Mooring sizing
Posted by oldmaninparadise@reddit | sailing | View on Reddit | 32 comments
Recently got a mooring spot from the town. I have a 14k lb boat. Bottom is mud. When diver first looked they found nothing on a quick look and mooring company was going to put in 2,000 lb cement block. Then diver did a more thorough dive and found a 500 lb mushroom completely buried in the mud. Service company than said will put 15' of 5/8" bottom chain (about 200 lbs) attached to 25' of 1/2" chain to mooring ball, then 15' 3/4" pennants.
I know a mushroom is different from a concrete block, but 500lbs vs 2,000 seems to be a big diff. If the current anchor down there adequate for my boat?
ONLYallcaps@reddit
Concrete will lose just about half its weight in water. So you’re closer to the recommended 700lbs than you think.
Raneynickelfire@reddit
I'm sorry, what?
Are you suggesting normal concrete is buoyant?
What do you mean it "loses half it's weight?" It will weigh the same as it does in air... half of it's mass isn't a buoyant force.
What are you actually saying?
Moist-Mess5144@reddit
Next time you go swimming, take a cinder block in with you and notice how much less it weighs under water. SCIENCE!
Lord-of_the-files@reddit
It's all about density. If your anchor had a density of 1, the same as water, it wouldn't sink at all. If your anchor had a density of 10, it would still effectively weigh 9 in the water. You just deduct 1 from the density value. It's the difference in density that creates buoyancy or lack of.
Let's say you had anchors made of different materials but they all weigh one tonne out of the water. Wood: density 0.8, it would actually float with 200kg of buoyancy. Concrete: density 2.5, it would have an effective weight of (1.5/2.5=0.6) 600kg Iron: density 5.5, so (4.5/5.5= 0.818) 818kg Lead: density 11, so (10/11= 0.91) 910kg
pfreexy@reddit
So, logically... If... she.. weighs the same as a duck, she's made of wood. And therefore--? A witch!
Strict-Air2434@reddit
The suggestion that concrete is buoyant is ABSOLUTELY CORRECT. No, it doesn't float but it will also not take the place of the mushroom.
ONLYallcaps@reddit
40-45% of the weight of concrete is water.
light24bulbs@reddit
It doesn't matter what material it is, it's the density that's the issue. The less dense something is the closer it is to floating, the less effective it will be.
light24bulbs@reddit
How much downforce do you think a wooden log gives you if you put it in a bathtub? Get it now?
Candygramformrmongo@reddit
The critical holding power there is the suction of the mud
Alturia2@reddit
Mushroom anchors have a lot more holding power compared to concrete blocks. Mooring Weight (Anchor): Mushroom Anchor: A common rule of thumb is a weight in pounds equal to 5 to 10 times the boat's length in feet (e.g., a 20-foot boat needs a 100–200 lb anchor). Deadweight Anchor: For stronger holding, regulations often require substantial weight. Examples: 18–26 ft boats: 1,500 lbs; 27–35 ft boats: 3,000 lbs.
oldmaninparadise@reddit (OP)
ok. thanks to both for the replies. 34' boat, so 500lb mushroom is for 25-50' boat, i am in the middle. Sounds like it is appropriate.
overthehillhat@reddit
Crucial Eye Thickness
Crucial
youngrichyoung@reddit
Defender says a 500lb mushroom is good for boats 37-39'. (https://defender.com/en_us/defender-mushroom-mooring-anchor)
Personally, I would rock what you got. But if you want to go a different route, the typical cheapo mooring is an old (stripped, cleaned) junkyard engine block encased in concrete. Concrete alone, sans engine block, is a really bad idea for reasons of density covered very well elsewhere in the comments.
oldmaninparadise@reddit (OP)
Here the old moorings are freight car railroad wheels.
rackman1@reddit
Definitely big enough mushroom. Chain length depends on water depth and tide change. Pendants probably too long.
DarkVoid42@reddit
i would connect it to the mushroom and connect the mushroom to a rocna vulcan 33 buried in the mud as a safety backup.
Lord-of_the-files@reddit
You can buy a Vulcan 33 and chain for $500?
DarkVoid42@reddit
https://citimarinestore.com/en/rocna-vulcan-galvanized/18889-rocna-vulcan-33lb-15kg-galvanized-anchor-vlc15gs.html
Lord-of_the-files@reddit
That's more like the price I'd expect to have to pay
RedditIsRectalCancer@reddit
No, and that's a stupid idea.
Lord-of_the-files@reddit
I didn't think so. Otherwise I'd be buying one for myself!
OberonsGhost@reddit
Don't know a lot about using a mooring ball but don't you put out a stern anchor as well so you don't swing at hit other boats in the mooring basin? And doesn't that give you some extra holding strength?
youngrichyoung@reddit
No, you definitely don't. Letting the boats all swing together is the better, safer option.
boatslut@reddit
Because: a)then your boat will hit others when they swing on their moorings. b)would need bigger anchors as the loads beam-on are a lot larger than head on
All of the moored boats swing in the same direction / weathervane, aligned with wind/current/tide, so they don't hit each other.
...unless there is no wind then they swing all over the place but no load so hits generally aren't an issue.
Suppose it might get interesting mixing power boats & sailboats in a mixed current/wind situation 🤔🤔
youngrichyoung@reddit
My dad has a rather tall motor boat on a mooring in Maine, where tidal currents can be quite strong. The folks running the moorings are careful not to put a sailboat too near him. Anything with a deep keel will swing to the tide, but dad's flybridge cruiser swings to the wind half the time.
pdq_sailor@reddit
The anchor might have plenty of grip - it’s depends how well it’s set and it sounds very well set. Concrete blocks are more brute force than design.
youngrichyoung@reddit
Set so well the diver couldn't even find it in the mud!
RedPh0enix@reddit
For comparison, the following mooring has held a 35 foot catamaran for several years in a partially sheltered bay through conditions up to and including a category 2 cyclone. * 1m cubed concrete block (approx 2300kg) * Sandy bottom with partial bury * 2m ships chain * 5m 16mm ground chain * 5m 13mm riser chain
mike21146@reddit
I agree with your diver and service company. Seems like the right setup. I have a 250lb mushroom with 5/8” + 1/2” chain on a 31’ 10k boat. Working well for years.
oldmaninparadise@reddit (OP)
Ty
iamcornholio2@reddit
My opinion is that might not be enough mooring and I would at least upsize to 3/4 inch bottom chain and 5/8 top chain for a 500lb mushroom. Where I live, moorings are heavily regulated and opinions don't matter. If I don't install what they require, my permit won't be approved. For a 30ft 8K lb sailboat, with fore and aft moorings, I'm required to have 300lb mushrooms, but have 500lb ones with 10' of 3/4, and 25'+ of 5/8. I have 4 feet of freeboard, 5.5 feet draft with zero clearance at low tide, and 7 feet of tide.