Russian Alfa Class

[rwtdiver]

[trout]

Will what you are lifting out of the water weigh more than 200 grams? Metric is so cool for us here, 1cc of water equals 1 gram of weight. 200 grams is around 7 ounces.

[type7]

Remember, you want the top of the cylinder under the water line or it is working against you instead of helping. Also, it is nice to have room around it for foam at the water line.

[Subculture]

You don't need to guess anything.

Displacement is key when sizing ballast tanks, not weight. Water weighs 1kg-1000g for every 1L-1000ml of displacement, and will vary by less than 1% depending on temperature and mineral content.

We size ballast tanks based on the amount of water displaced. Most unreinforced plastics e.g. ABS, polystyrene, pvc tend to have the same mass as water, but filled plastics and composites like glassfibre reinforced hulls are denser. If you use weight then you end up with a tank which is too big. PLA is a pretty dense thermoplastic.

With conventional precast hulls, we don't tend to know the volume above the waterline, and with hand laid fibreglass, they can vary from hull to hull, so it's best to use empirical methods to find out the hull displacement. The method for doing that is straightforward, trim the boat for neutral buoyancy (or close to it), then use foam blocks to bring the boat to the required waterline. The volume of foam blocks will equal the displacement of the hull- or close enough, the weight of the foam itself skews things a little.

With a 3d printed file we have no such worries, you can split the boat at the intended waterline in CAD, then check the properties to find out the volume of the structure above the waterline- easy peasy lemon squeezy .

[RanSan]

Can anyone who has set up a boat tell us if this sound right.

I sliced the model at the waterline and got a volume of 5.782 cu in (94747.16 cu mm). This does not include the rudder or bulkheads.

Randy

[He Who Shall Not Be Named]

Can anyone who has set up a boat tell us if this sound right.

I sliced the model at the waterline and got a volume of 5.782 cu in (94747.16 cu mm). This does not include the rudder or bulkheads.

Randy

Include ALL structures above water line open to sea.

David

[Subculture]

That's a smidge under 100ml or 3.5 ounces. Small tank if correct, those prints must be quite a thin cross section? Add on ten per cent to account for changing densities if you want the capacity to trim for different water densities.

[He Who Shall Not Be Named]

Sorry you guys! I did not mean to come off disrespectful to any of you! Sometimes with this hobby you can really get frustrated! Certainly did not mean to take out my frustrations on any of you! I understand you are just trying to help, and I do appreciate it!



Rob
"Firemen can stand the heat"

No sweat.

Hey, Rob, I'm with you, pal. Basically I'm a non-math-seat-of-your-pants engineer. But, once you decide to do something professionally that requires some math and mechanical skills -- if you want the gig bad enough, you apply yourself and learn the math, and figure out the mechanics of those things you will be responsible for. Had to happen when you took on fire-fighting. And it happened to me when I became determined to qualify in submarines, and later join the diving community -- there ARE absolutes in those games!

Thing is, with a hobby, you can flop around and do things so-so. No one dies or gets hurt (now that I think about that, I remember that I almost killed Gene Berger with some bad advice... but that's another story). Hobby mistakes are classroom lessons, not life altering tragedy. You lose a model submarine? So what, you still go home at night.

Your ballast tank, if its close enough to get the boat under... good enough. In time you will come to realize the utility of a few basic principles, such as Andy posted here recently, and will learn to apply them to make your road just a little less rocky.

David
The Horrible

[Subculture]

The piston tank system is usually the simplest system of all. It generally has the fewest components and is very reliable in use. Many consider it complex, because unless the boat is large enough to house an Engel piston tank, you have to make it yourself.

There's no mathematics needed for this area. Essentially what we are talking about is a law of physics first set down by a chap much older than any of us here- Archimedes of Syracuse (circa 200bc).

[SubHuman]

Yes, this was orignially designed for 72nd scale, so thicker walls, but I've printed in 96t and the bulkheads make it plenty strong, even with the thinner walls.

Bob

[He Who Shall Not Be Named]

Today I finished up all the file prints, and have moved on to the stern section! I have made the decision to go full out on this boat! (Yes it will DIVE) I am totally ready for the plunge. (No pun intended)



I have the brass pieces cut, and ready to install the sleeves and the shafts.





As you can see, the bottom rudder is larger (1/2" wide to 1 1/8" wide! I know this is not to scale, but i wanted to increase the boats turning radius for use in my pool.

Rob
"Firemen can stand the heat"

Good call. Enlarging that rudder was the right move. This boat will be a screamer. Set your transmitters ch-3 end-point to 30% ahead-astern for starters. Increase as you get more cocky with this little rocket.

David

[He Who Shall Not Be Named]

Why don't I just send you a white-metal propeller designed for a 1/96 ALFA?

[redboat219]

the bottom rudder is larger (1/2" wide to 1 1/8" wide!, wanted to increase the boats turning radius for use in my pool.

Rob
"Firemen can stand the heat"

As David mentioned in your Russian Borei build, you could use a clear rudder extension to increase you rudder's turning effect but keep everything "in scale".

[He Who Shall Not Be Named]

So, darling, you don't want to go out with me... is your Mom available tonight?

Hey! Whatever works, pal. Fortune smiled on the propeller front I see.

David

[RCJetDude]

Success! Nicely done Rob. That does look tight in there.