|SJ23 Tech Tip F18, (Reissued 2007-05-20, Bob Schimmel)|
a heavy mast on a sail boat can be a dangerous job. It can also be expensive to
replace a dropped mast, not to mention replacing what you've hit.
An SJ23 mast probably weighs close to 200 pounds plus whatever wind force
you have to deal with. For
these reasons it is important to control it as much as
possible. Don't take any chances.
In a trucker's world an A-frame secured to the back of a flat deck is usually called a "gin pole" and is used to easily lift a heavy object on or off the deck or manoeuvre it over the ground. Similarly, an A-frame can be mounted on the edge of a work barge as a very robust yet simple crane. You don't see them much anymore because it is quicker to rotate a hydraulic crane mounted on the barge than rotate the barge. Either one of these methods is simply a convenient way of moving a heavy object through the short range of the "gin pole" or A-frame. Years ago sail driven commercial canal boats in Holland were equipped with an A-frame as a permanent deck fixture to lower the mast so the boat can slide under a bridge. The boat's momentum carried it past the bridge and the mast was raised on the other side to resume sailing. This procedure had to operate very smooth and quick so the vessel would not loose way. Blocking the canal to other commercial traffic was considered a major blunder if you screwed up the procedure.
In the trailerable sailboat world, an A-frame comes into its own for stepping a mast. The advantage of using an A-frame is that you have lots of mechanical advantage to reduce the lifting effort and lots of control to minimize sideways movement. The longer or taller the A-frame is relative to the mast, the greater the mechanical advantage. The huge control that you achieve leads to the single biggest advantage, safety; in large part because you don't have to stand under the unsupported mast! If you step the mast hand over hand, with the aid of a block and tackle connected to the forestay, then you must steady the mast sideways so you don't twist the deck plate off. The most difficult part of a hoist is the transition from standing in the cockpit to standing on the cabin roof. It is during this CRITICAL TRANSITION that the deck plate is usually twisted loose or when you increase your odds of dropping the mast. I have stepped the mast in a side breeze using my A frame, there is that much control, but I don't recommend it. If the wind is strong, it much safer to point the hull into the wind and step the mast quickly. I have done this quite a few times with no problem. The less time you spend in the transition zone with an unsupported mast the better. If the wind is really strong, park the boat somewhere and go find a coffee shop to wait it out!
CONSTRUCTION - Fabricate your A-frame in the sequence that the components are described here. It reduces your chances of making an error relative to the effort required to make each component. Cut the poles, attach the foot hinge plates to the poles, bolt the plates to the T extrusion on the foot pads, screw the T extrusions to the wood pads and finally, cross the poles to form the apex and drill the hole through the two poles for the apex hinge. By following this procedure you eliminate a bunch of complex measuring that will likely be off by several degrees making for misaligned hinges that can't pivot. The chances of you measuring it correct are minimal! Remember, Murphy!
A-FRAME POLES - The aluminum poles of my A-frame are 2" OD with 1/4" thick wall. This size and thickness is overkill to the Nth degree but the price was right; 1/8" thick wall is sufficient, even down to a 1" OD tube, similar to a spinnaker pole. See COMMENT below. Each pole measures 101" long. The distance from the pivot bolt at the foot to the hinge bolt in the apex is 99" with 1" of pole beyond the apex. The apex fits just short of the forestay fitting, leaving room to easily transfer the forestay from the A-frame to the deck. It is prudent to attach the forestay to the deck quickly to ensure safety for the mast and the people standing around it. It is also convenient to leave the A-frame on deck for trailering or winter storage, as seen in these two photos.
COMMENT: When I designed this A frame I had no idea how much force I was dealing with so I erred on the side of safety by using heavy material. After using this A-frame on other boats as long as 30', I realize I overbuilt the assembly. I now know that lighter poles are quite OK since the load is all compression. In fact I have seen poles made from 3/4" conduit (1" would be better as they shouldn't vibrate or buckle under the load). I have also seen poles made from 1.5" spruce tree trunks, gnarled up 2" poplar trees and fir (2x4)"s. If you intend to use wood then choose clear straight grain wood. It would be relatively simple to cut a notch in the end of the wood pole to insert the hinge plate and slip a metal collar or hose clamps over the end to reinforce the pole end. If you saturate the pole ends with epoxy for strength and coat the wood with Cetol, it will protect it from the elements. Another simple method is to use 1/8" thick metal tubing slipped over the pole end, leaving 6" of metal protruding beyond the wood. Flatten the 6" protruding tube and bend it to align with the T extrusion to form the foot hinge. Light gauge aluminum poles would make it easier to carry the assembly. Be your own judge in this design. I have this habit of building everything to withstand WWIII. I hate flimsy Mickey Mouse stuff. No offence Walt!
If you want to fabricate an A-frame for a larger sailboat, scale the dimensions up proportionally. The length of the A-frame poles should be from the mast step to the forestay fitting. The pole diameter and wall thickness should be equivalent (or bigger) to a spinnaker pole designed for your boat. If the assembly is too bit than consider Two shorter poles joined with a sleeve to make a longer one. This would allow you to store the assembly in a small space. A great way to go if you are a globe trotting sailor who wishes to be independent of shore services. TOP
A-FRAME FOOT HINGE & DECK PAD - The hinge at the foot of each pole consists of a 1/4" thick aluminum plate fitted inside the bottom of each pole and is fastened with a 3/8" bolt with two centering spacers. The spacers are short sections of tube cut from an old aluminum ski pole. Click here for a cross profile of the hinge assembly. Notice the two notches cut into the pole to fit plate into. The spacers and notches hold the plate firmly inline with the tube. The plate is bent sideways 250 to align it with the aluminum T extrusion on the deck pad so the frame can tilt. The T extrusions must lie parallel to the center line of the hull or the turning axis of the hinge so the frame can pivot. (If you used a full articulating ball joint here, all of this critical alignment can be dispensed with as the joint would pivot freely regardless of the angle. These ball joints are not cheap but they work very well. The aircraft industry uses them extensively for perfect alignment of control arms). The hole in the hinge plate is drilled slightly forward of center so the A-frame can lay flat on the deck. The two deck pads are made of (2x8)" soft spruce to protect the gel-coat and are coated with tung oil to prevent rot. The 3" long aluminum T extrusions are screwed to each pad. Thus the hinge operates freely through the full 1350 arc that the frame must operate through. With the deck pad wedged against the toe rail and the stanchion, it doesn't move. All of this may sound complicated, as it takes a bit of finagling to bend the plate just right, but both hinges must turn freely. Take your time with this part of the job. TOP
APEX HINGE -
The simplest way to create a strong hinge at the
apex is to overlap the ends of the poles. It may look
but it works, it is easy to make and stores well. I
was well on the way to making a fancy hinge when common sense prevailed!
Assemble the feet, bolt the poles to the feet, cross lap the poles, lock
them together and
drill a 1/2" hole through the middle of both poles. Insert a 1/2" bolt
using a large nut as a spacer
between the poles to create room for the eye bolt nuts. The two eye
bolts (use cast type for strength) are through bolted, one in each pole,
just below the apex hinge bolt. If you can find a long enough eye
bolt to go through both poles so it also makes the hinge, all the
RIGGING - If you use a 4x1 block and tackle you will require 80' of 3/8" line. This length creates a long tail section which allows the tailing person to stand well out of the mast's drop zone. Some "jam tarts" are squeamish about a stick falling on them!
ASSEMBLY - Having assembled the frame on deck, mark the starboard and port poles with a felt pen for easy reference when setting it up on the deck the next time. It may not be obvious now but you'll thank me for this tid bit of advice later!
A-FRAME MAST STEPPING PROCEDURE - Inspect the standing rigging where it attaches to the mast. All cotter pins must be rolled over and show no sign of fatigue. All nuts must be screwed down to full depth and secure. There must be no "meat hooks" (broken strands) sticking out of the wire and there can be no kinks in the wire. The continual changing tension of the wire, between strained and released, will eventually fatigue it, resulting in breakage at the kink. If any clevis on a turnbuckle is kinked, replace it. Resist the temptation to straighten it. Oscillating bending will induce rapid fatigue and ultimate breakage. This is exactly the same process as flexing a piece of metal in your hands to break it. While this A-frame makes it is possible to step the mast by yourself, the job is still easier with two people.
you have never stepped a mast before, rehearse this procedure in
your mind so you know it cold when you actually do the job. Go through the motion, doing
several dry runs if you have to. Nobody will pass judgment on such
an important job as this. Practice, practice, practice till
everybody understands. The
astronauts do it all the time. Whenever I have a "green
horn" to help me, I always go through at least two dry runs with them till I know they understand.
You know they understand when that squirrelly look on their face changes
to a "light bulb" smile. If this doesn't happen change your description
of the process! Go slowly so no steps are missed.
1 - This is my first time using the A-frame and my buddy Ron was curious about my latest gadget so he came along to help. The road tie down lines were released, shrouds freed of deck fittings and deck is cleared of gear.
2 - Mast was carried aft and the foot aligned to the tabernacle. Here I'm twisting the mast into alignment so Ron can insert the hinge pin. Note that the mast is supported by the transom support post.
3 - Hinge pin inserted. I made this custom hinge pin because every helper had a difficult time inserting the factory pin through the tabernacle and mast base. The end of the pin is slightly tapered to facilitate easy insertion. The loop on the end makes it real easy to manipulate the pin.
3a - Hinge pin - The pin shown is made from 1/4" stainless steel rod. I bent one end back on itself to create a loop for easy operation and the other end has a hole drilled through the rod for a cotter pin.
4 - Final check of A-frame, forestay is attached to the apex of the A-frame, block & tackle line is attached between the apex and the bow. Halyards not yet attached to the A-frame.
5 - Windex and VHF antenna attached to mast head. Loosened turnbuckles standing up. All lines clear. Mast ready to be raised.
6 - Mast half way up. I steady it sideways during the bottom portion of the lift to protect the mast step when the boat is floating or in a side wind. Its a bit wiggly on a floating boat.
7 - Mast is almost vertical with the A-frame pulled down on the deck. It is important to push the mast forward while transferring the halyards to the pulpit so you can comfortably attach the forestay to the bow fitting.
NOTE - I have modified the above procedure to facilitate single man mast stepping by using the halyards to lift the mast with the forestay clipped to the A-Frame. See A-FRAME MAST STEPPING PROCEDURE, Step 6 above. TOP
MAST HINGE PIN - The factory hinge pin is difficult to insert through the four misalignment mast base holes or to remove since there is no hand hold. I made a replacement pin from 1/4" stainless steel rod. One end is bent back on itself to create a 1" diameter loop for easy handling. The other end is slightly tapered for easy insertion through the four holes and has a hole drilled through the rod to fit a hair pin through. You could drill a second hold near the ring for a second hair pin.
COMMENT - "Using
an A-frame to step the mast is so effortless that it takes all the worry
and frustration out of the job. There is minimal sideways movement of the
mast. We stopped several times during the lift to check on things and to
take these photos. I wouldn't dare stop in the middle of a lift using the hand over hand
method. The deck pads stayed in place and the hinges worked perfectly.
used this A-frame to step the mast of several other SJ23s and an SJ7.7M
and only tied the deck pads with a short length of line. This poses no
problem as they stay in place. There is only a slight force to push them
aft towards the stanchions.
Replacement SJ23 Mast - If you intend to break your mast or want other replacement rigging parts, contact Stephen Jensen at SAN JUAN SAILBOATS. He has lots of parts and can get just about anything else that isn't in stock.
Replacement SJ24, 26, 28 or 30 Mast - If you want replacement rigging parts for these models, phone SPAR TECH - 15230 NE, 92 St. Redmond, Washington. 1-206-883-2126.
NOTE 1 - If you wish to leave the A-frame in place while towing, then suspend the apex of the frame from the mast with a line. This prevents the frame from pounding on the deck and punching a hole through the gel-coat. In addition, you could use a tie down line to prevent the frame from bouncing up to the mast! To date I know of eight A-frames that have been built using these plans. Mine has stepped dozens of boat masts. Hmmm, I should say this qualifies for a free grog!