Extreme Waves and Ship Design


Extreme Waves and Ship Design
Craig B. Smith
Dockside Consultants, Inc.
Balboa, California, USA


(Kim Cowdroy) #2

The document gives a good account of probability of Extreme Waves, though it is aimed at improving the design of ships in order to be able to survive such waves, noting weak elements such as hatch covers. Some good historic accounts are given.

As far as seasteading is concerned, the formula of height in relation to significant wave height (Hs), which is defined as the average of the highest one-third of the wave heights, is the most useful ie

H (Extreme) = 2.3 x Hs

Other literature gives the minimum to be defined as an Extreme Wave as 2 or 2.2 times and the maximum as 2.4 times. So, for a particular area of sea, need to get the biggest significant wave heights that can be expected, to then get the worst case Extreme Wave.

Note the shape of the wave is very steep, and typically with a large trough before or after, which adds to the problem. Not mentioned is the crest is usually higher above water level than the trough is below. So for those designing a seastead, where platform or hull height is to be above the crest of an Extreme Wave, then the height needs to be more than half the estimated Extreme Wave height.

Note there are at least four main ways in which extreme waves can be produced:

  1. the interaction of strong currents with storm waves moving in the opposite direction eg east of South Africa;
  2. gales and storms ie when significant waves are largest;
  3. pile-up of waves in shallow depths eg along the continental shelves.
  4. constructive interference (superposition) of random waves.

Possible to largely avoid the first three. Cannot avoid the fourth!

(Wilfried Ellmer) #3

Cannot avoid - can not predict - that is the baseline after Draupner - the nonlinear wave model (Schroedinger) is on.

| conclusions | postulates |
  • Traditional wave height prediction models (which predicted maximum wave heights of 15m) are obsolete.

  • This puts the new stake for a minimum size of a safe “seawall style breakwater” extremly high. (was 15m is now 40m)

  • Spar type living space can still be impacted by waves when 40m above the watersurface

  • A bow and a turret mooring as in the Prelude concept can be considered a reasonable wave defence

Small floating real estate development with bow and turret mooring capeable to deal with extreme waves.

Concept: “The real estate in itself is the bow and the breakwater”

Artist: Matias Volco

Building concepts for seasteads: / Lens shell pictures overview / / Ramform floating home pictures / / c-shell floating home pictures / / Floating concrete building methods / / shell cluster pictures / / investor proposal list /

Development Axes for Seasteads:

Axes of ocean colonization: | Main Axes | Plate Seastead | Floating Real Estate | Catamaran concept | Captain Nemo Concept | Floating Breakwater Concept | Submerged Living Space Bubble Concept |

Surface concepts need to deal with the waves, tail events and their dynamic forces somehow - submerged concepts can be built for a much more predictible environment…

Concrete Floating Structures

Surface Floating Concepts:

The axes of ocean colonization / floating real estate building lots on the water / Plate Seastead - Plate Floating Element for Ocean Colonization / Catamaran Concrete Floating Elements - Base for Ocean Living / Floating Concrete Breakwater Marina / Ocean colonization how to get there / Ramform ship island as ocean base mobile stable scaleable / small honeycomb floating concrete structures in cartagena / Seabreaks for dampening colossal ocean waves / Ocean colonization technology / Ocean colonization company / Oustanding floating concrete structures / ocean colonization general considerations / Interesting projects for ocean colonization / Aquaculture, business, trade, mininig, energy, salvage, making money afloat /

Submerged Concepts:

The captain nemo float out - seasteading / Sub movement finished - Submarine Yacht / Is submarine living space expensive? / concrete pressure vessel / Concrete submarine project / submarine yacht / concrete submarine yacht supporter club / Submerged living space bubble concept basics / Exotic Submerged Bubble Hotel / sea orbiter / Current Turbine Concrete Hull /

Breakaway Civilization | Seasteading | Ocean Colonization | Advanced Oceanic Cities | Atlantis | Enlightenment | Oceanic Business Alliance | next big thing in business

Wave pattern analysis has proven that they can be predicted. The mass of one Extreme wave is roughly that of 2 waves, which are colliding and coalescing to create the large extreme wave.

The R.O.P.E. (Reduced Order Prediction of Extremes) method of prediction shows that the event and location can be predicted, given the correct inputs.


However, the purpose of the original article is that by generating the appropriate data for known events in a specific area, then vessels can be designed to deal with that energy and mass.

As was noted, by and large, the worst damage doesn’t come from the impact, as it does from the resulting greenwater, atop the vessel. The sheer mass needs to be shed as quickly as possible, which is a design requirement, but the structure has to withstand that mass, in the process, which is how vessel design must be developed, in order to withstand these events, to provide up-to-date engineering standards for construction.

Early detection of rogue waves in a chaotic wave field

(Kim Cowdroy) #5

In some sea locations, it would be necessary to consider the effect of a 30 metre or bigger rogue wave on the seastead.
Such very large waves would only occur in severe storm conditions in most locations. In such cases it would be expected people would be inside hurricane-proof conditions (or the vessel is sailed out of the way). The seastead still has to survive though.

However consider the tropics between 5 degrees N and 5 degrees S. In this case the mean significant wave height is mostly 2 metres or less. Also there are almost no recorded intense storms in this zone, so the maximum significant wave height is perhaps less than three times the mean, say 6 metres.

We can then say that the most Extreme Wave will be less than 2.4 times this ie less than 15 metres.

So depending on the seastead design, the absolute maximum height of the platform or hull in the tropics is 15 metres and should be much less than this if we can allow for the trough eg less than 12 metres.


Let’s not forget that Ivan tossed a record 90ft trough-to-peak and 600 ft long wave into the mix, in the GoM

(Kim Cowdroy) #7

I concur that If there are wave prediction instruments available, as suggested could be built, based on the Early Detection of Rogue Wave papers, then this would have a very significant effect on safety and size of the seastead.

One of the worst situations would be getting a rogue wave by surprise, particularly in relatively calm conditions, and washing someone overboard without warning.

A 30 second plus warning on a small seastead would give time to react in most situations. And it says the warning may even be a few minutes.


Like they say in real-estate and business: Location-location-location. IF you can predict the normal presence of rogue-wave forming conditions, avoid those places like the plague.

Personally, I was considering the zone off the Mississippi River Delta, until I started reading on how opposing currents and strong winds tend to create rogue waves… That’s where the Gulg loop and the Mississippi River collide and in hurricane-alley… Instant No-go.

Tip of the cap to @ellmer, but I plan NOT to be a submersible, however structure for submersion amounting to may predictable rogue-wave-heights. Whatever potentially goes OVER my hull, I plan to withstand as if submerged.


@Cowboy and @JL_Frusha, Indeed rogue waves are common here in Oregon where the nations 3rd largest river outflows to the pacific. The Columbia outlet is five-miles wide, and affects riptides and currents up to 200 miles north and south.

What is important is that rogue waves have a specific size; they are 2.3 times the height of the mean wave at that time, and less than 2-times the mass (i.e. they are tall and narrow). So that means the key building consideration is to know the mean waves of the proposed building location. In Key West, for instance, a rogue wave of 6-feet is pretty manageable, because the mean waves are only 2.5 feet tall.

All of this suggests what we know. A baystead in a non-hurricane zone is safer than being on the open ocean and/or in a hurricane/typhoon zone.

The document does suggest a building spec; take the tallest mean waves for a given zone in a 10-year or 100-year scenario, build to withstand 3-times that height, although for 2-times the mass. That’s not an unreasonable engineering standard.


The problem is that the mean-height in a storm is far different than on a calm day. For the structure to withstand the rogue waves in a storm, rather than a rogue wave on a calm day, is more to the point.

Say someone built for that 6 ft calm-weather rogue, then got hit with the 90 ft rogue from Ivan. This is a serious issue. Underestimating the forces of nature inevitable end with death and destruction.

My personal idea is to design the structure, but leave for the event. I plan to be permanently moored in the GoM. I was considering Oregon, but between Fukushima and the on-going red-tide, it’s not worth that battle, for me. I was working with several universities in the Pac NW, including Canada, when I became aware of the red-tide issue and its’ relation to the blob.

Since I am planning for the GoM, I need to be structured for hurricane alley. Not stupid enough to want to ride-out a hurricane, but I intend for the structure to withstand it, while me and mine are safely ashore, in a shelter.

To that end, I need my design to be strong, and to shed water. no horizontal hatches on deck, no hatchways facing the bow, and some very expensive, strong glazing.

In addition, I expect to use an active ballast-damping system, which can also be manually loaded for a bow-high attitude, to help cope with oncoming waves, as well as a passive design that is resistant to being overturned, and has an effective heave-plate structure.

Once prepped for the oncoming storm, simply evacuate, like the offshore rigs do, and return once the storm passes. Leave recording systems on and see what happens. As I gather more info, I will know what storms I can ride-out and which ones to avoid. no sense in being a loose egg inside and splattering myself on the walls…

Just found this…


“Big waves along Washington’s coast. High energy The Pacific Northwest coast has one of the highest wave energy levels in the world. Wave heights on average are large…”

(Paul Weathers) #11

Has anybody talked about the Gulf or California or the Big Bend area of Florida a little south of Apalachee Bay?


there are problems everywhere, one way, or another. i’m specifically aiming for the Gulf of Mexico, either within, Texas State waters, or possibly beyond that into the US waters (Contrary to popular belief, Texas waters do not extend to the full US distance, though Texas has a considerably wider reach than other coastal states). That will be dependent upon laws and regulations, as well as USACE and USCG regulations and requirements. However, that puts me in hurricane alley, which is why I started this topic.

Areas less affected by cyclones, typhoons, and hurricanes have their own special requirements, as well. Alaska and the Pac NW have severe wave conditions and storms equivalent to smaller hurricanes.

Take a look at any specific area that interests you, and begin studying, before you are fully committed to it. I was aiming for the Southern Oregon coast, but between Fukushima, oil spills, the blob, red tide, rogue waves, and earthquakes, I decided I’d rather not…

The GoM still has oil-spills, but has hurricanes, as well. There won’t actually BE a perfect place, anywhere. What problems are you willing to deal with? THAT is your starting point.

(Paul Weathers) #13

Texas does have a lot of intercoastal and barrier island areas that could be an attractive starting point. These areas would be easy to evacuate in case of a hurricane.

(system) closed #14

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