1/72 HMAS Rankin (Collins Class)

[Slats]

But its not all straight forward - the shipping of the BT bulkhead turned out to be inspected by customs and whether it was their rough hands or perhaps mine during the install, soon after I had a problem. The ballast tank push rod I noticed had an upward bend in it near its tip. The cure was to install a new 3/16" push rod. The only way to do this is get inside the bulkhead, which at this stage was neatly secured in the cylinder with the gas lines connected. So I did access it via the tube and a log screwdriver. With a bent push rod on the wet / ballast tank side I did not want to take any chances of pulling the bend, even if I thought i had straightened it out, through the water tight seal. So the cure involved cutting the push rod on the wet side of the seal.

Not much access - but you can get in there:



With the fix in place and the SD working well, was time to pay attention to torpedo installation in the sub and the interface back to the SD.

[Slats]

Thanks David, I'll be buying a couple. I plan to rig up Joel's Seawolf (when its released), with the double motor unit of the new 3.5" SD single shaft double motor. That beast will benefit from the extra torque.

J

[He Who Shall Not Be Named]

Now just add yet another product job to God's list, there will be a forward ballast tank end cap and conduit setup through the tank, like what I have done here in the works for the 3.5" SD kit. A must have for those running newer higher density / output batteries like Lipos and handy if your "old school" and run stick NimH batteries like me. The 3.5" SD needs a "dry" connected forward space.

J

I'm sold, John. New internal bulkheads for the 3.5" is in the works. Mostly based on your observations and good work with your SD. Thanks.

David,

[Slats]

Now just add yet another product job to God's list, there will be a forward ballast tank end cap and conduit setup through the tank, like what I have done here in the works for the 3.5" SD kit. A must have for those running newer higher density / output batteries like Lipos and handy if your "old school" and run stick NimH batteries like me. The 3.5" SD needs a "dry" connected forward space.

J

[Slats]

Great tutorial John! Wanna write my Seawolf manual for me? lol

Yeah sure mate. Happy to.

Glad you like the post - got to go back and fix up the grammar! I suck.

I'll be back on the Permit build real soon.

Best
J

[ManOwaR]

Great tutorial John! Wanna write my Seawolf manual for me? lol

[Slats]

Next dry fit the gas tank in position (no silicon).
When your happy put silicon RTV around the screws and top gas tank and push through the lexan holes. Secure it in place with the nuts supplied.



Now fit the O'ring back on the Ballast bulkhead and using some vaseline slide this bulkhead inside the lexan tube to where its screw seats meet the holes you drilled.
This amount of vaseline is excess and stupid, just a little around the o'ring is fine:


Secure the screws, then test the servo functionaility (which you should have already done). I then connected the ballast system, and finally slid the forward double end cap into position so it mates with both the lexan and the brass conduit. I then sealed the conduit in place with CA glue.



It will take a while to get right but you install the supplied screw for the vent valve in place and then RTV down atop the tank the vent valve.

Finally seal off front and rear ends of the SD (battery end cap forward and a end cap in the place of the motor end cap and check for leaks. A dunk in the test tank:



Invert the thing to fill the tank and see if there is any ingress of water into for or aft compartments, up right push down below the surface to see if there are leaks in the tank, especially around the vent.

More soon....

Best
J

[Slats]

The first order of business is determine the size of the ballast tank. In my case this was easy - having done so with the semi-aspirated system for this boat. With this done I marked the space up on a piece of 24" Lexan tube, and also noted the space I needed for the rear setion motor room tray and bulkhead.

With that done, you need to remove the O'ring from the ballast tank bulkhead and slide this bulkhead inside the 3.5" tube to the spot where this separates the ballast tank from the motor room space. When done so you will need to mark up and drill pilot holes into the screw supports that hold this bulkhead squarely in place. Take care not to drill into the end cap screw seats as these already are pre threaded.



In the above you can alos see the double end cap from Mike's Subworks and the conduit piece of brass I have added to facilitate a dry electrical tunnel between forward and aft sections.
I am using brass, as David has employed this previously in smaller diameter sub drivers.

Next you can see where I drilled out the ballast tank bulkhead to support the conduit, a correspondingly located hole is in the forward bulkhead.
Glue this in only the one bulkhead for now - the ballast bulkhead


Next you check a positioning fit of the screws.


After being happy with the position of everything you can then remove the bulkhead and drill out the holes for the gas tank installation and flood holes for the ballast tank


Note the use of a stepper drill for the free flood holes. About a 1" diameter is a good size. If you want more access - for maintenance inside the tank, I linked my flood holes together to form a slot openning. NB. Also note the support craddle to assist this. You will also need a firm hand hold on the work to be drilled.


The next hole to drill out is actually the oval type space for the vent valve. The position of this is simply to work out for the ballast tank bulkhead:

[Slats]

The installation and assembly of the 3.5" Subdriver Kit

The 3.5" SD is now available in kit form. I must say that previously all the SDs I have used have come pre-assembled, and that the kit was a logical next step.

Going to the Caswell site you will find, you can buy the gas tank, gas valve bulkhead with installed servo, hardware etc to deck this out along with Lexan tubing. Key to the SD is also the snort system, and the back end "engine room", which I reviewed recently at .........

http://forum.sub-driver.com/showthre...-motor-end-cap.

Shown below is where we are heading with assembly of the Subdriver Kit, note that in the foreground, the back end engine room (known as the motor end cap bulkhead and tray), is directly lifted from my semi-aspirated system. All that need be done to it was the addition of the snort pump and control for it. The channel that was controlling the semi-aspirated pump setup is now simply going to the servo controlling the ballast vent /blow. Hence you can buy this back end for different ballast setups - it is completely adaptable.




The engine room - a most adaptable platform:


You will note from the photo above that the SD has a water-tight section ahead of the ballast tank. A space for the battery. Whilst previous SDs of smaller diameters have this feature. I have been nagging David to mould up a forward BT bulkhead for to do so in the 3.5" for a number of years. The result is that herein, I have added this Bulkhead myself, utilising a double bulkhead sold by Mike's Sub works.

[Slats]

Those following my experimental dabble into semi-aspirated tanks would know that the system worked right up to the point of a failure with the BT (thankfully onthe bench). With the Australian subregatta - just around the corner (Easter 2010), it was timely a few weeks ago to grab tried and tested technology and deck out the boat with the new Merriman 3.5" Subdriver. Rankin is also a test vehicle for the new Torpedo system that David and Mike have introduced to the market. So rather than have three threads going all over the place, this thread will now contain:

The installation and assembly of the 3.5" Subdriver Kit + testing
The installation of 4 x 1/72 torpedo tubes, gas manifold, and electrical fire control unit + testing
The completion of HMAS Rankin and trials and testing of the equipment above.

[Slats]

Ok to rewind a bit - the ballasting above was primarily done to test my new ballast system, and secondarily check out the needs of this boat. Further ballasting will be required for two reasons, the first is that I want to improve the subs turning circle, and the second is that this boat will go to sea with the new D&E / Caswell torpedo system adding some weight forward. This final ballasting will be done hopefully in a couple of weekends time, just in time for the Australian Sub Regatta at easter, if the torpedo system is not ready to install, I have her ballasted to run without it.

In terms of ballasting a boat, when I first mucked about with subs I was ignorant and stupid, coming from a target world where ballasting simply meant a scale water line. Nowdays I am still learning and have recently re- reviewed David's cabal report on the Alfa (pt7) which is pretty much a tutorial on ballasting a sub as it is specific to the Alfa. See the link on this site....

http://support.caswellplating.com/index.php?_m=downloads&_a=view&parentcategoryid=23&pcid=5&nav=0,5

To quote David on some ballasting basics from this excellent report:
"Center Of Gravity Considerations Where the c.g. falls, longitudinally, on the hull is important for two reasons. First, the c.g. is, disregarding fluid forces on the moving hull, just below the vehicles center of rotation about the vehicles pitch and roll axis, and right on the vehicles yaw axis. The greater the vehicles control surface distance from the center of rotation (moment arms), the greater the force they exert about the axis point. But, put the c.g. too far forward and the boat becomes overly dynamically stable."

"With the c.g. too far forward the boat is too dynamically stable; the boat is difficult to steer about the yaw and pitch axis; the pitch and yaw rates are low. However, if you position the boats c.g. too far aft the boat becomes either dynamically astable (presenting to righting forces regardless of angle presented to the fluid stream) or unstable (the vehicle reorients and becomes stable at an undesired orientation to the fluid stream), making the boat a total ***** to drive. Good drivers strive for a boat that is astable -- the boat has good pitch and yaw rates, but requires constant attention by the Driver! The center of pressure (c.p.) on a vehicle is the point where the collected fluid forces gather on the hull -- a consequence of the friction produced by the fluid in contact with the vehicles outer envelop. Again, it takes considerable math skills to work out a specific shapes c.p. But, you can work out a
good estimate on paper. For idiots like me you simply make a profile drawing of the vehicle on graph paper and count the number of squares, you then find the longitudinal point on the drawing where the number of squares aft is equal to the number of squares forward, call that your models c.p. You want the models center of gravity (determined easily with a sling on the model) to be a bit forward of or on the c.p. (determined from the graph-paper study). Remember, an over-stabilized boat is a boat that is hard to turn!"

OK so c.p is therefore important, and as David says in his report we usually stick the BT about half way a long and it works out great - most times. That half way long pt is usually indeed a guess, but I wanted to try out, as I don't have a considerable maths brain either, using David's grid guestimate instead. Using herein with permission Steve Batchelador's profile, modified by me, I worked out a good way to grid this method up. - Use a Spreadsheet program - in this case Excel.

First I resized the Excel spreadsheet to have the cells reformatted so that the cells are squares. Next I pasted in the profile I worked on. Note here you don't need to post in a profile in the exact size of the model, you can use a profile in any scale that suits your ability to have it in a workable size on your computer. The profile should be preserve the dimensions of the boat in whatever scale the profile is. That is, be careful not to stretch the image by resizing it as you paste it in.

The profile image you paste in needs to have a grid over the top of it, so you need to make the image transparent, and you need to format the cells the image covers by puting a border on all those grid lines. The result is that you can then have a uniform grid to which count the cells (squares). The easy, most accuarte way of counting is to group sections of whole squares together, and then just multiple the area L x W. For areas containing portions of whole squares, group these together and estimate how many whole squares these equal. Simply count the ones nearest the curves etc too. Add up all the squares within the groups, getting the total squares for the whole profile. Then divide by 2 to get two equal areas of the boat's profile fore and aft . I then start at the stern and work forward, calculating how much area from the stern equates to half of the total. I marke up a demarcation line. At this point I know where the c.p is. To translate this to the model, I then measure the distance from the stern to this line (just hold a ruler up to your computer screen), and work out what percentage that is to the whole length of the profile on screen. In the case of Rankin its 56%, this then is translated to the whole length of my model.



In my case, the c.p was located 15mm further back from where I initially had the centre of my ballast tank. I was able to move the WTC back, by simply removing some excess lexan from the aft compartment.

Having now established where the c.p is you then can with a fully loaded sub (batteries etc) make this the centre of gravity (c.g) , by placing a sling under the sub at the c.p point, and adding trim weights fore and aft unitil the sub is balanced. Obviously I will have to do this exercise (sling and trim), when the torpedo gear arrives. After your happy with the balanced sub around the c.g at the c.p point - you then go back and put the sub in the water triming with foam. Using the sling last night it was a complete eye-openner as to the fact I had too much weight forward.

Thanks to David for sharing this approach via the cabal reports - I have learnt something - and David jump in here if I have got this wrong.

best
J

[Slats]

Time to update this thread the ballast system a - semi aspirated tank can be found here:

http://forum.sub-driver.com/showthread.php?778-My-prototype-of-a-semi-aspirated-ballast-tank-system

Using this system - I recently ballasted the boat in my test tank and then went for a couple of test sails at my local freshwater dam.
The system was thoroughly put through its paces along with the incorporated the new 3.5" Merriman SD motor end cap. A review of the new end cap can be found here:

http://forum.sub-driver.com/showthread.php?784-Review-The-new-3-5-Single-Shaft-twin-motor-Merriman-motor-end-cap

Some photos herein show more progress work on the Collins heading towards completion.

Whilst the boat will need final ballasting "tweaking" for all its finished bits and pieces added including its paint job, (eventually having the new torpedo system), I ballasted the boat recently for its main ballast lead and foam. Shortly afterward I hit the local dam for some initial trials.

Test tank: Ballasting - initial foam placement. Tank is at filled / pressure capacity - boat is setup slightly positive.






Deliberately going negative with extra lead weight to test surfacing beyond snort range using the compressed air inside the tank.

[Slats]

Spent much of the evening yesterday doing some ballast tank experimentation with Rankin. To do this I use a simple and inexpensive piece of PVC pipe and push fit end caps in place for the tank. Taking into consideration Dr David Batagol's Collins and Jim Russell's Collins, they advised that I would need a significantly large Ballast tank to get this boat to correct surface trim and then dived. Putting the new SD 3.5" with dual motors and single shaft in one dry section at the rear and putting the a new pump system I am trying with battery space in a forward section, I discovered I need 800ml of water in the tank to take her from surfaced to just a tiny bit positive (top 10mm of sail showing). Will post photos over the weekend, but for those clinging to RCABS as a system for everything, know that there is no way within the confines of this metre long slender model of generating 800ml of airbag lift as I painfully discovered through a costly exercise. This boat wil have minimum foam floatation, and whilst the WTC at 3.5" uses pretty much the whole beam of the boat there is plenty of clearance (annular height think its called), to the deck and room below the WTC for ballast weights.

Photos and more soon

[Slats]

I'm sorry John, but I don't agree with you here.

Quoted from the Evercoat data sheet-

Uses a unique blend of high strength polyester resin, and long strand bulk fibers for maximum strength and consistent performance.
Provides maximum impact and crack resistance in bulk filling applications and when bridging over shattered and heavily damaged fiberglass and metal.

If you mix glass fibres with polyester filler, it will work, but will be much weaker than mixing with resin, so they don't do it. I make my own fillers up all the time, cheaper than buying lots of tins of stuff. I do use Upol ready mixed polyester filler for master work though- convenient.

I get Andy, I think we talking about the same thing from different terms.
I use the term filler - but the ingredients are exactly that above i.e. resin. Meaculpa! Thanks

J

[Subculture]

I'm sorry John, but I don't agree with you here.

Quoted from the Evercoat data sheet-

Uses a unique blend of high strength polyester resin, and long strand bulk fibers for maximum strength and consistent performance.
Provides maximum impact and crack resistance in bulk filling applications and when bridging over shattered and heavily damaged fiberglass and metal.

If you mix glass fibres with polyester filler, it will work, but will be much weaker than mixing with resin, so they don't do it. I make my own fillers up all the time, cheaper than buying lots of tins of stuff. I do use Upol ready mixed polyester filler for master work though- convenient.