Raising the dinghy, easier!

The Davit System

The Vision 444 comes with a Carbon Fiber Davit system that is used to hoist a dinghy.  As time has gone on, some of the exact specifics of the davit system have evolved and changed slightly, but for our boat (Hull #11) and the ones near to it, this is how it operates. 

Two Main Steps

First, after attaching the dinghy to a forward and aft attachment line, the davit arms are raised; pivoting on axles which mount the davit to the transom of the boat.  This step is accomplished by attaching a line which runs through several blocks to the starboard, aft power winch.  Pressing "2" (low speed) on the winch power buttons and raising the davit into its full upright position, where it can be lashed to the boat with Dyneema loops.

Second, is to raise the dinghy to be close under the horizontal beams of the davit arms.  The dinghy attachment lines, that are attached to the dinghy's bridle, run up through a fixed block at the end of the davit arms and then to a "single block with becket" which can move along the length of the davit arm when pulled by the lifting line. 

The forward and aft dinghy lifting system is identical and operates as follows. A line begins at the becket of the "single block with becket".  It then travels to a fixed block mounted at the forward end of the davit arm, then travels back to the "single block with becket", going around the block and then back to the forward end of the davit arm, where it goes through a clutch.

The line is pulled through the clutch, which gives a 2:1 pulley system, reducing the amount of force needed by half, but requiring to pull twice as much line to raise the respective end of the dinghy.

It looks like this:

Photo of standard block setup - Photo Courtesy of Grant Mackenzie

Overall Thoughts

Even though there are some areas that I chose to improve, the system is very good.  Our friends that are on monohulls are left mouth agape when they see how easily and quickly we can raise our dinghy.  We are usually completely done lifting it, securing it for a passage and heading inside before they have gotten the dinghy even fully out of the water.

Some of the greatest attributes are:

• It uses an existing motor (a winch) instead of needing a separate specialty motor.
• It is a simple system that uses simple blocks.
• It lifts the dinghy exceptionally high out of the water, which is really important in bad weather, especially following seas where a low dinghy could get swamped.
• It is very easy to fully secure the dinghy for off-shore passages.
• It can be used to safely lift a dinghy by one person as long as it is not overly choppy or rolly.

We've found some aspects of it that have challenged us in its use.  After living on the boat for 21 months at this point, we have come up with quite a few solutions to those challenges.

Here are the parts we wanted to make better/easier:

• Lifting force required
  It is pretty difficult to lift the engine end of the dinghy (we have a 30HP Yamaha that weighs 53kg / 120 lbs) with a 2:1 pully system.  When hoisting the aft end, we are basically lifting the engine and half of the boat weight (about 30 kg), which is about 83kg / 182 lbs.  Even at half that with a 2:1 pully system, it's a lot of force required.
  The forward end is easier, but since the fuel tank (20kg when full) and the anchor and chain (5 kg) are at the bow, most of that weight is borne by the bow lifting line, so we estimate that at about 50kg / 110 lbs, which even with a 2:1 is not easy.
• Noise from the harken blocks when lifting
  The original blocks that allow for lifting of the davits are attached to pad eyes on the forward end of the davit arms using the standard stainless steel shackle that comes with the block.  As the davit is raised, the angle of the line changes slightly, which causes the shackle to change position on the pad eye. This movement causes a metal-on-metal noise that gets amplified through the tensioned lifting line. It's not anything that is causing any damage, but it's not a fun sound.
• Being able to quickly and easily hook and unhook the hoisting lines from the dinghy bridle
  This matters most in rough conditions, when you are trying to hook the dinghy in while also trying to balance and also trying to prevent the dinghy from bashing into the sugar scoops. But, it's also nice all the time for that process to be easy and safe.
• Stress on the Davits when lifting the dinghy in rolling conditions
  As delivered by the factory, the dinghy lifting lines that go from the moving "block with becket" on each davit arm to the dinghy attachment hook are a very high quality Dyneema line.  This is generally viewed as the best rope material to use on all parts of a cruising yacht. However, since Dyneema has exceptionally low stretch (~2% at 50% load rating), when we are hoisting the dinghy in rough conditions, the boat is bobbing up and down as the dinghy is fully raised from the water.  This results in the lines being slack and then fully tight as each waves passes by. This causes the davit arms to take a heck of a shock load and vibrate and also a torquing motion can be seen from one arm to the other.  These arms are made from carbon fiber, so addressing this is probably being overly cautious, but this was a point of stress for us when hoisting.
• Possibility of over tensioning when lifting the davit and absolutely destroying a block
  While lifting with the winch is great because it removes the need for one more (specialty) motor on the boat, it is not without it's minuses. When we hoist the davit arms, the goal is to pull the line just enough so that the davit is fully against the rubber stops at the top end, which allows us to easily attach the securing loops that take the tension off the hoisting line, blocks and clutch.  If we lift slightly too little, we can pull on the line that runs from one arm to the other to increase the tension the last little bit to be able to get the Dyneema loops attached.
  However, if we pull too much the Harken 46 electric winch can pull with 1300 kg / 2860 lbs /1.43 tons of force!! The 8mm double braid Dyneema line can handle that (2100kg breaking strength), but the poor little block that leads the davit hoisting line to the winch certainly cannot (1100kg breaking load). 
  Guess what happens if the winch is pressed for 1/2 second too long?  The Dyneema tensions and because the Dyneema stretches so little, the full force force of the winch is applied to and absolutely explodes the block, making it rain with the internal ball bearings landing in every direction.

How to improve on a great starting point

None of these solutions came about immediately, but since this is like taking our car our of the garage and we do it almost every day, we had plenty of time to think about solutions and try some things out.  Here is what we did to make the dinghy lifting process even better.

Lowering the Lifting Force Required

There are really only two options; reduce the weight (nope) or increase the mechanical advantage.

The goal with this was to increase the mechanical advantage without having to make the solution look ugly or have to drill extra holes in the davit arms.

To accomplish this, we needed the line to start at the fixed, forward end of the davit arm and add another pulley at the moving end. The "adding another pulley" part was easy, we simply replaced the "block with becket" (Harken 2601) with a "Fiddle Block" (Harken 2621).

A fiddle block is a double block that has two blocks inline (one smaller, one larger), instead of having two same-sized pulleys side-by-side.

The harder part was having the hoisting line start at the fixed end. We needed a fixed block (called a cheek block) with a becket, and we needed it to mount using the same hole pattern as the existing cheek block. That doesn't exist.  Actually, even a cheek block with a becket doesn't exist from Harken. We could always add another pad eye to the davit arm, but one of the goals was no more holes (not too mention, it would have been difficult, since adding a pad eye would require a backing plate to make sure the pad eye didn't just pull out of the carbon fiber).

The solution was to create a Dyneema loop of just the right length that is fed through the body of the existing cheek block and then is shackled to the end of the line. The only important point here is to make the loop just long enough so that the metal shackle is not applying force to the body of the cheek block.  I used a 4mm uncovered Dyneema line to do this and it is doubled up to get the required strength. This solved the problems and has made raising the dinghy so much easier!

Our solution after swapping out the aft block and making a new line connection

As an add-on note, we shared this solution with Kris and Pierre from Umbono (Hull #10) and Pierre implemented this part slightly differently.  Instead of the Dyneema loop and shackle, he made a soft shackle to a length that was just enough to thread through and attach to the eye in the end of the hoisting line.  I think this is a much better solution and is what I would recommend. It's on our list of enhancements! I would suggest a custom soft shackle (easy to make) that is made from 5 mm Dyneema.

Quiet down over there!

The metal-on-metal noise was basically fixed by replacing the two provided blocks (Harken 2600) that attach to pad eyes on the forward end of the davit arms with Harken 2151 blocks that attach with included loops of Dyneema.  Since there is some movement while under tension, I also added a Dyneema cover as a friction guard to the Dyneema line. Now, the connection is metal pad-eye to Dyneema cover which doesn't make a peep!

Harken 2151 block with Dyneema connection loop and protected by Dyneema cover

Hooking made easy

I don't remember what types of hooks came on the original hoisting lines because we changed this before leaving South Africa, but using a 3" / 75mm Safety Snap Hook has been wonderful.  We also spliced thimbles into the dinghy bridle, so clipping this safety snap hook on is utterly simple. Wichard (part 2481) makes a wonderful product for this, but it is pricey.  There are other brands out there and if they are rated for at least 400 kg working load, they should work fine.

Wichard Safety Snap Hook - Ⓒ Wichard Marine

Stop stressing me out!

The shock loading of the davit arms was very disconcerting, mainly because you could see the amount of force being applied to the arms as the dinghy got jerked up and down.  Our solution for this was to replace the double-braided Dyneema lines with three-strand nylon. Three strand nylon stretches a lot; approximately 12%!

This was simply a matter of replacing the provided lines with very inexpensive and easy to splice 3 strand nylon that is 3/8" in diameter (it's rated for 4,250 lbs of breaking strength, but working load is 5-20% of that depending on age and condition, so between 212 lbs and 850 lbs. Given that that can get close to the dinghy weight and because it is so cheap, I'll replace these lines after no more than 2 years to make sure they don't fail on us). 

The only thing that made it difficult was getting the length just right, given how much it stretches under load.  Unfortunately, I don't remember the final length of the loop I ended up at, but if your dinghy/motor have a different weight, it will likely vary by a little anyways.  

What I would suggest is to splice one end of each line directly to your davit bridle hook and then splice an eye onto the other end of the line for attachment to the shackle of the moving block.  The length should be such that you can't pull the hook up into contact with the block at the end of the arm, when the hoisting line is fully pulled in.  Err on the side of making the line too long as you can always undo your eye-splice and make the line shorter. If when you hoist your dinghy fully, there is still a lot of space between the fixed block and the bridle hook, re-splice the eye after taking a little less than distance of that gap.

Make sure the splices are tapered and clean, as the ends of the splices will have to go through the fixed block. Do not use knots, you will lose too much strength!

Shock-absorbing 3-strand rope spliced onto hook and with eye splice on forward end

Installing a safety valve to save blocks

Having a block that is being used to lift your dinghy suddenly explode into dozens of pieces is unsettling to say the least.  Fortunately, the block in question is located after the clutch, so, as long as the clutch is closed (which is should be) when the block does explode, the dinghy does not fall, it just stops lifting.  Still, far from ideal and blocks aren't terribly cheap.  Plus, without it, you can't lift the dinghy.

This solution is what I would call safe, but not ideal. It requires using a piece of 3 strand nylon rope beyond it's working load to take advantage of it's stretch. There is a backup piece of Dyneema for if/when the 3-strand rope breaks, but it's still not a perfect solution.  It does work really well though, as it provides for more margin of error when lifting the davit, and a safety valve in case it is still pulled too much (and it breaks).

I used 3/16" black 3-strand nylon rope.  It is rated at 1,300 lbs of breaking strength, so about 130 lbs of working load.  I made what's called a rope grommet, which is just a single loop that looks like regular three strand rope, but is made out of one strand that's a little over three times the length of the circumference of the loop.  Here is the video I used to figure out how to do this.

When I install this, I use it doubled over twice, so there are 4 segments of this rope, which effectively quadruples the strength of rope, so we are up to about 500 lbs of working load. This is honestly pushing it, however, the grommet is only under load when we are actively hoisting or lowering the dinghy.  

I could remake this from a larger diameter 3-strand rope to increase the strength, but it would also decrease the stretch.

Increasing this one size and making it from 1/4" would increase the working load to about 840 lbs, without having too profound an impact on stretch and is probably worth considering, however, it also increases the chances that the block would fail before the 3-strand grommet.  This would take some destructive testing that I'm not willing to do to find out for sure!

In addition to this three-strand quadrupled-up rope I mentioned, I have also tied a 5mm piece of Dyneema tied with a square knot to a length that is just a bit longer than what the 3-strand stretches to under load.  If (when?) the 3-strand breaks, the Dyneema will pick up the load immediately.

So far this has worked really well and reduced the mental stress of holding on to that winch button too long and destroying another block. 

3-strand grommet stretch point with Dyneema "safety"

Other Thoughts

• When we are doing a long passage, or anytime we expect especially rough conditions, it's a good idea to lash the hole in the Safety Snap Hook to the rod that goes from one davit arm to the other.
  
  The weakest link in the davit system when the davit is raised and the dinghy secured is the 3-strand rope that hoists up the bow and stern of the dinghy. The other points of failure are the carbon fiber arms themselves, the Safety Snap Hooks, the pivot point on the bottom of the davit, and the Dynemma safety loops that secures the davit arms in the fully up position (I guess also the dinghy attachment hooks and the bridle system). Those are all insanely strong. While the 3-strand is plenty strong for everyday conditions, if the boat is lunging up and down, the forces seen by everything is multiplied by a factor equal to the G-forces being seen at that point.  A 6mm or larger piece of Dyneema tying the hook to the davit rod is just another step for piece of mind while under way.
• Water is heavy!!  Make sure to pull out the drain plug on your dinghy when rain is expected.  It is easy to take on a hundred pounds of water or more overnight! (We use a loop of yellow Velcro looped around the hoisting line to remind us to put the drain plug back in.)
  
• Things moving around in the dinghy while it is hoisted and you are underway is not great.  We attached a carabiner to a piece of thick shock cord that is tied to a bridle anchor point in the dinghy.  Before we hoist the dinghy for the night, we clip the carabiner to the outboard handle so that the outboard can't pivot from side-to-side while we are underway.
• Oh yeah, hoist the dinghy for the night!  Unless you are in the safest of safe places, RAISE IT!  The most common entries on CSSN (Caribbean Safety and Security Net) start with the words, "An in the water and unlocked dinghy..." following by something bad.

What's Left?

Our Dinghy Davit system is near perfect.  There is really only one thing I can think of that would be better, and that is if we could prevent the side-to-side swing of the dinghy when we are raising it in rolly swell. 

The dinghy is hanging from about 30" lines before the fore and aft hoisting lines are pulled in, and that allows for a lot of sway.  When it is very rough at anchor, this requires both of us to be involved, one to hold the dinghy from swaying and the other to operate the winch.

I haven't come up with a good solution for this yet, but that would be about the last thing!

Do you have any thoughts?  Please post a comment below with any thoughts or questions!