Difference between revisions of "Design Features"
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Many designs for ocean going structures exists, and many have been suggested for the explicit purpose of seasteading. There is significant overlap between these different designs: often, these differences can be viewed as mere variations along a continuous spectrum of some parameter. | Many designs for ocean going structures exists, and many have been suggested for the explicit purpose of seasteading. There is significant overlap between these different designs: often, these differences can be viewed as mere variations along a continuous spectrum of some parameter. | ||
| − | This section is an attempt at identifying the main features or characteristics a design might | + | |
| + | This section is an attempt at identifying the main features or characteristics a design might employ to meet the challenges of providing a safe and comfortable piece of real-estate. In this way, we can look at seastead concepts in a more systematic way, avoid reinventing the wheel, and quickly get a qualitative feel for the properties of a given design. Not all designs can be perfectly categorized in such a way, but it creates some order in the chaos nonetheless. | ||
==Minimize waterplane area== | ==Minimize waterplane area== | ||
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* Rationale: minimize interactions with the waves. | * Rationale: minimize interactions with the waves. | ||
* Implications: Floating vessel derive their stable position on the water from the fact that moving them up and down changes the volume of displaced water. If there is little waterplane area, this coupling is weak. This means the waves will have relatively little effect. On the other hand, the total flotation has to come from somewhere; as can be seen from any of the examples, this implies that the flotation is located somewhere below the waterline. This necessarily implies a medium to high draft, which has significant drawbacks (see: Design requirements/incrementalism/draft). Roll-stability can derive from any source; through the use of very deepb allast (FLIP, Spar), or wide footprint (semi-sub), or a combination of both (clubstead) | * Implications: Floating vessel derive their stable position on the water from the fact that moving them up and down changes the volume of displaced water. If there is little waterplane area, this coupling is weak. This means the waves will have relatively little effect. On the other hand, the total flotation has to come from somewhere; as can be seen from any of the examples, this implies that the flotation is located somewhere below the waterline. This necessarily implies a medium to high draft, which has significant drawbacks (see: Design requirements/incrementalism/draft). Roll-stability can derive from any source; through the use of very deepb allast (FLIP, Spar), or wide footprint (semi-sub), or a combination of both (clubstead) | ||
| − | * | + | * Drawbacks: |
| + | ** Only works up to a given waveheight. How big of an air-gap do you design for? Being relatively unaffected by waves up to 10m is great; but how will you handle the 5m of a 15m wave that will hit your platform? | ||
| + | ** Poorly compatible with small scale designs | ||
| + | |||
| + | ==Big Footprint== | ||
| + | * Examples: cruiseship, clubstead, pontoon | ||
| + | * Rationale: increased stability by averaging out wave effects over a long span | ||
| + | * Discussion: 'being big' is the proven method for increasing stability out on the ocean. There are two attractive aspects to having a big footprint, pertaining to roll and heave. | ||
| + | ** With respect to roll: a wider structure has a more favorable metacentric height: any attempt to roll it over results in a large restoring force, which leads to smaller rolling motions. | ||
| + | ** With respect to heave: the upward forcing effect of the water and its waves is averaged out over a larger area, meaning the net heaving force | ||
| + | * Drawbacks: | ||
| + | ** A big footprint implies a big structure. In order for size to start to matter against oceanic waves, quite some size is needed. 20m is still small in ocean waves. Compare the roll and pitch motions of a ship; because of its elongated shape, it would much sooner roll than pitch. | ||
| + | ** Bigger means more fragile. The bigger a structure is, the bigger forces it can bring down upon itself. Driftwood doesnt break in a storm; boats do. Big boats need to get out of the way in big storms, or they run a risk of catastrophic damage (reference miguels presentation). | ||
Revision as of 18:18, 14 October 2009
Seastead design features
Many designs for ocean going structures exists, and many have been suggested for the explicit purpose of seasteading. There is significant overlap between these different designs: often, these differences can be viewed as mere variations along a continuous spectrum of some parameter.
This section is an attempt at identifying the main features or characteristics a design might employ to meet the challenges of providing a safe and comfortable piece of real-estate. In this way, we can look at seastead concepts in a more systematic way, avoid reinventing the wheel, and quickly get a qualitative feel for the properties of a given design. Not all designs can be perfectly categorized in such a way, but it creates some order in the chaos nonetheless.
Minimize waterplane area
- Examples: spar platforms, semisubmersibles, clubstead, FLIP
- Rationale: minimize interactions with the waves.
- Implications: Floating vessel derive their stable position on the water from the fact that moving them up and down changes the volume of displaced water. If there is little waterplane area, this coupling is weak. This means the waves will have relatively little effect. On the other hand, the total flotation has to come from somewhere; as can be seen from any of the examples, this implies that the flotation is located somewhere below the waterline. This necessarily implies a medium to high draft, which has significant drawbacks (see: Design requirements/incrementalism/draft). Roll-stability can derive from any source; through the use of very deepb allast (FLIP, Spar), or wide footprint (semi-sub), or a combination of both (clubstead)
- Drawbacks:
- Only works up to a given waveheight. How big of an air-gap do you design for? Being relatively unaffected by waves up to 10m is great; but how will you handle the 5m of a 15m wave that will hit your platform?
- Poorly compatible with small scale designs
Big Footprint
- Examples: cruiseship, clubstead, pontoon
- Rationale: increased stability by averaging out wave effects over a long span
- Discussion: 'being big' is the proven method for increasing stability out on the ocean. There are two attractive aspects to having a big footprint, pertaining to roll and heave.
- With respect to roll: a wider structure has a more favorable metacentric height: any attempt to roll it over results in a large restoring force, which leads to smaller rolling motions.
- With respect to heave: the upward forcing effect of the water and its waves is averaged out over a larger area, meaning the net heaving force
- Drawbacks:
- A big footprint implies a big structure. In order for size to start to matter against oceanic waves, quite some size is needed. 20m is still small in ocean waves. Compare the roll and pitch motions of a ship; because of its elongated shape, it would much sooner roll than pitch.
- Bigger means more fragile. The bigger a structure is, the bigger forces it can bring down upon itself. Driftwood doesnt break in a storm; boats do. Big boats need to get out of the way in big storms, or they run a risk of catastrophic damage (reference miguels presentation).
