Ouestion from a second class exam just completed.

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Ouestion from a second class exam just completed.

Postby Jason » Tue Mar 27, 2012 4:30 pm

This question comes from a second class general knowledge exam that i wrote, I was hoping someone can help me with the answer.

Question: Describe how you would go about fitting a blade to a propeller and adjust the pitch?

I have never seen this done or seen it in any text book.

Also i was wondering what to expect on the second class oral exam.

Thank you so much, any help well be great.

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Re: Ouestion from a second class exam just completed.

Postby JollyJack » Wed Mar 28, 2012 11:10 am

Sounds like General EKs. It must refer to a CPP Prop, where each individual blade of a built-up propellor is bolted to the propellor hub on a rotatable boss. The ones I have seen are all fitted bolts and dowels, don't know if you can adjust the pitch unless you can rotate the boss independently, but there are stranger things in heaven and earth....... However, you can check it by using a sprit level, a piece of string weighted on both ends, a measuring stick and a calculator to solve the formula tan alpha = AB divided by BC, where alpha (ACB) is opposite AB and angle ABC is 90 degrees. Angle CAB will be 180 - (alpha +90). You'll need a ladder or a manlift, too, get up to the prop blade.

Was this a recent exam?
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Re: Ouestion from a second class exam just completed.

Postby Jason » Wed Mar 28, 2012 4:28 pm

thanks a million Jack. This question was on a general knowledge exam that I worte about six weeks ago. I didn't attemp this question because i had idea about it but not 100%, I was more comfortable with answering the other questions. I'm getting ready to go wright my orals soon and was thinking that the examonier may throw this question at me.

Thanks again,

Do you have any advise for the orals??????

Jason

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Re: Ouestion from a second class exam just completed.

Postby JK » Thu Mar 29, 2012 1:40 am

Advice for the orals: remember to breath. You have studied everything you can and worked as hard as you can to get there. You can't control what the Examiner will ask, so try to stay calm and relaxed. I know, easier said then done.
I always wrote down the questions as soon as I got out of the exam and then went over the questions I didn't answer.

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Re: Ouestion from a second class exam just completed.

Postby JollyJack » Thu Mar 29, 2012 3:54 am

Going over what you didn't answer in EKM and EKG might be a good idea. Safety topics are quite important too, most deaths at sea are in confined spaces, so make sure you're covered for confined space entry. I was grilled (and I mean GRILLED!) on what to do in an engine room fire. ("That didn't work, NOW what do you do?" "Fire's getting bigger, where are your people?" "Hydrant's stuck, the 3rd hasn't checked it" "No grease on the vent flap hinges or butterfly nuts, WHAT DO YOU DO??") Keep in mind that heat damages wiring and electronic gizmos, so does water. Engine rooms have CO2 systems for a good reason!

SAFETY is Priority 1, especially as a 2nd Engineer, where you have the responsibility of your people as well as that of the Mechanical Gardens.

Did you have heat treatment of steel in your exams, hardening, tempering, annealing etc? You might get it in Orals.

Most importantly DO NOT BULLSHIT! The Examiner is a better bullshitter than you'll ever be, that's how he got to be an Examiner. If you don't know, say so, but don't play dumb, either. Orals give you a chance to correct any errors you made in the written papers. In EKG, I was asked to sketch and describe an instrument for measuring the density of brine and indicate the units on the scale. Well I sailed on reefers as 4th and 3rd for years, I knew all about a Twadle meter! Did a lovely sketch of it. When I got to Orals, (in Victoria) I was asked what happened when I added Calcium Chloride flakes to the brine. Did the meter go up or down? A horrifying realization hit me like a bucket of ice water, I had drawn the scale backwards! As soon as I said that, the Examiner smiled and said OK.

In Orals, as in the written exams, remember the K.I.S.S. principle. As this point, the last stage before the Certificate, it's more about what you've done than about what you've studied. The toughest Oral I ever did didn't contain one question. The Examiner just chatted about the job, (as Engineers are wont to do) talking "shop", discussing this and that, swapping experiences, telling sea stories. I didn't realise at the time (I thought he was being nice and putting me at ease), but I was being filleted! Bullshit may baffle brains, but don't think that in the Orals room, you're not in the same bullshit league!
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Re: Ouestion from a second class exam just completed.

Postby Jason » Fri Mar 30, 2012 8:53 am

thanks once again jack, you've been a great help. I wrote my exams in corner brook newfoundland but there going to st. John's to get correct. I was talking to them today, its almost two weeks I wrote my exam and they said that it won't be until next friday before its done. I think its a bet much but I guess that all you can do.

Thanks once again.

Jason.

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Re: Ouestion from a second class exam just completed.

Postby Big Pete » Mon Apr 02, 2012 3:02 am

Some CPP hubs have witness marks on the Hub and the blade Boss to indicate where zero pitch is.

Some large fixed pitch props also have bolted blades. I remember a few years ago Stone Manganese Bronze wanted Government subsidies to maintain a capacity for casting large fixed pitch propellers in the UK. The bean counters said no, they could buy prop castings from anywhere in the world
Next large prop they needed for a warship they ordered the castings from Poland, to be machined in the UK, every casting was flawed and had to be rejected, in the end they had to use built props. Larger boss, less efficient and noisier than a one piece prop, not good for anti submarine warfare.

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Re: Ouestion from a second class exam just completed.

Postby JK » Mon Apr 02, 2012 3:12 am

yes, the last stone marine propellers we bought were cast in China. Meanwhile our molds are lost somewhere in Montreal after the Stone foundry closed there.

We had a CPP propeller that vibrated the stern of the ship terribly. Brought the ship in, docked her, took the blades off and sent them for balancing and a pitch check. Not a thing wrong. Put them back and vibration gone. Still not quite sure what was wrong to cause the vibration other then the installation was faulty. Everything looked good when the blades were taken off.

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Re: Ouestion from a second class exam just completed.

Postby jimmys » Tue Jun 26, 2012 10:50 am

I did not notice this question till recently and off course to repace a blade or part of a blade you would use the burn on technique. The casting of a propeller only needs the pattern for one blade and the hob. The whole propeller is swept in to the mould. When you need a blade the blade pattern is available. The burn on technique means you heat up and cast a joint at the point of blade fracture. The pitch is always set finally by grinding and material is left on the blade for this. Procedures mentioned before are used to grind the propeller.
Old technique now forgotten with CP props but widely used in the sixties.
regards

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Re: Ouestion from a second class exam just completed.

Postby JollyJack » Tue Jun 26, 2012 5:45 pm

Thanks Jimmy, seems to me that stirs some long-forgotten memory in a dark recess somewhere :)
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