Rocksteadee
Well-Known Member
Sounds like when ordering props they got the 2 sizes right but had got clockwise and anti clockwise back to front
Prop pitch vs Diesel WOT revs.
- Thread starter oldgit
- Start date
Nauti Fox
Well-Known Member
Oh Lordy, last time Albert shot off and took an hour to find....on the railway line.
Rocksteadee
Well-Known Member
turning the prop would make no difference as a 20 inch clockwise prop when turned is still a 20 inch clockwise prop.....just the taper would be the wrong way
oldgit
Well-Known Member
Am going to search the interweb for "nearly good enough" props.Have got access to some machining stuff regards props although my props are a bit weedy compared to the barge and commercial stuff they normally fix.
Latestarter1
Well-Known Member
Shaft diameter??
oldgit
Well-Known Member
Believed to be 40mm if Vetus catalogue is correct.Outside chance of it being 45mm.
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pappaecho
Well-Known Member
Clearly the engine is being held back. The obvious solution would be to swap props, but the results would be interesting as they would be wrong handed!
I wonder if the prop has been repitched? It should be re-marked but is may not have been.
The only solution perhaps is to borrow a prop of the correct pitch, or perhaps as I have on my P33, accept that there is a disparity and live with it
I wonder if the prop has been repitched? It should be re-marked but is may not have been.
The only solution perhaps is to borrow a prop of the correct pitch, or perhaps as I have on my P33, accept that there is a disparity and live with it
MapisM
Well-Known Member
Well, I'm probably being thicker than yourself...
...but I don't understand why swapping props shouldn't be feasible.
Are you sure that the reduction ratio is different in forward and reverse?
Besides, I didn't understand why jfm said that your props are currently spinning inward (when going forward, I assume) and it's better to stick to such setup.
That's pretty unusual for any "normal" boat, and unless you're aware of any reason why props should spin inward, I would think that they MUST be swapped...
vas
Well-Known Member
also quite thick on these issues, just learning...
Is there any problem if gearboxes are effectively running in reverse throughout their life?
I mean, if you swap port to starboard prop, you need to change the cabling to the controls so that boat goes forward when levers move forward and not reverse, right? Other than that, I don't see anything else needed (ok this inward outward prop rotation I don't know but I cannot see it causing much problem, definitely less than running your two engines in such different loads)
V
Is there any problem if gearboxes are effectively running in reverse throughout their life?
I mean, if you swap port to starboard prop, you need to change the cabling to the controls so that boat goes forward when levers move forward and not reverse, right? Other than that, I don't see anything else needed (ok this inward outward prop rotation I don't know but I cannot see it causing much problem, definitely less than running your two engines in such different loads)
V
oldgit
Well-Known Member
See if this sounds right.
As for running the box constantly in reverse,there can be problems with some gearboxes and sometimes it is required to lock the shaft to prevent rotatation when being towed or running on one engine..
On this particular gearbox the "forward" raftio is 1.91.1 and the oil pump is positioned to provide maximum lubrication flow in this direction.A reduced oil flow is provided in reverse as this would normally only be for short period and less heat would be generated.
What would normally be "reverse" on this box has a 2.10.1 ratio and is used as the permanent forward drive by altering the oil pump position,giving most oil flow and therefore most cooling.
As for running the box constantly in reverse,there can be problems with some gearboxes and sometimes it is required to lock the shaft to prevent rotatation when being towed or running on one engine..
On this particular gearbox the "forward" raftio is 1.91.1 and the oil pump is positioned to provide maximum lubrication flow in this direction.A reduced oil flow is provided in reverse as this would normally only be for short period and less heat would be generated.
What would normally be "reverse" on this box has a 2.10.1 ratio and is used as the permanent forward drive by altering the oil pump position,giving most oil flow and therefore most cooling.
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coastwise
Well-Known Member
Nothing to do with "pitch issue", but you say you prefer inward turning props rather than the conventional counter-rotating outward turning on this boat. Why this preference on this boat?
Paul
Paul
Latestarter1
Well-Known Member
People here do not appear to be old enough to understand basic design of Borg Warner Velvet Drive gearboxes, you obviously do!
Having given me Metric not £ld prop shaft dimensions concerned me. Majority of second hand propellers on the market will not be Metric bored, yes you will be able to bore out 11/2 bored prop to 40mm but meat on boss may be marginal to go 45mm. Likewise you are looking for a right handed prop not the more common (single screw) left hand, you may strike lucky or get stuck by lightning.
How about some lateral thought, which requires some sweat but small expenditure.
Conventional wisdom is for outward turning propellers............They do not have to be. On on one repower I did the increased ooph caused vicious chine ride in certain conditions. Consulting some of the old boys from 60's power boat racing we came up with making set up inward turning props. Yes warned about handling changes, but it worked!
OK we do not have a planing vessel, however I did come across a technical paper from Australia discussing reserch into vessel noise in marine conservation zones which was clear that inward turning propellers were less noisy. Plus the fact that owner of the vessel changed to inward turning props was pretty relaxed regarding handling changes.
You obviously understand workings of your gearboxes, how about this for a wheeze. Switch lube pump orientation and props to make your vessel inward turning, leave props as they are for now, then suck and see. Cost of the exercise merely your grunt and quick lift to switch props.
Sorry to be pedantic, but did you take a look at Velvet Drive website? I still contend that you are 1.88:1 reduction.
Good luck.
Now my head is going around in circles!
I get it now..
#1 Switching sides will make zero difference you just take the wrong combination of reduction/prop to the other side of the vessel, am I being dumb or what.
#2 Against conventional wisdom you are already inward turning, which is why I suspect somebody screwed up props.
Sorry for confusing heck out of everybody. Just bite the bullett and spend £600 on a new prop.
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Rocksteadee
Well-Known Member
But does not one of the gearboxes run permenantly in reverse to provide for the anti clockwise prop?
If it is the positioning of the oil pump which designates whether the gearbox is a forward or reverse one....then couuld not the props be swapped and the pumps be changed and the orientation of the forward and reverse levers be changed.
I think I have not allowed for the question of would the ratios of each box stay the same or be swapped for forward or revese ratios
Have just read that back and it sounds like bo11ocks but I understood it
If it is the positioning of the oil pump which designates whether the gearbox is a forward or reverse one....then couuld not the props be swapped and the pumps be changed and the orientation of the forward and reverse levers be changed.
I think I have not allowed for the question of would the ratios of each box stay the same or be swapped for forward or revese ratios
Have just read that back and it sounds like bo11ocks but I understood it
Rocksteadee
Well-Known Member
Latestarter....you got that in whilst typing mine up LOL.....see my last post was not bo11ocks
Latestarter1
Well-Known Member
So was mine..see added talking rubbish.
Rocksteadee
Well-Known Member
It could be that this is already wrong and a new prop will be another error to counteract the first error to try to achieve a null errror
At 30 years old there could have been a few make believe engineers who only thought they knew what they were doing......pretty much like us LOL
We could be looking as curing the symptom and not the fault
Another scenario the gearboxes could have been removed and put back in, back to front.
with the props then being changed to counteract to try and equal the 2 compounded errors.....not quite equal as there is still an imbalance of prop ratio
So a new prop could be looking at curing the symptom and not the fault
At 30 years old there could have been a few make believe engineers who only thought they knew what they were doing......pretty much like us LOL
We could be looking as curing the symptom and not the fault
Another scenario the gearboxes could have been removed and put back in, back to front.
with the props then being changed to counteract to try and equal the 2 compounded errors.....not quite equal as there is still an imbalance of prop ratio
So a new prop could be looking at curing the symptom and not the fault
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vas
Well-Known Member
not sure I'm less confused now...
oldgit or LS1, am I right in understanding that the vessel has two IDENTICAL gearboxes, with different gear ratios on fwd and reverse?
If that's the case, then I've been talking bull, apologies.
V.
oldgit or LS1, am I right in understanding that the vessel has two IDENTICAL gearboxes, with different gear ratios on fwd and reverse?
If that's the case, then I've been talking bull, apologies.
V.
MapisM
Well-Known Member
Guilty as charged, your honour!
And thick as a brick, too. I still don't get how in practice a gearbox could/should change the reduction ratio depending on the rotation...
On the matter of inward vs. outward, I'm aware of various pros and cons of each choice (in no particular order: maneuverability - also if and when running on just one engine, stern lift vs. bow lift, chine walk as you're also saying, and ultimately top speed - I'm not surprised that racers suggested inward, in fact). But noise...?!? Geez, I can't get my head round that.
Anyway, I'm still curious to hear why the OP boat should "require" inward spinning props. Maybe because she was designed like that for some reason, and its rudders offset is consistent with that? Just a thought.
Latestarter1
Well-Known Member
Borg Warner Velvet Drives are a tad different to more modern designs, very efficient I might add due to epicylic not layshaft gears. BW72CR reduction box consists of conventional BW72C 1:1 box with reduction box on the rear. Unlike more modern gearboxes ahead is ahead and astern is astern you cannot alter that. On just one model, gearbox reverses engine rotation in ahead position with change to lube pump orientation.
Always worth considering BW71/72CR gearboxes in two halves, front end and reduction back end. Therefore 72CR 2.10:1 will always mirror engine rotation 72CR 1.88:1 reverses engine rotation.
Provided that you understand the BW concept and certain limitations they are real good boxes, and cost peanunts to repair.
Latestarter1
Well-Known Member
I AM suicidal now offset rudder hand grenade discussion has been lobbed in!