http://pub122.ezboard.com/fultra150frm1.showMessage?topicID=658.topic
Check out this link listing most popular Ultra set-ups. They're mostly spinning a solas 16/20. Can they turn this prop without motor mods? If so, I would think that would explain their speed. Even if they're spinning this thing with only a head, they're processing a lot of water.

The Ultra props are actually smaller just a steeper pitch.
Ultras use a 148mm pump (I think) compared to the 155mm pump used in the GPR. The GPR pump is capable of processing more water.
The ultras also have a lighter and flatter hull which allows them to run a steeper prop without hurtig the bottom end as much.

I knew about the flatter hull but not the smaller pump/prop size, that makes sense.

It's also a mixed flow pump, instead of an axial flow on the yamaha. The hub on an ultra prop is about 92mm wide, on the yamaha its about 62mm. The ultra hub is is over an inch and an 1/8 bigger
With smaller blades, they need to be taler to keep the velocity through the stator enough to get the top speed desired.

Oh yeah, doesn't the ultra also weigh quite a bit less?????

I just sent me 13/19 out to Carl. Cant wait to get it back and see what it can do. He is true/balacing and adding some pitch on the topend for a couple tenths of a mile per hour. Should end up being nice over stock.

16/20 dynafly is definitly the way to go on an Ultra.