| The foam core construction fell right in with my objectives.

To be clear, that is the objective of 3500# payload, right?

| Likewise the offset mast......a design feature which I have not yet become entirely comfortable with.  

     First off, I do not have an absolute payload objective........  I'd like to have a payload above 3000 lbs.   Remember that payload includes EVERYTHING other than the shell of the boat and the mast, and in the case of the KD 860, the engines are included in empty weight. 
    Every bit of ground tackle, sails and rigging, fuel and water as well as tanks, batteries, pumps, plumbing, head & shower fixtures, cooking and cleaning items, utensils, pots and pans, etc, refrigeration stuff, electrical generating stuff, electronics, and electrical, including lighting and wiring, fuse panel.  Any furnishing that is not part of the boat structure, then there is the matter of spares and tools, spare cordage, drogue & sea anchor, extra blocks, etc, watermaker if there is one, entertainment equipment & computing equipment, books, food, personal gear, dinghy, and emergency life raft if you carry one, live jackets, harnesses & jacklines, any posts and lifelines, bicycle, and on and on and on.    When one starts adding all this up, along with whatever I've forgotten, and I'm sure I've forgotten plenty, you go through payload very rapidly.   MOST boats that are being used are overloaded much if not all the time, and this is especially important with regard to multihulls.

    I've dealt with weight enough in the past that I don't need to have actual figures to realize how rapidly this is adding up.  NOTHING so so trivial that is should not be counted, as it all adds to the total.  On a passage, if one just totals up fresh water at an allowance of half a gallon per day, plus food for two people, allowing for 30 days as your margin of safety, one needs to look at weights like 600 pounds, not including the 500 pounds for the people themselves and their personal gear.   We are looking at 1100 pounds minimally right off the bat.   It continues on that way.  Anchors, chain, rode, sea anchor, drogue, and associated hardware is likely to take you up another 500 pounds easily.   It doesn't take a mental giant to see where we are headed......   ;-)  Yes, I'd love to have 3500 pounds payload, but I'm not going to get it.




I found this link of a kd 860 for sale. I include it because it has offset mounted Aero junk rig, which seems relevant to your interests.

https://www.apolloduck.com/boat.phtml?id=558987

It might show you what kind of rigging is needed for your one mast.

    You sent me a link to Oryx, Pete Hills boat with which I have been familiar for a long time, and was aware that it was for sale.   I've been following Pete's adventures through the blogs of his first and second wives, Anne, and Carley, who was tragically lost at see off South Africa.  The current iteration of his junk aero rig is very similar to what I have in mind.  It's his third rig on this boat, the middle one being a soft wing sail, the first being a kind of bastardized half Aero Junk.  I occasionally correspond with Paul McKay, the designer of the Aerojunk.    Oryx is NOT a KD 860, it really is a KD1000, a 10M boat based on the KD 860.   It's at least the third boat Pete has built, and he spent a year "on the beach" building it.  It is an absolutely beautiful boat, and a phenomenal value at the asking price, but it is not the boat I want.  I have dozens of photos of this boat, at least one of which I posted here.   Some of pete's ideas such as the knuckle and a few others were added to my "library" of ideas.
    I had settled on the Aerojunk long before I saw it on Oryx, largely because it uses flat fabric sails which take their camber from laying against the batten cage.  This means that sails are simple, and easy to make from whatever is available..... Part of not being "dependent", and part of "low cost".   

| I do want the main portion of my junk rig to be able to fly over the boat on those points of sail where it is oriented mostly laterally.  

Do you know why you want that?

| How much difference in performance is there is real world sailing with the camber 30% aft of the luff, or at the 50% point?

I guess it is a third order variable. Aspect ratio being first, foil profile being second. IMHO.

| Theory says it should be significant, but theory is not always borne out in real life sailing.   An example is the "good tack / bad tack" belief.
   
| This is relevant only in pointing out that our expectations are often not borne out in the real world. 

The whole world is like this I think.

|  I rather like the idea of having the option of hanging the main sail well over the side, or hanging it over the boat. 

    I'm partial to having the center of effort as close to the center of the boat as possible.  Moving it off center creates a yawing moment that must be countered

Have you thought through how the rigging will work? Perhaps some listers have some advice?

    Thought about it???   I've studied it.   I'm extremely familiar with the junk rig and every aspect of it.

| The boom will be quite long, as the aspect ratio will be low.

Long booms are a concern as gybes become terrifying or, perhaps, high energy events?

    Gybes are a terrifying event in a Bermuda rig because there is zero balance area on the sail. It's ALL behind the mast.   A junk rig will have from 15% to 30% forward, which has a big countering effect.  One of the many reasons for looking at the junk rig.  Like the Aerorig on the Harry Proa, it becomes a non issue.  In addition the boom will clear heads in the cockpit,   AND there are not shrouds to hit with the potential of breaking the boom or ripping a chain plate out or breaking a shroud fitting and being dismasted.

| The mast will not be tall, standing only about 9M above the top of the bridge deck cabin....

|  The shorter the mast has both advantages and disadvantages.  I will be sacrificing ultimate performance, but the low aspect sail will have a great deal of footage for light winds.

This is a non sequitur. Tall masts can have even more sq. ft. Afaik, there is no advantage to a short mast, but I look forward to learning your thoughts.

    A low aspect rig with a rectangular sail flies more sail per foot of mast than a triangular sail.   Obviously a short mast does not give greater sail area, but a square sail does.   I'm looking at keeping heeling force / capsize forces down down, as well as air draft, which will of course allow me to get into places you cannot with a 50' mast.  

I tried to look up materials costs of the KD860 but was unsuccessful.

I could send you a complete bill of materials (off list).........  

| Weight is proportional to cost until we start striving for extreme weight reduction, and then it describes a parabolic curve in the opposite direction.  Within a given weight range / cost range, the objective is to build the boat that provides the best living and sailing environment / most usable space.   The cat fulfills that very well. Cats increase rapidly in weight / cost with length.   The Woods Tamar for example, at 31 feet is almost double the weight of the KD 860 (stock) at 28 feet.  I don't expect the KD 9.  The Kohler Pelican at 11.5M has an empty weight of only 2200 KG, against the KD 860 at 1800 KG.   The weight per meter of length in this case is going down from 209 - 191 for the longer boat.   This is definitely the exception, NOT the rule.   Most boats go the other way.

Interesting thought. I would say this exception SHOWS that it is entirely reasonable to say one can design a longer, lighter boat.

Let me point out that Pellican is a longer heavier boat, not a longer lighter boat........

For example, the 12m Ex40 is ~900 kg = 75 kg per meter. Is that far enough down the parabola?

At half the weight, it is reasonable to assume half the cost to build. And designed and engineered to be built in foam and glass with the fastest cleanest build techniques. Not a retrofit of foam and glass into a plywood build.

This is another reason I moved away from the cat designs.

| Increasing length just for ride and speed is simply not on the table here.   Those are NOT priorities.

You misunderstand. I chose a CHEAPER boat to build. The Cats are too expensive. Speed and ride are second order variables for me too.

| Note the way Bernd created a "wing"
<snip> The full length hull molds would be far simpler with only two surfaces, the bottom and the side.   The wing can be an add on
|separately infused piece.

Yep. You will note the HP design does this kinda stuff all over.

    I'm not questioning or challenging your choice of boats.  The 40' HP just doesn't do it for me.......

|  Note the temporary bulkhead used during bridge deck cabin top construction.  The cabin top is a compound curve on both boats, and will have to be built "the hard way".... hand finished both top and bottom.  There is no way to produce this compound curve with a simple mold..  It's a case where it's easier to do the job the "hard way" than the "easy way".  The only compound curve on the entire boat.

I think there are a few ways to to do it the easy way. How big is your build space?

Big enough............ Please elaborate, I'm all ears.  Nothing I'd like better than to be able to easily make smooth fair female mold to infuse the entire structure in one swell foop.  

P.S.

I think you should convert your Kg per meter figures into $/m.

I'll leave that up to you.  KG and dollars are essentially proportional for a given build method


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Posted by: StoneTool <owly@ttc-cmc.net>

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