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Water Channel Construction

(Original article by Phil Sensibaugh, edited by Bill Pickl and Strike Models)
This material was originally published on the BDE/RC website as an instruction manual for getting started in Big Gun Model Warship Combat. This chapter is applicable to both Big Gun and Fast Gun formats. View the manual homepage.

Have you ever wondered why some ships settle fairly evenly in the water when they flood internally while others take on a severe list? The reason is most likely inadequate water channeling. Water, being a liquid will seek out the lowest point of the ship and move in that direction. It also follows the laws of physics and reacts whenever the ship moves. If the ship turns right the water will move to the left, and visa-versa. Also, when the ship moves forward the water will run towards the back. This is why nearly all ships sink by their stern, rather than bow first. In fact, of the several dozen of ships I have seen sink I have never seen one sink bow first. Although sinking bow first would be a good feature since this has the potential to save the rudders and props from damage when the ship hits the bottom, or is recovered. I say “potential” damage because after six years of battling the MBG (Midwest Battle Group) has yet to see any props or rudders damaged by sinking, but it could happen.

I’ve developed effective water channels with the past nine ships I’ve constructed and the method I have come to like the best is the foam filled water channel. I like this method since I’ve found it the easiest to accomplish. To make the water channel I first installed two wood stringers down the center of the hull and separated by about 2.75 inches. The stringers should be 1/4″ x 1/4″ hardwood. These stringers also serve to add some strength since the bottom plate of this ship (wood construction) was made up of seven sections to prevent warping. Next grind down the portion of rib that is glued to the base plate so that it will form a sloped line going from the 1/2″ tall height of the rib to the center 1/4″ tall strip (editor’s note: its easier to layout the rib patterns with this slope in mind and save the grinding). In addition to the channel down the middle you may want to leave an open section sized for your batteries so you can keep this large piece of weight low in your hull. Make this battery space an 1″ longer than the battery you intend to use and typically centered amidships with the batteries placed out towards the side of the ship to allow for a CO2 tank between them.

If you are putting a channel in a fiberglass hull your job is a bit easier. After attaching the sides of your channel to the bottom of the hull you will need to add a stringer that goes from the edge of the water channel out to the side of the hull about every 4″ along the length of the hull. You will need to cut a slope on them such that they are 1/4″ tall on the water channel edge and 1/2″ tall on the end near the side of the hull. I recommend you work with 3/4″ by 1/4″ hardwood strips. Measure off the length of stringer that will fit in the section of hull you are currently working on and measure in 1/4″ on opposite ends of the rectangle and draw a diagonal line between the two. The result should be a matched pair of wedges that are the same length and 1/4″ tall on one end and 1/2″ tall on the other. Make your diagonal cut first down the center then make the cross cut. Glue these two pieces to the hull and you’ve created your own “rib” stringers and you are ready for the next step.

I then installed a piece of balsa over the ribs between the water channel stringer and the side ribs of the ship as shown in the accompanying photos. Since the part of the ribs that were glued to the hull keel plate were sloped towards the center this allows any water coming in through holes on the sides to run into the water channel and towards the pump. Then I drilled a hole in the balsa sheet between each rib and using a can of “Great Stuff” minimal expanding spray foam I filled each rib section with the foam. My first attempt at this several years ago the foam simply forced off the balsa, cracking it to pieces. The accompanying photo shows how even minimum expanding foam still expands greatly (there are some new very minimal expansion foams on the market get some and experiment). The spaces between the ribs were only 2/3 filled!

Using a small blade on my pocketknife I cut away the excess foam, which was quite easily accomplished, then sheeted over it with more 1/16″ balsa sheet. Be sure to use epoxy glue for this since CA glue will melt foam, as will fiberglass resin. When the whole hull was sheeted on the inside so I couldn’t see foam anywhere I put a thin coat of “SolarEZ” UV cured polymer resin over the inside of the ship. This product won’t hurt the foam and cures more predictably than conventional fiberglass. The trick is sunlight must be able to reach it in order to cure the resin.

Now that the water channel is installed you should have a ship that will settle level as it takes on water.