Changing the sailplan?

[John Stevens]

I'm building a Minuet 15. I'd like to add a bimini but with the close quarters I was thinking shortening the boom and adding a mizzen might make it easier to have a bimini.

Any ideas on how I would change the sq. footage of the sail plan? Would I just add the sq ft. off the mizzen to what I took away from the main?

Is there a formula to figure this out?

I'm in the process of building a scale down version to get the idea of building the boat.

TIA,

John

[Frank Hagan]

I'll bet it gets more complicated than that because of lateral balance (I'm sure that's not the term, but the boat is designed with x amount of sail in a sloop configuration, and changing it with a mizzen ... yawl? ... changes where the wind is pushing against the boat.)

I do know that if you convert from a bermudan sail to a gaff you can increase the sail size without a loss in stability due to the lower center of effort of the gaffer. I think in this case you're going to remove some of the lower part of the sail to raise the boom, so you're raising the center of effort of that sail, and then trying to balance that with the addition of sail from the mizzen.

I'm a big fan of going through all the calculations and then trying different configurations with something inexpensive like polytarp sails to confirm the calculations. The pros will disagree with me, but I think there's still more art than science involved in these things.

[PAR]

Actually, placing a different rig on a boat isn't as difficult a problem as most think. The big issue generally, is appendage placement, which usually can't be moved to suit a new CE easily. You can design a new yawl or ketch rig to fit on the Minuet hull form, but mast placement, sprit length, mainsail, jib and jigger size and relationships will be different then the original design. You may get away with cutting the boom and converting to a ketch with yawl proportions, but you'd need to get lucky.

Minuet's lead varies (centerboards always do) but generally starts at about 12% and decreases to around 4% with the board fully deployed. This provides some latitude in rig placement.

With some reasonably simple geometry skills and a scale drawing of the hull/rig profile you can make these alterations. You just need to balance the new rig over the same lead built into the underwater profile. The current CE is located approximately 6' 6" aft of the bow at the sheer. If the new rig is drawn to keep this location, your boat will balance well enough to trim up with rig tuning adjustments, which are normal for a new boat.

Multiple masts, on a craft this size, adds a great deal of complication to an other wise simple boat. The efficiency of the rig will decrease, with the sails divided into smaller sizes and a weight penalty will also cost performance some, but this boat was never a speed demon in the first place.

If you need help, drop me an email.

[JeffM]

Wouldn't a bimini on a boat that small create tremendous wind drag? I've given up on a bimini for my Core Sound 20, partly over worries about excessive windage, and also the difficulty I had trimming a sail (the mizzen) that I couldn't see.

[John Stevens]

Thanks for the comments. I'm a long way away from building right now. I'm just building a scaled down version first. Thanks for offer the email help PAR, I'll be contacting you in the future.

Jeff- I'm not sure that a bimini would be a problem with wind, it's relative in size to the boat which is the real problem. BTW, although I've been in Florida for a long time, I grew up in Whitman.

John

[PAR]

Here's an example of rig changes, on a boat I designed and built many years ago and is now being refitted. The deck, cabin and interior furnishings have been removed. All that remains in the hull is a forward bulkhead and the centerboard case.

http://www.messing-about.com/photopost/data/500/619B_B-1-med.jpg

The first image is the stock rig, as I designed it for the cabin version. In removing the cabin, I also lowered the sheer 4", because I didn't need the freeboard for headroom below any more. This boat was under canvassed when completed and needed to sail in 15 knots plus to plane off. I was never very satisfied with her performance, I built her heavier then she needed and her abilities suffered because of it. Even in very strong gusts over 35 knots she never got to 45 degrees of heel, so I decided on an increase in sail area and a ketch rig.

Because I removed the super structure and interior (about 800 pounds) she would now have a lower CG and I could afford additional area and more ballast. She originally carried 600 pounds of lead in the stub keel and 150 pounds in the board's lower leading edge. As previously built she displaced 2,200 pounds on a 19' LWL, and a 7' 4" max LWL beam that has quite firm bilges and a reasonably flat run to plane on. I was relatively young 30 years ago when I did her and now look at the hull with disgust, for all the things I did wrong and didn't completely understand, which really stand out to my eye now. I don't know what I was thinking when I drew up the entry, but she is what she is.

http://www.messing-about.com/photopost/data/500/619B_B-2-med.jpg

The second image is keeping the CE located in the same place over the CLP (original sail plan is in red). This forces me to move the main mast well forward, install a sprit and the steering area of the cockpit has to be divided with a small section of decking to provide lateral support for the mizzen, which leaves little room to move around and I'd have to climb over this deck to go forward. The advantages are the hull doesn't need modification and the well balanced CE location is maintained. The draw backs are the cramped steering area of the cockpit, the deck section dividing the cockpit, the sprit causing trailering issues and the main mast is far enough forward to place weight where I really don't want any.

http://www.messing-about.com/photopost/data/500/619B_B-3-med.jpg

The third drawing shows a slightly smaller sail plan, but the CE and the CLP have been moved aft. This brings the rig inboard (no sprit) but requires an extension to the keel stub (note dotted line of the original) to increase lateral plane aft to balance the aft movement of the CE. This also means the centerboard can't be fully deployed as it was when she was a sloop. I suspect I'll have to move the board or at least lengthen it a bit to get the balance right, but this is the rig I've selected to replace the sloop. I'm hoping my newly designed rudder will help drag the CLP aft, possibly negating the need for moving the centerboard.

The point of this post was to show, you can install a new rig, but there are issues that need solving. Most can be fixed, but you'll have to work it out so that your chance of success will likely be positive, before you cut up mahogany planks. Here are two ketch rigs on a boat designed as a sloop. One keeps the CE/CLP relationship the same and has application specific issues to contend with. The other moves things around enough to fix some issues and generates some of it's own.

[John Stevens]

PAR,

Thanks for the detailed drawings. I understand your explanation but not how you came to it. I guess that's why you design boats and I just build and sail them.

A few more questions for you:

You said the Minuet was not a fast boat. Would a larger roach on the main make it any faster or just unstable? Is it the hull shape that slows it down?

As you can tell I know little about design but really enjoy learning about what makes sailboats do what they do.

Here's a shot of the model I'm building of the Minuet at 15 % the size of the original.

TIA,

John Stevens

[PAR]

I made major changes to this old design of mine. These were to address some issues I had with it and to accommodate the type of sailing I general did with the boat. The old boat had a cabin and "V" berth. The cabin was very rarely used and the "V" berth a fancy sail holder upper. The deck structure and cabin were not in keeping with my daysail uses, so I took a reciprocating saw to them. I wanted an open boat that could carry a number of people. The boat was also heavy and tossing the deck and cabin would help this issue. She was also under powered and overly stiff (shape of the bilge) so she needed more sail area.

I could have stuck a taller sloop rig on her and had a fast weatherly boat, but that's not what I do with the boat. The ketch rig fits my lazy sailing style and looks a bunch better too. This is why I made the changes.

The point of the post was to show you can change the rig, but there are steps and compromises that will be involved, after the calculations are made.

Minute's hull form limits her abilities. A big roached main will make her sail on her ear, but you'll not go much faster (speed increases would be measured in 1/10's of a knot and the leeward rail would be in the water). Specifically she has too much beam and rocker in her bottom. The boat is an overnight camper, so the additional beam and depth is provided for accommodations in the cabin. The extra drag this creates can't be over come easily. She's a displacement boat, that could surf down wave faces, if her reasonably flat aft sections can be held down, square with the water, by hiking out. If provided enough power (20 HP outboard), she could climb over her bow wave, but the bow will be point very high and you wouldn't be able to see where you're going too well. She's designed as a safe protected water cruiser, that will not surprise you with bad manners. Minute is a very popular boat and well liked by thousands of builders.

The Glen-L 15 on the other hand, will get up and scoot, but you loose the luxury of a cabin (also it's related weight and windage) and the cute looks of the Minute. It's also a rougher ride that will be more wet then the Minute. The Minute is a Volvo wagon, the Glen-L 15 is a Honda Civic with a V6.

[John Stevens]

Thanks for the reply PAR. Looks like the effort to make the sail changes might be more work than the bimini will be worth.

John