We got together at the Versailles pond this weekend for a little battling and boat tests. I was able to get the PT 564 prototype on the water for some tests. It runs pretty good, however I'm having problems at full speed: the torque from the single prop rolls the boat over whenever it gets fully on plane. Using an X430 metal prop or a plastic 32mm racing prop, the boat runs great on 2 cells, just not quite on plane. On 3 cells it planes nicely, however if I take it above about 1/2 throttle it starts rolling over. I think my problems come from the narrow beam of the boat, which requires more speed to get on plane and has limited stability once it is on top of the water. I tried a smaller prop, both a 3/4" and 1" three blade brass prop, but while there was no torque problems there also wasn't enough thrust to get the boat on plane. I don't want to use trim tabs because I want the boat to be as stock as possible. Any one have any ideas how to solve this problem? Completed PT boat below, with the YOG 86 in the background. Below is a video of the PT boat with 2 cells. It runs pretty good, fast enough to be fun and stable enough that you can put the rudder all the way over without rolling the boat.
It was great seeing that boat out there on the water. A couple of thoughts. Neither of which may sound very attractive. Go to a two-shaft arrangment, or a larger scale. I don't have any other ideas at this time. But I will give it more thought. I really think this will make the events more fun as it will allow us more flexability when it comes to entertaining the spectators during the down times. Well done. Mikey
Thanks Mikey for posting the high res pictures. The photos are of my trials when I was testing out a single trim tab on the starboard side. I was able to tweak the tab to counteract the torque roll tendency. However, the boat didn't go any faster as a result, every time I was able to get the bow down it slowed down. So it looks like I'll stick with the 2 cell pack - it has a scale look as it moves through the water, which is better than speed any day.
The PT boat is 17.5" long by 4" wide. That's smaller than your LST. However, because there are very few components, it has plenty of room inside.
I really have not tried to measure speed so I don't know how fast it is. It is much faster than a 22 sec destroyer, but of course it is not meant for combat. The easiest way to see the speed is to watch the video on the earlier post.
Counter rotating props would be interesting. I'm not sure that I could find props small enough to run on that motor combination.
Hi Mark, Did you ever come up with a solution to the torque roll problem? One thought I had would be to use a crown gear and pinion (similar to what slot cars use) , and transverse mount the motor 90°to the prop shaft (to one side not on top) so that torque rolled to the stern, helping pull her up on plane. You would, of course, have to counterweight the other side, to make up for the weight of the motor off to one side. This is a super cool boat by the way, looks like lots of fun to drive!
You could take a page from the WW2 German E-boats. They had 3 rudders. To cut down on wake & get them up on plane quicker, they could turn the two outboard rudders so they "toe out" slightly (or was it in? Cant' remember exactly). You could mount two fixed rudders each side of your working one to accomplish the same thing. To balance the torque issue, just tweak one of the outboards a little more.
I've kind of put this project aside for now so I can work on other things. I'm not so worried about the torque roll, you just have to limit power. Right now I need to figure out how to get a deck that seals and also refine the shape of the sides so that it fits together a little better.
