Why cant you just put your old stuff on n a pool? That will give you a start. You don't know just how much muscle or fat was lost. You can hang your rig on a pool orm a scale and find the buoyancy. If neg 8# then you in your suit was 8 light. Work from there. Put your old suit on and get in the pool and weight to get neutral. You will know by that weight how much your buoyancy has changed. Until then you done know what changes you need to make. Perhaps a new wet suit will do it. From what you said you have lost mass and lost muscle. they counter each other.
Lost 40lbs, need to change BP from SS to AL?
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The only real solution is a proper weight check - anything else is guesswork.
I'm in for fun doing a weight check on my next dive due to a complete kit change from rental gear to my own. I was weighted with 16Kg in a harness for a 7mm wetsuit with neoprene booties with a jacket BCD with rental fins and now will be diving with a membrane drysuit with attached boots (various undersuit combinations), BP&W and my own set of fins and a weight belt.
Not a clue how much weight I will need for that change!
In theory, yes, and in reality, some. But I suspect the area of neoprene covering your body is a much bigger factor in your diving buoyancy than your body composition. So, for example, if as a result of your weight loss you now use a Large wetsuit instead of a XXL wetsuit, that probably makes at least as great a difference as the loss of 20% body fat.
People seem to be overlooking the part of your original post where you said you "won't have the opportunity to do a weight check" before your trip. As you seem to understand, there is no way to get an accurate answer unless you do a weight check, by getting in water with your rig on, or weighing your rig by itself in a pool, etc. We're all just generalizing with our replies.
I am wondering whether the OP is on about not doing a weight check before leaving for the trip or not getting a chance while on the trip.
From what I hear about most dive trips, there is normally time for doing weight checks on site/off the boat.
From what I hear about most dive trips, there is normally time for doing weight checks on site/off the boat.
Neilwood, I think the concern is not having enough time to do a weight check with a new AL backplate versus not having an AL backplate ready for his trip. To the OP, I'm 6'1, about 165 pounds, and use my SS backplate everywhere, in all different exposure suits from skin (only happened once) to 3mm, 5mm, 7mm, and dry suit. The density of your muscle mass is definitely going to play a factor but it's not that much different than fat (when submerged in water) compared to the difference in the neoprene you'll be wearing. And muscle has a lot more water content than fat so it's more "neutral" in water, while fat floats. Neutral is a good thing when it comes to worrying about your weighting, right? (Or am I thinking of this from the wrong perspective with respect to the neutrality of the muscle?--Any one care to correct me?) The point being, I suspect you won't see much of an issue. You may be slightly overweighted but it should be well within the realm of manageable for this trip.
EDIT: Why the hell do my posts no longer have paragraph breaks?
EDIT: Why the hell do my posts no longer have paragraph breaks?
OP
fjpatrum is exactly right. I won't have an opportunity to do a weight check before my trip. I'll do my weight check on my first dive, but as my previous SS backplate setup required no additional weight, if I need to drop weight I have nothing to remove. My alternative option is to get an AL plate, but again, I won't have an opportunity to test it before my trip, and if I can't find someone who can lend me one, i'd have to buy.
There's only 2 changes on my coming trip vs. my last 500 dives. 1) I've lost 40lbs, mostly fat in theory would decrease my buoyancy, but i'm not sure by how much and 2) I've had to get a new 3mm full body wetsuit as my old one no longer fits, previous experience with new wetsuits with my SS plate had taught me that I can manage it with no weight changes, but my new wetsuit is quite a bit smaller, i've gone from XL to M. Lastly 3) I may opt to rent 15L tank for this trip because my GF is a fish, and would be nice for once if she didn't end her dive with over 120bar while i'm at 50. I've dove 15L before, and I've found the difference in buoyancy on my SS plate to be manageable without changing weighting, maybe 1-2lbs more negative.
Trying to theory craft if 1+2+3 means I should try hard to get an AL plate prior to my trip, considering that 1 and 3 are should make me more negative, and 2 should definitely be more negative once I get the fresh new neoprene squeezed.
There's only 2 changes on my coming trip vs. my last 500 dives. 1) I've lost 40lbs, mostly fat in theory would decrease my buoyancy, but i'm not sure by how much and 2) I've had to get a new 3mm full body wetsuit as my old one no longer fits, previous experience with new wetsuits with my SS plate had taught me that I can manage it with no weight changes, but my new wetsuit is quite a bit smaller, i've gone from XL to M. Lastly 3) I may opt to rent 15L tank for this trip because my GF is a fish, and would be nice for once if she didn't end her dive with over 120bar while i'm at 50. I've dove 15L before, and I've found the difference in buoyancy on my SS plate to be manageable without changing weighting, maybe 1-2lbs more negative.
Trying to theory craft if 1+2+3 means I should try hard to get an AL plate prior to my trip, considering that 1 and 3 are should make me more negative, and 2 should definitely be more negative once I get the fresh new neoprene squeezed.
fisheater
Contributor
In another thread on weight loss and scuba weighting, someone posted that the rule of thumb is that you can take one pound of lead off your weight belt for every ten pounds of weight loss. YMMV.
I would agree with what fisheater posted I have lost 34lbs over the last four months and I now carry four pounds less lead with the exact same gear and wetsuit setup. I purchased an AL plate for my warm water diving so I have the option it was not expensive.
You ar corrent about guess work. However guess work is necessary to establish a starting point. Once again you buoyancy issue is suit related. No need to rig up.. Hit the pol with the 7mm,, note the lead needed and do the same with the new suit. If its 8# different you are that much closer to where you need to go from he start. You being from scotland i dont suspect there will be much difference. you wll have more than enough to do working out the trim.
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