Difference concept of cruising catamarans

Where did you read 200 miles a day? After completing his 72 footer Klaar said:

"Otherwise had a fast trip up from Cape Verde–17 days to the Azores (sailed in the slipstream of a failed hurricane, Nadine), and got a perfect lift almost halfway by Day 5."

So the fastest part of the fast trip was almost 750 miles in 5 days, or 150 miles per day, which is still impressive.

Richard Woods said this of 200 mile days:

 

There is a fair amount on the web concerning Ontong Java 2 , you will find 180 to 200 miles a day as her avg. written on a number of the article,s .

 

The oldest appearance of that quote I can find is on Peter Evans' site tackingoutrigger.com. It was then repeated elsewhere. Possible it came from Atom voyages or wharram builders, but that data is gone. Evans has never met Klaar.

"Theoretical hull speed is 17 knots but Ontong Java rarely travels that fast. 180 to 200 miles a day is the norm, and that happens with barely lifting a finger."

This all sounds a bit too apocryphal when you compare the specs of Ontong to the Newick trimaran Moxie, referenced by Woods above. Moxie did less than 200 miles a day when it won the Ostar and broke the record by 3 days. Ontong Java weighs twice as much, has less sail area and a less efficient rig, yet performs similarly on a normal day without lifting a finger?

Anyway, this is way off topic, my point was that 200 miles a day is maybe not the most realistic goal for a box shaped vessel loaded up with furniture from Ikea.

Ontong Java

Displacement 11T
Sail area 1010 ft2 (est)
Waterline length 50.3 ft (est)

Newick Moxie

Disp 4.5T
Sail area 1160 ft2
LWL 46 ft

 

I understand your point , but if you read the goals stated at the start of the post the Ontong #2 meets many of those goals , you just have to overlook the ugly . I am not sure the Ontong is a true catamaran , and it is hard to come up with a LWL because the hulls differ in length ( 71' ) and ( 57' ? ) . But with a 50' lwl we are around 9.5 at disp. speed so 180 to 200 miles is doable in a long day . The man built a large cat on the cheap and has sailed around the world multiple times over the past 10 years , two hulls with a house .

 

The biggest flaw I see in your concept are the junk sails. They will need really big masts, probably carbon fiber, and those will cost you plenty. The sails themselves will be heavy, each one at least as heavy as your current detested mainsails, and that's if you go carbon for the battens, heavier if you do not. The upwind capabilities will not improve compared to a conventional rig, regardless of what you do.
If we compare apples to apples (meaning both systems have powered winches and are set up correctly for single handing) the only advantage is not having to use dedicated downwind sails.

The rest isn't so problematic, a pod cat in this size is unusual and that hurts resale value, but that added depreciation is insignificant for a junk rigged cat, even if professionally buildt.
Pivoting rudders integrated into transom steps are nothing new, there is no reason to go side mounted.
Diesel outboards while possible are not ideal. If you don't want saildrives or a fixed shaft, you can do a retractable shaft driveline. Since you only use the hulls for storage there is enough space to arrange for a top opening watertight box for the shaft and prop to live in, and you can service everything from inside the boat. This will allow you to use whatever diesel engine you fancy.

 

I'm not sure if this is scaled correctly, but it also looks like the junk sail is larger than the bali mainsail? I just scaled the Bali to the advertised LOA and Adrian's drawing to 46ft.

There is some reduction of area in the profile, mostly from the lower deckhouse. But this makes me wonder if that comes from less bridgedeck clearance or less headroom, or both?

 

The Bali 4.3 has a 52sqm mainsail, and a total air draft of 18.35m (the mast itself is shorter since it's deck stepped). The OP wants each of the junk sails to be 100sqm, and since the cabin is 7m wide and he shows masts at the cabin edge, the maximum batten lenght will be in the region of 6m. This means he will end up with masts around 25m long and an air draft around 21m.

 

@waterbear, let me start with the Bali 4.3:

I added the red lines:
Buttom: Waterline (it is not at the edge of the transom as the colouring suggest, the transoms are well immersed and that seems to be intended because all Balis are like this and the antifouling is also about 15cm higher than the edge of the transom)
Next is bridgedeck. Clearance is about 54cm measured at the stern but the bottom is parallel to the waterline.
Next is the floor level inside the deckhouse. I estimate the floor is 50cm high, the reason is the mast support structure as the mast is in the middle of the deckhouse
The top line is the ceiling inside the deckhouse.

I think you scaling is a bit wrong because you assume my design to be 46feet long, but it is actually 17,95 meter, which is nearly 59 feet. Bridgedeck clearance is 95cm, being about 5.4% of LWL (105cm would be 6%). As such, you also underestimated the battens, which are 7.8m. The sails are very large and I'm wondering if I didn't overdo it a little...I assumed 10 sqmt/ton would be nice. But the Bali 4.3 has 5.5 and the Leopard 6.7 (upwind sail area and max weight according to owner manuals), so maybe I could reduce the sails to 70m2 each to get to 7m2/t which would make everything smaller?

Scaling a Bali 5.4 up to 59 feet (ignore the blue sail shape of the 4.3):


@Rumars my airdraft is 19.3m / 63 feet (top of mast, sail fully up 20.9m). Mast length is 20m, of which 2.7m are buried under deck.

The biggest advantage of the junk rig for me is that I don't have to head up into the wind to change the sail area, followed by not needing a downwind sail and being able the sheet according to wind and not don't-break-the-battens-on-the-shrouds. What I also like is that the failure-point of a traditional rig doesn't exist: There is no standing rigging.
I understand your argument of weight, but I think on that size of boat the weight of the sail is anyways beyond what I can handle manually and I need winches for that.

I did a quick drawing for a more traditional rig: A mast stepped on the aft bulkhead of the deckhouse with a small main and two furling headsails. Sail area around 170sqmt. Airdraft in this is 23m, the mast being 19.5m long. Sailing would usually be only with the furling sails (poled out), the main would only be used upwind. Besides being more traditional I don't see many advantages. On the downside I need a lot of reinforcements for the mast base and forestays. I don't know if needing chainplates in different places (and distributing the loads) is an advantage over having all the loads in one place for the free standing mast?

 

Here is a comparison with the sail scaled down from 100sqmt to 70sqmt

Mast length reduced from 20m to 17m, airdraft from 19.3m to 16.3m (measured over mast, not sail). Batten length reduced from 7.8m to 6.5m.
The smaller sail is like having the big sail reefed by 2 panels.

I guess the bigger sail would be reefed to the second panel in ca. 15kn of wind, so the smaller sail would loose performance in less than 15kn of wind, but would be about equal in more than 15kn of wind (?)

I know how to calculate heeling and righting forces, but no Idea how reefing schedules are calculated, so the reefing above is just a wild guess...

 

@AdrianN, thanks for the clarification. Clearly I didn't read the original prompt carefully.

Now that I understand just how large the boat is, I'm curious to know why you would not utilize the space in the hulls? The hulls look to be huge. I estimate 9ft+ tall with 7ft of freeboard, and 6.5ft beam? This looks only slightly smaller than the bedroom cabins you have drawn. Not only that, you could have standing headroom with a 2-3ft "basement" below. This seems like an odd waste of space when space on boats is at such a premium.

And if not using the hull space for accommodation, then why so much freeboard?

Btw, your disdain for thruhulls and inboard motors reminds me of James Wharram. I believe many (all?) of his designs shun inboard motors for outboards, sometimes with retracting rigs (pods?) that raise up and down? Also, the sheer size of your boat reminds me of the Pahi 63, although not the form factor. Perhaps you could build the pahi hulls then add a box on top?

Finally, when I hear of giant catamaran projects, this comes to mind:

 

@waterbear The hulls are designed to sail well while displacing enough to carry the boat fully loaded. They are long and slender (12:1 at waterline), the height is simply to hide the deckhouse so it doesn't look too much like a container on floats. The reason for putting the accommodation in the deckhouse is that the hulls don't have straight edges, which means a lot of work for fitout and every piece has to be custom made to fit the odd angles. It is much easier to cut out a rectangular piece of the hulls (where the deckhouse protrudes into the hulls). Same for the cockpit, it "cuts" into the hulls. The space in the hulls under the deckhouse and cockpit is storage, the rest is "walking space". The compartment fore and aft provide floatation only and space for maybe fenders and lines.

The whole concept is not about maximizing space, in that case 46 feet would be more than enough. But putting all the accommodation and weight into 46 feet would means fatter hulls and end up close to what modern production cats are. If I wanted something like that I could just buy off the shelf and keep motorsailing.

Regarding the Pahi, the hulls simply lack displacement. Even for Wharram's small pods the boat ends up overloaded, imagine how low it would float with my deckhouse...

The reason why I dislike through-hull is this:

This happened on a 4 years old Bali. On our Leopard I replaced them all with composite ones from Trudesign, But still, not having a hole at all is much better than having a good through-hull.

 

4 year thru hull failure is a design/parts failure. I've seen bronze seacocks fail, but they were old... like decades old. I've seen thru hull on alloy Boats fail in shorter time from wrong alloy, and gave up on maralon after having more than a few give up the ghost in the cold.

This Fleet up here looks like Swiss cheese with all of the mandatory Refrigeration through holes, aside from the guys using random combinations of metal they usually last forever.

 

Ok, got it.

I don't think these long slender hulls are going to bestow the performance you are seeking on your boat. The long hulls add mass and wetted surface (especially with a box section) and will actually take more energy to drive up to a certain speed. On top of that you're adding windage, surface area and mass with very tall hulls that are mostly unused space, further increasing power requirements.

I think you are proposing a boat that you will not be able to handle comfortably, even with power equipment to move the sails, and will not come close to meeting your performance objectives. That said, I'm sure there are plenty of naval architects who will be happy to take your money!

 

I don't think you should reduce the sail area, even if you end up sailing reefed a lot of the time. To give an example, the Lagoon 450 wich is an honest 20-22t boat in cruising trim, flys a little over 200sqm downwind, and most owners calculate 6-7kn as average passage speed. The wetted surface area of your longer and slimmer hulls will be at least similar to the Lagoons shorter but wider hulls.

The batten lenght of 7.8m is probably to much, the sails have to not only clear the opposite mast but also the part of the sail that sticks forward. There is also some room to adjust batten position on the mast, and the overall aspect ratio of the sail to consider. I would be more comfortable with 6m battens, even if you can fit longer ones.

The overall advantages and disadvantages of freestanding rigs have been discussed a lot. In a nutshell, you have to get the engineering and manufacturing right the first time, there is no room to improve afterwards. The masts are going to be expensive, even if you take the additional weight of aluminium. Total rig expense will be significantly higher then a conventional rig.

Lots of people reef catamaran mainsails downwind, even ones with much bigger areas then you have. You should give it a try sometimes, maybe it solves some of your current problems with the Bali. Modern designs simply don't sail well without the mainsail, regardless of wind angle.

 

12:1 is probably too thin. You have to balance skin friction with wave making. Broadly slim hulls do better in strong winds fatter hulls do better in lighter winds. Designers have trended away from slimmer hulls in all but very specific applications as it's easier to fly bigger rigs and force fatter hulls along with wide overall beam.

Perhaps to illustrate the problem with some extreme examples...if you have a hemispherical hull in 2 knots of wind you can make it sail faster than an arrow of the same displacement because the arrow will have more drag. There are a lot of decent performing cats these days that are 9:1 on the water, and these boats win races. Personally I think that's a bit too fat but 10:1 or 11:1 are IMO optimum.

Mick Waller happens to publish on his website the hull beam ratios of his designs. He was drawing 9:1 hulls quite some time ago. Bit ahead of the pack in that regard.

As for rigs I don't know of anything that a junk rig does better than other options. If I were to do something unusual it'd be a crabclaw, on double spars stepped in the hulls and joined above the sail. Dead simple and good on all points.

2c...