|In response to your PS, here's a general description off what I want to do.

Thank you Howard.

|     It has gradually become obvious that the boat best suited to my needs is a small catamaran. I expect to be single handing more often than not, plan to live more or less permanently aboard while voyaging, exploring the world.

This is where I started too. I was attracted to Woods designs for all the obvious reasons, but also, his personal experiences sailing, with his family, his own designs around the world.

That gave me a sense of confidence that whatever came up, he would have a good idea what I had gotten myself into and how to get out of it.

| I originally looked at trimarans, but to get the payload I'm looking for I would need almost 40', and it is my desire to stay down to around 30' for a number of reasons.  Initial cost is less, less rig is required to drive a smaller boat, upkeep is lower. Above that length, costs tend to go up for everything fairly rapidly.

I would like to make a note here that, as I read this list, all of these come down to cost. As constraints, I think it is important to recognize you are optimizing for cost. Which is wise.

And here is where I think you might want to start reexamining your observed constraints.

Like, what if you can build a bigger boat, for the price of a smaller boat? What if you could have the much more pleasant ride, safety, and payload of bigger boat, with the costs and weight of a smaller?

These are the questions I started asking myself.

These kind of questions also lead me to the junk rig. (Aside; have you joined the junk rig association?). Because it allowed me to have the skills to actually make my own sails! Out of inexpensive materials. ( I have a life habit of doing my own maintenance too!). But I thought it smart to be able to fix all the crap on the contraption I depend on.

Another aside; I found Mr. Woods not very supportive of junk rigs. Or strange masts I could build myself.

Teaser Alert! I think Rob might have cheap sail making ideas for us too!

|Catamarans have close to double the payload of trimarans, provide better access to the stern, a roomier cockpit, and the cats that interest me have an integrated bridge deck cabin, on a level with the cockpit, and with a decent all around view for watch keeping in nasty weather.   And of course they have a shallow draft which is one of my primary criteria.

How do you compare a cat and a tri? Per foot? Or displacement? Or cost? Or accommodations?

Other than me having no idea of the value of stern access, I agree with all of this.

|    As a single hander, fatigue is a big consideration, and being able to live primarily on the bridge deck where I can keep tabs on things is important.  I expect to sleep on the bridge deck, either in the cabin or in the cockpit depending on weather, which is no real problem as I sleep in a recliner anyway, and a light weight "zero gravity" type recliner could serve that purpose, and be mounted either indoors or outdoors.

I think, as a single hander, I would just reef, and goto sleep. Wake up, set sail, and put coffee on.

Although I recently had a new sleeping concern.
https://m.youtube.com/watch?v=hHjbdOh8qDg

Poor fellow was thrown across the cabin and broke a rib. Now, I know nothing about sailing, but this lead me to some discussion on SA about the wisdom of a tight berth.

I was gonna do a thread in that, but, this is as good a spot as any I guess.. Anyone have thoughts, chime in.

| There will be a "direct deposit" head, consisting of nothing more than an opening through the bridge deck for use at sea, for safety. Most MOB situations are from pissing over the side ;-(

I did not know that! Although, the idea of a hole for me to drop important things directly into the ocean is a non starter for me. I'll take the composting head in the saloon.

| The rig will be a cambered split junk rig on a single central free standing mast, something I have yet to see on ANY cat.  It will take some engineering to support a free standing mast on the bridge deck, but it presents no insurmountable difficulties.

Cambered Junk I get. Why split the rig?

|     The free standing mast

Welcome to the church or the freestanding mast.

|     The junk rig offers huge advantages for a single hander. Blondie Hassler proved that when he came in second in the tiny folkboat, Jester in the first OSTAR back in 1960, sailing the Atlantic in bedroom slippers.  He basically didn't leave the safety of the round hatch on the top of the coach roof of Jester.

This church is a simple rig denomination. Not sure how into junks the rest of the congregation is, but this heathen is down.

|    The problem that keeps cropping up for me is payload....... I have a pretty good idea how quickly weight adds up, and this will be my home.    I expect to do long passages that could take from a few weeks to a month, and need to be able to carry what I need. It's also important to me to be able to fix my boat and the systems in it.   I've always done my own maintenance on everything..... the habit of a lifetime.
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|    The two boats that come closest to meeting my criteria are Richard Wood's beautiful Sagitta catamaran, and Bernd Kohler's equally beautiful KD 860.  

I liked both of these. But the cost and mast problems got me to move on.

|     My boat of choice would be Sagitta with the Kohler hulls..........
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|    Of course I haven't touched on balance.  Needless to say the junk rig shifts the center of effort well aft of normal unless the mast(s) are well forward.  This is obviously not possible with a single mast on the bridge deck of a cat.   The solution most people resort to is the biplane rig, where a mast is stepped into each hull, and it's a logical solution.   I don't want a biplane rig.  More masts, more sails, more rigging and hardware, more weight, and more complexity.     It does however make a lot of sense, allowing the masts to be low and the rigs small.

Putting the masts in the hulls simplify the structure. I had thought about one mast in one hull. I still don't know why that wouldn't work.

|     The shift of the center of effort aft, means that the center of lateral resistance must also move aft to avoid big issues with helm balance.   This among other things is one of the big reasons for building my own boat rather than doing a conversion.   In Sagitta for example, the daggerboards would no longer be in the galley and chart room.

The complexity of the balance of the thrust and control vectors bothered me.. It seemed a design was a better fit if it started from the ground up with the intention of the stated goals.

| The potential to reduce the empty weight by as much as 25%... which is probably a bit optimistic, adds up to another half a ton payload.

I think there are several important effects from optimizing for reduced empty weight. More lively in light airs. More apparent strength and durability, as the weight of the boat is less able to be used against itself. The force of most all movements is greatly reduced, making everything gentler, easier, faster.

| To achieve that additional half a ton of payload in plywood, I would have to build a much larger and heavier boat, and need a larger rig to drive it.. 

Climbing the wrong side of the design spiral is costly.

| The initial construction cost in foam sandwich will undoubtedly be higher than for the exact boat in plywood, though using XPS judicially will alleviate this significantly it looks like.    I have yet to locate and price the suitable XPS foams.    However even with the cost of Divinicell, and extra glass and epoxy, it would be foolish not to take into account the value of weight reduction, and it is considerable if you start comparing to larger boats.   That cost is not just initial cost, but ongoing higher costs.

I don't know this is true. I assert that it is cheaper to build in foam and glass, assuming Intelligent Infusion. One still has to glass both sides of the plywood or the foam. Infused glass and foam takes much less epoxy, and that is the most expensive item. No throw away frames or jig to build or align, just a flat table and sawhorses. Certainly work saved counts for something.

I also have a limited objection to the assertion of ongoing higher costs of a bigger boat. While generally true, there are some exceptions, which Rob has optimized. Assuming a typical Denny design, what costs are increased for a bigger boat?

The hull is lighter, so more easily driven. The durability and wear should favour the lighter boat. The only real direct cost I can think of is the marina fees, to which Rob has an integrated generous tender to mitigate. I can think of no other costs.

Finally, I assert a bigger boat can be cheaper than a smaller boat. I dare you to compare BOM's, for just the hull costs and sails, for the most similar accommodations to the designs you stated.

Then look at the one with the most similar payload.

Warning: when I did this exercise, I found myself trapped building a harryproa.

|     From being extremely skeptical, I've become extremely interested, not just in weight reduction but in the labor reduction of Rob's intelligent infusion methodology.

The lack of exposure to wet or dust of epoxy is also notable, along with the cost reduction of minimal epoxy use.

|     I was reluctant to completely come out of the closet so to speak initially.    My ideas may seem a bit crazy to some....... and that's OK.    I have for example no desire to sell the junk rig to anybody, or to win converts to my way of thinking.  All I want out of this is a catamaran capable of meeting my criteria well.   A boat that will not beat me up or wear me down that I can sail the world's oceans in and visit far away places while I'm still young and healthy enough to enjoy them. To meet fellow sailors in those places, and to meet the locals, making friends along the way.    A boat where I can stand on the floor, not the wall, and a boat where I don't need a lee cloth to sleep while under way or at anchor, where the stew stays in the pot, and where I can look out the window and really see where I am, and step out into the cockpit without climbing a ladder..  A boat with a shallow draft that will take me into quiet places others cannot go  A boat that I can sail single handed without wearing myself out.   A traveling home, all be it a small one.

Agreed!

|     I've been an admirer of Rob's Harry Proa designs for a short time.......... since I first looked at photos of them, and realized how ingenious many of his approaches.   The first comparisons to come to mind were Bucky Fuller and Phil Bolger, Jim Brown, and John Marples, Woody Brown, and a number of other innovators.   I hope to incorporate some of Rob's ideas into my own project. 

It took me longer to appreciate some of the choices Rob has made. I think his love/strong desire to engage discussion on the topic of sailing is a secret here. And you are adding to that.

|A proa will not fulfill my criteria for the same reason a trimaran won't, but I hope a few years down the road to sail into Oz have a chance to meet designers and builders down there.  Some like the late Ian farrier are no longer with us, but there seems to be an endless supply  down under.
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