Pros and cons of "max loading" a 10-ton CCA cruising sailboat

Discussion in 'Stability' started by souljour2000, Apr 29, 2015.

  1. souljour2000
    Joined: Aug 2009
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    Location: SW Florida

    souljour2000 Senior Member

    I have never gotten hold of the original brochures for my boat but want to add greater tankage, and for a long cruise would add great quantities of food and gear.etc...I want to learn about how much weight she could safely handle (if it were placed low and in the right places proportionately) and how she would necessarily behave if her lines were "buried to the bootstripe". My boat is a 1966 Columbia 40 CCA design with long overhangs and only 10' 8" beam. e.g.: Would max loading to the bootstripe add waterline and hence "speed" that might offset the extra weight(drag) or would they cancel each other?,etc...

    Hull Type: Keel/Cbrd. Rig Type: Masthead Sloop
    LOA: 39.50' / 12.04m LWL: 27.75' / 8.46m
    Beam: 10.50' / 3.20m Listed SA: 674 ft2 / 62.61 m2
    Draft (max.) 9.00' / 2.74m Draft (min.) 4.50' / 1.37m
    Disp. 18900 lbs./ 8573 kgs. Ballast: 8400 lbs. / 3810 kgs.
    SA/Disp.: 15.26 Bal./Disp.: 44.44% Disp./Len.: 394.84
    SA(Fore.): 326.25 ft2 / 30.31 m2 SA(Main): 347.80 ft2 / 32.31 m2
    Total(calc.)SA: 674.05 ft2 / 62.62 m2 DL ratio: 394.84
    SA/Disp: 15.26 Est. Forestay Len.: 46.01' / 14.02
     

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  2. PAR
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    PAR Yacht Designer/Builder

    From a technical sense, yes, you'll gain some LWL with a heavy load, but you'll also gain wetted surface and burden, so likely it's a trade off. For example, lets say you max the LWL out to 28.5', once the boot is buried. This is a 3% improvement in the length of the LWL, great right? Well This means you'll make 7.2 knots at hull speed on this increased LWL. But wait, the hull speed on the 27' 9" LWL is 7.1 knots. Damn a 1/10th of a knot, plus the increase in wetted surface and mass. Yeah, be grateful if you can still manage the 27' 9" LWL hull speed full up. My experience with these venerable old C-40's is, you can't make it go any faster no matter what you install or hang from it's sticks, short of a blown big block Chevy.
     
  3. souljour2000
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    souljour2000 Senior Member

    That's about what I expected to hear PAR...she'll hopefully be a slow but steady packhorse...though not a mule hopefully. I'm also likely to be stressing an old hull by heavyloading as well; though she has always seemed more tired due to age and Florida weather than from ever being pushed too hard in her past...but I plan to add some stringers to some of her longer buttocks panels when I'm done with the less than glorious re-coring/strengthening of the deck...
     
  4. souljour2000
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    souljour2000 Senior Member

    I would expect to be able to add quite a bit of weight ...i mean...my 120 lb dyer dhow-type dinghy has had more than 450 lbs in it regularly..(me plus gf) without any problems...and close to 600 lbs once(we won't re-visit that episode here..)....thats quite alot more weight than its disp. of 120 lbs or so. I know there's many variables and not to oversimplify but wouldn't that mean an 18,000 lb. disp. CCA cruiser might be able to easily carry another 3-4 tons without really stressing the stability envelope ... or even fairly easily... and might 5 tons be in the conversation on the outside...I mean..one could conceivably load a hell of alot of stuff...I suppose the trick has always been in getting it low enough though...and along the centerline.
     
  5. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Just be aware that adding weight increases stability and thus loads on the rig go up.
     
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  6. WindRaf
    Joined: Oct 2014
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    Location: Italy

    WindRaf Senior Member

    For sure will change the ratio sail area - displacement, and considering that each boat is designed to give the best in its water lines ... it is expected that you will have a slower boat although increases waterline length.
    Then you also have to be careful in weight distribution because too much stability can become very uncomfortable, and even dangerous, not only for the hull structures, but also for the seaworthy
     
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  7. souljour2000
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    souljour2000 Senior Member

    Thanks for your replies ...I guess the loads on the rudder/steering mechanism would also increase as the load increased and that's never good. I would certainly want to stay a couple inches shy of the bootstripe in order to leave some reserve bouyancy/performance and not stress the rig/hull/rudder more than necessary...
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I wouldn't be that concerned about the rig so much as the armature in the hull supporting the chain plates and step. These are known to develop "issues" with age. If the rig is good shape and the armature isn't swollen from rust, you'll be fine.
     
  9. souljour2000
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    souljour2000 Senior Member

    Ah yes..the vaunted old ss endo-skeleton ....Charlie Morgan's secret weapon...yeah...truth is..I just dont know if its completely shot...other than the last two feet in the bow section where it connects to the stemhead...that was rusted away into thick chunks...too much salt i guess over the years..,the other areas (show no outward signs like rust stains/exfoliation through the glass). I did replace the 1/2" stemcap bolts thru the deck part of the cap and two on the front of the cap and with large tripled up fender washers....the ss stem cap itself was in excellent shape...
     
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Usually the armature is okay, unless you've had major delaminating around it, or have permitted corrosion to go unchecked for many years, so that is mitigates along it's length. I've seen them as you describe, with bad ends or exposed portions, but also with completely rusted out sections, buried in the laminate. The rusted out ones usually had some damage someplace, that shook the armature loose and let in moisture. Stemhead and chain plate locations are common moisture entry areas to explore further.
     
  11. souljour2000
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    souljour2000 Senior Member

    Unfortunately some of those thick chunky pieces of that last 2-3 feet of rusted skeleton that attcahed to the stemcap...well they slid down into the remaining tube as it crumbled over the years and they are so heavy they are gonna be hard to vaccuum out of there where the pipe makes the turn to the bilge...probably a bunch sitting there andif i dont get those chunks they will rust through the pipe in that area.Maybe I will need a few powerful magnets on a strong wire...should be a fun project...:rolleyes:
     

  12. Chuck Losness
    Joined: Apr 2008
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    Chuck Losness Senior Member

    Where are you planning to cruise to? How many people will be on board? Most parts of the world close to the USA have plenty of places to re-provision and sometimes at cheaper prices. Everybody has to eat and have water to drink. Water is also readily available. If water is a big concern then get a watermaker. Way easier than adding tankage. If you think you need more fuel, carry jerry jugs on deck to start with. Most newbie cruisers add all kinds of unnecessary gear that they never use and end up selling along the way. Stick to the basics (adequate ground tackle, sails and rigging and reliable diesel, etc.) until you have been out for awhile and learn what you really need verses what the dock sitters tell you you have to have. You might be surprised at just how little you need to go cruising. While I was out cruising I continually ran into people with basic, simple boats. They were having just as much fun as the cruisers with every imaginable gadget and didn't have all of the maintenance issues.
    Determining how much weight it will take to sink your boat to the top of the boot stripe is easy. Just spread a bunch of trash cans evenly around the deck of your boat, fill them with water and see how many gallons of water it takes to sink your boat to the top of the boot stripe.
    Your boat will be slower with cruising gear added. The sail area to displacement ratio and the sail area to wetted surface will both go down. Don't make the mistake of thinking that you want less sail area. This will only compound the problem.
    Keep it simple and go cruising now rather than maybe never.
    Good luck.
     
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