Where to "Stick" it???

[lewisboats]

Pros and Cons Please. How would a boat handle that uses an oversized Jib or Genny on a mast that is at the approximate midship location with a Yawl style mizzen of about 1/3 the size of the J or G...and no "main" sail in between. The mizzen would sheet to a boomkin and back. This is something I have been knocking around as a small (very) shallow water cruiser. The reason I want the mast aft is so there is an uninterupted area for a decent double berth, with mast just aft of the bunk, and enough room for a bit of a galley, a head and maybe an easy chair and stove aft of the mast. Oh, and the LR would be Bilgeboards, Bilgekeels or (Ahem) Leeboards. Pardon the drawings as they were quickly done up in Freeship and Paint.

Steve

(I hope I got all the sail terminology right )

[lewisboats]

Wow...sorry about the size. They aren't that big on my 'Puter...

Steve

[Barry Pyeatt]

Seems like it is going to have an incredible amount of Lee helm with virtually nothing to balance the helm out. This is always an issue with working on sail plans. I'm no expert on this so perhaps some others with more design experience can add something to this.

One alternatative solution to where to put the mast and develop a more balanced sail plan is by placing it on a bridge which leaves the area beneath it open. Requires some real beefy construction to carry the stresses and tranfer them around and then down to the keel, but I've seen it done.

[Ken_Potts]

Here's a guy who seems to like staysails...

http://www.runningtideyachts.com/sail/

[Barry Pyeatt]

Ken,

That is the article I was looking for to post a link to. This is a managable solution with COE working as a driving force with the mast aft. And becoming a Ketch rig without a main. The challenge with working with just staysails forward is one of getting a manageable balance to the plan. How well it would work on this type of hull design is another question that would take some study.

[PAR]

A common misconception is that headsails are more efficient, hence an all headsail rig would be more efficient, though I understand this isn't your reasoning behind this rig. The jib is only efficient when close hauled and in concert with a mainsail. Once the boat is freed up a touch, the main becomes the more efficient sail.

Your rig can work, though you might as well take it to the next logical step, which is a aft mast design, which carries the stick well aft and is all headsail. This will eliminate the additional complication of the mizzen and it's poor sheeting arrangements with it that far aft. Appendage design and placement is the key here. Estimating the amount of lead, how much the camber will move, CE movement, etc. will be the success of the design. Frankly, your mainmast placement is about where a cutter's would be (approximately 40-45% of the LWL to my eye). The cutter rig on small craft is a waste of sail material, dividing up the sail plan unnecessarily. Leave the main stick where it is and hoist a conventional mainsail on it's after side and toss the mizzen over the side. You'd have a big jib (no staysail) and a main to balance it conventionally, less sticks to erect, strings to pull and sails to hoist or douse.

Aft mast designs, like everything else in yacht design, have their own set of issues to contend with. Since few have been built, these will be a trial and error experiments, which is a costly way to design things.

[Ken_Potts]

I think the staysail-only idea is really cool (I'm also quite enamored of kites). It's one of those ideas that seems to have a lot of potential but few people willing to jump in and experiment. I look forward to reading more input from experienced folks or those people willing to just jump in and figure it out.

I also look forward to having a spare hull to experiment with...

Keep us in the loop, Steve.

[Barry Pyeatt]

I forwarded the drawings and the original entry to my Marine Architect buddy for an opinion. His initial reply to me was, if he wants to place the mast in that location, add the main and consider a Gaff main which will keep the COE lower and more in keeping with a shallow draft design. Nothing wrong with the larger headsail concept but it needs to be balanced and the Yawl rig without a main and the mast in this location will most likely make this unworkable. He also said that if you don't want to use a main sail, for what ever reason, you'd most likely need to place the mast a lot further aft and a lot larger headsail that will bring the COE back to where it can balance out the entire rig. Some of these will work on some points of the wind but not on all and can be out and out dangerous under a lot of relatively normal conditions. He suggested that it will probably take an inordinate amount of trial and error building and re-rigging and trying different combinations to find something that will work well. But that it would be fun to try with an aft mast location and working with a huge headsail and yawl type of rig. He said it would be an interesting design challenge with lots of computer time, trial and error and creativity before ever committing to wood, or glass or whatever material.

[JeffM]

Fun stuff to think about! I gather the reason the main is so much more effective off the wind is that the boom holds it out, whereas a staysl would have to be poled, or something. Regarding LR, if you have to move this forward to balance out the rig then leeboards are out: they need to be about parallel to the hull sides, which limits both hull shape and leeboard placement.

[Ken_Potts]

You should be able to move leeboards about a bit - Just put wedge shaped boards on the hull to align the leeboards with the centerline of the boat.

[Barry Pyeatt]

Whisker poles! They hold the clew of the jib out from the sides to catch more of the wind going downwind. WE use a short one on the lapper on the Weekender sailing in Puget Sound. Very effective in light to moderate air. Not so good for shifting wind directions however.

[PAR]

The aft mast rig has been tried and has difficulties. The prime issue is the ineffective jib, once the sheet is eased. As a yawl, the huge separation between the two sails, prevents the jib from helping the mizzen, decreasing both sail's effective efficiency. Hoyt even raced one, to piss off the rating rule writers and get some changes made, which was a very effective use of the rig. His version had a ribbon of a mainsail (rule requirements), with the mast stepped well aft (much farther then shown here) and a huge jib, near the full length of the boat. It drove the boat well, but had control problems in increasing wind strengths (imagine that) and sheeting angles became the big game in town on that boat. This jib (mainsail?) had quadruple sheets, by the way and three tracks per side to handle it.

[lewisboats]

Well, I do like the discussion on the Mast aft topic but I think the general consensus is that the sketched set up would be much better with a main and Jib/Genoa. Would it be worth keeping the yawl config or just using up the extra space with more main sail. Perhaps a short Gaff rig?

Steve

[Barry Pyeatt]

It would help quite a bit to keep the COE low in a shallow draft hull like this. There are other options but a Gaff Rig is one possibility that may work. Lot depends up a many other design factors too.

This thread should probably be in the Design area rather than here.

[PAR]

You boat doesn't need the divided rig. The sail plan is of sufficient size that it can be handled, easily as a sloop, gaff, Bermudian or other wise. Divided rigs have some advantages, but can't get too close to the wind. The yawl is the closest winded of the divided rigs, but sheeting angles on these are very limited. On the plus side, you can fly a mizzen mule, which can liven up off wind performance.

Your beam/length ratio appears fat enough to carry a lofty rig, but a lower aspect ratio could help keep her flat footed without gymnastics. The windage of the raised foredeck will limit your windward ability to some extent, but, she looks to be a cruiser not a planning screamer.

Ultimately, you'll have to feel comfortable with the rig, usually by setting performance goals for the vessel, which some rigs fit better then others. Design a set of appendages around that rig, to maximize it's utility and you're ready to cut some material.

[PAR]

If you're interested in a spirited, though pretty thick discussion about the aft mast rig, with many links to other locations for even more information try this.

http://www.boatdesign.net/forums/showthread.php?t=623

Tom and Brian get into it reasonably well and it runs down the details with some clarity and vision.

[lewisboats]

Thanks for all the info... I think I'd go with a short gaffed, slightly higher aspect rig, with a single foresail...a gaff sloop rig if you will. I was just supposin' on the mast aft, looking for some more experienced opinions. I'd probably lose the bow sprit, or have a really stubby one of 8-10". If I could balance the rig to get the CE just right to have pivoting leeboard or bilge boards I think this would be a nice little beachable cruiser for 2 for a week or so. It woud be lightweight and trailerable at probably less than 600 lbs on the trailer (minus supplies of course).

Steve

[JeffM]

Steve, what are the dimensions of your hull? Your sketch made me curious, but we were all preoccupied with the rig. Now I'm wondering about her length, beam and draft, and about the size of the cockpit and that funny-looking cabin! I'm guessing this boat is on the small side, since my open-cockpit 20 footer comes in at about 600lb.

[lewisboats]

Well, here are all the hydrostatic goodies from Freeship

Design length : 17.135 [ft]

Length over all : 17.135 [ft]

Design beam : 6.943 [ft]

Beam over all : 6.937 [ft]

Design draft : 1.000 [ft]

Midship location : 8.568 [ft]

Water density : 63.989 [lbs/ft3]

Appendage coefficient : 1.0000

Volume properties:

Displaced volume : 39.580 [ft3]

Displacement : 1.131 [tons]

Total length of submerged body : 16.069 [ft]

Total beam of submerged body : 6.155 [ft]

Block coefficient : 0.4002

Prismatic coefficient : 0.6152

Vert. prismatic coefficient : 0.5327

Wetted surface area : 81.576 [ft2]

Longitudinal center of buoyancy : 8.039 [ft]

Longitudinal center of buoyancy : -3.292 [%]

Vertical center of buoyancy : 0.674 [ft]

Midship properties:

Midship section area : 4.004 [ft2]

Midship coefficient : 0.6506

Waterplane properties:

Length on waterline : 16.069 [ft]

Beam on waterline : 6.155 [ft]

Waterplane area : 74.302 [ft2]

Waterplane coefficient : 0.7513

Waterplane center of floatation : 7.442 [ft]

Entrance angle : 36.563 [degr.]

Transverse moment of inertia : 174.35 [ft4]

Longitudinal moment of inertia : 1112.8 [ft4]

Initial stability:

Transverse metacentric height : 5.079 [ft]

Longitudinal metacentric height : 28.790 [ft]

Lateral plane:

Lateral area : 12.674 [ft2]

Longitudinal center of effort : 8.476 [ft]

Vertical center of effort : 0.566 [ft]

The cockpit is about 5 ft long by up to 6 ft wide.

The displacement is a bit much at 1 ft of draft, so it would probably run around 8" draft with no appendages, which translates into a half ton or about 1100 lbs. If I aim for a hull wt of about 500 lbs, and look for 2 180 pounders that leaves 240 lbs of "stuff" but you wouldn't even sink an inch by adding an extra 100 lbs. Actually it would take 310 lbs to sink an inch, so this probably has more wt capacity than space to put it unless it is very dense.

Steve