Investigations Into Speeding Vessels

[Guest]

20 hours ago, BroadAmbition said:

almost turned us over!...

Really?

Griff

Hell Yea....I started having visions of Gene Hackman!

[Upcycler]

On 06/09/2020 at 05:26, grendel said:

excessive wash does come into it, as it is evidence of exceeding the speed limit. as hull type can be determined by boat type.

Now I do understand that speed limits are there to protect the river banks because of wash, but a hovercraft can break the speed limit associated with some rivers and cause much less wash than boats. Now if I am correct in saying that the rivers have boats of planning hulls to the flat bottom hulls concerning the hire industry. 

So please correct me if I am wrong, a planning hull causes more wash than your flat bottom hull type and the bigger the boat, the slower they should go?

[Upcycler]

On 06/09/2020 at 08:39, MauriceMynah said:

We shall say I'm in a 7mph (over land) speed limit. If I'm doing 7mph through the water against a 7mph tidal flow, My land speed is 0 mph. The speed of my wash against the bank is also 0 mph yet that wash might well be 30cm. Is that wash doing any damage to a soft bank? (I genuinely don't know).

But, if I turn and run with the tide and to maintain steerage have a speed through water of 3mph, my speed over land is now 10 mph, but with no wash. Should I be done for speeding?  

Sorry Double M, but I think you have gone over to the dark side with this way of thinking and have looked far too much into it.

[grendel]

except for the fact hovercraft are not allowed on the broads.

at the speed limits generally planing hulls cause more wash (the wash reduces once they are up on the plane)

displacement hulls (generally the type seen on most broads cruisers are limited to the efficient speed by a factor of the length of the boat (where the wavelength of the wash equals the length of the boat is the displacement speed), so a longer boat is capable of going faster, but wash is a factor of the shape of the hull and how the water reacts at the chines and stern of the vessel.

so without going into it too deeply, a well designed hull may well have less wash than one of a different design - as an example most martham boats have a low wash design, and barely produce a wash up to about 4.5mph, and not much after that unless you try and push them above the dispacement speed. whereas most fibreglass bathtub type boats will have more wash at 4mph than a martham boat at 5.5-6mph.

with all these factors in play, setting speed limits has to have a starting point.

[Vaughan]

9 hours ago, Upcycler said:

Sorry Double M, but I think you have gone over to the dark side with this way of thinking and have looked far too much into it.

You know, I have to say I think you sometimes make posts like that just to get a reaction.

In case you are serious, however, I can assure you that what MM has described is totally accurate. The full ebb on a spring tide does indeed go down through GYYS and Reedham at around 7MPH.  I think Griff can find a video on the forum somewhere of Broad Ambition going up through the Yacht Station against the full ebb. It is most impressive.

 

[BroadAmbition]

I think Griff can find a video on the forum somewhere of Broad Ambition going up through the Yacht Station against the full ebb. It is most impressive.

He probably can and it is, however not this morning as dashing out for my normal 10 x Hr day

Upcycler - Really?

Griff

[JanetAnne]

2 hours ago, grendel said:

except for the fact hovercraft are not allowed on the broads.

Irony at its best

[Vaughan]

8 minutes ago, JanetAnne said:

Irony at its best

Since they were invented on the Broads, and the first model flew off the slipway at Ripplecraft in Somerleyton?

[Timbo]

6 minutes ago, JanetAnne said:

Irony at its best

Iron Bridge?

[Vaughan]

1 hour ago, BroadAmbition said:

It is most impressive.

He probably can and it is, however not this morning as dashing out for my normal 10 x Hr day

Now that he has gone off to work, I can safely say that I'm glad he didn't try doing it backwards!  

 

       

[Cal]

3 hours ago, grendel said:

except for the fact hovercraft are not allowed on the broads.

at the speed limits generally planing hulls cause more wash (the wash reduces once they are up on the plane)

displacement hulls (generally the type seen on most broads cruisers are limited to the efficient speed by a factor of the length of the boat (where the wavelength of the wash equals the length of the boat is the displacement speed), so a longer boat is capable of going faster, but wash is a factor of the shape of the hull and how the water reacts at the chines and stern of the vessel.

so without going into it too deeply, a well designed hull may well have less wash than one of a different design - as an example most martham boats have a low wash design, and barely produce a wash up to about 4.5mph, and not much after that unless you try and push them above the dispacement speed. whereas most fibreglass bathtub type boats will have more wash at 4mph than a martham boat at 5.5-6mph.

with all these factors in play, setting speed limits has to have a starting point.

Our boat is a nightmare on the Broads, but we love it so we still come to visit.

 

It is a little planing hull. On a good day in tickover it can do the lowest 3mph speed limit, just, and at that speed it will be making barely a ripple on the water.

 

Yet get it to 6mph on the stretches where this is allowed and the wash it makes is far too much and isn't acceptable. We have to slow down.

[RealWindmill]

On 05/09/2020 at 13:40, marshman said:

I agree with Vaughan I am pleased to say!!!

However the ones who really irritate me apart from that speedboat, are the guys in their huge Broom style boat who can cruise only between Wroxham and Ludham and down beyond Acle - you can almost guarantee that even at tickover, they will exceed the posted limit, and they do! Do they ever realise how incongruous they look perched about 12' up in the air? What a stupid waste of money to keep them on the Northern Rivers - I suppose most don't know, or don't care , or both, how stupid they look!!!!! But I suppose each to their own but you would not catch me in one!!!!!

Totally agree with Marshy on this one, and definitely incongruous.

I recall posting on a different thread a short while ago : 

A greater hazard to navigation on the Cut can be the large seagoing boats that sometimes power down it at a rate of knots and set up sets of standing waves in the narrow waterway. Have witnessed this causing consternation to unsuspecting novice skippers and smaller boats  and to myself on occasion.

they can leave all sorts of problems in their wash - literally !

Slow Down - What's the big hurry .  We know its a boring bit of water...

 

When the crockery starts flying off the the sideboards it is a bit much , and mine is a heavy and  solid stable boat.

Yes i know I should practice good seamanship have everything secure and battened down for passage etc and across Breydon I  do,  but for goodness sake, i'm  talking about on an inland Cut of restricted water. !

 

Fair play to the BA =- go get 'em.

[JennyMorgan]

7 minutes ago, RealWindmill said:

Slow Down - What's the big hurry .  We know its a boring bit of water...

Added to which motor boating at less than walking pace can hardly be considered a thrilling occupation! 

[RealWindmill]

1 hour ago, Vaughan said:

Since they were invented on the Broads, and the first model flew off the slipway at Ripplecraft in Somerleyton?

Yes very ironic as you say , as Christopher Cockerill invented it there.

Why incidentally are they not allowed on the Broads ?

[Turnoar]

They would cause havoc to sailors. Not sure if it’s because they don’t reverse very well! Would make a good rescue craft on Bleydon mud flats though...

[grendel]

probably because they are difficult to steer at 5mph

[MauriceMynah]

I remember Jeremy Clarkson on Top Gear saying "On a hovercraft, if you see an obstacle, you are going to hit it."

I suspect that it's a truth, and that this is why they are banned.

[Vaughan]

44 minutes ago, MauriceMynah said:

"On a hovercraft, if you see an obstacle, you are going to hit it."

When I was in the Army I did several trips on the SRN6 hovercraft, which was being trialed by the Royal Corps of Transport at the time.  They were operated out of a beach just west of Portsmouth and could get to Cowes in what seemed like about 5 minutes.

What Clarkson says (on this occasion) is absolutely true!  When they are doing 50 Knots and you want to turn, it doesn't happen!  You can turn the hovercraft through 90 degrees, but its direction of travel remains the same!  The only way to stop them in a hurry is to "lift the skirt", which destroys the air cushion and they literally crash land into the water.

Not recommended on Wroxham Broad, I would think!

[RealWindmill]

Isn't the SRN6 one of the big ones? I'm thinking back to cross channel  days dover to calais.

I imagine Chris Cockerill's prototypes must have been a lot smaller to fit into the basin at Somerleyton, so perhaps really small ones could prove manouverable in the confines of the broads ?

 

Like the Breydon mudflats idea !

[Vaughan]

10 minutes ago, RealWindmill said:

Isn't the SRN6 one of the big ones? I'm thinking back to cross channel  days dover to calais.

Well, it seems it was the SRN5, from which the SRN6 was developed, after trials by my regiment.

Please excuse me, it was more than 40 years ago.

[wombat nee blownup]

I can remember travelling to Boulogne by hovercraft. Those numbers seem familiar.


Sent from my iPhone using Norfolk Broads Network

[Vaughan]

20 minutes ago, RealWindmill said:

I imagine Chris Cockerill's prototypes must have been a lot smaller to fit into the basin at Somerleyton,

My father knew Chris Cockerill and saw that model being demonstrated at Somerleyton.  In fairness, it was just a biscuit tin, with a little propeller petrol engine for kids' model aeroplanes.  But the principle was proved!  Later development was, of course, done further away on the south coast.

Whether a full size hovercraft ever flew on the Broads, I don't know.

By the way, in COLREGS, they were classified as a seaplane. I imagine they still are.

[RealWindmill]

 

13 minutes ago, Vaughan said:

Well, it seems it was the SRN5, from which the SRN6 was developed, after trials by my regiment.

Please excuse me, it was more than 40 years ago.

Sorry Vaughan, i wasn't critising your memory of these vessels.

I know absolutely nothing about hovercraft but do remember the thrill as a youngster of the dash across the channel in the big ones !

  (trying to find a hovercraft emoticon - but the don't seem to do one )

[Vaughan]

1 minute ago, RealWindmill said:

  (trying to find a hovercraft emoticon - but the don't seem to do one )

No - I was trying to find one myself!

Admin, where are you when we need you?

[RealWindmill]

15 minutes ago, Vaughan said:

My father knew Chris Cockerill and saw that model being demonstrated at Somerleyton.  In fairness, it was just a biscuit tin, with a little propeller petrol engine for kids' model aeroplanes.  But the principle was proved!  Later development was, of course, done further away on the south coast..

By the way, in COLREGS, they were classified as a seaplane. I imagine they still are.

Interesting  stuff. Thanks