Anchor size for 27’ sailboat (Mantus M1)

[PaulDaniel]

I just bought a 25 lbs Mantus for my Catalina 270. Now I’m regretting that I did not order the 17 lbs instead. I only day sail at my local 10,000 acre lake. The farthest I go from my marina is 5 miles. I DO like to go out when the wind is 20-25 mph sustained but it never goes above 30 mph. And we only go swimming when the wind is below 15 mph. So the only reason we would use the anchor above 15 MPH wind would be if the engine failed and somehow we weren’t able to sail back, which I find highly unlikely. The lake is very shallow so it’s easy to put out a ton of rode. The max lake depth is like 30 ft but the average depth is 15 ft. Deploying and retrieving the anchor involves handing the anchor with one hand sometimes, so a smaller anchor would be nice. I do not have a windlass.

The 17 lb Mantus M1 is recommended by Mantus for 25-30 ft boats for wind speeds up to 30 knots.

Did I buy too much anchor?

 

[PaulDaniel]

I’m pretty sure I’d like to return the 25 lbs anchor, even if there is a restocking fee.


So here’s my question:

If you were in my shoes, would you order the 17 lbs M1 (sufficient holding power in all cases), or go even smaller and get the 13 lbs version (easier handling, but might drag over 20 or 25 knots).

 

[PaulDaniel]

Additional info:
My lake bottom is all medium density or soft mud. That may not be the best for holding power but on the plus side, it’s extremely easy for the anchor to set.

 

[Don S/V ILLusion]

It’s a decision which should be based on holding power in mud, not weight.

sounds like you would be wise to have two anchors, one light weight and easy to deploy and retrieve and the second being the one you have for when you really need it.

 

[Richard19068]

Day sailing, less than 5 miles from home, shallow mud bottom. no windlass.

I would look at a Fortress FX-16 (10 pounds).

 

[PaulK]

Or a Danforsth. Heavier but cheaper.

 

[Foswick]

Yeah, I think you could get the performance you need with a much lighter anchor. Just look for something that performs well for whatever the bottom of that lake is. If you are not sleeping on anchor you can pretty safely round down in your size choice. I really agree with the advice that you could do well most of the time with a lightweight, inexpensive anchor and break out the larger anchor only when needed.

 

[dmax]

That Mantus MK I 25 lb. is a big anchor (dimensionally) especially with the hoop - I had one on a 35 footer and it was appropriate, a bit big for your boat. I now have a 17 lb. Mantus MKII - no more hoop. I think it would be a good choice for your lake - the Fortress/Danforth anchors are good in sand, not so good in mud. Plus one on a second lunch-hook anchor, no need to bring the big one out all the time.

 

[PaulDaniel]

I’m only interested in new generation anchors. I do sleep in the boat once or twice per year and I like knowing that if the wind changes, the anchor will reset itself. I didn’t know people still bought danforths and fortresses.

Don, maybe there is a misunderstanding: when comparing different anchors of the same make and product line, anchor weight correlates (albeit not linearly) to surface area, and surface area correlates (not linearly) to holding power. Specific holding power is not listed or advertised because because of the number of variables that affect it. I’ve tried to infer holding power based off of ABYC ground tackle working load recommendations, ABYC scope to maximum holding strength charts, and Mantus anchor size recommendations, but Mantus does not say what scope it uses to test it’s anchors. It’s a little bit of a shot in the dark.

My calculations conclude that I could probably get away with a 13 lb or even 10 lb for a “lunch hook” under 15 mph winds. But it would good to have a bigger anchor for emergency use.

There IS such thing as too much anchor, and I think the 25 lbs is just overkill for my use case. If I was cruising the Bahamas, it would be a great anchor to have.

Maybe I should keep the 25 lb Mantus for sleeping on the boat and use my 10 lbs Manson supreme for a “lunch hook”. The 10 lb still has great holding power with a 8:1 scope.

 

[thinwater]

Yes, the anchor is overkill.

However, 30 knots is not your worst case. Not even close. The worst case is something like going for a walk on the beach and while you are off the boat on the beach the wind increases from 10 knots to 30 knots and rotates 180 degrees. Common, with the approach of a squall. Or that thunderstorm has a 60-knot gust front; the smartest thing to do might be to anchor and wait it out.

Every situation is different. Yes, 17 pounds should be enough, with good technique.

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[Foswick]

I’m only interested in new generation anchors.

I wouldn't place too much emphasis on that as a selection factor. In fact, in your case, I wouldn't place any.

At the end of the day, you are on a modest-sized boat on a small lake (reservoir) with what appears to be a consistent bottom of sand/mud, with consistent depth and shallow max depth, and with sandy shore around the entire perimeter. It really doesn't get any less demanding on an anchor or technique than that. You really could use just about anything.

 

[PaulDaniel]

Yeah, 99.99% of the time I would be fine with a danforth. But an anchor IS a critical safety item on a boat, and when relying on it, it’s just nice to have a little extra peace of mind, and that’s worth the extra money to me vs using the danforth that came with the boat.

I’m going to return the 25 lbs anchor, even if there is a restocking fee. I don’t really need an anchor that can hold up to 50 knots of wind for my use case.

I’ll order the 17 lbs M1 anchor directly from Mantus. They have a 20% off July 4 sale right now. It looks like the Mantus has a smaller shaft than the Manson Supreme and Rocna Original, so I’m hoping it will fit in my
bow roller sideways. They have dimensions on their website but not of the height of the shaft. It’s also cheaper than the Rocna, it has more surface area, and if I want to buy a bigger primary anchor later on, I can unbolt the Mantus and stow it as a backup anchor.

I’ll keep a 200 ft 1/2” nylon double raid all rope rode for regular day use (that will get me a 10:1 scope in my shallow lake), and if I do an overnight, I’ll add 10 ft of chain for chafe resistance (I haven’t found any rocks in the lake bed yet, but you know murphey’s law…).

One thing about holding power:
Adding a lot of extra nylon rope to your rode not only increases your holding power by increasing the scope, it also increasing the holding power by greatly reducing shock loads. If I went from 200 ft to 300 ft of nylon rode, it won’t massively affect the scope, but it would SIGNIFICANTLY reduce shock loads. There are two reasons for this. The first and obvious reason is that a greater length of nylon rope will be more elastic. It delays the onset of peak load and reduces dynamic loading. The second reason which is probably not obvious to most people, is that a 300 ft nylon rope has significant catenary weight. Rigidity of a beam decreases with the cube of the length. So in other words, with a very long rope rode, even though it doesn’t weigh very much, it will have a a lot of sag in it. Usually people talk about this catenary effect only because it affects the angle of load on the anchor. But it also decreases shock loading by delaying the onset of peak load. Even though nylon rope doesn’t have a lot of weight, if there is enough length of it, there will be a significant amount of sag in it, and that will help reduce dynamic loading.

Sorry if that’s hard to read. I wrote it out fast. Happy July 4th y’all!

 

[PaulDaniel]

Okay after reading a lot more.......

I'm going to go with a Fortress FX4 and 200 ft of 3/8 nylon rode (no chain) for my lunch hook. This will also make an excellent kedge anchor.

- My lake gets an additional foot of clay rich silt every 30 years (approximately). It was impounded about 60 years ago so that's about 2 feet of additional dirt since its impoundment. There is VERY low abrasion risk.
- One of my main objectives is to prevent the sticky mud from coming up with the ground tackle, getting on the foredeck, and then migrating around the entire boat. Of course, safety supersedes my desire to keep the boat clean. This is my main reason for getting rid of the chain.
- The ABYC recommendations for ground tackle working load requirements are based on all-chain rode in a shallow anchorage (basically worst case scenario due to steeper waves and higher shock loads.). Many anchor manufacturers (but not all) base their anchor size recommendations off of these cautious ABYC guidelines. When using an all-rope rode in a deeper anchorage (like 20 ft deep), the holding power needed can typically be reducing by a factor of 3.
- My boat (Catalina 270) is not really made to accommodate a Mantus anchor on the bow roller. There's not really a great way to do this. There are different ways that I could customize the boat to accommodate a new generation anchor, but no good way that I can think of. The anchor locker is also small and would not accommodate a regular Mantus anchor (even the 13 pounder).
- The Fortress may not be as good as the Mantus at resetting, but it still can reset itself in many circumstances. For cruising, I would definitely want a Mantus, but for my purposes, I think the Fortress will do well.

I am tempted to get the 13 lbs Mantus stainless steel quick connect anchor and store it in my anchor locker as my primary anchor. But deploying and retrieving the anchor would take a bit longer and involve getting mud on my hands and into the anchor locker. If I thought I needed the Mantus for safety, I would get it, but I'm currently leaning towards the FX4. The FX4 can be stored easily on my bow roller and mud will not get on my hands or in the locker since it will be only on the flukes.

I don't mean to come across arrogant. I appreciate everyone's advice here!

 

[dmax]

The Fortress is a great anchor (not for muck though) - I think you should add a short length of chain (5 feet), it makes a big difference (Fortress recommends this). Otherwise, it will fly through the water when you're trying to set it, they are so light. Chain also helps keep it set.

 

[PaulDaniel]

Thanks for the feedback. I might be mistaken but I don't think the Lake Somerville lakebed would be classified as muck. I could share some photos or video when I get a chance. I REALLY don't want to use chain because it brings up a lot of mud onto the deck. It is hard to keep the mud off my swimsuit and shirt.

The Fortress has settings for 32 degrees (normal use), and 45 degrees (very soft mud).

- In order to achieve a 32 degree angle from the rode to lake bottom, my scope would need to be at least 1.89:1. That would just be to get the flukes parallel with the lake bottom. To get the flukes to dig in, I would want the angle between the shaft and lake bottom to be as close to 0 degrees as possible.
- There are two forces pushing the flukes into the lakebed and helping the anchor to set: 1) the weight of the flukes, and 2) the hydrodynamic force acting on the flukes as your boat slip to windward (or you motor backwards).
- If the flukes start to dig in, they are limited in how low they can point by the angle of the shaft and rode. This is where some extra catenary could help I guess.


Fortress says on their website that they recommend at least a 5:1 scope and 6 ft of chain. Maybe I could go without chain if I use the anchor on the 45 degree setting or with a 10:1 scope? Is that a horrible idea?



If I can't use the fortress without chain, then I will buy a Mantus 13 lbs quick connect anchor.

 

[dmax]

I wouldn't go with the Fortress without chain, it only weighs 4 pounds - you will have trouble setting it. But that's me.

 

[shemandr]

I was a Fortress skeptic until I did some RC on the Indian River Lagoon from a pontoon boat. We would normally anchor in 6 -7 feet with a muddy bottom. I was impressed with the performance of the anchor. I don't know the weight but it was light to haul in. Its holding was very good. And we didn't need so much scope.
Given that the OP primarily daysails I think a modest sized Fortress would serve well.
I don't like the idea of excessive scope. I think too much scope encourages sailing around on the anchor which I believe enhances the chance for the anchor to yank out.
I like chain. Install a wash down pump if the mud is that much of a problem. We used to just dip the anchor repeatedly as we slowly motored forward to remove mud. That will go more easily with a light anchor like the Fortress.
The Fortress also sails forward toward the bottom when launched which is nice.

 

[Foswick]

Fortress says on their website that they recommend at least a 5:1 scope and 6 ft of chain. Maybe I could go without chain if I use the anchor on the 45 degree setting or with a 10:1 scope? Is that a horrible idea?

Horrible? No. But ...

The bit of chain isn't really about holding power. So, the additional scope, while it will generally make you more secure, will not compensate for the lack of chain.

The chain is more about helping the anchor set, initially. Of course, it also offers abrasion protection near the anchor but, in your case, I don't think that is much of a concern. You could do without the chain, just fine, but you might find the anchor slightly trickier to set. Once set, the chain has pretty much done its job. With your seabed and conditions, I shouldn't think that resetting is much of an issue.

If you find the anchor fussy to set and you are really dead-set against some chain (even a coated chain), you can probably get improved success by adding a kellet a couple of feet from the anchor. The kellet has little effect on the anchor's holding power, contrary to some misconceptions about them. But, it does lower the initial angle of the rode while the anchor is setting. Once fully under tension, it hardly matters (unless you tied on a massive kellet). A little 8-lb mushroom anchor works well for this, but is even a bit more than you really need.

One small word of caution, with this, though. It is technically possible for the rode to wrap around the anchor in a way that defeats it. This would happen of the boat circled around behind the anchor without enough tension to move the kellet. Then, when tension was applied, it would drag the kellet around but with the short section of rode still held against the seabed, possibly causing it to pass under the anchor's arm. I bring this up only because it has been demonstrated that this is possible. It is actually not easy to do. And, it is also possible to do without the kellet, so ...

 

[shemandr]

Now that Foswick has mentioned a Kellet I’d have to to say we used a Keller, a mushroom anchor, but not for setting or holding. We wanted the anchor line to be more vertical so that boats starting the race could pass the bow without snagging the rode. We did this with marks as well.

 

[PaulDaniel]

Okay, I may have gone overboard but I was just tired of thinking about anchors. It has been taking up a lot of real estate in my mind these last few days.

I purchased:
- 13 lbs stainless quick connect Mantus M1 (will use as primary anchor and lunch hook... I will just keep it in my anchor locker on the bow)
- 2.5 lbs stainless quick connect Mantus M1 (throwable stern anchor for anchoring near beach... could also be used as a kedge anchor if not grounded)
- 4 lbs Fortress FX4 (this anchor is probably superfluous for my purposes but it could come in handy... it would be a good kedge anchor if grounded... I will experiment with it and if I can get it to set reliably without a chain, maybe I will use it as my lunch hook and keep the 13 lbs only for overnight usage only)

In Lake Somerville, I really don't think abrasion will ever be a risk, but I will keep 25 ft of chain on the boat in case I want extra peace of mind while sleeping. Even though Mantus recommends the 17 lbs anchor for day sailing (up to 30 knots), I think 13 lbs will be more than enough since I am using an all rope rode which dramatically reduces shock loading. On my previous boat I had a 10 lbs Manson Supreme, and it never failed to dig in instantly. Even though the Fortress would fit nicely on my bow roller when not deployed, I just really appreciate the ability of the new generation anchors to set reliably. Since I want to use an all rope rode, setting ability is especially important. Over the last couple weeks, I've used the 10 lbs Manson Supreme a few times without chain and it has set without problems, but that's only a few times.