what makes an anchor size what it is?

[MattInOz]

Hey guys.

So when I bought my boat I noticed that my anchor (danforth/fluke) looked about exactly the right size to keep a jetski in place. Apparently I need a 4kg/8lb anchor for my 4.35m boat and I found one going cheap on gumtree, but the vendor doesn't know what size it is and it doesn't appear to be stamped onto it. He says it "might be an 8lb or 10lb" and he thinks it weighs about 3.5kg... so how does one tell what size an anchor is? Can you just weigh it, or does the weight reference refer to something else? Is it the physical dimensions that define it?

Yes, apparently size does matter. Too big and it won't fit in the hole, and too small and it'll be useless. Sounds familiar.

Matt

[mangajack]

3.5kg is close to 8lb (7.7lb)   

It is subjective to the anchor design if you go entirely by weight to suit your boat.....some will hold at that weight...some won't.

A true Danforth 8lb should hold your 4.35m boat....as long as you have enough chain and rope out to suit the depth and the current....snig it short and it will fail 99% of the time.

[MattInOz]

Right... so the rated anchor size is is the actual weight of the anchor? Very good, I'll tell this guy I'll take it. Much thanks. It comes with 30m of rope and a couple of metres of chain so should be good for anchoring in 8-10m of water.

[Ed.]

I have always tended to use larger sized anchors on all my boats in the past, made all of them out of stainless, plus a chain with a minimum of 1-2 times the length of the boat, gave me piece of mind when anchored and the wind/waves start to push the boat around. When walking around marinas, I frequently wonder about the size of anchors on larger sized boats, I would often see 35ft boats which had anchors the size of what I would put on a 23ft boat. My last 17.5ft boat had an Danforth type anchor of 10kg.

[Ed.]

On 05/06/2023 at 7:07 PM, MattInOz said:

Right... so the rated anchor size is is the actual weight of the anchor? Very good, I'll tell this guy I'll take it. Much thanks. It comes with 30m of rope and a couple of metres of chain so should be good for anchoring in 8-10m of water.

If you aren't sleeping on it and in reasonable weather that would in my opinion be the very minimum, however I would not rely it holding your boat in place should your motor fail and the weather/ocean becomes rough. It might be just me but I consider my life and those of my passengers to be worth more than the cheapest option. A 3:1 ratio is not great 5:1 or more is better when the sea turns bad, having longer chain or a longer rope will improve your chances with that size anchor not to mention having a larger sized anchor to start with. Just something to consider!

As I said this is only my opinion.

Some links to help you decide:

https://www.whitsundaydiscountmarine.com.au/buying/better-boating-guides/choosing-the-correct-anchor/

https://www.whitworths.com.au/anchor_rope

 

[Sylvathorn]

yes, always having a decent length of chain of an appropriate size anchor is the best way to go!

[MattInOz]

On 06/06/2023 at 7:59 PM, Ed. said:

If you aren't sleeping on it and in reasonable weather that would in my opinion be the very minimum, however I would not rely it holding your boat in place should your motor fail and the weather/ocean becomes rough. It might be just me but I consider my life and those of my passengers to be worth more than the cheapest option. A 3:1 ratio is not great 5:1 or more is better when the sea turns bad, having longer chain or a longer rope will improve your chances with that size anchor not to mention having a larger sized anchor to start with. Just something to consider!

As I said this is only my opinion.

Some links to help you decide:

https://www.whitsundaydiscountmarine.com.au/buying/better-boating-guides/choosing-the-correct-anchor/

https://www.whitworths.com.au/anchor_rope

 

Yeah I thoroughly agree with you... the 8-10m figure I quoted assumed calm wealther and everyone awake. I won't be sleeping on board ever (there simply isn't room apart from anything else) and if I did get caught out in bad weather I'd be looking for less water to anchor in. It does bear considering a longer rope, maybe another 20m or so... but I'm compromised by the minimal size of the anchor well - it all has to fit in there. Also if the engine gives out while a storm's coming up I'm at the mercy of the sea gods anyway... if I happen to be in a 50m deep shipping channel at the time there's no way I'm going to have enough rode to make any difference... it's a case of throw out whatever anchor you have and get on the VHF to tell someone about it. I'm not planning on throwing away my existing anchor, however petite it may be... it'll be hidden away in storage in the stern so in really bad weather I'd be using it as a second bow anchor.

[Ed.]

Unfortunately that's the reality of smaller boats, by the time you stow all the safety gear, passengers and other essentials such as fishing gear, etc., there is almost no room left.

You probably know this already but if not,  sometimes getting into shallower water to ride out bad weather may not work, (assuming that your motor is still running) being in slightly deeper water may keep you out of the surf/breaker zone. Shallower water can get sloppier and rougher.

At least you are aware of the potential risks as otherwise you would not have asked the question in the first place! If nothing else, a spare coil of rope plus shackles is always a good thing to have on board.

 

[MattInOz]

Very sound advice... makes sense that shallower water would be rougher in bad westher. Assuming I have an engine my plan in a case like this is to run for a sheltered cove or bay or at least on the downwind side of an island. Considering I'll be doing 99% of my boating in Moreton Bay there should be plenty of hidey holes not too far away, and Manly Coast Guard's nearby.

I had a related chat with a friend of mine who thought I should remove the floatation foam from under the floor and use the space for storage but I refused... the foam won't make the boat unsinkable but in the worst case it'll slow it down enough to get life jackets and hit the emergency button on the vhf. I did find a couple of vids of people who remove the old fashion polystyrene foam, put in some foam "borders" to leave a central bilge down the centre of the hull, then fill the outer edges of the under floor space to the "borders" with expanding popyeurathane foam. I'm still researching that. I do like the idea if only because in the case of a fuel leak (in my under floor tank) polystyrene + petrol turns into flammable, non-bouyant sludge but I wouldn't want to reduce the floation or cause drainage problems. More research needed.

 

[Angry51]

I think if it was not needed the OM wouldn't have put the foam there in the first place, Leave it there.

More important to know your boat is under capable in rougher weather and not put yourself/ passengers in the predictament in the first place, Moral, only go out on days you are comfortable with and reduce the chance of being a victim . Happy boating.

[MattInOz]

Very sound advice... I'm in a 4.3m tinny, not the queen mary

[Sylvathorn]

14 hours ago, Ed. said:

Unfortunately that's the reality of smaller boats, by the time you stow all the safety gear, passengers and other essentials such as fishing gear, etc., there is almost no room left.

You probably know this already but if not,  sometimes getting into shallower water to ride out bad weather may not work, (assuming that your motor is still running) being in slightly deeper water may keep you out of the surf/breaker zone. Shallower water can get sloppier and rougher.

At least you are aware of the potential risks as otherwise you would not have asked the question in the first place! If nothing else, a spare coil of rope plus shackles is always a good thing to have on board.

 

absolutely Edmund!