What happens to SD60 with 2200rpm heavy-line prop-wrap??

[DougMc]

Yesterday, about 20 miles offshore we were motoring our Oceanis 45 at about 2200rpm when we saw a line floating ahead.

It was about 100feet of thick (maybe 1") floating line of a hard-to-see blue color. Luckily, we did see it and avoided it. It looked like it had some mooring stuff on it, so I guess it could have been dyneema from a commercial mooring? Or, maybe just polypropylene.

A few hours before, we'd been 40 miles ofshore motoring in the dark and would have absolutely not seen it!!

What is the likely outcome if we'd got such a heavy line tangled in our prop? I'm assuming it would stall the diesel but, in the process, would the saildrive sustain damage?

regards
Doug

[SailingHarmonie]

Damage would be very likely. Not only is damage likely, but it can be extremely difficult to get undone. If the line really wraps and gets tight as the shaft turns, it is not unusual for synthetic lines to melt from the friction, and fuse into a solid lump that will not readily yield to a knife.

On shaft drive boats I have seen shafts bent, struts twisted off the hull, engine mounts ripped out, or sometimes if the boat owner has lead a good and pure life, nothing damaged at all.

A propshaft line cutter is an excellent addition to boats that frequent areas with a lot of fishing gear in the water, or anywhere that you motor at night.

Here is the thought experiment I used to give my advanced students: "You are motorsailing along, and you see a pot buoy with a trailing line just ahead of you. You do not have time to maneuver. What is your best choice of action to avoid wrapping the prop?"

The (almost) universal answer was to shift into neutral. But that is unlikely to work, since with the boat coasting forward, the prop will continue to spin. Now, without engine power you are likely to have a less severe wrap, but still one that might attach you to the line. With the understanding that the best course of action might depend on boat specifics, I expect the best thing to do, in most cases, would be to stop the engine.

[rslifkin]

Originally Posted by SailingHarmonie

Here is the thought experiment I used to give my advanced students: "You are motorsailing along, and you see a pot buoy with a trailing line just ahead of you. You do not have time to maneuver. What is your best choice of action to avoid wrapping the prop?"

The (almost) universal answer was to shift into neutral. But that is unlikely to work, since with the boat coasting forward, the prop will continue to spin. Now, without engine power you are likely to have a less severe wrap, but still one that might attach you to the line. With the understanding that the best course of action might depend on boat specifics, I expect the best thing to do, in most cases, would be to stop the engine.

It depends on the drivetrain in question. On my (power) boat I have hydraulically engaged transmissions. So as soon as you kill the engine, fluid pressure drops and the trans ends up in neutral regardless of the shifter position. So shifting to neutral vs killing an engine makes no difference at all.

[DougMc]

Originally Posted by SailingHarmonie

Damage would be very likely. Not only is damage likely, but it can be extremely difficult to get undone. If the line really wraps and gets tight as the shaft turns, it is not unusual for synthetic lines to melt from the friction, and fuse into a solid lump that will not readily yield to a knife.

On shaft drive boats I have seen shafts bent, struts twisted off the hull, engine mounts ripped out, or sometimes if the boat owner has lead a good and pure life, nothing damaged at all.

A propshaft line cutter is an excellent addition to boats that frequent areas with a lot of fishing gear in the water, or anywhere that you motor at night.

Here is the thought experiment I used to give my advanced students: "You are motorsailing along, and you see a pot buoy with a trailing line just ahead of you. You do not have time to maneuver. What is your best choice of action to avoid wrapping the prop?"

The (almost) universal answer was to shift into neutral. But that is unlikely to work, since with the boat coasting forward, the prop will continue to spin. Now, without engine power you are likely to have a less severe wrap, but still one that might attach you to the line. With the understanding that the best course of action might depend on boat specifics, I expect the best thing to do, in most cases, would be to stop the engine.

Indeed, I was imagining that there could be damage. But, these saildrives have cone clutches and I was curious if they were cleverly designed as a "mechanical" fuse to slip in these circumstances.

I have had the same thought experiment and come to the same conclusion. However, I think the chances of someone have the quick-wittedness to find the button and stop the engine, if there wasn't even time to steer, seems remote. I think it's clear neutral would still be much preferable to having the engine running in gear, and that control, I reckon, is more easy and natural to reach for.

[dannc]

Originally Posted by DougMc

...
I have had the same thought experiment and come to the same conclusion. However, I think the chances of someone have the quick-wittedness to find the button and stop the engine, if there wasn't even time to steer, seems remote. I think it's clear neutral would still be much preferable to having the engine running in gear, and that control, I reckon, is more easy and natural to reach for.

Once Upon A Time, we were on a trawler threading our way between two lines of crab pots. It was overcast, rainy, a bit foggy and 30-35 knots of wind with 6-8 foot steep, breaking waves. There were three of us in the pilot house when I noticed, just in front of us, a crab pot marker. The crab pot float was white gallon jug that used to hold oil or fluid of some kind. It was very difficult to see, and even more so, in the breaking waves. We saw the float a boat length or so ahead and there was no time to do much.

I yelled out crab pot or some such and grabbed the nearest engine control and put the transmission in neutral just before we hit the float. It was all I had time to reach.

The float did not get wrapped in the prop thank goodness but it got hung up in the paravane which led to more fun for a few minutes.