Click for Abeking Click for Nordhavn Click for Ocean Alexander Click for Lurssen Click for Mag Bay

Shaft tubes

Discussion in 'Props, Shafts & Seals' started by Bluefin, Feb 25, 2010.

You need to be registered and signed in to view this content.
  1. Marmot

    Marmot Senior Member

    Joined:
    May 20, 2007
    Messages:
    3,320
    Location:
    9114 S. Central Ave
    About 2/3 (but shrinking) of the stern tubes on larger vessels (yachts included) are oil lubricated but that isn't what Henning brought up when he mentioned the totally enclosed shaft with antifriction bearings as opposed to resilient bearings and open shafts.
  2. Bamboo

    Bamboo Senior Member

    Joined:
    Dec 19, 2008
    Messages:
    935
    Location:
    Palm Beach, FL
    You have added ZERO to the OP's quest for information on this subject, yet you continue to post. Why do you post at all?
    Again you have added nothing yet continue to post to puff up your chest.
    A poor attempt, adding nothing but another attempt to puff up your own chest by slinging mud. Why are you posting again? It is surely not to answer the OP's questions.
    Blah blah blah. You have added nothing to the original discussion or the OP's quest for information. 370 foot non planing vessels are the same as 40-80 sportfishers? Go back to Troll land and drink your pee'd in coffee somewhere else. You more than anyone here derails threads with off topic pissing matches.
  3. Bamboo

    Bamboo Senior Member

    Joined:
    Dec 19, 2008
    Messages:
    935
    Location:
    Palm Beach, FL
    Viking had a certain engine that would not fit into the engine bed without a slight bump made on the hull bottom, so they made that bump. That little bump some 18 feet from the prop caused major prop burning at the base of all blades of four types of props. What is right next to the prop can cause issues, as well as things much further away. Some claim "physics is physics" like August Magnan.
  4. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    11,849
    Location:
    Fort Lauderdale
    A new(ish) Roscioli Donzi was built with these oil bath shaft tubes. Let me see if I can dig up the link to it. They claimed to have gained speed with them. I have no real world experience, but it does seem like you have more things that could go wrong. Here it is from the Power and Motoryacht website- Seatorque couplers (How true it is is hard to say)


    "Sea Torque is a small company from Stuart, Florida, that is making it big with its bolt-on shaft (B.O.S.) system. According to the company, the first benefit of installing its all-in-one shaft system is that it only takes about two hours for two technicians to fully assemble and install it. The next plus is the potential for as much as a five-percent reduction in fuel consumption and up to an eight-percent increase in horsepower due to the reduction of frictional losses in components such as the stuffing boxes, cutlass bearings, and water-lubricated seals. The entire system is enclosed in a non-rotating casing. Inside the unit there is, running from forward to aft, a transmission adapter, input shaft, double universal joint, thrust bearing assembly, output shaft and propeller bearing housing" http://www.******************.com/boat-tests/donzi/2008-donzi-r-80/index1.aspx
  5. Marmot

    Marmot Senior Member

    Joined:
    May 20, 2007
    Messages:
    3,320
    Location:
    9114 S. Central Ave
    All I can say is "wow" ... just because you can do something doesn't mean it is worth doing.

    The fact that the 75/90 weight gear oil temperature can be expected to rise to 210*F tells us that a lot of power is going into heating that very viscous oil instead of turning a prop. That heavy oil is needed to protect those very highly loaded bearings that are only protected by a pair of lip seals that monofilament cuts like butter. And how much does the redundant thrust bearing, the cardan shaft, and structural hull mods cost for what kind of benefit? On top of that the boat sees a larger diameter shaft dragging through the water ahead of the prop.

    No thanks.
  6. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    11,849
    Location:
    Fort Lauderdale
    I have no Idea, no experience with it, and no opinion on it. I just listed an example of a custom sportfish that is using it.
  7. Bluefin

    Bluefin New Member

    Joined:
    Dec 19, 2009
    Messages:
    26
    Location:
    Murrells Inlet, SC
    OK, here are the results. Before numbers were with 400 gallons less fuel and 100 gallons less water, so these are conservative for sure.

    Up to and including 1700 RPMs, there is almost no difference, except now the speed is about a half a knot faster. Load and fuel burn are almost identical.

    It gets better and better from 1700-1950, then goes back down a bit.

    Best numbers are at 1950:
    Before 70.1 GPH, 73% load and 29.9 kts
    After 68.4 GPH, 70% load, and 30.4 kts

    Since this is with a lot more weight, these numbers should hold up.
    Was it worth it? By the time I spend the extra $$ when it's time to change cutlass bearings, probably not. Interesting, nonetheless.
  8. SHAZAM

    SHAZAM Senior Member

    Joined:
    Jan 26, 2008
    Messages:
    605
    Location:
    The Ghetto
    That would have been the MK III 46.6 Bertram.
  9. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    11,849
    Location:
    Fort Lauderdale
    It depends on how much traveling you're doing. The more you're doing, the more this mod will pay for itself between cutlass bearing changes. What I would check is, run it up to 73% load now which should net you about the same 70gph as before, and let us know the speed. I would guess you'd be at close to 31.5 knots. and gained 5% efficiency.