Re: [PSUBS-MAILIST] k-350 Modifications

Dean,

You may not have a problem with your MBT valves located low. The problem comes in when they are located above the waterline. Depending on the depth of the bubble in the MBT, it may contain maybe one PSI of actual air pressure when inflated. If the valve is high above the water line, the air pressure has to be high enough to blow any remaining water in the line up and out of the vent, on top of the valve. On a K-350 it's often not enough so you have to open the hatch and lean out to blow in the vent tube to clear the line of water. It works, but sure doesn't look professional. I bet if a sharp looking lady was piloting it would really drew attention.

After dealing with this problem, I installed a T and a short piece of tubing that blows a jet of air into the line from the MBT side by giving my fill valve a fast blast. That clears the lines, but it's extra stuff to fix a problem. Better to not have the problem in the first place.

The most unstable time in the sub is when your in that transition stage of "not on top" and "not submerged." When a tank, whether it's fore and aft or side mounted, is partially above the water line, the sub is stable. When tanks are below water they add lift but tend to be unstable. The air bubble in a tank moves around (water sloshing) and acts on the sub with different amounts of leverage depending how far from the center the lift actually is. That is, if the sub pitches nose down the bubble in the aft tank runs back farther it has more of a lifting effect on the aft part of the sub making it pitch even lower in the front. Side tanks add another dimension to the problem. Install baffles if it's long. If their small so are the problems with them but if they are large and totally below the water line, you'll have to be careful with them. Any tank if unstable when it's partly full of water and totally submerged. You just have to work with it.

On the whole, the K-350 is a very stable sub. It's almost impossible to role it over. When surfaced I can stand on the side of the conning tower rim and it won't role to take on water. When diving there is little effect on role when one side thruster is thrusting up and the other is thrusting down. When a passenger moves from behind the pilot to the forward looking viewport the pitch changes by about 10 degrees.

My total weight added to dive my sub is, me at 160 pounds and about 400 pounds of lead weights. My hull is of the two person design and pretty much to the plans as far as hull weight. My side thrusters are probably each twenty pounds heavier then the original. If your using Minkota thrusters you'll save a bunch of weight. The K-thrusters as are heavy buggers.

I don't have the exact total weight in my head or here with me now, but it's a few pounds over 4000.

And I do agree about the plans. They contain 97% of what you need, but from a professional drafting point, they leave 20 % more to be desired. Did you get to the T bracket that isn't there yet? The important part is the hull, and it's pretty clear. You may have to guess at some other small stuff but the important stuff is covered, except that dam T-bracket. Mine is now a heavy triangle bracket of my own design. I know it's heavy enough.

Happy Building, Dan H.

----- Original Message -----

From: recon1st@aol.com

To: personal_submersibles@psubs.org

Sent: Friday, March 14, 2008 10:44 AM

Subject: Re: [PSUBS-MAILIST] k-350 Modifications

Dan I want to thank you for your post. Your experience is
of great value to me, and I am sure others.
Of concern at the moment is the problem of air lock on the MBTs, I had not thought of that.

I have mounted my MBT valves on the sides of the pressure hull, so they will actually be
under the water line on the surface. The plumbing is 1/2" sched 80 black pipe.
Do you think I wll have a problem with this?

I am planning, and will very soon extend the rear MBT at least 12" deeper. I am also adding
saddle tanks to make up for my additional weight. Do you foresee and problems with this?

Also I would like to know how much lead you ended up with. And how much your
total weight is.

Being an old Draftsman I am a little disappointed in the plans. I find them to be a little
confusing and not complete.

Dean Ackman

-----Original Message-----
From: Dan. H. <jumachine@comcast.net>
To: personal_submersibles@psubs.org
Sent: Fri, 14 Mar 2008 8:33 am
Subject: Re: [PSUBS-MAILIST] k-350 Modifications

Hi Scott,

Congratulations, in about a month. Building a sub is a great project. Plan to spend some time doing it. If you get frustrated, put it aside, but don't forget to get back to it. To many get started and not finished. Think long term and you'll have a sub.

I built a two man K-350 "Persistence." There are plans for a short one person version and the two person version. The two person version has a hull tube that is six feet long and then another foot for each end cap making the pressure hull eight feet long in total.

If your building the two person version, I would move the battery pods aft six inches to a foot. Study the plans to see what else this will effect but as it is, most of my internal weights are located far aft to trim to level. You could also lengthen the battery pods by one battery. If I take a second person with me, they usually prefer to lay on the deck under my seat. This puts their nose right up to the forward viewport, which is a great view, but it makes the sub nose heavy.

Enclosing the MBT's is a good idea. Mine are enclosed far more then the original and they work great. Just be careful not to enclose to much so if one tank got filled with air accidentally, you aren't totally nose up or down. If that happens you may not be able to blow the lower tank. A few holes drilled at the end should work.

The K sub plans don't give a clear idea of the size of the MBT's. I gauged mine by the size of the frame that supports them. Now I think my forward tank could be a bit bigger.

Another thing I'd change is, put your MBT vent valves right on top of the tanks and run linkage to the conning tower or where ever. Don't put those two valves in the conning tower then run lines to them. They take to long to vent and sometimes they get air locked when water is caught in the line.

Depending on how and where you plan to launch your sub you may want to consider saddle tanks also. Launching from the trailer I have it takes five feet of water to launch my sub. If I had saddle tanks that could get the sub up a but higher, it would be easier launching from shallow boat launches. As it is, there are many boat launches I can't use. My sub's water line is right at the lowest part of the weld that transitions the conning tower to the hull.

No need to lower the conning tower. When the sub is surfaced, you can't lay it over enough to take on water if you try. It's pretty stable but you sure don't want to be lower to the water and take in a wave. Don't change that.

Maybe a bigger front viewport would be nice, but your getting into a big structural change there.

Just my thought.

Good luck, Dan H.

----- Original Message -----

From: Scott Waters

To: personal_submersibles@psubs.org

Sent: Thursday, March 13, 2008 1:57 PM

Subject: [PSUBS-MAILIST] k-350 Modifications

I am going to start my k-350 here in about a month. We are pretty close to being prepped for the project. I would like to ask everyone for suggestions from previous experience about what modifications to the k-350 you all would have done if you could have gone back and done it again to improve the use and cost of production. I am pretty sure I am going to make the con tower a little bit shorter to reduce the above water weight while surfaced and to make the sub a little more stable. I have heard making an enclosed ballast is better to reduce settling. I have also heard rumors about using trawling motors instead of thrusters. Suggestions?
Thanks,
Scott Waters

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