Big Trimaran: 55, 70, or 110 kg Rocna

[Mike Banks]

I find that if your anchor windlass is permanently connected to the negative of your battery and the actuating switch is in the positive leg, you have effectively connected the chain and anchor to your battery, and your galvanizing may well disappear rapidly. The cure is to connect BOTH legs via mercury relays--so that when at anchor the windlass and chain and anchor are isolated entirely and not part of the earth system.

Even if your anchor winch is hydraulic, it is still a good idea to check that there are no connections to the battery of any kind.

[pbmaise]

Originally Posted by Mike Banks

I find that if your anchor windlass is permanently connected to the negative of your battery and the actuating switch is in the positive leg, you have effectively connected the chain and anchor to your battery, and your galvanizing may well disappear rapidly. The cure is to connect BOTH legs via mercury relays--so that when at anchor the windlass and chain and anchor are isolated entirely and not part of the earth system.

Even if your anchor winch is hydraulic, it is still a good idea to check that there are no connections to the battery of any kind.

I will need to look at this when I get back to my boat.

I have gone with the 70 kg Rocna and having a machine shop drill two holes 4.5" OC so I can bolt on an extra 1 kg of zinc. Unlike most sailors, owing to size, I usually am not on a mooring. So my anchor gets wet most of its life.

I also no longer use a swivel at the anchor. This means I have to monitor the chain for twists from daily wind shifts. I manually ensure the chain enters the water straight. I think work the twists out to a swivel mounted inside the anchor locker.

[noelex 77]

Originally Posted by Mike Banks

I find that if your anchor windlass is permanently connected to the negative of your battery and the actuating switch is in the positive leg, you have effectively connected the chain and anchor to your battery, and your galvanizing may well disappear rapidly. The cure is to connect BOTH legs via mercury relays--so that when at anchor the windlass and chain and anchor are isolated entirely and not part of the earth system.

The better metal boats do this on every circuit via double pole circuit breakers.

On a non metal boat this is overkill, but it is worth considering isolating the anchor winch and autopilot. These are the two items most likely to cause problems.

There is no need for relays. A simple double pole battery switch is all that is needed. An alternative that is commonly used is to have a single pole battery switch on the positive supply and the anchor winch circuit breaker on the negative side. Providing the anchor winch circuit breaker and the anchor winch battery switch are turned off both the negative and possitive supply are isolated.

[noelex 77]

Originally Posted by pbmaise

I will need to look at this when I get back to my boat.

I have gone with the 70 kg Rocna and having a machine shop drill two holes 4.5" OC so I can bolt on an extra 1 kg of zinc. Unlike most sailors, owing to size, I usually am not on a mooring. So my anchor gets wet most of its life.

I would be wary of doing this.

It is easy to upset the balance and/or the penetration of the anchor. An extra 1kg on the shank (even on a 70 kg anchor) would be enough to reduce the performance mainly by altering the COG. On the fluke it would cause less balance problems, but would still have some effect reducing the penetration.

The other things to consider are the extra holes weakening the anchor and also the effect on the warranty.

Finally, if the anode is a slightly different electrical potential to the zinc coating you risk that the zinc galvanising will sacrifice itself to protect the anode making the corrosion significantly worse.

If you really want to do this, give some thought to an aluminium anode, as it will minimise all the above problems.

[Mike Banks]

I still prefer the mercury relays because of the high currents involved in lifting an all chain rode plus an anchor of that mass.

[Mike Banks]

I think that you need some sort of method of preventing the chain twisting--and the easiest one is a good quality sealed bearing swivel, not the simple ones most chandlers sell which are OK for smaller vessels--it is the surge to a tight chain that snaps them. If you are using an all-chain rode the place for them is on the shank of the anchor. This is also the place I would have fixed an anode--simply shackle or bolt it to the chain--it need not be a particularly large one. No need to drill any holes and better if you do not--since you have just penetrated the galvanizing and introduced a weak spot.

If you feel you MUST put an anode on the anchor shaft--use a big propeller shaft anode and just bolt it on like a clamp. Do it just under the place the chain connects. I do not think it is necessary, but in any case an anode will NOT stop the corrosion an anchor gets when buried in mud containing sulphurous acid--because that is CHEMICAL corrosion, not stray currents or galvanic action. You will smell it on the anchor if it is present--it smells like rotten eggs. The only way of slowing THAT down is to paint the anchor with Poly-U 400 or something similar, which has good abrasion resistance and is impervious. It will need to be re-coated frequently on the bits most subject to abrasion, the fluke.
.



Trimarans stop a lot of wind and because of the slot effect of the hulls, love to race from side to side across the wind. They also do it to a lesser extent against the tide. this means that unless one streams a drogue or uses a stern anchor, the bower anchor is being pulled from side to side each time the vessel reaches the limit of its swing before it races off in the other direction. Using a bridle will lessen the effect but not always eliminate it. My boat is a Piver which has comparatively larger amas than most tris except perhaps a Horstman design, which have similar hulls to a Piver, although there the similarity ends..

I use a 60 pounds Manson on mine--but mine weighs only about five tons empty and no more than seven fully laden. I use an all chain rode with a kellet, and have an additional two hundred yards of 20mm nylon which can be added should I need to anchor in deeper water. My windlass will not lift the anchor plus an excessive length of short link 13 mm chain, so I have only two hundred feet of it.

I like to have a bit of over-kill where anchoring is concerned. I have had anchors drag before and constantly being awakened by the anchor alarm to discover that with each surge the boat is moving two or three metres while ploughing the ocean floor is no fun.

The only way of obviating a swivel and getting a good night's sleep is to anchor by the stern as well---this prevents the vessel from swinging with the tide and limits the ability of the vessel to swing to anchor. If you do you elect to use a stern anchor as well, make sure you are well clear of anyone likely to swing on to you as the tide or wind changes.

[Olddave]

Originally Posted by Mike Banks

I think that you need some sort of method of preventing the chain twisting--and the easiest one is a good quality sealed bearing swivel, not the simple ones most chandlers sell which are OK for smaller vessels--it is the surge to a tight chain that snaps them. If you are using an all-chain rode the place for them is on the shank of the anchor. This is also the place I would have fixed an anode--simply shackle or bolt it to the chain--it need not be a particularly large one. No need to drill any holes and better if you do not--since you have just penetrated the galvanizing and introduced a weak spot.

If you feel you MUST put an anode on the anchor shaft--use a big propeller shaft anode and just bolt it on like a clamp. Do it just under the place the chain connects. I do not think it is necessary, but in any case an anode will NOT stop the corrosion an anchor gets when buried in mud containing sulphurous acid--because that is CHEMICAL corrosion, not stray currents or galvanic action. You will smell it on the anchor if it is present--it smells like rotten eggs. The only way of slowing THAT down is to paint the anchor with Poly-U 400 or something similar, which has good abrasion resistance and is impervious. It will need to be re-coated frequently on the bits most subject to abrasion, the fluke.
.



Trimarans stop a lot of wind and because of the slot effect of the hulls, love to race from side to side across the wind. They also do it to a lesser extent against the tide. this means that unless one streams a drogue or uses a stern anchor, the bower anchor is being pulled from side to side each time the vessel reaches the limit of its swing before it races off in the other direction. Using a bridle will lessen the effect but not always eliminate it. My boat is a Piver which has comparatively larger amas than most tris except perhaps a Horstman design, which have similar hulls to a Piver, although there the similarity ends..

I use a 60 pounds Manson on mine--but mine weighs only about five tons empty and no more than seven fully laden. I use an all chain rode with a kellet, and have an additional two hundred yards of 20mm nylon which can be added should I need to anchor in deeper water. My windlass will not lift the anchor plus an excessive length of short link 13 mm chain, so I have only two hundred feet of it.

I like to have a bit of over-kill where anchoring is concerned. I have had anchors drag before and constantly being awakened by the anchor alarm to discover that with each surge the boat is moving two or three metres while ploughing the ocean floor is no fun.

The only way of obviating a swivel and getting a good night's sleep is to anchor by the stern as well---this prevents the vessel from swinging with the tide and limits the ability of the vessel to swing to anchor. If you do you elect to use a stern anchor as well, make sure you are well clear of anyone likely to swing on to you as the tide or wind changes.

Do you use a bridle? My Farrier 31 was a completely different kettle of fish to your Piver, but it showed no inclination to shear around on the anchor. I always used one and with the 6.2metre beam it was very effective.
I have a mono now and that does it more than the tri ever did. Traitor to the multi ranks? Not really, I bought an S&S hoping it would sail as well as a tri and therefore keep me happy!
Dave

[pbmaise]

Thanks for great suggestions. Yesterday I anchored in a very protected small bay with soft mud bottom. My crew returned to their home islands.

Fortunately while at machine shop, I had a different former crew member on shore notice a squall and my boat started dragging. He was able to start engine and attach to mooring plus anchor down too. I will have to untwist daily mooring and anchor line. Until I get set better.

I was anchored in close quarters and I think it was more a matter the anchor had not dug in enough when set on reverse. I only dragged about 10 meters.

Full power reverse is no where near the wind load of a decent 30-50 knot blow.

I had decided to remove the swivel mainly because it was stainless steel. I was worried about stories I heard of stainless failures. However, when I pulled out my 50 kg Bruce after a year in the water, I found zero evidence of corrosion on its swivel or either attachment point. This I attributed to being buried deep in mud.

New lessons learned..

#1 Do not consider anchor "set" and "holding" just under engine power. Wait till a big blow.

#2 Stainless combination problem is overrated especially if combination will be buried in mud.

#3 Leave water to engine open at anchor in case someone needs to start engine.

#4 I was lucky they had enough power to lift anchor. Maintain full battery charge and good battery reserve to start engine and lift anchor. Despite this being a former crew member, he didn't recall that my alternator is manually turned on.

Question: My alternator is an energy consumer when the engine is turned off. However, I now see a risk to turn it off. Thoughts?

[DumnMad]

Hi PBM Good that it turned out OK
Ordinary mild steel will not rust significantly in mud because of lack of oxygen in the mud. But, stainless can have crevice corrosion in areas of reduced oxygen so I wouldn't come to the conclusion that stainless is OK down there. Maybe OK if you can guarantee it will always be well buried.
What depth and scope did you have?

[Ibetitsthisway]

Guys... guess I got something wrong!

I translated snubber or snub line wrongly. I see now that what is ment is putting a 1m or alike rope to the anchorchain from the bow. .. some do two.


of course you should use this. That is common practise with higher winds - is it not?
Sorry - I was on the wrong track!


BY THE WAY:


talking about snubbers etc.. not many are using rope attached to the chain for deep anchor sites on HEAVY anchor systems, are they?





say you carry 100m chain - why not attach and carry another 100 m rope or so for 50m deep sites?
I have seldomly seen it and wonder, because there are ropes which can cope with 24000lbs pulling force... weighing much less than chain in the bow

[parkstone bay]

Originally Posted by pbmaise

According to their site:

Multihulls
Our chart is intended for monohulls. In general, an anchor for a multihull should be up to 50% larger than that for a monohull of the same LOA. Commonly this means going to the next higher recommendation (one size up), depending on how close the vessel is to the upper limit of a particular size range.

.........

I decided on the 70 kg model. This follows their recommendation to go one size up and will do two things. Increase anchor weight by almost 50% and hopefully improve reset capability.


Yes I do have unique problems especially with location. For example in the Mactan channel between Cebu and Mactan Islands I couldn't safely leave the boat until I had two anchors to port and two lines to shore on starboard.

Many areas I anchor are very soft mud which clogged the claw of my Bruce. Especially Brunei.

Overall I realized:

A. Until I have any new anchoring site proven after tide and wind shifts, I will still continue to run 27/7 anchor watch.

B. Even after proving a new anchor, I still will maintain a storm watch. During a storm we run the engine to reduce anchor loading.
During a cyclone, I either will anchor to shore, or put to sea. I have done both.

C. Likely I will still add 200 kg or more in kellet weight to the chain for any long term anchoring. This is simply two 55 gallon drums filled with pebbles tied with Dyneema line.

D. The 110 kilo Rocna is too heavy for two crew to easily lift by hand. Further it would require a larger chain.

********

Note: One issue with long term anchoring I found was removal of mud from the bottom. At my current anchorage I anchored in soft mud and my kellets sank deep into the mud too. Overtime, my anchor chain kept sweeping the mud away from below my vessel. Each tidal change there was less and less mud. Eventually the chain exposed long dead corals which in turn started damaging the galvanizing. Therefore, I am having to regalvanize my chain within two years.

I love the idea of a 27/7 anchor watch!