Adding sail & maintaining the CE balance!

Discussion in 'Boat Design' started by ecflyer, Sep 8, 2009.

  1. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    Adding sail and maintaining the CE balance

    --------------------------------------------------------------------------------

    I have a 46'-9" ketch sailboat that I would like to improve the sail area to increase performance in light airs. If I were to add 2.0' to the foot of the head sail via bowsprit and 4.0' to the foot of the mizzen, would I be maintaining the balance of the CE to center of lateral plane. I am unable to change the main. Additionally, would changing from a 130% genoa to a 150% change the helm balance, because I notice architects only use 100% of the foretriangle in calculating the CE. The current sail area is quite low at about 800 to 850 sqr ft. This is a new build so costs is not a factor. Thanks for your help.
     
  2. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Definitely think about a big genny if light air performance is what you are looking for. It's likely you could buy a used one easily for half what a new one costs. The bigger genny will only be a problem if you carry it in brisker winds, but in light air, you will see a nice speed increase.
     
  3. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    If it's a new build then have the designer work up a bigger sail plan. We use 100% of the fore triangle because if we counted it all, there would be a standard. In other words, some would use a 150, other a 170 others a 130, so comparatively the figures wouldn't be useful, which is the only point. What is your SA/D?

    Adding area to a new rig is a fairly easy thing on most ketches. You may also consider using typical light air sails, such as big headsails and mizzen mules (stay sails).
     
  4. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    PAR
    The designer says he has to work up a whole new sail plan and wants to charge $4000.00 . I think this is unneccessary and I don't have those monies in my budget. Can you tell me more about the mule. How do I rig it? Do I install a removable headstay off the mizzen that would attach to the base of the mainsail. Do I add a track aft (but where). I would prefur a mule as I understand that they are much more powerful & efficient than main sails; however, would this be a pain in the butt to use?

    Have a Great Day!
    Earl
     
  5. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Wow. $4000.00 for a sailplan! Ouch!
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A mule is a staysail attached at mizzen top. It can be set flying in small craft, but your boat will want a stay. Of course the stay has to be removable, so you can jibe the boat, so it's a sail you use selectively. It's quite powerful as you can imagine, but does have some inconvenience.

    What is your current SA/D, plus D/L, general hull from type, etc.?

    Your designer may not want to do the job, but $4,000 isn't unreasonable for a new sail plan, though this wouldn't be a new one, just an update to his files, so like I said, he may not want to do it. You can get a modified sail plan a good bit cheaper then that, assuming nothing major has to move (chain plates, mast steps, etc.).
     
  7. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    PAR
    SA/D = 14.34, D/L = 235, general hul type is rounded, full skeg hung rudder and keel is approx 4' deep x 13' long air foil shaped. Capsize ratio = 1.82
    Chain plates cannot be moved, nor can the 2 mast locations move, but designer still wants $4000 to increase sail performance. I have an 88 hp Yanmar diesel installed and hull speed is calc'd to be 8.39 knots. I believe this would be a great boat if sail performance could be significantly improved w/o increasing mast height so stability is retained
    Have a Great Day!
    Earl.
     
  8. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    14.34 is quite low and with her D/L, she'll need a fair bit of wind just to motivate her.

    It sounds like the designer has reached a point of no return and I'm not sure I blame him. Look at it this way, you don't want to raise the masts, you don't want the masts or chain plates to move, you don't want the stability to decrease and you'd like to retain the capsize screen. To me, this sounds like his hands are tied so badly he doesn't want to be bothered.

    You can raise the hoist of the masts without terribly or adversely affecting the yachts stability. You can still have a capsize screen below 2, which will prevent all but the Jolly Green Giant grabbing a hold and flipping you. It's also possible you could leave the masts where they are and maybe most if not all of the chain plates. All the while increasing sail area and performance potential. Generally, the tighter the hand cuffs, the more costly the deed.
     
  9. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    PAR
    I'll give you a little background. I am building my own sailboat because I love to build and create and my goal is to end up with the boat looking factory built (not homemade) with better than factory features. I have never been on a sailboat so all my limited knowledge is acquired from reading books. I selected a stock design before I had read any books so I based my plan selection decision on all the wrong criteria. However, I believe I lucked out as now that my knowledge has greatly improved, I would still select the same plans. I am building a cold molded wood boat w/pilothouse and the ketch version because, I believe two masts makes the boat look like a real sailboat. I have allready built the boat (70% complete), so not willing the make structural changes. The masts are deck stepped and I will design a hinge type mount so they can be raised and lowered maybe w/o crane. I would like to kick the sail performance up a notch, so as not to end up with a dog. Since I am not a sailor, maybe you could answer a few of my questions. ON A KETCH RIG; when figuring the CE do I use the entire Genoa sail insted of the 100% foretriangle? Do I figure the CE for all the different sail combinations and aim for the lead to be 20%-25% ahead of the CLR. Is it reasonable to slant the results toward the most often used sail combination. Remember, the plans already have the ketch rig balanced, I just have to make sure I don't screw it up with any changes I make. Thanks for your help!
    Have a Great Day!
    Earl
     
  10. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    PAR
    An example of some changes under consideration: Plans show a 130% genoa. I don't want to jag around and hassel with a spinaker, so I am considering going to a 150% genoa. If the larger genoa moves the CE aft, then maybe adding a 2' bowsprit would counter this and maintain sail balance. An alternate might be to add a larger foot to the mizzen sail to counter balance the effect of a bowsprit. I certainly don't know at this point but I will definitly find my answers out before making any changes.
    Earl
     
  11. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The CE is uses the area of the fore triangle, not the actual area of the headsails. The areas for the main and mizzen will also not include roach, unless it's quite significant, which it's not on your design. Generally, the CE is calculated for the working sails, not any special use sails, such as mules, staysails, spinnakers, big genoas, etc.

    Typically, the mizzen adds or subtracts a pretty small percentage of area to the sail plan, in relation to where the CE lands. Adding a little to the foot of the mizzen will not move the CE very far. The same affect will be noticed on the headsails, if the fore triangle foot is lengthened, though it will have a more significant affect on the CE.

    At this point it would be helpful to know which stock design you have, to see where the limitations are.

    Larger headsails are a "given" in lighter air, but will have to be changed out as wind strength increases. This is normal if you are carrying specialized sails. Most of these types of sails will have a limited range of usefulness before they have to come down.

    You concept of lead for a ketch is way off base. A typical lead for a ketch of normal proportions would be 12% to 13% of the LWL forward of the CLP. At 20% to 25%, I don't think the boat would be balanceable.

    Considering your novice sailing abilities, you should strongly consider leaving the sail plan adjustments to a skilled designer. I'll take a guess that this is a Buehler design?
     
  12. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    PAR
    Thanks for answering all my questions--that was just the info I needed to calc the CE. I did a full scale drawing of my boat and sail plan and found that the designer has used a 14% lead over CLP. In doing the drawing, I just noticed(despite my best intentions) that I made an error in the placement of my mizzen mast. I lenghten the boat by 7% and that must have contributed to my error. This error nix's any possibility of increasing the sail sqr footage. Oh well, I guess I am building a motor sailor. Sure glad I installed that 88hp Yanmar diesel with plenty of extra fuel tanks. Also have a 22" diameter full feathering prop that will now really be needed. Thanks again for your help!
    I do have one other question. It seems counter intuitive to only use the 100% foretriangle in figuring the CE because when you add all these other speciality sails--doesn't that throw the helm balance out of wack?
    Have a Great Day!
    Earl
     
  13. Gilbert
    Joined: Aug 2004
    Posts: 525
    Likes: 5, Points: 28, Legacy Rep: 28
    Location: Cathlamet, WA

    Gilbert Senior Member

    Unless the waters where I would be sailing had almost exclusively light winds I would be quite content with 14.45 sail area to displacement ratio. With that ratio and properly made and set sails you will do just fine. I would suggest a genaker though for light breezes; after using them, I have become a true believer.
     
  14. TeddyDiver
    Joined: Dec 2007
    Posts: 2,533
    Likes: 109, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    No. Helm balance is affectde by the heel also and in light wind with all sails you still staying quite "upright". When wind gets stronger, the heel becomes an issue, and the helm balance changes you also take the "specialty" canvas down, and in the next level reef the working sails, and then reef again and then change storm sails..
     

  15. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Gilbert, I'm not sure what you're used to, but most sailors sail in light winds. When small craft advisories are issued, most have long run for shore or tucked in a reef or two. An SA/D this low on a boat with a fairly high D/L means you're not going anywhere in light air, of which there is no excuse, from a design stand point. She's running on three legs before they open the gate. The only exception to this would be a custom design specifically intended for trade wind work, where the low SA/D will permit full working sails and less chafe.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.