Sandcasting a Propeller

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JK
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Sandcasting a Propeller

Postby JK » Wed Feb 17, 2016 6:44 am


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Merlyn
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Re: Sandcasting a Propeller

Postby Merlyn » Thu Feb 18, 2016 2:36 am

Interesting article, took me back a long way to the start of it all. On the firms slipways as a boy with a fitter, stripping out all stern gear and one bolt out of every skin fitting for electrolysis checking. All to be inspected by a surveyor and renewed as necessary. How to remove props on yachts and gunboats/ torpedo boats without the use of extractors and oxy/Acet. Dolly the boss and many , many careful hammer blows to the opposite boss and ensure the back nut was on a few threads to ensure when it did let go it didn't launch itself down the slipway and into the water when it let go. Some of the more difficult ones would sometimes go off with a bang like a shotgun being fired in your ears. Oh, and don't lose the key. Being told why the shafts were allways offset to the rudders? Ping the blades, if a dull dead sound job scrap. Catholic protection failure example here. I well remember straight ing the blades and grinding out damaged areas and using mini flux A rods attempting to braze the damaged areas, impossible on non pinging/ dead equipoise blades no matter how long you tried. A nice resilient ping was a good prop. Still got some at work now. Making up special extractors to change a damaged cutlass bearing without drawing the shaft. Recutting damaged prop key ways on the shaper machine, milling out the shaft and making up an oversize interference key to fit. Making up new castellated locknuts from octagonal brass metal, learning to recut tapers on new shafts etc and making sure contra rotating shafts had to have a correct rotation thread cut on it is L/H thread cut for anti-clockwise shafts and R/H threads for clockwise shafting to ensure both shafts were self tightening in normal use age. Some installations were both clockwise and some were handed. Ahead of the balanced rudders to counter the torque effect generated by same way rotation shafting sometimes would be on the top of the rudder a small trim tab bolted onto the rudder to counter the Starboard pull encountered on the wheel. Sometimes this would have to be " tuned " so the wheel stayed straight ahead, hands off at max speed. Measuring electronic leakages and slip ring performances etc on prop shafts concerning Cathodes and Anodes protection. No Anzipods here yet, not a lot of thrusters, no surface props, submarine props removed using PE ( plastic explosive ) but I never had a chance to get involved in any of that. So why were rudders always offset to shafts?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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JK
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Re: Sandcasting a Propeller

Postby JK » Fri Feb 19, 2016 2:32 am

Howboldts is a company I always enjoyed working with. They build and supply winches, cranes as well as other hydraulic systems. They balance and refurbish props. It is always a fascinating shop to visit.

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Merlyn
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Re: Sandcasting a Propeller

Postby Merlyn » Sat Feb 20, 2016 12:13 am

So come on then JK, offset rudders? Can't just be my secret since 1960. Straight off the top of your head mind, no cheating here.
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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JK
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Re: Sandcasting a Propeller

Postby JK » Sat Feb 20, 2016 5:22 am

All our older ships were. The oldest ship, you could see the props looking down over the stern. The newer ones not so much. I think that tells me more about your age Merlyn!

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Merlyn
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Re: Sandcasting a Propeller

Postby Merlyn » Sun Feb 21, 2016 3:18 am

Still running on all six ( so far ) But the offset rudders theory holds true today as it did then. So why are they offset? Back to Pounders for you methinks? More hours on my hour meter means I have drunk more beer than you perhaps?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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Merlyn
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Re: Sandcasting a Propeller

Postby Merlyn » Sun Feb 21, 2016 3:25 am

More hours on my total time run hour meter = I have drunk more beer than you, but the question remains unanswered " why are a lot of rudders offset to the shafts " ? Back to Pounders for you methinks. Can you remember by looking at a prop whether it is R/H or L/H?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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Big Pete
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Re: Sandcasting a Propeller

Postby Big Pete » Sun Feb 21, 2016 11:41 am

To counter the "prop walking" effect.
I remember reading about some tugs with Father and Son engines. The idea was that the small engine would be used for cruising and both engines for a heavy tow.
In order for the tug to steam straight the smaller engine, driving the smaller prop, was further from the centreline than the other engine and prop, and both shaft lines were slightly angled from the centreline so that the tug would naturally steam in a straight line under all conditions and combinations of engines.
BP
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Merlyn
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Re: Sandcasting a Propeller

Postby Merlyn » Mon Feb 22, 2016 8:32 am

Nope. Shades of T.T.T.T. Coming up here?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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Merlyn
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Re: Sandcasting a Propeller

Postby Merlyn » Tue Feb 23, 2016 12:43 am

image.jpeg
image.jpeg
Looks like I may be online for yet another One of Martins Stomper Medals with this one. Just took a couple of photos which if you look closely will virtually tell you why the rudders are offset. It's a 33 foot power boat we have in for a winter refit. It's a deep vee planing hull and a superb sea boat in the rough. You can clearly see from the two leading edges of both props that they are both right handed. The small trim tab on each rudders leading edges removes the torque generated . Easy boat to prop walk once you get the knack. Both rudders hard a port, one engine slow astern, one slow ahead and keep changing the configuration and in she goes. So why is it offset?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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JollyJack
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Re: Sandcasting a Propeller

Postby JollyJack » Wed Feb 24, 2016 9:45 am

The paddle wheel effect of the props (both are right handed, as you point out) will cause the stern to move to starboard, the rudders, offset to port, should correct that tendency.
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Merlyn
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Re: Sandcasting a Propeller

Postby Merlyn » Wed Feb 24, 2016 12:29 pm

Yes, but note the rather large trim tab on the trailing edge of the Stb.rudder cranked over to Stb. which virtually wipes out any torque effect on the wheel. It's cranked over to Stb. to enable you to have a hands off situation throught the rpm range and indeed astern. Whilst it true what you say the million dollar question still remains. Why are these rudders offset? The picture tells you? Think maybe of a stern gear overhaul?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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Merlyn
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Re: Sandcasting a Propeller

Postby Merlyn » Wed Feb 24, 2016 12:51 pm

Further thoughts re the mark eights J.J.? Did this apply to them?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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JollyJack
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Re: Sandcasting a Propeller

Postby JollyJack » Thu Feb 25, 2016 8:03 am

No, the rudders were on the shaft centre lines.
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Re: Sandcasting a Propeller

Postby JollyJack » Thu Feb 25, 2016 8:04 am

Mark VIIIs? Christmas, that's going back a bit! :) I was still squeezing plooks in these days!
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