Rocna 73 for a 40’ Cat

[Brassmonkeys]

With approximately 200 feet of 5/16 inch chain, would a 73lbs rocna but too big (I know you can never go too big) for a 40 foot catamaran with a displacement of 8000 pounds?

My thinking is that paying the few hundred dollars extra for extra piece of mind at night is worth the price, I’m just worried if it’s crazy to have such a big anchor

[rslifkin]

If you look at the weight of the boat it sounds like a lot. But with the windage of a 40 foot cat, I'd consider it reasonable. I've got a 73lb Rocna Vulcan on my 38 ft powerboat (moderately high windage and 26k lbs). I certainly don't consider mine too big, even though the Rocna chart says I only need a 55lb.

[tkeithlu]

It's a lot of anchor even for that chain. If you are anchoring under conditions that justify the anchor, I suggest you consider upping to 3/8 chain.

This is all a judgement call. I can say that I don't use that much anchor on a 65,000 pound boat; my larger CQR is less than that. On the other hand, I'm not about to advise you to use a smaller anchor when I don't know your conditions or your anxiety level when it comes to a good night's sleep at anchor.

[rslifkin]

Originally Posted by tkeithlu

It's a lot of anchor even for that chain. If you are anchoring under conditions that justify the anchor, I suggest you consider upping to 3/8 chain.

This is all a judgement call. I can say that I don't use that much anchor on a 65,000 pound boat; my larger CQR is less than that. On the other hand, I'm not about to advise you to use a smaller anchor when I don't know your conditions or your anxiety level when it comes to a good night's sleep at anchor.

Rocna also recommends 3/8 G43 chain for the 73 lb anchors. That said, I'm using 5/16" G43 with mine, as there's no way my boat will generate enough force to exceed the WLL of the 5/16" chain (in anything short of a hurricane) even though the anchor would hold more in a good bottom. The generous anchor sizing is usually for better holding in a crap bottom or at short scope where the attainable holding power is nothing crazy even with a big anchor.

[ggray]

This:

Originally Posted by rslifkin

Rocna also recommends 3/8 G43 chain for the 73 lb anchors. That said, I'm using 5/16" G43 with mine, as there's no way my boat will generate enough force to exceed the WLL of the 5/16" chain (in anything short of a hurricane) even though the anchor would hold more in a good bottom. The generous anchor sizing is usually for better holding in a crap bottom or at short scope where the attainable holding power is nothing crazy even with a big anchor.

[BillKny]

Originally Posted by Brassmonkeys

With approximately 200 feet of 5/16 inch chain, would a 73lbs rocna but too big (I know you can never go too big) for a 40 foot catamaran with a displacement of 8000 pounds?

My thinking is that paying the few hundred dollars extra for extra piece of mind at night is worth the price, I’m just worried if it’s crazy to have such a big anchor

No, you are NOT crazy. In out travels we see a LOT of catamarans with anchors that are too small, and the fraction of catamarans that drag in severe weather is much higher because of it.

Just to show you that you REALLY aren't crazy... let's take a critical look at the Rocna sizing recommendations. If we were talking a monohull of your length and weight, Rocna would suggest a 33 lb anchor, then have you go up one size (to 44lbs) for adding the second hull. Based on that... you might still think you are crazy.

But.... read the fine print on the sizing chart. They base the sizing recommendations on 50 knots of wind. Most thunderstorms will have gusts a lot higher than this, and a good strong cold front blowing through the Bahamas can reach 55 knots, and gusting higher for an hour or more. If you are out long enough, you'll see winds a lot higher than this. Our highest anchoring winds were 70+ when Dorian blew right over us in eastern Canada.

Bumping up another size (or two) for real world cruising is not at all unreasonable. We are talking about a total weight change of 30 lbs here. Seriously. That's nothing. If it bothers you, cut off 5 meters of chain and your total weight is back to where you started with a much more capable anchor.

I think Rocna's recommendations are conservative--for the weekend casual cruiser. For the full time cruiser living on the hook who has to take what ever Mother Nature throws at them, bigger IS better. Size DOES matter.

[Jim Cate]

Again, as mentioned above the serious cruiser wants an anchor that will hold in a crappy bottom on short scope. Yeah, I know that's not good practice, but it is what the gods will throw at you now and then, just to see if you have been paying attention to the good advice on CF!

Other than wallet-ache, there are no serious downsides to using a bigger than spec anchor... if it will fit on your foredeck/roller.

Jim

[meirriba]

Originally Posted by Brassmonkeys

With approximately 200 feet of 5/16 inch chain, would a 73lbs rocna but too big (I know you can never go too big) for a 40 foot catamaran with a displacement of 8000 pounds?

My thinking is that paying the few hundred dollars extra for extra piece of mind at night is worth the price, I’m just worried if it’s crazy to have such a big anchor

Just curious - what boat do you sail that at 40' displaces only 8,000 lbs?
Our 40' Lagoon400 weighs ~12,000Kg when loaded which is about 26,400 lbs...

Anyway - if your windlass and bow-roller are happy with the anchor than I do not see a reason to downgrade. However, I will be happy with a 10mm (3/8") chain for anchor of such weight.
WE are currently sailing the a.m. cat of 40' with 3/8 chain and 66 lbs anchor (Spade) that never slipped, BUT never experienced anything stronger than 50Kn wind while anchoring, so you also need to consider where are you planning to sail. You may need different setups for different weather expected.