From the ground up the vessel design has been optimised for the use of outboard engines which is why so many of the vessel features and engineering functions centre around the outboard engine deployment. None the less we realise that some owners will consider that the specific advantages of inboard diesel engines outweigh those of outboard engines.
The diesel version has a semi tunnel hull that allows the propellers to effectively run with a reduced draft. The engines are located in the existing aft deck locker space inside a sound deadoning engine cover. There is still ample room for stowage of deck furniture.
Diesel engines are an additional cost option for the vessel. They will offer a fuel efficiency advantage over the standard outboard version and will be able to maintain a similar cruise speed for less horsepower. The factors influencing the choice of inboard diesel vs. outboard petrol are summarized below:
Parameter |
Outboard Petrol |
Inboard Diesel |
| Vessel Draft |
Best - At 600 millimeters the outboard wins. The boat is capable of exploring shallow areas with the leg just tilted in which case the vessel bottom will make contact first. |
The propeller runs partly in a tunnel cavity formed in the aft section of the hull in order to minimize the vessel draft. But even so, the draft is only increased by around 100 mm to 700 mm. |
| Cruising Range |
Around 1 liter per nautical mile at 8 knots. |
Better - Predicted to have a 15% improvement at a similar speed. |
| Battery Charging |
Outboards contribute about 25 amps each while running. Charge current is not sufficient to warrant running an outboard at anchor asa main charging source. Outboard vessels rely on solar energy or an auxiliary generator for battery charging. |
Alternative - Diesel engines may be fitted with high output alternators that make it feasible to run an engine at anchor in order to charge batteries. This can be a viable alternative to full solar charging in the case of the fly bridge vessel where solar panel area is more limited then the saloon version. |
| Hot Water Heating |
The outboard vessels are fitted heat pump hot water heating. |
Alternative - Waste engine heat can provide hot water heating however this is only the case if an associated engine has been recently run. |
| Initial Cost |
Best - The outboards are the most economical purchase option. |
Inboard diesels and the resulting engineering support add a significant cost to the vessel purchase price. |
| Engine Maintenance |
Best - Outboards typically come with a 5 year consumer warranty. Commercial operators can quickly change an engine if required. |
A diesel engine installation is far more complex in that it requires additional engineering for the exhaust system, propeller shaft and underwater rudders. |
| Propeller Maintenance |
Best - The outboard leg and propeller is completely clear of the water when moored. No antifouling is required. |
The propeller and drive gear must be anti fouled to stop marine growth. Periodic underwater cleaning will probably be required if the vessel is not used on a very regular basis. |
