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Thread: Propeller shaft question

  1. #1
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    Default Propeller shaft question

    The plans call for a 1" shaft on centerline in a shaft log. I assume the propeller should be in a sleeve inside the log. What material should I use for the sleeve, what diameter, how do I seal between the sleeve and the log?

    My initial thought is a 1-1/4" ID schedule 40 pvc sleeve with 3M5200 as far in as I can get at each end.

    Thanks

  2. #2
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    Default Re: Propeller shaft question

    What sort of bearings and or glands are you using on both ends of the shaft log.
    It really is quite difficult to build an ugly wooden boat.

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  3. #3
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    Default Re: Propeller shaft question

    A bit more about the boat, your progress thus far, and all that would help. Is the log even drilled?

    Some boats call for lining the log. Some don't. And of all ages. I've seen new builds with PVC and some with just wood. I've seen old boats, had one, with a bronze lining. And I had another old boat with an unlined log.

    What does the plan call for?

  4. #4
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    Default Re: Propeller shaft question

    What Nick said, plus what boat are you building?
    Hope for the best, but plan for the worst.

  5. #5
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    Default Re: Propeller shaft question

    The boat is a 23' fantail launch. I am still in the lofting stage. This is my first fossil fuel powered boat. I have not thought about bearings or glands. My intent is to power it with a Honda V-Twin engine, but that will be the subject of a whole set of future questions. Now I am just trying to figure out the hole size in the shaft log and if I need a sleeve.

    Thanks again

  6. #6
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    Default Re: Propeller shaft question

    Quote Originally Posted by pglonek View Post
    The boat is a 23' fantail launch. I am still in the lofting stage. This is my first fossil fuel powered boat. I have not thought about bearings or glands. My intent is to power it with a Honda V-Twin engine, but that will be the subject of a whole set of future questions. Now I am just trying to figure out the hole size in the shaft log and if I need a sleeve.

    Thanks again
    Look at your catalogues for stern glands and bearings, there are several types also affected by the position of the engine and the length of the shaft within the hull and whether it needs steady bearings. You may go for stuffing glands at both ends of the shaft log, or water lubricated cutlass bearings with a flexible mount to the water tight gland on the inside. You need to design all of that and make your selection before you know whether the two glands are screwed to the shaft tube, or how it is arranged. If water lubricated you need to consider whether you have gribble or teredo worm in your waters as you will not be able to antifoul the inside of the tube,.
    It really is quite difficult to build an ugly wooden boat.

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  7. #7
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    Default Re: Propeller shaft question

    Was the launch designed by a qualified designer with scantlings and mechanicals worked out?

  8. #8
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    Default Re: Propeller shaft question

    I believe Paul Gartside specifies a fiberglass stern tube. I like the idea of a copper tube with a bronze shaft. The tube can be turned for a snug fit into the sleeve of the stern bearing aft and packing gland forward. It could even be threaded into them. If the copper is a snug fit in the hole, it will be better than just about anything at preventing critters and fungus from taking up a residence.

  9. #9
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    Default Re: Propeller shaft question

    A bedded shaft tube is the best method to build, but many builders delete this. Some slush the shaft bore with epoxy , some do it with anti-foul, some (fools, IMHO) leave it bare. I don't much like stuffing glands at the outboard end (sorry, Nick). On my 27-foot Cape Islander design that had a 1" diameter shaft I specified a Buck-Algonquin stern casting with integral cutless bearing (part #00STB0100) at the prop end, a 1.25" diam. Sch. 80 PVC pipe liner bedded in 3M 5200, and a Buck-Algonquin shaft log with integral stuffing and packing nut (part #00SL100A). The boat was built in 2005 and as far as I know has had no issues with the shaft system.
    Hope for the best, but plan for the worst.

  10. #10
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    Default Re: Propeller shaft question

    Quote Originally Posted by J.Madison View Post
    I believe Paul Gartside specifies a fiberglass stern tube. I like the idea of a copper tube with a bronze shaft. The tube can be turned for a snug fit into the sleeve of the stern bearing aft and packing gland forward. It could even be threaded into them. If the copper is a snug fit in the hole, it will be better than just about anything at preventing critters and fungus from taking up a residence.
    If the boat stays in the water, copper is used here. If not, then fibreglass, Tufnol or similar.

    Rick

  11. #11
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    Default Re: Propeller shaft question

    I've never even seen a stuffing box on the outside. You want water in the tube to keep things calm and cool. I've also not seen tubes any larger than needed.

    Speaking of water in the tube, one handy trick is to tap a small line off the raw water exit just before where it goes to the muffler. Run that to the shaft tube just outside the stuffing box. Now you have something really positive.

  12. #12
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    Default Re: Propeller shaft question

    Appreciate all of the input. Here is some more info:

    The boat will be trailered and only floated in fresh water. I live on the prairie and boat mechanics/suppliers are scarce.

    The plans were prepared by a designer named Bolger. They show bearings at the front and rear of the shaft log with a "flex necked stuffing box" at the front. There does not appear to be a sleeve, but it is tough to tell. The shaft extends about 4' forward of the shaft log to the engine.

    What is a cutlass bearing, where do I find a catalogue showing these doohickeys.

    Much thanks

  13. #13
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    Default Re: Propeller shaft question

    A cutless bearing (note "e", not "a") - is a support for the shaft aft of the opening.

    The material ,looks like:



    And is in a housing like this:



    Water flows though it:

    "If it ain't broke, you're not trying." - Red Green

  14. #14
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    Default Re: Propeller shaft question

    Here's the list of one of the two US cutless bearing makers.
    http://www.duramaxmarine.com/pdf/CutlessBearingMS.pdf

    Buck Algonquin is a supplier of stuffing boxes.


    I would much prefer a fiberglass (G10) shaft tube over PVC (weak) or metal.

    A 4' shaft will likely require a steady bearing in the middle. This could get complicated, expensive and a pain to align.

  15. #15
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    Default Re: Propeller shaft question

    You need to determine the exact setup you propose for your boat before determining shaft size and stern tube.
    Is the shaft the correct size for the engine, length of shaft, gearbox (presumably reduction box) and prop size?
    A marine engineer or supplier can do those determinations.
    You cannot spin a large prop on a thin shaft.....likewise your engine may not be able to be efficient with direct drive.
    You cannot have a long shaft insufficiently supported.
    Once you have the correct sizes determined, then you can determine your stern tube setup.
    If you use a thrust bearing between the gearbox and the shaft you may only require a single phenolic bearing at the stern end of the stern tube.
    Long shafts may need two to prevent whipping.
    Use a cutlass bearing seal at the star of the shaft and pump some surplus water down it to keep it cool.
    I would avoid Bolger's suggested "flex necked stuffing box" - you will leave a faint trail of grease and oil all round the lake.
    Water is a great lubricant and clean - a green solution.
    Likewise avoid metal stern tubes - drill your shaft log for the stern tube and epoxy a fibreglass/polester stern tube.
    There has been a lot of discussion about electrolysis on wood in these pages, so use a polymer based solution that does not transfer electric current.
    This on line catalogue may help you with its 4 pages of choices. https://www.vetus.com/en/stern-gear-...tern-gear.html

  16. #16
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    Default Re: Propeller shaft question

    On both of my boats I ..... fiberglassed (heavily) over a cardboard tube with epoxy. I took the rough tube to a machine shop along with my cutlass bearing and had them machine the inside of one end of the tube to accept the bearing. I disc sanded the outside of the other end of the tube to take the hose for the stuffing box. Both tubes are permanently epoxied into the boat. One was planned before the boat was built so I left a big ol place for it, the other was retro fit a few inches to the side of the keel on the outside.

  17. #17
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    Default Re: Propeller shaft question

    Quote Originally Posted by JimConlin View Post
    A 4' shaft will likely require a steady bearing in the middle. This could get complicated, expensive and a pain to align.
    Very helpful post. Thank you.

    What is the longest propeller shaft that wouldn't require a steady bearing in the middle. And, is this distance measured from the transmission to the propeller? I would assume so, but just asking.

    Thanks.

  18. #18
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    Default Re: Propeller shaft question

    Quote Originally Posted by chollapete View Post
    Very helpful post. Thank you.

    What is the longest propeller shaft that wouldn't require a steady bearing in the middle. And, is this distance measured from the transmission to the propeller? I would assume so, but just asking.

    Thanks.
    The steady bearing is a function of the length of the unsupported shaft, with an internal stuffing gland on a flexible hose as some are, that would be from the gearbox flange to the external bearing. If the internal stuffing box is rigidly mounted and includes a bearing, then from there to the gearbox. The other factors are shaft diameter and maximum revolutions. You need expert advice.
    It really is quite difficult to build an ugly wooden boat.

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  19. #19
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    Default Re: Propeller shaft question

    Mine is one inch dia,60 inches long , no middle bearing. My top shaft speed is about 1300. Normal shaft speed is 800 ish.

  20. #20
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    Default Re: Propeller shaft question

    Can you tell us which design you are building? In general, for a trailered boat used in fresh water, I do not think you need any tube at all. You need a cutlass bearing outside, and a flexible hose packing gland inside. I've seen lots of shaft runs longer than 4' without a support, but with a high speed shaft support might be warranted. Of course, this assumes it is supported at each end. If the prop shaft has a long run outside the hull, common on high speed boats, additional support at the prop is mandatory.

    We need to see the hull shape to know engine placement, length of shaft log, amount of shaft outboard, approximate shaft speed, etc...

    I don't understand the comment about a flexible gland leaving grease on the lake. I think its referring to this: No grease involved.


  21. #21
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    Default Re: Propeller shaft question

    A 1" diameter Type 316 stainless steel shaft powered by a 25 hp motor turning no greater than 1,000 rpm should have support (cutless bearing, steady bearing, gearbox output flange) spaced no greater than 66" apart. Lower shaft rpm results in greater bearing spacing, greater rpm needs shorter spacing. Different shaft materials requires different bearing spacings. Be aware that putting your engine of flexible mounts introduces movement in the shaft that may become a problem. To be sure of spacing for your specific application, talk to your friendly neighbourhood boat designer or NA.
    Hope for the best, but plan for the worst.

  22. #22
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    Default Re: Propeller shaft question

    I bought a a glass fibre tube and shaft from vetus, tube comes fitted with an aft bearing for a 1in shaft. Using a local Volvo type flexible gland on the inside which has a water injection point to lubricate the shaft from engine cooling water. From what i have read, maximum suggested unsupported length of shaft is around 40 times the shaft diameter...so 40 inbetween bearings, i note MD has given a greater span, given the various metals a shaft can be constructed from, im sure bearing distance is not written in stone.

  23. #23
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    Default Re: Propeller shaft question

    No, bearing distances are not rigid, as there are several factors to consider. Hence the urging to talk to someone studied in the topic. Installing a shaft that is a quarter inch too large, or bearing spacings too close, is more insurance than problem; however, erring in the other direction can get very, very expensive and a monster to re-do.
    Hope for the best, but plan for the worst.

  24. #24
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    Default Re: Propeller shaft question

    Dave Gerr's book "Boat Mechanical Systems....." gives good info on shaft dias, bearing spacing, etc - worth a read (worth buying!)

  25. #25
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    Default Re: Propeller shaft question

    ^ Also covered very well in his book, Propeller Handbook.
    Hope for the best, but plan for the worst.

  26. #26
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    Default Re: Propeller shaft question

    Thanks everyone for all of the input, it has been very helpful. I have attached (I think) a copy of the portion of the plan drawing showing the shaft log. This is all the info I have on this portion of the design. Here are my questions:

    Does anyone know if the fore and aft bearings and the stuffing box as shown on this drawing are available, and if so where can I order them? Ditto the propeller.

    What size hole do I need in the shaft log for the 1" driveshaft.

    I am planning an air cooled 20hp engine, no cooling liquid for the bearings.

    Thanks for any assistance
    Attached Images Attached Images

  27. #27
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    Default Re: Propeller shaft question

    Bolger is a well known, if somewhat controversial, boat designer. Which design are you working on? That would be a very helpful bit of info.
    There's the plan, then there's what actually happens.

    Ben Sebens, RN

    15' Welsford Navigator Inconceivable
    16' W. Simmons Mattinicus double ender ​Matty

  28. #28
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    Default Re: Propeller shaft question

    pglonek, please refer to my post No. 9 for part numbers from Buck-Algonquin.
    Hope for the best, but plan for the worst.

  29. #29
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    Default Re: Propeller shaft question

    Thanks mmd, that is what I was looking for. Any suggestions on hole size in the shaft log?

    Thanks again

  30. #30
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    Default Re: Propeller shaft question

    That will depend on a.) whether you install a liner, and b.) what the OD of the liner (if installed) is. I am one of those 'design and spec everything before building' designers and dislike modifying things (especially such fundamental items as the drivetrain) mid-project, so I wouldn't feel comfortable telling you such specifics as bore size before you have the hardware that goes in it locked down. Especially when you are contemplating a non-standard powerplant. Sorry...
    Hope for the best, but plan for the worst.

  31. #31
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    Default Re: Propeller shaft question

    PG, The plans you have quoted call for a dirt standard old school unlined timber shaft log with with a cutlass bearing in a bronze housing aft, and a packing gland on flex hose forward, both of which can be sourced from Buck Algonquin or the like, generally that shaft bore will be accomplished by building a split, or two piece assembly fastened together after you cut a half of the bore on the upper and lower sections, these exposed surfaces of the bore are generally poisoned with anti-fouling paint...linings for the shaft bore of this sort of boat are difficult to get correct, plastic pipe is decidedly not a good idea.
    As others have mentioned, all of the shaft details are subject to the needs of the power plant choices, this set of drawing was tailored to the engine intended, any alternatives power sources should likely mean some adjustments to size and detail.
    FYI, The cutlass bearing and stuffing box are cooled and lubricated with water that enters at the aft end of the shaft bore.
    Are these drawing really Bolger? They are quite old school if so, pretty boat, what we can see of her...Cheers, Steve

  32. #32
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    Default Re: Propeller shaft question

    Thanks boattruck

    Yes the plans are by Phillip C. Bolger Gloucester MA. No date. 23' fantail launch.

    I will split the shaft log, since I am not confident I can get a straight bore in a 4'11" log. I am planning a 1-1/4" hole cut with a half round router bit and no lining. Antifouling paint sounds like a better idea than soaking in linseed oil like I was considering.

    Do I need to cut side holes to allow water into the driveshaft hole, or does enough cooling water come in through the cutless bearing?

    The plans call for a single cylinder Yanmar diesel engine but I am thinking about an air cooled gas engine for simplicity of construction and maintenance. I only need 10-12 hp. I would also need a marine gear, but I think Hurth makes one that would not require a separate thrust block. Noise has me concerned though. In either case I believe the 1" shaft with the setup you described will work as long as I keep close to the horsepower and propeller rpms shown on the plans.

    My previous project was a carvel planked 16' knockabout designed by John Alden from 1923. Prior to that was a 15' plywood catboat. I intend to strip plank this one; haven't done that before and I always like something new.

  33. #33
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    Default Re: Propeller shaft question

    You wont want to be on the boat very long with an air-cooled 12-hp engine. Go take someone's lawn tractor for a ride for an example of the noise level.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  34. #34
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    Default Re: Propeller shaft question

    Quote Originally Posted by pglonek View Post
    .

    Do I need to cut side holes to allow water into the driveshaft hole, or does enough cooling water come in through the cutless bearing?

    .
    You need to purchase an aft bearing with a housing that gets water feed to keep the bearing lubricated.



    The shaft log itself may run dry while underway, so you need the water scoop style gland. Your inboard end can use a standard type greaser with flax or synthetic packing. I would seal the inside of your shaft log with at least 3 coats of epoxy coal tar, or epoxy.

  35. #35
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    Default Re: Propeller shaft question

    Quote Originally Posted by Breakaway View Post
    You wont want to be on the boat very long with an air-cooled 12-hp engine. Go take someone's lawn tractor for a ride for an example of the noise level.

    Kevin
    or go to a machine gun meet without ear protection

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