SubCar 2004

[SubCarBuilder]

Hi, I am a novice at boat building. Some friends and I have started building a SubBoat, but are encountering troubles with getting the car to sink. Would anyone know how much water would be needed in Litres or Gallons, to sink a 1400lbs car. I know that the air volume will need to be calculated, but my math isn't so strong. The Box inside the car is 3' 6" by 6', sealed. Exterior tanks are being mounted to the side of the vehicle to take on the water.

Sorry if this is confusing

Mike Harrison
Project ShallowDive 2004
mikeonatrike@hotmail.com

[duluthboats]

Forgive me if I’m wrong I know nothing about subs I always thought the idea was to have enough tank space to keep the sub from sinking. Then when you want to go down you flood the tanks. So if the sub doesn’t sink without the tanks start adding lead until it sinks. I’m thinking if the math for displacement is hard on you, doing the math for hull strength is going to give you a headache.

Gary

[foxxaero]

Originally Posted by SubCarBuilder

Hi, I am a novice at boat building. Some friends and I have started building a SubBoat, but are encountering troubles with getting the car to sink. Would anyone know how much water would be needed in Litres or Gallons, to sink a 1400lbs car. I know that the air volume will need to be calculated, but my math isn't so strong. The Box inside the car is 3' 6" by 6', sealed. Exterior tanks are being mounted to the side of the vehicle to take on the water.

Hi Mike, interesting concept you are working on. It wouldn't happen
to be a Lotus car would it? I don't know much about subs but it
seems to me that if the car won't sink, you just open a valve which
allows water to enter the sealed compartment and down you go ... course
this wouldn't be ideal if you were sitting in the sealed compartment :-) .

Here's a page with links to a number of sub sites. If you follow
the links you will find websites related to submarines (some of which
are very informative about sub operations). Just a suggestion, but I
think I would do some serious research before taking that baby out for sea
trials. Do you have any pictures of your subcar that you could post?

http://foxxaero.homestead.com/indsub.html

Cheers

Russ

[Red Pike]

The numbers to use, for sea water (divide by 1.025 for fresh) are 35 cubic feet per long ton (2240 lbs). So, calculate the cubic feet of the molded volume (exterior of car), multiply by 2240/35 to get the neutrally bouyant mass, subtract the mass of the car to get the mass of water required to achieve neutral buoyancy. Take that mass of water and convert back to whatever volumetric units you desire...

[jehardiman]

As a Naval Architect who is involved in designing submarines and sub systems for a living these past 20 years, I would suggest that you do a little bit more research into basic sub theory before beginning the design. Load to submerge is a rudimentary calculation, the first of about 20 you will need just to manage the submergence (first rule of submarine design...it has to be a submarine, not a boat, not a rock). And then you have to get the boat up again. And we haven’t even begun to talk about stability, propulsive, atmospheric, or structural issues. Get a copy of the old Principles of Naval Architecture (single volume); there is more than enough information in there to keep you working for several days on just the requirements for submergence.

There are many people out there that think that submarines, like boats, ships, cars, trains, and airplanes are fairly safe. This is because you rarely hear about accidents. This is because the tens of thousands of man-hours that you don't see that go into failure modes and analysis on every component and system, and fact that subs (and cars and planes) are built upon pre-proven and pre-tested design components. However, unlike a car or even a plane, I realistically cannot go down and buy a certified component off the shelf. Designing submarines, especially dry subs (you said the compartment was "sealed"), is not a game, and is not for the unknowing. The loads on the structure even at the shallow depth of 33 feet would crush most vehicle compartments and shatter most automotive glass This is of course providing you could get the compartment sealed (Whats the difference between a leak and a flooding casuality?...When you fear for your life!). There are a thousand ways to kill people in a submarine and you need to address every one that can be addressed. Not ensuring safety because you didn't know is not an option. Personally, I don't care if you kill yourself , but I would ask you to pause and think of your mother/friends/wife/children and the rescue divers who will risk their lives to drag your dead body out of the wreckage.

[jehardiman]

Originally Posted by Red Pike

The numbers to use, for sea water (divide by 1.025 for fresh) are 35 cubic feet per long ton (2240 lbs). So, calculate the cubic feet of the molded volume (exterior of car), multiply by 2240/35 to get the neutrally bouyant mass, subtract the mass of the car to get the mass of water required to achieve neutral buoyancy. Take that mass of water and convert back to whatever volumetric units you desire...

NO...This will NOT work. This is a common mistake made when using an "outside-in" submerged displacement calculation. The above calculation ignores the "weight" added to the vehicle when the "freeflood tank" fills.

He should not take the moulded volume of the exterior of the car, but the moulded volume of the exterior of the "ever-buoyant hull", then calculate the actual volume of the freeflooded structure (i.e. the body structure itself, not the void space) to get the "ever-buoyant" submerged volume. From this point he could he can determine his buoyancy from which to balance his weight.

[Red Pike]

Jehardiman;

Mine was a simple calculation to give him a starting point, and was based on his request for how to sink the car, without having the tanks attached. Obviously any added mass (and volume) would have to be considered in the final product.

As a former submariner (13 years operating, maintaining and repairing US Naval Nuclear Submarines, an additional 2 years working on 48 passenger tourist submersibles, and a Naval Architecture internship at Electric Boat assigned to the SSN-21 modifications group) I concur with your sentiment that submarines can be dangerous, and should always be designed and operated with caution (just ask the crews of the Scorpion and Thresher).

[jehardiman]

Originally Posted by Red Pike

Obviously any added mass (and volume) would have to be considered in the final product.

Steve, this is the problem with a quick answer, someone with lots of experience would "assume" that the other would take care of the details. The problem is that some people who ask these questions have no concept of the details. Whenever someone (from SECNAV rank on down) comes to us (my project group) and asks a question we ask back: "why do you want to know?". Most of the times the person doesn't even know the question to ask. It frightens me, especially now after they have eviscerared NAVSEA tech codes and EB and NGNN has retired out all the old guys that knew what was going on. Having had contact with a lot of the 21, 22, and 23 people at EB, my money says that one of the 21 class will be the next boat lost.

(BTW...20 years US Navy, Ocean Engineering, Deep Submergence)