Todd Wasson
Junior Member
- Joined
- Feb 24, 2015
- Posts
- 37
- Reaction score
- 3
- Location
- St. Paul, MN
Thanks, guys. I appreciate the comments and encouragement.
Tiny: The sketch idea is a good point. Maybe it could be promoted at some point that way, I'm just very leary of making it out to be something that it might not be. Standard marketing hype practices annoy the hell out of me and I don't want to engage in that kind of thing. If you've got something good you shouldn't have to BS people. So yeah, I'll just call it a sim/game until guys like you come along and say it's more than that. It'd be more honest at least.
I like your sketch idea and description you put forward for that where it might be useful as a sort of playpen to test ideas before moving on to more advanced software that will do a more accurate job. Yeah, that might be an angle on it. I've learned a lot about chine walk dynamics just by playing with the designs in the sim, so it appears useful for at least gaining an understanding of some of the hows and whys of the various dynamics even if the transom deadrise angle you use on a real boat might be a litte different and that sort of thing. I think it's probably useful for getting a general idea of how some of this stuff works, changing "this" variable in this direction tends to make this or that problem worse or better, that kind of thing.
Trying to minimize wetted area while not blowing over is a fun challenge too. The skin friction/viscous drag is done without any empirical constants at all (the model uses a Reynold's number approach) which works better than I expected it to, so the top speeds seem to be in the right ballpark as far as I can tell. There are no lift/drag coefficients anywhere here as you might find in a flight simulator, it's just force computations directly on the boat mesh in the direction of the triangle surface normals (and a tangent force for friction in the triangle plane). So it's pretty remarkable that it works as well as it does.
I would be ecstatic to find out some day that designers were using it at any stage of their design process, and even happier to find that it was actually helping them. If nothing else, it'd lend credibility to the realism of the simulator which I'd get a lot of personal satisfaction in knowing. Part of the reason I'm making this is because I couldn't find a game or sim that really captured the interesting dynamics at all. When the boat started chine walking without telling it to, and I figured out that it was curable by tweaking the pad and/or transom deadrise angle in a way that widened the wetted area at the stern at high speeds to counteract the prop torque, it brought a big smile to my face and I knew I was on the right track. When it blew over at about the right speeds without telling it to, well, that was another victory.
I just worry somebody's going to hurt himself somewhere down the line by taking the model too seriously. I trust engineers to understand the limits in various computer models because they're appropriately trained and educated, but Joe Schmoe building a boat in his garage won't understand those limitations. So I've got to be real careful about how I promote it and figure it'll probably be best to leave comments about how useful it is for real design to whatever users engage in that. They'll know better than I will anyway.
On another topic: While I've got a couple of attentive ears, maybe somebody here could help me with some real boat data? I have a couple of concerns at the moment. One is that I'm computing mass properties by integrating the surface area of the mesh, so as you change the boat design, the mass and inertia tensor change automatically. I just assume some thickness to the boat surface rea, effectively assigning different densities to the bottom, stern, bow cover, etc., then add masses for the driver, fuel, and engine.
The trouble I have is that I don't know how these things are really built so I'm left guessing at the relative densities. Because of this I'm not very certain of the accuracy of the center of mass of the boat as well as the engine. With the cm too high you of course get problems turning, the boat at some point wants to lean out of the turn as you can see happen in a few places in that last video. I know at some point that should probably happen, but I don't know what lateral acceleration limit might be typical before you see it roll out like that. Very small changes in cm location affect it a lot (especially height), so there's room here to play still.
What would be helpful is to get center of mass location data on some boats of this general type, the small, high speed Hydrostreams and so forth. It'd also be great to get some telemetry with lateral acceleration data (maybe roll angle too to spot roll reversals in very hard turns). The trouble is I'm having to recall from 20+ years ago how hard our family boat turned, and my butt is not a particularly good accelerometer after 20+ years. I have almost no data here other than a couple of YouTube videos where some boats were turned at maybe 0.5g, but I have no idea if that's just a lazy turn or if that's about as hard as somebody would want to go. I understand that cats will turn like the devil (they will in my sim too), but I'm just not too sure about the limits with vee bottoms. Any thoughts, insight, or data on anything like that would be appreciated, even if it's just a gut reaction.
Thanks again for your comments and engaging me in conversation on all this. I appreciate it.
Tiny: The sketch idea is a good point. Maybe it could be promoted at some point that way, I'm just very leary of making it out to be something that it might not be. Standard marketing hype practices annoy the hell out of me and I don't want to engage in that kind of thing. If you've got something good you shouldn't have to BS people. So yeah, I'll just call it a sim/game until guys like you come along and say it's more than that. It'd be more honest at least.
I like your sketch idea and description you put forward for that where it might be useful as a sort of playpen to test ideas before moving on to more advanced software that will do a more accurate job. Yeah, that might be an angle on it. I've learned a lot about chine walk dynamics just by playing with the designs in the sim, so it appears useful for at least gaining an understanding of some of the hows and whys of the various dynamics even if the transom deadrise angle you use on a real boat might be a litte different and that sort of thing. I think it's probably useful for getting a general idea of how some of this stuff works, changing "this" variable in this direction tends to make this or that problem worse or better, that kind of thing.
Trying to minimize wetted area while not blowing over is a fun challenge too. The skin friction/viscous drag is done without any empirical constants at all (the model uses a Reynold's number approach) which works better than I expected it to, so the top speeds seem to be in the right ballpark as far as I can tell. There are no lift/drag coefficients anywhere here as you might find in a flight simulator, it's just force computations directly on the boat mesh in the direction of the triangle surface normals (and a tangent force for friction in the triangle plane). So it's pretty remarkable that it works as well as it does.
I would be ecstatic to find out some day that designers were using it at any stage of their design process, and even happier to find that it was actually helping them. If nothing else, it'd lend credibility to the realism of the simulator which I'd get a lot of personal satisfaction in knowing. Part of the reason I'm making this is because I couldn't find a game or sim that really captured the interesting dynamics at all. When the boat started chine walking without telling it to, and I figured out that it was curable by tweaking the pad and/or transom deadrise angle in a way that widened the wetted area at the stern at high speeds to counteract the prop torque, it brought a big smile to my face and I knew I was on the right track. When it blew over at about the right speeds without telling it to, well, that was another victory.
I just worry somebody's going to hurt himself somewhere down the line by taking the model too seriously. I trust engineers to understand the limits in various computer models because they're appropriately trained and educated, but Joe Schmoe building a boat in his garage won't understand those limitations. So I've got to be real careful about how I promote it and figure it'll probably be best to leave comments about how useful it is for real design to whatever users engage in that. They'll know better than I will anyway.
On another topic: While I've got a couple of attentive ears, maybe somebody here could help me with some real boat data? I have a couple of concerns at the moment. One is that I'm computing mass properties by integrating the surface area of the mesh, so as you change the boat design, the mass and inertia tensor change automatically. I just assume some thickness to the boat surface rea, effectively assigning different densities to the bottom, stern, bow cover, etc., then add masses for the driver, fuel, and engine.
The trouble I have is that I don't know how these things are really built so I'm left guessing at the relative densities. Because of this I'm not very certain of the accuracy of the center of mass of the boat as well as the engine. With the cm too high you of course get problems turning, the boat at some point wants to lean out of the turn as you can see happen in a few places in that last video. I know at some point that should probably happen, but I don't know what lateral acceleration limit might be typical before you see it roll out like that. Very small changes in cm location affect it a lot (especially height), so there's room here to play still.
What would be helpful is to get center of mass location data on some boats of this general type, the small, high speed Hydrostreams and so forth. It'd also be great to get some telemetry with lateral acceleration data (maybe roll angle too to spot roll reversals in very hard turns). The trouble is I'm having to recall from 20+ years ago how hard our family boat turned, and my butt is not a particularly good accelerometer after 20+ years. I have almost no data here other than a couple of YouTube videos where some boats were turned at maybe 0.5g, but I have no idea if that's just a lazy turn or if that's about as hard as somebody would want to go. I understand that cats will turn like the devil (they will in my sim too), but I'm just not too sure about the limits with vee bottoms. Any thoughts, insight, or data on anything like that would be appreciated, even if it's just a gut reaction.
Thanks again for your comments and engaging me in conversation on all this. I appreciate it.
