On Jan 11, 1:03*pm, Nyal Williams
wrote:
Methinks you are treading on thin ice with the phrase
'my interpretation.' ...

I concur, very thin ice indeed. According to 14CFR part 103.1:

**************begin paste from ecfr.gpoaccess.gov **************

§ 103.1 Applicability.

This part prescribes rules governing the operation of ultralight
vehicles in the United States. For the purposes of this part, an
ultralight vehicle is a vehicle that:

(a) Is used or intended to be used for manned operation in the air by
a single occupant;

(b) Is used or intended to be used for recreation or sport purposes
only;

(c) Does not have any U.S. or foreign airworthiness certificate; and

(d) If unpowered, weighs less than 155 pounds; or

(e) If powered:

(1) Weighs less than 254 pounds empty weight, excluding floats and
safety devices which are intended for deployment in a potentially
catastrophic situation;

(2) Has a fuel capacity not exceeding 5 U.S. gallons;

(3) Is not capable of more than 55 knots calibrated airspeed at full
power in level flight; and

(4) Has a power-off stall speed which does not exceed 24 knots
calibrated airspeed.

**************end paste from ecfr.gpoaccess.gov **************

Note that there is indeed an exception to the 254 lb empty weight for
powered ultralights, and that it applies to floats and certain "safety
devices."

However, note also that:

* The empty weight exception allowed by 14CFR103.1(e)(1) applies to
the 254 lb empty weight of powered ultralights, but does not apply to
the 155 lb empty weight of unpowered ultralights.

* The "safety devices" that 14CFR103.1(e)(1) allows in addition to the
empty weight is explicitly limited to those "which are intended for
deployment in a potentially catastrophic situation."

Thanks, Bob K.