Paddles on the wheels - err me, no - in theory, if it was to stay permanently in the water - yes, but as it's probably going to be a land tank with a water ability then the tracks won't go round with paddles on the wheels, if it is a period vehicle (and being a crusader that means WII) then I would go with what was available - like the M4 shermans, just what do you have that could be converted to two props - you do cars etc - any spare radiator fans ?
Knowing what we know nowadays, drop tanks as sponsons would be a better option than the drop curtain employed on the M4's, or just large inflatable underwater sponsons would have been better.
Me personally I would have built a roll on roll off barge with side panel sponsons that had enormous tank tracks at each corner, with a foot print that would allow for the barge to crawl up the beach, it would have had an angled segmented roof of ship grade armour plate to deflect the shells of the expected gun batteries and engines that would drive two props on each side, both front and back with drop down ramps and gaps in the roof armour where the transported tanks turrets would poke out to give covering fire whilst approaching the beach, the idea would for it to crawl up the beach until it became difficult, then when the front dropped, the two front tanks push a large roll of metal mesh out onto the beach they would then move forward and give further coverage when they moved to the sides, the next tank would be the mesh carrier rolling out another roll after the first length to get further up the beach, followed by another two M4's, whilst this is going on the mesh carrier returns and collects more rolls of mesh and works to widen / lengthen the coverage, another barge would then have got up being the first and the two ramps dropped to allow the second barge to deliver its tanks, if the tide went out other barges could close up behind the other barges providing a sort of causeway for troops and tanks, but thats me thinking out of the box.
