Volvo BB140 in a Maine Lobster Boat

Discussion in 'Inboards' started by Jon A, Aug 4, 2013.

  1. Jon A
    Joined: Jun 2013
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    Location: Bourne, Ma

    Jon A Junior Member

    Greetings all,
    First post here but I can see from reading some of the older stuff that there is no lack of expertise. I have owned a 21' Repco with a Volvo BB140 ( 4 cyl, 129 hp, gasoline) for about 5 years. This is a fiberglass round bottom boat with an oak keel added and set up as an inboard. This is a great little boat, nice easy ride and very good on gas and has very low hours. We use it mainly for family picnics and jaunts out into Buzzards Bay.
    I am trying to make the boat run quieter and smoother, especially at high speeds (above 3,000 rpm). I have done all the easy stuff, muffler on the wet exhaust, sound deadening in the engine box, aligning the drive shaft, all with limited success. There is still a rumble from under the boat that bothers us.
    The engine mounts which I believe were part of the Volvo kit include rubber pads and sit on the oak stringers. the 1 1/4' shaft runs thru a traditional stuffing box and exits the keel with another stuffing box in place of a real cutlass bearing. I have been told that builders sometimes did this with workboats.
    Also, the flow to the prop is rough, the keel is not properly faired and the prop passes very close to the stringer that runs under it to support the bottom of the rudder post.
    Could this second stuffing box be causing the noise? Are the rubber mounts wrong for this set-up? Would the prop not seeing good flow result in noise?
    Any suggestions or advise would be appriciated. This is my first inboard (unless you count a 210' many years ago in the Coast guard!). Up until now it's all been outboards.

    Thanks,
    Jon
     
  2. Toolate
    Joined: Sep 2013
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    Toolate Junior Member

    My understanding is that 30% of prop diameter should be provided between prop tips and hull/skeg to avoid vibration. Also helps to have a keel that is tapered at the aft end and have good clearance between the prop fore and aft from rear of keel and front of rudder.

    Had prop balanced?
    Rudder bearings in good shape?
     
  3. Jon A
    Joined: Jun 2013
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    Location: Bourne, Ma

    Jon A Junior Member

    Thanks for the comments, this gives me a starting point.
    I can tell you without measuring that I do not have 30% clearance. When I haul the boat I will measure. The prop appears to be in good condition, no dings or nicks but it has not been balanced. I believe the original owner changed to a larger prop to improve performance. He may not have known what he was doing.
    Rudder bearings are solid.

    Jon
     
  4. Toolate
    Joined: Sep 2013
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    Location: CT (Western)

    Toolate Junior Member

    I would talk to a propeller shop. Would probably record some speeds from a GPS at different RPMs too for that conversation. Maybe every 200 rpms from idle to WOT. They should be able to set you straight after that.
     
  5. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Within reason a smaller diameter prop with more pitch will be fairly close in performance if more tip clearence will keep the hull from drumming.
     
  6. Bglad
    Joined: May 2010
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    Location: Jacksonville, Florida

    Bglad Senior Member

    You have received some good comments already regarding prop clearance, prop sizing and fairing the keel. From my experience keel drives are a little less efficient and noisier. I have a brother who routinely replaces wood keels on fiberglass work boats in the Florida Keys with welded steel keels. They much improve water flow, increase speed and break things they touch versus receiving damage.

    The steel keel concept originally started back when single engine fishing boats had a Y-strut with the wood keel terminating beneath it just forward of the prop. Someone knocked the last part of the keel off and bent the lower skeg on the strut. Welders don't work with wood so they just made a longer metal skeg and attached it to the keel remains. The result was better performance.

    I did a few of the metal keel extensions in Key West using mild steel. It was inexpensive, easy to work with and they held up well. I left the Keys in 1987 and my dad evolved the keel extension into a complete steel keel and my brother continues to this day doing them that way even on new builds. Oh yeah, the worms don't eat them either:)
     
  7. Jon A
    Joined: Jun 2013
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    Location: Bourne, Ma

    Jon A Junior Member

    The keel on this boat is a massive oak structure, added to the smaller keel that was molded into the hull. I believe the size is for the boat to more easily sit on the gear when lobstering. The rudder is oversize also, because this was built with lobstering in mind.
    My first thought is to try the simple things, fair in the keel more and try to get another prop.
    When the boat is hauled in a few weeks I will try to post some pictures.
    Thanks for all the comments,
    Jon
     
  8. Bglad
    Joined: May 2010
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    Location: Jacksonville, Florida

    Bglad Senior Member

    The boats in the Keys also haul lobster and crab pots. Keel is a good thing to have in that business.
     
  9. Bglad
    Joined: May 2010
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    Location: Jacksonville, Florida

    Bglad Senior Member

    Key West abbreviated keel

    Found this picture in a photo album I have.
     

    Attached Files:

  10. Jon A
    Joined: Jun 2013
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    Location: Bourne, Ma

    Jon A Junior Member

    Attached is a picture of my prop assembly. Critical dimensions are as follows:
    Prop is 14 dia x 13 pitch (Michigan Dyna-Jet)
    Prop blade to underside of hull = 2 3/4"
    Prop blade forward to keel = 4 3/4"
    Prop blade back to rudder = 4 1/2"
    Prop blade to bottom of cutout in skeg = 1 3/8"
    (cutout is 1 1/8" deep.)

    Also, the max rpm's out of the engine is 4,000. Manufacturer recommends 4500 to 5100 rpm.

    Any suggestions as to what I can do as a reasonable fix? The boat is not worth taking apart, repositioning the engine and rebuilding the keel. Wish I had her surveyed before I purchased. Too arragant, I thought I knew enough. There's a whole sad story about a fiberglass gas tank the first year we owned her but that's a story for another time.....

    Thanks,
    Jon
     

    Attached Files:

  11. Toolate
    Joined: Sep 2013
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    Location: CT (Western)

    Toolate Junior Member

    Is that a 2 blade prop? Think I would switch to a 4 right away- smoother. Cant believe it is but sure looks like one.
     
  12. Jon A
    Joined: Jun 2013
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    Location: Bourne, Ma

    Jon A Junior Member

    it's a 3 blade prop.
     
  13. Jon A
    Joined: Jun 2013
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    Location: Bourne, Ma

    Jon A Junior Member

    So, here's my plan:
    Run a 2 3/4" x 3/8" x 52" piece of galv. steel under the existing wood keel and skeg out to the rudder post and lag and bolt to existing. this will give me support so I can carve away more of the oak under the prop and provide more clearance for the blades.

    Fair in more at the deadwood to give slightly better flow to the prop.

    Switch to a 4 blade prop. Anyone know where I can find a 13 or 14", 4 blade prop with a 1 1/4' shaft? Doesn't seem to be too common.

    I'll leave the stuffing box used as a stern bearing for now. there isn't enough space to fit in a conventional stern bearing without serious surgery. I can cut the deadwood to fit one but will probably hold off on that until I see how these other changes work.

    Any comments or suggestions would be welcome. It's an adventure.

    Thanks,
    Jon
     
  14. Bglad
    Joined: May 2010
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    Location: Jacksonville, Florida

    Bglad Senior Member

    I don't think a flat bar will do much to stiffen the wood skeg. How about cutting away the wood skeg and go with a steel channel. You could notch it into the keel or bolt it underneath. Run it far enough forward forward so if/when you decide to cut away the keel and build a strut it will be ready to go. The bottom of the Key West style keel I posted uses a channel for the skeg. You can cut short sections of the channel and stack them to reach the rudder shaft. There are many ways to skin this cat. Just depends on your skill set...
     

  15. Jon A
    Joined: Jun 2013
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    Location: Bourne, Ma

    Jon A Junior Member

    Steel channel is a good suggestion. By the time I get thru carving away the wood skeg there won't be much left anyway. I could easily notch it into the keel and make a pretty good looking job of it.
    Anyone know where I can get a small 4 blade prop with a 1 1/4" bore?

    Jon
     
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