HP Tanks on SoCal Boats

[MWilliamson]

I am fairly new and mostly do shore dives in Laguna. I have an opportunity to dive Farnsworth Banks next month and wonder if my tank is adequate. I own a HP80 which works great for shore diving because I can get it filled to capacity, but according to what I read and my own experience on most local boats, the best they fill tanks to is 3000psi and 2500psi is not uncommon.

If I use my tank and the boat fills it to 3000psi, I'd have about 70cf and if it only gets filled to 2500psi, the capacity drops to 58cf. That's a 20% loss of air!

My question is what do you recommend in this situation? Should I rent an AL80 or maybe purchase a HP100? Or is there another solution?

 

[fnfalman]

Very few SoCal boats can fill up to 3500-psi. Most of the time they can do 3100 or if pushed, 3300. Of course it's a hot fill so when you jump in, it'd go down another couple hundred PSIs if not more.

If you're going to do Farnsworth Bank, then chances are you might do just one dive there and then move in somewhere shallower for the next dives. So fill up your tank from a shop and make sure that you're properly topped off for Farnsworth. If you're going to do multiple dives at Farnsworth then I'd suggest bringing a bigger tank to compensate for the compressor not giving you full boost. Or rent an LP77, LP90 or something of similar ilk.

 

[mathauck0814]

Contact the boat. Some boats have no problem with high pressure fills, others do. If you're really concerned, bring all your own gas in multiple tanks and stow them under the bench. Boat gas is sometimes wet (and I try not to use it) anyway.

 

[lamarpaulski]

You are smart to be concerned. Farnsworth can be challenging, deep, current-affected and you can burn through your air very quickly. If I recall the top of the bank is at 65-70 feet..thats the shallowest it gets. Air consumption would be much faster than typical Laguna Beach dive. May not be a good dive for a fairly new diver but definately get your best fill even if you have to rent a 100.

Some divers go the low pressure route if they boat dive a lot or bring 2 tanks (if allowed).

 

[scjoe]

I know a lot of people dive Farnsworth with 80CF tanks, but I wouldn't recommend it. It's a deep dive. I would use a 100CF or 120CF. One solution some people prefer is to have a low pressure tank for boat diving. A LP 95 is one option.

 

[SteveRoquemore]

Even the boats that fill to 3450, it will be a very hot fill as very few of the boats have adequate chillers for their fill lines. Best boat strategy is to either use LP tanks with a plus hydro or bring your own from the shop that you have a relationship with. Even shop filled tanks will only be filled hot to 3450, but you can tell them that it must be 3450 to go out the door. If you are going through the effort to get a tank filled at the shop, you should also consider nitrox for better bottom time at 100 feet. If the shop is using partial pressure system it is easy to pump the tank up to a full fill or more if requested. I use a LP 95 and the boats usually fill to 3,000 psi which is giving me 100 plus cf. This tank has never passed a vis as mentioned above boat fills can be wet air.

 

[drbill]

You'll want the gas as the peak we dive starts at about 60 fsw. Check with the boat operator first, then decide if you should take the HP tank (if they fill to at least 3300) or use an Al 80 (most boats have tanks on board) at 3000 psi

 

[geoff w]

A HP80 filled to 3,000 PSI gives you about 72 cu ft of air. The good news is when you get out from a dive, your tank will be cold and a little less likely to get hot. The bad news is high pressure tanks, especially HP80s, get really hot when filled, and will cool a lot over time and hence lose pressure. If you're planning your dive so close 10 cu ft of air is going to make a difference between having enough air or not, you should definitely look at a larger tank or consider a smaller (20 to 40 cu ft) stage bottle as a backup. The only time I've gotten a full fill quickly, a dive shop filled my tank to 4,000 PSI and when it cooled down it was just under 3,500.

A HP80 will give you the best buoyancy characteristics of any option. A HP100 will probably need 1 or 2 more pounds of lead to account for the buoyancy change from full to empty, and you'll need to add 6 to 7 pounds of lead to your rig if you switch to an Al80, and the Al80 is heavier out of the water to begin with. Something else to consider. On a more positive note, Al80s are way less susceptible to corrosion from moisture in fills than HP tanks

 

[MWilliamson]

You'll want the gas as the peak we dive starts at about 60 fsw. Check with the boat operator first, then decide if you should take the HP tank (if they fill to at least 3300) or use an Al 80 (most boats have tanks on board) at 3000 psi

First, it is quite an honor to have the famous Dr. Bill reply. Thank you.

Second, I know that the boat only fills to 3000 psi and don't supply tanks :depressed:, so I will be renting them.

---------- Post added April 22nd, 2014 at 10:32 AM ----------

A HP80 filled to 3,000 PSI gives you about 72 cu ft of air. The good news is when you get out from a dive, your tank will be cold and a little less likely to get hot. The bad news is high pressure tanks, especially HP80s, get really hot when filled, and will cool a lot over time and hence lose pressure. If you're planning your dive so close 10 cu ft of air is going to make a difference between having enough air or not, you should definitely look at a larger tank... Al80s are way less susceptible to corrosion from moisture in fills than HP tanks

I agree with you that if 10 cu ft of air is essential to my plan, I might want to rethink both my plan and the dive. My issue is that I wouldn't have ANY bottom time before I had to start back up with a safe amount of pressure in the tank. I'm just trying to be careful and not put myself at any great risk.

I've talked to a few people and all of them agree that an AL80 will be fine. I'll be renting one and I am comfortable with that. I have my log book and have always recorded the amount of weight needed for each dive, including AL80s, so my buoyancy should be ok and I plan on doing a dive Thursday with a rental tank just to make sure. I should be ok.

I've also read that boat fills are sometimes wet and can cause corrosion and I think using a rental tank is a bonus because of that.

I'm looking forward to the dive, but am nervous about the current.

 

[jscan1]

If you're putting this much thought into this dive, and already heading to Farnsworth....Like a lot of us you sound hooked! My as well succumb to the GAS(Gear acquisition syndrome) and get yourself a nice Fat Steel tank! I got a nice LP95 on EBAY then got it hydro'd all in for $200. My local shop usually fills it to about 2700- 3000 PSI, and most of the boat fills come out at about 2500 . Steel is nice you get to drop about 6lbs from the belt!