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Sizing a crane for dinghy handling

Apr 24, 2013
Factor in some extra lifting power when it comes time to choose a crane for launching and recovering a dinghy.

Factor in some extra lifting power when it comes time to choose a crane for launching and recovering a dinghy.

John Kettlewell

Their dinghy exploration of the coral reefs over, it was time to get the dinghy back on board. The cable was hooked up to the lifting harness and the dinghy began to rise out of the water. Then — nothing. What now? Weighing some 900 pounds, give or take a hundred, there was no way to get the dink aboard without the crane. The nearest possible marine repair shop was almost 200 miles away from their location in the remote San Blas Islands of Panama. The only option being a long tow, the yacht owners began to make preparations and checked the weather, looking for a smooth window that would allow them to safely make it back to a marina where repairs would be possible.

Sound unlikely? That was a real problem faced by some power voyagers in the San Blas a few years ago. With the popularity of ever-larger hard-bottom inflatables, powered by ever-larger outboards, comes the need for ever-larger and more powerful yacht davits or cranes. It is very easy to under-spec this critical piece of equipment.

Bigger is better
Yacht davit and crane maker Nick Jackson Co. out of Redmond, Wash., recommends having your dink, with motor, fuel, and all of its usual gear weighed before choosing a crane. They say you can’t go by the manufacturer’s printed specifications for things like motors, which are often listed at dry weight (no oil). And, who knows what was included in the dinghy weight — were the seats in? Once you have a realistic weight, add 20 percent for a margin of safety, and to allow for things like water in the bottom, or equipment that might get added later.

In other words, if your dink and all its equipment weighs 1,000 pounds, you need a crane with a minimum capacity of 1,200 pounds. This is the first and most important step in preventing the difficult scenario outlined in the first paragraph. Needless to say, when in doubt go up a size rather than cutting it too close. For example, the Nautical Structures Hydraulic Mini Crane (HMC) system comes in an HMC-1100 and an HMC-1600 configuration. Using our example of a 1,000-pound dinghy, with the safety factor of 20 percent bringing it up to 1,200 pounds, it would be best to go for the HMC-1600 with a capacity of 1,600 pounds.

Similarly, if you already own the vessel and the crane, you need to choose a dinghy and outboard that is light enough to allow for that 20 percent margin. Steelhead Marine from Langley, B.C., Canada, supplies the ES 1500 crane used on the Nordhavn 55. An owner with this crane would want to keep the complete dinghy load less than about 1,250 pounds. This is something important to compare between similar-sized vessels, as cranes vary a lot in capacity. You can’t assume that two yachts of the same size can handle the same dink. For example, the Fleming 55 comes with a Steelhead ES 1000 crane, meaning you need to keep that dink load less than about 833 pounds.

A new option is coming from Auckland, New Zealand, company C-Quip. The company claims to have produced the world’s first carbon fiber Lloyds-certified SOLAS and MCA approved rescue boat (MOB) crane, and now they are selling carbon fiber dinghy cranes as well. They offer powered and manual models with capacities from 50 kilograms to 10 tons, and units made with the more common aluminum or stainless steel structural arms.

Power play
Cranes can have electric winches or electric-hydraulic units, where a motor powers a hydraulic pump, which then powers the winches. Many larger crane and davit units utilize electric hydraulic pumps, or the yacht’s hydraulic system. Typical power draws are 150 to 190 amps at 12 volts, so your electrical system has to be robust.

Brower Systems Inc., of Costa Mesa, Calif., like other companies, offers units with 12-, 24-, 120-, and 220-volt motors powering the hydraulic systems. With the high load requirements some will opt for the 120- or 220-volt option, meaning the generator must be running; while others prefer to go with 12- or 24-volt motors in order to have the option of using just battery power with or without the main engine or the generator running. The 12- or 24-volt option means that a voyaging yacht is not totally dependent on a functioning generator.

Leave it astern
Some long-distance power voyagers like to have two options for dinghy storage, for inshore or offshore use. Transom davits are generally more convenient for daily use, keeping dripping saltwater off the boat and in general requiring less effort. A stern-hung dinghy is also a great place to keep gas tanks and not have the fumes wafting through the boat. It is very handy to keep everything in the dink for fast launching. One disadvantage to the stern location is that the dink is more prone to theft, which is a concern in some areas.

Smaller boats utilizing lighter davits with block and tackle arrangements have relatively limited capacity. Edson Corp., of New Bedford, Mass., recommends that its dinghy davits should not be loaded beyond the safe working load of one davit, or 250 pounds (boat and motor). It sounds like a lot, but if you have a 9.9-hp four-stroke outboard (around 95 pounds), and a tank with five gallons of gasoline in it (around 35 pounds), you can only have 120 pounds of boat., which is just enough to accommodate a Zodiac Cadet 8.5-foot RIB. And, watch out that it doesn’t fill up with rain in a thunder squall!

Of course, there are higher capacity transom davits for those with heavier dinghies. Olsson Mfg., Inc. of Seattle said they pioneered the transom fork dinghy davit design 25 years ago. The company makes the RS-1 and RS-1 HD transom davits with capacities of up to 1,200 pounds. The Olsson transom fork design hinges the bottom of the davits on the transom, lowering the arms of the davits down towards the dinghy. This makes for a much simpler mechanism, fewer moving parts, and increased strength. The transom of many vessels is a particularly strong mounting base, without the need to make major structural modifications.

Details, details
There are numerous other considerations in choosing your davits or crane. For cranes, it is important to consider reach: how far the crane extends from the side of the yacht, and/or how much extension the crane allows. As with capacity, it is better to have a bit more reach than the minimum. For example, you may need to offload the tender while tied up in a marina, and having additional reach would allow the dink to be deposited on the dock. Units require different types of mounting bases, and of course the structure of your yacht will help determine where they can be mounted. For cranes, in general, the closer to the edge of the yacht’s deck, the better.

In the useful-to-have category, Brower makes wireless remote proportional controls, to allow you to control the speed of the swing of the crane as you rotate it out from the side of the vessel. Wireless controls allow one person to both direct the operation of the crane from the best vantage point, and if necessary handle a guy rope from below to keep the dinghy from swinging around in the wind.

Also handy is a small manual crane that can be used to lift the motor off the dink for repair purposes, or to unload supplies (or your big dog) without having to deploy the large powered crane. Forespar Products Corp. of Rancho Santa Margarita, Calif., makes the CargoMate portable crane that only weighs 32 pounds yet can lift up to 250 pounds with its hand-cranked winch. Forespar also makes a range of lightweight dinghy davits. Their Nova Davit is suitable for up to 350 pounds.

Like other complicated and powerful boat systems, maintenance of powered cranes and davits is important. A visual inspection of the cable should be made monthly, and it should be retired if it shows flattening, kinks, corrosion, broken strands (meat hooks), or if it makes unusual squeaking or snapping sounds. The hydraulic fluid must be kept topped up, and Brower recommends servicing the hydraulic system annually or every 50 hours of use.

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John Kettlewell has cruised the waters between Labrador and South America for more than 35 years. He’s the author of the Intracoastal Waterway Chartbook, now in its sixth edition. He’s a member of the Taunton and Cuttyhunk Yacht Clubs.
 

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