Help Me Plan My Mooring

[tafelice]

Hi Gang,  I'm going to put in a mooring for my boat (30', 10,000 lbs, 5' draft).  I have a permit for this mooring (they don't get specific on what is below at all) and have a temporary place holder (a 5 gal pail of concrete with a mooring ball attached).  Here is my plan, please make any suggestions, criticisms etc.  Remember, I'd like to save money where I can.

I plan to sink 3 different rebar reinforced concrete slabs in an equalateral  triangle about 30 ft apart .  Each slab will take 3 80 lbs bags which will be about 240# each.  Each slab will have a stainless steel eyebolt in the center.  Swivels attached to each eyebolt and the 3 chains (attached to the swivels) will be attached together with swivels so that the height will be at maximum river (oh yes, it's a river, no tides) height (it's controlled by TVA and will not flood above a certain height).  In those slabs, I at first thought to make them round but don't see much point and will probably make it square.  Also I planned to reserve a few coffee can size holes in the slab so that it might act eventually like a mushroom anchor allowing sand and pebbles to work up through the holes helping to self-bury the slab. 

[Captain Smollett]

I plan to sink 3 different rebar reinforced concrete slabs in an equalateral  triangle about 30 ft apart .  Each slab will take 3 80 lbs bags which will be about 240# each.

That seems a bit overkill to me.  For a boat that size, something of the order of 350 lbs for a single weighted anchor "should be" sufficient, at least based on the suggested sizes I've read while planning my mooring (for a similar sized boat).  I think I got my numbers from Hiscock's Cruising Under Sail.  Ah yes, here it is...Hiscock (not known for pushing the limit in a way likely to endanger the boat) recommends 50 lbs per ton of boat.  Therefore, for your 5 tonner, 250 lbs is a good working minimum. 

If you need more than one anchor to limit swing, you can do a Bahamian Moor with much lighter anchors - actually, you can use regular anchors sized for the boat (Danforth's, Bruces, whatever is appropriate for the bottom).  Join them by a chain at least 6x times the max water depth, put a swivel in the middle and attach mooring lines to that swivel.  You can add a third in the equilateral triangle arrangement similar to what you are planning, but used this way, they don't need to be 240 lbs EACH.  If you use lighter anchors in a 3-anchor mooring, you can pull them for inspection or if you move your boat.

Each slab will have a stainless steel eyebolt in the center.  Swivels attached to each eyebolt and the 3 chains (attached to the swivels)

I would not do this.  You are introducing TWO weak points.    An eyebolt as you describe is susceptible to being pulled straight out - embedded in concrete, it is weak in tension.  The Pardey's show a diagram of a slab mooring anchor in The Cost Concious Cruiser that has the chain embedded directly into the concrete (no eyebolt).  The important part is to set the chain in a "J" shape in the concrete so it is "hooked."  Thus an outward pull on the chain has to pull chain through multiple directions in the concrete.  Also, you don't really need swivels at the anchors.  Apply KISS with as few potential 'moving parts' and I think the whole thing will be stronger.

That's my $0.02.

Regards,

John

[AdriftAtSea]

A couple of points to consider. 

First, what is the buoyant weight of the rebar-reinforced concrete.  Salt water has a density of about 64 lbs per cubic foot.  Concrete typically has a density of about 150 lbs per cubic foot, so the effective weight will be about 55% of the actual weight of the concrete.  A 500 lb. concrete anchor, has an effective weight of 275 lbs.  All three anchors will have a total weight of about 720 lbs., but have an effective weight of 400 lbs. 

However, pulling the 240 lb. anchors out to inspect them regularly is going to be a royal pain, and installing them is probably going to be more difficult than using smaller steel anchors as suggested by Capn Smollett.  The three-anchor setup he suggests is probably a better way to go, both in terms of durability and in terms of ease of setup and installation.

If you do decide to go the concrete slab route, do not use stainless steel under water.  Stainless steel is not very corrosion resistant when it is embedded in concrete, where crevice corrosion and oxygen deprivation are going to accellerate the corrosion process.

Another way to create a connection point is to take a piece of 3" diameter galvanized pipe and bend it in a U-shape and embed it in the concrete when you pour it.  Pass your chain through the tubing, and you have a very solid connection to the mooring weight that is not likely to pull through or rust out.  The tubing protects the concrete from being abraded by the chain.

I also think a square shape to the slabs will help them hold better, since it will have square edges that are more likely to grab than a round shape would.

[tafelice]

This is great.  Good ideas.  I think that perhaps I may go with the 3 point system and here is why.  When TVA lets the water level down for "winter pool" my distance to shore and low water is a factor.  The only limitation that they, TVA, puts on me is that my mooring can't be too far from the shore.  So a 6 to 1 swing will ground me for sure.  I understand the 3 point system limits swing, so that is why I wanted it.  Right now it is swinging on an 18 lb dansforth and a 31 lb claw.   I was thinking that I would put 2 points of the triangle parallel to shore to allow smaller scope and double holding with an on-shore wind, which btw is the predominant and the strongest, and of course 1 point nearest shore where it can swing out to deeper water.  Would 3 31 lb claws be sufficient?  (btw the 31 lb claw is overrated one boat size above mine, which I like)  What I like about the 3 lighter weight steel anchors is that I can check them easily and move them more easily.  With a 3 point the boat's lateral scope would be reduced thus limiting the anchors doing a 180 and possibly working out.  Also, this is fresh water.  And thanks alot for your input this is really helping.  I don't want to assume something stupid but I'm assuming recommendations by the Hiscock's and Pardey's to be sunk weight rather than buoyant weight unless specified such.  Or is that a bad assumption?

[Captain Smollett]

This is great.  Good ideas.  I think that perhaps I may go with the 3 point system and here is why.  When TVA lets the water level down for "winter pool" my distance to shore and low water is a factor.  The only limitation that they, TVA, puts on me is that my mooring can't be too far from the shore.  So a 6 to 1 swing will ground me for sure. 

Point of Clarification from my earlier post:

In a two-anchor Bahamian Moor, you use 6:1 for the chain that connects the two anchors.  Your lines to the boat attach to the MIDDLE of that chain.  If you think about it, because of the two anchors (set one upstream and one downstream of the boat itself), you don't swing as much as on a normal single anchor with 6:1 scope.  It really is more like a 'mooring.'

Sorry if I was not clear.

I understand the 3 point system limits swing, so that is why I wanted it.

Yes, but so will the two anchor Bahamian Moor.  If you feel better with three, go with three.  The true advantage of three over two is if you cannot really determine with any certainty what will be the dominant wind/current direction.  Since you know that, you PROBABLY could get away with two if you wanted to.  Three certainly won't hurt anything - just more to lay and recover.

Right now it is swinging on an 18 lb dansforth and a 31 lb claw.   I was thinking that I would put 2 points of the triangle parallel to shore to allow smaller scope and double holding with an on-shore wind, which btw is the predominant and the strongest, and of course 1 point nearest shore where it can swing out to deeper water.

Yeah, okay, I think I see your point.  Three would probably be better, laid as you describe.  I was thinking the river current setting downstream was your biggest 'concern.'

Would 3 31 lb claws be sufficient?  (btw the 31 lb claw is overrated one boat size above mine, which I like)

I'd think so.  The Pardey's emphasize in their description that you are using gear normally carried on the boat.  The idea is to NOT expend addtional money for your mooring.  So, use whatever size ground tackle you would normally carry.  That said, 3 31 lb claws sound more than adequate.

What I like about the 3 lighter weight steel anchors is that I can check them easily and move them more easily.  With a 3 point the boat's lateral scope would be reduced thus limiting the anchors doing a 180 and possibly working out.

Exactly.  You are thinking about this the same way I am, which may or may not mean a whole lot.   ;D

I'm assuming recommendations by the Hiscock's and Pardey's to be sunk weight rather than buoyant weight unless specified such.

Right.  I don't know any cruising writer that fools around with buoyant weight when sizing anchor systems.

[skylark]

What kind of ground is it? clay? mud? sand? are there weeds?

[Fortis]

My mooring is delightfully simple. I went to a scrap yard and bought a train wheel. That's it, just a nice big worn out train wheel. Cost me $40 AUD.

I fabricated a plate (well, cut it off a length of strap) of 10mm steel that is larger then the axle hole in the wheel. I drilled the centre of this plate and bolted and spot welded a pivot (Using a very big bolt. 32mm, I think).

the plate then gets put under the wheel, the pivot sticks up through the hole and chain is attached to the pivot. The whole thing sinks into the mud at our mooring and holds like nobody's business. We have leant our mooring to a big wooden boat owned by a visiting friend, About two months of the roughest weather in the year, with a boat that is easily five times the weight of ours, with very much more windage...and it din't move an inch.

That will do.

Total cost; $80, plus chain.

I do my inspections in-situ by diving down on it.

P.S...there seems to be a good notion in adding annodes to your mooring. I put a couple of annodes onto the swivel and such and they are getting eaten away. the actual fittings are doing fine.



Alex.

[tafelice]

re the bottom, it is sand and loose rock.  very little weeds or none.

I like the idea of adding zincs.  seems that would help.  I have heard of sending down an engine block.  But all these good ideas would have to be done in triplicate.  You see it is not just the holding but the possible water level swings that I could have.  1) I can't be too far from shore, so says my permit. 2) there could be 25 feet of difference between low water and high water, it's a TVA controlled flood area.  Nice thing is that they can reasonably assure us it will not flood above the control line but then they have the right to move the water level as they see fit.  We may experience a big rise or decline for rain that fell or may fall 800 miles away. 

So short swing, with enough scope to reach flood level are the two primary considerations, then holding is third.  I've been giving it thought and perhaps overkill on the weight for each of the mooring weights might be more in order while shortening up on the scope.  What do you think.

[skylark]

Assuming you are in about 30' of water depth: Find 3 big steel danforth type anchors, and chain them together to a center point with at least 50' of chain for each anchor to a center swivel.  From the swivel, add about 40' of chain to the back end of a heavy anchor, could be a bruce, claw, cqr or knock off of any of these.  The heavy anchor should be sized appropriately for the boat for normal use, in your case at least 35lbs.  Use at least 100 foot of chain from the center anchor towards the boat to a swivel. From add heavy rode of about the depth of the water to a buoy, and from the buoy, bring two mooring lines in which connect to the boat.

As best you can, lay the danforths out in a star pattern, with one directly in line into the prevailing storm wind direction.  Set the critical one, set the others as best you can.  Connect the back end of your main anchor to the swivel and lay it down and set it so it is set for the prevailing storm wind direction.

I laid to a setup like this for a summer and had no problems in heavy clay/mud.  You can pull up the main anchor occasionally and check for chain wrap around it, I did experince a couple of wraps over a period of 2 months.

If the main anchor fails, you have a backup from at least 3 compass points.  The danger is if the main anchor fouls another anchor but I don't think this is likely.  More likely it will snag the other anchor chain and the system will still hold.

Danforths hold strong if you don't ask them to change direction.

[tafelice]

Hi Skylark, I'm trying to follow you.  Let me repeat and you correct me.  Firstly, I am now in normal summer pool (normal water from memorial day to labor day, then it goes to winter pool, down about 6 feet from labor day to memorial day.... however, in between anything can happen according to how TVA has to control water elsewhere.... we can be 20 feet higher from here).  I'm now in 14' of water, I could be in 34' at max flood.

So, I would take 3 good size steel dansforths and lay them out in a star pattern so that the 3 x 50' chains linking them together in the center would somewhat lay on the bottom (except for my inefficiencies of stretching out the star pattern?).  One of those dansforths is laying out to the south (predominant wind, strongest wind, biggest fetch).  Now, if I were to use this system I would probably use a claw for that critical anchor you mention but I'm confused as to where this one connects to the dansforth star (at the center swivel that lays at the bottom or elsewhere?).  The critical anchor is on a 40' chain, but where does that 100' of chain go?

There is several things about the above I don't understand but that aside, if I did have it laid right then from that center star swivel that lays at the bottom the water depth chain would go to the mooring ball, and then two mooring lines to be used on the boat.

Please fill in.

Thanks, Tom

[skylark]

Shackle the three danforth chains together to a swivel in the middle of the star.  Connect another chain about the same length as the danforth chains to the center swivel.  The other end of that chain gets connected to the back end of your heavy anchor (to the hole usually used for a trip line).  Then the 100 foot length of chain is connected to the normal connection point on your heavy anchor, and the other end of the chain goes to rode - buoy - mooring lines.

This will allow a lot of swing, maybe more swing than you want.  You can change the lengths of the chain and rode to shorter lengths if you want but for 30 feet depth you generally want about 100 feet of chain . 

[Captain Smollett]

Tom,

We are all basically describing the same set-up.  There can be discussion in the details.

Do you have a copy of Chapman's Seamanship and Small Boat Handling? If so, the 3-acnhor mooring is shown in the anchoring chapter.  There is also a diagram in the Pardey's The Cost Conscious Cruiser and Hiscock's Cruising Under Sail describes it but does not give a diagram.  It is probably described/diagrammed elsewhere as well.

For example, this guy describes it and shows a diagram:



Note that this is his HURRICANE mooring and his biggest anchor is a 22 lb Delta.

This system derives it's strength/reliability not from the mass of the anchors or scope in the way you normally think of it.  You are never really lying to one anchor (except those instances when you are exactly in line with one, but due to yawing, this is a small amount of total time), and each 'backs' the others up.  As the current or wind shifts, you change the PROPORTIONS each anchor is holding, but overall, you are nearly always pulling on at least two of the three.

Because you are pulling from the middle, and the system limits the swing arc (by 50% or more), you never pull on an anchor in a direction that can "unset" it.  Well, perhaps I should not use "never" cuz anything can happen, but you get the point.

This is why you can use MUCH lighter (ie, normal sized) anchors AND limit swing (so it seems like there is smaller scope).  It really does not matter how much chain you lay on the ground from the center to each anchor - make it as long as practical to you (how much chain can you afford, how much chain do you want to lift, etc).  If you lay 100 ft of chain on each leg, that does NOT mean you will swing through a 100 ft arc.

To figure the arc, make a diagram of the system you plan.  At each anchor, draw a circle that has a radius equal to the "scope" - that is, from the swivel to that anchor, plus the length of your mooring lines (which do not need to be that long, in general).  After you have drawn all three circles, color or shade only that area occupied by ALL THREE circles - that is the area where the boat will lie.

For example, you can have 100 ft rode (mooring line + swivel to anchor length) and swing very little.  On a single anchor, your arc will cover 200 ft, on a Bahamian Moor or three anchors, it will be less than two times the mooring line length.

So, the trick is to use the chain length on the bottom to get most of your scope (if you can, if you have the room), and use the mooring line ONLY to get from the bottom to the surface (for maximum depth).  If your max water depth is 35 ft, pick say a 50 ft or so mooring line and you will swing within a circle of a little under 100 ft in diameter.  For a thirty foot boat, that's only THREE BOAT LENGTHS.

Regards,

John

[tafelice]

Yes, I understand.  What confused me was the addition of the "critical" anchor that skylark described.  That was a good system but the extra anchor added extra swing.  You make a good point I need to put my extra chain in the star at the bottom.  This will give me the holding from the scope it creates and the "swivel to bow" length, which controls my actual swing, can then be just what I need to handle the max flood water height.  Great, thanks.

[skylark]

The system I described may be overkill.  But I worry about relying only on danforths, even in sand or mud.  I also like the kellet effect.  This is a system that worked for me and I left it in all summer.  It was not too difficult to remove. 

I have also used one big CQR with a danforth chained to the end of the CQR.  Big means 35lb CQR for a 28 foot boat with quite a bit of windage, high topsides, hard dodger.  That would probably work for you too with an appropriately oversized CQR.

Danforth---50 ft chain---CQR---50ft chain---swivel...30 ft rode...buoy:::two mooring lines:::cleat on foredeck

[AdriftAtSea]

I would trust the three-anchor star-shaped mooring more than two anchors in tandem.  I would think that the anchors can become fouled on the 50' link between them if one should drag.  Of course, with the weight anchors you're talking about — a 35 lb. CQR and 50' of chain, it might not get a chance to drag at all... since that is quite a bit of weight and anchor for a 28' boat.

[tafelice]

My plan is crystallizing.  Now it will be 3 star on long arms coming together I will attach a smallish mushroom or bucket of concrete to act as sentinel to all three.  Then swivel then chain to buoy swivel mooring lines.

[Captain Smollett]

My plan is crystallizing. 

That's a great feeling, isn't it?   :)

Sounds like a good, strong system.  Best of luck.