Fighting the Elements

by Web FishAug 15, 2012 @ 04:26pm

 

So what does a model boat crossing the Pacific ocean face? Short answer: A LOT! Here's a quick summary of the environment factor's we'll need to figure in when making the final decision on energy source(s), configuration and propulsion system:

  • Waves

If you've ever witnessed first-hand the power of ocean waves you'll agree that this is quite possibly the biggest challenge both from structural and navigational point of view. Structurally the vessel will have to withstand the dynamic loads associated with wave breaks. Even though waves usually break in shallow water near the coast, a wave break can occur anywhere where the amplitude is sufficient. This will add excess torsional and flexural loads (twisting and flexing) that we have to account for.

Another aspect of ocean waves on a small vessel (1 meter or less) is the rotational forces around the horizontal plane (flipping force). Unlike a larger vessel, a boat of this size will be very easy to flip during the course of a normal passage even by a medium size wave. Since pretty much every energy source we are considering above is strictly directional (available only above the water surface and only with the proper orientation of the harvesting element) maintaining the proper orientation for the boat will be critical. After all, a sail, wind turbine or solar panel will not do much good if they are submerged under the capsized hull. There are many self-righting designs (a very nice deep keel & asymmetrical deck solution by the SCOUT team here), almost all of them having one major limitation - being applicable to single hull vessels only. Solving the flip-over problem will be right at the top of the engineering tasks during the final configuration consideration.

  • Weather systems

The vessel will need to be designed to withstand any weather system it may encounter during the passage. In addition to significantly increasing the impact of the wave factors above, a special consideration will be needed for wind-based propulsion. A vessel rigging designed for 10 knots wind might exhibit some problems in a gale.

  • Corrosive effect of ocean water

Almost all model boats are designed for use in fresh water basins. In addition to the basic corrosive effect of the water itself, mixing metals with different electrode potentials (e.g. steel and zinc or copper) leads to accelerated galvanic corrosion.

  • Salt / hard water deposits on dry surfaces

This is mostly a solar panel issue - a thin film of salt deposits will significantly decrease the efficiency of the solar power harvest.

  • Biological deposits 

Barnacles are a threat to any size ship.

  • Small size biological / foreign objects in the water

In addition to the various sea weed species floating near the surface, there is (unfortunately!) an increasing amount of man-made debris circulating the world oceans. According to some studies, the amount of man made (mostly plastic) content in some spots of the Great North Pacific Garbage Patch exceeds up to 6 times the normal plankton in the same volume of water. While plastic bottles and (especially) fishing line might not present real danger for a 300 foot boat, they can be deadly for a model boat.

  • Large birds / fish / animals

Jaws anyone? 

  • Navigational obstacles

Land masses are fairly static and can (usually) be avoided with proper planning and navigation. Commercial and recreational ship traffic - not so much.

 

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