SVG version of Image:Triskele-Symbol-spiral-five-thirds-turns.png .

Converted from the following PostScript code:

%!
/archimdouble{
%%%%%%%%%%%%%%%%
% PostScript program to display an Archimedean spiral by approximating
% it with Bezier curves.  Can display a double spiral (two spirals
% rotated by 180 degrees with respect to each other).
%%%  Parameters:
                 % centerx = horizontal coordinate of center of spiral
                 % centery = vertical coordinate of center of spiral
                 % rotf = degrees to rotate
/sepwid 110 def  % width separating successive turnings of spiral
                 % (half this if double spiral is selected)
/incrm 15 def    % insert a curve point after this number of degrees
/sweeps 1.67 def    % number of 360 degree turnings to show
/double 1 def    % change to 0 to display single spiral
%%%  Procedures:
/pi 3.1415926535898 def/radians 57.295779513082 def
/sepwid sepwid pi div 2 div def
gsave centerx centery translate rotf rotate
/aspiral{/prevbezy 0 def 0 0 moveto
    0 incrm sweeps 360 mul{7{dup}repeat
        phase add cos/costh exch def
        phase add sin/sinth exch def
        costh mul radians div/thcosth exch def
        sinth mul radians div/thsinth exch def
        thcosth sepwid mul/x exch def
        thsinth sepwid mul/y exch def
        /slope sinth thcosth add costh thsinth sub div def
        sinth 0 gt sinth 0 eq costh -1 eq and or{/flag -1 def}{/flag 1
            def}ifelse
        /A exch def A 49.29348 lt A 180 gt A 196.273450852 lt and A 360
            gt A 368.8301 lt and A 540 gt A 545.9907 lt and A 720 gt A
            724.5217 lt and A 900 gt A 903.6281968 lt and or or or or
            or{/flag flag neg def}if
        incrm sub 3{dup}repeat phase add cos sepwid mul mul radians div
            /prevx exch def phase add sin sepwid mul mul radians div
            /prevy exch def
        incrm add 3{dup}repeat phase add cos sepwid mul mul radians div
            /nextx exch def phase add sin sepwid mul mul radians div
            /nexty exch def
        /prevdist x prevx sub dup mul y prevy sub dup mul add sqrt pi
            div def
        /nextdist x nextx sub dup mul y nexty sub dup mul add sqrt pi
            div def
        /normaliz slope slope mul 1 add sqrt def
        0 eq{/prevbezx phase cos nextdist mul def}{prevbezx prevbezy
        x 1 flag mul normaliz div prevdist mul sub y slope flag mul
            normaliz div prevdist mul sub
        x y curveto
        /prevbezx x 1 flag mul normaliz div nextdist mul add def
        /prevbezy y slope flag mul normaliz div nextdist mul add def}ifelse}
    for stroke}def
/phase 0 def aspiral
%%% If different sweeps parameter for second spiral, define here:
/sweeps 1.34 def
%%%
double 0 ne{/phase 180 def aspiral}if grestore
%%%%%%%%%%%%%%%%
}def
gsave
792 -230 translate -.95 .95 scale -4 rotate
/centerx 304 def/centery 550 def/rotf 120 def archimdouble
/centerx 634 def/centery 550 def/rotf 240 def archimdouble
/centerx 469 def/centery 835.7884 def/rotf 0 def archimdouble
grestore
showpage
%EOF