Tomcat

I use FreeCad and it is indeed free (for non commercial use) but it does have some limitations, particularly if you want to build up a really complex structure.
You can do it but it is a rather long winded process. I suspect this comes from a structure that was required by earlier lower powered PCs.

Of course what you may be able to design and shown as a 3D image 'floating in the air' does not necessarily mean it can be satisfactorily printed!

Tomcat update. Well the Tomcat had it's maiden on floats a few days ago. Although it performed well on takeoff, landing & in the air, steering on water left a lot to be desired to say the least ! The water rudders proved to be ineffective, so back to the drawing board & make some new ones.
The design is very simple, a carbon fiber tube glued to the back of each float, with the rudder glued to a carbon shaft & the control arms screwed & glued in position one the shaft is inserted. Nylon washers were fitted to the top of each shaft to give good freeplay. A piece of 3 mm foam was then glued across the back of the float as extra support for the tube, & given a generous coat of laminating epoxy. The rudders are cut from plastic tool box dividers, & are approximately 2 .5 times the area of the original. The pushrod connecting the two rudders was fairly heavy weight stainless welding wire, anything lighter tended to flex over that distance. I saved a little weight by replacing it with 1 mm inserted through a carbon tube.
If this doesn't improve the steering I'm not sure what will ! It will be interesting to see how the larger rudders affect it in the air as well. The only other thing I will have to be careful of is submerged weeds, as the rudders are fixed in the down posistion.

Is it me but the new rudders dont look that much bigger in the photo crash, i do like the way you improvise on your building materials, a flying tool box now

From my limited hydrodynamic knowledge I suspect it is the shape of the floats coupled with a high CofG at least as far as the floats are concerned.
Each of your floats is practically a flat bottomed hull with a substantial flat side area. This will make it tend to want to run straight despite the effect of the rudder. A float with some 'keel rocker' (the keel rises towards each end) will make it much more responsive to rudder inputs. Of course this has to be traded for a suitable shape for a hull to 'plane' in the water.
The high CofG also creates a negative turn effect. As the rudders impart a turn, say to port the high CofG makes the plane lean outwards submerging the starboard float a bit more increasing the drag and vice versa for the port one. The net result is for the floats to resist the effect of the turn. A V bottom hull shape does provide a degree of a self righting moment when under side slip as well as a rapidly rising 'floatation' force as it is submerged.
Ultimately however float planes do not handle as well as a flying boat which can make better use of conventional hull hydrodynamics.

BB. It's the perspective of the photo, I had the original closer to the lens. :oops:
You are right Simon, the floats are virtually flat from the step back & have a shallow V forward of the step. Not a particularly good design on my part, but it does appear to 'unstick' from the water fairly easy. I will endeavour to improve the design if I build another set.

As I posted in 'been flying' the new water rudders work great, only problem is I now have a very fast boat ! They are simply causing to much drag for it to unstick, added to which I found a small leak in one pontoon. I decided the solution to the first problem was more power, 4s. I had flown it once before like that, but it cut out on me. I mistakenly thought the motor was only rated for 3s, fortunately that was not the problem, it's the ESC. I have now changed that from a 30 amp to 40 amp, & propped it with a 10 X 6. That combo on 4s draws 36 amps at full chat, close to the limit I know, but that's the only spare ESC I have. Throttle economy will be required !
The plan with the floats is repair the leak for the time being, so it useable. I have started on a set of better designed solid foam ones, heavier yes, but I hope the more efficient shape & 4s power will compensate. It may take a while to finish them, as time is at a premium at the moment ! :pinch:

It's not uncommon to do a full circle and then use the wake wave to cause an unstick with planes that are a bit reluctant.

I was going to say the same Klippy, maybe it needs a bit of a chop on the water to unstick?

That's also why floats are deep-'VEE' shaped, with a 'step' just aft of the c of g.
then you aren't trying to pull a flat plate out of the water.

With a lot going on at the moment I haven't had the time to make a new set of floats, so I have made an interim fix on the old ones. I cut & glued a 20 mm triangular piece of extruded foam down the center of the front half of the floats, up to the step. Then formed the green foam over it, glued it all round & gave the whole thing a good coat of laminating epoxy to waterproof it. The result is a much deeper V up to the step. The rudders have had 10 mm removed from the bottom to reduce drag. 20 grams was removed from the nose to get the CG back, which is approximately 1/2" in front of the step. I have decided to make it a dedicated float plane for two reasons; 1. I have plenty of others on wheels. 2. The lake is the largest landing area we have at the current site, so might as well take full advantage of it ! Hopefully the alterations, plus going to 4s, will be more than adequate. All that remains is to find a day when I have time & the wind has dropped from the 15 ms we've had for the past week to try it.

That step looks a little deep for my liking, but I know nothing about float planes.

Commercial floats - intended for my TL2000
Note the high aspect ratio - ie very long for the width, the vee runs the whole length of the float, and the underside is curved with the deepest portion just ahead of the step.
(apologies for the background clutter - I'm not going to rearrange my kitchen for ten seconds of photography! :evil: