Sterntube and shaft design help for new build 10m boat

Discussion in 'Inboards' started by yodani, Mar 24, 2013.

  1. yodani
    Joined: Nov 2010
    Posts: 190
    Likes: 2, Points: 18, Legacy Rep: 16
    Location: Danube Delta

    yodani Senior Member

    Hi there,

    I have not been around for a long time as I was busy with my job and boats. Now the spring is coming and it is time to start building a new boat for the shallow, muddy waters of the Danube Delta.

    From my previous experiences wit my other boats in the past 20 years I wish to try and improve the classic shaft with bronze bearing and leaking stuffing box. Also change from hard mounted engine to soft mounted plus try keel cooling.

    My current problems with the boats are:

    Shaft - Due to muddy, sandy waters the bearings get worn out every 1000- 1500 hours and that results in a worn shaft that needs to be weld corrected. Groves resulted on the shaft due to stuffing box wear.

    Drive - The engines are hard mounted and are separate from the gear box (these are stand alone modified Russian gear boxes). Aligning this system takes ages and has to be done over and over again. The miss alignment leads to vibration, broken couplings, worn shaft and bearings.

    Cooling system - as the boat is used on shallow lakes it sometimes pllows the bottom for kilometres and no matter how many filters you have they will get clogged.

    Now for the new boat:

    This is an old life boat 9m long and 3m wide with a draft of about 1.2m. The build will be done in house and there will be nothing fancy but rugged and tank like just to withstand the harsh environment we have here. (See pictures).

    At the moment I have the following parts ready for this boat:

    - Engine I bought from Ebay about 3300 EURO- new MAN D0824 E701 marinised by MAN - 100HP@2800 RPM - that is a bit big but I intend to use it to max 60 HP at 1800 RPM for long life and efficiency.

    - Gear box - PRM 500 1:2 gear ratio good hydraulic gear box from England - also Ebay. 500 EURO

    - Propeller - 3 blades - 22R17 - Ebay - 80 EURO - a bit large for the set up but we come to that in a minute.

    - BMW E33 rear CV joint rated to 250 HP (in a car) - I bought locally for about 20 EUR (two of them).


    Now my imperfect plan needs your help and advise:

    As you can see from the pictures attached I have decided to go with:
    - Sterntube - stainless steel -100mm x 5mm thick - I can go with a smaller diameter but I would like to know what is the ideal thickness of the cutlass bearing made of Vasconite Hilube.
    - Cutlass bearing made of Vasconite Hilube - 200mm long with outer diameter - 190mm and inside diameter - 55mm with 5mm deep groves. Anyone have any experience with this material? Do you have an alternative to it? What should be the thickness of the bearing?
    - on the engine side I have a "stuffing box" that has 3 seals plus a Vasconite Cutlass bearing in it. This space will be oil filled with a feed from a small reservoir. This will be screwed in the stern tube and secured with screws. There will be a valve on the tube so the air in it can be burped out after boat is put on water. So this is the tricky part - do you think it will work?

    - The propeller I have has a large hole for the shaft hence the need of such a large diameter tube. I have the intention to fit a Quickcutter rope cutter on the boat as the weeds are a big problem too. (see picture) any thought on that?

    - on to the shaft - 50mm diameter steel shaft on witch I have added wear rings (practically needle bearing inner rings). This rings are there to protect the shaft from getting groved by the abrasive suspensions and to be easily removed and replaced when needed. Has anyone used such sleeves on shafts? Do you think this is a good idea?

    - The Thrust bearing - Since I want to use a CV joint I need to use a Thrust bearing in a housing and also a a way to couple the shaft to it. The Python Drive system seems well engineered so I thought of implementing something similar. A shaft locking flange from tollok will be used. Now here I have two questions:

    1. Is this Tollok locking system reliable? and if so do you think this one would do: TLK 130 - the one I am interested in is d50 x D85mm

    2. The thrust bearing would be this one - http://www.skf.com/group/products/bearings-units-housings/ball-bearings/angular-contact-ball-bearings/double-row/index.html?prodid=125012210&imperial=false

    Anybody familiar with bearing ratings? How can I calculate the thrust of the prop?

    The CV joint is from the auto industry but I think it will take the thrust well. The shaft on it is 30mm but it is a high quality hardened steel.


    Should i use also a prop saver with it or a bullflex type coupling to avoid gear box damage in case of impact? There are quite a few trees under the water and sometimes they can't be avoided... The bullflex is dam expensive for my taste so I would probably improvise something from truck tire a system I used before and it works.


    [​IMG]

    http://www.q-marine.co.nz/images/QMI Product Images/pythondrive/Python- Mega on gearbox.png

    And the final question - in my case what would be the ideal distance from the prop to the rudder? I found the answer fro the distance - hull to prop - 15 to 20 % of prop diameter but it does not seem to be a good answer for the rudder to prop.

    Wow this took longer than I expected but I hope you can help me decide if this is a good way to go or something should be changed. Your experience would probably help me build a better boat.

    Thanks,

    Daniel
     

    Attached Files:

  2. tunnels

    tunnels Previous Member

    Do you get any trouble with your keel cooler dragging along the bottom and trees and stumps etc etc ??
     
  3. yodani
    Joined: Nov 2010
    Posts: 190
    Likes: 2, Points: 18, Legacy Rep: 16
    Location: Danube Delta

    yodani Senior Member

    Hy Tunnels,

    I have no clue about the keel cooler as this is my first atempt to build one. But i intend to locate it at the stern. I forgot to ask if anyone has a good solution for that. I am thinking a recessed cooler would do.
     
  4. tunnels

    tunnels Previous Member

    My thought was what about a radiator out of a truck with a thermostat conrolled electric fan and a good direct air supply!!, like up on deck !! eliminates a wealth of problems !!
    Surely a fully enclosed prop shaft inside a heavy duty steel case so just the prop is exspossed must be worth a real serious look at !! No bearings or seals exsposed to anything either end just the prop and the case !!Could make a small sleeve on the tube with a wearing ring against the propeller
    If the crap cant get in it wont wear out !!:idea: ???
     
  5. CDK
    Joined: Aug 2007
    Posts: 3,324
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    Location: Adriatic sea

    CDK retired engineer

    Looks quite good Yodani!
    In my stern tubes I've used a ball bearing and two seals at the prop end, with the whole stern tube filled with ordinary engine oil. An oil reservoir is mounted above the waterline: if any oil escapes the level will show that.

    When I completed the installation 5 years ago, the oil level dropped after every night and air bubbles came up in the morning when the sun warmed the tubes. After a few weeks the level remained stable so all air had left. I refilled the reservoirs to 3/4 and marked the level; there have been no change since then.
     
  6. yodani
    Joined: Nov 2010
    Posts: 190
    Likes: 2, Points: 18, Legacy Rep: 16
    Location: Danube Delta

    yodani Senior Member

    @ tunnels
    Yeah I thought about that option but than the noise on board is increasing and it is hard to control. Since this is a tour boat for wildlife enthusiasts I would like to avoid that. I think the position of the cooler will be away from harmful things but you never know.

    @ CDK

    hi there, I thought you would bring up your stern tube. I was inspired by your work but I wanted to avoid using ball bearings in the tube so I thought about this solution with two bearings - one is water lubricated and the other is oil lubricated. The advantage I see here is that the fragile seals are away from any debris and they solve the stuffing box problem. Sure I have no clue what unexpected problems might arise from this set up but I hope someone can prove me wrong. How are your shafts performing? Did you replace any seals or bearings? How many hours on the shafts now?

    Thanks,


    Daniel
     
  7. CDK
    Joined: Aug 2007
    Posts: 3,324
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    Location: Adriatic sea

    CDK retired engineer

    The one thing I have doubts about are the needle bearing rings you want to use.
    Difficult to install them that far from the end of the shaft if you intent to heat them first, no guarantee they stay in place if you do it cold.
    And you need stainless ones of course.....

    How many hours on the shafts I can't tell you. I relied on the Navman depth sounder for that information, but the display died a few years ago. A case of sunstroke so I replaced the whole unit and discovered much later that the engine hours counter was crazy.

    But I have no worries about their longevity, more so about the rest of the boat!
     
  8. yodani
    Joined: Nov 2010
    Posts: 190
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    Location: Danube Delta

    yodani Senior Member

    Sorry CDK, i read your message on my phone and missunderstood the question. so disregard the below...

    I intend to fix the rings on the shaft by machining it to bearing size and force them down. Once they are in there will be no twisting but I will find a solution to make them stay in place. Sometimes a epoxy glue works wonders or even a welding spot at the end. I could also take the heating approach but that will not be 100% safe.

    Iside the oil bath part there is another "plastic" vasconite bearing just like the one near the prop. I could have gone for a water cooled cutlass but there will be no water available for it at all times as I will use the keel cooling to avoid clogging of filters etc in the shallow water. As I told you I wanted to avoid using ball or needle bearings because of the shocks the props are taking sometimes from the impact with the bottom or debris.

    Se a couple of pictures showing the bearing in the housing.

    Daniel
     

    Attached Files:

  9. yodani
    Joined: Nov 2010
    Posts: 190
    Likes: 2, Points: 18, Legacy Rep: 16
    Location: Danube Delta

    yodani Senior Member

    Back on track

    Hi there,

    After a long busy period I found some time for the boat build I have started to plan.

    As the first post was explaining, I have started to fabricate some of the parts for the drive. There are some modifications in comparison with the original plan but in general they have remained the same.

    Attached you can see my CV joint assembly and the thrust bearing with the rubber bushing plus the self tightening system. I also found a cheap Vetus bearing for the shaft - 50mm so I will go with that.

    The only problem I have now is about the stuffing box design. I would go for a standard packing gland but i currently run some of those on the boats and they seem reliable with only one problem - the shaft is wearing down after a few years and it needs re-machining. Till now I have used iron shaft and that was not such a big problem but now I will use stainless steel and that is going to give me some headache... Any ideas about this?

    The current solutions are - http://www.lasdrop.com/ - They say they have improved on the bellows fatigue problems by eliminating it but a seal for my 50mm schaft will be 600 USD... and they seem to require water injection at all times. As I will use keel cooling water injection will not be available
    http://www.shaftseal.com/ - PSS shaft seal seems to be the same thing but with a bellows and it seems to work without injection for slow boats like mine.

    http://www.duramaxmarine.com/shaft-seal.htm - Same as Lasdop but with a air seal and other components. Only inch models

    http://www.norscotshaftseal.com/index.html - Lip seal type - no metric either. - This one I could make myself at a fraction of the price.

    I have a question - if I want to avoid using that rubber hose and fit the seal rigid to the stern tube with another bearing centering it there what would be the inconvenience? I know that the wear of the stern bearing will miss-align the shaft a bit but will this ruin the lip seal?

    Cheers,

    Daniel
     

    Attached Files:

  10. yodani
    Joined: Nov 2010
    Posts: 190
    Likes: 2, Points: 18, Legacy Rep: 16
    Location: Danube Delta

    yodani Senior Member

    Cleaned up hull

    Here are a few pictures of the hull after the clean up... Had to remove a lot of material from it and a lot of water from the ... water tight compartments. It looks better now....

    I have two of those but the other one will have to wait a few years :)

    Cheers,

    Daniel
     

    Attached Files:

  11. TeddyDiver
    Joined: Dec 2007
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    Location: Finland/Norway

    TeddyDiver Gollywobbler

  12. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Packing gland I use GFO marine packing, it is soft black graphite impregnated and does not wear shafts, and it is drip free. I like this a lot.
    http://gfopacking.com/?gclid=CjwKEA...-aoBydnyVw7UB7j2TfY-7B_WkxPJfZGP8LxoCCDnw_wcB

    I bought mine from emarine.
    http://www.emarineinc.com/categories/GFO-Marine-Shaft-Packing/

    I have the Vesconite shaft bushings and they are good.
    One thing I noticed is the crab traps, I ran over some and the small 1/4 inch line wrapped into the space between prop and strut and wore into the vesconite slightly on one end.
    Vesconite bushings are cheap and good.
     
  13. yodani
    Joined: Nov 2010
    Posts: 190
    Likes: 2, Points: 18, Legacy Rep: 16
    Location: Danube Delta

    yodani Senior Member

    Hi sdowney717,

    Thank you for your reply. I am now leaning towards this classic packing gland and Vesconite bearings. I hope i can source some of that packing also here in EU. Vesconite has now stock also here so itcwill beceasy to get from UK.

    Since when do you use the Vesconite and is it realy that good? I've been trying to find somebody that has first hand experience. Could you tell me how nany hours on the drive and if the shaft is getting damaged?

    Do you inject water in the stern tube or just siphon the tube? I will have keel cooling so there will be no cooling water available.

    Thanks and cheers,

    Daniel
     
  14. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    I have a conventional shafting which is an external strut and that packing gland on the inside of boat attached to shaft log with a rubber hose.
    There is no water injection. I am very pleased with what I have now.
    I just pulled the boat after 4.5 years in the water and there is no wear on the vesconite. And the GFO packing also has not worn out.
    Hours, less then 200 hours I figure. It is not worn out cause it is not leaking.

    Shafts are undamaged by either. The shaft where the packing gland sits was damaged by decades of owners using hard flax packing. Shaft had a slight corosion pitting on the surface. I coated with some epoxy. Anyway the GFO marine packing worked. The flax packing was constantly leaking dripping. When I bought the boat it was a gushing stream, the owner had a large pipe wrench and said he always had to tighten it up. Me too, after every boat trip, it was gushing water in.

    In 4.5 years I have tightened the GFO packing twice. Likely due to worn shaft very very slowly wearing the GFO packing.
    I also used GFO on the rudder glands.

    Our boat is in the lower Chesapeake bay near LAFB in Virginia on Harris creek..
     

  15. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    [​IMG]

    I know it's still called a shaft log, but there are much better ways to do it now with more modern packings.
     
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