A7 Duo-Prop update - Impeller gone Bad!
A7 Duo-Prop update
Posted by NoSlack on Jan-18-04 at 07:14 PM
Today was the first day out with the new A7 props and I didn't get past the 5 MPH buoys.
As I rounded the corner and headed out the channel I kicked up the speed to 7 knots to take my first set of data. Everything was looking good, 1600 RPM ant the temp was still down below 160 where she normally runs at that speed. The next bump in throttle is were the day got interesting.
I kicked her up to 2500 RPM and look down to see the temp at 190 and climbing. I thought I picked up some kelp so I backed down real hard and continued on my way. The temp never recovered so I shut her down to check the basket strainer and raise the outdrive for a quick inspection. I didn't see anything out of the norm so I started her back up and still had temperature problems so I drop the hook at the 5 MPH buoys and called Vessel Assist. Lucky for me he was just outside the channel and had me back on the trailer within a few minutes.
Back at the ranch I start looking for my problem. Fist thing off was the water pump. Not one rubber vein left on the pump. I never found any rubber in the basket so now the search was on to find all the chunks. I tried blowing water from the outdrive through to the tube below the basket strainer. Very little flow so I reversed the flow and blew from the basket tube to the outdrive. Again very little flow but I could see a few chunks inside the lower unit suction area.
I pulled all the tubing and hoses off and blew them out 1 at a time. My blockage turned out to be in the stainless tube that goes through the outdrive with a few pieces bobbing around inside the water cavity of the lower unit.
It took me almost 2 hours to dislodge all the pieces and clean out all the tubes using a combination of high pressure water and a mini drain snake I made out of my old Sum Log cable. Those of you replacing your Sum Log, save some of the flex cable. Cut your self a 5' piece, put a little bend in on end and us it with a cordless drill. You will be amazed how sharp of a bend you can push that snake through.
In conclusion:
I think I sucked up a bag and completely block my water flow off which burnt up the impeller. I say this because I found no rubber in the basket. If the pump failed over a short period of time, I think there should have been enough flow to deposit some of the rubber in the basket.
Mike
Top speed for the day was on the way back in.
http://members.cox.net/noslack/IM000655.JPG
New impeller on the left, old one on the right.
http://members.cox.net/noslack/IM000656.JPG
Chunks on the left were in the tube and the chunks on the right were in the outdrive.
http://members.cox.net/noslack/IM000657.JPG
--------------------------------------------------------------------------------
#1, RE: A7 Duo-Prop update
Posted by Nomad on Jan-18-04 at 07:25 PM
In response to message #0
Just missed you Mike as I ran into Jeff putting a shine on the Doghouse in the parking lot. Sorry to hear the test run didn't go so well.
Charlie
--------------------------------------------------------------------------------
#2, RE: A7 Duo-Prop update
Posted by NoSlack on Jan-18-04 at 07:50 PM
In response to message #1
LAST EDITED ON Jan-18-04 AT 07:50 PM (PST)
You've got to take the good day along with the bad ones.
Some days you're putting a hurting on the fish, some days you're putting a hurting on your knuckles in the bilge.
Mike
--------------------------------------------------------------------------------
#3, RE: A7 Duo-Prop update
Posted by Yellowfin1 on Jan-18-04 at 08:14 PM
In response to message #2
Geez Mike,
That water pump looks as blackened as mine did when I burnt it up last Spring. Don't ya love that burnt rubber smell? Guess it didn't get hot enough to burn up your seals on the shaft eh? It would be interesting to know if the A-7's would have worked had you not encountered heat problems (bag?). As you know, I am running the same engine/duoprop setup as you are. I am running re-pitched A-6's and they seem to be fine. Previous owner said don't run anything bigger than A-6's. But your boat is certainly lighter so you may be able to get away with it.
--------------------------------------------------------------------------------
#4, RE: A7 Duo-Prop update
Posted by DOGHOUSE26 on Jan-19-04 at 10:24 PM
In response to message #3
LAST EDITED ON Jan-19-04 AT 10:27 PM (PST)
Mike,
I still think you might have developed an air lock in your system; they don't happen all the time just occasionally. If you crack your raw water strainer cap just for a second to let water leak from the side just after start up, you can eliminate this problem. When you cruise at idle through the 5 mile zones you don't need very much water at all. I don't understand how the pieces went backwards through the system unless when the water drained out on ther trailer.
Very Interesting!
You're right, probably a lobster jamming plastic into your intake to protect his last remaining loved ones!
--------------------------------------------------------------------------------
#5, RE: A7 Duo-Prop update
Posted by Wizard on Jan-19-04 at 10:56 PM
In response to message #4
Glad it happened so close to MB. I've seen that before when the engine gets too hot or waterflow is blocked. Always bothered me where all the pieces went. You don't think you are running hot with the new duoprop and prop setup? Probably not if you had just left the dock in the 5 mile zone mostly.
On another interesting note to Mike. Learned today my duoprops are B4s. My spares are A6. No idea the history of that setup and those spares. The smaller the number means what again? Higher pitch? Still curious the exact explanation between 'A' (Gas) and 'B' series (Diesel).
Glenn
--------------------------------------------------------------------------------
#6, RE: A7 Duo-Prop update
Posted by NoSlack on Jan-20-04 at 08:23 AM
In response to message #5
Here is what I think I learned about Duo-props over the past 5 weeks.
The A series is designed for diesel boats, with 3 blades in the front/ 4 on the rear.
The B series is designed for gas boats, with 3 blades in the front/ 3 on the rear.
The A series is supposed to give the boat more lift and help the heavier diesel boats plane sooner. Other than that a A5 or B5 should perform about the same at cruise speed.
The number system work like gears on a 10 speed. The higher the number the faster you go with more load on the engine.
If your engine is comfortable pushing B4s you might have a hard time pushing the A6s. The only way to find out is put them on and give them a test run. If you find the to be to much for your boat, I might be interested in them later on this summer if Ed can pitch them to A8s.
Mike
--------------------------------------------------------------------------------
#7, RE: A7 Duo-Prop update
Posted by NoSlack on Jan-20-04 at 08:34 AM
In response to message #4
When we talked at the ramp, you got me to re-think the way I start the boat.
For the first 7 years I owned the boat I always pre-filled the basket so the pump would be wet on start up. During that period of time I had 1 minor impeller failure (1 chunk came off) but broke 1 basket and 1 lid do to all the wear and tear from opening the basket so many times.
The basket and lid cost 3 time as much as an impeller so I stopped pre-filling. I’ve been running this way for the past 3 year with Sunday being my first pump failure.
I wish I knew for sure if I sucked up a bag or was just air locked.
Mike
