Re: [PSUBS-MAILIST] Drop Weights

Hello Frank
Ive been thinking the same thing.  I notice that a lot of the K boats have to 
have extra lead inside to get the boat to the correct diving weight.  I was 
thinking of putting that extra weight outside and make it droppable.  (if i need 
to, i have excess weight in my endcaps as they are thicker than they need to be)
I suppose its a balancing act between stability, ascent rate and increased 
bouyancy.  I believe the K 350 weights are supposed to allow you to surface with 
a totally flooded battery pod.  Not sure on the weight as i havent made them 
yet.
Not sure who but someone said a while back "you dont want to drop the weights 
and come up upside down!".  Could be more of an issue with your saucer shape?
The wheels on the keel sounds like a great idea.
Regards
James





----- Original Message -----
From: ShellyDalg@aol.com [mailto:ShellyDalg@aol.com]
To: personal_submersibles@psubs.org
Sent: Tue, 15 Sep 2009 11:52:51 EDT
Subject: Re: [PSUBS-MAILIST] Drop Weights

Dean, you mentioned that your drop weight was not very big and the front  
was a little light.
It started me thinking about the size of my planned drop weight. I've read  
about a lot of subs and there doesn't seem to be a lot of commonality in  
percentage of drop weight used for the various sizes of psubs.
I remember the little video about towing the Delta sub and during the  
submerged part of the video they said it had a 40 pound weight that could be  
dropped.
Other subs had drop weights that ranged up to 400 pounds.
I wonder if there's a danger in having too big a drop weight. Can it cause  
problems when it's released?
An advantage to a large drop weight would be that when dropped the sub  
would have more buoyancy and be able to "tear free" from a minor entanglement  
like the kelp we have around here.
The disadvantage could be a too rapid ascent and maybe some instability  
once you reached the surface.
Both of these could be quite dangerous.
The surface instability may not be that critical because at least you're  
back up where you can be reached by the surface crew and a line can be 
attached  to the sub. 
The uncontrolled ascent rate is the thing that I was worrying about.
I had planned on a pretty large drop weight. More like 750 pounds. The drop 
 weight mechanism is designed in a keel shape, and has a bunch of wheel 
rollers  so I can roll the sub around when it's on the floor in the shop, and 
when  launching the sub it can roll on and off the trailer.
The actual lead weights will be shaped to fit inside the steel keel form  
and bolted in. The total weight can then be adjusted by adding/removing 
weights  but the steel keel mechanism itself weighs about 250 pounds.
The total lead ballast needed to sink the sub is going to be close to 1800  
pounds. Most of this is bolted to the floor inside with some of it on a 
sliding  mechanism to adjust trim angle.
These are rough numbers at this point of the build and my float test will  
determine exactly how much is actually needed depending on what all I put 
into  the interior of the sub.
Adding a passenger, equipment, and later improvements like a manipulator  
arm or whatever can be compensated with the underfloor weights.
In the model testing I did the sub wobbled during ascent when it was  
simulated dropping the weight but it stayed level and fairly stable on the  
surface. It's the wobbling when coming up that concerns me.
Anybody got any thoughts on this?
Frank D.