No propulsion

woodster · Jun 20, 2015

cedge said:
I'm new to sailing and have a 25ft keel boat which when using the inboard engine did not have any real reverse and a couple of weekends back it started getting difficult to get forward drive. The gearbox (Hurth 50) was a bit cluncky I talked to some marine engineers who suggested getting the gearbox checked out which I did the box was fully serviced and I installed it today with a new drive plate. Now the gearbox sounds sweet and shifts nicely. Here's where the problem starts it drives the prop shaft both forward and reverse but Im getting no propulsion. In neutral I can turn the shaft freely. When it was running there was no vibration ,knocking or lumpy drive. Any members that can give some insight into what I should do next please do.Would a rope or plastic bag cause this problem ?
many thanks

not sure about the rope but do you have the prop back on or have you lost it by chance

Alec · Jun 20, 2015

A plastic bag wrapped around the prop will definately cause loss of drive or as Woodster said you may have lost your prop. In any case it's time to take a swim!

Capt jgw · Jun 20, 2015

Folding or feathering prop stuck closed? Be careful of diving under the boat if you're in a marina. If the dock or another boat is leaking AC into the water you can be electrocuted. Happens fairly often, a lot of marina's have signs warning not to swim there.

Johnb · Jun 20, 2015

I second the warning about going into the water in a marina but you do need to check the propeller. I had personal experience of someone who's propeller was so overgrown it rotated without producing any thrust at all. Hopefully that or something wrapped around it is the problem.

Good luck.

fstbttms · Jun 22, 2015

Capt jgw said:
If the dock or another boat is leaking AC into the water you can be electrocuted. Happens fairly often, a lot of marina's have signs warning not to swim there.

Johnb said:
I second the warning about going into the water in a marina...

Almost exclusively a freshwater phenomenon. Very rare to non-existent in saltwater marinas.

Capt jgw · Jun 23, 2015

fstbttms said:
Almost exclusively a freshwater phenomenon. Very rare to non-existent in saltwater marinas.

I'm in fresh water and it is a problem here, never heard of it not happening in salt. Salt water is a much better conductor of electricity, maybe it trips the breakers quicker?

fstbttms · Jun 23, 2015

Capt jgw said:
I'm in fresh water and it is a problem here, never heard of it not happening in salt. Salt water is a much better conductor of electricity, maybe it trips the breakers quicker?

Salt-water is anywhere from 50 to 1,000 times more conductive than fresh water. The conductivity of the human body when wet lies between the two, but is much closer to saltwater than fresh. In saltwater, the human body only slows electricity down, so most of it will go around a swimmer on its way back to ground unless the swimmer grabs hold of something — like a propeller or a swim ladder — that's electrified. In fresh water, the current gets "stuck" trying to return to its source and generates voltage gradients that will take a shortcut through the human body. A voltage gradient of just 2 volts AC per foot in fresh water can deliver sufficient current to kill a swimmer who bridges it.

http://www.boatus.com/seaworthy/magazine/2013/july/electric-shock-drowning-explained.asp

kito · Jun 23, 2015

Stupid question here......but with all the problems and dangers with stray currents, would not a ground fault circuit at each power pole eliminate this problem? Would they be tripping constantly or just not work properly?

Capt jgw · Jun 23, 2015

fstbttms said:
Salt-water is anywhere from 50 to 1,000 times more conductive than fresh water. The conductivity of the human body when wet lies between the two, but is much closer to saltwater than fresh. In saltwater, the human body only slows electricity down, so most of it will go around a swimmer on its way back to ground unless the swimmer grabs hold of something — like a propeller or a swim ladder — that's electrified. In fresh water, the current gets "stuck" trying to return to its source and generates voltage gradients that will take a shortcut through the human body. A voltage gradient of just 2 volts AC per foot in fresh water can deliver sufficient current to kill a swimmer who bridges it.

http://www.boatus.com/seaworthy/magazine/2013/july/electric-shock-drowning-explained.asp

Great explanation, thanks.

Chief RA · Jun 23, 2015

fstbttms: Yes, I really liked your explaination, especially since I am an Electronic Eng.. You made it so obvious that current "takes the path of least resistance"! Chief

fstbttms · Jun 23, 2015

Chief RA said:
fstbttms: Yes, I really liked your explaination, especially since I am an Electronic Eng.. You made it so obvious that current "takes the path of least resistance"! Chief

Well, I only quoted an article from Seaworthy Magazine. Can't take credit for the explanation.

Chief RA · Jun 23, 2015

No problem with that. Your profession and diving experience gave you the knowledge, and also knowing what to quote. I had not thought of the increased salt water conductivity being a major factor and it is indirectly in my profession. Thanks, Chief

fstbttms · Jun 23, 2015

I will say this about swimming in saltwater marinas however:

I have been working in the water in Bay Area saltwater marinas since 1994. Since that time, over 1,000,000 in-water hull cleaning events have ocurred here (probably actually much closer to 2,000,000. But I like to err on the side of caution) and to my certain knowledge, not one of those dives has resulted in serious injury or death, due to any cause. That's a pretty impressive saftey record, IMHO and I'd say it proves that swimming in saltwater marinas is not inherently dangerous.

That said; one should take sensible precautions whenever working around water (of any kind) and electricity. I personally unplug from the shorepower any boat I dive on, for instance.