Cobra25
New member
Any one have the correct specs for laying a permanent mooring for a 26 foot yacht where it dries out on sand. TIA
Laying a mooring specifications
- Thread starter Cobra25
- Start date
oldharry
Well-known member
No such thing as 'correct specs' as such, because moorings vary so much according to where they are, so that a mooring entirely satisfactory for one area would fail rapidly somewhere else. Also if the area is subject to Harbour Board regulation then almost certainly they will have a 'preferred' mooring system
The most common system is a heavy shaped weight buried in the seabed, with a riser chain, but this may not work for you if the sand shifts a lot or is subject to strong currents as the sinker weight may become exposed and lose its grip.
I laid and maintained my own mooring for a 22 footer in a sandy estuary which was subject to regular tidal scouring, and had no trouble with it, using the following system:
I laid a ground chain of ex industrial 1 inch black chain, aprox 50 ft, with a 20lb anchor at each end to secure it, and dug the anchors well in. From the centre of the ground chain I took a riser which was 1.5x the maximum depth of the water (space for swinging was a bit limited), also in 1" black chain. A large buoy supported it, and a swivel was inserted in the half inch galvanised chain pennant from the buoy to the boat.
It is desireable to have the swivel out of the water as it wears much less so is less likely to fail.
In the ten years the ground chain never shifted over more than half its length, and I reckoned that the anchors had never been subject to any serious pull.
Go to a commercial scrap metal merchant for black chain - industrial use chain has to be replaced after a certain length of time reardless of its condition under H&S legislation, and is nearly always in good condition - and you will be charged the scrap weight price!
And wire all the shackles!
The most common system is a heavy shaped weight buried in the seabed, with a riser chain, but this may not work for you if the sand shifts a lot or is subject to strong currents as the sinker weight may become exposed and lose its grip.
I laid and maintained my own mooring for a 22 footer in a sandy estuary which was subject to regular tidal scouring, and had no trouble with it, using the following system:
I laid a ground chain of ex industrial 1 inch black chain, aprox 50 ft, with a 20lb anchor at each end to secure it, and dug the anchors well in. From the centre of the ground chain I took a riser which was 1.5x the maximum depth of the water (space for swinging was a bit limited), also in 1" black chain. A large buoy supported it, and a swivel was inserted in the half inch galvanised chain pennant from the buoy to the boat.
It is desireable to have the swivel out of the water as it wears much less so is less likely to fail.
In the ten years the ground chain never shifted over more than half its length, and I reckoned that the anchors had never been subject to any serious pull.
Go to a commercial scrap metal merchant for black chain - industrial use chain has to be replaced after a certain length of time reardless of its condition under H&S legislation, and is nearly always in good condition - and you will be charged the scrap weight price!
And wire all the shackles!
Lakesailor
New member
[ QUOTE ]
The most common system is a heavy shaped weight buried in the seabed, with a riser chain, but this may not work for you if the sand shifts a lot or is subject to strong currents as the sinker weight may become exposed and lose its grip.
[/ QUOTE ]
I recently had an old gas boiler refurbished on my British Gas contract. They replaced the heat exchanger which was a masive cast iron casting. They left it for a reclaimation company to collect. I thought it would make an excellent sinker weight for a mooring. Very heavy, virtually cubic in shape with slots through the core to put chains through. However it was so heavy that I could forsee back injury looming. When the guys arrived to collect it they were quite willing to leave it with me, but by that time I had convinced myself it would be the Work of Satan to get it out to my mooring so I let it go.
It's a thought though.
The most common system is a heavy shaped weight buried in the seabed, with a riser chain, but this may not work for you if the sand shifts a lot or is subject to strong currents as the sinker weight may become exposed and lose its grip.
[/ QUOTE ]
I recently had an old gas boiler refurbished on my British Gas contract. They replaced the heat exchanger which was a masive cast iron casting. They left it for a reclaimation company to collect. I thought it would make an excellent sinker weight for a mooring. Very heavy, virtually cubic in shape with slots through the core to put chains through. However it was so heavy that I could forsee back injury looming. When the guys arrived to collect it they were quite willing to leave it with me, but by that time I had convinced myself it would be the Work of Satan to get it out to my mooring so I let it go.
It's a thought though.
oldharry
Well-known member
I should also have added - check out and see what other mooring owners have found works in your area.
And lakeSailor, weight is not the only consideration when laying a mooring. You may have had difficulty picking up your casting, but your boat would not! An effective mooring weight is shaped to create suction beneath it, thereby enormously increasing its holding power. You might well have found the boat took off quite happily with your casting in tow in the next bad blow.
Many years ago Exchange and Mart carried an advert for a Stuart Turner engine: "Fully reconditioned, many new parts, in excellent condition: would make good mooring weight" Sadly, it in fact would not even fulfil that function, because the shape is wrong, and would not grip the seabed.
And lakeSailor, weight is not the only consideration when laying a mooring. You may have had difficulty picking up your casting, but your boat would not! An effective mooring weight is shaped to create suction beneath it, thereby enormously increasing its holding power. You might well have found the boat took off quite happily with your casting in tow in the next bad blow.
Many years ago Exchange and Mart carried an advert for a Stuart Turner engine: "Fully reconditioned, many new parts, in excellent condition: would make good mooring weight" Sadly, it in fact would not even fulfil that function, because the shape is wrong, and would not grip the seabed.
Lakesailor
New member
Should have been more precise. I was considering adding it to my concrete slab as a secondary weight on a second chain. Belt and braces.
hylass
New member
Can you give me also the beam of your boat and I will give you the exact weight and volume of concrete you will need for your boat
Every info are in my book "Tout savoir sur le mouillage" in French or in the German version "Besser Ankern". I hope to have the English version published before the end of this year...
Every info are in my book "Tout savoir sur le mouillage" in French or in the German version "Besser Ankern". I hope to have the English version published before the end of this year...
Stemar
Well-known member
I once read of an interesting idea when using a cast (concrete) sinker: Cast in a tube of sufficient diameter to allow the chain to pass freely through in a u shape around a reinforcing bar. Now use a double chain up to the swivel just short of the buoy. When the time comes to replace the chain, there's no need to lift the sinker, just connect the new chain to one end of the old one and pull it through.
Any reason why this shouldn't work?
Any reason why this shouldn't work?
William_H
Well-known member
it might work if the chain can run freely. May just save the cost of a diver however i reckon you shoyuld buy a wet suit and scuba tank.
The comments on bshape of weight are interesting but not necessarily the best way to go. Weights should primarily be something you can get for cheap and something you can manouvre yourself. If it is not enough weight then use anchors spikes or more weights to keep it in place. As with o0rdinary anchoring the weight even if small aids i n the operation of more weights or anchors. And I would reiterate the heavier the chain the better. partly because heavy chain doesn't move much so doesn't wear so much and of course has more metal to wear away. You can have as many anchors as you like to provide your level of confidence.
Even if a weight does drag it won't be too far but if a chain or shackle wears through boat has gone to ......... regards will
The comments on bshape of weight are interesting but not necessarily the best way to go. Weights should primarily be something you can get for cheap and something you can manouvre yourself. If it is not enough weight then use anchors spikes or more weights to keep it in place. As with o0rdinary anchoring the weight even if small aids i n the operation of more weights or anchors. And I would reiterate the heavier the chain the better. partly because heavy chain doesn't move much so doesn't wear so much and of course has more metal to wear away. You can have as many anchors as you like to provide your level of confidence.
Even if a weight does drag it won't be too far but if a chain or shackle wears through boat has gone to ......... regards will
snoozydude
New member
I am very interested in this as I plan to do it in the near future, the guy at the chandlery I asked, put me on to a train wheel with a big chain and foam filled float.
I think I could get it in place by putting a large drum onto the wheel at low tide, waiting for the high to lift it, then tow it into place.
I borrowed a copy of Chapmans seamanship from the library, and it has a section about moorings which mentions using a mushroom ahchor with two differing gauges of chain, one called a pennant or pendant (seems to be a typo in the book), it gives sizes and weights (but the books at home) can give you details if you like - will read it again tonight.
I think I could get it in place by putting a large drum onto the wheel at low tide, waiting for the high to lift it, then tow it into place.
I borrowed a copy of Chapmans seamanship from the library, and it has a section about moorings which mentions using a mushroom ahchor with two differing gauges of chain, one called a pennant or pendant (seems to be a typo in the book), it gives sizes and weights (but the books at home) can give you details if you like - will read it again tonight.
gjeffery
New member
_hylas_
=================================================
"I will give you the exact weight and volume of concrete you will need for your boat"
=================================================
This problem has many variables, and it would be very interesting to see the model that you would use to yield an exact solution.
=================================================
"I will give you the exact weight and volume of concrete you will need for your boat"
=================================================
This problem has many variables, and it would be very interesting to see the model that you would use to yield an exact solution.
claymore
Well-known member
I've seen old truck engine blocks used and I once used a polo mint shaped piece of concrete from a manhole system - that worked well as it seemed to sit flat then work its way into the mud.
Someone once told me that if you get a slightly convex shape it forms some kind of a vacuum. Not sure about this!
Someone once told me that if you get a slightly convex shape it forms some kind of a vacuum. Not sure about this!
Cobra25
New member
Hi Hylas
The beam is 9' 8" about 3 metres
Thanks for your help
The beam is 9' 8" about 3 metres
Thanks for your help
Cobra25
New member
Hi Dug
Yes please it would be good to get all the info we can
Thanks
Yes please it would be good to get all the info we can
Thanks
hylass
New member
For a 26 foot yacht, the weight of the concrete block should be at least 810 kg or about 0, 324 cubic meter.
If using a chain, the diameter of the chain should be bigger than 8 mm and the rope should have a diameter of at least 14 mm.
Please find below an abstract of the English version of my book "Tout savoir sur le mouillage"
- In contrast with embedded anchors, for which the pulling angle must be inferior to 8 degrees, mooring blocks also work well with a short, almost vertical rode which keeps the swinging radius to a minimum.
Solid blocks present a mooring technique where weight really does matter. The heavier your concrete mooring block, the better the holding power. Because the load is imposed almost vertically, the weight must be at least equivalent to the maximal load. The mooring block’s bottom surface should be as large as possible to create a kind of suction cup effect which will increase the holding power. This suction effect is most successful in soft bottoms such as mud, and much less successful in coarse sand or rocky bottoms. Also, this holding power increases with time as the slab sinks deeper and deeper into the seafloor.
Boat Dimensions (Meters) Wind Load (DaN)
Overall Length Beam Motorboat Beam - Sailboat Force 9 – 45 knots Concrete Weight – kg
(Volume m3)
4,50 1,80 1,50 225 410 - (0,164)
6 2,40 2,20 325 590 - ( 0,236)
7,50 2,75 2,40 445 810 - ( 0,324)
9 3,35 2,75 635 1115 - ( 0,446)
10,50 3,95 3 820 1490 - ( 0,596)
12 4,26 3,35 1100 2000 - ( 0,800)
15 5 3,95 1450 2635 - ( 1,055)
18 5,50 4,50 1800 3270 - (1,300)
21 6 5,20 2500 4545 - ( 1,820)
25 6,70 5,80 3250 5910 - ( 2,365)
Table 15: Estimated Average Loads on mooring blocks due to wind
Assuming that it will be set in relatively sheltered waters, the mooring should be designed to withstand winds of 45 knots (Force 9) with the attached vessel. To calculate the weight of the concrete block, you must account for the density of the chosen material, and its actual weight when immersed. Remember that the following materials retain only a percentage of their dry weight:
Steel– 86 % - Concrete – 55 % - Rock – 64 %.
Because cement’s holding power is only slightly above 50% of its dry weight, casting wire or other heavy steel elements into its bottom can increase its weight and thus holding power.
The above table and the table in Chapter 2 can give you an idea of the static load due to wind one must expect on a mooring given a particular boat type and length, as well as the weight of the immersed cement block necessary to hold this vertically exerted load. The value in parenthesis gives an indication of the block’s volume, assuming one uses standard steel reinforced concrete (if using only lightly reinforced concrete, multiply this value by 1.25). If establishing the mooring in a hurricane zone, these values should be multiplied by four.
Consider installing several medium sized concrete blocks in the place of one large block to facilitate installation and maintenance. These blocks would then be linked up as described in the multiple anchor mooring described above, united with an oversized chain.
If installing the mooring in a river or estuary, or anywhere with a heavy current change, twin deadweight anchors configured as a Bahamian mooring (or two groups of twin blocks) may be the best solution with the boat secured between. One principle mooring line is vertically attached to one block, to which in turn is attached a weighted messenger line, allowing the pickup of the secondary stern mooring.
Mooring Lines:
Since the mooring line needn’t be hauled aboard, over dimensioning can only be beneficial; since it rarely needs to be removed, a thicker line will better withstand continual use and chafe.
In a multiple-anchor mooring, the riding chains should be attached with the largest central shackle possible, which is in turn attached to what we will call a “storm-riding” chain. This chain should be 1.5 times the high water depth, with its work load at least the equivalent of the deadweight anchor. It will mostly sit at the seafloor and can serve as a shock absorber in strong winds. This chain will then be attached to what we call the principle chain by a shackle one diameter size bigger than the principle chain. The length of this chain should be equivalent to the sum of one high water scope plus enough to surpass your free board and attach to the buoy.
Confirm that all the consecutive parts of this configuration, especially your shackles and swivels, have a minimum work load equal to the weight of your concrete slab or deadweight anchor. This is especially true for your mooring buoy. Its floating volume must be around twice as much as the secondary chain’s weight, the ideal being a buoy with a central tubing through which the principle chain can pass. Otherwise it is important that the buoy’s ring load be transmitted to the chain by a metallic axle whose work load is at least that of the chain.
Regulations vary as to whether your mooring block may stay in the water year round. Consider it a bittersweet blessing if you must remove it at the end of every season, since this allows you to inspect and maintain it much more easily. If you are allowed to leave your mooring in year round, you still should inspect all aspects of it every year and don’t allow more than 2 years to pass without refurbishing.
Do-it-yourself Deadweight Anchors:
Once you have determined both the weight and volume of your deadweight anchor, build a mold using solid wooden boards, making sure the mooring’s bottom surface is as large as possible to increase the “suction cup” effect. With muddy seafloors, this suction force will be greatest, and to maximize on this, consider creating at the bottom of your mold a spherical volume with sand, then covered with a plastic sheet. On sandy bottoms, the suction force is almost non existent, and it is advantageous to create the opposite, that is to carve out a pyramidal cavity (again covered in plastic sheet) so that the bottom of your deadweight will bury in the most ideal manner. Use at least two welded 8 mm wire gratings and the thickest possible steel wire omega shaped. Considering the heavy weight of the concrete, the best is to have a truckload of cement ordered to fill the mold directly. If possible, make sure the concrete is vibrated to eliminate air bubbles. Give the block 2-3 days to dry, and if possible an entire week (28 days would be theoretically the ideal.)
Transportation and positioning of deadweight moorings:
The best solution is to hire a company specialized in lifting and handling these large objects, and have them placed in the water professionally. If the deadweight anchors are not too heavy (especially if using several in triangular or star formation) and if you’ve been able to build them in proximity of the beach near your mooring spot, one could wait for low tide to pull the deadweights as close to the water as possible and attach each one to two large 120 liter barrels. When the water rises, the deadweights will float, and you can drag them to the spot you wish to place them. If the area is subject to extreme tidal range, you can also place the deadweight on the water’s edge at low tide, and once high tide arrives, use a very strong line to pull them with the bow of the boat to the desired spot for immersion.
If using a chain, the diameter of the chain should be bigger than 8 mm and the rope should have a diameter of at least 14 mm.
Please find below an abstract of the English version of my book "Tout savoir sur le mouillage"
- In contrast with embedded anchors, for which the pulling angle must be inferior to 8 degrees, mooring blocks also work well with a short, almost vertical rode which keeps the swinging radius to a minimum.
Solid blocks present a mooring technique where weight really does matter. The heavier your concrete mooring block, the better the holding power. Because the load is imposed almost vertically, the weight must be at least equivalent to the maximal load. The mooring block’s bottom surface should be as large as possible to create a kind of suction cup effect which will increase the holding power. This suction effect is most successful in soft bottoms such as mud, and much less successful in coarse sand or rocky bottoms. Also, this holding power increases with time as the slab sinks deeper and deeper into the seafloor.
Boat Dimensions (Meters) Wind Load (DaN)
Overall Length Beam Motorboat Beam - Sailboat Force 9 – 45 knots Concrete Weight – kg
(Volume m3)
4,50 1,80 1,50 225 410 - (0,164)
6 2,40 2,20 325 590 - ( 0,236)
7,50 2,75 2,40 445 810 - ( 0,324)
9 3,35 2,75 635 1115 - ( 0,446)
10,50 3,95 3 820 1490 - ( 0,596)
12 4,26 3,35 1100 2000 - ( 0,800)
15 5 3,95 1450 2635 - ( 1,055)
18 5,50 4,50 1800 3270 - (1,300)
21 6 5,20 2500 4545 - ( 1,820)
25 6,70 5,80 3250 5910 - ( 2,365)
Table 15: Estimated Average Loads on mooring blocks due to wind
Assuming that it will be set in relatively sheltered waters, the mooring should be designed to withstand winds of 45 knots (Force 9) with the attached vessel. To calculate the weight of the concrete block, you must account for the density of the chosen material, and its actual weight when immersed. Remember that the following materials retain only a percentage of their dry weight:
Steel– 86 % - Concrete – 55 % - Rock – 64 %.
Because cement’s holding power is only slightly above 50% of its dry weight, casting wire or other heavy steel elements into its bottom can increase its weight and thus holding power.
The above table and the table in Chapter 2 can give you an idea of the static load due to wind one must expect on a mooring given a particular boat type and length, as well as the weight of the immersed cement block necessary to hold this vertically exerted load. The value in parenthesis gives an indication of the block’s volume, assuming one uses standard steel reinforced concrete (if using only lightly reinforced concrete, multiply this value by 1.25). If establishing the mooring in a hurricane zone, these values should be multiplied by four.
Consider installing several medium sized concrete blocks in the place of one large block to facilitate installation and maintenance. These blocks would then be linked up as described in the multiple anchor mooring described above, united with an oversized chain.
If installing the mooring in a river or estuary, or anywhere with a heavy current change, twin deadweight anchors configured as a Bahamian mooring (or two groups of twin blocks) may be the best solution with the boat secured between. One principle mooring line is vertically attached to one block, to which in turn is attached a weighted messenger line, allowing the pickup of the secondary stern mooring.
Mooring Lines:
Since the mooring line needn’t be hauled aboard, over dimensioning can only be beneficial; since it rarely needs to be removed, a thicker line will better withstand continual use and chafe.
In a multiple-anchor mooring, the riding chains should be attached with the largest central shackle possible, which is in turn attached to what we will call a “storm-riding” chain. This chain should be 1.5 times the high water depth, with its work load at least the equivalent of the deadweight anchor. It will mostly sit at the seafloor and can serve as a shock absorber in strong winds. This chain will then be attached to what we call the principle chain by a shackle one diameter size bigger than the principle chain. The length of this chain should be equivalent to the sum of one high water scope plus enough to surpass your free board and attach to the buoy.
Confirm that all the consecutive parts of this configuration, especially your shackles and swivels, have a minimum work load equal to the weight of your concrete slab or deadweight anchor. This is especially true for your mooring buoy. Its floating volume must be around twice as much as the secondary chain’s weight, the ideal being a buoy with a central tubing through which the principle chain can pass. Otherwise it is important that the buoy’s ring load be transmitted to the chain by a metallic axle whose work load is at least that of the chain.
Regulations vary as to whether your mooring block may stay in the water year round. Consider it a bittersweet blessing if you must remove it at the end of every season, since this allows you to inspect and maintain it much more easily. If you are allowed to leave your mooring in year round, you still should inspect all aspects of it every year and don’t allow more than 2 years to pass without refurbishing.
Do-it-yourself Deadweight Anchors:
Once you have determined both the weight and volume of your deadweight anchor, build a mold using solid wooden boards, making sure the mooring’s bottom surface is as large as possible to increase the “suction cup” effect. With muddy seafloors, this suction force will be greatest, and to maximize on this, consider creating at the bottom of your mold a spherical volume with sand, then covered with a plastic sheet. On sandy bottoms, the suction force is almost non existent, and it is advantageous to create the opposite, that is to carve out a pyramidal cavity (again covered in plastic sheet) so that the bottom of your deadweight will bury in the most ideal manner. Use at least two welded 8 mm wire gratings and the thickest possible steel wire omega shaped. Considering the heavy weight of the concrete, the best is to have a truckload of cement ordered to fill the mold directly. If possible, make sure the concrete is vibrated to eliminate air bubbles. Give the block 2-3 days to dry, and if possible an entire week (28 days would be theoretically the ideal.)
Transportation and positioning of deadweight moorings:
The best solution is to hire a company specialized in lifting and handling these large objects, and have them placed in the water professionally. If the deadweight anchors are not too heavy (especially if using several in triangular or star formation) and if you’ve been able to build them in proximity of the beach near your mooring spot, one could wait for low tide to pull the deadweights as close to the water as possible and attach each one to two large 120 liter barrels. When the water rises, the deadweights will float, and you can drag them to the spot you wish to place them. If the area is subject to extreme tidal range, you can also place the deadweight on the water’s edge at low tide, and once high tide arrives, use a very strong line to pull them with the bow of the boat to the desired spot for immersion.
