Passing moored widebeams

[Sea Dog]

It's all about the passing boat shifting water proportionate to its displacement, isn't it? Ergo, I'd have thought a 60' Narrowboat would have a similar effect on a 60' widebeam as a 30' Narrowboat would have on him. Less, but still worthy of consideration. 

[WotEver]

My thoughts are that a narrowboat is constantly displacing x litres of water. Whether on a canal or river, shallow or deep, the volume of displaced water is constant. It therefore surely follows that x litres of water acting on a moored boat which also displaces x litres will have more effect than it will on a boat which displaces 2x litres. 

No?

[cereal tiller]

4 minutes ago, WotEver said:

My thoughts are that a narrowboat is constantly displacing x litres of water. Whether on a canal or river, shallow or deep, the volume of displaced water is constant. It therefore surely follows that x litres of water acting on a moored boat which also displaces x litres will have more effect than it will on a boat which displaces 2x litres. 

No?

I would have thought that a PhatBoat would be disturbed less as they are usually lees deep in the Water,so some of the displaced Water would flow underneath it?

[bizzard]

We sometimes get Otters swimmin about up here during the winter. They don't half rock the boat,  telling em to slow down is a waste of time, they take no notice.

[WotEver]

Just now, bizzard said:

We sometimes get Otters swimmin about up here during the winter. They don't half rock the boat,  telling em to slow down is a waste of time, they take no notice.

Do they get bothered by the ducks tapping on the hull?

3 minutes ago, cereal tiller said:

I would have thought that a PhatBoat would be disturbed less as they are usually lees deep in the Water,so some of the displaced Water would flow underneath it?

My thinking is that where the water goes is less relevant than the fact that it's proportionally less than the boat displaces itself. 

[MtB]

On 17/04/2017 at 10:06, cereal tiller said:

I would have thought that a PhatBoat would be disturbed less as they are usually lees deep in the Water,so some of the displaced Water would flow underneath it?

 

Yes that's a good point, and probably the explanation.

Does this mean we don't need to slow down when passing moored widebeams? 

[mark99]

32 minutes ago, WotEver said:

My thoughts are that a narrowboat is constantly displacing x litres of water. Whether on a canal or river, shallow or deep, the volume of displaced water is constant. It therefore surely follows that x litres of water acting on a moored boat which also displaces x litres will have more effect than it will on a boat which displaces 2x litres. 

No?

 

25 minutes ago, cereal tiller said:

I would have thought that a PhatBoat would be disturbed less as they are usually lees deep in the Water,so some of the displaced Water would flow underneath it?

 

I think these two thoughts above are about correct. Adding that transient water pressure acting on widebeam hull will be approx 1/2 too. (Same forces distributed across 2* surface area).

Taking things to ridiculous extremes often demonstrates the concept. Observe a narrowboat passing a Destroyer or a rowing boat. Which moves around the most?

 

Edited April 17, 2017 by mark99

[MtB]

I wouldn't know for sure as I've yet to pass a Destroyer on the K&A, but maybe there is on around the next bend...

[NickF]

1 hour ago, Mike the Boilerman said:

 

To expand on my OP, logic suggests to me NickF would be right but I notice when passing widebeams on this narrow canal, they appear visually to be less affected by surge than a narrow boat.

So I wondered what widebeam owners thought and why this would be, if it is indeed the case.

May be widebeam owners moor better, or you get a better angle on the mooring line from a wider boat?

[BWM]

It never fails to amaze me how much a fast moving canoe can wobble a moored narrow boat. In general, I believe that the way a boat is ballasted has more to do with the amount of disturbance caused by a passing boat, rather than the size of either.

[WotEver]

22 minutes ago, BWM said:

It never fails to amaze me how much a fast moving canoe can wobble a moored narrow boat. In general, I believe that the way a boat is ballasted has more to do with the amount of disturbance caused by a passing boat, rather than the size of either.

I stepped on board a newly built unballasted tug a few years ago. It was as tender as a rowing boat. It actually felt top heavy. 

[NickF]

2 hours ago, WotEver said:

My thoughts are that a narrowboat is constantly displacing x litres of water. Whether on a canal or river, shallow or deep, the volume of displaced water is constant. It therefore surely follows that x litres of water acting on a moored boat which also displaces x litres will have more effect than it will on a boat which displaces 2x litres. 

No?

The size of the waterway makes a difference as with a really wide river there is plenty of space for the displaced water to flow past the moving boat, not so on a narrow canal, just look at the water around the hull next time you go through a narrow bridge hole to see this theory in action.

 

[WotEver]

31 minutes ago, NickF said:

The size of the waterway makes a difference as with a really wide river there is plenty of space for the displaced water to flow past the moving boat, not so on a narrow canal, just look at the water around the hull next time you go through a narrow bridge hole to see this theory in action.

Yes of course the flow will differ but that's not what's being discussed. We have been talking about the difference in the effect that flow will have on a narrowboat vs a wide beam. 

Or are you suggesting that the ratio of the effect changes along with the cross section of the water course?

[J R ALSOP]

Posted this last week, thought it would have had more of a reaction. Been on their maps for the last 25years.

[mark99]

18 minutes ago, J R ALSOP said:

Posted this last week, thought it would have had more of a reaction. Been on their maps for the last 25years.

That's been mentioned on here quite a few times - maybe reason why no reaction.

3 hours ago, Mike the Boilerman said:

I wouldn't know for sure as I've yet to pass a Destroyer on the K&A, but maybe there is on around the next bend...

 

Not even a U bote?

[NickF]

1 hour ago, WotEver said:

Yes of course the flow will differ but that's not what's being discussed. We have been talking about the difference in the effect that flow will have on a narrowboat vs a wide beam. 

Or are you suggesting that the ratio of the effect changes along with the cross section of the water course?

Absolutely the cross section of the water course makes a difference. The same amount of water has to flow past the hull whether the canal is wide or narrow, if the canal is wide then that can be achieved across the full width of the water course so the water does not need to travel so quickly to achieve the same amount of water movement

[WotEver]

19 minutes ago, NickF said:

Absolutely the cross section of the water course makes a difference. The same amount of water has to flow past the hull whether the canal is wide or narrow, if the canal is wide then that can be achieved across the full width of the water course so the water does not need to travel so quickly to achieve the same amount of water movement

????

So are you saying it will affect wb more than nb? Or are you saying it will affect wb less than nb? Or are you saying it depends on the profile of the water course? If the latter then how does that affect the difference between wb and nb?

Nobody is suggesting the water flow won't be different in a narrow and shallow canal compared to a wide and deep river, I repeat that isn't what's being discussed. 

[Robbo]

Just now, WotEver said:

????

So are you saying it will affect wb more than nb? Or are you saying it will affect wb less than nb? Or are you saying it depends on the profile of the water course? If the latter then how does that affect the difference between wb and nb?

For the same weight boat it will effect a wider boat more.   Boats are more efficient been long and thin rather than short n fat due to the water drag.

[WotEver]

1 minute ago, Robbo said:

For the same weight boat it will effect a wider boat more.   Boats are more efficient been long and thin rather than short n fat due to the water drag.

So you are saying that a moored wide boat will be more affected by a passing boat than a moored narrowboat? I don't believe you. 

As was said earlier, take it to extremes, a destroyer vs a rowing boat... the answer is obvious. 

[Robbo]

19 minutes ago, WotEver said:

So you are saying that a moored wide boat will be more affected by a passing boat than a moored narrowboat? I don't believe you. 

As was said earlier, take it to extremes, a destroyer vs a rowing boat... the answer is obvious. 

That depends, for the same moored boat weight, the water removal from around the boat will pull the boat more, but the wake will effect a narrow boat more.   Of course this depends on the boat that is passing as small boats cause more wake than heavier long boats which cause more surge.  So there is no right or wrong answer, but for the average canal boat, the average widebeam on the average canal, I think the narrowboat will be more effected.

[WotEver]

15 minutes ago, Robbo said:

for the average canal boat, the average widebeam on the average canal, I think the narrowboat will be more effected.

Which was what I said about a dozen posts back. 

[Robbo]

Just now, WotEver said:

Which was what I said about a dozen posts back. 

Not to the post I was replying too.  Wide beams are on average heavier than a narrowboat so will be less effected, but if It was lighter like a GRP it would be more effected.

[WotEver]

13 minutes ago, Robbo said:

Not to the post I was replying too.  Wide beams are on average heavier than a narrowboat so will be less effected, but if It was lighter like a GRP it would be more effected.

But if you keep it in context I said 

Quote

My thoughts are that a narrowboat is constantly displacing x litres of water. Whether on a canal or river, shallow or deep, the volume of displaced water is constant. It therefore surely follows that x litres of water acting on a moored boat which also displaces x litres will have more effect than it will on a boat which displaces 2x litres. 

No?

It was Frank who started confusing matters by bringing in the water course profile, and you who spoke about wb boats 'of the same weight'

Edited April 17, 2017 by WotEver

[Dingle]

What about Speed?

A vessel just making way has a lot less effect on the water it shoves around than one going at full pelt...

[peterboat]

7 hours ago, frangar said:

At least they are the correct craft for the waterway....it seems that just because they fit it a lock then it's assumed they are ok to use...I really hope CRT start charging them double plus some quite soon...

I do to then give us a two thirds discount because we can only use one third of the canal networks