Storing the Dinghy

By Jan Mundy

One of the pleasures of boating is landing at a favorite anchorage, launching the dinghy then going touring, visiting other boats, water-skiing or diving, fishing or exploring ashore.
All dinghies, whether inflatable or hardshell, require secure storage. Towing isn't practical all of the time and downright risky in rough weather. Ditto for deck storage on most boats. Better quarters for the dinghy are davits, systems that hold the dinghy, keep it clean and deter theft.
When accurately configured for your boat, properly sized to the dinghy, aptly installed and correctly set up, davits should function trouble-free. Most problems occur from overloading, faulty installation or an unbridled dinghy – if not secured so absolutely motionless, a swaying 200 pound dinghy can be a lethal load.
Because of the myriad boat styles and mounting arrangements, davit systems are built on a semi-custom basis and typically purchased manufacturer direct. This way, the buyer presumably gets expert advice in mixing and matching components to obtain the best configuration for their boat.

Before davit selection can begin, however, you need to do some planning: select the dinghy, decide where it will be mounted, and then determine the overall lifting weight.
DINGHY SELECTION
Before purchasing a davit system, you should first choose a dinghy and decide where best to store it. Saltwater cruisers may need a more robust dinghy than inland boaters, one that handles seas without drenching the crew or swamping. A good rule of thumb is to have the dinghy's load capacity twice that of its weight. For example, a dinghy weighing 200 pounds should be able to safely load 400 pounds.
Another consideration is the potential to change a boat's handling characteristics by adding a heavy mass concentrated in a small area. A typical 10-foot dinghy, with a 15 horsepower motor, weighs anywhere from 250 to 280 pounds in actual weight. Transom mounting a dinghy with a 6-horsepower engine in davits on a 32-footer likely will have no effect. Double the weight by carrying a personal watercraft (PWC) on the same boat and you're sure to alter the characteristics.
Examine your boat's transom (or deck) and determine the amount of usable space without interference from engine vents, ladder, platform, tanks and other items. Most stern-mounted davits look best when they are mounted perpendicular to stanchions (rails). Measure the distance apart for mounting of the davit arms. As a rule, the reach of the arms for stern davits is half the beam of the dinghy, except on boats with canoe sterns, which generally require a greater reach.
To help configure the best system for your boat, some manufacturers supply full-size paper templates at no-charge, to be cut out, mounted onto cardboard and placed onboard.
Many of the answers to storage questions lie in how much your tender weighs.
Now estimate the location of the dinghy pick-up points. You'll need to mate these points to the davit spacing, because many systems allow for a misalignment of only a few inches. The next step is to marry the dinghy to a davit system properly sized to your boat.
PRODUCTS AND OPTIONS
There are five basic systems to hoist a dinghy: clip-on, where the dinghy rests on end on the swim platform; rail mounts, both fixed and rotating, which fasten to stanchions and the dinghy hangs over the deck or stern; traditional bolts to the deck or transom, so the dinghy hangs over the stern; rotating mounts on foredeck, bridge deck or swim platform; and professionally installed, hydraulic-powered elevators that mount on a swim platform to lift large dinghies or PWC of 1,000 pounds or more. There are also newer, more exotic options, but we'll stick to the basics.
Clip-on davits, also called Weaver davits, are an economical choice for powerboats in sheltered waters with small inflatables and outboards up to 10 horsepower, but the motor must be removed before hoisting. If you want to leave the motor on, you'll need a rail, traditional or rotating system. Of these solutions, rail mounts are the least expensive and most popular, especially for sailboats.
Easily installed in a couple hours, fittings fasten to the rail and universal bases mount to the deck or transom. If your dinghy is heavier than a rail-mount davit system can safely carry, you'll need a traditional or rotating system. Designed for heavier dinghy-engine packages, deck- or transom-mounted traditional davit systems come with fixed or adjustable riser arms in lengths of 10 to 40 inches, depending on the boat's requirements. Heavy dinghies may require optional support kits mounted on the transom or swim platform.
Rotating davits lift, rotate, then put the dinghy onto the foredeck, bridge deck or a wide swim platform. If the deck can support the load, these systems can be flush mounted, rather than placing a compression post through the deck to the keel. Manually-operated rotating systems can lift about 180 pounds onto a swim platform, and 150 pounds up on the foredeck. The higher you lift the more difficult hoisting becomes. Optional electric winches simplify this task, but mechanical hand winches with a 25:1 purchase, which means 25 cranks for every 1 inch of lift, aren't practical to manually hoist a dinghy six feet or higher. Dinghies with large motors (30 horsepower or more) often combine a rotating davit on the transom with a cradle mounted on the swim platform.
GLEN JUSTICEDavits can be a single crane or a pair of lifts, depending on your needs.
Swim platform lifts have become popular on large yachts to lift heavy dinghies or PWC. Most are hydraulic powered and not easily owner installed. Prices for davit systems increase incrementally with the lifting load – the heavier the dinghy, the more expensive the system. Installation, if done professionally, adds to the price tag. And there also costs you may not anticipate. Many published prices do not include complete systems. Tie-downs, ratcheted straps, lifting slings, stabilizing bars, transom strut supports and manual or 12-volt winches are some such additional equipment. Boats with weak rails or decks that cannot support the extra weight sometimes require support kits.
Where the lift is higher than six feet, you should consider a power winch system–and that too can add to the cost. One of the most popular options is a tackle upgrade with purchases ranging from 2:1 to 8:1. With a 4:1 block and tackle you can comfortably hoist an 80-pound dinghy. Add a 10 horsepower outboard and you'll likely need a 6:1 tackle.
Davits are generally fabricated of stainless-steel pipe, bent to shape and welded, or cast aluminum and anodized. Bent pipe davits have a high-gloss finish compared to less attractive, satin-coated cast units, but require frequent cleaning to deter corrosion. Because welding changes the molecular structure of the stainless steel, look for small welds, usually formed by TIG welding, compared to the hotter MIG welding method that forms large welds that may corrode. The wall thickness of the tubing also varies: .083 tube is more expensive than .065, but has greater weight carrying limits.
CALCULATING LOADS
Bigger is better when it comes to buying a davit system. It should be able to take the strain of a 600-mile passage, support a rainwater-filled dinghy and in rough weather ensure the dinghy won't break loose and hole the transom.
The strength of a davit system is a function of dinghy weight and boat speed. Davits are rated by breaking load, lifting capacity, test load or safe working load (SWL), which is the preferred rating as it measures the raw lift-and-hold capacity of one davit arm. The faster the boat, the greater the pounding forces. When comparing an express cruiser and trawler with identical dinghies, for example, davit loading is substantially higher on the cruiser.
To determine the SWL, multiply the total load (dinghy plus gear and motor) by 75 percent, then add a 15 percent safety factor (that allows for a water-filled dinghy). Consider this example for stern-mount davits: a 10-foot dinghy and 10 horsepower motor with a total weight of 150 pounds times .75 equals 112.5 pounds. Multiply that by two (there are two davits) for a davit system carrying capacity of 225 pounds. Factor in the 15-percent safety margin, and the SWL is 180 pouns for the pair of davits. For a single crane davit, the SWL equals the total dinghy weight plus 15 percent.
FORMULAA PWC can weigh substantially more than an average inflatable tender.
With dinghy selection and placement completed, you'll need to provide the davit manufacturer with boat year and model, packaged weight, selected davit type, mounting distance between davit arms (if it is a dual arm system), davit arm height and reach plus desired options. Many builders have a database of designs, so they know the boat's basic layout, but customization and add-ons can alter the mounting.
INSTALLATION GUIDE
Since davits put tremendous loads on the hull (or deck), few boatbuilders recommend installing them, especially on the rail or transom. Lifting a 100-pound package, for example, loads on the mounting base can be as high as 500 pounds with the boat stationary.
As a rule, fiberglass boats built before 1992 often have stronger transoms than newer boats, particularly sailboats with sloped transoms. That is an area where builders have cut thickness to save weight. Some boats require transom or deck reinforcing, as well as optional support kits. Since rail davit systems are limited by the strength of the rail, boats may require reinforcing and optional cable or strut support kits to reduce the load. Teak railings almost always require a complex rail-support structure.
Large loads may require adding extra layers of fiberglass under mounting brackets, or rail bases for rail davits, together with oversized backing plates at least the dimension of the davit base (and preferably as large as space allows). Because all boats and mounts are different, refer to the installation instructions supplied with the davit. These “manuals” range from excellent to poor, and some manufacturers offer a toll-free helpline as back-up. Depending on your mechanical ability, installation of a simple rail system may take only a few hours. For more complex systems, the job may take 40 hours or more. Power davits are more complicated, especially the wiring, and often require professional installation.

This story was previously published in Mad Mariner's DIY Boat Owner.