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Removing Propellers with Explosives

Discussion in 'Technical Discussion' started by Zeke, Apr 29, 2011.

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  1. Zeke, Apr 29, 2011
    #1
    Zeke

    Zeke Member

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    Hello,

    We need to pull propellers off of a 100' yacht and a diver said that he would wrap a small explosives on the shaft to blow them loose. This sounds insane to me, but others have confirmed that this is one way to unseat props underwater. We would prefer not to haul right now. Has anyone heard of this?

    Z
  2. Bill106, Apr 29, 2011
    #2
    Bill106

    Bill106 Senior Member

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    It is done all the time around here on trawlers and larger headboats. Great way to find out if the shaft keyways are cracked :)
    Be sure to warn everyone on the dock or they're liable to jump out of their skins! Also if you have a dip net, get ready to catch the fish jumping out of the water!
  3. Capt Bill11, Apr 29, 2011
    #3
    Capt Bill11

    Capt Bill11 Senior Member

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    I've heard of it for much larger vessels. But never for something that size.

    Is this some kind of a last resort?
  4. NYCAP123, Apr 29, 2011
    #4
    NYCAP123

    NYCAP123 Senior Member

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    Ditto. Hope they tried a prop-puller or a hammer 1st. Also hope you have a steel hull.
  5. Zeke, Apr 29, 2011
    #5
    Zeke

    Zeke Member

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    It is primer cord I guess, not blasting caps. Fiberglass hull. This is their default course of action. Everyone at the dock thinks this is OK. Are they right?
  6. K1W1, Apr 29, 2011
    #6
    K1W1

    K1W1 Senior Member

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    Hi,

    I guess you will soon know, post back and let us know how it went will ya?
  7. Pascal, Apr 29, 2011
    #7
    Pascal

    Pascal Senior Member

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    down here a short haul is just $5 a ft (a year ago, for a 70 footer) so it's not worth using a diver to swap props... if your props are too damaged to get the boat to a yard i guess it's worth a try but i'd make sure the diver is insured in case something goes wrong and your own insurer backs out.
  8. Marmot, Apr 29, 2011
    #8
    Marmot

    Marmot Senior Member

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    It's no big deal. Loosen the nut, wrap a couple of turns of primacord held to the forward face of the hub (not the shaft) with modeling clay (plasticine to our Euro cousins) with a cap touched off from on deck and the prop is loose ... usually.

    There is no big bang or column of water, no theatrics, no dead fish usually and it is normally anticlimactic. We did it all the time on submarines because we routinely dinged the props for various reasons and all you heard from just a couple of feet above the prop was a snapping noise. The work is done by a rapid shock, not a large displacement of water like you see from a torpedo warhead or other slower burning explosive.
  9. NYCAP123, Apr 29, 2011
    #9
    NYCAP123

    NYCAP123 Senior Member

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    What are your thought about a fiberglass hull?
  10. Marmot, Apr 29, 2011
    #10
    Marmot

    Marmot Senior Member

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    "What are your thought about a fiberglass hull?"

    I wouldn't worry about it at all. The overpressure is so small it is very unlikely to cause any damage. The amount of explosive in a few inches or a foot of detonating cord is very small. It works because it burns so quickly and creates a shock wave that is very sharp but of low duration, a property called brisance, which is just the opposite of what you would want to blow the bottom out of the boat from a charge in the water.
  11. Fireman431, May 1, 2011
    #11
    Fireman431

    Fireman431 Senior Member

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    Get someone that has an underwater video camers to record the removal. Obviously, he would not want to be down there with it, but could it be tethered in place? It would be a decent educational and possibly sales tool.

    Plus...I wanna see it...
  12. Bamboo, May 2, 2011
    #12
    Bamboo

    Bamboo Senior Member

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    If the prop has pulling holes what's wrong with using a PropSmith?
  13. NYCAP123, May 2, 2011
    #13
    NYCAP123

    NYCAP123 Senior Member

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    Check post 4. I'd assume it'd be tried first.
  14. chesapeake46, May 3, 2011
    #14
    chesapeake46

    chesapeake46 Senior Member

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    Me too...........
  15. yr2012, May 13, 2011
    #15
    yr2012

    yr2012 New Member

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    Inquiring minds want to know
  16. Bamboo, May 17, 2011
    #16
    Bamboo

    Bamboo Senior Member

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    Bump...

    How'd it work out,Zeke?



    I don't assume as you've done, and don't believe everyone knows what a propsmith is- thus the post.
  17. Zeke, May 26, 2011
    #17
    Zeke

    Zeke Member

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    So here's the run-down...

    I spoke with a few local captains who confirmed that this diving team does perform this regularly - on steel commercial ships as well as fiberglass yachts and that this was a time-proven method. I had my reservations, but charters were booked to go out, so gave it the green light....

    The detcord shook the boat, enough to knock down some velcroed panels. REALLY made me uncomfortable. But the props came right off and now the yacht is running fine with new props and no discerable damage from using this method.

    We'll haul the boat in a year or so for the bottom paint, so I'll know then if there is any visible impact from this. So verdict right now is a tentative success until proven otherwise...
  18. K1W1, May 26, 2011
    #18
    K1W1

    K1W1 Senior Member

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    Hi,

    Thanks for posting back with your experiences.

    It is good to read the outcome of someone's idea/troubles rather than a lot of suggestions and ideas and then the thread goes dead.

    It helps to build the knowledge base here at YF and can often be of use to others who know how to use the search function.
  19. Capt Bill11, May 26, 2011
    #19
    Capt Bill11

    Capt Bill11 Senior Member

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    +1 to all of the above.
  20. NYCAP123, May 27, 2011
    #20
    NYCAP123

    NYCAP123 Senior Member

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    Glad it worked out.
    Given:
    I think I'd be keeping an eye on stuffing boxes and shaft seals for a while.
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