Are cats or monhulls nmore prone to anchor dragging?

SAWDOC

SAWDOC

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Are cats or monhulls more prone to anchor dragging?

Hi Folks,
I was wondering if a change from mono to cat (assume both around 33 foot mark) would result in greater or lesser risk of anchor dragging? How does one balance less displacement versus higher windage? We have many shallow harbours in these parts and I thought a cat might suit on a number of headings - such as less draft, and an ability to take the ground easier? Don't have any experience of cruising cats so could I invite comment please.
 
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I would have thought that the seabed you are anchoring in was more important than the type of boat on top, i.e. weedy and rocky or soft and gloopy.

Multihulls requiring less water can get into parts other boats cannot reach, which is also important for finding good protection.
 
We have had 2 cats and 3 monohulls, I would find it difficult to compare though. The cats 9m and 8m have been very stable at anchor never ranging around but under certain conditions One of the monohulls used to be always rangeing around and snatching which would drag in conditions where I know the cats wouldnt have .....But... last year at Porlock weir, we were anchored with force 8 blowing off the land for several hours I had to reset the anchor twice dragging due to windage, the ground is large pebbles and we might not have dragged in the Mono, then again could have just been the weight of anchor in combination with the large pebbles.

Me I would have a cat for taking the ground , all though we have taken the ground many times in the westerly .One of the things I really like about the cat is being able to watch the world outside when at rest .In a mono unless its a motor sailer with a big doghouse you cant see out.
Only MHO everybody to his/her own .
 
As you said : Catamarans can usually get in more shallow waters than monohulls, particularly those that have daggerboards. This gives them more opportunity to use a greater rode scope for a given anchoring radius. This gives them more holding power for a given anchor/ground type.

However, catamarans do have more windage, and this may become a problem in extreme conditions. Generally for a given length of boat, catamarans should carry the next size of anchor up from the same length monohull ....... although there weight carrying capacity would not encourage this.

Another variable, this time for monohulls, is that they tend to fishtail on anchor. This can break an anchor out. Not all monohulls fishtail. I've never known a catamaran to fishtail, probably due to using an anchor bridle, but they can fore-reach ...... but I have never seen this pull a properly set anchor out.

In reality you will probably find cruising monohulls carrying substantially larger anchors than recommended by the manufacturers. On my monohull (36 foot) I have a 35 kg CQR backed up with 2 15kg danforths. On my 40 foot cat I carry a 22kg claw, backed up by a Fortress FX37 and a 15kg danforth type. To date I have only dragged in poor ground conditions ..... boulders and silt, generally using the wrong anchour for the ground conditions ...... CQR's plow in silt, danforths excel.

It is generally understood that you wont get reliable holding below 5:1 scope, 7:1 being preferred. More scope would be require for more extreme conditions.
 
TradewindSailor said:
As you said : Catamarans can usually get in more shallow waters than monohulls, particularly those that have daggerboards. This gives them more opportunity to use a greater rode scope for a given anchoring radius. This gives them more holding power for a given anchor/ground type.

However, catamarans do have more windage, and this may become a problem in extreme conditions. Generally for a given length of boat, catamarans should carry the next size of anchor up from the same length monohull ....... although there weight carrying capacity would not encourage this.

Another variable, this time for monohulls, is that they tend to fishtail on anchor. This can break an anchor out. Not all monohulls fishtail. I've never known a catamaran to fishtail, probably due to using an anchor bridle, but they can fore-reach ...... but I have never seen this pull a properly set anchor out.

In reality you will probably find cruising monohulls carrying substantially larger anchors than recommended by the manufacturers. On my monohull (36 foot) I have a 35 kg CQR backed up with 2 15kg danforths. On my 40 foot cat I carry a 22kg claw, backed up by a Fortress FX37 and a 15kg danforth type. To date I have only dragged in poor ground conditions ..... boulders and silt, generally using the wrong anchour for the ground conditions ...... CQR's plow in silt, danforths excel.

It is generally understood that you wont get reliable holding below 5:1 scope, 7:1 being preferred. More scope would be require for more extreme conditions.
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Thank you for a very good reply. I don't understand your use of the term "fishtailing" - is that excessive swinging about the anchor position? Could you explain please?
 
Having sailed both I think the advantages of the cat are that you can get in to more sheltered anchorages because of shallow draught as others have said. However, especially in a river with wind against tide (which is inevitable either on the ebb or flow) the cat will range about far more than a monohull due to the fact that the keel effect is far less. If in shallow water where you may wish to stay for a day or so a swivel joint is a good idea sometimes as you really can tie knots in the chain otherwise. Also the idea of paying out more chain, while attractive on your own is often a PITA to others as you will sail in bloody great circles all over the anchorage! As far as dragging the anchor in a gale is concerned, there is no real practical difference although with a cat a bridle will help. (anchor set with a heavy rope line from each bow to a chain shackle in the middle). It will also reduce snatching as the bows rise and fall. Sometimes however a bridle is also a PITA in shallow water and can get cought up if the boat "sails over the anchor" (as they do!) All in all it's not better or worse, it's just different. There is no substitute for experience which will tell you in time how your particular boat behaves.
 
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The first time we dropped the pick from our cat she wandered from side to side and this was on a bridle.

We managed to add a couple of lengths of heavy line and extended the length of the bridle by about ten feet, so the chain was underwater an extra ten feet from the roller.

The result, wandering all but stopped. I later replaced the extension ropes with a new longer bridal made by the local rigger and added a swivel to the anchor; no problems since and we have been in wind against tide, heavy wind and all but glassed out.

I also remember the quarter toner we had years ago would swing all over the place, we had anchor well clear of the fleet in tight areas; never did work out why.

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Fishtailing

Is it not the case some hull shapes are more prone to fishtailing as they are aerodymamically drawn towards the wind like an aircraft wing ?

This is obviously much more the case with a monohull than a Cat.
 
What a loaded question! There are so many variables, as we have already seen in the responses that I dont think there can be any clear answer. However, I would say that a large cruising cat is likely to have greater windage than a monohull at anchor, and therefore applies a higher load to the ground tackle than a similar length monohull.

Even that is not clear. I would be fairly certain for example that my 24 foot Trident has greater windage at anchor than a 24 ft Strider cat, and therefore breaks my rule of thumb.

But there are so many other factors that have been highlighted already - the sheering about of a monohull places heavy shock loads at differing angles which can break an anchor out. On the other hand, Cats are more prone to pitching or 'hobbyhorsing' which can have the same effect.

So I think one can only really make a comparison by comparing specific Models. Its a bit like asking which make of car is more likely to be involved in an accident - Ford or Toyota? :)
 
SAWDOC said:
Thank you for a very good reply. I don't understand your use of the term "fishtailing" - is that excessive swinging about the anchor position? Could you explain please?
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Fishtailing : when a boat swings from one side to the other at anchor. This is due mainly to windage, but it can also be due to hydrodynamic drag on the keel.

Consider a kite for a moment: It is secured by a piece of string about 1/4 to 1/3 back from it's leading edge. If you flick it up into the wind it will get some aerodynamic lift and rise into the air. This is what happens to an anchored monohull ..... breeze (or current) catches the boat slightly off head on, and creates lift. The boat then sails off to one side until the tension on the anchor rode increases enough to pull the bow round onto the other tack and the boat goes off on this new direction. The boats on light rodes, like nylon, are far more likely to fishtail than those with chain.

Catamaran bridles : the minimum length of a bridle from the bow to the rode is 1.5 x the beam. Shorter than this: your putting a large compression load into your front beam and bow structure in strong winds.

If you use a chain hook for the snubber or bridle : make sure it never touched the ground or it could come off. Shackles are a better solution in shallow water.
 
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