Reinforcing the uxter plate

[bizzard]

 

A thing maybe worth bearing in mind is that IF it is the uxter flexing in these conditions it will likely be flexing overall forming a gentle arc. If you stiffen the width of the plate any continuing flex will be uniquely at the weld, which could cause failure there. It's a fatique point on some working narrowboats where the frame angles finish just short of the central kelson for exactly that reason.

 

Tam

Yes lets call the engine mounts the Keelson albeit sort of a double one providing that the mount sides are vertical and level. So to stop any flexing at the uxter plate to swim welds maybe long transverse triangular gusset plates welded upright (on edge) between the steel engine mount side and the swim, on both sides. My narrow boat has two of these triangular gusset plates welded to either side like the above.

Edited December 22, 2013 by bizzard

[blackrose]

I wouldnt have thought adding any steel running along the length of boat to be worthwhile. Lengthwise the steels would just sit on the curve of plate (assuming it does infact curve up and into the boat if you see what I mean) and flex up and down with it.

Think of your baseplate, which is even wider and the steel channel/angle always run across the boat.

I worked on a nb recently that had the last two floor bearers 4 ft apart (dont know why, perhaps run out of steel!), had 10mm base plate and that had quite a curve to it in the middle.

 

My uxter plate doesn't curve. It's flat, the same as most narrowboats. But I do agree - crossmembers seem more sensible to me.

 

 

Ok didn't see that. Just saying - you would have to be a tiny ooopah lumpah to be able to access the dry side of our uxter and weld it.

 

There's about 2 and a half ft between the uxter plate and the underside of the stern deck on my boat. I regularly crawl in to top up my batteries.

 

A thing maybe worth bearing in mind is that IF it is the uxter flexing in these conditions it will likely be flexing overall forming a gentle arc. If you stiffen the width of the plate any continuing flex will be uniquely at the weld, which could cause failure there. It's a fatique point on some working narrowboats where the frame angles finish just short of the central kelson for exactly that reason.

 

Tam

 

In that case the angle would go right up to the sides of the boat and the ends would be welded to the sides. Pehaps knees could be welded on to the sides with short lengths of angle. (Is knee the right term?)

 

 

if you can afford the loss in height that would be fine.

 

If I was putting angle in at say 2ft centres then I'd just store stuff between them.

Edited December 22, 2013 by blackrose

[MtB]

On reflection I think all this conjecture is putting the cart before the horse. The cause of the noise needs definitively diagnosing before steelwork is designed, purchased and welded into place or there is a risk the noise will persist despite the work done to 'fix' it.

 

I think finding someone to steer Mike's boat for him on waters that cause the noise is the priority so he can spend a happy hour crawling about on the uxter and hopefully positively identify where it is coming from.

 

MtB

[blackrose]

On reflection I think all this conjecture is putting the cart before the horse. The cause of the noise needs definitively diagnosing before steelwork is designed, purchased and welded into place or there is a risk the noise will persist despite the work done to 'fix' it.

 

I think finding someone to steer Mike's boat for him on waters that cause the noise is the priority so he can spend a happy hour crawling about on the uxter and hopefully positively identify where it is coming from.

 

MtB

 

Yes, I think you're probably right Mike. Anyone fancy a trip steering my boat up and down the Severn on a windy day next spring?

Edited December 22, 2013 by blackrose

[bizzard]

On reflection I think all this conjecture is putting the cart before the horse. The cause of the noise needs definitively diagnosing before steelwork is designed, purchased and welded into place or there is a risk the noise will persist despite the work done to 'fix' it.

 

I think finding someone to steer Mike's boat for him on waters that cause the noise is the priority so he can spend a happy hour crawling about on the uxter and hopefully positively identify where it is coming from.

 

MtB

With a stethoscope.

[Captain Fizz]

Yes, I think you're probably right Mike. Anyone fancy a trip steering my boat up and down the Severn on a windy day next spring?

Sounds like an excellent day out to me, sign me up!

And if you subsequently decide to put in the angle, I can even do the welding for you.

[Tam & Di]

 

 

In that case the angle would go right up to the sides of the boat and the ends would be welded to the sides. Pehaps knees could be welded on to the sides with short lengths of angle. (Is knee the right term?)

 

Carrying the stiffeners on as knees up the side would certainly stop any continuing flex occuring uniquely at the weld where the uxter meets the side at the counter. However I think Mike is correct that further investigation is required before going to all that trouble and expense.

[MtB]

Sounds like an excellent day out to me, sign me up!

And if you subsequently decide to put in the angle, I can even do the welding for you.

 

I'll do it too!

 

(And I've got a stethoscope )

 

MtB

[blackrose]

Thanks all. I will let you all know when I have time off work and can get down to the Severn. Probably April/May time. It's only 2 days from my mooring to Tewkesbury.

 

I've only been on the Severn once before but I think the wind can whip up some foot high waves if it's blowing against the current. Alternatively I could go down to Sharpness and out onto the estuary assuming it's possible to go out and back around high tide and someone knows the sandbanks? I don't want to pay for a pilot just to go out there for a couple of hours.

Edited December 22, 2013 by blackrose

[BEngo]

A stethoscope is a bit localised for what you need here. However if the boat is ballasted bow up and the normally dry side of the uxter is covered with water the vibration pattern will be visible on the surface of the water as standing waves. With a photo of the pattern it is then not too hard to work out which bits need to be stiffened and which way the flat, or angle needs to run.

 

N

Edited December 23, 2013 by BEngo

[bizzard]

A stethoscope is a bit localised for what you need here. However if the boat is ballasted bow up and the normally dry side of the uxter is covered with water the vibration pattern will be visible on the surface of the water as standing waves. With a photo of the pattern it is then not too hard to work out which bits need to be stiffened and which way the flat, or angle needs to run.

 

N

Good lord, that sounds like one of my theories.

[Albion]

Thanks all. I will let you all know when I have time off work and can get down to the Severn. Probably April/May time. It's only 2 days from my mooring to Tewkesbury.

 

I've only been on the Severn once before but I think the wind can whip up some foot high waves if it's blowing against the current. Alternatively I could go down to Sharpness and out onto the estuary assuming it's possible to go out and back around high tide and someone knows the sandbanks? I don't want to pay for a pilot just to go out there for a couple of hours.

Just a thought but wouldn't a few heavy sandbags do the job. Do the run without the sandbags, but with them on the aft deck (so that it isn't ballast trim affecting anything), listen to the generated noise. Lay the sandbags on the uxter plate and compare noises. If the noises have disappeared then your theory about uxter plate vibration would seem to be correct.

Roger

[bizzard]

Or a mega sound amplification listening device could be made using a huge pouring funnel with a length of hosepipe shoved on the spout. Plonk the funnel bell down on the uxter plate, stuff the other end of the hose in your ear and listen for the BOOMS!. And by lengthening the hose it can be used afterwards for telecommunication purposes with another funnel fixed to the other end.

[mark99]

If you crawl into the space you could feel the flex (or not).

[bizzard]

If you crawl into the space you could feel the flex (or not).

That sounds too sensible for Mike, he seems to like things nice and complicated. Although I'm sure when he gets home from work that he'll be absolutely delighted with all the suggestions so far.

[onionbargee]

with respect MTB do you have qualifications in or even ever worked in the fabrication industry, you really should not be making up advice off the top of your head like this. I stand corrected if you have.

[The Pipe]

Without screwing my brain back in place and trying to work out what the loads imposed by not very large waves passing over a flat to the water surface.

I doubt if the loads are enough to cause movement to create a "groaning" in the uxter plate. The only true way of checking would be to actually measure the deflection (easy way would be with a Dial Test Indicater on a magnetic mount on the hull side).

I personnally would not be too concerned as I doubt if there is anything going on to give you a fatigue issue especially as the amount of time involved in rough water is small.

I would be looking more for things like ventilation under the uxter plate than movement.

Thinking about it Gazelle "groans" on the tidal Thames when rough it is ventilation under the uxter plate and probably more the propeller loosing it's "bite".

[bizzard]

I've got it. If lots of holes were drill in the afterdeck over the uxterplate, sticks of bamboo cane could be planted in all these holes so that when the boat bobs about over waves the sticks should all jiggle up and down with the flexing plate. These could be monitored in comfort on the deck whilst underway and a general jiggle of certain highs and lows would determine the area of the groaning and booming. Little bells of varying musical pitch of the musical scale could be attached to the top of the sticks, the rythmic and melodious strains of which could be tape recorded and can later be listened to at leisure, umpteen times, scrutinized bit by bit, note by note, tinkle by tinkle until the area of the groaning uxter plate is pin pointed, especially if the happen to play ''Riding along on the crest of a wave'' or better still ''Jingle bells''.

I reckon old Mike would really enjoy employing this highly technical method of defining where his groans are coming from and would keep him happily occupied for ages.

[blackrose]

A stethoscope is a bit localised for what you need here. However if the boat is ballasted bow up and the normally dry side of the uxter is covered with water the vibration pattern will be visible on the surface of the water as standing waves. With a photo of the pattern it is then not too hard to work out which bits need to be stiffened and which way the flat, or angle needs to run.

 

N

 

Nice idea but not possible as the water would just roll off the uxter onto the baseplate - especially if the boat was rolling about in waves. Even if you could keeo the water on the uxter plates then taking a photo of the standing waves seems like another problem.

Just a thought but wouldn't a few heavy sandbags do the job. Do the run without the sandbags, but with them on the aft deck (so that it isn't ballast trim affecting anything), listen to the generated noise. Lay the sandbags on the uxter plate and compare noises. If the noises have disappeared then your theory about uxter plate vibration would seem to be correct.

Roger

 

Do you really think the flexing of 6mm thick steel plates would be prevented by a few sandbags?

If you crawl into the space you could feel the flex (or not).

 

Yes, that seems like the simplest idea to me.

That sounds too sensible for Mike, he seems to like things nice and complicated. Although I'm sure when he gets home from work that he'll be absolutely delighted with all the suggestions so far.

 

On the contrary - if you bothered to read the thread you'd see that I had suggested crawling down there originally.

I've got it. If lots of holes were drill in the afterdeck over the uxterplate, sticks of bamboo cane could be planted in all these holes so that when the boat bobs about over waves the sticks should all jiggle up and down with the flexing plate. These could be monitored in comfort on the deck whilst underway and a general jiggle of certain highs and lows would determine the area of the groaning and booming. Little bells of varying musical pitch of the musical scale could be attached to the top of the sticks, the rythmic and melodious strains of which could be tape recorded and can later be listened to at leisure, umpteen times, scrutinized bit by bit, note by note, tinkle by tinkle until the area of the groaning uxter plate is pin pointed, especially if the happen to play ''Riding along on the crest of a wave'' or better still ''Jingle bells''.

I reckon old Mike would really enjoy employing this highly technical method of defining where his groans are coming from and would keep him happily occupied for ages.

 

I reckon old Bizzard needs a trip to specsavers so he can read threads properly...

Edited December 23, 2013 by blackrose

[Albion]

Do you really think the flexing of 6mm thick steel plates would be prevented by a few sandbags?

Not prevented but deadened, thus leading to a diagnosis.....but as an engineer what would I know?

Roger

[blackrose]

Not prevented but deadened, thus leading to a diagnosis.....but as an engineer what would I know?

Roger'

 

I've no idea what you would know...

 

You're entitiled to your opinion of course, but as another engineer I don't think it would work. I've got loads of heavy stuff sitting on those uxter plates already including a 1/4 of a tonne of bricks on each side. If it deadens the vibration the effect is not perceptible.

 

In my opinion it would be much more direct and effective to simply lay on the uxter as someone else steers the boat through waves and feel for any vibration or flexing.

 

Mike

Edited December 24, 2013 by blackrose

[Albion]

 

I've no idea what you would know...

 

You're entitiled to your opinion of course, but as another engineer I don't think it would work. I've got loads of heavy stuff sitting on those uxter plates already including a 1/4 of a tonne of bricks on each side. If it deadens the vibration the effect is not perceptible.

 

In my opinion it would be much more direct and effective to simply lay on the uxter as someone else steers the boat through waves and feel for any vibration or flexing.

 

Mike

This is excellent new info then because you now already have what you need to help diagnose the problem. You won't even need my sandbags.

We can deduce, from what you have said (a 1/4 of a tonne of bricks on each side), that the bricks are sitting on the sides of the swim where the uxter plate is much stiffer anyway as it tapers away towards the front of the swim so you wouldn't expect to see any damping effect at this position This is not the area that is likely to be giving you the problem that you describe. The problem area (if it is indeed the problem) is going to be the large unsupported uxter plate aft of, say, a line drawn across the boat behind the tail of the gear box (either side of the swim) and going past the point of the swim right back to the stern of the boat. This will be a large unsupported sheet of steel on a widebeam like yours. If you spread the ballast bricks that you describe over that area of uxter plate you will deaden the vibration/panting of the plate to some extent while you steer the boat allowing you to make a diagnosis.

Doing the tests as I describe also has two other significant advantages for you:

1. You won't have to liaise with another helmsman to be available at the right place, the right time and the right choppy water conditions, because you'll be able to do the test unaided.

2. You won't need to be crawling around the engine bay area in choppy water conditions fairly close to a rotating prop shaft.

 

You also informed us late last night (in the bit that you have now edited out at 01.23 am) that you are an engineer specialising/expert in (and I can't remember now the exact words) vibration of substances with varying input stimuli. This should mean, as it is a claimed area of expertise, that you can calculate the harmonic resonant frequencies of a large sheet of 6mm steel secured around its periphery. If you then do another calculation with the addition of a uniformly distributed unsprung mass over the top surface (the bricks, or for that matter sandbags) you will, of course, find that the addition of the bricks WILL have a significant affect on the harmonic resonant frequencies (reducing them) thus proving to yourself that the addition of weights will affect the response of the large unsupported uxter plate to varying input stimuli.

Hope this helps.

Roger

Edited December 24, 2013 by Albion

[blackrose]

I do appreciate your ideas, but while that all sounds fine in theory it sounds far too analytical for what I need. Also I really don't think it would work. As I already said, there is loads of heavy stuff on the uxter plates already, including on the wide unsupported areas. I use the uxters for storage of tools and a whole load of boxes of spares including tiles, flooring, and various junk that I'm too OCD to get rid of. I'm afraid it doesn't make any difference to the vibrations. I don't have the equipment to measure the resonance either.

 

It's much simpler in my opinion to get down there and see what's happening for myself. I'm sure whoever is steering would agree to take the boat out of gear for a minute so I can avoid the rotating propshaft while I position myself.

Edited December 24, 2013 by blackrose

[RLWP]

This is excellent new info then because you now already have what you need to help diagnose the problem. You won't even need my sandbags.

We can deduce, from what you have said (a 1/4 of a tonne of bricks on each side), that the bricks are sitting on the sides of the swim where the uxter plate is much stiffer anyway as it tapers away towards the front of the swim so you wouldn't expect to see any damping effect at this position This is not the area that is likely to be giving you the problem that you describe. The problem area (if it is indeed the problem) is going to be the large unsupported uxter plate aft of, say, a line drawn across the boat behind the tail of the gear box (either side of the swim) and going past the point of the swim right back to the stern of the boat. This will be a large unsupported sheet of steel on a widebeam like yours. If you spread the ballast bricks that you describe over that area of uxter plate you will deaden the vibration/panting of the plate to some extent while you steer the boat allowing you to make a diagnosis.

Doing the tests as I describe also has two other significant advantages for you:

1. You won't have to liaise with another helmsman to be available at the right place, the right time and the right choppy water conditions, because you'll be able to do the test unaided.

2. You won't need to be crawling around the engine bay area in choppy water conditions fairly close to a rotating prop shaft.

 

You also informed us late last night (in the bit that you have now edited out at 01.23 am) that you are an engineer specialising/expert in (and I can't remember now the exact words) vibration of substances with varying input stimuli. This should mean, as it is a claimed area of expertise, that you can calculate the harmonic resonant frequencies of a large sheet of 6mm steel secured around its periphery. If you then do another calculation with the addition of a uniformly distributed unsprung mass over the top surface (the bricks, or for that matter sandbags) you will, of course, find that the addition of the bricks WILL have a significant affect on the harmonic resonant frequencies (reducing them) thus proving to yourself that the addition of weights will affect the response of the large unsupported uxter plate to varying input stimuli.

Hope this helps.

Roger

Don't forget the distributed load from the water pressure

 

Richard

[Albion]

I do appreciate your ideas, but while that all sounds fine in theory it sounds far too analytical for what I need. Also I really don't think it would work. As I already said, there is loads of heavy stuff on the uxter plates already, including on the wide unsupported areas. I use the uxters for storage of tools and a whole load of boxes of spares including tiles, flooring, and various junk that I'm too OCD to get rid of. I'm afraid it doesn't make any difference to the vibrations. I don't have the equipment to measure the resonance either.

 

It's much simpler in my opinion to get down there and see what's happening for myself. I'm sure whoever is steering would agree to take the boat out of gear for a minute so I can avoid the rotating propshaft while I position myself.

Ahh, now that we are aware that you have loads of heavy stuff on the larger areas of the uxter plate then, going back to the original purpose of your question (would welding reinforcing bards to my uxter plate cure a suspected noise from that area?), I have some doubt as to whether the uxter plate is the true source of your problem. Even on a wide beam, if the plate is heavily laden with 'stuff' it should dampen any panting from the plate so, unless some of the stuff on the plate is chafing against each other creating the noise, then I'm not sure that it would be worth welding bars across. I'm pretty sure that accurate diagnosis of the problem source could prevent possible unnecessary trouble and expenditure. Have you thought that it might be air getting sucked under the uxter plate in choppy conditions? We certainly had air getting sucked under the uxter of our narrow boat on the Severn when we were passed by high speed cruisers going the other way and we were crossing their wash. This was so bad that the prop used to grip and slip as we crested/dug in on the chop from their wake and air was sucked under, and that was on a reasonably deep drafted nb with a good size prop.

 

Don't forget the distributed load from the water pressure

 

Richard

Richard, I wasn't suggesting that you could calculate your way to a solution of this noise. There are so many variables to take into consideration that I would think it would be extremely difficult. My proposal that loading the uxter with a distributed load would alter the response of the uxter to any input stimulus had been pooh-poohed so I was suggesting that, for an engineer skilled in the vibration of materials, one could prove to oneself that adding a distributed load would dampen the resonant vibration (as if one would really need proof, of course).

Roger