How do you measure the draught of a boat?.........

[Wanderer Vagabond]

I made brief mention of this on another thread, but having checked the search facility on the subject, I haven't really found an answer to the question.

 

I know it sounds like a daft question since the way I measured Rune's draught was last time it was out of the water being blacked I measured from the waterline to the bottom of the skeg and thought 'job done', but it doesn't really work like that does it? I have since realised (OK, I'm a slow learner) that the boat is deeper at the stern than it is at the bow, by quite a lot. What that means is that if you are travelling along a canal and the stern scrapes the mud, the boat, being a bit like a 60 see-saw, will lift at the back and drop at the front so essentially being 2'8" at the stern doesn't mean that you cannot pass anywhere shallower than 2'8" since, up to a point, the boat will ride over it. I would guess it rather depends upon where the weight pivot point is given that the greatest weight (engine) is in the stern. Your progress will only stop completely when you reach a point where too much of the baseplate is in contact with the bottom of the canal.

 

I  seem to have some memory that when we went through Standedge the CRT bod used a gauge of some sort along the side of the boat and just said, "Yes, that's OK", but I'm not entirely sure exactly where he measured it. Any idea of how to get an accurate measure of the boat draught?

[mrsmelly]

I think your first thoughts are correct. If you go on a canal for instance with a concrete lining at 2ft 7inch depth I reckon you would be in trouble.

[Wanderer Vagabond]

3 minutes ago, mrsmelly said:

I think your first thoughts are correct. If you go on a canal for instance with a concrete lining at 2ft 7inch depth I reckon you would be in trouble.

I thought that until I did Savick Brook which is supposed to be 2'3" in a 2'8" boat. Have also been to the top of Llangollen which is also supposed to be 2'3", I should say I'm not disagreeing, just puzzled as to how its done.

[matty40s]

It will be interesting to see if CRT blame the knackered cill on the Rochdale on those old boats which are too deep......conveniently forgetting that the water is low because they have sold off all the reservoirs and cant buy water back.

[mrsmelly]

1 minute ago, Wanderer Vagabond said:

I thought that until I did Savick Brook which is supposed to be 2'3" in a 2'8" boat. Have also been to the top of Llangollen which is also supposed to be 2'3", I should say I'm not disagreeing, just puzzled as to how its done.

I reckon with a silted soft canal bed it may well be possible to do the see/saw thingy. If the bed is solid then floating an inch higher will be improbable? 

[dccruiser]

1 minute ago, Wanderer Vagabond said:

I thought that until I did Savick Brook which is supposed to be 2'3" in a 2'8" boat. Have also been to the top of Llangollen which is also supposed to be 2'3", I should say I'm not disagreeing, just puzzled as to how its done.

I also draw 2'8" at the stern and I did Llangollen a couple of weeks ago up to the basin, also the Monty which i was told is shallower ... in both cases there were times i felt the bottom but it certainly wasnt enough to stop me and incidentally looking at the pilings the water was around 6" down 

 

Rick

[peterboat]

I watched a a gin palace leave Torksey lock last week he drew over 3 feet with legs up, with a see saw movement he got over the cill!!

[Wanderer Vagabond]

1 minute ago, peterboat said:

I watched a a gin palace leave Torksey lock last week he drew over 3 feet with legs up, with a see saw movement he got over the cill!!

Not sure I'd be keen in a gin palace, gelcoat is a bit less resistant than 10mm of steel and blacking.

[CaptAWOL]

The see-saw effect is basically when your stern wave catches up with you, this happens when traveling at a speed'ish rate and then pulling back quite heavily on the rev's or even knocking it out of gear

[Wanderer Vagabond]

5 minutes ago, CaptAWOL said:

The see-saw effect is basically when your stern wave catches up with you, this happens when traveling at a speed'ish rate and then pulling back quite heavily on the rev's or even knocking it out of gear

The see-saw effect I was thinking of was more like I experienced on the Kennet & Avon, I think it was approaching Burghfield road bridge, when the stern of the boat lifted up as I went over a sand bar at normal cruising speed (first year on the boat, frightened the life out of me?). The bow had passed over the sand bar but when the stern hit it we rode up and over it with the stern lifting and the bow going down.

[nicknorman]

You can measure the draught of the boat by putting a tape measure down the weedhatch, hooking it under the skeg and measuring to the water line. Normally the skeg is the lowest part of a narrowboat.

 

Of course that only measure the static draught, when under way the stern will sit deeper in the water, depending on how much power/speed you have on.

[Wanderer Vagabond]

Just now, nicknorman said:

You can measure the draught of the boat by putting a tape measure down the weedhatch, hooking it under the skeg and measuring to the water line. Normally the skeg is the lowest part of a narrowboat.

 

Of course that only measure the static draught, when under way the stern will sit deeper in the water, depending on how much power/speed you have on.

That's where I measured Rune, but just because it is 2'8" at the skeg doesn't seem to mean it cannot go through waters less than 2'8" deep (see above). If you drag the skeg on the bottom, the nature of the boat would mean that it is possible for the stern to lift (and bow to go down) to ride over it. I'm wondering whether the draught should be measured at some pivot point, which is probably what the bod from CRT did before we went through Standedge tunnel

[peterboat]

34 minutes ago, Wanderer Vagabond said:

Not sure I'd be keen in a gin palace, gelcoat is a bit less resistant than 10mm of steel and blacking.

Same here but he had to be somewhere and this was his last chance for a number of days [very small neap tides and no water in the Trent]

[nicknorman]

9 minutes ago, Wanderer Vagabond said:

That's where I measured Rune, but just because it is 2'8" at the skeg doesn't seem to mean it cannot go through waters less than 2'8" deep (see above). If you drag the skeg on the bottom, the nature of the boat would mean that it is possible for the stern to lift (and bow to go down) to ride over it. I'm wondering whether the draught should be measured at some pivot point, which is probably what the bod from CRT did before we went through Standedge tunnel

I suggest you can only “seesaw” over very short distances. So to bounce over an obstruction, yes. But to take a 2’8” boat through water only 2’7” deep with a solid bottom, I think friction would bring you to a stop fairly quickly. And of course if you add more power, the back sinks down even more (or tries to).

 

i can’t remember what the draught limit for standedge was, but we got through last year no probs at 2’8 1/2” . If you can reach Standedge via the low and silted pounds of the W HNC then I’m sure you can get through the tunnel - which seemed pretty deep by comparison!

Edited June 4, 2019 by nicknorman

[howardang]

It's not rocket science. A piece of string with a small weight in the middle passed over the bow wil passed over the bow will show the draft on each side of the bow. You already know how to measure the draft using the weed hatch. Alternatively, if that is too sophisticated, a long  piece of wood with a shorter piece of wood nailed to it at right angles and with the shorter piece passed under the boat at any point will allow you to measure the approximate draft at that point.

 

Howard

[Wanderer Vagabond]

1 minute ago, howardang said:

It's not rocket science. A piece of string with a small weight in the middle passed over the bow wil passed over the bow will show the draft on each side of the bow. You already know how to measure the draft using the weed hatch. Alternatively, if that is too sophisticated, a long  piece of wood with a shorter piece of wood nailed to it at right angles and with the shorter piece passed under the boat at any point will allow you to measure the approximate draft at that point.

 

Howard

I think that is the crucial point, the draught of the boat varies from bow to stern (obviously) but it seems to me that it is the average draught that is what will bring the boat to a stop (or not)

17 minutes ago, nicknorman said:

I suggest you can only “seesaw” over very short distances. So to bounce over an obstruction, yes. But to take a 2’8” boat through water only 2’7” deep with a solid bottom, I think friction would bring you to a stop fairly quickly. And of course if you add more power, the back sinks down even more (or tries to).

 

i can’t remember what the draught limit for standedge was, but we got through last year no probs at 2’8 1/2” . If you can reach Standedge via the low and silted pounds of the W HNC then I’m sure you can get through the tunnel - which seemed pretty deep by comparison!

I agree that more power when you drag the bottom is the worst thing you can do, you just move more water, not the boat, but knock the boat into neutral and drift and it is often possible to ride over shallow cills. I have even had cills that I couldn't 'drive' the boat over but was able to bow haul it out of the lock.

 

Yes, I can indeed get through Standedge but the bod who did the measuring did so along the side of the boat, not at the skeg. I can't remember what the draught limit for the tunnel is without looking it up (I think it is actually quite deep in parts) but I just remember him measuring it for some reason, and it wasn't at the deepest part (skeg). he was happy with the draught and we got through OK.

[David Mack]

1 hour ago, matty40s said:

It will be interesting to see if CRT blame the knackered cill on the Rochdale on those old boats which are too deep......conveniently forgetting that the water is low because they have sold off all the reservoirs and cant buy water back.

 

As owner of one of those old  boats, I can confirm that the cills you can see (the top gate cills) are a lot deeper down than the lengths of canal between the locks, which is where we grounded from time to time.  No problems getting over the cills, although going down in one lock one of the other boats did seem to land on something in the middle of hte chamber, and had to be flushed off.

[DandV]

In a shallow narrow canal, eg  the huddersfield narrow, the prop acts as a pump removing water from under the boat, so lowering the water level. Best tactic, and speed, under those circumstances, we found was dead slow, if we were moving forward that was the best we could hope for, If the boat started gently to rise, sometimes with a loss of directional control, this indicated a meeting between the bottom of the canal and the bottom of the boat. Then a prompt brief change to astern, before you had come to a complete stop, pumped enough water back under the boat to refloat it before actually going backwards, whence progress ahead could be resumed. 

[Pluto]

11 hours ago, matty40s said:

It will be interesting to see if CRT blame the knackered cill on the Rochdale on those old boats which are too deep......conveniently forgetting that the water is low because they have sold off all the reservoirs and cant buy water back.

You can hardly blame CRT for lack of water supplies as the reservoirs were sold off in 1923. If you want to blame someone, it was naïve of the Rochdale Canal Society and subsequent funders to suggest restoration without considering the water supplies. BW only took over responsibility for the canal after restoration.

[billh]

11 hours ago, David Mack said:

 

As owner of one of those old  boats, I can confirm that the cills you can see (the top gate cills) are a lot deeper down than the lengths of canal between the locks, which is where we grounded from time to time.  No problems getting over the cills, although going down in one lock one of the other boats did seem to land on something in the middle of hte chamber, and had to be flushed off.

As another operator of those old boats,did you notice the  recently repaired top gate cills on some locks have the holding down studs and nuts protruding above the cill by a couple of inches instead of recessed into the wood? So, low water level  and a boat catches  a stud, bends it and loosens the cill, canal closed. Recessed studs, boat slides over smooth top of cill, no problem. Happen it's the same with bottom gate cills, but you don't usually get to see them.None of this does the boat  bottom any good either ,especially wood ones.

And another thing: low water  and we didn't get stuck on a cill, it was very obvious that a stop plank had been left in the grooves at the head end of a lock, can't remember which one.I know that makes for ease of sealing when planks next have to go in, but not helpful from a navigation point of view.

Edited June 5, 2019 by billh

[ditchcrawler]

Just gently cill your boat by about 1  to 2 inches and try and drive it or even pull it off the cill, you will soon see what is the important measurement

 

[MtB]

4 minutes ago, ditchcrawler said:

Just gently cill your boat by about 1  to 2 inches and try and drive it or even pull it off the cill, you will soon see what is the important measurement

 

 

If you cill a full length boat by 1", there will be about half a tonne of downward force on the cill I reckon. 

 

But I'm not sure. It might be 1/4 tonne. 

 

 

[bizzard]

Years ago this happened to the QE2. It was doing cruises to the Carribee's out of New York when it had had engine trouble in the Carribee's. So on its way back to New York it sped up to make up lost time. Whilst passing over a shallowish bit off the east coast it dragged its bottom and damaged its sterngear. The ship always passed that way but at moderate speed, but the extra speed lowered the ship by about 5 meters or so.  You'd have thought the crew would have realised this. Why I don't don't trust cruise ships.

[MtB]

23 minutes ago, bizzard said:

Years ago this happened to the QE2. It was doing cruises to the Carribee's out of New York when it had had engine trouble in the Carribee's. So on its way back to New York it sped up to make up lost time. Whilst passing over a shallowish bit off the east coast it dragged its bottom and damaged its sterngear. The ship always passed that way but at moderate speed, but the extra speed lowered the ship by about 5 meters or so.  You'd have thought the crew would have realised this. Why I don't don't trust cruise ships.

 

Shear arrogance, ignoring all the shouts of "SLOW DOWN" from all the moored ships they were passing, presumably.....

 

 

[Naughty Cal]

14 hours ago, Wanderer Vagabond said:

Not sure I'd be keen in a gin palace, gelcoat is a bit less resistant than 10mm of steel and blacking.

We have landed on the middle cill in Torksey before with NC. We knew we were going to be close for depth so were going very slowly at the time. The lockie flushed us off and I hung over the bow which was enough to get us up and over the cill. Didn't damage the boat at all, in fact the next time it was lifted there was no evidence of the cill strike or grounding. Can't imagine it was very nice for the 2 small boats that were in the lock behind us though as they will have been rocked around as the lockie let some water down for us!