Alan's site is excellent and I do recommend it. However, since the OP's question was very specific let me say that I have had great success with the Little Tarheel II. Use the cowl mount suggested by another poster to get it over some metal. Bond as much of the metal to the frame as you can using copper strap. Include bonding the muffler/tailpipe. You should be good to go and I think you will be happy with the Tarheel II....I know I have been
Tarheel model 100
Which of the two Antenna mention above has the greater efficiency?
>>> Maximizing antenna efficiency should be the Holy Grail of every mobile operator. Because ground losses dominate the efficiency equation, decreasing them by just one ohm, can make a significant difference. Further, excessive ground losses directly relate to the level of common mode currents. Common mode causes RFI issues, both ingress and egress, and a can drastically reduce SNR. This point should not be under estimated! Put another way, excessive ground losses can turn an otherwise efficient antenna, into an also-ran. <<< (snip from Alan's Ground, RF& DC)
The Proverbial "Wet Noodle" is capable of making contact with good propagation.
Does that means that the Wet Noodle is Efficient?
There is no rule that is written in concrete saying that there has to be "Metal" under the Antenna. http://www.k0bg.com/ground.html
Another way of viewing a Screwdriver Antenna is to look at it as .......
[ A tunable " Longwire" physically shortens ( coiled ) and stand upright with a 1 to 1 Balun at the feedpoint ] - Overly simplified.
Two things are evident here.
1) COIL Efficiency
2) Feed point Choke of sufficient Ohmic resistance to nullified the amount of COMMON Mode Current that will be present
IMHO - The Lil Tarheel only looks " CUTE "
Just my $0.02 worth.