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## Submerge the Ship!

The initial problem to solve for all radio-controlled submarine projects is how to get a buoyant model submarine to submerge below the water and come back up under the control of an operator. Early hobby pioneers discovered two basic solutions to the problem: a submarine model can be built using either a Dynamic Diving System or a Static Diving System.

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A Dynamic Diving System is one where dynamic forces are used to overcome a models' buoyancy. These forces consist of a sufficient forward speed in combination with a set of hydroplanes (forward or aft). In much the same way an airplane's wing creates lift by moving forward through the air mass, as a submarine moves forward through water with sufficient speed, the hydroplanes create a force that pushes the model below the surface. As long as the force is sufficient to overcome the buoyancy of the boat it will remain submerged.

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There are both pros and cons to the dynamic system. Generally, a boat must make considerable speed to overcome its buoyancy. This can result in a less-than-scale looking dive. It also limits the ability to operate submerged at a slow speed. However, because of its inherently positive buoyant trim it has a built in failsafe in case of power loss. Once the forward motion ceases, the boat rises quickly to the surface, minimizing the possibility of loss of the model. It can be less expensive to build and maintain as well.

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A Static Diving System is one where a model submerges by changing its overall buoyancy. This occurs through the use of an onboard ballast system. As a result, a model can submerge when it is stationary and operate below the surface at any speed.

Static diving systems usually vary a boat's buoyancy through the displacement of water. The ballast system is built around a tank that contains a volume of air sufficient to float the boat. In order to submerge the boat, water is introduced into the tank. As the water fills the tank, the boat loses buoyancy to the point that it is negatively buoyant. In order to resurface, the water is then removed from the tank and replaced with air, making the boat positively buoyant again.

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Static diving systems are more mechanically complex than dynamic diving systems and thus require more maintenance. They usually require extra safety features to prevent loss of the model in case of power or system failure. Ballast systems have been successfully designed using a number of different mechanical means to vary buoyancy. See our ballast system curriculum to learn more.

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## Watertight Integrity

With the goal of getting a surface running model (or "target" in R/C sub parlance) to operate underwater, keeping liquid from harming sensitive equipment such as electronics and motors is a top priority. This is accomplished by using watertight compartments to house the R/C equipment and keep it dry. In model submarine construction there are two approaches to this task as well: Dry Hull Boats and Wet Hull Boats.

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Dry Hull Boats get their name from the fact that a major portion of the internal hull of the model is made watertight. Watertight hatches in the hull are used to service the internal equipment. With the hull completely dry the model becomes in essence a very large ballast tank. This requires a significant amount of ballast to get it to float at the proper waterline. As a result, dry hull boats are usually heavier than wet hull boats.

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As SC member Andy Lawrence recently observed, "Dry hulls are really a throwback to an era when batteries and radio equipment were physically much bulkier. In order to get sufficient space to house them the hull was made completely buoyant. These days, unless it's a small boat, a dry hull doesn't offer any advantage and you're just building something that will keep your chiropractor well employed."

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Many dry hull proponents use a watertight bayonet ring to secure the stern section to the boat. This makes for a virtually seamless hull form. All the internal gear is mounted on a long "tech rack" which is mounted to the stern and slid forward into the hull. This method was perfected by modelers in Europe and performs quite well. Model kits from Alexander Engel utilize dry hull construction to great effect.

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Wet Hull Boats are so named because their hulls are free flooding. Watertight compartments are either built into the hull itself or designed as a removable unit to minimize space. The vast majority of these removable watertight units are built from a clear Lexan cylinder and are thus termed Watertight Cylinders or "WTC" for short. Since the mid 1990s, when reliable WTCs became commercially available, permanent watertight compartments in wet hull boats have decreased significantly.

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Today, the WTC has become a ubiquitous part of the North American R/C sub scene. WTCs are manufactured by several different vendors and component pieces can be purchased to construct custom units.

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Dynamic or Static, Wet Hull or Dry, R/C submarines offer modeling challenges to meet any taste or skill level with each approach leading to successful operations.

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