// tested with 30mm dia 3 bladed. Was over propped. Motor got hot quickly and
// boat was unable to get onto the plane.
// 30mm 2 bladed seems much more lively, though I'd also removed
// the grease from the drive shaft and taken out some of the bend in the shaft.
// only the open water will tell - though I'll also be added a bigger rudder,
// the original 20mm high and 20mm long just wasn't enough. Doesn't help
// that the throw is +-25 degrees.

// 2 bladed 30mm was okay, but got the impression it was under propped.
// trying 2 bladed 34mm.
// and that had a reasonable plane. Motor and speed controller were cold,
// so decided to increase the dia to 36 mm, and pitch to 45 degrees.
// Which was too much, 36mm at 45 degrees didnt have the speed of the 34mm at 30 degrees.
// trying 34mm at 40 degrees.

blades=2;
diameter=34;  // 36mm is closer to the maximum, 40mm would be too much with it
                         // also being further along the drive shaft.
                        

drivedia=5;   // hole in hub
hubdia=8;      // out hub diameter
hublenback=10;
hublenfront=6;

attackang=40;

bladethickness=1.5;
bladetipthickness=0.4;

bladelength=10;

bladeoffset=4;  // how far forward is blade edge from center?

$fn=100;

rotate([180,0,0])  // make it the right way up for printing
difference()
 {   
     union()
       {
          translate([0,0,-hublenback])
             cylinder(hublenback+hublenfront,hubdia/2,hubdia/2);  // hub
          intersection()
            { 
               for(i = [0:360/blades:360])  // draw blades
                   rotate([0,attackang,i])
                       translate([-bladeoffset,drivedia*0,0])
                           union()
                            {
                                cube([bladelength,diameter/2,bladethickness]);
                                $rotate([90,0,0])
                                hull()
                                 {
                                     translate([0,0,0])cylinder(diameter,bladetipthickness,bladetipthickness);
                                     translate([bladelength/2,0,0])cylinder(diameter,bladethickness,bladethickness);
                                     translate([bladelength,0,0])cylinder(diameter,bladetipthickness,bladetipthickness);
                                 }
                                 }
               
               translate([0,0,-hublenback])  // enforce blades no more than diameter
                   cylinder(hublenback+hublenfront,diameter/2,diameter/2);
           }
       }
     
     translate([0,0,-hublenback-0.5])  // subtract drive shaft
        cylinder(hublenback+hublenfront+1,drivedia/2,drivedia/2);
 }