Cat boat design

a 36 to 42 ft boat with a single 1000 sf sail would be a lot to handle, particularly solo. it would be dangerous in high winds if something fouled.

I would suggest go with about 30 to 32 ft hull, smaller more efficient motor, and design it so it is an efficient motor boat, with a modest sail (perhaps 500-600 sf) to assist the motor when the conditions are good, or for lea surly sailing in calm conditions. than a single sail would make sense, and a simple junk rig would be a good choice.

Junks are easy to solo handle, and fairly light because the stress on the composts are lower than a conventional sloop of the same size (loads are spread out over more components). they are also very efficient at all points of sail except their ability to point is not as good (which you can plan around, or use your motor for any long legs into the wind). the boomlets stay on the same side of the mast, and yes, one tack is "dirty" and one is "clean", but it will not make a lot of difference at the speeds you will be going and on mostly down wind legs.

Junks are popular for solo sailing because they self tend and are easy to handle, even very large sails.

It seems to me if your main motivation is an efficient motoring yacht, with the ability to sail occasionally, or when conditions are good for it, the junk would be a good choice. OTOH, if you want an efficient sailboat, with the ability to motor occationally, than I would go with a larger sloop rig sailboat (or even a ketch), with a smaller motor.

the sail itself is the redundant part of your propulsion system, the motor is your main means of forward movement (with perhaps an appropriate sized outboard stowed in a locker as a back up), with the sail as a third means of keeping the boat moving forward.

this would meet the redundancy requirement for ocean cursing. The single smallish sail and rig would take up less space and cost much less, and require much less maintenance, than a muli-masted sailboat. This can also be done with a single conventional cat rig (I do not think I would use a gaff if I was intending to solo sail), but the easr of handling a junk rig would make it real attractive for an occasionally sailed motor sailor.

 

Your are quite correct on the first part and grossly misunderstanding the realities of frictional resistance on the second.

 

Could you explain your answer, please?

"Frictional resistance" of what?
Of the bearing to rotate the mast?
Of the air in the boundary layer? This resistance is already included in the C_drag.

 

Nick I have learned quite a bit about designing aircraft, and find learning about designing boats is actually harder harder mostly because info is harder to get.
I first thought a wing sail to be crazy, on second thoughts it is actually very clever.
However it is inappropriate for the type of boat I have in mind. My overriding goal is an Atlantic capable boat with minimum technology. Shrouds and stays cost a lot of money and maintenance. A broken stay could mean a broken mast, thus I chose an unstayed mast which would naturally be limited in its length. This would give a lower CE, also part of my plan.

My secondary target is a hull easily powered to SL 1.34 by both power and sail. I have not given up the idea yet but it begins to feel like I might have more success throwing rocks at the moon

 

Buy an old Freedom 40.

 

Re: hull

Several month ago I've seen an unusual advertizement. According to the advertizement:
A shipyard failed to build an ocean racing yacht in time to participite in competitions, then the racing rules were changed, the project didn't non comply with new rules and was abandoned. Now the aluminium hull (22м long) is sold for $30K (the price of a car). Just the hull. Nothing inside, no keel, no mast.

Images
http://forum.katera.ru/index.php?ap...ttach&attach_rel_module=post&attach_id=257964
http://forum.katera.ru/index.php?ap...ttach&attach_rel_module=post&attach_id=260621

I don't know, whether the ad is correct or some kind of fraud.
I don't know the prices for the second-hand racing yachts. The seller of the hull mentioned, that he has seen "America's Cup" racing yachts sold for $50K after the race.
I don't know, whether the hull of a racing yacht is practical for the everyday use (how strong is it).
Although, I think this ad is interesting. http://forum.katera.ru/index.php?/topic/43772-prodaiu-korpus-lodki-22m-aliuminii/

 

None of these things make sailing or maintenance costly. They are cheap, low maintenance substitutes for other more costly options. If you think a 50:1 two speed motorized winch is costly, try hiring a crewman instead. If you think they are costly to maintain, consider 10 of the 11 winches on my boat are original, and the one that was replaced was replaced by an older model. Maintenance costs nothing. Take them apart and lube every few years. If you think a freestanding rig is cheaper than a stayed rig, you haven't a clue. It is about twice as expensive. My 38'er has a 60' double spreader rig with wires upsized one from the racing rig. A 60' flagpole rig would weigh about 250 pounds more than my setup. That would require at least an additional 1000 pounds of ballast to stand up. That 1000# of ballast would need about 150# of hull material to be added for strength. So now you are at 1400 pounds more weight. Figured at about $10/pound for hull stuff, that is $14,000 more money, and maintenance is mostly proportional to weight. My rigging costs about $100/yr to maintain (140 year payback). 100/yr is on a par with basic do-it-yourself maintenance on a moderate use small diesel. My diesel, by the way, is designated as 27 hp, but the factory install is a bit goofy and the cooling is challenged in tropical waters. Forty years of owners' experience says to just pretend its a 16-20 hp motor and prop it accordingly and all is well. I think 1 hp for every $8K-$10K of new boat is about right for blue water cruisers. Coastal cruisers want a bit more than that, though. And more still if you plan on hiring a delivery captain to shift it a couple times a year. My boat costs about $1.50 an hour extra to operate either on sail or motor vs just sitting on the mooring. I think if you budget roughly equal amounts for diesel; rig and sail; and electrical, instruments, and controls; say about $25K each, you can end up with a passable boat that will operate for 40 years on the stuff you build into it.

 

Phil
Much of what you have just posted contradicts what I believe to be true. However I understand your point of view, so I will restate what I believe.
1. Masts, sails and rigging can cost a great deal of money. Anything mechanical can breakdown furthermore higher levels of technology cost more and can prove unreliable. Auto furling sail mechanisms are not cheap, they are unnecessary in my view.
2. I truly believe unstayed masts were cheaper alternative (even if limited by mast diameter).
3. Maintenance usually costs money.
I considered any boat going across large stretches of open water need a backup power source (sail), so I might as well be a good set of sails.

 

If you want an inexpensive unstayed mast, it will probably be solid. Being solid, it will have to be quite short, to keep its top hamper in hand.

Its shortness will likely dictate the kind of rig you will need. It will probably be a low aspect ratio one, with either a gaff or a yard at the top. It can be a short, squat Chinese lug, if that's what you want. You will need at least one winch to hoist this heavy sail.

The only way I know of avoiding boat maintenance is to not have a boat