A bit of newbie confusion about "headroom"

[Tom Morgan]

Today my Nicholson Guide arrived and it tells me that the maximum headroom on the Staffs. and Worcs. Canal is 6' 0".  Does this mean headroom measured from the towpath or from the waterline?  I have recently bought a 1970 Norman 23 with the one-piece GRP windscreen.  I don't know the height of the windscreen above the water, and can't easily get to the boat (still on the seller's marina) to measure.  I'm now worried that my boat might not be able to navigate my preferred canal!  As always, I'd be very grateful for any advice.

[Phil.]

On a canal, headroom is the height from the water line which is fairly constant. On tidal rivers the height can change so different calculations are required.

[BruceinSanity]

We’ve never had any worries about air draught on the S&W in SA, not even scraped the digital radio aerial, which must be over 6’ above water level at the tip. One or two of the lock tail bridges are a bit neat, I guess.

 

If you know the model of your Norman, can’t you find the specs online?

[arbutus]

I had a Norman 23 with a fixed windscreen. I moored at Ashwood marina on the Staffs & Worcs. It certainly went under the bridges between Autherley junction and the marina. 

[bizzard]

If you lack headroom, a little grease daubed upon the pate, or better still a caster wheel screwed onto the head which wood run along your ceiling reducing the friction, making it much easier to get about inside.

[Mike Hurley]

Jones boatyard list one, sold, airdraft  6 feet 10 inches.

[David Mack]

Headroom is a rather imprecise concept. It's fine for flat decked bridges, but arched bridges will be higher than the quoted headroom at the centre, but may well be lower than quoted towards the sides. So whether a particular boat will fit through depends also on the width of the cabin top (or in the OP's case windscreen) at the highest point.

[Jen-in-Wellies]

1 hour ago, David Mack said:

Headroom is a rather imprecise concept. It's fine for flat decked bridges, but arched bridges will be higher than the quoted headroom at the centre, but may well be lower than quoted towards the sides. So whether a particular boat will fit through depends also on the width of the cabin top (or in the OP's case windscreen) at the highest point.

Arched bridges and tunnels are a problem depends on the width of the cabin at the highest point. The only place I have seen this laid out in great detail is the cabin roof width versus air draft requirements for the Standedge tunnel, where they will check and refuse you passage if your boat can't be made to meet it.

 

One of these?

 From this site http://www.normanboats.co.uk/norman_range.htm

Gives an internal cabin height of 5' 10.5", draft of 1'10 at the back. Subtract one from the other and add a few inches for cabin bilge, ceiling and a foot or so for the fixed windscreen surround still puts it below 6' I reckon.

 

Don't see a Norman 23 having a problem on most of the canal network.  They are not tall boats. Except ironically enough at Standedge tunnel, where fibreglass hulls are banned!

 

Jen

Edited September 25, 2018 by Jen-in-Wellies

[X Alan W]

If you are to high regarding   air draft which I doubt you will be, laying on the cabin top engine/boat stopped& push on the underside of the bridge sort of vertical legging should push the boat down without to much bother full water ;fuel tanks should help  remembering from way back the lowest bridge I remember was the girder bridge near the pottery that the "Milton Maid use to tie by just over 5 ft due to subsidence

[roland elsdon]

1 hour ago, X Alan W said:

If you are to high regarding   air draft which I doubt you will be, laying on the cabin top engine/boat stopped& push on the underside of the bridge sort of vertical legging should push the boat down without to much bother full water ;fuel tanks should help  remembering from way back the lowest bridge I remember was the girder bridge near the pottery that the "Milton Maid use to tie by just over 5 ft due to subsidence

I warned our co owner about that bridge having pinged the headlight. He ignored my advice... he then spent a happy winter rebuilding mast cross planks and stands. What frightened him most was the top planks sliding down the cabin top as he hit the deck board on the bridge.. 

[Tom Morgan]

Thanks, all, for your advice. Jen-in-Wellies - yes, my boat's the same as the one in your photo.

[Phil Ambrose]

9 hours ago, Phil. said:

On a canal, headroom is the height from the water line which is fairly constant. On tidal rivers the height can change so different calculations are required.

Are you confusing airdraft with headroom. A boats airdraft always remains the same albeit with a slight variation due to water load and fuel load. 

Headroom will of course alter due to water levels, tides etc.

Both airdraft and headroom are measured from the waterline.

Phil 

[Alan de Enfield]

11 minutes ago, Phil Ambrose said:

A boats airdraft always remains the same albeit with a slight variation due to water load and fuel load. 

True (in some respects) but if you are planning any salty water sailing be very aware that as you leave salt water and come onto fresh water (or vice versa) there will be a difference in both Air draft and 'water' draft.

 

Air draft will be higher in sea water, and 'water' draft will be less that it is in fresh water by approximately 3%

[bizzard]

Hence a Plimsoll Line.

[Alan de Enfield]

10 minutes ago, bizzard said:

Hence a Plimsoll Line.

Called 'Trainers' these day, but doesn't have quite the same 'ring' to it.

[Phil Ambrose]

15 minutes ago, Alan de Enfield said:

True (in some respects) but if you are planning any salty water sailing be very aware that as you leave salt water and come onto fresh water (or vice versa) there will be a difference in both Air draft and 'water' draft.

 

Air draft will be higher in sea water, and 'water' draft will be less that it is in fresh water by approximately 3%

True, but I chose to omit this little nugget because by and large airdraft is not usually a problem at sea

Phil 

[Alan de Enfield]

1 minute ago, Phil Ambrose said:

True, but I chose to omit this little nugget because by and large airdraft is not usually a problem at sea

Phil 

On entering Scotland's Canals, (particularly the Caledonian) they suggest that you recalculate your draft(s)

[bizzard]

20 minutes ago, Alan de Enfield said:

Called 'Trainers' these day, but doesn't have quite the same 'ring' to it.

I walked past BOOTS in the High st the other day. Opened the door and shouted SANDALS and ran off.

Edited September 25, 2018 by bizzard

[Iain_S]

2 hours ago, Alan de Enfield said:

On entering Scotland's Canals, (particularly the Caledonian) they suggest that you recalculate your draft(s)

Surely only the below water one, as the Caledonian has infinite headroom?

[doratheexplorer]

Nicholson's Guide are full of mistakes about headroom.  My four counties ring one says the headroom on the Trent and Mersey is 5'9".  Which it obviously isn't.

[colmac]

The only bridge we have an issue with on the S&W is White Horse bridge near Kinver. We have an air draught of around 6ft and find it quite snug but no real problems.

[Alan de Enfield]

7 hours ago, Iain_S said:

Surely only the below water one, as the Caledonian has infinite headroom?

Not quite - sailing vessels do need to consider air draft (ours is 60 foot)

 

MAXIMUM DIMENSIONS 45.72 m (150ft) long; 10.67m (35ft) beam; 4.1m (13.5ft) draft.  Vessels with draft over 3.8m (12.5ft) are advised to contact the Canal Office before arrival. Maximum mast height in the canal is 35m (115ft) above the waterline, but clearance under the Kessock Bridge on the Inverness Firth is lower at 27.4m (89.8ft)

[X Alan W]

13 hours ago, roland elsdon said:

I warned our co owner about that bridge having pinged the headlight. He ignored my advice... he then spent a happy winter rebuilding mast cross planks and stands. What frightened him most was the top planks sliding down the cabin top as he hit the deck board on the bridge.. 

He was not the only one JackTolley demolished his deck board & all aft to near the aft stand & his butty hit him up the a**e pushing him further under & totally jamming his boat twixt bottom & a clutter of masts /stands/ planks under the bridge "Tirfor" to the rescue followed by expletives & cigarette bobbing violently up & down attached to lower lip

[Tom Morgan]

Thanks you all for your advice.  There's a whole jetty full of GRP cruisers at my proposed Marina.  The manager tells me that no-one has ever reported a problem. The cockpit covers have to come down, of course.   So I'm confident again.  All the parts of the jigsaw-like arrangements for moving my boat are falling into place, so here's hoping!

 

[BruceinSanity]

11 hours ago, doratheexplorer said:

Nicholson's Guide are full of mistakes about headroom.  My four counties ring one says the headroom on the Trent and Mersey is 5'9".  Which it obviously isn't.

It’s the official headroom of Harecastle Tunnel, I believe, but they normally keep the summit pound an inch or two below datum to provide a bit more.