[PSUBS-MAILIST] Hydrodynamic question

Mon Dec 18 20:27:18 EST 2023

 Jim,As someone who has spent thousands of hours piloting 18 to 25 foot long subs with 10 hp motors, I can say with utter certainty that you would get some degree of use out of ANY additional maneuvering thrusters and/or control surfaces. The Perry boats generally had at least three small on/off reversible thrusters (usually fore and aft lateral, and forward vertical) plus a barn door rudder and side mounted dive planes (chord section all with end plates). The Hyco vehicles I operated had exactly none of those. Aquarius had one lonely pivoting hymak in the stern, and Leo and the Pisces boats had a pair of side thrusters pivoting on a common shaft. The JSLs had thrusters hanging all over them, so everything was done electrically, and It took a BIG battery to run that thing for 3 to 4 hours max. In any case. all of them had excellent trim systems, and none of them used that trim system for anything beyond initial attitude adjustments and fine buoyancy control in the water column. Long story short, I can tell you without equivocation that a Perry boat would, did, and will run rings around the competition. Ain't saying you can't do it simpler. Just saying that good control makes life easier down there in the cold dark wet places.Vance
    On Monday, December 18, 2023, 05:37:08 PM EST, james hughes via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

  Thank you Alec for that reply!  I have a bit more hope now that I can do without those dive planes.  I should have also mentioned that I will be adding two trim tanks that should hold about 45 pounds of water each (for "fine tuning" the trim).
God bless, Jim
     On Monday, December 18, 2023 at 12:05:21 PM PST, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hi Jim,

That is quite the addition to the fleet, I can't wait to see it in the water! I recall one PSUBBER with a large sub, though not quite as large as yours, who keeps a largish weight inside the cabin. I'm guessing it was maybe 30 lbs, but it was years ago. The weight had a handle on top and carpet glued underneath. He simply slid it forward or aft to trim the boat. Longitudinal trim is very sensitive to weight displacement. For example, a K250 changes trim visibly just when you open the hatch (the weight of the hatch is further aft when open.) With that sort of length to move things around in, I would not expect you to need dive planes.
Best,Alec 
On Mon, Dec 18, 2023 at 2:43 PM james hughes via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hello Gang,My sub is nearing completion after many years of work.  I based the design primarily on the K-250 blueprints I have but instead of having thrusters on the sides I have a 16 inch propeller under the aft ballast tank (linked to a 10 horsepower motor on the inside) and a 108 pound thrust trolling motor mounted under the forward ballast tank to help me turn port or starboard at low speeds.  My question is: Do I need to add dive planes in order to keep the thing level as I cruise along above the sea floor at about 2 to 3 knots?  The boat is 25 feet long, 5 feet in diameter and will weigh in at about 8 tons (with about the bottom 12 inches of the sub filled with lead ingots).  Attached is an old picture to give you a visual of what it looks like (I'll post some new ones soon).  Any input would be very much appreciated  but I would really like to hear from anyone who has operated something like a K-350 using just the aft motor when submerged.  I don't mind making changes / additions at this point but really want to get this thing done and in the water so I'm hoping I can go without the need for dive planes.  Please let me know what you think!
God bless and Merry Christmas to all!  Jim_______________________________________________
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