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Old 23-09-2018, 14:34   #1
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Absolutely couldnít get out of the slip today

Well this is a bit embarrassing. I was all set for a nice day on the water got all ready to go but it simply wasnít to be.
14-16 kts off the port stern and barely got back in without hitting anyone. Edit- I failed to look at the wind instruments until after the trouble started.
:bang head:

I simply could not get any headway astern full on throttle and I got out just to fend off the neighbors boat. Managed to make it back with help from a neighbor.
This is a c&c 27, atomic4 with a three bladed prop but absolutely no go.
Now I know what it canít do and will be aware of any future situations where I could be in serious trouble.

Lesson learned.
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Old 23-09-2018, 14:36   #2
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Re: Absolutely couldnít get out of the slip today

Check to see if the prop is fouled. Thatís not normal.
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Old 23-09-2018, 14:46   #3
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Re: Absolutely couldnít get out of the slip today

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Check to see if the prop is fouled. Thatís not normal.


Possibly as Iíve never had any problem getting out of this slip. Iíll have to check by trying static powering up to see if I get any strain on the lines appropriate to expectations.
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Old 23-09-2018, 17:08   #4
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Re: Absolutely couldnít get out of the slip today

If there's decent visibility in the water where the boat is, you can just dive and have a look. I, too, would expect fouling of some sort. It is possible that you picked up a plastic bag, and it shall since have fallen off. If that's the case, there will be no sign of it, but the engine/prop test while you're tied up will show you to be good to go.

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Old 23-09-2018, 17:16   #5
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Re: Absolutely couldnít get out of the slip today

My previous boat had an Atomic-4. Going in reverse was always a challenge. It never seemed to generate much thrust. I recall someone who seemed to now more than I telling me these engines use some sort of weird clutching to go in reverse that produces 1/2 the thrust of forward.
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Old 24-09-2018, 04:53   #6
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Re: Absolutely couldnít get out of the slip today

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... these engines use some sort of weird clutching to go in reverse that produces 1/2 the thrust of forward.
Indeed.
In reverse, the A4 tail shaft rotates opposite to the crankshaft, but at only 75% of engine RPM (1.33:1). The reverse speed of your prop is only 75% of the forward speed for the same engine rpm's, which is why you have to use a lot higher RPM's in reverse to accomplish a similar response from the prop, and why backing the boat is so much harder to accomplish for a given engine speed.
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Old 24-09-2018, 05:11   #7
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Re: Absolutely couldnít get out of the slip today

Also take a look down at the output shaft on the transmission and see if it is turning about what you think it should.


You can strip the output shaft keyway and have weak reverse and still have forward thrust, until you don't.



There is a two beer story involved in how I learned about that A4 failure mode.
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Old 24-09-2018, 05:53   #8
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Re: Absolutely couldnít get out of the slip today

I don't have any experience with th A4, but I learned from an old salt years ago how to gauge the fouliness of my prop without having to dive it - when in the slip and tied off well, put the engine in gear at a fairly low rpm and watch the prop wash while in forward gear. The amount of wash that goes to the side instead of straight back is an indication of how much gunk is living on the prop.
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Old 24-09-2018, 06:09   #9
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Re: Absolutely couldnít get out of the slip today

I would have a look at the prop, first thing. Is it a folding prop? Sometimes they don't unfold as they should. Marine growth can inhibit proper operation of folders. A few minutes work with a scraper and you will be right as rain. A Scotchbright pad for shining up the blades will have it cutting water cleanly and efficiently. You should be able to do this with snorkel gear, if you are not a diver. Folding prop blades should swing easily back and forth between trailing and driving position.



A very good and extremely cheap and easy addition to your C&C would be a digital prop shaft tachometer. The type I am talking about uses a magnet stuck on the shaft and a hall effect sensor mounted near it, and is totally independant of the engine electrical system so is useful for any type of engine. The hall effect sensor detects the passage of the magnet and sends a pulse to the display unit. Three wires to the sensor: DC+, GND, and SIGNAL. Easy hookup. Most will run on 12v systems and cost under $20 shipped free from China via fleabay. The display unit is a simple 4 digit LED or LCD display that gives you RPM of whatever shaft you mount the sensor and magnet on. As a bonus it even tells you the shaft RPM when the transmission is set to Neutral. Be sure to install an on/off switch.



You can also buy a laser tachometer but they don't work quite as well as a magnetic type. The laser type is usually handheld. Stick a small piece of reflective tape on the shaft coupling and point the tach at it from a foot or two away. Have a helper put the trans in reverse and advance throttle to full. Do the same in FWD. Depending on your transmission it should give you the same or about 3/4 the RPM in REV as compared to FWD. If there is a failure to lock up in REV, the RPM difference might be as it ought to be at idle, but not when you advance the throttle. Slippage will occur at higher engine loads first. This is not a common problem with A4 transmissions but it is possible. Luckily a used unit should be pretty easy to find for chimp change. Lots of dead raw water cooled Atomics around.
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Old 24-09-2018, 08:44   #10
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Re: Absolutely couldnít get out of the slip today

+1 for founded prop. Don’t ask how I know...
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Old 24-09-2018, 09:20   #11
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Re: Absolutely couldnít get out of the slip today

Could be the prop, but sometimes gusts and adverse currents can pin you in the slip. See how it handles the next time you take her out in moderate winds.
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Old 24-09-2018, 09:48   #12
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Re: Absolutely couldnít get out of the slip today

We got an expected call from our marina to move Mana so they could dredge our dock area one afternoon last week. The wind was off our port quarter at 20 kts with slightly higher gusts when we got there. It was the very bottom of a pretty low tide and we were really clouding up the water as we warmed up the diesel in gear. Mana does not go to starboard in reverse without goosing the engine to get some steerage and then going into neutral to get stop the prop walk. Did not work, I could not go to starboard at all as the silt we were moving through stopped all motion immediately and I was lucky my next door neighbor had already moved from our double wide slip, as that is where I ended up. Next morning with 5 kts of wind and a high tide I went to my new temporary spot no problems. Sorry, I am old, and this thread reminded me of sailing my first boat in 1974, Tramp, a 50 year old converted wooden Navy whaleboat ketch with a giant rusty Graymarine that only ran a few hours while I owned it, and that after several hours messing with it each time. So when it gave up the ghost I used to stop on my way home from work sometimes and take a line attached to the bow and throw it from finger to finger behind the 5 boats between me and the end of the dock. Then I would raise the mizzen and the staysl', tie the tiller to pull her away from the docks, push her out into the channel, give one last big shove on the bowsprit and run willy nilly to the end tie where I would pull with much of my might until Tramp went by and jump on untie the tiller and turn to catch some breeze and go sailing. I suppose I could have tried to make friends instead. The good old days, no insurance, no worries, possibly no brains.
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Old 24-09-2018, 10:07   #13
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Re: Absolutely couldnít get out of the slip today

I can't imagine, for myself, not checking wind direction when entering or leaving any docking situation. Just like when I fly, I'm looking at flags etc for clues.

We always keep two stout dock lines in the cockpit to aid us in the event of an engine failure or any other docking calamity. We also keep our windlass powered on when in close quarters.
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Old 24-09-2018, 12:42   #14
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Re: Absolutely couldnít get out of the slip today

So , you had no headway forward, astern or both?
When my prop is fouled my 3GM smokes And wont achieve standard rpm's.

I had trouble backing, clean prop or not.
Until I got a kiwiprop, now it is a breeze. Backing is fun.
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Old 24-09-2018, 13:04   #15
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Re: Absolutely couldnít get out of the slip today

One particularly fertile summer, I was taking a friend out (which essentially meant solo) and figured no problem, cast off from the mooring, finish raising the sail, work my way back to the cockpit...Ah, no, the breeze came up and the boat wanted to drift the wrong way and things got BUSY because the engine just didn't seem to be doing anything.

Which is how I learned that in under one month of sitting still, a folding prop can become a big useless ball of barnacles. Memo, always check the engines (the polite white ones and the noisy combustion one) *before* casting off any lines.
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