Stranger needs advise

[cweeks]

That idea hadn't crossed my

That idea hadn't crossed my mind but a thought occurs that you are just shifting the awkward sticking out threaded rod for a sticking out tube. Or am I being simple again !

[Guest]

That is correct, but the

That is correct, but the awkward 'sticking out tube' will move into the free flood space, it won't take up room inside the wtc which may, or may not be available i.e. dependant on the layout of your boat.

Andy

[cweeks]

Got ya, missed that subtlety.

Got ya, missed that subtlety.

[anonymous]

Hi,

If you are interested in

Hi,

If you are interested in the bellows approach instead of piston/cylinder- I was having a chat with it's inventor (David Jacques) this weekend.

He produced a small booklet on the system for the AMS some years ago and we could perhaps get hold of a copy.

It works well apparently and uses something like a steering gaiter(haunt car accessory shops!)

It sounds like ypur main problem with bellows or cylinder is minimising the actuator screw length.

Have you had a look at Norbert Bruggens book - Model Submarine Technology - lots of ideas in there.

Good luck and let us know how you get on.

Davy

[cweeks]

Yet another idea that hadn't

Yet another idea that hadn't crossed my mind. I do have the Model Submarine Technology book but I think they are only given a mention in there, not much detail. I would love to see a copy of the small booklet you mention. I can't see a down side to them, easy to make, easy to obtain materials, are they still as proportional as piston tanks ?

[anonymous]

Apparently so, yes.

He had one

Apparently so, yes.

He had one sinking after the bellows crushed on a very deep dive (20-30 feet ) but I imagine that a piston one could run out of power at that depth also.

Glad you've got the Norbert Bruggen book - it is a mine of useful info. I was wondering if he had anything to say on enclosed screws etc. I think he also mentions rack and pinion drive for a small cylinder.

Davy

[Guest]

Norbert mentions in his book

Norbert mentions in his book how to make a piston tank that is good for 30 feet.

I think the main disadvantage with bellows is that they don't retract fully, so they're a bit more cumbersome i.e. they take up a bit more space than an equivalent piston design.

Plus you may get a small variation in depth control as the bellows 'squeeze-up' as you dive deeper.

You can use the same control system for bellows as a piston tank- the method of winding them in and out remains the same.

Andy

[cweeks]

Once again thanks for the

Once again thanks for the info. Bellows are looking like a strong contender now. Even if they aren't perfect they will serve as a proof of concept. Should further refinement be needed I can move to piston tanks.

Davy - No mention in Norbert's book that I noticed on enclosed screws.

Cam.

[subshop]

wtc

cam
i did not read the entire post, but have you considered a ballast system other than piston type? if you have a bit of room in your wtc you could use pvc tanks forward and aft . then in your wtc you use two small water pumps to pump water in or out to surface or dive. hope this helps, neil

[cweeks]

Pardon the ignorance, i'm a

Pardon the ignorance, i'm a newbie, pvc tanks ? are they bladder tanks ?

[subshop]

WTC

IN my gato i used 3" pvc pipe capped the ends, i drilled the bottom so i could attach a fitting for the tubing. the tubing goes to a fuel transfer pump made by Slimline. they make products for r/c cars and planes. it is a peristaltic pump and works on 12v. see here http://www.slimlineproducts.com ... it pumps both ways so you need a reversing circuit but it works and you don't need any valves because the internal rollers keep the water from going either way when stopped. neil

[cweeks]

Is it the Boxxer pump

Is it the Boxxer pump ? http://www.slimlineproducts.com/onli...oxxer_pump.htm

And again pardon the questions but is this system classified as a "Pressure ballast tank" as per http://www.heiszwolf.com/subs/tech/tech01.html

[subshop]

wtc

yes it is the boxxer pump and you would classify it as a Pressure ballast tank.
neil

[anonymous]

Interesting topic this!

You are

Interesting topic this!

You are starting to head into the problem of "design trade offs" , I think.

Complexity versus precision of control etc.

I would put piston tanks at the top of the list for precision of control followed by bellows and then pumped systems.

For simplicity a single, baffled, centrally located ballast tank has to be the winner. Even for this length of model you would still be able to use this without other trim tanks etc. (You would need to play around with lead and foam, though.)

At the risk of making things more complicated, don't forget about moving the batteries to adjust trim. I think Andy has experience of this and it only needs a small movement (An inch, say?) to adjust the trim angle significantly.

Davy

[Guest]

Pressure tank is as described

Pressure tank is as described at the heiszwolf site.

I wouldn't use a peristaltic pump for a boat with large tanks- they're very slow at pumping in comparison to centrifugal and geared pumps.

In my opinion, they're only virtue is that they are self-sealing. You also need to pump both ways, or install a secondary circuit with a valve.

Norbert sells a system using a perstaltic pump and flexible bladder (he calls it a 'gummysack'). This system works well enough, but people who have built the boats using this system (i.e. Delta) report dive times are a tad slow, and that is a boat with quite low freeboard.

Ballast shifting is very well covered in Norberts book.