Comments by "Keit Hammleter" (@keithammleter3824) on "Titanic's Propeller Mystery" video.

@rrice1705 Ocean Liner Designs reused old footage. We told him he got it wrong the first time he used it.
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@alfascav1754 You must have been at a dodgy university. I am an engineer. Been a competent engineer for decades. I am not a designer - I have practically no design ability. An aspect of this that is well known by the general public is building construction. You need an architect to do the design - that is, devise how the building will look (be attractive), how it will function (don't make the kitchens a thoroughfare ) and you need engineers - electrical, hydraulic, civil, to do the engineering calculations to ensure the building is safe and won't catch fire or fall down. An architect can't do an engineer's job and vice-versa. My university degree is in electronic engineering. That means for example, I can work out the circuit of an amplifier and calculate the specifications of all the parts so it will work efficiently and not break down a lot. But not the design - the exterior styling, making it look up to date vis-a-vis fashion, ergonomics of the user controls, etc. When I went to university, us engineering students mainly used 3 buildings devoted to engineering. About a 100 metres away was the Art and Design building, where the industrial design students did their thing.
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@paulroberts3639 That would mean leaving an oil slick behind everywhere the ship went, and continually pumping out oil when tied up in port. No way that would be accepted.
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Mike omitted an important factor with regard to vibration: Whenever you have 2 or more propellors, you get propellor beating - pressure changes in the water as a blade of one propellor sweeps past/near a blade of the other propellor. There are three ways of addressing this: 1) separate the propellors laterally - there is limited scope for this on a big ship, especially if there are three or more propellors; 2) separate the propellors longitudinally (ie at different distances from the stern) - this reduces hull volume at the rear of the ship, which is not a good thing; 3) fit different numbers of blades, eg 3 on the outboard props and 4 on the inboard. I gather that Mike's conclusion that Titanic had a three-bladed centre prop is really solely based on a single digit in some engineer's personal notebook. This is not good research - it could be just an error by that engineer, we have no way of knowing. Mike said that the H&W engineers could have been doing a comparison experiment with the two sister ships but this does not make much commercial sense. An engineer would seek to come up with the best configuration he can, and that won't change until one of the ships completes sufficient voyages to show up a problem. An engineer would be risking his job if he was seen to intentionally make one ship inferior to the other, as must be the case if they are different. Sure, ships got their props changed back then (in pleasure boats today they still occasionally do) but in response to an encountered problem that needed addressing, not on speculation
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@journeyman_philosopher I certainly did watch Mike's video. I did not say he's definitely wrong , I said that he drew conclusions on very thin ice. The only reference I could find that Titanic had a three-blade centre prop is the same one Mike quoted - that engineer's notebook. The only reference I could find that H&W were experimenting 4-blades vs 3 blades is a discussion on a Reddit forum about Titanic - hardly a reliable reference. I think you are misunderstanding the engineering of propellor specifications as it was back then. Sure, it was rule of thumb methods rather than finite element fluid dynamics, but they weren't stupid. Considerable experience with propellor applications had been built up. I've worked for a marine engine dealer - we used much the same methods to match props to hulls and engines - and got it pretty right nearly every time if the hull people got their bit (hull drag) right. (Props are like gears in a car - you must have the right prop blade angle etc for the ship's speed through the water, just as you need the right gear for the speed you are doing in a car.) But sometimes the hull guys got it wrong, and they sometimes did back in Titanic's day too. When that happened, propellors got changed. Incidentally, be aware of why professional engineers keep personal notebooks. These are the main reasons (then and now):- 1. Professional associations require the production of notebooks as proof of experience when granting corporate memberships;. 2. Source material for updating one's CV and job applications;. 3. In the event of a patent dispute or getting sued for infringement, a notebook can be presented in court as evidence of prior art; A high level of accuracy is not required; indeed, some young chaps don't bother with a notebook until they have to produce it, and then spend a couple of evenings writing one, trying to remember what they did in their earlier years.
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@gokulgopan4397 But back then there was only 2 kinds of test they could do: a) try a configuration out in a ship, which may need several or many voyages to get enough data on various sailing conditions; or b) tank testing. Tank testing has serious limitations, due to the need to scale the dimensions and velocities, coupled with the effects of Reynolds Number being non-linear. All this means that for any given ship, they could get things a bit wrong, realise it from either excessive fuel consumption, excessive or too low engine RPM for a given hull velocity, or excessive vibration, or any combination of these three. If so, they could decide to try a different propellor, making an informed guesstimate as to what difference(s) the new prop should have. If the new ship is very different to what the shipyard had built before (eg twice the displacement through increased length) there is obviously more scope to get it wrong. But to launch two identical ships into commercial service with different propellors in order see which one works best - I don't accept that. Its just not a way to get the company manager's respect. You do your calculations (rule of thumb) and the answer is the answer - the best you can do, uncertainty notwithstanding. If you launch the two ships with different propellors - you know that there is 100% certainty you are going to have to dry dock one of them early at huge expense and loss of revenue. If you launch 2 ships with your best idea of what the props should be, it will more than likely never be any need to early drydock one of them.
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@journeyman_philosopher Mike provided only one example of two identical new hulls getting different propellors as an experiment to find out which prop was better - the Titanic and Olympic, which might or might not be truth. What is known beyond doubt is the photos showing a 4-blade prop are of Olympic or Olympic's prop. There are no known photos of Titanic's prop, so we just don't know. Olympic got dry docked and a shaft intended for Titanic fitted due to collision damage, and also had a propeller change due to having lost a blade. Can you give a reference that states they were experimenting, as distinct from fitting what was quickly available and through that fortuitously discovering that 4 blades on the centre prop was better (which of course confirms they got it right the first time)? From ordering to delivery, the time taken to obtain a large ship propeller was around two months or more. Leaving a damaged ship out of revenue service that long just for a propeller is something not to be countenanced. Use what you have if it is roughly right. Order the correct propeller and fit it when it arrives - that takes only a day or so. Can you give an example of two identical ships (other than Olympic Class) launched with different propeller specs for test purposes? I think not.
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@journeyman_philosopher No, I don't know the answer. Nobody alive does. That's my point. The centre prop might have been 4-bladed, it might have been 3-bladed. Thorough digging turns up lots of leads - books, YouTube videos etc, but they all lead back to that infamous engineer's notebook. Take that dubious source away and you are left with pure speculation.
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