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I need help with Warship Hulls Unlimited type IX

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I need help with Warship Hulls Unlimited type IX

Postby flying jeep » Mon Feb 07, 2011 9:05 pm

I need help with an old Warship Hulls Unlimited U-boat. I started this boat almost 20 years ago, pre-internet, and I've never had much luck getting it to submerge and return to the scale waterline. I based my pressure hull design on the 32'nd parallel type VII with a center WTC and two ballast tanks. I used a water pump with a snork to the conning tower that would drive the receiver nuts even with caps installed on the motor. I used long stuffing boxes and double sided Dumas pushrod seals glued to the pushrods. I never had any major leaks even with all the screws through the plexiglass top. My problem is with full ballast tanks it would not submerge. So I added a lead keel. Cool, goes down. But will now only go up to decks awash. As this sub is based on old technology, is the pressure hull too large and have too much displacement? Do I need to rip it all out and go to one of those fancy, high priced, tube kits? I attached lots of photos so you can have a better idea of what I'm up against. Sorry about the dust, it's been years since I played around with it.

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Re: I need help with Warship Hulls Unlimited type IX

Postby subdude » Mon Feb 07, 2011 10:08 pm

Without getting too far into theory here, the short answer is that your ballast tanks are of insufficient size to lift the weight of the boat above surfaced waterline out of the water. You have 2 options to correct this.

1. Increase the size of the ballast tanks.
2. Decrease the weight of the part of the boat which is above waterline.

If your pressure compartment is above waterline at all, you'll need to be lifting it out of the water. Also, any part of your ballast tank that's above waterline is not doing anything, the entire tank needs to be below surfaced waterline.

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Re: I need help with Warship Hulls Unlimited type IX

Postby flying jeep » Mon Feb 07, 2011 10:19 pm

Well, then I'm pretty much screwed. I have no way to incrrease the tank size as they were custom made to be as large as possible and there is only more detail and weight to be added above the waterline. Sounds like my pressure hull is too large.
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Re: I need help with Warship Hulls Unlimited type IX

Postby the dark knight » Mon Feb 07, 2011 11:35 pm

could you add some foam below the water line to help this out? just a thought... :?
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Re: I need help with Warship Hulls Unlimited type IX

Postby subdude » Tue Feb 08, 2011 8:40 am

Foam below the waterline will do nothing to affect the issue at hand. All that will do is raise the "tanks empty" waterline, then the boat will be unable to submerge.

The issue is the direct relationship: capacity of ballast tanks below waterline MUST equal or exceed weight of boat above waterline.

Is the pressure hull extending above waterline?
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Re: I need help with Warship Hulls Unlimited type IX

Postby JWLaRue » Tue Feb 08, 2011 12:29 pm

subdude wrote:Decrease the weight of the part of the boat which is above waterline.


To be completely technically accurate....

Decrease the displacement of the part of the boat which is above waterline.

We do tend to combine/interchange the two terms, usually without a problem. But in this case, the difference may may be important. The boat is already supporting the full weight of the part above the waterline....otherwise it wouldn't float at all. :) So what you'd like to do is to get rid of enough of the above the waterline parts to change the amount of water displaced by that part of the boat.

What is above the waterline that you can remove? Is there any floatation foam? Any really thick partitions/bulkheads/etc. that can be thinned or removed?

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Re: I need help with Warship Hulls Unlimited type IX

Postby flying jeep » Tue Feb 08, 2011 9:09 pm

There is a very small amount of pressure hull above the water line. The upper decks are solid plastic or fiberglass. There is no foam anywhere anymore. Per the earlier post, if I can reduce the displacement of the pressure hull the balast tanks may be enough? Can I do that by adding a flooded compartment within the pressure hull? With the samller components, I may have room to do just that.
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Re: I need help with Warship Hulls Unlimited type IX

Postby subdude » Tue Feb 08, 2011 9:28 pm

Hi Jay

Please refer to the previous equation.

The capacity of the ballast tanks below waterline MUST equal or exceed the weight of water displaced by whatever is above the waterline.

The only things that matter in this equation are the volume of the tanks, and the amount of stuff ABOVE WATERLINE. That's it. You can add weight, foam, change the size of the pressure hull, or whatever below waterline and it's not going to make any difference at all to the ability of the ballast tanks to lift the boat to surfaced waterline.

Bigger tanks, or less (or lighter) stuff above waterline.

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Re: I need help with Warship Hulls Unlimited type IX

Postby flying jeep » Tue Feb 08, 2011 10:04 pm

Okay, smaller pressure hull + larger balast tanks = sub goes higher in the water? Sometimes ya really gotta dumb down the math for us fixed wing avaition types :roll: So all that heavy plastic and fiberglass conning tower and deck is killing me. Now add a couple AA guns, bollards, etc. and I need a couple empty one gallon milk jugs to keep this thing at the waterline. But why was I having such a hard time getting it to sink? Is it just the amount of displacement of my large poorly built pressure hull full of 1980's radio equipment and rheostat speed controllers? :shock:

Thanks for all your help. This has been an equation that I've been trying to figure out for a long, long time.

Jay
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Re: I need help with Warship Hulls Unlimited type IX

Postby subdude » Tue Feb 08, 2011 10:19 pm

Jay,

Now you've got it!

And yes, the large displacement pressure compartment requires a lot of weight to get it to submerge. That's why "dry hull" boats are so doggone heavy, then need to weigh as much as the total amount of water they displace.

So, where on the planet are you? Is there a local chapter that could lend a hand?

Jim
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Re: I need help with Warship Hulls Unlimited type IX

Postby flying jeep » Wed Feb 09, 2011 7:11 pm

I'm on the west side of Indianapolis. We have the Indianapolis Admirals, and I plan on joining, but I don't know if they have any sub gurus. Looks like I'm gonna gut the sub and start over. Does anyone make a cylinder water tight compartment for this size sub? And while I'm asking stupid questions, and I know I've seen others ask this before...Why do the "guts" of a sub cost so much? I was trolling though the Mikes sub works and saw the prices of the pushrod seals, drive motor assemblies, endcaps, etc, are not out of sight. Is it the design and assembly of a working sub driver that cost $500? I guess if I had to charge by the hour to build one of my fixed wing planes it would cost a fortune as well.

How are the tube style comartments fastened inside a scale hull? Are internal components usually fastened to the endcap? I read the article from Rogue sub works about how to build a RCABS and was wondering why some folks poo poo this design. Is it better than a snokel design or just another means to an end? And what the heck does RCABS stand for??

Thanks guys,
Jay
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Re: I need help with Warship Hulls Unlimited type IX

Postby Art Broder » Wed Feb 09, 2011 11:12 pm

RCABS stands for Recirculating Compressed Air Ballast System. It's a simple system that does not require snorkeling outside air.
The cylinders can be secured on semi-circular mounting braces attached inside the hull, by rubber bands or Velcro straps, to allow for easy removal for adjustments or to use the cylinder in different hulls.
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Re: I need help with Warship Hulls Unlimited type IX

Postby subdude » Thu Feb 10, 2011 8:54 am

Art, thanks for explaining.

Jay, FYI Art pioneered RCABS

As to your questions, you're on the money. A developed, built up internal watertight compartment is expensive, and it's because you're paying for someone's time to develop and build it. Like many other things, you can do it yourself for far less money, but have to invest the time. You can build a house for less than you can buy one, but you'll need to be ready to (and able to ) do a bunch of work. Or, you pay someone else to do it for you. As a side note, I'm notoriously cheap, and build my own (hey, it's a hobby, right?)

Many tube style compartments use a sliding tray to mount the components, which attaches to an end cap.

RCABS works well, as does a snorkel, onboard gas, displacement pump, piston tanks, etc. Lots of different ways to skin the same cat.

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Re: I need help with Warship Hulls Unlimited type IX

Postby flying jeep » Thu Feb 10, 2011 8:31 pm

Thanks guys, but let's take this step by step. As nobody has stepped and said there's a made to order sub system for this boat, I'll need to build my own, again. And I don't like making the same mistake twice. I've seen lots of examples of dive systems all based on the same tube format. Sounds good, I'll follow the trend. I prefer the snorkle as I did before, decided then. I now know the weight of water is .036127 lbs per sq inch and the volume of a cylinder is:
V=pi x radius squared x height. And you will need the same amount of weight as the wight of water times the square inches of your cylinder to make it sink. What I've not found out is the lifting force of air under water. I googled "bouyancy" and got some real long haired math. I never did understand Neuton meters of force. Has anyone found a rule of thumb like, for every inch of 3" tube you will need 4.5 inches of balast tank?

Thanks,
Jay
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Re: I need help with Warship Hulls Unlimited type IX

Postby flying jeep » Thu Feb 10, 2011 9:08 pm

I'm still banging my head against the wall with this problem. I've done the math on a 3"x6" cylinder, it will take 2.21lbs to make it sink. But all the forumlas I can find refer to how much upward force is on an object already afloat. But I'm going the other way! My initional thoughts were this sub would be just slightly bouyant with full tanks and take just a small amout of air in the tanks to lift to the water line. This thought was based on the 32nt Parallel plans. Is it just me, or have you ever noticed that an un-opened beer in a can just barely floats? I wonder how much air it would take to float that beer 50% out of the water? But that's not right either as I would never need to lift the pressure hull out of the water. Oh, my head hurts and now I need a beer....

Jay
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