Thank you for the very interesting video! I was in fact planning on using a series of brackets, beams, and plates to transfer the forces to the mounting points of the original mast. I figured if I set it up to transfer the forces to the original step, a bracket at the front, and brackets near the original chainplates, that should be good. It's very likely any mounting setup I built will be massively overbuilt, as I have access to a bunch of aluminum, and more metal means a stiffer construction which means a more even transfer of forces across the mounting points. After giving the existing setup another look, I believe I'm significantly overthinking how large the forces will actually be.

I ran some numbers and figured out that I should probably go with a 6 inch mast. Even tripling up on irrigation pipe, a 4 inch mast wouldn't be strong enough. I'd have to get thicker wall 4 inch pipe, and that would be extremely expensive. On the flip side, used 6 inch irrigation pipe sells for around $2/ft in my area, which is more within budget. The only downside of 6 inch pipe is the clamping brackets are much bigger. A 6 inch mast with a 10 foot double wall, and a 6 foot triple wall is around 50 pounds. I'll probably incorporate some sort of hinged method of raising the mast.

Having the mast hovering over the front hatch is sure to feel a little silly, but it should work as long as I get my triangles right. I'll have to make up a simplified cad model of the roof so I can do my work properly.

It'll be difficult to move the mast forward, unless I figure out how to keep the mast base from intruding into the cabin. That's doable with larger mounting hardware, probably some struts that transfer the forces backwards. I need to get some measurements and make a basic model of the roof of the boat in CAD so I can start brainstorming. It would be nice to avoid drilling a giant hole in the roof. I do like having a shorter mast though, anything to make it easier to step.

One other issue with your picture is that the new mast would be located right at the forward hatch, I'll have to think about that as well. Perhaps that might make things easier, who knows?

Should I try to use 4 inch aluminum pipe? Perhaps with some extra inserted in the bottom ala Minimus II?

So I just bought a nice 1983 Hunter 20 for a song. It's my first large sailboat, after building dinghies. However, looking at the mess of standing rigging, and the daunting prospect of raising the mast mostly by myself, is instilling a very strong itch to convert it to a junk rig. I'm sure that itch will only grow every time I have to step the mast, so I might as well give in and start making plans for the winter.

I built a lovely dinghy junk rig a few years ago, so I'm no stranger to the rig and the basic sailing concepts. I also have access to all the cad and cnc machining I need to make things like mounting brackets and the like. I should be able to do everything involved in such a conversion, especially at the sizes needed for this boat. However, my budget is fairly tight, so my projects tend to have a unique contrast of perfect cnc machined parts held together by a redneck assemblage of 2x4s and rebar.

I'm currently making my way through the practical junk rig book, so that should help me figure out the sail and line logistics, but the first (and biggest) design task is picking and sourcing a mast, followed by mounting it.

A quick browse of my local marketplace reveals a few different options. First, there is aluminum irrigation pipe, mostly 6 inch but with some 4 inch diameter available for almost free. This pipe usually has a wall thickness of 0.050", which may be too thin? However there is also someone selling 20 foot sections of stainless steel exhaust pipe at 4in OD x 0.065" wall. 20 feet is too short to make an entire mast, but I can always top it with wood.

The sailboat data site says that the original sail area is around 160 square feet, with a ratio of 19:1. Should I target a similar area? a 16ft x 10ft junk sail would give me an equal area, and would be easy to source a heavy duty tarp of that size to make it all one piece.

Any advice on mast selection would be helpful. I attached pictures of the current mast step, and the structure inside that cabin that appears to transmit some of the mast forces into the swing keel assembly.

Oh, and this is going to be freshwater only on a trailer sailer, so mixing aluminum and stainless isn't nearly as big of a deal.