Here was where we left off;
I have some experience with the Zenair design amphib but primarily on a Rans S7 with a 100 hp 912 and a warp drive prop. It was a great performer (comparable to straight float SuperCub) but the floats used were the smaller 1250 sized amphibs. By comparison, it appears the yellow Highlander in the picture is using the Zenair 1450 amphib. And while the 1450 appears to be nothing more than a scaled up version of the original 1150/1250 Zenair amphib, it might actually be a bit too large a float for a Highlander? If the float is larger than it needs to be, takeoff distance, climb, and cruise speeds will suffer due to the extra weight and drag. The larger float however will handle being overloaded better, and will sit higher in the water.I don't know Bob myself, but the other Highlander builder here does and he mentioned that Bob likes them. Bob's Highlander has a 912ULS 100hp. His Zenair amphibs are a bit slow getting off the water, but I think any amphib float is going to seem that way, especially if you are used to straight floats. Like Dane mentioned, they may not be set up 100% correct for his plane either. Personally, I am willing to trade off a bit of take-off distance in favour of the versatility of amphibs and for the cost Zenair is pretty hard to beat. The larger wheels on the Zenairs also appear to be better for grass strips than most amphibs.
So how do you know what size float you need?
I like to use the formula the FAA uses (FAR 23.751) for float sizing. Using a 1430 lb max weight LSA seaplane as our example we can calculate how big of a float we need; First divide the 143o by two to come up with how much weight each float needs to support in fresh water (715 lbs in this case). Then add 80% more bouyancy (another 572 lbs) to the 715 lbs and you now have a total of 1287 lbs total displacement or bouyancy needed for each float.
Of course, now you have to know the actual displacement of the floats you are considering as many float manufacturers don't always represent their floats true displacement in their model number or size descriptions. But I have found in my experience with most that they typically understate the total displacement rather than overstate it.
And that stands to reason based on my experience with the CZ 1300 amphibs. They work exceptionally well on a Highlander, with plenty of floatation while still performing well. And the 1250's also work very well based on my experience with a Rans S7 (even at 1550+ lbs I may add - I've done that more than once ). Again, the larger floats will better tolerate overloading due to having a much higher reserve buoyancy, but performance in more standard operating weights is likely to suffer compared to the slightly smaller float.
However, knowing all that, if I felt I needed to fly on a regular basis in the 1550 lb weight range, I would probably go with the bigger floats. My float math at 1550 lbs shows I would need a 1395 lb displacement float. So the 1450 would probably be a good option in that case.
All this is why getting a good performing seaplane, especially an amphib, is not easy. But it is still worth it. Put your Highlander on floats and you will have a hard time going back to flying wheels. It absolutely comes into its own as a seaplane...