Need holes in shaft log?

Discussion in 'Metal Boat Building' started by Capt JZ, Feb 2, 2010.

  1. Capt JZ
    Joined: Dec 2009
    Posts: 14
    Likes: 1, Points: 0, Legacy Rep: 24
    Location: New Harmony IN USA

    Capt JZ Capt JZ

    I'm building a 50' steel vessel with a single screw and a 2' shaft. I have a normal 8" long cutlass bearing at the after end of the log. The shaft is mounted. Now my question: I had an experienced capt stop by and tell me to drill holes in the shaft log so that water could get into the log...and importantly...create a FLOW of water to cool the viens in the cutlass. Of course these holes would be drilled fwd of the cutlass bearing. I worry about debris (think sand) getting in and not getting out very easily. I can see that, with no holes, there would be almost no flow up through th cutlass ...flow that should lubricate the bearing. What should I do? Drill holes and allow steel drill filings to fall into the (otherwise sealed) shaft log?..filings that quite possibly will end up cutting the cutlass bearing. I think, until I hear from some of you REAL PROS, I'm not going to drill this for now.
     
    1 person likes this.
  2. mark775

    mark775 Guest

    Yes, pull your shaft, drill at an angle a 3/4" hole on each side, round forward edges of holes, leave aft edge sharp, vacuum shavings. Your cutless requires not just being wet but a forced flow. The shaft actually rides on a film of water on the rubber of the bearing. The bearing isn't as delicate as one might think - don't worry about sand as if you run in very silt-laden waters, you'll just have to replace the $100 bearing in a few years. Small price to pay to take care of your shaft (My 2" shaft has been in there since 1979 set up like you are about to). An even bigger concern is enough water getting to your stuffing box... then have fun with your new boat!
     
  3. gonzo
    Joined: Aug 2002
    Posts: 15,194
    Likes: 925, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Holes are standard practice.
     
  4. Capt JZ
    Joined: Dec 2009
    Posts: 14
    Likes: 1, Points: 0, Legacy Rep: 24
    Location: New Harmony IN USA

    Capt JZ Capt JZ

    I have a dripless (PSS) shaft seal, so it doesn't need water lubrication.
    I will do what you've said, but never have seen holes on any boat that I've been around or owned. Your idea makes sense though. I do worry about sand getting in and being too big to be flushed past the cutlass and just building-up in there. It is much less likely to get in without the holes. But there has to be some fluid flow or the bearing could overheat. Thanks for your advice.
     
  5. gonzo
    Joined: Aug 2002
    Posts: 15,194
    Likes: 925, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Dripless shaft seals have a water supply from the engine.
     
  6. mark775

    mark775 Guest

    It is a turbulent environment that self cleanses. The holes will flush it better if just ahead of the bearing. Sand doesn't build up. I once thought of going with no holes, as well, and the Duramax rep told me the water film thing...In a system with no holes, there might be enough water to keep the bearing from overheating but not enough that horsepower isn't robbed. Ever turn a dry shaft in a rubber bearing, add a bit of soapy water and try again?
     
  7. Capt JZ
    Joined: Dec 2009
    Posts: 14
    Likes: 1, Points: 0, Legacy Rep: 24
    Location: New Harmony IN USA

    Capt JZ Capt JZ

    My dripless seal (PSS) doesn't have a water supply from the engine.
    My last one was a "Lasdrop" and didn't either. There is a vent tube (only) in front of the bellows that allows the shaft log to fill with water. Even with that vent, it's a good idea to "burp" the bellows after first launching. But there's no supply from "the engine."
     
  8. Capt JZ
    Joined: Dec 2009
    Posts: 14
    Likes: 1, Points: 0, Legacy Rep: 24
    Location: New Harmony IN USA

    Capt JZ Capt JZ

    After your comments, I'm going to install the holes. Thanks.
     
  9. gonzo
    Joined: Aug 2002
    Posts: 15,194
    Likes: 925, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Depending on the installation you have to put a water supply. It depends on the speed of the boat too. Slow boats with the bellows below the waterline only get a vent.
     

  10. Capt JZ
    Joined: Dec 2009
    Posts: 14
    Likes: 1, Points: 0, Legacy Rep: 24
    Location: New Harmony IN USA

    Capt JZ Capt JZ

    Right. I have a displacement hull. Thanks.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.