A Skipjack in Ireland

[The Boattrainman]

Hi Albion,

I'm hoping that the Pitch Controller will help with keeping the sub on the level when diving (when under way), as I was forced to mount the piston tank with the cell flooding from the aft on dive.

Just saw your thread on the ballast shifter, very good, Norbert Bruggen would be impressed!

Rob

[Albion]

Sorry to rain on your parade like this, Rob. But better to give you a steer now than watch you roll off the cliff later.

The three liabilities of a horizontally sitting piston-pump: The less than ideal use of available internal WTC volume for the ballast sub-system (a problem shared with bladder type sub-systems); A significant load on the battery; and the c.g. shift as water is taken off/on. The nice feature is the ability to hover the boat (an over-rated feature in my book).

David

During transition from surface to submerge with a single tank you will get some weird angles. I have a single tank in my koryu but due to the fact it sits at an angle in surface trim the descent doesn't look too funky. I did put a ballast shifter on mine so that i can hover the boat ;), and trim it to suit the hover point. All a bit irrellevent as i need to secure that module inside my hull, if i raise to quickly the module moves and i end up with a permanently porpoised Sub :(

https://forum.sub-driver.com/forum/b...ighlight=koryu

This is a very interesting build and waiting to see how it goes next. i also suffer from not having toys like lathes available all the time and having to improvise

[He Who Shall Not Be Named]

Very good. The nice thing about the WTC concept (wet-hull with removable system) is that if you get the ballast water amount wrong the first time, you can revisit it later with a different or modified WTC that corrects the problem.

I'm very much enjoying the high level of craftsmanship of display as I read your WIP. You're taking us all back to school with some of this stuff. Most informative, sir.

David

[The Boattrainman]

Hi Dave,

You're not raining on my parade at all, delighted to get expert feedback from you and the other guys, I very much enjoy the banter here.

If it's a compromise this time on being a partially dynamic/partially static diver, then so be it, this build is very much a proving exercise in what I can scratchbuild, as I'm already looking at the next project which will be much more expensive than the 64.99 Euro I paid for the Skipjack kit!

Anyway, here is a couple of shots of the flap that will hold the battery in place.





Keep those thoughts a coming.

The Boattrainman

[He Who Shall Not Be Named]

Dave,

I bow to you superior knowledge on this.

So, it;s back to Engel equipment, as it happens they have a 750ml piston tank which equates to 25 Fl Ozs, but it's just not feasible. They'll custom build a tank, so I'll get the measuring stick out and see what I can get into my WTC, I'm thinking 600ml might be my absolute limit................................


Rob

Sorry to rain on your parade like this, Rob. But better to give you a steer now than watch you roll off the cliff later.

The three liabilities of a horizontally sitting piston-pump: The less than ideal use of available internal WTC volume for the ballast sub-system (a problem shared with bladder type sub-systems); A significant load on the battery; and the c.g. shift as water is taken off/on. The nice feature is the ability to hover the boat (an over-rated feature in my book).

David

[The Boattrainman]

Dave,

I bow to you superior knowledge on this.

So, it;s back to Engel equipment, as it happens they have a 750ml piston tank which equates to 25 Fl Ozs, but it's just not feasible. They'll custom build a tank, so I'll get the measuring stick out and see what I can get into my WTC, I'm thinking 600ml might be my absolute limit................................


Rob

[He Who Shall Not Be Named]

Hi Guys,

I'm working off the following assumptions.

The biggest requirement to sink the sub will be getting the WTC itself below the surface as its filled with air. The volume of the WTC with no equipment inside is approx 3,300ml, and taking the accepted view of a flooding cell of 10% - 15%, this puts the 450ml piston tank at 13.5% which is right on the money. Factor in a reduction of air due to the tech rack and equipment and that percentage will be even higher ,which should cover the hull and sail above the water line, so I'm not anticipating a problem.

I have room for a 500ml tank from Engel (just about, very tight fit), I'm hoping the 450ml will give me a bit of wriggle room, and I want to try to get a tank that fills to capacity for a 1 metre dive depth, as I've managed to centre the piston tank very well along the centre of gravity of the sub so far.

Rob

Ain't going to cut it. And you're calculating from the wrong end to find required ballast tank weight/volume.

Its the displacement of the above waterline structures, not the weight of those structures.

And your WTC is already immersed in surface trim, so is not any part of the 'reserve buoyancy' calculation. It's not the weight. The thing could be made of depleted Uranium or duck feathers ... don't matter as all of that was countered with the floatation you put in below waterline when you established submerged trim. Its the weight of the water displaced by the structure that matters. A neutrally trimmed object displaces a weight of water equal to the weight of the object; buoyant force equals weight of object -- net vertical force, zero!

(Archimedes, call your office!)





I found it takes about 25 ounces of ballast water weight to get the model to surface to designed waterline. The 450ml piston tank ain't go'n to cut it (15 ounces of floodable volume!? .... Bzzzzzz!). That's why the video of Arkmodel's SKIPJACK shows it sitting so low in the water when in surface trim. Not enough ballast tank. His piston pump does not have the ass to push the boat up to designed waterline. (What was Feng thinking, anyway?!)



Our 1/72 SKIPJACK SD has a ballast tank that holds 25 ounces of water and will get this beast up to the designed waterline.





This is what a properly trimmed 1/72, Moebius SKIPJACK looks like on and below the surface:

https://youtu.be/7aaAVtlnbVM

David

[The Boattrainman]

Hi Guys,

I'm working off the following assumptions.

The biggest requirement to sink the sub will be getting the WTC itself below the surface as its filled with air. The volume of the WTC with no equipment inside is approx 3,300ml, and taking the accepted view of a flooding cell of 10% - 15%, this puts the 450ml piston tank at 13.5% which is right on the money. Factor in a reduction of air due to the tech rack and equipment and that percentage will be even higher ,which should cover the hull and sail above the water line, so I'm not anticipating a problem.

I have room for a 500ml tank from Engel (just about, very tight fit), I'm hoping the 450ml will give me a bit of wriggle room, and I want to try to get a tank that fills to capacity for a 1 metre dive depth, as I've managed to centre the piston tank very well along the centre of gravity of the sub so far.

Rob

[greenman407]

I would contact them here for clarification. Then click on "contact"

[greenman407]

I don't know where I got 100ml. It does say 450ml, right on the label. If that's the case then that's 15.75 ounces. Right?

[Albion]

Well I noticed that the videos didn't show the model in surface trim. I think I would check with Dave Merriman if 100ml of water is good enough for good submerged to surface reserve buoyancy. Perhaps you might need a bigger one. Check it out first.

the unit posted is 450Ml, might be ok for a wet hull. My koryu is dry hull and uses 500ml, but it doesnt need much freeboard

[greenman407]

As near as I can figure, that's only 3.5 ounces, not nearly enough

[greenman407]

Well I noticed that the videos didn't show the model in surface trim. I think I would check with Dave Merriman if 100ml of water is good enough for good submerged to surface reserve buoyancy. Perhaps you might need a bigger one. Check it out first.

[The Boattrainman]

Thanks Greenman, looking good for Arkmodel!

[greenman407]

Heres a link you might want to look at. It has a couple of videos in it of it in operation.