Fancy building a sub' without the expense and commitment? Glynn Guest shows the way – FREE PLAN!
Most areas of human activity have some ultimate challenge that if not impossible, is going to be very hard to achieve. That is, until someone succeeds and it soon becomes unremarkable, if not commonplace. Two examples of this are the four-minute mile and supersonic flight, both once considered difficult but now hardly worth mentioning. Our hobby is probably no different and many ultimate types of models have slipped into the commonplace zone, often with ‘Ready to Run’ (RTR) commercial examples now available at modest prices. I can recall when R/C helicopters were a pipedream, but now you can find them on supermarket shelves. However, there is still one type of R/C model boat that, whilst not unknown, is often considered to be too complicated or difficult for the likes of us average modellers, and that is a working submarine.
Why don’t more people try building an R/C submarine? There are several possible reasons for this, the obvious ones being that they have never tried to build one before and are put off by the tales of them being very complicated, expensive and risky to operate. True, some people, even if they've never attempted to build an R/C submarine, will regale you with tales of the vast amounts of money and time needed with these models, plus, if that were not enough, you have to be a modelling genius to achieve success. Certainly, lots of commercial items can be bought to achieve what a purist would consider to be a proper working model of a submarine. That is, one capable of static diving which involves changing the density of the model, usually with ballast tanks. Likewise, maintaining a level trim when running submerged can be automated. All of this costs money, unless you want to design and fabricate everything yourself which will cost more time and, unless your initial designs are perfect, probably even more money. After all that, you're going to drop your model in the water and watch it sink from view, a worrying thought at the best of times. So, you have to fit some sort of fail-safe device that should resurface the craft in event of problems, but even that might not be enough if your pride and joy encounters something like a supermarket trolley when underwater. When you start to consider all this it's no wonder why we see so few R/C submarines at the pondside.
I've often been accused of never going that extra distance to produce a perfect result, but for me it is more an appreciation of the law of ‘diminishing returns’, i.e. the more you approach perfection, the more expensive and difficult it becomes, usually in an exponential fashion. My philosophy is to settle for an adequate job that works reliably and effectively. In terms of our hobby I might not be using all the whistles and bells that are available, but I still get a lot of relaxing fun. The 80/20 term particularly relates to 80% effort and 20% cost. I’ll admit the percentages will vary from model to model, but within this ballpark is still good enough for me.
Applying this 80/20 approach to building a submarine means that all the complex stuff has to go. Nixie contains no ballast tanks or automatic depth controls, just the standard items found in R/C surface models. Likewise, its construction, whilst having to make a watertight container for the R/C equipment, is nothing that the average modeller should not be capable. All of this, then, tends towards a dynamic diving type of model. This is one which submerges by using hydrodynamic forces as the model moves through the water. It has the safety feature that, with any loss of power, the model will resurface. That said, it will still not stop you getting stuck inside a submerged shopping trolley!
One problem with dynamic diving submarines is that it is tricky to maintain a steady depth and you can quickly end up over-controlling, which often results in ‘porpoising’, a cycle of vigorously surfacing and diving, usually to the amusement of any spectators. The answer to this problem has its origins in the Vic Smeed Sprat design from the 1960s which was a small free running model powered by an electric motor and a couple of dry cells. The plan featured forward hydroplanes which were spring-loaded to a negative angle, thus the model would start to dive. A vertical length of wire was attached to the hydroplanes with a ‘drag plate’ fitted to the top. When the model had dived to the depth where this drag plate entered the water, the force on it rotated the hydroplanes to a positive angle and the model headed towards the surface. As soon as the drag plate left the water, the spring returned the hydroplanes to a negative angle. This resulted in the model progressing underwater in an oscillating fashion with just the drag plate dipping in and out of the water. Well that was the idea, but the keen but inexperienced and unskilled schoolboy that I was then could never get it to work properly. I returned to this idea some years later and dispensed with the forward hydroplanes, using the rear ones to lift the stern and allow the motor to drive the model under. The drag plate idea was still used, but with a fixed wire secured to the conning tower. When the plate entered the water it caused the whole of the model to rotate and rise to the surface. Thus, the same sort of underwater oscillating path as intended with Vic’s Sprat was then achieved.
Adding radio control
Buoyed with the confidence that this simple little model had given, a year or so later a more ambitious R/C submarine was built. With only single-channel gear available to me then (still a poor student), the model could only use rudder control, but the drag plate idea allowed it to run in an oscillating sub-surface fashion. In my next model, many years later, rudder, hydroplane and motor control was included. I stuck with using just rear hydroplanes, as the front mounted ones always looked vulnerable, and the receiver’s aerial was a length of plastic coated steel wire mounted vertically and running through the detachable deck and conning tower. The plan was to fit a clear plastic drag plate to the aerial wire and adjust its position until the model’s oscillating motion was satisfactory, but much to my surprise I found that the drag plate was not needed. The model’s speed was sufficiently high that the drag force on the aerial alone was large enough to control the model’s diving depth. In fact, with careful adjustments of speed and hydroplane angle it was possible to sail this model submerged in a hands-off fashion and just like a normal surface boat, concentrate on steering it around the lake.
The only drawback was that it was built using balsa with solid bow and stern blocks, which resulted in it needing a lot of ballast to obtain the correct static trim; dynamic diving submarines have to float with their decks almost awash. This model though became the Spook design and the plan was published in the October 1998 issue of MB. Several years later, another submarine was built, this time loosely based on the German Type 17 U-Boat. This also worked and it appeared in the April 2006 issue of this magazine.
It has taken about ten years to get around to building another submarine. Learning from the previous models means that it will use the same control system, but to avoid loading it up with lead ballast, it has the radio gear in a central watertight box and the bow and stern spaces are free flooding. To keep it attractive to the average modeller, it has been built from plywood with a little balsa for the curved bits at each end, with no need for heavy duty construction, as it’s just going to slip below the waves and not plumb the depths of the Mariana Trench. Also, as a bonus, the top of the aerial enables you to know where Nixie is when operating with other surface craft.
The resulting submarine is based on a modern diesel-electric submarine and the use of plywood has resulted in a boxy rather than rounded hull cross section, but this has not had any noticeable effect on its performance. To keep it simple, fixed vertical surfaces which carry the rudder and hydroplanes aft of the propeller have been used, as on the previous submarines, rather than a modern X-tail, which can be very complicated to set-up.
Be honest with yourself?
Although a simple model that requires no exotic skills or equipment to build, this still needs care, notably sound glued joints are essential together with accurate construction and since any leaks might be fatal, it must be totally waterproof and watertight.
You must also be consistent and thorough in your pre-sailing preparations as well as being confident when your creation and the R/C gear it carries disappears under the water. You will need to use a 27 or 40MHz radio system for this model as 2.4GHz radios don’t work underwater for us modellers.
Fancy having a go? Get the October 2017 back issue containing the FREE plan and Glynn's full build article
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