These tables are showing you buoyancy numbers for the tank and valve, nothing else. Doesn't take into account the buoyancy of other parts of the kit (BCD/bp/wing, regulators, the DIVER, exposure suit, lead ballast).
Can we agree that the important thing is that regardless of what tank you select, the important thing (in this regard) is to be able to hold a stop at the end of the dive?
In order to do that, you must be able to establish neutral buoyancy for the whole kit. Let's say that given your body composition, and exposure suit, and regs, etc... that requires X lbs of lead. If the gas you consumed weighed about 5 lbs, then that means your tank was 5 lbs heavier at the start of the dive, so you were 5lbs overweight.
The question of steel vs. aluminum simply adjusts how much of the [tank + kit + diver + exposure suit + lead] equation is in the tank part and how much is in the lead part. If the sum of that gets you neutral at the end of the dive, then you must have started out heavy by the weight of the gas you consumed.
To clarify, the only thing I was pointing out was that you do not need to add 5 pounds to your lead to offset lost air at the end of a dive with a steel tank. I absolutely agree that the important thing is to be able to hold a stop at the end of the dive. If we really want to get technical, it doesn't even matter if a diver is "overweighted" or "underweighted" since it's good enough if they can do that at the end of a dive.
I agree that the air obviously is going to weigh the same regardless of the container it's in, however, a steel tank weighs more so you don't need as much lead in your BCD or weight belt as a result thereof. I probably could have been more clear in stating why the 5 pounds was unnecessary; it's not because there's "less air" in the aluminum tank but because you just don't need as much weight in general if you're using a steel tank. My statement still stands for the extra 5 pounds if using an aluminum tank...go look it up in the PADI books. If you hate PADI for X reason, go look it up in SSI, NAUI, etc....I'm sure it says something similar. *shrugs*
As long as we're off topic... Physics 101
The debate between steel and aluminum is purely about how much total weight you need to have as steel tanks are generally more efficient in that they can hold more air for a given external volume of a tank, which is what drives buoyancy. Low pressure steel tanks are generally heavier than aluminum which means the aluminum tank diver will need more lead, but overall the total weight (Tank + lead) will be identical if the tanks have the same external dimensions and contain the same amount of air. Steel's advantage is that it can hold the same amount of air as an aluminum tank, but in a smaller package with similar weight (more efficient), making it displace less water (less buoyant) which means that it will sink like lead so you don't need as much additional weight.
Air is a constant (ignoring minor density changes due to temperature) and at 60F is .07786 lbs/cuft. 80 cubic feet weighs 6.2 lbs and in doesn't matter if it is in a steel tank, aluminum tank or a giant plastic bag. As the air leaves the tank it becomes lighter at the same rate for either tank (or plastic bag) and the change from full to empty is identical.
The absolute best way to determine how much weight you NEED is to make adjustments with an empty tank. If you can just barely descend with an empty tank, your weighting is perfect.
.
What I bolded in your reply is basically what I'm getting at. You don't need to add on an extra 5 pounds if using a steel tank to compensate for the air, because if you're using a steel tank, you're using less weight anyway. Sure, if we want to get completely anal about it, you actuall still add on an extra 5 pounds to account for the lost air but then you're subtracting at least 5 pounds if using a steel tank because it's about that much more negatively buoyant so they cancel each other out. I won't say the distinction doesn't matter, but in this instance, it isn't a concern.
You are correct that doing weight checks and adjustments with an empty tank is the best way to go. As Rhlee said, ultimately it doesn't really matter as long as you can maintain a safety stop and control your buoyancy.
One of the advantages of a beach dive is that you can do things at your own pace. I definitely found my first boat dives in California to be a little hectic compared to the resort diving I had done elsewhere. Especially when dealing with new gear or when getting accustomed to a new environment, both having to assemble gear in the confined space of the boat deck and feeling a bit of pressure to hit the water in timely manner can be added stressors.
This is true, time is a factor as far as boat diving goes, but if the only thing changing is the temperature and conditions of the water then I would say it depends. If the diver is already used to doing boat dives, even in tropical conditions, then that diver is used to being on a time table and getting their gear set up in a confined space in a limited amount of time. However, yes it will add a stressor, although I'm not entirely convinced it would make that much of a difference.
In addition, if you're being really conscientious about dialing in your buoyancy, you might make several trips in and out of the water as you add or remove lead. This is something of a painful exercise either on the boat or at the beach. But at the beach, you won't be worried about holding up the show; in my opinion, you're more likely to take the time to get it right. Moreover, on a beach dive you'll be fooling around with gear in waist-deep water. That's far more forgiving than jumping in and sitting on top of, say, Ballbuster.
On a beach, you have to swim back to shore and put on that weight then swim back out every time you do that. On a boat, unless the crew sucks, they'll be more than willing to hand you extra weight if you need it. Honestly, these weighting changes should take a max of 5-10 minutes and would obviously only shave that time off one dive. Hardly what I'd call a problem for boat diving.
Also, you're assuming that fooling around with gear in waist-deep water on a beach dive is safe. I can assure you if there's any appreciable amount of surf it's anything but forgiving. Granted, Breakwater usually does not have a lot of surf so that may or may not be a factor for a beach dive, but even that site I've seen with 6+ foot surf. I don't think someone fooling around in the surf zone with gear issues would be a pretty sight.
A beach dive is probably also going to offer a less aggressive dive profile. Adopting a forgiving profile is probably your best bet in any new environment, and going from warm water to cold water no doubt makes this doubly true. Among other things, the buoyancy swing with depth in a 7mm wetsuit is profoundly more substantial than in a 3mm. So a new Monterey diver might be better served by making the slow, mellow ascent afforded by just swimming on in at most shore sites, rather than attempting a direct ascent in blue water at some boat site.
Agreed.
As for "surf on top of everything," well I'd recommend that a new diver not dive if there's surf. Simple.
All that said, the OP is likely to have great dive on the Cypress Sea. As others have said, it's a nice boat with a good crew. But since you asked, these are just a few reasons why some folks (me included) argue that a shore dive might be the preferable way to get acquainted with California diving.
Fair enough, but then most people who go somewhere to dive who had to travel to get there are not going to be as likely to call the dive even if they should.
I'm not saying you're wrong as far as a shore dive being preferable, although I do have my disagreements on some of what was said, but at the end of the day as long as the diver dives within his/her limits it really doesn't matter if it's a shore dive or a boat dive. I'm sure the OP will have a great time on the Cypress; that's an awesome dive boat.
Nope, it's exactly accurate, for the reasons rhlee gave.
Not really, but I can agree to disagree since it's not like I (or anyone else) should expect someone to rush out and change their weighting because they read what someone said on an internet forum that may or may not be true.
