|SJ23 Tech Tip B27, (Updated 2015-04-26) Bob Schimmel|
Mooring Design for a Pocket Cruiser.
It is often said, "there are those who have run aground and there are those who are gonna run aground!" I prefer to belong to the latter group and hope the storm gods will be kind to my boat should she break loose. I used to moor Panache on the north shore of Wabamun Lake, Alberta, along with a dozen other boats. The anchorage was located just West of Whitewood Point at 16W, 530 34' 06" N. & 1140 35' 47" and about 1 KM east of "fabled" Coal Point, the choke point of the lake. For you land lubbers, that's approximately 70 km west of Edmonton on Highway 16W. The anchorage is protected from NW to NE winds. The majority of it blows from the NW but the worst of it comes from the SE, thankfully not as often because it is fully exposed from that direction. We could count on at least one major storm in early Spring and several major thunderstorms during June. The thunder storms have a nasty habit of delivering golf ball size hail and the odd tornado. In 2003 a tornado skipped over the moored fleet, just above mast height, saving the boats from major damage. However, just to remind us of the brute force, it obliterated solar panels, some windows, many Windexes and stripped all the foliage off the trees. What a day that was. Once a major storm is raging through an anchorage, it's too risky to row to your boat to beef up your mooring lines. This is why an exposed boat requires a strong, dependable mooring ALL the time. The mooring design that follows may seem like overkill, but it's a system that allows us to sleep at night! It is scaled to handle a pocket cruiser sailboat, weighing up to 3000 lbs, moored in 10' (3M) deep water. Many 27' (8.5M) cruisers copy the design by scaling up the components. The picture above shows the overall design of an all chain mooring equipped with a small mooring buoy. If you use a large buoy then use a single heavy chain right to the buoy. What follows is a description of each component from bottom to top of the design. Today's weather forecast.
MOORING WEIGHT - Somewhat by accident (and maybe with a bit of intelligence) one of our previous club members discovered that a surplus truck brake drum (Kenworth size or larger) makes an excellent mooring weight. At 110 lbs, one of these 16" steel drums will suck itself into the bottom goop (mud and sand) in our anchorage so well that it sticks like the proverbial "shit to a blanket" phrase. The "secret ingredient" is the open rim that settles into the soft bottom, leaving no projections that might foul the chain and shorten the rode. Once the drum is buried, it is an ideal shape to handle the 3600 swing of the mooring chain. The drum must be placed on the bottom with the open side down to ensure it sinks straight down into the mud, which is extremely desirable. Some drums sink so much that the chain is the only thing showing at the bottom; perfect. We generally let a new mooring drum settle into the bottom for about a week before using it.
For those of you who cannot find a surplus truck brake drum you could imbed scrap steel in a steel container or imbed it in cement. Use as little cement as you can so the majority of the weight is steel. Include a steel rod equipped with a ring to attach the chain to. Only the ring should be outside the concrete. Make your form from heavy timber or dig a hole in the ground. A very effective shape is an inverted pyramid, with the ring sticking out the base. This is a design idea from Texas where it works well to hold a navigation marker.
A truck brake drum can be converted to a mooring weight quite easily using one of the methods described below. The drum shown in the picture at right uses the first method. The good part of this design is that steel does not corrode in deep fresh water. The metal is in pristine condition. I replaced a corroded section of my chain after 20 years.
For years I moored my 3000 lb San Juan 23 with 30' of 5/16" bottom
and 8' of 1/4" top chain tied to a brake drum in 10' deep water. See
diagram above. She never
dragged her mooring in winds that reached 70 knots. The reason I used 1/4"
top chain is
that I didn't want to sink the small ball. Now that I have a
large ball with lots of buoyancy the chain has been changed to all
The heavier chain results in a smoother ride. The bottom in
our anchorage consists of light goop or mud over sand. (This goop is
locally known as "Loon
shit," being named after a beautiful bird that doesn't deserve this label!
Go figure). The drum works itself into the sand in only a few weeks, thereby increasing the holding
power due to the suction. However,
some sailors are adamant about adding more weight to their mooring and do
so by lowering a second drum over (on top of) the first one. The technique for
doing this is
to stretch the chain up vertical over the drum while dropping the
new drum down over the taught chain. It is quite the experience to feel
a 90 pound drum sinking to the bottom. It feels like it will snag
the chain and pull you down.
Shown here are two photos of assembled guest moorings, ready to be deployed.
- The catenary effect of a heavy chain is very effective at holding a bow
down. It dampens the pitching forces that result in a boat riding quieter
at anchor. If the effect is strong enough it may even eliminate "hunting"
but not unlikely. Therefore, use 3/8" or heavier chain.
If you use larger chain it will stand up longer to the chemical corrosion
and abrasion on the lake bottom.
If you use
grade 70 chain, which is 10 times harder than grade 30 chain, it can
withstand the abrasion that much better.
In my experience corrosion is the problem, not abrasion. If you want extreme strength and weight, use closed link chain. However, this
is also a very costly stuff and difficult to acquire! When you think about
it though, the chain is cheap
compared to the cost of repairing your boat! A 4x1 scope for an all chain
rode is adequate at Wabamun Lake. Considering that the average
mooring depth is 10', then the bottom chain should be about 45' long. (Includes freeboard). See LIGHT
TOP CHAIN for the remaining portion of the rode.
TOP CHAIN - If you
have a small mooring ball (12") or moor in 10' deep water with a larger
ball (16") then use 8' of 1/4" chain from the
surface down to the heavy bottom chain. Cut
the length of 1/4"
chain 2' shorter than the depth at your mooring. This ensures that the
heavy bottom chain takes the wear and corrosion in the rotting
vegetation on the lake bottom. Attach the light chain to the end of the heavy chain
with a quick link or a double clevis adapter. For security, wire
both pins shut using mild steel wire. Use water proof grease on the thread
of the quick link so you can remove it later.
- All chain fittings MUST have a rating of at
least 1 ton. Lock all pins with mild steel wire, not stainless steel wire.
Dissimilar metal will corrode in one year on the coal-laden bottom of
Don't use a nylon tie-wrap to lock your fasteners. They rot in only one year under water. This surprises me since nylon
line lasts "forever" under water.
- The ball MUST be equipped with a swivel, either internal or external, to
prevent torque loading (twisting) of the chain and premature wear. Twisted chain
wears much faster than strain relieved chain. Most rigid foam filled or inflated mooring balls are equipped with an internal
so attach your light chain directly to the bottom ring using a shackle. Wire all screw pins
shut using mild steel wire in such a way that the chain cannot rub against
it. See the picture below.
OWNERSHIP - Label your mooring ball with the name of your vessel, owner name, address and phone number to designate ownership. This is a mandatory regulation under the Canadian Coast Guard Aids to Navigation and it sure minimizes confusion when a guest arrives in the anchorage. I've been told that these rules are seldom enforced by the Canadian Coast Guard but it may be legally advantageous to comply should another vessel founder after striking your mooring ball. Ask a lawyer!!!!
- I like the security of two mooring lines instead of a single one. If I know a
huge storm is approaching I will temporarily add a third line from the bow
eye on the stem directly to the chain at the bottom of the ball. I
enough slack so the ball has just enough room to move as if the third line
were not there. My two
main mooring lines consist of two
equal length of 1/2" (minimum) triple plait nylon with a loop spliced at the top
end. Set at least six tucks in the splice. Do NOT use a
knot. A splice is 50% stronger and lies flat on the deck. These lines should have no more than
1' of slack in calm water to ensure that they don't wrap around the
mooring chain and that the bow picks up the chain
when the wind starts to blow. This helps to dampen the hunting at
the mooring and keeps the ball from bouncing against the hull. Avoid the temptation to
use all the line you bought simply because you don't want to waste
it. Pennants longer than described above will droop in the water and then wrap around the
chain below the ball as the boat ghosts around the mooring ball.
That's exactly the situation to avoid during a storm as the line will
abrade right where it wraps around the chain. Another
way to prevent the pennants from wrapping around the chain is to make the
lines float by slipping a foam tube over each. Use the type of foam tubing that kids play with
in the water. While preventing a line from sinking it also makes it
easier to pick up when you approach the mooring. If you use lime
green foam they stick out like a sore thumb in the anchorage. Don't
use red, you won't be able to see it at night. Don't use floating
yellow poly line because it rots with the UV.
FITTINGS - On Panache
there are two ways to run the 1/2" mooring pennants; through the mooring chocks mounted on the edge
of the deck (shown above)
or over the anchor rollers
(shown right). In either case the pennants terminate at their deck mounted cleat.
I also tie the pennants to the
rollers to ensure they stay there. The boat rides quieter when the
lines are attached further forward. All deck fittings MUST be
firmly through bolted, equipped with a generous solid wood backing plate
and sealed to the deck with marine adhesive, Sikaflex, 3M or butyl rubber
to prevent movement and water leakage. Use a large metal plate that
straddles both mounting bolts of the chock or cleat to distribute the load
equally. Use nylock nuts on the bolts to ensure they stay tight with
vibration. Imagine that you have to hold 1/3 of the boat's weight from the
cleats! Use 3/4" rubber garden hose (not vinyl) as chafe gear around
your pennants as shown at right. Slip the line through the hose BEFORE
splicing your loops in the end.
SET A MOORING DRUM FROM A SAILBOAT - Attach the chain to the drum and roll it into waist deep water so you can float the bow over it. Slip a 30' length of 1/2" yacht braid through a chain link, run it up to the bow and tighten the line. This should pull the bow down so when you walk to the stern it should lift the drum off the bottom. Slowly motor to your previously marked mooring spot and let out the line so the drum settles to the bottom in a controlled fashion. This ensures that the drum rests upright on the bottom. In 10' of water you require about 30' of line to have a workable tail end on deck. Keep the line taught to the surface while you retrieve it. A flat barge is another excellent platform for this type of work. In many ways I prefer it due to the extra stability and walking area.
SET A MOORING DRUM FROM A DINGHY - Attach the chain to the drum and slide it into knee deep water over a plank laid on the bottom. Lash a 6' long (2x8)" on top of a dinghy so it sticks out 6" past the transom with the rest over the center seat. Lash it securely to the middle seat and sit on the plank. Float the dinghy transom above the drum. Slip a 30' length of 1/2" yacht braid through a chain link (just above the weight) and pull both free ends over the (2x8)". Snug up the line and secure both ends to a cleat on the plank. This will pull the stern down but as you sit in the dinghy your weight should counter balance the drum so it lifts off the bottom. Slowly row to your marked mooring spot and let out one of the lines (wearing gloves) so the drum settles to the bottom in a controlled fashion. This ensures that the drum rests upright on the bottom. Allow the chain to pay out freely, keeping some tension on it so the chain does not get trapped under the weight. In 10' of water you require about 30' of line to have a tail end of workable line in the dinghy. Keep the line taught to the surface while you retrieve it. Remember to attach a float to the end of the chain before you lower the weight to the bottom!
MOVING A MOORING DRUM - This can be a heck of a task if the drum has settled in for many years. We like to run a 3/8" poly line through one of the links in the chain and bring both ends of the line up to the bow sprit of a Venture 23 that is equipped with a bow sprit. With a couple of guys standing on the bow we pull the line as tight as we can, pulling the bow down as much as we can. Then we walk to the stern which usually loosens the drum from the bottom. Sometimes a couple of pushes from the 6HP engine are required to break it loose. Be patient so you don't break things. Having loosened the drum, we retighten the poly line to remove the slack. Once we get the drum under way, we DO NOT STOP till we reach the new location. This job is easier when moving from shallow to deeper water. If you move to shallower water you will have to suck up the poly line several times to keep the drum just above the bottom. Beer sure tastes good afterwards.
SAFETY - ALWAYS WEAR GLOVES when working with chain, heavy weights or line that has the potential of zinging through your hands like a greased pig. You'd be amazed at how fast poly line can remove flesh, leaving nice white bones to look at! Damn that smarts.
MOORING INITIATION - The very first time you connect your boat to your new mooring should be done in calm weather. It takes a week or more before the drum settles into the bottom, which is when the holding power really increases. How long it actually takes depends on how soft the bottom is. At Wabamun Lake, where the bottom is mostly sand and thin mud, this process takes a couple of weeks. If you have a gravel bottom it will likely take much longer. I couldn't begin to predict how tidal current affects the settling. That being the case I would suggest adding a second drum. Anyway, I think that slight tugging on the mooring chain during calm weather will hasten the settling process. The tidal current should help sink it as well. DO NOT connect the boat to a new mooring with a storm arriving. You will likely find her against a shore somewhere.
WINTER STORAGE and SPRING RETRIEVAL - If the water in your area freezes during winter, you have to remove the ball and lower the chain to the bottom before it turns hard. Trust me, you don't want to attach a sacrificial float and let it freeze in the ice. You will likely find your mooring quite some distance from where you left it. Ice moves in winter! The clever thing to do is stay under the ice. Attach enough 1/8" nylon line to the end of your chain to extend it to shore. When close to shore bury the line in the bottom so the ice can't get at it. Ever hear of ice moving a beach? I didn't think so. Tie the end of the line to a rock or something else you can find in the Spring. I usually do this in 1 foot of water. No sense in getting any wetter than you have to. The beauty of nylon is that it sinks to the bottom where it can stay under a fisherman's hook. Occasionally the line sinks just into the bottom all the way to the mooring. You couldn't ask for better protection. One last point with regard to pulling the chain up to the surface in Spring, attach enough 3/8" nylon line from the end of the chain to reach the surface. This way so you can really haul up on the heavy chain without fear of breaking the light 1/8" line. Oops. Chain has a nasty habit of settling into the bottom over a winter and sometimes it can be quite a tug to rip it out of the mud. Once you get it to the surface, flip the chain over the gunwale, shove a screw driver though it and into the oar lock to keep it there, attach your mooring ball and flip the whole works back into the drink so you are good to go for another season. OK you were supposed to pull the screw driver out before flipping it all into the drink!
HUNTING OR SAILING AT THE MOORING (or ANCHOR) - Some hull designs continually "hunt" or sail at the mooring. This is really uncomfortable to the crew and hard on the deck fittings and mooring line. If your SJ23 hunts then consider the following hints:
AT ANCHOR - If I have to anchor in rough weather, onset of white caps, I like to set 2 anchors 400 apart with equal scope. While this eliminates the majority of the hunting, allowing you to get some rest, you also have to be vigilant of winds shifts. Any shift greater than 200 and you will have to consider resetting one of the anchors. Not a pleasant task at night!
HOW LONG WILL A MOORING LAST? - The consensus by many sailors on Wabamun Lake is that a sail boat mooring will probably last a person's life time. This is probably true of the mooring weight but the same cannot be said of the mooring chain. In 2004 a old mooring chain broke at Poole Sail Club. For a while we didn't know what the cause was but when the broken mooring chain was compared to several broken dock chains at Sunshine Bay Yacht Club I noticed similarities. The surprising thing about all the chains was that the failure was in the same short section. This was the 1 meter of chain that rose up from the bottom muck. In all the chains the links above and below the failed section were in excellent condition. But just to add confusion, some PSC moorings have lasted longer than others, so this failure is not totally predictable. You have to keep an open mind. These similar failures started me wondering about the source of the problem. In the final outcome it is hoped that if a person can understand the factors then we should be able to guestimate the state of a chain and form an inspection and replacement schedule to prevent breakage.
CORROSION - Much of the metal corrosion that occurs in a prairie lake has to do with the chemical cocktail at the lake bottom in the Littoral zone. This is the zone that extends from shore out to the depths of where vegetation growth ends, which is the zone in which we install our moorings. In most northern prairie lakes the Littoral zone has a bottom consistency of sand, mud, decaying vegetation ("loon shit") and in the case of Wabamun lake, coal dust. The water in this zone is also warm and contains the majority of the oxygen; two other components required for corrosion. This chemical cocktail produces a mild sulphuric acid that will corrode a steel mooring chain laying in the vegetation. Hence the rational of why the 1M of chain that leaves the bottom corrodes, leaving the rest in pristine condition. But the answer is not as simple as this.
So why do some moorings last longer than others? This question can be answered by the factors that contribute to the rate of combustion or rot of vegetation; water temperature and oxygen content. Just slightly deeper than the Littoral zone is the thermo cline. If you SCUBA dive you can actually float on this denser cold water, it is that pronounced. It is bitterly cold if you dip your toes into it. The water below the thermo cline is usually very clean with good visibility. The important factor about this boundary layer of cold water is that it has less oxygen and a lower temperature that make for poor combustion. If a mooring is below the thermo cline, the steel remains virtually pristine and might actually outlast most boat owners. Steel in shallow warm water is usually immersed in mud and will stay relatively pristine due to the absence of oxygen. In addition, this steel cannot abrade because it does not rub against anything. In fact, I have pulled my mooring chain up out of the mud and it literally "rips" out of the bottom to reveal pristine metal. This almost make one consider not installing the drum, but I won't go that far!
The pictures below are from a mooring that was below the thermo cline. The chain is 20 years old. Note the excellent condition of the links below the ball. However, at about 12 feet down the corrosion starts abruptly. Unfortunately the rest of the chain is still on the lake bottom so I cannot show it to you but, as I've seen pristine chain on other moorings, the damage does not occur when the chain is buried in the mud.
While corrosion is at play, abrasion can't be ruled out. There can be little doubt that a chain rolling over a sandy bottom will experience abrasion. Consider it as slow motion grinding. If you have ever seen how quickly wet sand paper can remove material, you will understand the nature of this problem. But if the problem were just abrasion then the sides of the links would be worn smooth, which they aren't. It's only the ends of the links that are worn! Very perplexing. Without doing an in-depth chemical analysis of the processes or wishing to spend ten years underwater to observe the motion, we are left to conclude that both factors affect the chain but at varying degrees, based on local conditions. Regardless of which factors affect your mooring chain, the damage almost always occurs where the horizontal chain meets the vertical rise; just where the acid and sand are located.
SOLUTION - To repair your chain just lift the damaged section to the surface, cut it out, and insert a new section using two repair links. Since we now know what to look for and where to find it, inspect your chain annually to avoid a sudden and catastrophic failure during a storm.
CONCLUSION - This mooring design should keep your boat secured so you and everyone else can sleep peacefully at night. It would be sheer hell to hear about the trip that your boat made "slipping" through the anchorage, bouncing from one boat to another, unattended. There is no guarantee in this design and I do not assume liability for damage to your boat. If you have a heavier boat, simply scale up the dimensions to match the requirements of your boat. To date almost everyone at PSC has converted to it with complete success and peace of mind. If you intend to use this design please send me an email as I've been told that many people around the world have copied it and I'm curious to know where this design is used. I'd be interested in hearing about any improvements you have made. Good luck with your mooring and I hope this design works well for you.
|NOTE - The rules and regulations stated in this Tech Tip apply to Canadian waters. You should comply to the regulations in your local waters.|