Portager's Light Weight Engine

[Portager]

I’ve been looking for weight savings on Portager, so I started with the main engine. Rhumb Runner needs 160 HP to do 12 knots on a millpond, so I added 20% margin which brought the total to 192 HP. I started with the Steyr marine diesel since it leads the industry in power to weight ratio. The primary reason for the Steyr engines light weight is the Monoblock engine. In the Monoblock engine the cylinder heads and the block are a single piece, so the head joint is eliminated, saving the weight of the head joint, which must be extremely stiff to maintain the head seal. Steyr also uses a high percentage of high strength to weight ratio alloys (i.e. aluminum alloys).

I wanted to do a comparison of the Steyr and Yanmar diesels, but Steyr rates maximum horsepower and Yanmar rates continuous horsepower. I couldn’t find Steyr’s continuous power, but I did find Yanmar’s maximum power and Yanmar’s continuous rating is 80% of their maximum, so I assumed the same ratio for the Steyr.

Comparing the Steyr 246 to the Yanmar 4LH-STE, the Steyr is an inline 6 cylinder while the Yanmar is a 4 cylinder. Displacement is 3.2 liters versus 3.455 or the Yanmar is 8% higher. Continuous power is 192 versus 190, or the Yanmar is 1% lower. Weight is 683 lbs versus 827 lbs, so the Steyr is 144 lbs lighter or 21% lighter.

Comparing the Steyr 246 to the Yanmar 6LPA-DTP, they are both 6 cylinders. Displacement is 3.2 liters versus 4.163 or the Yanmar is 30% higher. Continuous power is 192 versus 210, or the Yanmar is 8.4% higher. Weight is 683 lbs versus 837 lbs, so the Steyr is 154 lbs lighter or 22.5% lighter.

The weight savings of the Steyr is very attractive, but I wish it had a longer track record and better support world wide. I am also nervous of designing Portager around a single engine option. The good news is the Steyr is showing up in more and more boats, so it is only a matter of time.

Anybody have any suggestions of high or higher power to weight ratio engine alternatives or comments on Steyr?

Regards;
Mike Schooley