Anchor Size/Type

[snaps]

Hello there,

 

I Will be long term mooring on the River Weaver (Weaver Navigation) and realise I will need an Anchor, but what size will be required for a 53FT narrow boat. I don't want the situation arising where I rely on it and it does do its job. They seem to be around 7 to 15 kg, I guess the shape is important to depending on the amount of silt? etc

 

Any ideas.

 

Regards

 

Si

[Alastair]

Hello there,

 

I Will be long term mooring on the River Weaver (Weaver Navigation) and realise I will need an Anchor, but what size will be required for a 53FT narrow boat. I don't want the situation arising where I rely on it and it does do its job. They seem to be around 7 to 15 kg, I guess the shape is important to depending on the amount of silt? etc

 

Any ideas.

 

Regards

 

Si

I think 15Kg is far too light. For a 53ft boat, 20-25kg would be better. Carry a lighter one as well, for anchoring when it is calmish, and the heavy one for emergencies.

 

You also need chain - either 3xmaximum depth, or (2xmaximum depth + 2-3xmaximum depth in rope).

 

see http://www.anchor-marine.com.au/anchor&.htm for some useful info.

[Keeping Up]

Most people settle for 15kg on the basis that even with the weight of the chain it is still possible to haul it back on board again without a winch. You are likely to be discouraged from deploying the anchor in a developing emergency situation, if you know that after doing so you will have no option but to leave it behind when the emergency is over and you want to proceed.

 

I've seen virtually no definitive advice that has been based on the real and measured needs of a narrowboat; the published tables generally assume a different sort of boat altogether (where a 53 ft boat is a large multi-decked gin palace weighing 100 tone or more).

 

Personally I've got a 15kg anchor, plus a long length of heavy chain (about 20m) and finally a short length of rope (about 5m). I don't know how it would perform in an emergency, thankfully I've never had to use it in one.

[WJM]

Why do we need such a long chain?

 

I understand the chain is required to make the anchor fall over and thus bite the river bed ie: without it the anchor will sit upright and do nothing - but why does the chain need to be so long?

[howardang]

Why do we need such a long chain?

 

I understand the chain is required to make the anchor fall over and thus bite the river bed ie: without it the anchor will sit upright and do nothing - but why does the chain need to be so long?

Because of its weight chain gives a more horizontal pull, which allows the anchor to bed in and hold better than a more upright pull which rope gives. A long length of chain also forms a catenary which allows some "give" when weight comes on to the anchor/chain combination. In other words it acts as a spring, whereas all rope will have less give and therefore requires more length proportinally than chain. 3-4 times water depth for chain as opposed to 6-7 times water depth for rope as a rule of thumb.

 

As regards the comment earlier about being less inclined to deploy an anchor if it is too heavy to recover, buoy it with a fender for recovery later.

 

Howard

[Yoda]

Most people settle for 15kg on the basis that even with the weight of the chain it is still possible to haul it back on board again without a winch. You are likely to be discouraged from deploying the anchor in a developing emergency situation, if you know that after doing so you will have no option but to leave it behind when the emergency is over and you want to proceed.

 

I've seen virtually no definitive advice that has been based on the real and measured needs of a narrowboat; the published tables generally assume a different sort of boat altogether (where a 53 ft boat is a large multi-decked gin palace weighing 100 tone or more).

 

Personally I've got a 15kg anchor, plus a long length of heavy chain (about 20m) and finally a short length of rope (about 5m). I don't know how it would perform in an emergency, thankfully I've never had to use it in one.

 

Yes this is the case. No point in having an anchor set up that you cannot lift into or out of the water. I dont know about 20 metres of chain, but that weight would help the anchor. I would have more than 5 metres of rope and would have a boay attached to it. You forgot the most important item that should be on the list, a one handed knife. Dont try to use a knife that requires two hands to open it. If you have got it out, you need to use it quickly. Hence the need to use a rope onto the anchor chain.

 

The boay is there to refind the anchor when you have cut away from it!

[MoominPapa]

Yes this is the case. No point in having an anchor set up that you cannot lift into or out of the water. I dont know about 20 metres of chain, but that weight would help the anchor. I would have more than 5 metres of rope and would have a boay attached to it. You forgot the most important item that should be on the list, a one handed knife. Dont try to use a knife that requires two hands to open it. If you have got it out, you need to use it quickly. Hence the need to use a rope onto the anchor chain.

 

The boay is there to refind the anchor when you have cut away from it!

I've seen this advice before, but I don't understand it. I thought the point of having an anchor on rivers was as a way to stop a boat with a disabled engine so that it doesn't get swept over a weir, or out sea. Under what circumstances on a river would one need to cut away an anchor quickly? I'm not disputing your advice, just trying to educate myself.

 

Also, on a trad boat, as far as I can see the only place to keep an anchor is at the bows, attached to the forward T-stud. Presumably, if I'm going downstream when my engine blows up, thowing the anchor over the side will result in some interesting rotation before the boat finally stops, pointing upstream. Is that a problem? Is there a better way?

 

MP.

[saltysplash]

I've seen this advice before, but I don't understand it. I thought the point of having an anchor on rivers was as a way to stop a boat with a disabled engine so that it doesn't get swept over a weir, or out sea. Under what circumstances on a river would one need to cut away an anchor quickly? I'm not disputing your advice, just trying to educate myself.

 

Also, on a trad boat, as far as I can see the only place to keep an anchor is at the bows, attached to the forward T-stud. Presumably, if I'm going downstream when my engine blows up, thowing the anchor over the side will result in some interesting rotation before the boat finally stops, pointing upstream. Is that a problem? Is there a better way?

 

MP.

 

 

That is indeed the normal use including those times where you may want to anchor and wait for a tide if there is no where to moor, and yes, you would swing round into the flow. The only time i can imagine cutting loose the anchor would be if you find it impossible to recover or are about to be rammed by a Fire Ship and to avoid your rigging being set ablaze and endangering the magazine a quick escape is required.

 

Ive only ever used chain, which provides much more grip for the anchor and i think i remember that the general rule is the length of chain deployed needs to be 3 times the expected depth whereas with warp, its 4 or 5 times the expected maximum depth

[Yoda]

I'm feeling so bad with this virus I've had for a while that I'm finding it difficult to spell bouy properly/

[blackrose]

Also, on a trad boat, as far as I can see the only place to keep an anchor is at the bows, attached to the forward T-stud. Presumably, if I'm going downstream when my engine blows up, thowing the anchor over the side will result in some interesting rotation before the boat finally stops, pointing upstream. Is that a problem? Is there a better way?

 

MP.

 

That is indeed the problem of dropping (not throwing!) an anchor from the bows of your boat when going downstream. The boat will swing around until the bows face upstream. If the river is not wide enough or there are bridges or other traffic nearby this could be dangerous, so some people keep the anchor at the stern if going downstream. However if you deploy an anchor from the stern there is the possibility that in certain conditions your stern could get flooded by a strong current or ebb tide. I would feel far more comfortable anchored in a strong current with my bows facing upstream.

 

Unfortunately here is no easy answer to this dilemma, but basically it's a good idea to have anchors at both ends and then you're ready to do what you think is best at the time, according to the particular situation.

Edited March 10, 2008 by blackrose

[Alastair]

Yes this is the case. No point in having an anchor set up that you cannot lift into or out of the water.

I have to take issue with this. There is absolutely no point in having an anchor that can't hold your boat in the conditions. If you can't haul the anchor out, you can buoy it and disconnect yourself from the anchor rope or chain. Retrieve it later, when you can get help.

 

Conditions can vary; I've had a prop shaft go on the Ouse, in the tidal section. The 35Kg anchor only held once we'd streamed out all the chain (about 30ft) + 40ft of rope. That was on a 50ft widebeam boat, only weighing 12 ton. No wind.

 

Bear in mind that you are only likely to deploy your anchor in an emergency. You need to be confident that it will work. I've had emergencies 3 times, and each time was very glad I had an anchor.

 

You could keep your anchor on the roof, in the centre. Run a rope from it back to the cockpit or bow, depending on whether you are going downstream or upstream. If you are anchoring in a fast current, then the attachment point should be on the centreline of your boat, and as low down as possible. Many narrowboats have an eye low down on the bow, this is a better point to attach the anchor chain or rope than the T-stud. Run a short length of rope down from the bow to the chain, so you can haul it up to the bow.

 

I much prefer chain to rope, simply because it is unlikely to get caught on your prop. If there are two of you onboard, one person hauls in the anchor, the other cons the boat. Start hauling in, and simultaneously motor the boat forwards towards the anchor. This eases getting the anchor up considerably. If the anchor has 'set' solidly, you haul in as much as possible and tie off the anchor chain. Then motor forcibly forwards, which will usually 'break out' the anchor. Once the anchor has broken out, haul the rest in.

 

It's easier than it sounds.

[magnetman]

Alastair - out of interest what were the circumstances of the 3 emergency situations you mentioned?

[blackrose]

I have to take issue with this. There is absolutely no point in having an anchor that can't hold your boat in the conditions. If you can't haul the anchor out, you can buoy it and disconnect yourself from the anchor rope or chain. Retrieve it later, when you can get help.

 

I agree. Recovering your anchor is secondary.

 

First you have to get the bow of your boat (assuming the anchor was deployed from the bow), over the anchor and then bring in the rope/chain. If you don't have an anchor windlass fitted (and most NBs don't), then the most difficult part of the lift will be when the anchor itself reaches the surface of the water. If you can't get it out the water and back onboard, don't injure yourself trying to do so. With the anchor at the surface your boat is free to move. Tie off the chain carefully to a cleat, stud or bit, perhaps even tie it off to two places for safety and get the anchor back on board later.

Edited March 10, 2008 by blackrose

[DHutch]

I have to take issue with this. There is absolutely no point in having an anchor that can't hold your boat in the conditions.

Agreed.

- We have an anchor around 25kilos for emilyanne (well, its as heavy as a modern size sack of coal i recon).

- Never had to use it in ernest, but i wouldnt want anything small than that for a 56ft 22tonne lump on a river.

 

We have (apprently) around 60ft of chain. Tied at the end with a loop of rope (incase it needs cutting). With a chain winch on the boat.

 

I also agree that if going down stream on a river narrower than the boat is long, the anchor should be moved to the rear of the boat.

 

Although there is also an argument that in heavy/flood conditions you should go down a river backwards anyway, so for that, anchor at bow.

 

 

 

Daniel

[MoominPapa]

.... in heavy/flood conditions you should go down a river backwards anyway,

Doing that would really mess with my brain.

 

MP

[RobinJ]

Because of its weight chain gives a more horizontal pull, which allows the anchor to bed in and hold better than a more upright pull which rope gives. A long length of chain also forms a catenary which allows some "give" when weight comes on to the anchor/chain combination. In other words it acts as a spring, whereas all rope will have less give and therefore requires more length proportinally than chain. 3-4 times water depth for chain as opposed to 6-7 times water depth for rope as a rule of thumb.

People tend to skimp on chain because of storage, DON'T. The more chain the better!

You don't know how deep the water is going to be when you do get into trouble (i.e. Flood). If you spend money on an anchor you want to make sure it digs in and holds when you actually have to use it. Going downstream backwards on the Trent in a 23ft cruiser at 6 knots is too late to you wish you had bought an extra 6 metres of chain!

[Alastair]

Alastair - out of interest what were the circumstances of the 3 emergency situations you mentioned?

 

Coming out of Grimsby docks, a coupling on the prop shaft snapped. Ebbing 3 knot tide sweeping us towards a very large jetty. We anchored and used the VHF to contact the harbourmaster. He contacted a small trawler, who towed us back to the lock.

 

Half-way between Goole and Selby, overheating on a prop-shaft bearing. 3-4knot ebbing tide. Anchored, cleaned out bearing and re-greased, then carried on without incident.

 

Travelling down to Goole for a survey, with prospective buyer onboard. The other part of the prop shaft coupling snapped. Anchored with difficulty, as we were being swept downstream very rapidly. Phoned for a tow.

 

The lessons to learn from this are:

 

A) Make sure your anchor is big enough and you have enough rope+chain

 

Don't rely on home-made propshaft couplings.

 

I replaced the troublesome coupling with a Pythondrive, what a difference. The boat became wonderfully quiet, and I was even more sorry that I had to sell her.

 

Note that these incidents all occurred on fast-flowing water, when the engine and drive were more stressed than normal. I'd had the boat for over a year, and run in some hairy conditions in the non-tidal Ouse without problem. Even doing an emergency chase and tow for someone else's 40ton widebeam in a strong current. I had no reason to believe that there would be any problems with the boat when taking it for a survey.

[blackrose]

People tend to skimp on chain because of storage, DON'T. The more chain the better!

 

Isn't the chain guage also relevant? (as well as the displacement of the boat you're trying to stop.)

 

I've got 10m of 10mm link chain attached to about 30m of 22mm rope on a 30kg anchor, but by the sound of things this isn't enough chain (or rope). My boat's about 28-30 tonnes, but when I go out on the tidal Thames I've no idea how deep it is? 50ft in the middle perhaps? That would mean I'd need 150ft (or 45m) of chain! Or can I reduce the chain length with a better chain/rope combo?

[CJT]

Isn't the chain guage also relevant? (as well as the displacement of the boat you're trying to stop.)

 

I've got 10m of 10mm link chain attached to about 30m of 22mm rope on a 30kg anchor, but by the sound of things this isn't enough chain (or rope). My boat's about 28-30 tonnes, but when I go out on the tidal Thames I've no idea how deep it is? 50ft in the middle perhaps? That would mean I'd need 150ft (or 45m) of chain! Or can I reduce the chain length with a better chain/rope combo?

 

 

 

I've seen advertised somewhere "weighted rope" as a substitute for chain. Does anyone have any experience of this?

 

Chris

[carlt]

Your chain and rope diameter is fine though you could use more chain. The chain should be at least as long as your boat, though, preferably more.

[Dalesman]

Isn't the chain guage also relevant? (as well as the displacement of the boat you're trying to stop.)I've got 10m of 10mm link chain attached to about 30m of 22mm rope on a 30kg anchor, but by the sound of things this isn't enough chain (or rope). My boat's about 28-30 tonnes, but when I go out on the tidal Thames I've no idea how deep it is? 50ft in the middle perhaps? That would mean I'd need 150ft (or 45m) of chain! Or can I reduce the chain length with a better chain/rope combo?

Depending on the type of river bed you are going to anchor in ie: mud, clay, shingle etc and the flow of the river you will need between 3 and FIVE times the depth of water, the more chain you have out the better.

[carlt]

Depending on the type of river bed you are going to anchor in ie: mud, clay, shingle etc and the flow of the river you will need between 3 and FIVE times the depth of water, the more chain you have out the better.

That's the total scope length, most boats don't have that amount of chain. If you are in more than 10m of water your scope should be no more than 5 times the depth of water.

 

(The scope is the combined chain/rope length)

 

Edited to say: This is a reasonable guide to scope length:

 

" The scope (length of anchor line) should be determined according to the water depth below your keel and the wind conditions -

less 10m : 3 times the water depth, up to Force 3;

5 times the water depth, up to Force 6;

7 times the water depth, up to Force 9.

 

More than 10 m : no more than 5 times the water depth.

 

• Beyond Force 9, you should set 2 anchors, either each on its own line (allowing a 60° to 90° angle or both anchors on the same line with a 2 to 5 m chain interval.

Edited March 11, 2008 by carlt

[magnetman]

Where i am the water is 4ft deep and it's force six so i guess i need a 20ft scope

[carlt]

Where i am the water is 4ft deep and it's force six so i guess i need a 20ft scope

If you can't reach the bank I'd chuck a mud-weight, tied to a mooring line, in.

[GUMPY]

Isn't the chain guage also relevant? (as well as the displacement of the boat you're trying to stop.)

 

I've got 10m of 10mm link chain attached to about 30m of 22mm rope on a 30kg anchor, but by the sound of things this isn't enough chain (or rope). My boat's about 28-30 tonnes, but when I go out on the tidal Thames I've no idea how deep it is? 50ft in the middle perhaps? That would mean I'd need 150ft (or 45m) of chain! Or can I reduce the chain length with a better chain/rope combo?

 

Parglena weighs 34ton and I have a 30kg danforth (which is a bit light) 40m of 10mm chain and 50m of 18mm rope.

The most that I have used ( in 8m of water at high tide ) was all the chain, when it came to weigh anchor the next morning it took me the best part of half an hour to get the anchor up as it had gone so deeply into the mud. In the end I just drove over it to pull it out, the bow went down about two feet before it released.

 

 

A couple of interesting sites:

http://www.bluemoment.com/anchorrodes.html

http://www.johnsboatstuff.com/Articles/anchor.htm

 

The second has an intersting spreadsheet at the end.

 

Julian