Anchors and ladders for a 12' RIB

[NW Dive Dawg]

I agree that a small Danforth with 10- 15 ft of chain would be good for a small inflatable. If diving solo, or even in teams, obviously always dive up current for the entire dive and work your compass so when surfacing you can easily coast back to the boat. Also, consider clipping a strobe about 10ft off the bottom to your anchor line to help you find your way home. Lastly. if diving solo, make sure to leave a 20 to 50ft tag line off the stern so you have options if you miss the boat on the return

 

[rjack321]

Now that my RIB is holding air finally and I think I have the correct fittings for the fuel system, it's time to start thinking about actually using it for diving. I'm curious what size and type of anchor people use and also what you use for getting into the boat. Would operating and diving solo from the boat change your answers any?

The common Danforth anchor seems awkward and pointy for handling in a small inflatable boat, so I am thinking of something more like a mushroom anchor. A 30 lb mushroom would take up a fairly small amount of space and shouldn't go anywhere unless there is a hurricane blowing topside.

Mushrooms are terrible in gravel or anything but the softest mud. They also won't grab through kelp on the bottom. For that size boat and diving go up about 2 sizes from the "recommended" size. You will end up anchoring in places that arent really anchorages and in much deeper than "anchorage" depths. The majority of decent dive site anchoring spots will end up being some form of gravel mixed with sand. Usually on a slope and with a short scope or you'll end up swinging onto the beach/rocks.

On my 16ft RIB I use a claw (historically called Bruce). It doesnt have pointy parts to rip or wear holes in the RIB yet has much more mass than a danforth and isn't quite as reliant on scope to hold. Also has enough bite to poke through kelp clumps drapped over the bottom and stick into the underlying sand or gravel. You aren't just worried about winds topside, the amount of drag an anchored boat has in a current can be surprising. If you anchor at the tail end of an ebb, splash and dive on the slack and then exit on the start of a flood your boat can twist and turn all sorts of ways. You often have to short scope the anchor to avoid it swinging onto the rocks or beach due to wind or tide changes. Most of our better dive sites will have a sloping bottom where you are constrained by the beach or rocks on one side and excessively deep water on the other - short scoping something with no bite in that scenario is a recipe for the anchor to drag and then the boat is drifting off into the channel with the anchor hanging 60ft below.

For a 12ft RIB I would go with a 5lb + 12lbs of 5/16ths chain or a 11lb if you want to shorten up a bit on the chain. Then 200ft of 3/8" line. You will be anchoring with short scope more often than not and in marginal places with bottoms sloping the "wrong" way - so go bigger if in doubt.

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[Russjstewart]

Another thing to think about is what are you going to tie the anchor rode off to on the RIB. Do not use anything that is only glued on. The glue will eventually fail. Try and avoid running the rode over the pontoon material if possible. This will become an exercise to see what wears out first as the boat moves and the two rub on each other.
I have had success putting a short line through the u bolt on the bow that you use for the trailer winch. It also doubles as a painter when docking. Just make sure it is shorter than the boat length, so if it falls overboard it will not reach the propellor