Hey Jeff LaRue - Pistons in a WTC question.

[hampboats]

This question concerns the retaining rods used for the end caps. Jeff , what method are you using to tie the rods through the end caps, retain a water seal on the rods and still be able to remove the cylinder from the caps. I know you have a simple way of doing it and I don't want to over engineer it.

[JWLaRue]

Hi Dave!

Each of the knurled

Hi Dave!

Each of the knurled brass knobs that are screwed onto the ends of the tie rods have a small recessed area for an o-ring to fit into. When the knobs are tight against the surface of the end caps, the o-ring serves to provide a watertight seal.



..and here is a photo of a pair of the knobs, one with the o-ring in place and one without][/url]

These nicely made knobs were made for me by Bob Dimmack of OTW.

-hope this helps!

Jeff

p.s. is this for your Vessiko?

[hampboats]

Type 206a

The Vesikko is staying with a bladder system. This installation is for a '07 Subregatta acquisition, a fully loaded Engel Type 206a. It had all of the Engel electronics and two pistons plus the conning tower gear unit. I am not a real fan of the bolt down system so I gutted the hull. I plan on using one or two pistons and a WTC(s) Based on what I have read in the forum, this WTC should be plenty big enough for this size piston. I have the room for one or two pistons and multiple WTC if needed. Do you think one piston would be enough to provide adequate ballast. I also plan on trying the odd conclave and convex dive plane system. Your installation is a work of art. I welcome all suggestions from the forum. These photos are prior to stripping and repainting.




This photo shows both planes deployed, only one is deployed at a time.

[JWLaRue]

Dave,

re: two or one piston

Dave,

re: two or one piston - I'm of mixed minds over that.

On the one hand, a single piston, if large enough, will work fine....as it does in my Seehund. The trade-off is that with a single piston, the trim of the boat will change as water is taken on (and expelled). This can't be helped since the piston is taking on water from only one end. This creates a dynamically changing trim where the centers of buoyancy and gravity keep shifting. In the Seehund, I used this to my "advantage".....meaning that I made the best of the situation......the piston has been oriented so that it fills from the front end, causing the bow to dip down when submerging. Looks really good! What I could not overcome was the reverse - when surfacing, the stern tends to want to come up first.

On the other hand, a two piston setup will (should) not create a trim problem when between surfaced and submerged trim. The trade-off for this is, of course, the extra room needed for two pistons and the air space needed within the dive module to allow the air in the piston to be 'pushed' into.

What we really need is a piston of around half the diameter of the Engel product........

-Jeff

[bigdave]

Hi Jeff,
The big problem

Hi Jeff,
The big problem with that is the length would increase a lot keeping the same volume. The lead screw would be quite long. BD.
No pun intended.

[hampboats]

More questions!! Need help with the math.

This is my first effort at using the piston style of ballasting.So I have a lot of novice questions.

My boat is 55'' long. I have two 500ml tanks available, each is 7" long outside length. I plan on using a 4" WTC that will be at least 24" in length if I use just one tank. To the best of your knowledge guys will one tank work for this boat. It seems as though one tank has enough volume for this size of boat. If I use both, I would most likely have two separate WTCs to be able to get the tanks far enough apart. If I use one piston tank, will the water travel within the 7" length be a major factor in the shifting of the CG? Does the length of the boat make any difference in the issue of the aft end coming up first? I welcome your suggestions.

[JWLaRue]

BigDave,

It's not strictly necessary to

BigDave,

It's not strictly necessary to increase the length of the dive module to accommodate the piston jack (lead) screw. Take a close(r) look at the photo of my dive module.....and you'll see the brass tube that is sticking out the center of the end cap. Guess what it's for? That's where the jack screw goes into! This allowed me to shorten the dive module by several inches. Of course, for a two piston setup, the jack screws would normally be pointed towards each other.

Dave,

It sounds like a single piston tank would work for your hull. It really depends on how much water your above-the-waterline parts displace.......

You will have to deal with the shifting CG as I did, but I think that the longer the boat, the easier it will be to counter it's effect.

-Jeff

[bigdave]

Cool!
But still the longer you

Cool!
But still the longer you make the pump body the worse the problem will be. You would actually want to make it shorter so the water weight is distributed over less of an area. That is the way I am looking at it anyway. BD.

[JWLaRue]

BigDave,

Absolutely! The perfect solution would

BigDave,

Absolutely! The perfect solution would actually have the piston sit vertically.

-Jeff

[Guest]

If you invest in a

If you invest in a small lathe, then you can make piston tanks to any size, and very cheaply. Typically a small lathe will pay for itself the first couple of tanks you make.

Good sources for piston tank tubing include-

1. Spent caulking gun tubing, smooth and accurate. About 2" diameter.

2. Pump action toothpaste tubing. Only about 1.5" diameter, so good for small models or a piston trim tank.

3. Laser printer or photocopier toner cartridge rollers. These contain thin-walled seamless aluminium tubing with an excellent internal finish.
The laser printers tend to be about 1 1/8" internal diameter, photocopier tubing can be very large, if you can find it.

4. Syringes.

5. Laminate your own tubing with resin and glass (polyester or epoxy) on a former. Long winded, but it does result in a custom made tube that is fairly accurate (better than drainpipe etc.)

To seal the piston, you can use o-rings, or Airzet rings which are available from Freudenberg/Simrit.

Another advantage of making your own tanks is that you can specify high quality motors. Maxon, Buhler and Pittman motors are available cheaply on ebay, often complete with high quality planetary gearboxes. These are superb for our uses, and compact.

Andy

[tsenecal]

I can attest to both

I can attest to both a vertical oriented piston (not shifting the CG), and a very slender WTC surrounding little more than the piston itself: