Mooring Loads

[r.fairman]

Does anyone know what loads a typical M type imposes on the mooring gear. I have genoa with cover,mainsail cover with lazyjacks and Mercury 50 4 stroke I am not concerned with the chain as I am using 30 m of 10mm. I have cast in reinforced concrete 350 kilos of anchor blocks. As failsafe I have spread this load over 6 separate blocks and will moor in approx 3 to 5 meters of water with a sandy or rocky bottom I propose including a snubber in the final pickup rope to reduce shock in the gear I could include an permanent 30 kilo anchor in this setup which will reduce drag I presume.

I live in Turkey with winds of force 4 to 5 during the summer midday meltemi.

[Catigale]

An all chain rode will put a lot of shock on the hull in rough weather - Im not an expert on this but I dont think a snubber will have the same stretch characteristics of 10 meters of good rode. In terms of load, that 10mm chain is plenty strong enough though.

[NiceAft]

I found this site which may be of help? whats needed for your Boat Mooring (click in order to go to the site).

I also would assume the greatest weight for your M (5,000 lbs or 2268 kilograms) for your calculations. Someday you may be sleeping on that M while moored, and you don't want to wake up to find that you are now in the Bosporus

I would also attach something like this to your bouy. . It makes it easier to grab the mooring from the cockpit of your boat

Ray

[James V]

There is a discussion on this in the SSCA forum several months ago. I know that the force on the moring in 20 mph winds can be well over 200 pounds and at 50 mph you may be looking at over 1000 pounds. You will also need to add wave shock loads.

I would suggest that you try 2 different sizes snubbers, both need to streach. You are looking at working loads and not breaking loads.

1/4 and 3/8. Make the 1/4 longer. The theory is that you will need the shock absorbed with the smaller one with the lighter winds and when it starts to blow the bigger one will take over. Latter you can go out and replace the smaller one. Most cruisers have 2 or 3 different sizes of snumbers for the winds they expect.

I do not know how to convert the US mesurements to EU. I hope you do.

[Catigale]

Your wind force will vary with Wind Speed^2

If the mooring force is proportional to wind force, which it probably is, the increase from 20 to 50 mph would be a 2.5^2 = 6x more force!!

Yikes!!

[r.fairman]

Thanks for all the input. I have seen quoted that a M26 should have at least 1 tonne (1000 kilos) = 2225 lbs as a ground anchor. This seems ecessive as I cannot believe a M26 will impose 2225 lbs of force on its ground tackle.

[Craig LaForce]

Concrete blocks are just a bad idea for any tiype of anchor or mooring.

Can you get a steel mushroommooring anchor (it digs into the mud over time) or failing that 3 large anchors that can be set in hard in the bottom 120 degrees apart and then led to a central rode that is brought up to the mooring buoy.

Hook up the ground tackle with the chain and then switch to 3 strand nylon at some point for shock absorption. this not only lessens the forces on the boat and fittings, but also on the anchor, allowing it to stay set when it might otherwise pull out.

I would also use 1/2 inch 3 strand nylon with lots of chafe protection and then maybe a chain as a loose safety rode.

[James V]

Yes it can! A mojor problem is the sway and above water. When the boat is more beam to the wind it produces a lot more drag. In a 15 knot breeze I move down wind at 3.5 mph without the sails.

[Night Sailor]

The authors I've read on anchoring safety stress that wind load is only one factor. The major one that causes failures in storms is the load repeated waves put on the tackle in addition to the wind. The more blunt the bow entry or the more broad the beam, the more resistance to wave action is forced on the rode and anchor.

I can readily image light gale winds and a six or eight foot swell on a long reach putting 2500 lbs of force on the rode and anchor or mooring. Our light displacement Macs will ride on the surface taking the brunt of the force as the bow moves both up due to wave passing underneath, and back as the wind blows against everything topside.

[James V]

If I had to ride out a gale in 6 to 8 foot swells in my Mac I would not be able to raise the anchor for a few days. That would be a rough time for me and the boat.

[Catigale]

I can readily image light gale winds and a six or eight foot swell on a long reach putting 2500 lbs of force on the rode and anchor or mooring. Our light displacement Macs will ride on the surface taking the brunt of the force as the bow moves both up due to wave passing underneath, and back as the wind blows against everything topside.

2000# plus still seems extreme to me...to put it in perspective its saying that half the weight of the boat is being transmitted

Working load of 1/2 inch braid is about 2000# IIRC, to put that 2500# load in perspective....

[Craig LaForce]

I have anchored when there was too much force to pull the boat up to the anchor by hand.

However, you can sail the anchor out. Just raise the main and the boat will start to sail and tack a couple times about the anchor and out it comes.

If a second person is aboard you could also just motor up to the anchor.

By the way, if anyone is interested in anchoring science and some other stuff, there is a book called "Modern Seamanship", which ironically is a bit out of date, but there are about 80 pages giving a thorough treatise on anchoring techniques and gear.

[Rockabill]

If you can find them, old locomotive wheels make good mooring weights on a sandy sea bed.

For our 26M swinging mooring in 4m of water we use a locomotive wheel (480Kg), connected to 6m of 75mm Ground Chain, connected to 12m of 16mm Rising Chain, connected to a 25mm swivel. Off the swivel is a A4 size bouy on 1m of 13mm chain and 2no. 18mm dia x 6m mooring warps.

Doubling up on your mooring warps is not a big expense when you consider the whole and gives you a bit of security if one fails (chaffs).

Additionally, we fitted larger mooring cleats (to suit the 18 dia. warps) and fairleads to the bow.

Regards,
Rockabill

[eric3a]

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[puggsy]

Make this up and it will not shift...even on hard limestone bottom with minimal soft sand. Three anchors each made with railway line in the shope of the letter "T". The shank about 5/6 feet and the cross bar about 3/4 feet. Place two triangular 'teeth' at each end of the crossbar, both facing down. and a securing ring at the base if the shaft. Place all three anchors flat on the bottom with the teeth facing down in a triangular pattern. distance apart will depend on available space. tight anchorage or not. about twenty feet is o.k. Run chain from all three rings to a central ring, then a single chain with swivel up to the surface. length depending on depth. Preferably, the chain three times the water depth. Does not matter which way the wind blows, you are always pulling on at least one achor. And none of it sticks up on which the hull can be punctured in the case of a low tide and iffy winds. Especially with the Mac which tends to swing a lot.
Mine was recently slightly damaged on a low tide when it swung to extremes while the neighbouring keel boat swung less...we tangled and my prop chewed his hull while his mooring float scratched my hull...not a nice situation...Hope this helps...Puggsy