Can't get my trim right

[seabass]

I have worked for the last few hours of diving to get my trim correct. I read another thread about zept who had a similar problem to the one that I am having

Aluminum backplate, one piece single tank adapter, 27# wing.
3/2 1 piece full wetsuit
AL 80
fresh water
No weightbelt.
5 9"
150 pounds


I may be overweighted with the backplate and STA (6-7 pounds) but I haven't run the air to 500 to make sure yet. With my back inflate BC (oceanic chute 2) I only needed to wear 4 pounds. My problem is that my feet sink when I try to remain motionless. When I try to stay horizontal I have to do very slight kicks which make me move forward. This makes it hard to watch something closely on a reef for example.

I have the tank positioned with the top band at the neck of the tank, I will try to move the tank 4 inches or so higher. My head already almost hits the regulator, but I will see if that helps. Does anyone have any suggestions?

Things that I have read
1) tank weights (don't want to do this because I am already overweighted, all my weight is on the backplate).
2) Thicker booties
3) Moving the tank higher

Any others? My bouyancy is ok, but I just cant quite get the trim. I don't have a lot of trouble swimming in any position (I like to swim heads down so I can look at the bottom without stirring things up) but I would really like to be horizontal and motionless.

 

[sheck33]

seabass once bubbled...
I have worked for the last few hours of diving to get my trim correct. I read another thread about zept who had a similar problem to the one that I am having

Aluminum backplate, one piece single tank adapter, 27# wing.
3/2 1 piece full wetsuit
AL 80
fresh water
No weightbelt.
5 9"
150 pounds


I may be overweighted with the backplate and STA (6-7 pounds) but I haven't run the air to 500 to make sure yet. With my back inflate BC (oceanic chute 2) I only needed to wear 4 pounds. My problem is that my feet sink when I try to remain motionless. When I try to stay horizontal I have to do very slight kicks which make me move forward. This makes it hard to watch something closely on a reef for example.

I have the tank positioned with the top band at the neck of the tank, I will try to move the tank 4 inches or so higher. My head already almost hits the regulator, but I will see if that helps. Does anyone have any suggestions?

Things that I have read
1) tank weights (don't want to do this because I am already overweighted, all my weight is on the backplate).
2) Thicker booties
3) Moving the tank higher

Any others? My bouyancy is ok, but I just cant quite get the trim. I don't have a lot of trouble swimming in any position (I like to swim heads down so I can look at the bottom without stirring things up) but I would really like to be horizontal and motionless.

One thing i'd suggest is bending your knees, that will move your center of gravity in the right direction. AL tanks seem to have bad bouyancy characteristics but i am not sure to what extent that contributes to your problem. No, you are right adding weight is not the solution if you are heavy already. As said try bending your knees up and arching your back.

 

[jbd]

sheck33. What you are doing is getting the center of gravity lined up with your center of bouyancy. When those match you should have no trouble being motionless and horizontal.

 

[divernva]

... and by no means have I mastered it.

I agree with the last two posts. Make sure you're head is up, and your back is arched. Get into a slightly shoulder down position. Bend your knees and bring your fins to your torso. If you do it correctly, you will tip upside down. That's actually a good thing. Now all you have to do is to straighten your legs until you stop tipping down. This would be trim nirvana. Again, you're using your legs to move your center of gravity more inline with your center of bouyancy.

In the end, you will actually be slightly upper torso down. If you drop your head and exhale, some bubbles will travel along your torso.

Here's how to position your tank (and it should have little relevance to trim). The top of your BP should be at the second vertabrae. You should be able to reach it (top of BP) with your right hand. The break of the tank should line up with the top of the BP. Helps to make harness/BP adjustments w/o tank, and the harness will be tight. In this position, you should be able to reach your valve in case of an emergency. Which is the real consideration for tank position.

Another tip. Since the harness will be very tight. Slide the harness straps off by hooking your thumbs through the D-rings.

Hope this helps. Any more info and I may have to charge the DIR-F fee.

Ken

 

[seabass]

I forgot to mention that bending my knees doesn't help. I have brought my knees all the way back and I still go vertical. I also tried going more heads down to change the line of center of gravity. This works, but I have to go nearly vertically inverted to be stable. I am trying to figure out how to be stable horizontally.

 

[detroit diver]

The slightest change in tank position makes a hugh difference in trim. Try moving about 1/4 inch at a time and see what happens.

 

[scottg]

You need to be thinking about your CG (center of gravity) if you are sure your bouyancy is correct. Something on the order of a steel low pressure tank that may be a few more lbs. negative and then remove a few lbs. from your belt might just tip you forward a little more.

 

[scottg]

You need to be thinking about your CG (center of gravity) if you are sure your bouyancy is correct. Something on the order of a steel low pressure tank that may be a few more lbs. negative and then remove a few lbs. from your belt might just tip you forward a little more.

Oops! Sorry... Just noticed you weren't using a weight belt. Your back plate is going to give you all the foward weight a LPS tank would give you so we haven't gained anything there.

Sheez... neck weights?

 

[buff]

Your center of gravity is determined to a great extent by your body's proportions. Women tend to have longer legs relative to torso and men the opposite. Moving your B/P down will probably make you uncomfortable since I would guess you have positioned exactly where you want it.

I have very long legs and they are big legs. This combination makes it difficult(perhaps impossible) to maintain a horizontal position U/W. In addition, my Mares Quattors are negative in the water(I think). All these factors make it hard for me to maintain a horizontal position in the water. I would have to postion my BC over my butt to make it work!

Perhaps you could try a fin that is has some inherent bouyancy-OR booties with the same quality i.e. thicker booties.

But I suspect your problem is the result of body proprtions and not bad technique. You might be overweighted, too. Tank position can make a big differnece-especially with an AL80 since its bouyancy characteristics change so much as the tank empties. Moving the tank as far back as possible might give you the "rear end lift" you need.

 

[seabass]

I spent an hour in the pool this morning and discovered a few things.

It turns out I am actually not overweighted with the backplate as I thought. I had never done a proper bouyancy check and it turns out that at 500 psi and an empty bladder I can just barely float with completely full lungs. Anything less than full and I sink. In salt water I can probably actually wear some ditchable weight.

How much weight would I carry on my weightbelt in salt water?

I didn't try moving the tank an inch at a time but I did move it about 3-4 inches so that the hoses were coming over my head rather than behind and around. It looks a little ridiculous and people probably think I have no idea what I am doing, but it worked and I could maintain trim front and back (pitch). My pitch isn't perfect, but it is at least in the ballpark. I will try to move the tank a little lower next time.

Now I have a problem with a very slight tendency to roll to the right. I think it might be due to carring a UK Light cannon on my right side. But I am not sure. Any suggestions? In fresh water I am already fully weighted and all my weight is on the backplate. In salt water I will probaby add 2-3 pounds so I have some weight to work with.