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💬 Re: One problem down one to go
5 days ago by Martin555 (
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Well Cash you have been a busy boy.
Your boat looks fantastic, and I really like the paint job. Despite having a few problems that i am sure you will sort out I think you will enjoy wizzing her around the pond. Now the question that everyone will like to know the answer to. What is next ? Is it an aircraft carrier that will be bit enough for Errol ? Martin555. 👍 Like
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💬 Re: One problem down one to go
10 days ago by CaptLarry (
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Cash,
They are somewhat, still a plaining hull is affected by propeller torque. It is a function of ascending and descending blade caused by pitch attitude, and direction of blade rotation. This is why runaway boats veer off to the left when the helm is unattended (eventually causes helm hard-over). Are you running a 2 or 3 bladed screw? 👍 Like
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💬 Re: One problem down one to go
10 days ago by Cashrc (
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Jonathon, my buddy JP is very knowledgeable about OpenTX, in fact I think he helped with the project a bit as it was and I think still is an open source OS
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💬 Re: One problem down one to go
10 days ago by Cashrc (
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Larry, one question. I thought PT boats were planing hulls. Am I mistaken or are they a little of both. When I hear the term displacement hull I’m thinking of hulls like my little Coast Guard boat and my tug. Correct me if I’m wrong please sir.
Cash 👍 Like
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💬 Re: One problem down one to go
10 days ago by ToraDog (
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Cash,
it sounds like you are making good progress. Well done. Too bad about your antenna, but it appears to be an easy fix. I am using OpenTX on my FrSky X9E to run my fleet. It seems to me, and I am WAY out of my depth on OTX, that you should be able to set up an automatic dual rate for you rudder based on throttle position. I am not sure that this is allowed, but on RC Groups forum there is thread dedicated to just OTX and the folks are quite tolerant of folks like me, still using a rotary dial phone, asking very rudimentary questions. I would strongly suggest that you try approaching them, or another forum dedicated to OTX. Another skin the cat suggestion is to consider splitting your battery pack. Whether this will help you at all, I don't know, but it will sometimes allow you to distribute their weight more to your advantage. All in all, it sounds like you are almost there. Bravo Zulu. I would love to see some photos of her in action. Jonathan 👍 Like
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💬 Re: One problem down one to go
11 days ago by CaptLarry (
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Oh by the way, that is with rudder amidships.....if you have very much freeboard, windage may affect the accuracy of your test.
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💬 Re: One problem down one to go
11 days ago by CaptLarry (
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Cash,
Is your PT a single screw? If so, then your turning problem is related to propeller torque. Common on all displacement hull single screw vessels. You can test this at slow (idle) speed by putting it in forward and noting the direction of turn...then put it in reverse and noting direction of backing turn....if it is opposite = torque. I teach new skippers how to u-turn a sailboat in close quarters utilizing this torque (walking the boat). 👍 Like
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💬 Re: One more thing
11 days ago by Cashrc (
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It looks like I can make a custom automatic dual rate for the PT. The Radiomaster’s operating system is OpenTX. My buddy JP and I were discussing the PTs turning habits, and I told him about this post concerning the full size boats turning. JP is very familiar with what can and can’t be done in OpenTX, and he’s pretty sure it’s possible to have an automatic dual rate that’s throttle controlled, i.e it will actuate past a certain throttle setting. He’s also reasonably sure I can set it up to have less throw to starboard than port once actuated. Stay tuned...
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💬 Re: One more thing
12 days ago by ToraDog (
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PS: You can find Jerry's complete post here: http://www.ptboatforum.com/cgi-bin/MB2/netboardr.cgi?fid=102...
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💬 Re: One more thing
12 days ago by ToraDog (
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Cash,
I reached out to folks on the PT Forum and Gerry Gilmartin kindly responded with the following information and link. 58ft Higgins for Dutch PT6 Port 368 Stbd 256 Higgins 78 ft PT69 Port 336 Stbd 274 77 foot Elco PT20 Port 432 Stbd 382 Phila Navy Yards PT8 Port 443 Stbd 340 Here is a video of PT658 in a HS turn you can watch: https://www.youtube.com/watch?v=aloAg5HAgHk As you can see by the video, they did not turn tight and the bow does not dive. All of the figures for turns are in yards, so the Higgins 78 turned to stbd in 274 yds, port in 336 yds. You should have no trouble scaling those figures to allow adjusting your rudder(s) throw. Now to measure out my ELCO! Good luck . I hope this helps. Jonathan 👍 Like
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💬 Re: One more thing
13 days ago by Black Shoe (
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To add to Toradog's comments, another detail is too much rudder angle is as bad as not enough. Anything over about 35 degrees of rudder throw begins to become a detriment leading to some of the symptoms you described. In most cases and tight quarters, max rudder (at 35 degrees) and a momentary increase in RPM may help a turn.
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💬 Re: One more thing
13 days ago by ToraDog (
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Cash,
Going back and reading thru your build, I gather that you are running one shaft and rudder. Both the Higgins and the ELCO ran three shafts and rudders. of course all three props turned in the same direction, so turning was better in one direction over the other. I suspect that a lot of your issues are from the single rudder, which would not be huge by any stretch. I have seen folks build theirs with a single shaft and two or three rudders which gave good response to the helm without excessive rudder throw and thereby avoided the the snap roll you are experiencing. BYT nuclear subs suffer from the same effect when at speed and high amounts of rudder are ordered. Another reason that they like deeeep waters too play in. But I digress. If at all possible add two more rudders. This may not be practical without ripping the boat apart, been there, done that, don't encourage it, OR consider a slip on enlargement of the existing rudder that you can bolt into place for running. Removable for display it would leave only to small holes thru your rudder. increasing the surface area of the rudder will increase it's effect and allow you to limit your rudder throw, keeping you away from snap rolls. KISS principal. Just don't tell the cat. 👍 Like
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💬 Re: One more thing
13 days ago by Cashrc (
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Toradog, i think you’re right. I did my best to keep my weight aft, all radio and power with the exception of the motor are in the aft 30/40 percent of the boat. She has no problems getting on plane in a straight line, but in a turn she tends to scrub her bow. I’m adding close to a pound of ballast just aft of the motor, it will be secured temporarily until I get her right. If I get her a little too aft heavy, I’ll go from 7 to 6 cells. I have plenty of power on tap so I can lose a cell and it’ll just be a little slower. Balance first👍
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💬 Re: One more thing
14 days ago by ToraDog (
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If you will allow me another comment. Pt's are sensitive to fore/aft weight distribution. It sounds like too much weight is forward. This would make the rudder less effective and cause digging in of the bow when in a hard turn. Remember that the rudder's action changes as the boat heels. The more off of vertical the rudder becomes, the more it tends to act as an elevator, lifting the stern and driving the bow downwards.
My first suggestion it to carefully mark the scale waterline on the hull. 90% of the weight of the guts of the model should go as far back as possible, which usually entails putting you battery as far aft as possible. I digress... After carefully marking the waterline, distribute the guts in a way the makes everything accessible and safe, ie, in a potentially dry protected position.( sometimes easier said than done, but a receiver in a baggy is not a bad idea). Now place your build in a test tank( a bathtub works great if it will fit.) Move the guts around until you have a level waterline, fore/aft and side to side, remembering that the heaviest item should be almost at the transom. I would suggest aiming for straight line performance first. Easy to get onto plane, correct running attitude and reasonable response to the helm. If you can attain that, then work on your turning, remembering that she will turn like a single rudder destroyer(even when they had 3 rudders) except that you may find reducing throttle during a turn helps to balance your rudder input and reduce bow dive. I hope this helps. I am still learning and adjusting my 1/16th ELCO, but she runs better than I drive her. 👍 Like
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💬 Re: Needs ballast
14 days ago by Cashrc (
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Hi Toradog. I usually mount my rx’s high, but in this case I had it a bit too low because I didn’t want to use an extension..🤔. It wasn’t on the floor, but the extreme roll helped it take a bath. I’ve fitted an extension and have it much higher up now...plus it’s had a bath in CorrosionX.
Cash 👍 Like
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💬 Re: Needs ballast
14 days ago by ToraDog (
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Well done!
two comments. 1)PT's had a notoriously large turning radius, even the Higgins which had a tighter one than the ELCO. If too much rudder is applied, they lift their sterns and dig in the bow. My ELCO is notorious for that when I try to turn sharply. Solution is to reduce the rudder throw. 2) as a general rule, do not put the receiver in the lowest or low point of the hull, for the exact reason that you ran into, ie, shorting out the receiver. Rather, mount it high and safe( better radio reception as well there). To accomplish your needed routing of the servo lead, add an extension to it. Very inexpensive insurance. 👍 Like
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💬 Re: Needs ballast
14 days ago by RNinMunich (
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Agreed Rowen,
Plus the axial torque created by the rotating mass of motor, shaft and RH prop (flywheel effect), plus the force of the water shoved up under the hull by the rising prop blades! With a clockwise rotating prop (seen from behind when going ahead 😮🙈) the 'shove' would be on the underside of the port hull. Conversely, on the starboard side the blades are driving water down, away from the hull, creating suction. Both effects summate adding to the torque roll effect in light, fast boats with a single screw. Combined with the rudder 'elevator' effect you describe the boat could I suppose in an extreme case 'corkscrew' under! 😮😭 I guess you'd really really have to over motorise and fit a BIG rudder to actually push it under though - I hope!🤞 (Thinks💡 might work on my U-25 though! 😁) BTW Cash; on a more practical note - bilge keels might help 👍 But most of that problem is probably due to fitting only one drive train (motor, shaft, prop). Surely the Higgins PT boats, like the more numerous ELCO version, would have had three shafts? Thus helping to dampen the torque roll effect. Cheers, Doug 😎 PS Curiously all the descriptions of the PTBs that I've read mention the 'high manoeuvrability', which doesn't quite gel with 'a notoriously large turning radius'!? PPS The angle at which you have set the prop shaft (relative to the horizontal WL at rest / keel line) might also contribute to a pitching effect over the CG/Centre of Buoyancy, thus pushing the bow down when thrust is applied. Combined with the other effects described it could well explain a bow over + list condition!? Pitch & Roll Man!! Real solution: fit three drive trains as in the originals (or at least two for balance). 😉 👍 Like
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💬 Re: Needs ballast
14 days ago by RHBaker (
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The tendancy to dig one side of the hull in on turns is caused by the propeller rotation as it pushes water against the turned rudder surface.
It is particulary apparent on single screw installations as twins are usually contrarotating and counter each other. Although my Brave Borderer is triple screw it will do the same. Perhaps rather less noticably because the outer screws tend to even and damp the forces out. Not sure there is much you can do about it, I just reduce the centre screw rpm on RH turns. Ballasting the hull might help reduce skittishness. Would have guessed that model is typically around 6/7lbs weight. Never a problem for me as my models tend to be overweight anyway! 👍 Like
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💬 Re: Needs ballast
15 days ago by Ianh (
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Hi Cash
I believe this is a problem with the Dumas kits of PT212 and 109 Cheers Ian 👍 Like
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💬 Re: Ready for the Pacific
1 month ago by Cashrc (
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Errol’s a pretty big cat...he might get transferred to a destroyer😁
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💬 Re: Ready for the Pacific
1 month ago by jbkiwi (
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Nice job Cash, don't forget the video camera😊
JB 👍 Like
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💬 Re: Ready for the Pacific
1 month ago by RNinMunich (
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A Mean Machine Man 👍
BRAVO ZULU Commander. 😎 PS Once Lt. (Feline🐱) Errol gets aboard I don't think you'll need any more ballast!! 👍 Like
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💬 Re: Oerlikon gun and other things.
2 months ago by CaptLarry (
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Cash,
The flux will clean a little as you solder, but it causes the solder to run where ever the flux flows to. A dry surface cleaned with Isopro will help you keep the solder where you want it.....experiment with it, and you will see that it takes less heat and solder for your application. Another thing that helps is to “shock” your iron tip each time before your next solder application. When it comes up to temperature, wipe the tip on a wet/damp sponge...this removes old flux residue and tired solder...gives you a fresh iron tip for a cleaner joint, and new solder flows smoother. Again, less heat and less solder. 👍 Like
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💬 Re: Oerlikon gun and other things.
2 months ago by Cashrc (
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Larry, I have a habit of just hitting the brass with StayBrite flux, the soldering it together. Probably if hadn’t been so cold in the garage I’d done a neater job😂.
I never knew about cleaning the brass with alcohol, thanks for the tip!! Cash 👍 Like
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💬 Re: Oerlikon gun and other things.
2 months ago by CaptLarry (
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Cash,
I was looking closely at your brass solder joints. Are you cleaning your brass tubing, and solder with isopropyl alcohol before you solder it together? It gets rid of oxidation, and makes a smoother solder joint. Just a hint... OW....PT lookin’ good! 👍 👍 Like
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💬 Re: Did a little over the weekend
2 months ago by Martin555 (
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Good work Cash.
coming along nicely. Martin555. 👍 Like
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💬 Re: Did a little over the weekend
2 months ago by jbkiwi (
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Looking good Cash👍
JB 👍 Like
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💬 Re: Baby it’s cold....in the garage!!
2 months ago by redpmg (
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At least that's one thing we don't have Cash - that white stuff only appears on the distant mountains for a very short while. Having said that it was sweltering weather of mid 30c followed a day later by an icy front from the Antartic...........
Detail coming along well as usual with your builds - good to watch ........... 👍 Like
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💬 Re: Full Speed Ahead!!
2 months ago by Martin555 (
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Looking good Cash,
They will really come to life when you have paint on them. Martin555. 👍 Like
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💬 Re: D###! The torpedoes!!!!
2 months ago by redpmg (
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Hi Cash - belated birthday wishes - a relative spring chicken compared to most of us. What did Errol give you ? Glad you treated yourself too.
Good to hear you enjoy cooking for yourself. As usual you are making a great job of building the boat - lucky you too - you should be able to complete your wishlist if you stop adding to it now.......... At 15 years older (nearer 16) find it would take at least another lifetime........... 👍 Like
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💬 Re: D###! The torpedoes!!!!
3 months ago by Cashrc (
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Thanks Martin!! To be honest, somdays I feel like a “sprung “ chicken😂
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💬 Re: D###! The torpedoes!!!!
3 months ago by Martin555 (
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Hi Cash,
Happy Birthday, still a spring chicken like me LOL!!. The Torpedo Tubes are coming along nicely. Keep it up. Martin555. 👍 Like
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