Obviously having too much time on my hands, I was wondering why boat-hulled planes can land in far higher sea states (Beaufort scale) than twin float planes?
Is it due to the design of the floats i.e. their V hull is not deep enough or the length of the floats (both things which in normal vessels affect ride), the lack of volume in the 2 floats as opposed to single hull or indeed the surface area in connection with the water, the fact that aircraft weight is generally lighter for a floatplane or is the fact that generally floatplanes do not have outrigger floats to stabilise in Bad Weather?
Thanks in advance.
Best
FG

I don't believe that assumption is totally true. Acceptable sea state is certainly related somewhat to hull design, but try putting a similar size aircraft into that sea state, and you may find that the limits are closer than you might think. Compare a Lake amphib to a comparable size floatplane for example, and I think you'll find the Lake pilot back off FAIRLY close to where the twin float pilot does.

That said, there are very different float designs, and some are much better rough water hulls than others.

There are conditions I'd land a Beaver in that I'd not land a Cessna 206 in, not because of the landing, but because of the takeoff.

MTV

MTV,

Thanks for your speedy response, what would be the limitations on takeoff?

Best

FG

I know zilch about float plane flying, other than the one intro lesson I had up in BC some time ago. But I have over 60 years of boating experience, and there are lots of similarities to consider. Size, weight, strength, hull design, speed across the water (i.e., touch-down speed and lift-off speed) would all make a huge difference.

For instance, comparing the Beaver to the 206, although the Beav is probably built more tank-like than is the 206, the biggest factor would be the Vso of the Beaver at 39 knots vs. the 206's Vso of 52 knots, which would allow the Beaver to touch down or lift off at a much lower ground speed. Even at the Beaver's slower speed, it doesn't take much boating experience to recognize how much pounding any hulls will take at roughly 45 knots lift off speed. Lakes' Vso vary by model, from 39 to 49 knots.

Cary

flyinggibbon wrote:MTV,

Thanks for your speedy response, what would be the limitations on takeoff?

Best

FG

FG,

Cary is going down the right path. Takeoff is the real test, though, because of the considerable drag of the water. On landing, keep the airplane relatively level, and the hulls don't pound as much, but the hydrodynamic drag will decelerate the airplane rather quickly.

During takeoff, on the other hand, you have to accelerate to flying speed, all the while trying to overcome that substantial hydrodynamic drag. And all the while getting pounded (and decelerated) by every one of those waves you hit.

The worst condition is a swell with little or no wind, or a crosswind, both for takeoff and landing, but still worst for takeoff.

I've said before that In a way, a Super Cub or Husky are some of the best "rough water" float planes, because they'll only hit three or four waves on takeoff, ASSUMING there's a strong wind, of course.

There are other factors, of course, including hull design. If you're going to play in rough water in aCessna 185, put it on PeeKay floats, not EDOs, and so on. That is a difference in hull design.

Hull types have an additional advantage in that their wings are MUCH closer to the surface than a twin float equipped airplane, particularly in something like a Lake. This feature means that the hull type will exhibit substantially stronger ground effect. That allows the hull type to takeoff at slower speed, then fly slower in ground effect, then accelerate to flying speed AFTER its shed itself of that powerful hydrodynamic drag.

ETC

MTV

That is interesting, so in that case why don't trim tabs get used on floats to reduce this drag on takeoff (given that you have a large enough thrust from the engine)?

This is a fair introduction to the concept of boat trim tabs: http://www.midcoastmarine.net.au/images ... s-info.pdf

Thanks for all the comments so far.

Best

FG