Which sail rig for my Cat?

If you assume from the beginning that you will only sail downwind/reach and motor or motor sail upwind it makes a rig much easier.

My dad is putting a small junk rig on his motor sailor (mono-hull). No illusions about going upwind, but a cheap rig he can handle without leaving the deckhouse that will push the boat along nicely downwind in a breeze.

You could save a lot of money of you give up thoughts of of upwind efficiency. Won't need dagger boards either then.

 

You could have a longer boom and still have the main sheet led to the aft cabin bulkhead - just don't attach the sheet to the end of the boom. No traveler is needed. You can have the sheet led to a single point, and use a line to the gunwale as a vang/preventer. This will have much more leverage than a traditional vang. You do want to run the sheet so that it is easily released from the helm station, and that may be a bit tricky from the top of the cabin.

I'm not sure you need so much overlap with the jib. You could sheet it to a point just behind the cabin and have the winches mounted just inside the coaming. A Barber hauler led to the gunwale would adjust the sheeting angle for reaching and running. The Barber hauler wouldn't have to be rigged all the time, just when needed, so it isn't a tripping hazard when under power.

As for the boards, I think it makes sense to put them in cases or even blisters on the outside of the hulls. Sort of like a cross between a daggerboard and a leeboard. The structural side of the boat can be flat and the board can sit in a bulge of the contour outside the flat structural panel. That way the cases don't interfere with the cabin space or be an obstacle on deck. And if you run aground and jam the board backwards, it may split the case but it won't jeopardize the watertight integrity of the hull itself. The loads on a leeward board are such that it pushes against the hull at the bottom of the case and pulls away from the hull at the top, so it's fairly easy to run fibers from the deck around the top of the board trunk and back to the deck to take the loads in tension at the top. The bottom of the trunk is supported by the bottom of the boat, in compression.


The rudders can be in cassettes in the sugar scoops so they can kick up. Here's how Chris White designed it for my Hammerhead 34:



If it's not obvious, the turning blocks for the steering cables are located along the kick-up axis, so there's no change in tension when the rudder is kicked back. A line led from the end of the sugar scoop, up and over the cassette, and up to the deck holds the cassette in place. The drawback, especially for a power cat, is the fixed skeg above the movable rudder. This allows the rudder to still turn when kicked up and contributes stability while reducing the maneuverability.

But the really bad thing is the is rudder dangerously over-balanced when under power if the rudder has a swept leading edge and straight trailing edge - as mine does. This is because the prop blows on the top of the rudder, where there's considerable area ahead of the axis of rotation. However, if you made the leading edge vertical and swept the trailing edge, then the rudder would become more stable under power because the blown portion would have a greater proportion of its area behind the pivot axis. Arranging the same percentage of the chord ahead and behind the pivot axis all along the span would eliminate this change in balance between power and sail.

 

Good ideas tom, i like a well justified response...

Ok so what about the mainsail area, i went with a rather modest size, short boom etc... The idea was to keep the main small and run a larger genoa for most of the time, is this an efficient idea or is it better to run a larger main with smaller Jib - in typical reaching conditions?

Your boat is a similar size to my cat, have you any ideas on maximizing the efficiency of the rig without simply increasing the size of everything upto racing rig dimensions?

For the rudders, i was thinking of mounting them on the inside of the hull - in the tunnel via a bracket and case hinge. Lead the pivot axis tube up through the bridgedeck floor and drop a tiller head handle ontop so i can sail it from the aft cockpit. Slide the rudders out from the cases and stow when not sailing, hold them down via the rope like yours.

 

An idea came to me regarding the danggerboards also - perhaps I can mount them on the inboard side of the hulls, so the bottom of the case exits the bridgedeck chamfer panel and the top exits the deck beside the front corner of the cabin? This space is only dedicated to a cupboard at present and its longitudinal position is about right.
In addition, I could add a lifting surface to the bottom of the dagger to make L boards and compensate for the low forward bouyancy of the existing hull.

Besides the above reasoning, if the case is damaged by impact, its above the waterline making repairs easy and little risk of water entering the boat.
Thoughts?

 

I don't think L boards are a good idea for this kind of boat. For one thing, you'd have to lift the boat way up to insert the boards from the bottom. Much easier to have a straight board that you can take out the top. Especially when you catch some weed on it or damage it.

L boards are not a good substitute for forward buoyancy. They are only effective when going fast, but a dangerous time is when you're turning down at low speed.

This isn't a race boat. The solution to the rig overpowering the forward buoyancy is to size the rig to the buoyancy instead of the other way around.

 

sail rig

Using wing sail will push back the CE. A freestanding rig removes a lot of clutter and boom obstruction that could be a problem above coachhouse roof.
To compare efficiency of wing sail check out
http://www.afms.org.au/conference/18/285 - Blakeley.pdf
note the characteristics in the last 2 graphs
looking at Cl = 4 , 15% flap deflection.
wind tunnel results (2D only)
However a 2 element 3D wing sail might provide roughly 1/2 the sail area than the conventional main sail and jib .

also check
http://www.harborwingtech.com/technology_wingsail.htm
this wing sail arrangement uses vanes like the wind vanes on cruising yachts (some with double vane for stability). An interesting possibility (if the top half and bottom flap halves are independently controllable) is twist off for wing depowering.

- regarding windage at anchor - all boats have the problem to some extent with the possibility of anchor drag. With one wing sail, it might be possible to sail over the top of your anchor if hunting back and forth occurs, that might cause anchor dislodgement.

this can be avoided with twin wingfoils (side by side) - no need for vanes
a single foil with independent top/bottom flap and adequate twist off might also work.

 

I do not know why, but I keep thinking radio antenna when I look at those 'wings.'

And I am really concerned about a 'wing' I need a computer to control. Something just does not sound right.

But, I may be wrong.

Wayne

 

And I thought you were porting in WA?

And I thought you were porting in WA?

Tell everyone I said 'Hola, amigos.'

Wayne

 

It is in WA! The picture was taken when the boat was being packed up for shipment to WA. It was originally owned by the builder, Jim George of Lonestar Multihulls in Brownsville and kept at Port Isabel.

Not only is it home-ported in Seattle, now I even have moorage in Des Moines that is only 5 blocks from my house! Which would be really convenient if I were actually living in my house instead of San Francisco.

 

Jim George, I remember him, I think. I know Georges from Brownsville and Wolfe City.

You are more confused about accommodations than I.

 

OK, Back to the OP.

Why not fly a kite?

Seriously, a kite would give you more pull per square foot than a sail - typically flies in higher wind speeds. It would be much easier to mount, would be mountable anywhere - just about. I would not be dependent upon surface winds - winds usually are measured - don't kill me if I miss this, but every 5,000 feet?

Winds are faster off of the surface, so more power for the kite to catch. And they do change directions some, you can see that if you have ever flown a kite, wind is one way on the ground, but a few degrees different at altitude.

This would eliminate your down wind or up wind issues with your mast.

http://www.all-science-fair-projects.com/print_project_1159_21

http://www.all-science-fair-projects.com/print_project_1159_21

If only we could harness the jet stream ....

 

The confusion as to just where I live recently got worse, when I got married. My wife lives in Martinez, CA. So now I have two houses and an apartment that I can call "home". I'm not as bad as Yasser Arafat, who never slept two nights in a row in the same bed, but I rarely spend more than 5 nights in a row in the same city.

Home is where the boat is, right?

 

And that did not save Yasser Arafat. I think the only terrorist without the fearful necessity to move around was Adolf.

I am trying to remember if Stalin and Lenin were that way, and I think they were.

Are you trying to communicate some deap hidden meaning?



Yes, I gotta get a boat here. I am already dreading the flight back to the US ....

 

Kites are great, ive been kitesurfing for more than 10 years, windsurfing before that... the problem with high L/D kites is they need constant attention to keep them in the air and generating power. The only kites you can set and forget are like the outleader style kites, they have much lower L/D however not much different to a spinaker and can only be used on very downwind runs.

Now imagine actively flying a kite - like they do in the small kiteboats- ALL day everyday on a week long voyage... you have sunburnt eyes and a sore neck, nevermind the boredom... can you see the problem now?

Now the wingsails... what happens when you reach safe anchorage and the storm hits... wind is swirling around over the lee side of the island... how much windage are the twin wings making now? Will you be able to hold anchor? Are the wings strong enough to handle a gale? Can the boat capsize from the windage alone? It just doesnt seem like a safe option even tho I like the performance ideals of the system.

 

I can make a furling wing sail .... that is sooo easy. And I can furl faster than a regular sail.

The kite? Not that big of an issue if you buy one of the commercial rigs they are making. I agree it is not a perfect solution.

But, converting a motor boat into a motor sailer is not as easy as converting a motor sailer into a motor boat - IMHO.

So, we have to make compromises.