As with everything, if an extreme is required in one area than a compromise has to made somewhere else. If speed is the key requirement does a compromise have to made on endurance?
For some years I have been working on a design concept called “Endurance” and, no surprise, it is a design study in creating the ultimate yacht as far as endurance is concerned. She is big and spacious in order to provide all the things necessary for long term and independent cruising or standing by. Simple enough? Not really….
Her proportions developed from the design brief “to accommodate 12 guests in comfort for 90 days”. Space is probably the greatest requirement to accommodating endurance. Space for machinery, for victuals, fuel, spares, equipment, training. In addition to this, space for privacy is at the top of the list, so that after 90 days confined on board everyone is still friends! To be able to tick all these boxes the concept grew and grew, the result of the study shows a very large sailing yacht. The sails are necessary to reduce fuel consumption and not as the primary means of propulsion, it also lends the project a “green” aspect.
Having completed the design for one of the two options I thought it would make sense to take a look at the other, speed.
This turns out to be a lot harder because when we go for the extreme in speed then actually there is no space for the yacht aspects anymore. You just end up with a vessel large enough to keep some very big engines afloat and not much more. In order to make a realistic comparison I used a common design brief, to accommodate 12 guests in comfort at 40 knots.
Of course it is possible to design a vessel so long and powerful that a she could attain the required speed without the need for a “planing” hull but I wasn’t designing the second SS “United States”! Really what I needed to do was make them both the same volume to see where all the resources go (machinery, victuals, fuel, spares, equipment and privacy)
Some way into the design it became apparent that at 40 knots the bar is set high. The main engine plant becomes very large. A big part of the required volume for the propulsion machinery is the air handling capacity necessary to keep those big engines supplied with air. Also the exhaust system necessary to reduce noise and temperatures is taking up large chunks of volume. The quantity of fuel carried is not so much different but of course project “Speed” eats through it a lot quicker.
Noise and vibration control becomes a big topic with such large engines transmitting power down shafts to large propellers.
In terms of engineering, the difference is in the type and scale of engineering each vessel requires but there is not much difference in complexity. Significant space is taken up with accommodating large propulsion units and everything that involves. This takes up far more space than extra stores and cool rooms needed for those 90 days endurance.
However, to keep the experiment relevant we have to keep the overall volume of both vessels the same. After the power plant is installed the space left over that we can allocate to accommodation is greatly reduced on “Speed”, perhaps by some 30%.
Perhaps in the end, the trade off is actually between speed and privacy.