|
|
|
|
|||||
|
||||||
Subject: TWL: TLW: Re: Props
From: Jim Fidler (fidlerjim@XXX.XXX)
Date: Fri Mar 01 2002 - 14:08:02 EST
Sonny
When I bought my boat the sea trial found a bad vibration on the starboard
engine only. The surveyor checked the props, shafts, cutless bearings, etc.
To me the props "looked" perfect. Surveyor concluded that the props were
fine and the shafts were OK but the outer cutless bearings were worn too
much. Seller agreed to pay for replacement and I decided to buy the boat.
Vibration improved only slightly. I checked engine to shaft alignment.
Both were out of alignment and I could tell that both shafts were somewhat
bent. I aligned the starboard engine as best it could be and got a very
slight improvement.
I lived with the vibration for a year, until the next bottom job. At that
time I asked the marina to pull the props and shafts so I could get them
fixed. When I arrived with my trailer to get the shafts, the marina said
they had already sent the props to their prop shop. I took the shafts to
Mike Hood in Houston for straightening and depended on the marina to get the
props done. Hood said they had difficulty straightening the shafts,
primarily because they were bronze and soft, but got them "pretty straight."
He recommended new stainless steel shafts. The serviced props looked like
new, of course. But, again the vibration was only slightly improved. Very
disappointing.
Next I bought new shafts and had the boat pulled just to install the shafts.
You guessed it. Starboard still vibrating, port smooth as silk.
At the next bottom job I personally took the props to Baumann Propeller in
Houston for computer scanning. The props still looked perfect, but the
computer found that one blade on the starboard prop was way out of spec. In
order to repair it they had to reduce the prop diameter by an inch. This
was fine by me as there was probably inadequate prop clearance to the hull
(less than 10 percent). Of course they did both props.
Vibration gone. Mr. Baumann said it looked like the offending prop had been
improperly repaired after a hard grounding and was cosmetically good but
actually very bad.
My only regret is that I didn't have it done years earlier. I highly
recommend Baumann. They used the Hale MRI System. You can get extensive
details about it at www.halepropeller.com. You can ship your props to Hale
for service as one of my friends did.
There are several different levels of accuracy, or ISO Classes, for props.
For pleasure boating, the lowest (and least expensive) level is all you
need. A prop that has been worked to this level is as good or even better
than new. The other levels are for high speeds, racing or other exotic
service. Also, I did not get my props dynamically balanced. As I
understand it, if the computer scan of the blade profiles is OK, the prop
must be in pretty good balance. Spin balancing is only necessary for high
speed or special purposes.
Hope this helps you
Jim Fidler
"Fiddlesticks"
|