I'll be using the exact same gear so the only difference should be the salt water vs fresh water. I'll start out with about 7lbs extra and see where I end up. It just seems like it will be hard to do a weight check in the water while everyone else is jumping in and starting their dives. I haven't done a boat dive before, will they give everyone time to get their weight sorted out before starting the timer for when you have to be back on the boat?
There is great variety in how dive boats manage getting divers in and out of the water. A lot of this is dependent on the size of the boat. I've been on small boats in the Caribbean where people do back rolls from a seated position. I've also been on large boats here in SoCal where people take a giant stride off of the side of the boat 10-15 ft above the surface of the water. With regard to timing logistics, many of our local charters set "gate times" that specify when divers are permitted to
enter the water. In setting the gate time, the crew takes into consideration when the divers will actually be
exiting the water. In most cases, divers will conduct dives that last 30 min to 1 hour. It's courteous to let the crew know how long you intend to stay down. This usually isn't a big deal for a newbie diver, but it can be a big issue for a rebreather diver who can stay down a loooooong time on his breathing apparatus.
If you want to do a weight check before doing your first dive, I would discuss this ahead of time with the DM/captain/whoever is charge of helping divers enter the water. You don't want to "tie up" the entry point futzing around with lead while others are trying to splash in. That would be inconsiderate. Discussing it ahead of time allows the crew to figure out how/when/where to help you. It
might be best for you to get in last, swim around to the back of the boat, and have a crew member hand small increments of weight from the swimstep. You should discuss your plan well before you arrive at the dive site. Once there, the crew will probably be busy setting the anchor or tying up to a mooring buoy and counting heads going in/out of water.
If you are doing a weight check at the beginning of your dive with a full tank, please consider that you will be using up gas in your tank during the course of your dive and change the amount of lead to compensate for this. For instance, if you are properly weighted at the surface with a full AL80 at the beginning of your dive, then add another 6 lbs. to offset the weight of your gas. For a HP100 steel tank, the weight of the gas is about 7.5 lbs. Recall that you want to have enough ballast to hold a safety stop with a near empty tank at the end of your dive.
Many divers who have a ballpark idea of their weighting requirements will simply plan to be a little overweighted on that first dive. At the end of the dive, they'll surface safely with plenty of air. Near the boat, they'll purge their tank down to about 500 psi and test their buoyancy. Holding a normal breath with reg in mouth, the water should be at eye level. To account for the remaining gas in their tank, they'll add 1 more pound. That's what I do.
Good luck and have fun...
