Three Simple Rules For A Perfectly Trimmed Sub
Building a model submarine is not a project for the faint of heart, the impatient, or the untalented. There is a reason that you don't see these at every lake.
Building a model submarine is hard.
It is, honestly, a hobby reserved for the elite of the RC community. On top of the aesthetic building of the boat itself; the painting, the weathering and excruciating attention to detail, there is the functional aspect of making everything work. Access must be created for the interior of the boat. Concession must be made for the installation and removal of the watertight cylinder. Control surfaces must move freely and throughout their entire range of motion.
On top of this, there is the fact that everything must be waterproof. Not a drop of water can enter the hallowed sanctuary of your expensive and complicated electronics. Linkages seals must not only seal out the water, but allow free and unrestricted actuation of the linkages themselves. The main prop shaft seal must, likewise, keep out the water while allowing free rotation without binding.
Now, on top of all of this, there is another and potentially more important aspect to sub-building. That is the proper trimming of the sub.
An improperly trimmed boat will perform poorly, be difficult to operate, and could ultimately end up contributing to the complete loss of the boat at the bottom of some murky pond or lake.
On the flip side, a boat that is properly trimmed out can handle like a dream, offering up control that is intuitive, smooth, and safe.
Getting that proper state of trim is of vital importance and is the area of the build that more people struggle with than any other. It's like magic, science and art all rolled into one. People will try to trim out the boat only to have it mysteriously pitch over on its side or even upside down. It may sit perfectly when surfaced and on its nose when submerged. It might sit perfectly when submerged, but crash dive when suddenly slowing or applying reverse thrust.
Over time, I have developed what I like to call "Bob's 3 Rules" for trimming out a model submarine. If followed properly, with patience and dedication to detail, you'll end up with a well-trimmed boat that will be fun to operate.
Before we get into the rules, let's look at the two materials we use to trim out a model submarine.
The first material is lead (or other heavy weight). This comes in various forms, but the one that I like the most is lead pellets. You can put them in a plastic bag and massage them into almost any nook or cranny. Add some resin and you have a removable ballast weight that perfectly conforms to your hull. You can also use lead ingots, lead strips, fishing weights, bolts, nuts, or anything heavy and dense. Just make sure you use water-friendly material. The last thing you want it to have streaks of rust pooling in the bottom of your boat and streaming out the drain holes of your model.
The second material is foam, or more specifically, closed-cell construction foam. You can get this from any home hardware store and it usually comes in pink or blue sheets of varying thicknesses. It's easy to cut, easy to sand, it's cheap, and weighs virtually nothing. Be sure to use closed-cell foam that is rigid versus the pellet-style foam that is easy to compress. The reason for this is that water pressure is relentless and can crush your foam if you ever end up at greater depths, resulting in a loss of flotation, and potentially the death for your submarine.
With those materials in hand, let's check out the procedure that I use to trim out my boats:
RULE #1: Cylinder goes low: