when I changed my props out from a 1.75 to a 1.25 inch, I switched over from a 14T to an 18T gear on the motor which went from a 2.5:1 to a 1.94:1 ratio and got really good results. I am sitting at about 60% of my endpoints at that. Is the pitch shallower on the 4 blade props?
never seen pitch translated into a metric length. usually comes in degrees or some esoteric form such as radians.
Pitch is measurement of how far the propeller will move in 1 revolution with all other things being equal. So 56mm per rotation on the 3 blade guys, 49mm per rotation on the 4 blade guys. This is actually the traditional measurement of prop pitch for 1:1 model boats. A 19 pitch propeller on a typical fishing boat would move 19 inches forward per revolution.
and now I know. interesting. I don't think that small of a change will throw you off much, but changing the gear ratio out in unison will give you a fair amount of play with regard to the limits of your motors.
Once again all other things being equal, at my shaft RPM, its a difference of roughly 179 meters per minute vs 157 meters per minute. This is not accounting for slip in the water, drag, etc. These numbers are just suggestions, real world testing will give the actual answer. It should be about 10% slower with the 4 blade props, but with more power.
He must have changed the props from the pictures he has posted just above his sea trials, they are are turning out in that picture.
Yes, I had known they were backwards for some time and didnt get around to fixing it until before sea trials. After paint I swapped them.
Aw dude, you have enough roof shelf there for your props. it's gotta be something else. When I was experimenting with props, I ran 40 pitch 1.75" in both spins, and one was significantly less cavitation. when I switched over to the 20 pitch 1.5" and the same spin direction as the reduced cavitation in the 1.75, the cavitation problem went away. It may have been a function of pitch, or diameter that helped me too, so I am really hoping your experiment with those other props yields cluse. but looking at that photo you have just as much overhang as I do with my props. So this is an engineering battle that you can win!!!
Oh god no not that small! 1.25 are good for a Texas, but I doubt they'll work well for acceleration on a boat that is 33% larger and heavier.
My plan is to try going from 14t gears on the motors to 18t. That'll take me from a 2.28 to a 1.77 ratio. Then put on the 4 blade props. Theyre a little shallower pitch, but the gear change should result in overall higher speed and hopefully acceleration. Dont know about the cavitation, but we'll see.
Bart is strapped down and ready for transport. Tomorrow loading up the car before bed, Thursday leaving in the early AM to try and get around the DC traffic. Relocated her to the stools to clear up bench space for Suffren. Also, I am super corny for doing this, but I'm 3d printing out a plaque to put on the carrier with the ship's name. Why? Because reasons. The text below her name says "Battleship of the National Navy" with Marine Nationale being what the French call their navy. There were two translations because the French have two different terms to refer to "battleships". Earlier pre-dreadnoughts and dreadnought type battleships were commonly called "Curiasse de Ligne" which when translated literally is Armored Ship of the Line. The later interwar fast battleship type designs like Dunkerque and Richelieu were referred to as Batiment de Ligne, which loosely translates into Ship of the line. Curiasse is commonly used as the direct translation of Battleship, so that's what I went with. We have come a long way boys and girls. 10 pages of build, 8 months of work. Lots of lessons learned, new techniques attempted, tried and true methods followed. When I get back from NC and the boat actually has some combat experience I'll make a longer post with pros/cons/regrets/good ideas. For now, I want to just sit back and enjoy the ride that got us here. The earliest picture I have of the assembly process, not counting the 3d modeling or pictures of just plans on kitchen tables. Where we are now, strapped down and ready for transport.
Post-Battle Performance Assessment: Jean Bart performed great for her first ever battle. I had some technical issues that I predicted and a few that I couldn't have planned for. Issue 1 was the gun solenoids started to act up and would only fire some of the time. This was resolved by lakeside soldering some 7.4 lipo packs to use for the solenoids vs the 6.6v LiFE packs I had been using. This also solved intermittent firing issues for Rob S. I knew going into the event that the solenoids could be picky about voltage but I didn't have a chance to finish putting ends on the 7.4 packs until we got there. My second main problem was pump issues all around. Friday, I had the aux pump give up. Curious as to whether it was the motor or the ESC, I took the aux pump ESC and plugged it into the main pump. Well, doing this caused a massive burst of smoke from the main pump motor. Add that ESC to the trash bin. No idea what caused that. Never had an ESC burn up a motor, only ever the opposite. Not to be deterred I dropped in my backup brushless pump for main pump duty and just ran a full 50rd load of ammo in the stern gun, losing .5 of a unit for the rest of the weekend. No huge deal. Saturday the boat worked pretty great. Served a large portion of the damage it took to down HMS Queen Elizabeth and tango'd with HMS Revenge. Took minimal damage in return, no danger of sinking. Had to withdraw from 2nd battle 2nd sortie however due to....*drumroll* pump issues! Turns out the backup pump I dropped in the boat was using my first prototype print of my brushless outrunner pump shield. This was PLA and was never meant to end up in a boat. Whoops. The shield melted to the pump motor. I snapped the shield off the pump and battled it that way for sunday. Suffered my first sink Sunday which was a combination of pumping issues and driver overconfidence due to my previous success. @Kevin P. 's HMS Agincourt and Marty Hayes in USS Salem beat me up, coupled with poor pump performance compared to Fri/Sat and JB's bad habit of listing aggressively into her turns sent her under. I had sporadic drive issues that were all related back to the props. The blades aren't the sturdiest and with how narrow the butt end of the boat is they overhang the sides of the ship by a considerable amount. More than once I heard my props chopping at the impenetrable bottom of another boat next to me, followed by the loss of a shaft or direction of travel. The good news is my ESC's overload protection works great, they are fine and would simply reset when the prop bent and bound against the stuffing tube strut. The bad news is I still lost maneuvering for periods of time. When she did maneuver, the new 4 blade props and 18t gears worked great to get the boat's speed up. Her acceleration was "acceptable" but I feel like there is more waiting in this drivetrain. All in all it was awesome fun and a good learning experience about the boat and her capabilities. Had some issues with rams (Sorry Rob and Tommy!) as I learned to drive the Battle Baguette but the more time spent with her the more I'll understand how exactly to drive her. Design changes/upgrades/things to do differently: First and foremost, the listing issues. JB really lays over into high speed turns. The combination of superstructure weight and all the weight from the forward guns/tanks/valves/solenoids being mounted to the deck gives her a lot of mass up top. I'm already looking at re-printing the SS even lighter than it is now, but there isn't much that can be done about the gun weight. To try and help I'm adding the ship's 4 bilge keels, but I am skeptical about their ability to eliminate the list. I'm sure they'll help, but I can't expect miracles from 3/8" pieces of basswood. See picture below: Props bending/driveline durability. I am looking at some stronger cast props in the kort nozzle shape. I am also thinking of moving the drag discs farther aft to serve double duty as bumpers to keep the props off of adjacent ships. Hull construction. No major gripes here other than my boat's lack of impenetrable area. I didn't realize that the rib calculator on the IRCWCC site is broken, so I built the ship using 19 3/8 ribs. Turns out, I'm allowed 25 3/8 ribs. That's 2.25" of impenetrable space I'm missing out on. Also, the impenetrable area that is the raised center section of the hull. I need to bring that down to the subdeck area, right now it ends at the top of the subdeck, so I'm missing out on 3/8" more impenetrable along that entire section. These issues I'll take care of when I re-sheet before NATs, no use ripping into the boat right now in the Spring Regionals season. Sheeting. I decided to try something different and use the Tyng 50/50 titebond mixture to apply the tissue to the balsa for sheeting. While this gave a very nice smooth finish, in combat the results have been extremely unsatisfactory. As explained to me by Steve A, the titebond woodglue soaks into the balsa and hardens it which greatly increases it's chance of cracking with the grain of the wood. He had predicted this before the battle but the boat was already sheeted so it was too late. His predictions turned out to be 100% accurate, I'm having issues with the sheeting cracking with the grain of the wood (longways down the hull). Oh well, this is how lessons are learned. Next time, traditional 3m Super 77 spray glue for paper/wood adhesion. I am already prepping new sheeting for the pre-NATs refit. Note, this Tyng method may be satisfactory for something like a Cruiser that will only ever get a few holes, but for a 6 foot long dual sidemount boat that attracts all the attention it is not a solution. All in all, this was a great weekend for me. I have some stuff to work on to make JB even better, and need some more time with her in the pond to get used to judging appropriate gun ranges/stopping distances. Can't wait for the next battle.
Glad to hear you did well and had a great time! She's a beautiful boat, and it's good to see the froggies represented on the water.
Glorious! There are some great action shots in there. Love the belly-up battleship. Just a comment on bilge keels: they only help with one aspect of stability. A bilge keel adds lots or angular friction, so when a ship starts to rock it only rocks a few times. If your ship is "tippy" and likes to swing back and forth rapidly, then bilge keels are the solution. My PDN picks up a nasty roll when I turn, and then it keeps rocking back and forth for a while afterwards. I'm installing bilge keels, and those should significantly reduce that bad habit. If your ship likes to "lean" during turns, that's more likely a weight distribution issue, and not something that bilge keels can fix.
She rolls in her turns and with slight rudder adjustments at speed tips back and forth very quickly. Even if they don't help, for $4 in basswood and some epoxy what the heck might as well. I'm looking at other places to reduce topside weight, but the 8lb~ forward gun deck is a killer.
How about lead bilge keels? I did mine by using plastic and then gluing on various widths to test to see what shape/height made the most difference. Easy to change pond side, and once you get the "correct" shape just rip off and make a clean version (as the test version may have 4-8 layers of plastic). Just a thought from a key banger
Pun intended? good double whammy to deal with both factors. my refit on Texas put about a pound of weight in my top deck, and I'm a tad concerned it'll impact rolling and maneuver like yours. Lead Bilge Keels will be my go-to if the problem develops--I'll remove the ballast I have in the hull and replace it with bilge keels of equal weight.
