1) Since you posted a question to my callsign, I thought I should at least respond...
2) As others have already answered, your idea is a going to be an effort in futility!!
Originally Posted by Hamsailor
A 10 element Yagi beam for 1.6 GHz would be only about .5 meter (1.5 ft) long.
It would give a 60 degree fan beam. (Fan, not cone.)
Not too sharp to be impossible to point....
In brief, gjorgensen gave you good advice...you're best bet is to get a broad-beamwidth antenna (Omni above the horizon) with a clean pattern, mounted out in the open, away from other metallic objects / structures...
L-band patch antennas are very cheap
to make, and are surprisingly good at this application....hence why they're recommended / sold for this...
3) And, as Evans (and ssscruz and gjorgensen) elegantly put it....it is this small, simple, wide-beamwidth antenna, out in the clear AND the coax / connections, that makes or breaks the system!!
And, unless you have a really big boat, requiring more than 50' of coax....there is no need to use an "active" antenna with Iridium.....this is, of course, not the case with INMARSAT, but for Iridium, passive antennas work very well!!!
4) As for 1.6Ghz yagi's....
I built some 1691mhz "loop-yagi's", about 30 years ago for GOES weather
....and they worked great....but that's a stationary target, and I was on land!!!
(I also built 12-turn helix's for 432mhz and 1296mhz, many years ago...with good results....but these too, are way too high-gain / too narrow pattern for Iridium use on-board...)
With the multiple beams, having an antenna with a clean pattern (low sidelobes), becomes important as well....and HB yagis are not known to have the cleanest of patterns...
And, I'm not sure how you calculate a 60* beamwidth for a 10-ele yagi?
'Cause the real figure is about 35* - 40* (3db beamwidth), depending on design / construction....
5) Evans, as for using on-line calculators to determine the best time to use Iridium?? This is a new one to me!
(I know this is an absolute for Globalstar
....but never heard of anyone propagating this for Iridium...)
P.S. On a side note, I've also designed/built antenna systems for AMSAT use, etc. (as well as for 2-m EME)....and my cheapest/simplest antenna was ironically one of my favorites....
Over 30 years ago, I built a 2-m turnstyle using 8 ga copper wire, over metal window screen
, all supported on a 2x2 wooden frame...
I used this antenna (and if you don't mind some bragging, my operator skills) to successfully complete 2-way contacts with the first ham in space, W5LFL, in the SpaceLab in the Shuttle....one of only 300 stations worldwide to do so, and one of < 100 that did so "on random, non-sked"....and one of only 3 stations in Florida
to do so...(and one of those others was a sked with Motorola in Ft. Laud)
The reason I'm posting
this is not be a bragging, obnoxious, know--it-all....but rather to point out that fast moving comm targets, using line-of-sight paths, require one of two things:
a) clean, wide-pattern antennas....(cheap and easy to do on-board a boat)
b) precise, accurate, instant, aiming of antennas....(a pain in the ass to homebrew and do on a boat)
I hope this helps!!