drive line

Discussion in 'Powerboats' started by seacat, Dec 11, 2012.

  1. El_Guero

    El_Guero Previous Member

    SeaCat,

    What CDK is getting at, and I know I am asking, is WHY?

    If you do not have a vibration, why are you worried about vibration.

    From an engineering point of view, we are usually fixing our last major problem and not addressing our future needs.

    Do you HAVE a problem with vibration NOW? Do you have a problem with your u-joints now?

    If NOT, then why are you worried about them?

    In other words, I am asking, "What is your REAL question?"

    If you do not have u-joints; and you do not have a vibration problem; and your ship is properly designed; THEN you should not be worried about this.

    It is not a 'problem.' And there are always problems we could be fixing ....

    Does my question make sense to you?

    Wayne
     
  2. seacat
    Joined: Dec 2012
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cebu philippines

    seacat boatbuilder/designer

    El_Guero San - sir, indeed the probs as per my first message are vibration problem, thrust line, resultant thrust and shaft angle.....i hope you guys may give me essential and intellegent ideas / validated design regarding my current problem...thank you sirs in advance...
     
  3. El_Guero

    El_Guero Previous Member

    SeaCat San,

    You say it again.

    1. Do you CURRENTLY have a vibration problem?

    2. Is this a FUTURE boat?
     
  4. seacat
    Joined: Dec 2012
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cebu philippines

    seacat boatbuilder/designer

    El_Guero San - 1> boat is newly built... all are done except the mounting of the drive line/shafting, thus im asking which set-up to take to minimize vibration and optimize thus to avoid resultant thrust force <zero degree angle or 9 degrees down angle>
    2>. not a future boat.. this is a boat with pending works <drive/shaft line/cooling system>..

    thank you El_Guero San !!!!!
     
  5. El_Guero

    El_Guero Previous Member

    OK.

    This is an engineering design question. And you will need to talk to the manufacturers' support people.

    But, the simple answer is:

    U-joints should have some angle. How much angle is your supplier's responsibility. Most cars have a very narrow tolerance for the angle. Some u-joints have a great tolerance of angle.

    1. That answer needs to come from the manufacturer of your u-joints.

    http://www.sdp-si.com/D757/couplings3.htm

    http://www.hurst-drivelines.com/files/Universal_Joint_Alignment_Proc_111606.pdf

    2. Vibration.

    You may need to study up on harmonics.

    But, a simple answer is that will be very difficult to determine without using the equipment .... Your drive shaft has a harmonic, so will your prop, your engine, your engine mounts, your frame (the ship), and your u-joints.

    Forgive me, but this has been a long time since I studied about harmonics.

    But, I think I remember if two or more of your operating parameters have a complementary harmonic, they will increase your vibration. This can lead to a system failure.

    That is why I asked about "why" you are focusing on this issue. Usually someone who has had failed u-joints worries about them failing again.

    OK, your u-joints and drive train "should not" have a problem. You are installing new equipment. But, I would check with the manufacturers and ask them,

    "1. Are there any service warnings about vibration?

    2. If yes, at what operating range and temperature?

    3. Could you resolve the vibration by maintenance (usually lubrication) or did you have to replace parts?

    4. What is your MTBF (mean time between failure), not how long is it warrantied for, but how long until the equipment needs to be replaced ....

    5. How many failures have there been? What were the number of operating hours before
    failure? Average number of hours and MINIMUM number of hours."

    Pictures will help. But, several of your questions can only be answered by the manufacturer.

    If they tell you there "Have been NO failures."

    I can tell you that almost NEVER happens in the real world.

    But, you are asking questions ahead of time, so you will be ahead of any issues, not behind them.

    As you already know. The FIRST culprit in vibration is often the u-joints. But, it can be many other things, including the actual vehicle. Usually we do not operate vehicles fast enough to have problems with their natural harmonic, but you never know.

    So, keep asking questions.
     
  6. seacat
    Joined: Dec 2012
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cebu philippines

    seacat boatbuilder/designer

    El_Guero San - thank you very much for the above vital info....
     
  7. Frosty

    Frosty Previous Member

    Sea cat --the problem I am hiving with this is that you have fitted engines . You have fitted seafury transom drives.

    So why do you ask what the angle should be zero or 9 degrees.

    If engine and drive is fitted then you have no choice. Unless I don't understand your description.
     
  8. seacat
    Joined: Dec 2012
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cebu philippines

    seacat boatbuilder/designer

    @ frosty san- please refer to previous messages...
    - not seafury drives.. but a seafury concept transom mount
    - engines are fitted but not the drive shaft/stern tubes...
    - angle were ask to get the optimized thrust
     
  9. Frosty

    Frosty Previous Member

    What is a seafury concept transom mount?
     
  10. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 145, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    OK Seacat, I understand. You want to use surface piercing props and your question refers to the prop shaft angle.

    To get the center of the prop near the (dynamic) waterline, the shaft must have a 5-10 degrees angle. That does reduce thrust with only few percent: if you draw a vector diagram you'll see that the upward component is still very small at these angles.
    With zero angle you may gain a bit, but the prop position is too high, so there you loose more than that.
    Seafury uses a 6 degrees angle for their smaller models.
     
  11. Frosty

    Frosty Previous Member

    No--he says he is using hard water propellers, I dont understand iether. Surface props do not use 10 degrees thats way too much. Mine for instance are 5 with a down 8 degree box so that means at running plane i have horizontal engines
     
  12. seacat
    Joined: Dec 2012
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cebu philippines

    seacat boatbuilder/designer

    @ CDK san - transom mount (seafury concept) in a hard water propeller 4 bladed 28" diameter x 30-32-34" progressive pitch: engine 360hp turbo diesel, torque rating 1460 n-m @ 1200 rpm, max rpm 2000, gear ratio 1.75:1. my draft as per computed (archimides principle at loaded displacement is 3.75ft). the transom mount stern tube is only about 4-6" above the keel. my assessment i think its hard for the boat to plane , thus it will not came into planning mode and cant be a surface piercing propeller. Thank you very much sir for your time in giving vital info and helping my current probs with my stern tube set up.
     
  13. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 145, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    You are correct, the hull doesn't reach planing mode. But there will still be considerable lift at hull speed.

    With the figures you have given, there is approx. 2 ft. of water above the prop at rest and there is 0 degrees shaft angle, probably not enough to prevent air reaching it when the boat is in motion. That is very hard to predict, much depends on the way the water flows around the transom. You could install a shroud above the props but that also causes drag, so it is probably better to take the safe path and lower the prop position.
     
  14. seacat
    Joined: Dec 2012
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cebu philippines

    seacat boatbuilder/designer

    CDK san- sir, with your recommendations and did my transom mount stern tube @ 9 degrees down angle. by the way sir, what best distant i would take from transom to propeller. for now its 3 feet distance from transom to propeller location. with your expertise what best distance to take. thus the 3 feet can propel my boat on its optimized speed or farther from transom is better? which is which?
     

  15. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 145, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    Seacat, you are asking questions that cannot be answered unless you provide pictures or drawings.
    A distance of 3 ft can be sufficient when all angles are generously faired and at no point the flow of water is deflected more than 12 degrees.
     
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.