Power boat, sailboat and yacht builders and dealers

 Bulletin: RollerTrol™ Automation Systems is Launched!  
  • We have been busy making and selling 12v marine roller blinds for some time, and we have decided to start selling the components at RollerTrol.com so others can do the same.
  • Take a look at our online store for tubular motors and other associated products - make your own custom blinds that fit your boat perfectly!
  • While you're at it, check out our tubular motors with built-in radio controllers. When used with our multi-channel remotes, you can control all your blinds with a single remote!
  • AND DON'T MISS OUR SUPER LOW DRAW LIGHT SENSING SWITCH - perfect for automatic night-time light sensing operation of your ANCHOR LIGHT!!
  End Bulletin: RollerTrol™ Automation Systems  
 
Mount an articulated dinghy davit system on your sailboat with outboard
Installing a retractable tender davit system
that works even with outboard propulsion on sailboat
by Adrian Biffen

 
I didn't like dragging my dinghy through the water while sailing Serenade, our 30' sloop. It creates considerable drag, puts considerable stress on the tender, and encourages marine growth below the waterline.

Normally, you can solve this problem by installing a simple davit system on the stern of your boat, but that wasn't an easy option for us because of the 4 stroke outboard motor that is our main propulsion engine for Serenade. There were several other options, none of which I liked - putting it upside down on the foredeck (blocks foredeck space, hard to lift out of the water), deflating and stowing it (way too much hassle), strapping it on top of the bimini (puts weight up high and blocks the solar panel). 

So I decided to come up with a retractable stern davit design that would allow the tender to swing up and over the outboard on the stern of Serenade. This created some problems, because there is no way to reach the tender to attach the lifting lines, as it has to come out of the water about 6' away from the stern of the sailboat, in order to be able to lift up and over the outboard. 

The key to this was to separate the lifting lines from the articulated raising mechanism. This allows you to attach the lifting lines while the tender is beside the mothership, with the boarding ladder in place. The boarding ladder had to be moved to the side, again because of the stern mounted outboard (but this turned out to be a better location anyway, because you don't have to climb over the stern rail).

There was also the issue of this added weight hanging out over the stern, upsetting the balance of the boat. When I bought the dinghy, I chose the high pressure inflated floor version that still provides a rigid floor that you can stand up on, while keeping the weight down. The inflatable only weighs 70 lbs, and the total added stern weight probably reaches about 100 lbs if you include the mount. If you leave the kicker on the dinghy (which I want to do at times, on short hops), it adds another 50 lbs.

I'm happy to report that I can't really notice any difference in the sailing ability of Serenade due to the extra weight on the stern with the dinghy in the raised position, except that she has no problem reaching speeds over 6.5 knots under sail, whereas I could only do about 5.5 knots dragging the tender. I also enjoy not having to look back to make sure the dinghy is still there while under tow (the line broke and I already lost it once).

Rather than try to describe this somewhat unusual construction, I've created a sequence of pictures below, with annotations, that demonstrate the various steps of how it works.

This is a picture of the davits in their final shape. All the pictures below were taken before I modified it to raise the tender a little higher and to streamline the appearance. Note that the joints are drilled and pinned any place where there is a pulling force as opposed to a compression force. For example, the very top bars and the Holy Jesus seats* have horizontal loads that will pull the tubing out of the connectors, even with the set screws fully tightened. articulated dinghy davit system - final form
Here's where it starts, with the tender at the port side of the cockpit. Our normal docking side is starboard, due to the orientation of our slip. Note how the boarding ladder holds the dinghy tight against the hull, with almost no chafing. It is an easy step down from the cockpit and very stable, with plenty of stainless steel structure to hold onto, and the rigid inflatable floor allows you to stand on it before you sit down. It is actually a better place than the original stern mount because you don't have to climb over the railing. articulated dinghy davit system
Here's another view of the starting position, this time taken from the cockpit. My hi-tech ABS  outboard tiller extender is visible in this picture. articulated tender davit system showing boarding position
The first step is to open the drain cock and drain the water out of the tender. I use the outboard block and tackle to do this. Water weighs about 10 lbs per gallon, so 10 gallons of rain water adds an extra 100 lbs! draining the water out of the dinghy prior to lifting on davits
Here's another view of the dinghy being drained, showing how the lifting lines, leading off the ends of the davit structure, have already been attached to the forward and aft lifting points. I inserted a stainless steel H bar assembly under the inflated floor and side tubes to provide a strong forward lifting point for the dinghy. The nylon straps with hooks that are attached to the H bar are just visible under the seat; the transom on the rear already has a strong lifting ring. draining the water out of the dinghy, lifting lines attached
After the dinghy is drained, the boarding ladder is lifted and the lifting lines are pulled in from the stern of Serenade, causing the tender to swing around into the lifting position. The davit structure has also been cranked down close to its lifting start position. You can see the double line going around the blocks that raises the mechanism - this is entirely independent of the attached lifting lines, so that the tender can be moved around to the boarding ladder. dinghy lifting lines are pulled back to move dinghy to lifting position
Here's a side view of the tender in the pre-raising start position, before it gets taken out of the water. You can clearly see the stainless steel davit structure in this picture. dinghy in lifting position - side view
One more angled view of the lifting position, prior to raising. The two davit struts are clearly visible, as are the doubled lines that haul up the entire contraption out of the water, using an ordinary boat trailer winch. The two main struts are 1" stainless pipe, with 7/8" pipe inserted inside to give it double wall thickness and strength. dinghy in lifting position - angled side view
Finally, the winch is cranked to begin the lifting phase. Here, the dinghy is just clear of the water, with its full weight in suspension. This is the point of maximum stress that the entire system must be strong enough to handle - the stresses diminish as it approaches the fully raised position and becomes more or less a vertical load. tender is lifted clear of the water
It is important to adjust the independent lifting lines to give the tender some forward-aft tilt re rain water drainage. Here, I've exaggerated it somewhat for demonstration purposes. Also, DON'T FORGET to leave the drain plug out! adjusting the tilt angle of the tender re water drainage
Now, the dinghy is about halfway up, set to the angle I want for drainage. dinghy has been lifted halfway and drain angle set
Finally, the tender reaches its fully retracted position, locking into the aft superstructure. The winch keeps it fastened tight, and additional nylon safety straps act as backup lashngs in case of structural failure, and prevent any further movement. dinghy is winched into its final stowage position
Here's a side view of the final raised position. You can see the oak slats of the Holy Jesus seats* that I incorporated in to the locking superstructure. dinghy raised position - side view
A final view from forward. The process is reversed for launching, and it gets into the water fast in an emergency. If the mechanism jams somehow during an emergency, it can be quickly dropped without any damage by severing the lines. dinghy raised position- front view

[*Holy Jesus seats - so called because that's what you're likely to be saying if you're sitting up there when I lay her down flat!]

 
We have initiated a number of improvement projects for Serenade since she was purchased, and we have created a series of articles detailing the work that has been done. Here are the relevant pages in this series:

 (1)
Wireless remote control autopilot
 (2) Diesel removal & 4 stroke outboard engine mount
 (3) Cockpit Bimini (this page)
 (4) Tender davits on stern
 (5) Waste management holding tank system
 (6) Solar panel, PWM charge controller and deep cycle battery system
 (7) Propane Fireplace