Gear box: Position A or Position B - Does it matter?

[P69]

Tell me why this is a bad idea.

Problem:  Intend to replace old PSS with stuffing box, but with right handed prop, I can't get stuffing box with 1 1/8" shaft and 2 5/16" shaft log OD. I can get a stuffing box for my shaft and log for a left hand prop.

1. Engine: Universal 5444, clockwise rotation
2. Gearbox (hurth ZF 15M aka Hurth HBW 150) has two reduction ratios: Direction A = 1.88 and Direction B = 1.95
3. Walter RV26 is a 1:1 gear ratio
4. With current setup, putting shifter lever in fwd pushes the morse cable, which pushes the gearbox lever to position B.
5. I know I can get a PSS, but I'd rather have stuffing box, so please go along with me on this one.
6. Pearson 367 hull # 42 (not that it matters, but maybe it does)
7. This whole issue centers on the right or left handed thread on the stuffing box. The thread has to be opposite the prop rotation. Thanks to Pete for illuminating that for me.
8. Just because current setup puts position B as forward, doesn't mean that it is correct. PO might have gotten it wrong.

Solution: Get left handed prop (been meaning to get a 3 blade anyway) and change the morse cable  so that the position that spins prop left hand is the forward gear (the Postion A with 1.88 ratio). I might have this backwards because I don't remember if the v drive changes the rotation.

Question #1: with this gear box,  which direction is reverse and which is fwd (1.95 vs the 1.88)?

Question #2: Does it matter which way the gear box is running for forward (1.88 vs 1.95 ratio)?

Question #3: Does it matter to the V drive which direction is reverse or fwd?

Question #4: If I use position A for fwd (currently using Position B for fwd) will the difference in gear reduction be noticeable or a problem for any part of the propulsion system?

Question #5: When Hurth fails, I will likely replace with Twin Disc MG-360. How do questions 1 - 4 apply to that gear box?

Bottom line question is: Does it matter which direction is forward:  Position A or B?

Please be candid and tell me if this is a dumb ass idea or if it feasible.

[PeteW]

None of the twin clutch gearbox designs that I have looked at have a forward or a reverse per say.  What you call forward depends on whether your prop is RH or LH. My Liberty Series Borg Warner manual shows opposite shift lever positions for forward depending on if your prop is left or right hand. Hence A and B.

The data sheet for the HBW15 rates position A and B both at 53 HP for continuous duty cycle. They are serious about not exceeding that also. So a bigger prop needs to be carefully designed to make sure you have margin on the amount of HP you are putting to the water. That box has a bolt on water cooler and that is a good idea. I've seen the clutch plates overheat and burn out in no time in those smaller Hurth gearboxes. Although the HBW15 should provide margin. A friend of mine is on his third Hurth gearbox in as many years although he has the same motor with an HBW10 on it.

Some owners of that Universal have gone to high deflection damper plates to minimize the peak torque pulses that cause the clutch plates to constantly slip and overheat with good results. The 3 cylinder Universal runs a little lumpier than a 4 cylinder diesel which is inherently smoother.

In summary there was no real reason to go to a RH prop with the setup you have.

Note that none of those hydraulic twin clutch design gearboxes should ever be started in gear. Without full hydraulic pressure the gearbox will lock up in reverse and forward simultaneously and this will cause serious damage. My Borg Warner has a neutral interlock switch to prevent me from ever doing this.


All the V drives I have looked at wear over time predominantly in the forward direction. Since they rarely run in reverse the teeth tend to pit on the reverse gear face where water can accumulate. So a V drive that is nicely worn in in one direction may not be as reliable when pressed into service in the opposite direction. It all depends on the condition of the drive gears and how well the oil was maintained.  I cant say if there is a preferred forward direction based on thrust in those gears. Perhaps its a question for Walter machine. If there is a preferred forward rotation you will most likely achieve that by returning to a LH prop.



Pete

[P69]

Thank you Pete.

If the engine produces max 44 hp @ 3100 rpm, how would it be possible to exceed the 53 hp?
A local prop shop gave me a ball park of 3 blade of 17 x 9 (I told him I had an 18 x 10  2 blade )   Campbell Sailer quote was for a 16 x 8.

When I rebuilt the vdrive, there were no issues with the gears, they all looked great, no wear (it's a 1:1 ratio in v drive).

I'm fixin to call walter tomorrow to check on direction issues

when comparing propellers, can one use the dia:pitch ratios or is there any way to compare a 3 blade with a 2 blade?

I've heard serveral stories about the hurth gear boxes failing 2, 3, 4 times. That's why I'm looking into a replacement so I can have that info all lined up when this one fails.

Called ZF today and the confirmed that there is no problem using A or B for fwd.
When I run the following numbers in the vicprop calculator, I get a 17.6 x 10.5

displ: 19000
Lwl: 30
BWL: 10
draft (excluding keel): 3'
engines: 1
max hp: 40
max rpm: 2500
ratio: 1.88 (that's position A, which makes it a LH prop)
# bearings: 1
kts: 7.3

[S/V Deo Volente]

I can tell you that I am running a 17 X 11 3 blade" Sailor" prop. It will let me get to 95% of the 3000 RPM maximum on my Westerbeke 50. The numbers fit well with what vicprop comes up with.
FYI the boat originally came with a 17 X 9 and I had it re-pitched when I realized it was grossly underpropped.

[P69]

Bob,
Thanks for the feedback on the prop dimensions.