Denied the capacity to fiddle with rig and sails, we have filled this void by experimenting with props. Our three bladed test being concluded after 8000+ miles of usage, we are back to the fours.
We had Palmetto Prop in Charleston add 5% to the pitch of these, which previously allowed full RPM. What we are looking for is data on these props with the now derated engines, and how this ties to the predictions of the various models we use.
We shall report in due course.
Posted by Steve Dashew (June 22, 2011)
June 22nd, 2011 at 8:47 am
As an engineer (Naval Academy) I am still amazed at how seemingly “simple” systems that have been in use for hundreds of years (i.e. propellers) are still beyond our prediction abilities. So much is still trial and error. Fascinating.
June 22nd, 2011 at 5:07 pm
Hi David:
I have an old racing buddy who has spent billions of our tax dollars on submarine props doing the same thing!
June 23rd, 2011 at 7:45 pm
Steve,
To clarify, were you disappointed with the 3-bladed props at all, or are you just moving on to the next phase of fiddling?
-chris
June 23rd, 2011 at 9:02 pm
Hi Chris:
The three bladed props did mostly what they were expected to do, including be a little rougher running than we were used to. The efficiency was not as expected, down about three percent from projected. Now that could be considered within the margin of measurement error, but the bottom line is that we were off more than we like.
With a first day’s run behind us we have an immediate comparison on noise – the four blades are indeed quieter. It remains for us to get out into the ocean before we check efficiency.