Hatter_in_MD
New Member
Short version: I think I bent my prop shaft when I hit a rock. The shaft seems to be between 1/8 and 1/4 inch out of round if I spin the shaft by hand.
Question: would a bent prop shaft cause the prop to appear to be slipping (higher revs at the same speed)?
Details for the novel readers out there:
The boat is a 1998 190 BR, 4.3L Alpha One outdrive (1.81 ratio) running a SS 14.25R23 prop. I should be turning about 4800 rpm and making just over 40 knots at WOT. At present I can get the revs up to more than 5400 (for about one second before I backed off) and the boat is making about 32 - 35 knots at 4800 revs. Speeds are based on speedometer, not GPS readings.sev.
I hit the rock launching the boat near low tide, and had the outdrive fully trimmed down, and was no where near planing speed when I "found" the rock, perhaps 10 mph. I heard a strong CLUNK from the back of the boat, and thought at first we had fouled and cut a docking line.
I cut the engine, stopped, raised the outdrive and started checking for water in the bilge and engine compartment... no water found. Checked the prop, it had a flat spot on one fin, but was not mangled or broken off. No lines or other foreign objects wrapped around the prop.
Put the outdrive back down, started up the engine, and all sounded good. Put it gently into gear and felt my way into deeper water. The boat seemed a bit sluggish, but no strong vibration or rattling/banging noises. Engine sounded fine.
After a few minutes I figured out that I was dragging a mat of vines from the outdrive, removed vines, boat moved much better.
We made a short day of it, and did not stray far from the landing.
Everything seemed to be working ok but didnt want to take chances. Upon pulling the boat out of the water, I found that the leading edge of the skeg had takend a pretty good hit, and was missing a fair sized chunk. No other visible damage.
I got one of the SkegGuard repair kits and installed it. Had to bend back a very slight bend in the tip of the skeg to do so, and ground down the other sharp edges with a grinder.
I also ground the flat off of the prop, trying to change the shape of the blade as little a possible. I also dressed up some other nicks on the leading edges of the blades at the same time (smoothing and polishing, not cutting out large chunks).
I am sure the prop is not a well balanced as when new, but the ground smooth area on the prop did not look like it would unbalance the prop too badly. I checked the prop hub to see if it had been "spun" and it did not appear to be so. When I turn the prop by hand with the gears ingaged I can feel the compression stroke beginning, prop does not turn in relation to the shaft.
Put it back into the water on the weekend, and got the symptoms noted above (higer revs than expected, lower speed than expected). Before I could push the revs to about 3200 and get on plane pretty quickly. Now to get to plane in the same amount of time I am up closer to 4000 rpm.
End of novel.
Any ideas, suggestions, troubleshooting procedures I should try? What does it cost to have a prop shaft replaced, and should I attemt the job myself? Are there any special tools required?
Any suggestions or ideas gratefully accepted. Any jibes about hitting the rock will be endured with a smile.
Thanks in advance for any help you can provide.
Question: would a bent prop shaft cause the prop to appear to be slipping (higher revs at the same speed)?
Details for the novel readers out there:
The boat is a 1998 190 BR, 4.3L Alpha One outdrive (1.81 ratio) running a SS 14.25R23 prop. I should be turning about 4800 rpm and making just over 40 knots at WOT. At present I can get the revs up to more than 5400 (for about one second before I backed off) and the boat is making about 32 - 35 knots at 4800 revs. Speeds are based on speedometer, not GPS readings.sev.
I hit the rock launching the boat near low tide, and had the outdrive fully trimmed down, and was no where near planing speed when I "found" the rock, perhaps 10 mph. I heard a strong CLUNK from the back of the boat, and thought at first we had fouled and cut a docking line.
I cut the engine, stopped, raised the outdrive and started checking for water in the bilge and engine compartment... no water found. Checked the prop, it had a flat spot on one fin, but was not mangled or broken off. No lines or other foreign objects wrapped around the prop.
Put the outdrive back down, started up the engine, and all sounded good. Put it gently into gear and felt my way into deeper water. The boat seemed a bit sluggish, but no strong vibration or rattling/banging noises. Engine sounded fine.
After a few minutes I figured out that I was dragging a mat of vines from the outdrive, removed vines, boat moved much better.
We made a short day of it, and did not stray far from the landing.
Everything seemed to be working ok but didnt want to take chances. Upon pulling the boat out of the water, I found that the leading edge of the skeg had takend a pretty good hit, and was missing a fair sized chunk. No other visible damage.
I got one of the SkegGuard repair kits and installed it. Had to bend back a very slight bend in the tip of the skeg to do so, and ground down the other sharp edges with a grinder.
I also ground the flat off of the prop, trying to change the shape of the blade as little a possible. I also dressed up some other nicks on the leading edges of the blades at the same time (smoothing and polishing, not cutting out large chunks).
I am sure the prop is not a well balanced as when new, but the ground smooth area on the prop did not look like it would unbalance the prop too badly. I checked the prop hub to see if it had been "spun" and it did not appear to be so. When I turn the prop by hand with the gears ingaged I can feel the compression stroke beginning, prop does not turn in relation to the shaft.
Put it back into the water on the weekend, and got the symptoms noted above (higer revs than expected, lower speed than expected). Before I could push the revs to about 3200 and get on plane pretty quickly. Now to get to plane in the same amount of time I am up closer to 4000 rpm.
End of novel.
Any ideas, suggestions, troubleshooting procedures I should try? What does it cost to have a prop shaft replaced, and should I attemt the job myself? Are there any special tools required?
Any suggestions or ideas gratefully accepted. Any jibes about hitting the rock will be endured with a smile.
Thanks in advance for any help you can provide.
