Another way to think about your question: The Given Facts: 1) A pump's job is to offset water coming in by removing it. Once the pump is overcome you will sink given sufficient time. 2) A pump requires a certain depth of water before it can pump an effective stream of water. Let us declare this to be 1/4" for the sake of this argument. 3) A pump can pump out an amount of water equal to the amount let in by a given number of holes of an average size, for this let us declare that to be 5 below the waterline holes in an average position. (a completely randomly picked number) 4) Water channeling on a ship with an 8+ inch beam creates a trough approximately 2 inches (or 25% of the beam) in width that runs for probably 66-80% of the ship's length. Let us declare your water channel to be 3/8" deep - deep enough that 1/4" of water, a sufficient amount to prime your pump is easily held within it. 5) A cubic inch of water weighs 0.036127 lbs Let us assume two scenarios. In both scenarios we assume you are sailing a rectangular box, 36inches long, 8 inches wide with a pump located somewhere along the centerline. In both scenarios let us examine what happens with our predetermined number of holes that the pump can keep up with, 5, below the waterline and let us place 5 above the waterline such that 1lb of additional ballast will settle your ship low enough that they let water in. We shall assume no environmental factors, you are floating peacefully on a placid pond. We shall also assume that your pump will instantly begin pumping at the magic water depth of 1/4". In the first we assume your water channel to be 36inches long, 2 inches wide and 3/8" deep. In the second we assume you have no water channeling. Scenario one: Given your 5 holes, water will be entering your ship. It runs into your water channel where it begins to pool. Once it reaches 1/4" you will have 18ci of water in your ship. (36*2*0.25). This is aprox 0.65lbs of water and insufficient to settle the above the waterline holes low enough to let in water. The pump will now pump the water out, but because you have the exact number of holes as your pump can keep up with, you maintain 1/4" of water and pump continuously. Scenario two: (no water channel) Given your 5 holes, water will be entering your ship. It pools evenly across the bottom of your perfect box. Once it reaches 1/4" you will have 72ci of water in your ship (36*8*0.25). This is aprox 2.6lbs of water and more than sufficient to settle your above the waterline holes low enough to let water in. The pump, having the required 1/4" of water available, will begin pumping. Unfortunately because you have 2+ lbs of water and have settles, your 5 above the waterline holes are letting water in at the same rate as your early 5 belows. Since your pump is inexplicably silly and can only handle 5 holes letting in water at once your pump cannot keep up and is seriously outmatched. In scenario 2, you are now inevitably sunk, even though you had the same damage and same pump as the box in scenario 1 - the difference is that in scenario 1 you spent the time to maximize the factors that you can control, by allowing your pump to start earlier, with less compromising of your reserve buoyancy whereas in scenario 2, you took the approach that only the pump's output matters. Water channeling, if nothing else, buys you time on the surface.
Nick, Thanks for taking the time to address this question, assume explanation. Length x width x depth and the weight of water. Without water channeling, the entire bottom of the boat would need to be about .25 deep before the bilge pump would start to pump it out. The bigger the boat the more volume of water and heavier it would be. That would be a lot of water versus a 1.5 wide and .25 deep channel the water would flow to, allowing the pump to start to pump out. going to give the water channeling a go and hoveys idea of concrete sealent and a bigger co2 bottle thx
One other advantage of water channeling is avoiding the 'free surface" effect... you have a pool of water sloshing around in your hull (as mentioned by others), you suddenly stop (or start) and all that water sloshes to the other end, pulling your bow (or stern) underwater and sinking you abruptly. Water channeling prevents this by both allowing the pump to go into action earlier and by ensuring any water in the hull is concentrated where the pump can get it. A note regarding your water channeling & batteries / rc box: weight as low in the hull as possible is good for stability. But if you put your batteries flat on the bottom, you've blocked your water channel. I always set my batteries in "sockets" in the water channel that hold them from shifting, but at the same time keep them at least 1/4" off the bottom to allow water to flow under them. (See the pics in the "Baden Refit" thread)
Nice job so far. I am very impressed with the way you actually listen to suggestions and work them in. This should be a good boat when you are done.
The best thing about this web site is you can draw from the knowledge and experience of other warship builders. Everybody has something to offer and you can use others ideas if it fits your style (personalize your build). as far as waterchanneling, everybody pretty much was for it, so taking the time to put it in and see how it go.
Hi, looks great! One thing though, you may want to leave a small space for water to get through to the pump from the after section behind the motor mount. There may be one, but I can't see it in the pics. Jay
the first idea was to also fill in the back end to divert the water fwd to the water channel. but the back end of the boat is heavier now with the water channeling that has been added so stoping here. yes, now going to carve out a spot for the water to get by the motor mount and drive shaft support
Water Channeling 1) Estimated the weight of water in the hull @ .25 inch depth = 3.8 lbs 2) the current water channeling would displace approx 1.6 lbs 3) added weight due to water channeling approx 1.4 lbs the water will now be dirrected to the water channel, but at a cost of adding 1.4 lbs to the boat.. water channeling does dispaces 1.6 lbs but with a net effect of .2 lbs of water. the pump can start pumping earlier but the boat already weighs the same amount (minus the .2 lbs) if there was not any water channeling at 3.8 lbs.
By your argument you shouldn't add more than one battery either since it adds weight which would settle your boat lower in the water. But since your boat needs ballast to get it down to its scale water line to be legal, you have to put weight inside of it. Some of that is from your water channeling and some of that is from internal systems like batteries, motors, and structure. After adding all that and it is at its scale water line is when you can do the water enters your hull thing and can start the settling process. Your combat weight should be about 40 lbs. You allocated about 1.4 lbs to water channeling and the rest to other parts. With water channeling you only need 1.6 lbs of water to start pumping. With out water channeling your boat still weights 40 lbs because it has to be at its scale waterline to be legal. So you gained 1.4 lbs to do other things with, most likely it will be extra ballast (like Alex's bean bags). But since you dont have water channeling you will now have to take on 3.8 lbs of water before you can start pumping. Water channeling keeps you higher in the water by a much larger amount than you give it credit for.
Not arguing against water channeling, just a discussion on it. Battiers can also be used to displace water if the geometry of the boat allows for them to be placed on the bottom of the boat. A 12 ah battery 6 X 3 X 2inchs weighs 4.4 lbs. If you use .25 inches instead of 2 inches depth, it would displace 0.2 lbs. So with three 12 ah hour batteries you would displace 0.6 lbs. of water. .25 inches of water in the bottom of the boat is 3.8 lbs. Water channeling displaces 1.4 lbs. of water and directs it Three 12 ah battery’s displace .6 lbs. of water So, 3.8lbs minus (1.4 + .6) means you only need 1.8 lbs. of water before the pump starts to work. Three battery’s also adds 13.2 lbs. to the boat and give the ah needed. Thinking of using some 6 ah hour battery’s also to get the weight up to 40 lb. and displace more water so less is needed in boat before the pump starts to work. only one problem, geomery does not allow the batterys to be place on the bottom of the boat to displace the water. smaller 6ah batterys just mite
I guess I wasn't clear. Your math is fine but one of your assumptions is off. What you are computing is how much each component weighs in water, which is interesting but not quite the same thing. Hence why your particular water channeling material only gives a small amount of buoyancy (the stuff actually floats but not very well). The boat will weigh 40 lbs when dry one way or another. How ever you get there isn't really that big of a deal. But you still have to get to that magic number. So the weight of the water channeling doesn't add additional weight to the boat. It is already part of that 40 lbs. Just like batteries, framing, a pump, lead ballast, or any other part of the boat. This is because we have this rule that says you will sit on your scale waterline, something real ship designers don't have to deal with in quite the same way. If you had used helium batteries that weigh -1.5 lbs then you would have to add more weight to the boat to get her down to her waterline but instead you chose SLA batteries and so a good portion of that 40 lbs is lead. Either way she would still be 40 lbs when dry. So your weight when you can start pumping with water channeling is 42.2 lbs (40 + 3.8 (weight of the water) -1.6 (weight of water displaced by channeling)) and without you weigh 43.8 lbs (40+ 3.8). That is a 1.6 lb difference in weight. But your boat still has the same dry weight of 40lbs. Water channeling doesn't add weight to a ship it just uses up a certain amount of the weight your ship is allocated.
I lay my batteries on the bottom and displace water. I just leave a gap in the middle. Too much ado bout nothing, ship weight is weight, the bis has it.
For some reason I forgot the dry weight needs to be 40 lbs. thx for the explanation, very clear and concise now Hovey. back to the build when xmas is over
I am now feeling a strong urge to stencil names onto my ships before the start of the season just to see how long it takes until they're illegible.
