I like this approach. My mast probably weighs over 200 lbs so I'm not sure the 2x4's would handle it.
I'll keep looking for the detailed instruction and video... It might be on one of my backup drives. Anyway... let me give some of the highlights.
The supports are 2x6, unlike the pictured 2x4's. There are four leg pieces... two bolted together make one leg. 12-18" overlap... 4 or 5 carriage bolts. The two legs are joined at the top with a large, 5" hinge. The lifting block is secured to the inside of the frame close to the top with a strong piece of rope or metal bar reaved through holes on the frame.
On the Catalina 27, the chainplate posts can be used to secure the A frame legs at the bottom by splitting another hinge, fixing a leaf to each leg and using a long carriage bolt to slip through the hinge pin hole and connect to the chain plate stud.
The height of the a frame must be enough to get the balance loop to the halfway point on the mast... on my Cat 27, 4 10 ft 2x6's, mounted on the deck, put the lifting block at the spreader level. The balance point on my mast is approx. 12-18 inches below the spreaders, just above the steaming light.
Besides each leg base, the A frame is supported fore and aft with 2 or 3 guy lines. We found that two guys forward and one back worked well... the guys are lengths of line tied to eye bolts set into the frame legs around 3/4 of the way up... then knotted to the pulpit and pushpit respectively.
The lifting line is long enough to run through a turning block secured to the deck or toe rail a little forward of the frame... then back to the primary winch.... There is no need for multi purchase tackle... the winch will give you all the power.
In the video the guy made his wife stand off to the side and lift the entire package by hand... what an idiot!!!!! You'll notice it was way too much for her to handle... Plus, she was standing way off to the side... and it is unlikely you'd have that much space if you're doing the job at your dock.
The best way is to have someone in the cockpit manning the winch handle, with another standing dockside with the tail of the line.
When setting the lifting line, a loop is tied around the mast...leaving a very long tail... the loop is hoisted up to the mast's balance point...then the tail of the line is tied to a cleat on the mast near the bottom with enough tail left so that it can be used to control the spar while it's in the air.
The winch operator lifts the mast high enough to clear the collar of the step while the mast man sets in on a block of wood so any internal wiring can be attended to... then the mast can be lifted up a bit more before the mast man tilts the spar to horizontal, avoiding the guy lines and maneuvering it into position to lower onto its supports.
We used three people... two on the boat (mast and winch station) and one on the dock to help where needed.
Because the A frame is mounted in front of the mast... it allows the base to be brought forward as the lifting line is lowered. ... The dock man and winch person can manipulate the upper part while the mast man stays on the foredeck and controls the bottom.
Keeping the boat steady is easier if no one tries to get on or off while the mast is free swinging.
