Anchor size for a Elba 45

[peterp]

I have a 35KG Ultra anchor on my 2021 Elba 45, I have found it some times allows the Elba to drag in relatively light winds, I suspect I should have ordered the next size up however the 35 KG is the correct size on the Ultra Catamaran chart, next size up on the chart is 45KG a bit too big I thought, they dont list a 40KG. Any thoughts.?

[rslifkin]

The 35 isn't huge for that boat, but I don't think it's particularly undersized either and the Ultra is a good performer. If you're dragging in light winds, there's something else going on with your setup or technique. I don't think it's the anchor that's the issue here.

[Tin Tin]

Using the Rocna sizing chart a 14m boat weighing more than 13T and then moving up one size for a multihull lands on 40KG Rocna or Vulcan. Whether any other brand or make is significantly better is much debated on this forum, however if you are dragging on average sea bed, then your anchor is either incorrectly set or too small and the sizing chart from Ultra does not work for you.

[Tin Tin]

Further to the above, could you please advise anchoring depth, the scope you let out, chain size and type of sea bed, harbor location would be useful too.

[peterp]

Originally Posted by Tin Tin

Further to the above, could you please advise anchoring depth, the scope you let out, chain size and type of sea bed, harbor location would be useful too.

1/ Varies 4M to 6M and more.
the scope you let out.
2/ Around three times for lunch 6 times for overnight.
Chain size.
3/ 10MM Hi tensile gal. 100M in length.
And type of sea bed.
4/ Sand, heavy weed once held well in that weed.
Location.
5/ Port Phillip Bay, Victoria, Australia.

So Tin-Tin, I am not stating my anchor is not fit for use, it has only dragged on the odd occasion in relatively mild conditions, however on my last Cat a Lagoon 400 fitted with a Delta anchor by the Factory some ten years ago I don’t recall dragging at all in the same cruising area, however the Elba 45 is a very different Cat, larger, heavier, I just feel my anchor size may well be a bit light on, I need to talk to Ultra to see if they agree that I may be under sized with the 35KG, I welcome any other thoughts.

[peterp]

[QUOTE=rslifkin;3874523]The 35 isn't huge for that boat, but I don't think it's particularly undersized either and the Ultra is a good performer. If you're dragging in light winds, there's something else going on with your setup or technique. I don't think it's the anchor that's the issue here.

In thinking about technique as you have pointed out, I may not be applying enough reverse power, and for long enough, I do have the 60HP TC Volvo’s so plenty of grunt.

With respect to set up my setup is simply normal there is nothing one can change that I am aware of, I have attached a couple of photos on prior response.

[Tin Tin]

OK these are the further thoughts:
Is the boat fully loaded when this happens ie a lot of guests - + toys so could be around 20T?
Tide in your anchorage is say around 1.5m
Depth say 6m at low tide so 7.5m at high
Height of cross beam 2m ?
Total 8.5m
For lunch scope 3:1 you would need to let out 8.5*3 = 26m of chain.
For overnight 6:1 = 51m of chain.
Would that be correct?


Did the boat drag after a wind direction or tide change?



What size was the Delta on the L400?

Don't mean to be condescending, you may know this stuff already but we don't know that you do.

[Kettlewell]

You probably know all this, but be sure when calculating required scope you include the bow roller height above water in the calculations, including any tidal change. As an example, if the roller is 2m off the water, and you anchor at low tide where the rise will be 1m, you need to add a total of 3m to the water depth before multiplying times your desired scope. So if the water is 6m deep when you drop the hook, in this example, add 3m, for a total of 9m, then multiply by your desired scope of 6 to know you need to let out 54m of chain. Plus, make sure your chain measurements are correct. I recently remeasured my chain markings and discovered they were way off for some reason. If any anchor on proper scope properly set lets your boat drag in under 30 knots of wind, the anchor is a bad one.

[JustMurph]

35kg really should be fine on yours.

One of the most common errors is not calculating the scope using the distance between the bridge attachment points to the bottom on the highest tide you'll see.

So firstly, make sure you know how your depth is calibrated. Is it from the transducer, or does it have an offset programmed to give you the depth from the keel or depth from the waters surface.

Next, depth when calculating scope = measured depth from surface + height of bridle + range from the current tide to the high tide.

[Kettlewell]

Whoops! I see that three of us are writing the same things on this. Sorry for the duplication.

[JustMurph]

Haha! All good!

[David Mathis]

For daytime anchoring in light wind, a Danforth of about 5-6 kg with about 8' of 1/4" chain and 3/8 line holds our 43' powerboat with no problems. Yes, for overnights or stronger wind we use a much larger anchor, chain , and line but the point is, the small Danforth has never dragged in light wind. If you're dragging your much heavier anchor in light wind, my guess is that the problem is caused by insufficient scope or a difficult bottom.