Re: [PSUBS-MAILIST] Re Variable Ballast Calculations

Myles,

Thanks again, but the math is either right or wrong. It is a theoretical problem please review it.

Submerged displacement = 28,637 lbs

Minus vessel dry weight - 10,000 lbs

Variable ballast required 18,637 lbs = 2,330 gallons of seawater in tanks

Cubic feet of ballast tanks required = 291 cf required to reach theoretical neutral buoyancy

From: Myles Hall <myles.h@sasktel.net>
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Re Variable Ballast Calculations
Date: Sun, 13 Nov 2005 10:36:00 -0600

Joe,

   There are two forces at work here. Bouyancy (which is determined by how much water the object displaces) and weight. Bouyancy = Up. Weight = Down. If you want to be able to submerge an object that displaces 28t of water, it has to weigh at least 28t. If you want neutral bouyancy (which is the magical situation for a sub. Too bouyant = boat. Not bouyant enough = sink to bottom and die), then displacement must = weight. 28t is a pretty big sub, getting up there in the Carsten and Peter league :)

   I agree totally with your comment about why build something like this. It's so that at the end of the day, you can stand back and say "I did it." For me, just learning the skills and aquiring the resources to even THINK about it, has made me a better person both in terms of having confidence in that I CAN actually do something if I try, and adding to my personal skill set. The sub is just a nice by product.   ....that's the way I see it. The sense of accomplishment that the guys that actually get a sub built and sailed must be phenomenal. That's what I'm after.

   At this point, the largest challenge before me is setting up the shop to build the sub. A two car garage isn't much of a "shop".

Myles.

----- Original Message -----

From: Joseph Perkel

To: personal_submersibles@psubs.org

Sent: Sunday, November 13, 2005 9:40 AM

Subject: [PSUBS-MAILIST] Re Variable Ballast Calculations

Hi Dan,

Very valuable input on your part and the practicality issues all have to be looked at closely. The reverse thinking idea you mentioned, is how I came up with the 28k submerged displacement. I took the external dimensions off of a scale drawing that I drew of the hull itself and calculated the total volume. Then applied an imaginary external force to submerge this volume to get "X" displacement of seawater.

So I ask myself, what would it take to "submerge" a vessel that has a (submerged) total displacement of 28k? The 10k dry weight is totally arbitrary and just easier to work with. So this was an exercise in the mathematical requirements of submergence to theoretical neutral. I then posted the results to check myself to see if I have the concept down correctly. Incidentally, I did "internalize" the tanks within that volume and discovered precisely what you said.

As Rick M said, a "great boat but lousy sub" is correct however, apparently the concept of a submersible "boat" has been applied successfully as in the example of the "Proteus", although on a much larger scale. And as Carsten points out, the concept of large volume water ballast is not new, and I found his link fascinating.

http://www.prismnet.com/~moki/20050322.141703/120tGlidingsub.jpg

Although I am not planning on hydrofoils, I found the schematic of the ballast tanks interesting in that they appear to be well baffled.

You are precisely correct about the issues of trailering practicality and there are no doubt other issues to be worked out however, I have not been clear about my intention with regard to trailer ability.

It is has been my experience as a long term boat owner, that most boats do in fact sit unused (mine included) for most of their lives. This was true even when I had my own dock in the backyard on the intra-coastal waterway. So by far, the biggest costs (acquisition costs aside) are long term storage costs.

I am talking about a flatbed 5th wheel trailer with a cradle that can be stored on my little farm in central Florida during those long periods of non use. You want to explore the Florida Keys for three weeks? Have the marina sling you in and out and leave the rig at home. This option offers up different design considerations, all dependent upon G.V.W. Check out the weights of these vehicles at the link below.

http://www.tetonhomes.com/royal06.asp

Now this is a whole different monkey in the cage.

Why do this knowing it will sit unused most of its life and cost me a small fortune in the process? I suspect for the same reasons a Harvard Medical school grad risks his neck climbing Everest, the personal challenge.

Thanks a bunch

Joe

Bill,

As always, your links are truly fascinating! I will sit back and look them over today...thanks!

From: "Dan H." <jmachine@adelphia.net>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: Re: [PSUBS-MAILIST] Variable Ballast Calculations
Date: Sat, 12 Nov 2005 21:08:54 -0500

Joe,

I think your best approach would be to determine what you consider a weight you can haul on a trailer and then use that weight for your sub's displacement. You'll quickly see that what your designing is way to large for anything other then a tractor and semi trailer.

Water weighs nothing in water! If your planning to trailer a light sub and later take on water to make your sub heavy enough to dive, your just building a big tank attached to your sub to take down with you. The only way that water ballast is effective is if it's contained within your existing hull's displacement. Adding on ballast tanks to make a large sub heavy enough to dive is futile. The only way to make a sub heavier with water is to increase your weight without increasing the displacement. That is, reduce your sub's interior space with water tanks.

You have to trailer all the weight with you, either in or on your sub, to dive it when your ready to launch. If your sub displaces 28,637 lbs you must have your sub weigh that much with your hard tank full of water or you aren't going down. Your trailer must be capable of hauling that much weight minus the water your hard tank holds.

As Carsten advised, your hard tank volume is only a small percentage of your subs total weight. It's for adjusting buoyancy and not practical to add significant weight to an under weighted sub.

You have several options,  A smaller sub (less displacement), and less to trailer.

                                      A large sub with a lot of fixed lead weight either inside or outside of the hull

                                                (if outside, you have to consider the water it displaces also).

                                      Make your sub out of heavier or thicker material and let the weight of that extra material

                                                do some work for you by allowing you to dive deeper.

No matter how you cut it, you have to trailer the subs displacement weight to the launch ramp or your sub will be a surface boat..

I think you'll find that 5000 to 7000 pounds is about the upper practical limit. One additional reason not to get to large is, most boat ramps aren't deep enough to launch a large diameter sub from a trailer.

Dan H.

----- Original Message -----

From: Joseph Perkel

To: personal_submersibles@psubs.org

Sent: Saturday, November 12, 2005 5:45 PM

Subject: [PSUBS-MAILIST] Variable Ballast Calculations

Carsten,

Yes you did understand me correctly, the soft water ballast ratio is indeed high in this example. However, the response indicates to me that I understand the principles much better than when I started out. The target range you mention of 20 to 30% of dry weight for a sea boat is extremely helpful, thank you. I am still learning, with help from those such as yourself, what is and what is not possible.

I am trying to work the numbers for a dry ambient boat that would be large but still be trailer able. It will take me months but if I will post schematics when I have what I believe to be a practical solution. See the link below to follow my train of thought.

Thank you

Joe Perkel

Miami, Florida

Rick,

Same as above, the numbers represent a new upslope in the learning curve for me. They are indeed lopsided as you and Carsten point out, but they are in the theoretical ballpark if not a practical one. Exomos (see the link) has a submersible "surface" yacht (Proteus) that has a displacement of 45 tons. They do not specify if this is submerged or not but the thing does 25 knots on the surface.

I don't want to go 25 knots, but I suspect that the dry weight to ballast numbers look something "like" my example in order for it to plane at that speed.

To answer your question about size, whatever is possible for a crew of three in relative comfort?

http://exomos.com/exomos_main_content.html

Thank you as well.

Myles,

Dry weight and displacement are not the same thing. I appreciate the effort however.

Thanks

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