Albin 25 prop shaft question

[SamNassar]

hello all
just getting started next month to repower A25 with 3GM30F
Did I see a posting that suggested using a trailer wheel hub as a intermediate bearing? Would also take the thrust loads. My thought is to use agricultural PTO adapters to the new 1" shaft and a agricultural flange adapter/ to 6 spline AG PTO at the transmission end. with 2 u-joints one on each end of the PTO shaft the engine placement and alignment would not be too critical and the Yanmar soft mounts would be accommodated. I am familiar with the PTO drive components by way of my prior life as an apple grower.
Thanks for any input
Sam

[tribologist]

Even if there are advantages of having independent thrust bearings, the added time and complexity of that design work and install makes it very questionable in my mind. Making various adapters, shafts, laminating up mounting faces etc will likely double the time for the refit. You still need to have that bearing aligned to the shaft. Its also likely to be quite hard to fit in two universial joints axially. I think the ones used are typically CV joints? That said, if you decide to go ahead i have made cad models. I never got around to model the engine pan but there is a CAD model in onshape with the 3YM30 included. There are engine bed details in that model too.

[SamNassar]

Thanks for the reply with your thoughts
As a new poster, how much detail and back and forth is in keeping with customary posting?
I am in Florida now and the boat is in NH, so I am going on my 77yr memory. I bored the 25mm shaft bearings to 1” and a one piece shaft from engine to propeller seems pretty long, especially with the yanmar flexible mounting.
If you are an engineer that knows stuff, maybe you can advise about a self alignment flange ball bearing to take the thrust load I picked the wheel hub because the tapered bearings take thrust. The agricultural PTO in minor offset is what I have proposed two u-joints back to back phased properly.
Thanks
From memory? Hull1143 1971-2
3GM30F year ? Transmission ratio 3.14? (From a sail drive)
Propeller 17x 15 RH assuming 1:16 taper
Thanks Sam

[tribologist]

Lol. Some posts are 40+ pages. Its much more meaninful to add things here than on facebook where there is no search etc. You cant wear us down. (Look up what a tribologist do..) Yes, shaft is on the long side but since you have a very large gear ratio, your shaft speed will be slow. 25kW at 7 mph is about 1800 lb force. My guess is that you have 1/2 that if even. There is a paralell discussion here on the stern tube, that has the drawing. One thing with the original shaft seal was that it act as a damper. Our had to have a support bearing fitted to minimize shaft whip

[SamNassar]

Ok
You are a engineer that considers, among other things, lubricants?
I am intrigued about the process of determining “thrust “. I have noticed that the 3GM engine in our application uses about 1/2 gallon diesel per hour @ 6-7kts. Diesel engines have a burn rate of 17-21 horsepower per gallon per hour, so it seems 10 horsepower will move the boat. If a deep groove ball bearing flange bearing has a thrust limit of about 1500# then one of those will work for my center bearing. For my convenience, I would like to have a 2 piece shaft one end at the propeller and the other end what ever inches forward of the flange bearing, then the PTO shaft to the transmission.
With “timed” u-joints and very little angle deflection, the shaft vibration would be minimal. Agricultural PTO shafts are also expandable length wise and easily cut down if the collapsed length is too long. Adapters for the transmission flange are available and adapters for the 1” shaft are also available.

[tribologist]

Sorry for late answer. Funny enough, I happen to have a phd in bearing lubrication lol.. The load capacity “C” is the load the bearing would have 10% probability of a failure after 1 million revs. (Lundgren-Palmgrens life model from soon 100 years ago..) modern steels etc makes it obsolete but good enough for this. You scale it with inverse of load to the power 3. In this case i would do a rated load/load (C/P) of about 10-20. That get you near infinite life and a bearing that will fail gracefully if something goes wrong. The thrust can be calculated by simply divide power with speed. (SI units) power in Watt/ speed in m/s = thrust in N. Propellers are quite efficient so its close enough. At 15hp and 7.5 mph you get about 3.3 kN or 750 lbf so you need a rated load of about 10,000 lb in thrust. Thrust capacity of a ball bearing is about 50% of radial. Larger clearance like C3 is better but you will still end up with a nasty large bearing. Spherical ball bearings has poor thrust load capacity due to non conforming contacts at the outer ring. A ball bearing with a flexible mount is better. However, by far the best solution is to let the transmission bearing in the engine take the thrust like its been done in millions of boats.

[dkirsop]

Keep in mind that a 100A alternator will typically add another 1.5 horsepower to the engine loading when at maximum output. A 1/2 USgal of diesel at 6 knots is close to my average fuel consumption.

I have an original AD21 in my boat. Two cylinder, 21 HP. It is well suited to our cruising waters. I use a Balmar marine regulator to ease the initial belt load as the alternator output rises to meet the charging load.

[Dieselram94]

This is very interesting… I have a 1.25” shaft that is one piece from propeller to transmission flange. Ron’s through a standard stuffing box. I have been considering adding a support bearing about two inches in front of stuffing box to make absolutely sure the shaft never contacts the stern tube. The boat had loose engine mount bolts (some with no nuts even!) and was never actually aligned to the shaft. Installed in 1991 it ran about 2000 hrs that way before I got it. It now has new stainless steel shaft and is in perfect alignment and mounts all tight. I will admit with as much as the motor bounces around at certain rpm’s and the history of it loosening it’s mounting bolts I’m nervous I can hold its alignment long term.

[tribologist]

Dieselram94, maybe you need to look over the engine mounts. I been eying the oil filled Vetus ones.. but this year the new trailer axles, the compost toilet and the hot water system was each a B.O.A.T thing…. This year i passed the point where I have more $ in it in equipment and parts than i paid for the boat in the first place but having everything work just right is what it takes to make it a very comfortable boat for the way we use it.

[Dieselram94]

I have not seen those mounts, however I am going to look them up now.
I fully understand the costs, like you say having the boat comfortable and functioning properly costs. That’s part of it I guess, but when I think about what a boat like this would cost if it was new it is easier to swallow.

[Dieselram94]

Tribologist, I looked into those mounts. Unfortunately they aren’t rated high enough for my engine. I have a Perkins 4.108 (50hp). Thank you for the suggestion though.