Going Deep- Ballast adjustments with SD?

[Slats]

Am yet to go deep with my SD - by deep I mean that I am yet to venture down to my local olympic pool and play in the dive pool depths, but I am wondering about how the SD will handle deeper conditions - like over 5 plus feet in terms of the boats bouyancy.

I have noticed in my pump ballasted boats over the years the deeper you go the heavy the boat becomes and I countered this by letting small amounts of ballast out. In fact I was able to get on a few occassions perfectly neutral bouyancy. I.e. Stopped the boat about 8 ft down (not on the bottom), and left her there "suspended" whilst I had lunch! (true).

The problem I see in going deep with the SD is as David states - the ballast tank should be used in only two states - 100% full OR 100% empty. With the SD, I ballast the boat so in fresh water the boat is slightly positive. This means that I get close to neutral a little way under, with slight dynamic forces in play to dive. As you go deeper - won't the boat therefore become negative? In my pump boat set ups I would let a little water out to counter this, but this is not possible with the SD if the ballast tank when dived should be 100% full, and as most would attest, commanding a blow usually means the boat comes up fast.

Is there a way around this? Or is this something that is not an issue?

J

[Subculture]

The only way around it is to use a ballast system which is either sealed off from outside water pressure, i.e a water pump ballast system with a valve or a peristaltic pump (self sealing). Or use a piston tank, which is adjustable but has no exposed water surface with a compressible air bubble.

You can of course make hybrid systems, where you mix say a small piston tank (syringe?) with the gas ballast system, incorporate a simple and cheap trim system in your existing module. A servo is strong enough to work a 60ml syringe, therefore the system can be made proportional.

Alternatively, you could use a peristaltic pump, and a separate small trim tank or even pump into a syringe.

[Albion]

anything compressible will compress, and you lose bouyancy, so you need something to offset this loss

[He Who Shall Not Be Named]

Assume your ballast tank is bubble-free and the boat is neutrally buoyant at periscope depth:

Your SD displaces less water as the cylinder is compressed around the 'dry' sections of the cylinder (box compression as a consequence of increased hydrostatic pressure). As depth increases overall boat displacement decreases and the boat transitions from a neutral to a negative condition; the deeper your boat goes, the more displacement it looses, the more negatively buoyant the boat becomes.

The box compression phenomena is more extreme with the thin-walled Lexan cylinders we're using today.

Expect catastrophic structural failure of the SD at a depth over thirty-feet.

Deal with it.

David,

[Albion]

Expect catastrophic structural failure of the SD at a depth over thirty-feet.

sounds like a youtube experiment :)

[Slats]

Thanks guys.

J

[He Who Shall Not Be Named]

(sent your 3/16" watertight seal today -- sorry about the delay)

[Slats]

no problem - much appreciate it David.
best
J

[redboat219]

"The box compression phenomena is more extreme with the thin-walled Lexan cylinders we're using today. Expect catastrophic structural failure of the SD at a depth over thirty-feet."

Let's see if this myth is busted, plausible or confirmed.

[He Who Shall Not Be Named]

"The box compression phenomena is more extreme with the thin-walled Lexan cylinders we're using today. Expect catastrophic structural failure of the SD at a depth over thirty-feet."

Let's see if this myth is busted, plausible or confirmed.

You first.

David,

[RCSubGuy]

There is also the foam to consider as well. The closed-cell foam that we use for trimming will "squish" at greater depths, reducing buoyancy and sending your boat down, down, down....

[redboat219]

How about using a Syntactic Foam http://en.wikipedia.org/wiki/Syntactic_foam to trim a sub? Easy enough to duplicate with some resin and microballoons and can be cast to fill in the space in the hull completely.