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Old 01-21-2020, 09:54 AM   #1
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Anchor sizing confirmation

Before I buy an anchor for my new setup, I want to double check my thoughts on sizing. Based on the proportions of my pulpit and roller setup, I can't run anything with a roll bar as even the tall Mantus roll bar won't make it over the end of the pulpit on retrieval (roller to end of pulpit is about 19"). So the plan is a Rocna Vulcan, which seems like it'll fit well other than a slight modification to the pulpit to account for the width of the shank.

The boat is 38 feet (hull length, not counting pulpit and swim platform). Loaded weight is about 26,000 lbs. Based on that, Rocna's chart suggests the 25kg / 55lb anchor. There's lots of weight headroom in the chart for that size at 39ft and even if I look at the 46ft row, I'm still under the suggested max boat weight. The next size up is 33kg / 73 lbs, which is a pretty big jump in weight. It'll fit on the pulpit, but it'll be a bit tighter, particularly in terms of tip to hull clearance for retrieval.

I'm thinking based on how we use the boat, not having any plans of staying overnight in unprotected anchorages with heavy winds, and being well below the top end of the boat size range for the 25kg anchor, that's probably the correct size and going up one would be extra cost and extra weight to carry (with a planing hull) for little to no real benefit.

For some perspective, the boat came to me with a slightly undersized Fortress G-23 on the bow. I haven't found it particularly inadequate, but I know it's marginal, as I did drag it a few feet in sticky, silty mud (not very far and it never broke loose completely) over the course of several hours of getting whacked with 30 kt wind gusts (and a few of those gusts hit while we were swung almost 90 degrees to the fairly inconsistent wind). I also only had about 4:1 scope out that day due to depth and only having 150ft of rode on board (that's getting fixed). The Fortress will go in the bilge as a spare.

So what does everyone think? Is the 25kg / 55lb Vulcan big enough or should I go a size bigger?
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Old 01-21-2020, 10:17 AM   #2
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I'm pretty sure that nobody plans of staying overnight in unprotected anchorages with heavy winds... but if you end up in that situation the 25kg Rocna is plenty.
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Old 01-21-2020, 10:22 AM   #3
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Looks good to me. But what anchor rode are you using. 5/16" G4 or G43 chain and 9/16" nylon would be my minimum.


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Old 01-21-2020, 10:26 AM   #4
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Looks good to me. But what anchor rode are you using. 5/16" G4 or G43 chain and 9/16" nylon would be my minimum.
The existing rode (which will become spare, likely with new line) is 6ft of 1/2" BBB and 150 ft of 5/8" 3 strand.

The new primary rode will be 75ft of 5/16" G43 and 300ft (or maybe a bit more) of 5/8" 8 plait.
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Old 01-21-2020, 11:14 AM   #5
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I think you’ve got it figured out pretty well.
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Old 01-21-2020, 11:29 AM   #6
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I think youíve got it figured out pretty well.
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Old 01-21-2020, 11:53 AM   #7
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May I suggest when picking your anchor (I have a Rocna) from the manufacture's table, pick the anchor which is the "next size larger" than what they recommend.
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Old 01-21-2020, 12:33 PM   #8
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The boat is 38 feet (hull length, not counting pulpit and swim platform). Loaded weight is about 26,000 lbs. Based on that, Rocna's chart suggests the 25kg / 55lb anchor. There's lots of weight headroom in the chart for that size at 39ft and even if I look at the 46ft row, I'm still under the suggested max boat weight. The next size up is 33kg / 73 lbs, which is a pretty big jump in weight. It'll fit on the pulpit, but it'll be a bit tighter, particularly in terms of tip to hull clearance for retrieval.

For some perspective, the boat came to me with a slightly undersized Fortress G-23 on the bow. I haven't found it particularly inadequate, but I know it's marginal, as I did drag it a few feet in sticky, silty mud (not very far and it never broke loose completely) over the course of several hours of getting whacked with 30 kt wind gusts (and a few of those gusts hit while we were swung almost 90 degrees to the fairly inconsistent wind). I also only had about 4:1 scope out that day due to depth and only having 150ft of rode on board (that's getting fixed). The Fortress will go in the bilge as a spare.

So what does everyone think? Is the 25kg / 55lb Vulcan big enough or should I go a size bigger?
Didn't look at the charts, but it sounds like you're on the right track with the Vulcan, assuming you've compared that to all other other newgen anchors in the same weight range before making your selection. Another factor I take into account is the weight I'm willing to lift manually if the windlass goes south... and 50-55 lbs is right about my limit.

I'd get a bigger Fortress for backup, though. The 37 is still light enough to schlep around, it still stows easily enough when dismantled, etc.

-Chris
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Old 01-21-2020, 12:47 PM   #9
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Didn't look at the charts, but it sounds like you're on the right track with the Vulcan, assuming you've compared that to all other other newgen anchors in the same weight range before making your selection. Another factor I take into account is the weight I'm willing to lift manually if the windlass goes south... and 50-55 lbs is right about my limit.

I'd get a bigger Fortress for backup, though. The 37 is still light enough to schlep around, it still stows easily enough when dismantled, etc.

-Chris
I did compare the Vulcan to a bunch of the other new gen anchors. The Spade is out due to cost. And out of the rest, the Vulcan seems to be the best fit on the bow. The worst case manual lift would be rough, but manageable with 55 lbs of anchor plus chain weight (especially if I'm in 50 feet of water).

Upgrading the Fortress to an FX-37 is in the plans at some point (and I can fit it under the forward stateroom even fully assembled). But I'm not traveling far and wide and spending tons of time anchored at this point, so the smaller Fortress will do for now and I can upgrade it later.
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Old 01-21-2020, 01:42 PM   #10
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Keep in mind this one point when considering your ground tackle. Will it keep you and your family safe during a bad storm? The differance between cheap tackle and good, quality tackle could mean risking your lives or damage to your boat or someone else's boat. Cost should not be a consideration.
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Old 01-21-2020, 01:49 PM   #11
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I did compare the Vulcan to a bunch of the other new gen anchors. The Spade is out due to cost. And out of the rest, the Vulcan seems to be the best fit on the bow. The worst case manual lift would be rough, but manageable with 55 lbs of anchor plus chain weight (especially if I'm in 50 feet of water).

Did you include SuperMAX in your comparison? Our adjustable version is right around 50-lbs... and it's semi-customizable (?) for bottom material...

Kinda ugly, though; looks sorta like the bucket on a backhoe...

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Old 01-21-2020, 01:57 PM   #12
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Did you include SuperMAX in your comparison? Our adjustable version is right around 50-lbs... and it's semi-customizable (?) for bottom material...

Kinda ugly, though; looks sorta like the bucket on a backhoe...
I did look at those, but based on the specs given, it would hit the hull unless I move the roller further out on the pulpit. So it basically just doesn't fit the boat.
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Old 01-21-2020, 02:33 PM   #13
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Your anchor is a good size even for nasty blows. In discussions about rode, what is your average anchoring depth. And is anchorages "tight," lots of boats with not so much room (on the west coast this would describe many places in Desolation Sound). By tight I mean do you have the ability to put out a 5:1 ratio of rode with all the boats around you. If you can't do "proper" rode ratios, then more chain might be in order (and a snubber).
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Old 01-21-2020, 02:51 PM   #14
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Average anchoring depth varies a good bit. When anchoring for the day near home, depending on exactly where I am and how many other boats are out, I could be in anywhere from 20 to 50 feet of water. When we do the Thousand Islands this summer, depths for places we'll likely want to anchor overnight will likely be more like 8 - 15 feet.

Usually in the deeper areas we've got plenty of space to work with, so putting out 5:1 or better isn't an issue as far as swing room. As a personal rule of thumb, if I don't have space to put out at least 5:1, I'm not staying there overnight. I'll have gear for a snubber or bridle on hand, of course, for any situation where I don't have 20+ feet of nylon out beyond the chain. I find a lot of people (at least around here) tend to try to anchor fairly shallow, so being willing to anchor in deeper water often provides good spots to anchor without as many close neighbors, even on busy summer days.

My bow roller is just under 6 feet off the water, so I typically figure 6 feet for scope calculation just to make it easy.

ASD, out of curiosity, what size is your Rocna? Judging by a picture of your boat, you've got a good bit more windage than I do and I'm sure a lot more weight as well.
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Old 01-21-2020, 03:35 PM   #15
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rslifkin,
I agree with what you are considering. I have a Nordic Tug 37 (40 feet overall) with about the same weight as yours. We use a Vulcan 25 kg. Rocna sizing charts are considered "conservative", so you will be fine even in a bit of a blow. As RSN 48 suggests, more chain is actually "better". It puts more weight on the system (for holding), does not "chafe" on the bottom (coral, rocks, etc.), and can allow for some "short scoping" if needed. We use 250 feet of chain, with 150 feet of rope for those "deep" anchorages we sometimes have to use, but mostly we are "all chain".
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Old 01-21-2020, 03:51 PM   #16
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Firehoser - What's your opinion of the Vulcan 25? Satisfied with it? I do have more windage than an NT37, but less than someone with a canvas enclosed flybridge.

My aversion to adding more chain is strictly weight related. The boat is a planing hull and at least at our typical cruising speeds, weight up forward hurts performance. A 130 lb person walking from the aft end of the boat to the bow while cruising at 17 kts is enough to slow us down by 0.1 - 0.2 kts even with trim adjustment. When they walk back aft, the speed comes back.

Based on that and our cruising area not having coral or a lot of rocky bottoms, I figure 75 feet of chain should be enough to avoid chafe issues, etc. without adding an excessive amount of weight. The planned 75/300 chain/line combo will weigh about 110 lbs, plus a few for wet line.

Going to all chain at the same 375ft total length would be 280 lbs heavier, which is a lot of extra weight. All of my ground tackle including the spare Fortress and rode totals up to about 220 lbs, so going to all chain for the primary would be more than doubling the weight I'm carrying up there. If I were cruising in areas that demanded more chain, then of course I'd carry it. And if I had a slow, heavy boat where an extra 100 lbs is irrelevant, I'd carry at least somewhat more regardless of cruising grounds.
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Old 01-21-2020, 03:54 PM   #17
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Go bigger.
No one who has been at anchor in big weather has wished they had a smaller one.

And, as US boats seem to love parking on top of each other in an anchorage, the short scope ability will be an advantage.

https://setsail.com/anchors-and-sizing/
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Old 01-21-2020, 07:22 PM   #18
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The 25Kg Vulcan will be fine for your CC. I had the 20Kg on my GB36 (same weight) and it was tried severely and came up a winner each time.
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Old 01-21-2020, 07:55 PM   #19
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Another factor I take into account is the weight I'm willing to lift manually if the windlass goes south... and 50-55 lbs is right about my limit.

Don't forget the "getting older factor" when plotting how much you can carry and move around. A 55 pound anchor with chain would not be in my personal agenda ever.

The nice thing about boating in the OP's area (Great Lakes), you don't have to worry about tide. So your rode length depends on your maximum rode ratio. Be lazy and drop one foot from your bow to water distance so your maximum depth would be 55 feet (50 actual depth and 5 feet of bow to water depth). So if you are happy with an 8:1 ratio you rode will be at least 440 feet and to be lazy round it to 450 feet. And of course at 10:1 (really bad wind) 550 feet of rode.

I have gone through several schools of "Rode Philosophy."

First Phase: have the chain on your rode be at least one foot for every foot of boat, then line.

Phase two: 150 feet of chain, 250 feet of line.

Third phase: all chain rode with snubber.

Phase four: one hundred feet of rode with much 350 to 450 line. I am basing my latest phase on this article from the Rocna knowledge base:

Rode optimizations (Rocna Knowledge Base)
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Old 01-21-2020, 08:57 PM   #20
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ASD wrote;
“May I suggest when picking your anchor from the manufacture's table, pick the anchor which is the "next size larger" than what they recommend.”

That’s full of flaws and variables.
But it’s not an unusual practice.

It assumes the anchor manufacturer is putting his numbers on the ragged edge w no room for unexpected conditions.
Some actually recommend more than one size up compared to other manufacturers. And the capabilities of all anchors are different. Some actually recommend anchors two sizes up from the norm. If you went up a size and the manufacturer was already up two you’ wind up w a very big (heavy) anchor.

One variation of ASD’s “one size up” would work quite well but require some research. Pick a boat and weight of boat and note what weight anchor is recommended by numerous main stream anchor manufacturers. Then average all these numbers and you would already be above the ideal anchor weight because recommended sizes are already inflated .. but the variations of how much too big would be averaged and minimized and a real useable anchor weight would result. But if you just added one size that was on top of an anchor rated one size too big to that you’ll be oversized by 1 to 2 sizes .. possibly even more depending on the many variables. So taking a guess and going up 1/2 a size over an average size recommendation of all those anchors in this survey would probably be very close to an ideal weight/size anchor.

I’m not going to do the research but if someone did it may be a useful tool for the rest of us.

Then if you assume most all or all anchor manufacturers were not (in their opinion) under rating their anchors you would have a reasonably close assemblage of slightly inflated anchor weights to choose from.

A much easier way to arrive at much the same thing is to check 4 or 5 manufacturers of similar anchors that appear to be close and reasonable and average that one would be far better off than applying “one size up” from any one manufacturer’s recommendation.
But of course there would be a small amount of work.
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