You said that you were happy with the prop work you had done a couple of years ago, so does that mean that it took care of any vibration? Could you tell a difference in anything? Speed, fuel consumption, handling? Also if you don't mind, I am wondering what the cost of this work was
We had the prop work done almost "accidentally."* Not because we thought they were the source of vibration.* We had been told the props were worn out (yes, they can wear out over time).* After asking a whole lot of people in various aspects of the local marine industry who the best prop shop in Seattle was and getting the same answer every time--- Kruger and Sons--- we took the props in there to get replacements.* (I know Eric doesn't like Kruger but he's the only person I've heard from who doesn't and I don't know the particulars of the problem he had.)
They determined that the props weren't worn out but they were horribly set up with all sorts of problems stemming--- they said-- from the methods whoever set them up last had used.* (This would have been prior to our buying the boat.)* They explained in great detail what had probably been done but while it all made sense at the time it was way over my head and I've forgotten most of it.
They charged (two years ago) $350 each to completely rework the props.* We had been prepared to spend $1700 to $2000 per prop for new ones so this was happy news.
The reworked props made no difference whatsoever to the various vibrations our boat has and had when we bought it.* What the reworked props did was eliminate the tendency of the boat to wander off to one side due to assymetrical thrust, and we idle between half and one knot slower now because the props were repitched one and two inches down respectively.* So instead of 17" and 18" they are now both 16".* At cruise power the EGT readings are a wee bit lower now because the engines are not working quite as hard as they were.
We also had one shaft trued and one replaced.* We had both of the original shaft "setscrew" couplers replaced with much larger and deeper "split couplers" which hold the shafts much more securely and consequently do a better job of maintaining shaft alignment.* At the same time we did this we had the cutless bearings replaced.
None of this work--- props, shafts, couplers, cutless bearings, and the requisite engine alignments--- made any difference in the vibrations in the boat.* But vibration was not what we were doing all this work to correct.
We've not noticed any obvious difference in fuel consumption but we don't have a FlowScan or any accurate sort of fuel-use measurement system on board.* We have a fuel gauge on the day tank and that's it.* But it doesn't look like we're using fuel any faster or slower than we always have.
The boat is extremely maneuverable (in my opinon but I don't have a lot of comparison experience). In large part this is because we have four-bladed props instead of the original three-bladed props. The more blades you have the more pronounced the prop walk will be, and in a twin you want the maximum prop walk you can possibly have with regards to low-speed or no-speed maneuvering.* I have noticed no change from the re-worked props in the maneuverability of the boat with regards to splitting the prop thrust or working thrust on one prop only.
Prior to our having the prop work done--- when we thought we needed to buy new props--- I had called Kruger to find out what sort of information they needed to properly size the new props.* They wanted me to bring in the rpm reading for each engine at WOT, they wanted to know the type of engine, its horsepwer and its maximum rated rpm, they wanted to know the gear ratio of the transmissions (they are not the same, port and starboard, on a GB), and they wanted to physically have the old props.
Neither engine would get near the maximum rated rpm at WOT.* GB typically overpropped its boats to give a bit more speed for a given amount of fuel burn since the engines they were using--- even the old FL120--- had the power and torque to deal with this up to a point, but we didn't have the original props on so whatever GB had set up on our boat when it was built didn't apply anymore.
Armed with this information--- plus the fact that Kruger has put props on probably 8 million GBs--- they had the information they needed to rework our props once they determined we didn't need new ones.* Had we needed new ones we were going to go back to three-bladed props because they're more efficient than four bladed props.* But as it turned out, we still have the four-bladed Michigans on the boat.* Which is great for maneuvering, less so for efficiency.
And that is pretty much everything I can tell you about that.
-- Edited by Marin on Saturday 18th of September 2010 11:08:16 PM