Princess crashes into Richmond Bridge

[Richard Shead]

To be fair there have been others....

http://en.wikipedia.org/wiki/Richmond_Bridge,_London



This was Sir Donald Goslings Brave Goose being launched and just before she got stuck under the bridge.

 

[rafiki_]

Firstly, just like to say 100% agree with Hurricane, and as an owner of the same boat an excellent judge!

Just reading Uricanejack first post on the subject, he mentions that he does not come on the Mobo forum much, having a quick look and the chap seems to reside mostly on scuttlebutt, therefore my assumption is he's got a sailing boat. Now having sailed a little bit there is an incredible difference between how a motorboat reacts to steerage when engine is in neutral compared to a sailing boat. Took me by surprise when I first turned to motor... But for the simple reason as shown below comparing my rudder with my parents boat.....size is everything! Giving him the benefit of the doubt perhaps Uricanejack has not indeed helmed a large... or even small motor boat to experience the difference.

The keels on sailing boats also make a big difference to stability.

 

[kcrane]

Good point.
What has been said so far remains valid in principle, but if the min speed (mind, in reverse, if you make the attempt bow first, as more logical - and 5kts sounds like a helluva minimum reverse speed!)

I've never checked what speed I go backwards in idle Assuming higher water resistance and less efficient props (is that true?) then maybe 3knts?

Aside from the obvious one, i.e. not attempting the maneuver at all, as already suggested.

+1 Seconded

 

[MapisM]

Assuming higher water resistance and less efficient props (is that true?)

Yes it is. And on top of that, the gearbox ratio is normally deeper in reverse.

 

[kcrane]

Yes it is. And on top of that, the gearbox ratio is normally deeper in reverse.

I forget about gear ratios, I think of it just being the forward/back lever... sad I know

 

[jfm]

Uricanejack
Your post #124 treats rudders as though they are a constant item, the same from boat to boat. They aren't: fine pitch props/big rudders is a completely different thing from what we have here which is coarse props and tiny rudders. Your post 124 reads as though you have experience in boats with fine props and big rudders, and in that scenario I fully agree what you say (my brother has an 8 knot TSDY, displacement, and he/I drive it exactly as you describe).

However I specifically said in my post that the P67 (like any 30knot P boat of its genre) has ultra coarse props (40-50 inch at 300rpm in idle mode), and it also has tiny rudders. My comments were stated to be specific to that scenario

The coarse props create huge sideways forces (bigger than any sternthruster, and I've never specced a P boat to add a stern thruster) and the small rudders you have on such boats do almost zero in comparison.

Your comments about flow of water over the rudders don't change that. The rudders on a P boat are so tiny that the ~5 knot water flows we are talking about here result in forces in the order of a few hundred newtons on a good day. Absolutely nowt compared with the side kick from 45P props. It would be totally different on D boat with fine props and big rudders. BTW, on a P boat you do get rudder forces in reverse as well as forward, contrary to what you said, because in reverse a big prop close to a tiny rudder induces most of the flow over the rudder that you would get when running forwards

Above you wrote "If you use your rudder's you can parallel park a twin screw vessel equipped with a BP." I absolutely assure you (having owned as self driver of this type of boat for 15 years) that you can move a P67 and any boat of its genre perfectly sideways using just the two props and the BP, leaving rudders amidships. Using or not using the rudders adds/subtracts nothing material. You comment relates to an entirely different type of boat from this one

So we're in full agreement, for the type of boat (I think) you had in mind! Best wishes (and welcome to the mobo forum! Please stick around. It has a different character from scuttlebutt )

 

[jfm]

I'm trying to imagine actually doing the "reverse through the bridge" manoeuvre. I think you are saying that, if you are in a river running at 4knts, and you drive forward into that stream at 3knts then the bow isn't going to fall off any more than it would if you were in still water driving forward at 3knts. The difference between the two is that in one case your speed over the ground is -1knt (hopefully reversing through the bridge) and in the other it is +3knts. The bow of the boat doesn't 'know' the difference.

I can intuit that quiet easily, and it is intuition I need when driving a boat as I'm too slow to work it out from first principles when I panic

So, I'm sliding the boat back by driving forward slower than the speed of the stream and I'm getting close to the bridge, wondering if I will fit underneath. The trouble is my boat drives forward at 5knts in idle, so I'm having to slip in and out of gear to do less than 5knts, so my speed is varying, as I can't provide a steady power source. Once near the bridge I keep the power on for longer to go ahead slightly faster, up to 4knts, to slow while I check the gap. The boat is now going to act as though it is going forwards at 4knts.

If I start juggling the throttles to try to move left or right I will likely move the boat out of line with the stream, and a 4knt current will catch one side of the bow or the other. Um, not sure I like the sound of that. I think, again intuition, that I'd hold the boat in the stream on both engines, but try and move left and right with bow & stern thrusters working together. They couldn't hold me against the stream, as the P67 discovered, but they would move me left and right. I wouldn't be in a hurry to touch the wheel, something I never do when manoeuvring.

The above just me pondering how it could work, truth be told I wouldn't risk that bridge in that boat in those conditions.

K, the mind plays tricks. Imagine this daft scenario:
1. You are in flat water in the med. No wind, no current, bliss
2. You're doing 4 knots SOG and STW at idle speed in a twin shafts boat, steering manually or a/pilot set to 1 foot XTE in a straight line, easy peasy.
3. After an hour, strangely you see a big fibreglass bridge replica floating in the sea behind you. Perfect replica of Richmond bridge. This bridge replica is driven by multiple pods and a computer and military grade GPS and is driving (sort of sideways as it were) towards you from astern in a perfect straight line, at 4.5 knots SOG. As it gets close you notice by coincidence it is following same ground track as you. If you do absolutely nothing and hold your course, the arch of the bridge will pass right over you at 0.5 knots relative speed and you wont collide. What fun you think! So you hold your course

In this scenario, would you lose your bow? Of course you wouldn't. You haven't lost it in the last hour so why should you lose it now?

I think you're on same page as me so far. But then we come to your 2nd last para:
If I start juggling the throttles to try to move left or right I will likely move the boat out of line with the stream, and a 4knt current will catch one side of the bow or the other. Um, not sure I like the sound of that. I think, again intuition, that I'd hold the boat in the stream on both engines, but try and move left and right with bow & stern thrusters working together. They couldn't hold me against the stream, as the P67 discovered, but they would move me left and right. I wouldn't be in a hurry to touch the wheel, something I never do when manoeuvring.
Actually in real life as you cruise in a straight line you are correcting the steering by tweaking the rudders (or prop/thruster kicking). As you do that, the stern of your boat is pushed (if using rudders) slightly left or right all the time, as these constant tiny corrections are made. You don't usually notice it but you need in my scenario about about a foot of water each side to allow the stern of a P67 to nudge left and right and hold an overall straight line coarse. IF you were driving a 5m beam boat in a 5.1m wide canal you wouldn't be able to nudge the stern left/right or rotate the boat and you WOULD then lose the bow, but that isn't the scenario here because there is some width clearance under this bridge.

So answering your question, you are close to the bridge at 0kts SOG and 4kts STW and you decide you are out of line and want to move leftwards. If using rudders (though prop kick and thrusters would have same effect; you choose which to use) you nudge the steering wheel left momentarily then re-centre it (you do that by intuition), This makes the boat turn a/clockwise viewed from above, let's say by 3 degrees. Re-centring the wheel makes it hold that 3 degrees. You're now out of line with the current and you're question is, will I lose the bow? No you wont! Your stern has moved a foot to the right and your bow a foot to the left to create that 3 degrees, but you are still doing 4kt STW (ignoring cosine effect of 3 degrees!). The boat will simply ferry glide to the left, which is exactly what you wanted. When the boat reaches the centreline of the bridge arch you nudge the steering to the right and rotate clockwise 3 degrees, then you're all set.

My point is that this is EXACTLY how you drive a boat in a straight line. If there was a white line painted on the sea and you wanted your keel to follow it at 4kts SOG (or any speed for that matter) you'd be constantly kicking the stern (if using rudders) left or right to follow the line (and the bow would be kick t'other way, because the boat rotates clockwise/anticlockwise about a turning point midships somewhere). It might not occur to you, but that's what the steering wheel does. If you were 1 metre to the right of the white line you could easily get back onto the line by micro adjustments to the wheel that you wouldn't even think about because they'd be so intuitive, and AT NO POINT WOULD YOU LOSE THE BOW!

This is textbook because in the real Richmond bridge there are sideways forces and eddies and stuff, none of which should be a match for a pair of 45x45 props btw, but I'm just answering your question

 

[John100156]

I think Hurricane summed it all up perfectly well and having crewed for him when maneuvering his P67 into what is a tight boat hoist slot (for that size of boat) in SCM, albeit with less tide but more wind, I can tell you he really knows how to handle this boat. I have learned a lot just from watching him!

On my F43, I am fortunate enough to have both bow and stern thrusters, the BT is smaller but with less grip in the water quickly brings the bow over, the ST is much larger but takes longer to move the stern, for obvious reasons. Blooming useful as with either throttle and using either the BT or ST you have two speed options to move the boat almost sideways, although sometimes you can spin the throttles and use either BT or ST and move perfectly sideways, depending on conditions of course. The rudders are of no use whatsoever even on my F43 at less than 5k unless, as has been said, occasionally to encourage a tighter turn.

Its a real shame that this beautiful boat got damaged but it will be repaired soon I am sure, the skippers pride may take longer to repair but it shouldn't. So what have I learned so far? Oh if only he had backed out a little further, hung on the props, gathered his thoughts and tried again!

I am a great believer in taking it slow and easy and if in any doubt whatsoever, just pull out, relax and start again! I could not give a jot about onlookers, if they think its easy let them try! Its my boat and I will do precisely what I want with it! It also bugs me when people are reluctant to use BT and ST - I agree, you should not over use them because you don't want to drain batteries but why the heck have them for if you're embarrassed to use them? Great bits of kit IMO.

Now a question: When the P67 was stb on to the bridge, which would be the best manouvre to pull her off: 1)port forward/stb astern and BT to port keeping props safer or 2) stb forward/port astern and ST to port? Which would produce the most sideways power/movement - I would probably have selected 2) on my boat using the engines to power the bow over and dropping port to neutral if the bow came over to fast and to keep the props away from trouble?

 

[Uricanejack]

+1 No offence intended to Uricanejack but he's obviously never driven a twin engined planing hulled boat

None taken, though it would appear I might have given some or at least ruffled a few feather's, not my intent. just a difference of opinion.

As predicted by someone else my own boat is a smaller sailboat 35ft fin keel no skeg and quite different.
I have driven lots of different types sises and propulsion system vessel's, mostly displacement. In addition to my sailing vessel I also own a small planning hull mobo for fishing, it is twin screw but no rudders and the 2nd screw is just a kicker for trolling.

As I stated I'm not familiar with Princess. I have run other planning hull vessels most had legs one had jets both quite different and the closest would be semi displacement with props and rudders.
I found them use full.

 

[Uricanejack]

Uricanejack
Your post #124 treats rudders as though they are a constant item, the same from boat to boat. They aren't: fine pitch props/big rudders is a completely different thing from what we have here which is coarse props and tiny rudders. Your post 124 reads as though you have experience in boats with fine props and big rudders, and in that scenario I fully agree what you say (my brother has an 8 knot TSDY, displacement, and he/I drive it exactly as you describe).

However I specifically said in my post that the P67 (like any 30knot P boat of its genre) has ultra coarse props (40-50 inch at 300rpm in idle mode), and it also has tiny rudders. My comments were stated to be specific to that scenario

The coarse props create huge sideways forces (bigger than any sternthruster, and I've never specced a P boat to add a stern thruster) and the small rudders you have on such boats do almost zero in comparison.

Your comments about flow of water over the rudders don't change that. The rudders on a P boat are so tiny that the ~5 knot water flows we are talking about here result in forces in the order of a few hundred newtons on a good day. Absolutely nowt compared with the side kick from 45P props. It would be totally different on D boat with fine props and big rudders. BTW, on a P boat you do get rudder forces in reverse as well as forward, contrary to what you said, because in reverse a big prop close to a tiny rudder induces most of the flow over the rudder that you would get when running forwards

Above you wrote "If you use your rudder's you can parallel park a twin screw vessel equipped with a BP." I absolutely assure you (having owned as self driver of this type of boat for 15 years) that you can move a P67 and any boat of its genre perfectly sideways using just the two props and the BP, leaving rudders amidships. Using or not using the rudders adds/subtracts nothing material. You comment relates to an entirely different type of boat from this one

So we're in full agreement, for the type of boat (I think) you had in mind! Best wishes (and welcome to the mobo forum! Please stick around. It has a different character from scuttlebutt )

We probably are in agreement, mostly.
Not much is constant about boats, they are all a bit different. Your brothers 8kn TSDY is probably closer to most of my experience than a Princess.
You obviously understand what I was talking about.
The question remaining is relative effect. On your vessel you find the relative effect of the rudder to small to bother with.

I generally find I use basic principles on an unfamiliar boat until I get a feel of it. For me this includes the rudder, perhaps out of habit, based on the majority of boats big and small I handle have been displacement.

 

[MapisM]

then we come to your 2nd last para:
If I start juggling the throttles to try to move left or right I will likely move the boat out of line with the stream, and a 4knt current will catch one side of the bow or the other. Um, not sure I like the sound of that. I think, again intuition, that I'd hold the boat in the stream on both engines, but try and move left and right with bow & stern thrusters working together. They couldn't hold me against the stream, as the P67 discovered, but they would move me left and right. I wouldn't be in a hurry to touch the wheel, something I never do when manoeuvring.
Actually in real life as you cruise in a straight line you are correcting the steering by tweaking the rudders (or prop/thruster kicking). As you do that, the stern of your boat is pushed (if using rudders) slightly left or right all the time, as these constant tiny corrections are made.

All agreed, but in fairness towards kcrane, in the scenario he described, you can't do just that, because the STW he wants to keep (4kts) is lower than the min idle speed (5kts).
This introduces the need to engage/disengage gear constantly, with a "discrete" variation in thrust - hence possibly also direction.
Not impossible to handle, but surely not as easy as when you can keep your course in an "analogue" way, as is the case with rudders alone (which is what also the a/p does), or by fine tuning the rpm with both engines constantly engaged.

 

[MapisM]

Your brothers 8kn TSDY is probably closer to most of my experience than a Princess.

Actually, also my boat has a deep keel and a full displacement hull, but I would still count MUCH more on the engines than on the rudders, on the situation which is being debated.
Yes, P and D hulls have somewhat different behaviours and require a slightly different approach when maneuvering, but that has more to see with the higher inertia/delayed response of the latter vs the first, than anything else.
The only shaft mobos whose rudder is significantly more effective also at slow speed are those with a single screw.
Which of course are D boats, but it's not the hull shape that matters most.
It's the fact that single screw boats NEED a proper rudder, for obvious reasons, and they are built accordingly.
As sailboats also are, of course.

 

[jfm]

We probably are in agreement, mostly.
Not much is constant about boats, they are all a bit different. Your brothers 8kn TSDY is probably closer to most of my experience than a Princess.
You obviously understand what I was talking about.
The question remaining is relative effect. On your vessel you find the relative effect of the rudder to small to bother with. .

Yup we're agreeing . And I agree that when deciding how to drive a particular boat it's good to know the relative effect. My view on that Princess 67 on Richmond bridge, which is similar to several boats I've owned and my current boat, is that the relative effect is something like 90-10, ie the props do 90% of the turning at those speeds and the rudders bring 10% to the party. It's literally that extreme. Given that spinning a steering wheel is an extra task you'd be glad not to have to do in such a challenging situation, the rudders are simply not worth bothering with imho
Best wishes

 

[jfm]

All agreed, but in fairness towards kcrane, in the scenario he described, you can't do just that, because the STW he wants to keep (4kts) is lower than the min idle speed (5kts).
This introduces the need to engage/disengage gear constantly, with a "discrete" variation in thrust - hence possibly also direction.
Not impossible to handle, but surely not as easy as when you can keep your course in an "analogue" way, as is the case with rudders alone (which is what also the a/p does), or by fine tuning the rpm with both engines constantly engaged.

Yes agreed. The flicking in/out of gear to get 4 knots STW rather than 5 is an extra feature and an extra mental challenge for the helmsman in a situation like P67/Richmond bridge, but it doesn't change the physics and the fundamentals nor create a "lose the bow" risk

If you were actually going through that bridge backwards (not something I'd choose; I'm in the go forwards camp as Mr Skinner eventually did successfully) you'd likely be on one engine quite a lot of the time anyway, in order to kicking the stern constantly into the correct alignment. Therefore you might find the 4 knots rather than 5 comes naturally

It would be an interesting new thread for people to recount their actual experiences of most difficult berthing manoeuvring thing they've ever had to do

 

[Uricanejack]

I'd given up replying to this thread but this is SO outrageous that I've got to comment.
Not only do I have some small experience with Princesses, I actually own a Princess 67 - same model as the one in this thread.

JFM is absolutely correct and I'm sure that most on this forum will totally agree.

Our rudders are almost completely useless until the boat is making way through the water at, at least 4 knots - and even then not a lot of use either.

Four your info, the P67 in this thread is the same as most flybridge boats and has two small rudders placed almost immediately aft of the props
When the props are turning at slow speed, they have very little effect on steerage.
This said, sometimes when the boat is not moving fast enough for the rudders to have any effect, I do often use them, particularly for very tight turns
The P67 is fitted with "fly by wire" ruder controls so it is very easy to convert from fully one "lock" to the other.
For me, for maneuvering, the rudders are only any use if you want to turn the boat in its own length, in which case I "split the throttles" (one engine forward and one astern) and use what there is a rudders to help the turn.
Other that that they are completely useless in slow speed maneuvering.

You also imply that the bow won't "fall off" if facing into the stream.
I don't know what kind of boat you are use to - maybe one with a large keel
But you have to remember that these flybridge boats are essentially "flat bottom" and have very little resistance to any sideways drift.
For me, it is the stern that is important - if you can keep the "props" in safe water, the bow will "fall away" (being influenced by external effects - tide, stream and wind etc)
That is why I say "hang on the props"

Now then - would I go through that bridge forwards or backwards - neither - this is not the place for this kind of boat
I'm sorry but attempting that kind of thing is foolish and the skipper shouldn't have done it.
Maybe I'm not as brave - but I wouldn't have done it
If I really had to do it, I would have kept the stern into the stream which is what I think this skipper did anyway.

Remember also, this boat is just short of 50 tons and had two and a half thousand horsepower available.
Sorry wrong boat wrong location.

Oh yes - and you are very wrong about the rudders

EDIT
I've just found this pic on my Photobucket account - this is the rudder arrangement on the P67
Note that the props are the lowest part of the boat in the water - the rest is, essentially "flat bottom"

Thanks nice picture. better than 1000 words.

As suspected I don't spend a lot of time on boats of this type.
Looking at the picture. I would expect wash from this prop to have an effect. How this effect compares to the twist effect of the offset prop along with the transvers thrust I couldn;t say.
Mr jfm indicates a prop of this size will cause an effective flow past the rudder when engaged astern. This would tend to counter the effect of the rudder and fwd thrust. he also indicates the effectiveness of the rudder is not much.

Hope fully without causing outrage or offence feel free to disagree.
Just a comment or two about loosing the bow.
A steady current acting upon a free floating vessel will move a vessel bodily in the direction of flow of the current.
The current does not act more on the boats bow or stern regardless of draft, displacement, shape or anything else I can think of.

A sheer occurs when the current is different at opposite ends of the vessel. Sheer’s are likely when approaching any restriction to a flowing current where eddies and back eddies may occur.
A sheer could cause your bow to go somewhere you don’t intend it to.

Generally I find the force which tends to be inconveniently irregular on light displacement boats is the wind. Bows tend to blow off.
Happens on heavier boats to.

I'd agree with your assessment on going under the bridge with this size of boat. I see other's have done it though.

 

[Uricanejack]

It would be an interesting new thread for people to recount their actual experiences of most difficult berthing manoeuvring thing they've ever had to do

I'd find it interesting.

I was once asked at an interview. To recount my best memory of boat handling which I had done particularly well.
I told her unfortunately the good ones are soon forgotten. It's the really bad ones I can remember. One chap laughed but I didn't get the job.

 

[Richard Shead]

And finally our local rag grabs the scoop......

http://www.richmondandtwickenhamtim...yacht_crashes_into_Richmond_Bridge/?ref=var_0

 

[jfm]

And finally our local rag grabs the scoop......

http://www.richmondandtwickenhamtim...yacht_crashes_into_Richmond_Bridge/?ref=var_0

It reports that the windscreen glass broke, which unfortunately is going to make for quite a bit more repair work. I hope Trend still have the files and whatever else is needed to bend a one-off set of replacement glass - I expect they do

 

[Richard Shead]

It reports that the windscreen glass broke, which unfortunately is going to make for quite a bit more repair work. I hope Trend still have the files and whatever else is needed to bend a one-off set of replacement glass - I expect they do

They also said it was a 57....but agreed

Have not heard from the skipper for a while lets hope he is still employed.

On a different note can you imagine the coverage Brave Goose would have had (see my last post) if we all had mobile phones with cameras back then!

 

[jimmy_the_builder]

It reports that the windscreen glass broke, which unfortunately is going to make for quite a bit more repair work. I hope Trend still have the files and whatever else is needed to bend a one-off set of replacement glass - I expect they do

Do you think they actually meant the windscreen? I wondered if they were referring instead to the wind deflector round the flybridge, which iirc is a single piece of plastic.