Sub physics - experts needed

[TopTorp '92]

Originally Posted by Dr.Sid

I'm tuning my first simple movement model for my subsim. I'm trying to set it to some realistic behavior. There is however too many things I don't know. So I have few questions.

I found on internet some data about subs, for example good old 688. I have weight, size, engine power, maximum speed. Now this alone is almost enough for much of the simulation. But not all, and I also need as much real data as possible to see if my model indeed is realistic. I'd like to know:

1) Acceleration at different speeds, especially at 0. (Too technical for recent memory)
2) How long the subs takes to stop after engines are cut off. (No recollection)
3) Does sub have screw with variable pitch ? How is it used exactly ? (Screw isn't variable)
4) What is the turning rate at different speeds ? How much rudder is needed to achieve this ? (ruder angle combined with speed determines turn rate. Generaly, we were looking for about 3-5 degrees per second. If you turn too fast you risk rolling the ship over.)
5) Why do subs have lower max speed on the surface ? (Lower surface speed because of its shape. It looks like a pipe or a cigar.)
6) How is the depth controlled ? How much does the tanks, how much the planes ? How strong effect trim tanks has ? How are they used ? How are the common surface and dive procedures from these aspects ? (See link below. That book does a really good job at describing most of the control features of submarines. In brief, the trim system controls ship's weight with reference to achieving one of three states: Light overall (LOA), heavy overall (HOA), or OK overall (OKOA.) When I was a chief of the watch we always trimmed the ship LOA and used control surfaces to maintain depth. However, if you decide to start shooting several torpedoes, then you will trim the ship HOA expecting the ship to lighten up after you finish shooting torpedoes.

Please don't wild guess. I can do that too. I want some real info, with references, if possible.

See link below. This book does a nice job of explaining much of the complexity associated with trim systems and control surfaces.

Complete Idiots Guide to Submarines: http://www.amazon.com/Complete-Idiot...6082917&sr=8-1

[jmr]

^^^^
That's a hard to find book. I can't even find it on eBay.

[Linton]

Here is a copy.It is over $260!!!!
http://www.dualj.com/bookstore/item_...mID=0028644719

[OneShot]

No kidding, I found one copy on Amazon.de but the company wanted a hefty 183€ for this ... Guess I pass on that one.

[Dr.Sid]

I guess I'll pass to. Anyway for the diving I now have all data needed. On the other hand I'm extra busy at work, I was working whole weekend and all evenings. So please be patient.

[Dr.Sid]

Just an idea how to determine real sub lift coeficients. Have you ever heard about diving sub without filling the ballast tanks ? It should be possible, at some speed and pitch angle. Or the opposite .. surfacing sub with tanks full (and staying surfaced).
I understand both maneuvers are nonsense, but maybe somebody ever this, even theoretically.

[Bubblehead Nuke]

Originally Posted by Dr.Sid

Just an idea how to determine real sub lift coeficients. Have you ever heard about diving sub without filling the ballast tanks ? It should be possible, at some speed and pitch angle. Or the opposite .. surfacing sub with tanks full (and staying surfaced).
I understand both maneuvers are nonsense, but maybe somebody ever this, even theoretically.

Nonsense maybe, but lets think this out.


Diving with the ballast tanks bown dry:

MAYBE, if you had bowplanes (they would be under the surface and thus effective).. and were going flat out on the surface, you MIGHT be able to push the bow down enough to get the water flowing over the hull, thus turning the upper hull into a massive plane surface. The old nuke boats of before the Albacore hulls (pre 637 hulls) had this problem at high speeds. They had to be careful at high speed putting angles on the hull less they lose depth control. I do believe that the rounded hull surface all but eliminated the issue.

They also have a LOT of reserve bouyancy designed into the hull. I do not think you could do this if you tried.

Surfacing the boat with the ballast tanks full:

Yes, easily. You just drive the ship up using the planes and the engines. Once on the surface you have the surface tension of the water to help support you (this is the same thing that allows a needle to 'float' on the suface of the water.

One term for surfacing without blowing the tanks is called 'broaching'. We hate doing it as when you have fairwater planes, you can make a rather LOUD noise and REALLY shake the boat when the planes come down back into the water.

[Bill Nichols]

Originally Posted by Linton

Here is a copy.It is over $260!!!!
http://www.dualj.com/bookstore/item_...mID=0028644719

Wow! I'd better take mine off the bookshelf and put it in a safe deposit box...