was to his requirements. Note that the operator’s seat has been removed and replaced with a bollard design. The teak flooring was also a customer specification. Keith explained that about half of the company’s customers want custom work like this with the remainder buying simply the basic boat. Pricing is yet to be finalised but it’s likely a basic boat with the diesel conversion would be in the region of $160,000. A fitout to this level might add $50,000 to the final bill.

Many people have had boats like this (Caribbeans and other types) for decades, having bought them new. Most quality makes still have sound hulls so refurbishing and repowering them is more economical than updating to a new boat, which is why many people are doing it. Repairing any damage, repainting, reupholstering, rewiring, replacing windscreens, bright-work, biminis etc, and repowering is certainly more time consuming than simply buying a new boat (provided it’s available) but it still works out cheaper. Reduced operating costs through diesel repowering will make boating in this league even less expensive.

Of course, the practicality of repowering with diesel engines depends on how much you use your boat. If you don’t have it out all that often the extra cost involved in fitting diesels over petrol engines may not be justified. But if you do use your boat frequently it may be the option for you.

If you’d like to know more about how to get one of these boats, or about repowering with diesel engines, phone Nautical Marine on (03) 5984 1666, email: or visit;;

Specifications - Caribbean 27 Diesel

Price as tested: Approx $200,000

22 degrees

2560kg (dry)


2 x Cummins MerCruiser QSD
Four-cylinder electronic turbo diesel w/ common rail injection
EPA Tier 2
Gear ratio:
Mercury ENERTIA 14 x 19in stainless steel three-blade


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