The addition of a compass to Olympic and Britannic

Bob_Read

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Early Olympic and Titanic had their standard compass mounted atop a compass platform amidships. After Olympic’s 1913 refit and in Britannic’s initial configuration, an additional compass was added on the roof of the navigating bridge. The amidships compass was retained on both ships. What was the purpose of the additional compass on the roof of the navigating bridge of both these ships?
 

Jim Currie

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Can't say for sure, Bob, but I can offer 2 reasons.

1: the standard compass on the top of the wheelhouse would have fewer induced magnetism errors and
2.: A standard compass on top of the bridge would allow the fitting of a periscope-type reflector viewer leading down to the steering position on the open bridge in front of the enclosed wheelhouse.

Thus the man on the wheel could view the standard course direct via a viewing mirror in front of his eyes. He would still have a steering compass but the error between the two would be very easy to ascertain.
These eventually became standard in every ship. They looked a bit like this.
1569864612650.png
 
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Bob_Read

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Hi Jim: I found a discussion in the ET forum archives primarily between David G. Brown and Sam Halpern and the question that couldn’t be answered was if the compass on the roof of the navigating bridge was more desirable as a standard compass then why retain the midship compass?
 

Jim Currie

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That's a good question, Bob. I can only guess that it was left there because it was less costly than removing it and perhaps they thought it might serve as an extra conning position in the event of a bridge fire or something. Just guessing.
 

Bob_Read

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Hi Jim: Speculation is about all anybody has been able to come up with. David G. Brown has a novel theory that I can’t buy but beyond that it remains a mystery.
 
Mar 22, 2003
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The only reason they had a compass on an amidships platform was that it was thought to have less deviation error than any other location. The funnels made that location not too desirable for taking bearings looking forward, and the amidship's compass still had some deviation error that needed to be compensated for. Then there came the gyro compass which gave true headings. They still had a compass comparison book for Olympic where they recorded steering and standard compass reading against the gyro readings. If I recall, heading entries were recorded about every 4 hours.
 
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Bob, are you asking if they had a gyro compass why would they have a standard magnetic compass? Or, are you asking if they had a standard compass amidships why have another standard compass on over the navigating bridge?
 
Mar 22, 2003
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OK, thanks for the clarification.
The compass added over the wheelhouse was a 10-inch Kelvin patent standard compass, same as amidships. Standard compasses were equipped with an azimuth mirror to take stellar bearings. My guess, as was Jim's, is that the amidship's compass was left as a backup, being more costly to remove it.
The advantage of placing the "standard" above the wheelhouse was that it eliminated the clumsy push-bell signaling used when steadying the ship by standard. Course laid out were always done so by standard, including when heading down channel waters. When turning onto a new course heading the ship needed to be steadied by standard. When done from the amidship's platform it used that push-bell method with required the officer on the platform to signal the bridge in a similar method used by the lookouts on the bell in the nest, 1-bell to turn to starboard, 2-bells to turn to port, 3-bells when on-course straight ahead. It was clumsy method and took some time to do.
 

Bob_Read

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Hi Sam: I could maybe buy your Olympic explanation if it weren’t for Britannic. Both compasses were installed on her from the start and both were planned for RMS Britannic according to her Specification Book. Do you buy David G. Brown’s contention that the midship compass was left so as not to raise suspicion that the midship placement of the standard compass was actually the cause of the collision with the iceberg by Titanic?
 
Mar 22, 2003
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Do you buy David G. Brown’s contention that the midship compass was left so as not to raise suspicion that the midship placement of the standard compass was actually the cause of the collision with the iceberg by Titanic?
Just saw this Bob. My simple answer to your question is, no, I don't buy that.
 
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Sajm, I suspect you don't buy my vuew ihaving two standard compasses as preposterous from the point of view of seamanship or navigation simply because I said it. But, you can't defend two standards by referring to standard nautical practices. So, why leave the platform compass? My hypothesis is based on the very real problem of tort law, even under Admiralty Law. Truth is the first victim when something is argued in court -- so why not leave the redundant old standard compass in place to avoid the stupidity of the legal profession? Just hunch on my part, but it certainly was not done for safety at sea.

Somebody else suggested it may have been left in position to save the cost of removiing it. This implies that buying a new binnacle and accompanying compass instrument. This iopposed to unbolting a full working setup and carrying it about 250 feet forward to the roof of the officers quarters. An, then removing the platform for the high scrap value of its non-magnetic parts.

Sometimes the best way to hide something is in plain sight.

-- David G. Brown
 
Mar 22, 2003
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Or perhaps, David, the amidships location was thought to produce less deviation error that other compasses could be compared to, thus being 'the standard compass' on the ship, while placing a compass on top of the wheelhouse made the job of steadying up much easier, and gave an almost an unobstructed view when taking compass bearings ahead.
 

Bob_Read

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Would a telephone between the compass platform and the wheelhouse interfere with the accuracy of the standard compass on the compass platform?
 
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It is still difficult for me to type. My new eyeballs have not been delivered yet from the Far East.

Anyway...in order of postings...Sam, please you're embarassing yourself. As a scientist you know that measurements must be made to the same standard. For example, when woodworking I use one and only one rule for all of my measrements because no two tapes or rules are exactly the same. That carryies over to the mariner's compass. No two give exactly the same reading on all headings. It wuld have been against sound nautical practices, IMM?WSL rules, and even some lregulations to do what you suggest in 1912. There was on and only one "standard" instrument against which all others were compared.

Something else. TVMDC or CDMVT -- math compass corrections would have had to be computed for both compass to even attempt what Sam suggests. That's doube the work with double the chance of error.

Next, I want to assure Bob Read that I most certainly do hold to my theory that the placement of the standard compass played a role in the accident. My thoughts are more refined now and some of my ideas have been discarded in the process. But, yes, I do stand by what I've written as of the date of publication. Whe I can see the keyboard again I'll ibe glad to go into detail.


LDoug Criner --- I see the accident as a result losss of situational awareness brought on by some outdated bridge team management pactices. Of course, in 1912, these concepts were not yet developed. Captain Smith almost certainly had never heaard of either or how they are intertwined. Not his fault. He had never heard of computers, cell phones, or McDonalds, either.
.

Thats it for now. More anon.

-- David G. Brown


PS -- I go by "Dave." The use of my name is a feeble attempt to avoid confusinn with all the other "David Browns" in the world.
 

Bob_Read

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One thing I do agree with Dave about is that there can only be one standard compass. It is the standard to which other compasses aboard are adjusted. There are a number of things I want to set forth as what I understand. If I am wrong then I welcome correction:
1. I can possibly understand the designation of a standard compass on the wheelhouse roof of Olympic which would render the midship compass to an unknown role.
2. What I can't understand is that while the change in compass locations on Olympic was a retrofit, the same cannot be said of Britannic.
3.While Britannic was being planned for mercantile service, her Specification Book lists both a wheelhouse roof compass and a midship compass.
4. This Britannic compass configuration can be confirmed by photos of HMHS Britannic.
5. It is obvious that the wheelhouse roof placement of a standard compass would be more convenient.
6. It is most likely that the midship standard compass location would have the least magnetic interference.

These observations still don't explain why if the wheelhouse roof compass was the standard compass then what purpose would the midship compass serve? The opposite statement would also hold true. Attached are two entries in the Britannic Specification Book. The one specifies all compasses aboard but does not designate which would be the standard compass. Another interesting side note is the description of the midship compass platform. In the Shipbuilder journal for Olympic it describes the compass platform as "brasswork". In the Britannic Specification Book the compass platform is described as galvanized ironwork.



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compasses Britannic specification bookb.jpg


compass platform2b.jpg
 

Jim Currie

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The Mid-ship position was all to do with induced magnetism.
A ship, if constructed with ferrous metal, is actually a giant magnetic needle which is usually constantly changing its orientation withing the earths magnetic field. The earth's field induces magnetism into the hull.
Would a telephone between the compass platform and the wheelhouse interfere with the accuracy of the standard compass on the compass platform?
Yes, unless the cables are led in a specific way.