New Build: KD 860 Open

I have decided after much time and research to build the KD 860 Open

I have a few questions, for those with more sailing experience then I

Rig selection

I don't have the sailing experience on multi's et to decide which rig i should choose.

The boats going to be used in Florida

A: Live aboard on the hook, way down south
B: Day sailing
C: Extended trips to the Bahamas and south.

He offers two rigs in the plane

A: Two masted bi sail rig
B: Sail with a wish bone boom looks like a free-standing mast setup
C: Wharram type soft wing sail setup
D: Modern square top with jib and head sails


Keeping in mind, day sailing is part of it, but i dont want the rig based on day sailing, there will be extended, long range trips involved one day

 

Minor threat, can you give a link to the wishbone version ?

 

Sorry this is all i got

 

Tried a little harder, better size

 

Quote BY {Oldmulti}

GREAT POST BY HIM!

"This is new variation of Bernd Kohler KD 860 catamaran. Bernd has designed an open bridge deck variation of the KD 860 catamaran with a biplane rig. The cat is 28 x 18.5 open bridge deck cat that weighs 2900 lbs (this version is 1100 lbs lighter than the full bridge deck KD 860) and displaces 6200 lbs. The biplane rig has a carbon fibre mast in each hull with each mast having a 230 square foot mainsail. The length to beam is 11:1 and the prismatic coefficient is 0.57. This is a performance cruiser. The hull draft is 1.3 foot and over the rudders 2.3 foot. There is vortex keels, but low aspect ratio or daggerboards would be possible. The rudders are stern mounted kickups. The outboard can be 10 HP.

The accommodation layout is a large double berth and separate toilet area in one hull and in the other hull a dinette that can be converted to a double berth with a large galley area. The headroom in each hull is 6 foot. This cat could be a relatively cheap long term cruiser for a couple. The open cockpit is between the 2 hulls. This boat is not designed to be transportable, it’s a permanent mooring cat.

The KD 860 parts can be built separately for assemble near a shoreline built once launched it is a single integrated unit. I am assuming the majority of the build is very similar to the KD860 bridge deck shell, therefore the hull skin and decks will be 8 mm plywood and is covered with light glass epoxy. There are 25 x 38 mm stringers at 400 mm centre lines and 8 plywood 8 mm bulkheads. I am guessing here but the underwing is likely to be 12 mm with 32 x 50 mm stringers at 800 mm centre lines. The main cross beam and rear crossbeam bulkheads are 12 mm ply with 450 gsm 45/45 on either side with top and bottom flanges of timber. The rudders are NACA 4412 sections. The blades are 1470 mm long and 250 mm wide. The skins are 4 mm ocume ply placed in a V mould of 52 degrees then epoxy is poured into the bottom of the V to 15 mm deep. A 20 x 20 mm spar with 2 layers of 400 gsm uni directional on the length of the spar. The spar is placed 78 mm back from the bottom of the nose V. The tail pieces of the ply are pulled together to meet a tapered 25 mm piece of timber to form a foil. The entire outside is covered with 2 layers of 240 gsm cloth. Construction time is estimated by the designer to be about 1200 hours. The KD 860 Open is by its very nature is simple which results in a lighter better performing cat that is also more affordable than the KD 860 bridge deck.

The difference between the KD 860 Open and the Evergreen 8 mentioned earlier is the Evergreen 8 is a slightly smaller, lighter and is possibly more transportable (that does not mean trailable for a weekend, it means you could take it home for yearly maintenance). Both would be excellent cats, both are designed to be easily built in ply epoxy but I suspect the Evergreen 8 will use less materials and has a smaller rig and therefore will be cheaper. The KD 860 has more interior room and slightly more performance potential. Your choice, the cheaper simpler Evergreen 8 or the slightly larger higher performance KD 860"

 

Some more info about this boat on the Duckworks site, but no mention of the two masted rig.
KD 860 Plans https://duckworks.com/kd-860-plans/

 

"I don't have the sailing experience "


A: Two masted bi sail rig No, bad. You "don't have the sailing experience". Hard for you.
B: Sail with a wish bone boom looks like a free-standing mast setup. Ok..
C: Wharram type soft wing sail setup. No.
D: Modern square top with jib and head sails. Ok

 

Thanks, care to elaborate on each ok and no?

I was under the impression that a wharram rig is pretty easy sail once the learning is complete?

A modern square top with large head sails is ok?

Thxs for the reply

Everything I read says the bi rig is the safest way to go


All these take training, obviously, but when the rig is learned, is when I want
Reliable, safe, good performance, and reasonable cost

 

What crickets???

Explain your points?

 

Hi MT. Thanks for sharing your project with us. Just so you know Guzzi3 has had some strokes in recent years and it takes a bit of time to recover after each one. Realize he's doing the best he can at this time. Typing is a bit of a challenge for him but we are glad he's here and contributing. I personally like the bi mast arrangement and would use it myself and don't feel the learning curve is insurmountable. It isn't a performance rig normally and some wind directions may prove challenging but there are means to cope in that scenario. Best wishes.

 

Thanks for the suggestions

I like the bi also I think. It's not a pure performance rig, but as OldMulti said to me, top speed is not as important as safe, with good performance, rather then top speed I agre

 

We've got a wishbone cat in the family. The boom is comparatively light and works well.

There have been years of actual on-water experience in racing classes that demonstrate that the performance advantage of a setup like the Wharram "wing" is minimal, and in many cases non-existent. Wharram mentions that the rig was inspired partly by Marchaj, but Marchaj's published work that "shows" the problems with airflow around a mast can be seen to be fatally flawed because he used completely disporportionate mast sizes; I think the smallest one he used was 1/1oth of the mainsail foot length, compared to the standard of around 1/4oth.

Wharram's claims about his rig seem to follow the standard pattern of claiming that a conventional rig requires more controls, when in fact the "extra" controls allegedly used by standard rigs are only there to give superior shape control; a bermudan rig that sacrifices shape control as much as the Wharram rig does is at least as simple. For example the boomless Wharram rig does not allow the control of sail depth independent of sheet tension, as a boomed sail does. This means that when you ease the sheet, the sail becomes extremely full (which is of course disastrous if trying to depower) and also the first part of the sail that generates power when you pull the sheet back in is the leach. That means that when you start to sheet in, the centre of effort is right aft and trying to push the boat into the breeze - a problem when you are sheeting back in after a tack. One of our cats (a little Hobie Bravo) comes in standard form without a boom and is much harder to tack than with the optional boom because of this effect.

One issue about squaretops is that they normally use a diagonal top batten (which seems to be the KD 860 system) and that can be a hassle since you may have to climb up and get it in or out every time you drop or hoist the mainsail. Not a big deal, but annoying if you are daysailing and dropping the main a couple of times per day.

 

With free standing masts on a bi rig, no storm jib on inner forestay, no headsails no screecher no code zeros no asymmetric or even symmetrical spinnakers. No thanks. This stuff looks good on paper but when it comes to making miles you don’t get to choose what comes at you and this rig is an empty tool box.

 

Thanks for the reply, I'm kinda back and forth on the rig. I think, I need not reinvent the wheel on this boat.

So looking at the photos, how would the more experienced sailers with cat miles undertaker belt rig this boat
For sailing Florida south into the Caribbean?

Thxs

 

My 0.02c's worth:

Biplane rig will cost the most, take the longest to build. It will be unique, so if it breaks you have to make your own replacement. Reportedly, worst point of sail is beam reaching, which is a cat's happy place. Will probably interfere with any bimini/shade roof over the cockpit.

Wharram wingsail has raising/lowering issues, windward performance average, and you'll have to build the mast.

Bermudan standard fractional sloop: Good chance of getting a suitable used mast cheap. Can be set up as simple or complex as you like.
Is the bit of extra speed you get from a square top worth the extra hassle and expense? If you're cruising, not really.
Wishbone boom is worth looking into. People who have them are generally happy and wouldn't change.