Anchoring a swim raft
 

Looking for some help here --

We've just placed a 12' x 8' pontoon raft in about 9' of water. We used 2 250lb cement blocks each with its own SS chain on two sides of the raft. It's still floating away! In about two hours, it drifted ten feet. :eek: There was no slack in the chain - but we still have 3-4' of chain to spare on each side. In the area where it is, we get a lot of waves (boat wake) and we're thinking it's causing it to lift and move??

What can we do to keep it in place? Do we need more weight? Should we consider using snubbers? (I know what they are but need some advice as to how to use them in this case.)

Thanks in advance for your help and advice!

You need more chain.
It's called scope.
Rode or scope is at least 5 to 1
Google it.

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Why did you use two chains? The lifting force of even a small raft is way more than 500 pounds. So you need to make sure the chain is long enough so that the waves will not lift the anchors. My raft is about 8X8 and is anchored by one 500# concrete cylinder. It doesn't move. The anchor is in about 11 feet of water, and the chain comes about 1 foot out of the water, so it is about 12 feet long. My raft has a leader that is about 5 feet long that attaches to the middle of the raft, underneath, the other end attaches to the chain. There is a swivel at the anchor and a swivel at the leader connection. My raft has not moved in over 15 years and we get a lot of wave action here.

You need slack in the chain so the waves don't lift the concrete. I would go with one chain myself. Also remember that the concrete weighs less in water because of the buoyancy effect.

Or you will need much heavier anchors.

I think you may be confusing rode for a boat anchor with chain for cement blocks. But even if that's not the case, 45' of chain is likely to make placement that is both legal and enjoyable impossible--the raft will swing in a radius of something like 40'.

I'd recommend bungee cords--purpose designed models are available on Amazon.

No mistake
That's what it needs to stay put.
Or a pileing


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We can't have it "spin". The ladder needs to be facing the shoreline.


Was that professionally installed? I can't imagine moving that block of concrete.


So what do the swivels do exactly? I guess I don't understand their purpose.


That's what I was thinking myself, but wasn't sure if it was our only problem. The wing dings who anchored it previously used old radiators. ::roll eyes::


I'd love to, but I'm sure it would spin.

We See Rafts Floating-by with every Summer Storm...
 

Unless you have a diving board, nine-feet is a lot of water-depth for a swim raft!

(Although distant Winter Harbor neighbors have strung three swim rafts together—presumably to limit the proximity to their shoreline of noisy V-hull speedsters). :eek2:

☻ You definitely need more scope, but there's other things to try first.

☻ Swivels keep a raft's chain from "getting shorter" (and weaker) upon twisting.

☻ To limit the time the raft can spin, use one chain and re-attach it to the end that faces the prevailing wind (NW in most places): or attach a second ladder.

☻ If your blocks truly weigh 250 pounds each, that would be enough if they were connected in tandem.

☻ Your "wing-dings" may have used straight-concrete, and not added [heavier] rocks or iron to the mix. Concrete "looks" heavy, but it's not when submerged.

☻ Contact professional renters of swim rafts—find out what they use—then quadruple-up on it!

☻ At the end of the trailing (second) block, add a boat anchor. I would use heavy nylon line where it's buried under sand, silt, or mud. There are occasions when storms could move your raft more than a mile! :eek:

☻ You'll still need a swivel next to the raft.

☻ On a calm day, drag a garden hose to the site, and "pressure-bury" the blocks and anchor as much as possible. Attach the hose to a 10-foot length of PVC pipe if you don't have teenagers to hire! ;)

☻ Check that the attachment of the stainless-steel chain is secured to adequate hardware at the bottom.

The proliferation of oversized boats can be witnessed with the new breakwaters formerly off-limits to some shorelines. :eek: Even boat-lifts are appearing in Winter Harbor, which is protected from most windstorms.

>

My raft spins, I figure if people are capable of swimming to the raft, they are capable of swimming to the opposite side from shore to access the ladder. If they are not able to do that they shouldn't be swimming to the raft. The swivels keep the chain from twisting up.

The raft was bought from and installed by Production dock many years ago, not sure if they are still around. One guy showed up with the raft and anchor on a trailer. He slid the raft into the water. The anchor is a cylinder of concrete, he positioned the raft to the shore, put a large plank as a ramp from the shore to the raft and rolled the anchor onto the raft, that was the plan any way. He controlled and moved the anchor with a large pry bar. When he got the anchor on the plank he lost control of the anchor and it rolled off the plank. He started to use his leg to stop the anchor, so I screamed at him to let it go, he pulled back and it ended up next to the raft. We laughed about me yelling, he thanked me and said he knew better but did it automatically. He repositioned the ramp, I helped him roll the anchor onto the raft. He paddled the raft out to the spot, rolled it off the raft and there it sits.

I'm thinking the bungee idea may be the best for you. I think you said you have extra chain, I would try letting the slack out then using a bungee setup to keep the chain taut, to minimize the spin, but allow slack so the dock can rise and fall without moving the anchors. Maybe you could attach the bungee about halfway down the chain, from one chain to the other, you would have to experiment or find someone who has done it before. Most of the places that sell them are real helpful, just tell them what's going on up front and I'm sure they'd give you ideas. Let us know what you come up with.

A reasonable density to use for concrete is 145 lb/cu.ft. In water, subtract 62.4 to get net downward weight, or around 83 lb/cuft, only 57% of the weight on dry land. So a 250 lb concrete weight would net you only 142 when submerged.

Ditto on the huge uplifting potential of a raft with no slack on the chain. In fact, I originally had our raft too far out, using a concrete-filled automobile tire for the anchor. I actually rolled this "anchor" over a plank and onto the raft to do its launch. Anyway, to relocate the anchor, I connected a cable winch between raft and chain, used the buoyancy of the raft to lift the anchor, and paddled the assembly further toward shore. It hasn't budged since.

bungee cords? Never seen them strong enough. The snubbers look like oversized bungee cords .... not them?

My raft uses a pair of these fixed to a single chain:

https://www.amazon.com/AIRHEAD-AHDL-...0982358&sr=8-1

5 to 1 scope for a swim raft is ludicrous!

Ours was held by either a 250 or 500lb concrete disk with stainless chain. There was enough chain for it to be pulled a few feet out of the water at full lake. I cant recall which weight, but it was definitely no more than 500 because we never would have been able to move it. We bought the package at Watermark and towed it out. The weight and chain were on a pallet on the raft, when we got it into place a few of us tilted the pallet the weight was on and dumped it in and set. It has never moved an inch.

.... the Inflata-Bull swim raft
 

Measuring 96"x77"x32", shipping weight-14 lbs, price-about $60; would a single 250-lb concrete mooring block be adequate, in six foot water depth with a www.intexcorp.com/56285ep.html inflatabull swim raft what with the continuous incoming, weekend 2-3' motorboat wakes .....or would the bull get pushed onto the rocky shoreline....and start leaking?

Who knows ..... this bull might turn out to be a very happy bull .... what with the big weekend waves.....and if not, it is usually pretty easy to return website items to the local Walmart ...... sixty dollars ....... big decision here .....dunno?

I agree!

My raft (when I had one) was held in place on the West side of Welch (crazy wind) with a 1000 lb concrete weight and about 5 extra feet of chain above high water mark. It never moved in the least....

Dan

question
 

I was told you lose half the weight when you put in water. Is that right.

Dave M

I believe that is pretty close for concrete...

Dan

Just saw this on West Marine:

Anchor Type
Size
Holding Power

Helix
10" screw
10,000lb.

Dor-Mor
650lb.
6,500lb.

Mushroom
500lb.
1,200lb.

Concrete
2,000lb.
800lb.

Concrete
8,000lb.
4,000lb.


I don't understand the difference between the two concrete but clearly 500 pounds without slack and/or snubbers isn't going to do it.

I think we're going to start with adding slack & snubbers before the added expense of more weight and chain.

I can tell you this... A single 1000 lb. concrete mooring weight with 6 extra feet of chain from the high water mark, will hold your raft anywhere on the lake....

Dan

I think slack will solve your problem, I would experiment, with slack first, hopefully you can get enough so the anchors don't lift and the raft stays in the orientation you want.

That's exactly what our plan is. We got the weights reset. The left one had worked itself all the way to the right and set itself into a hole of sorts underwater. My husband thinks it will work in our favor, so he unhooked the right side and attached it to that sunken weight. He moved the other on the right back to the left. We used the full length of chain (12') and in the middle of each chain we placed a 6' snubber which will stretch to 9'.

The water was a bit calmer than it normally is on an average weekend -- but it didn't move. Crossing our fingers that this will do it!