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Thread: 15 foot Beam, on a 40 foot catamaran

  1. #21

    Default Re: 15 foot Beam, on a 40 foot catamaran

    Hey! Thanks!
    ...now maybe I am a moron, but I did read through your entire website and did understand: Zip! Zilch! Nada! Zero!

    I (seriously) have the deepest respect for people like you who quite obviously KNOW what they are talking about - but as it so frequently happens in situations like this, the level you are communicating on, and the level I am just about able to follow are WAYS apart! :-)

    Also it would be interesting to learn why those unusual rigs - which according to your site offer a lot of advantages over a conventional rig, dont find the acceptance on the market they seem to deserve?

    I also looked at that one website with the many pictures and found the 8 reefing lines led into the cockpit, per bow, VERY confusing, even so it said: "It's simple!"
    Especially those wing/-- rigs would be nice to see in action aka on a real boat, pref. out at sea in real conditions. Hard to believe that they would offer less resistance than a conv. marconi?

    ....and, of course, I still am searching for an answer if that 42' x 17.2' cat of mine would have to be considered "too narrow" to be safe?

  2. #22
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    Amibon, I don't have the numbers for your Solaris 42 either, but yes I am confident that it is 'safe', although the beam is only slightly better than 40% of the LOA (I calculate 41% using the advertised beam of 17'3"), rather than the 50% or greater that is now in vogue. With respect to capsize resistance, beam is important. However, as you have already noted, so are a number of other factors including:

    CG - the center of gravity of your boat is much lower than what is currently in vogue as a result of a lower rig and a galley down, but principally due to lower bridgedeck clearance;
    CE of the sailplan - again, as you point out, the CE is substantially lower, being spread more for and aft. Further, the absence of a flat top main reduces it even more, both with full sail up and when reefed;
    Displacement - increased displacement increases resistance to capsize and your 42 has substantial displacement for its size (she was heavily constructed);
    Freeboard - lower freeboard results in a smaller side profile and hence a smaller area upon which wind/waves can generate forces (not to mention, the design, while out of date, would tend to allow wind to slip over the boat more readily than the current slab-sided designs).

    Of boats that are currently in production, consider the still popular Gemini, which has a BOA/LOA ratio comparable to your boat, but has in relative terms, lower displacement, a higher CG and higher CE for the sailplan. I have never heard of one capsizing and, although it would not be my preference due to its size and light construction, a number are now being used for offshore sailing including at least one circumnavigation. Your boat should have much greater resistance to capsize than the Gemini.

    I should also point out that there are a number of features that will make your boat very resistant to pitchpoling - something many believe is an even greater risk when sailing offshore in a catamaran:
    1. the bows are very full and bouyant.
    2. the bows have knuckles, which not only further increase bouyancy when depressed to that point, but provide additional hydrodynamic resistance to being further depressed.
    3. all else being equal on a catamaran, the smaller the ratio of BOA/LOA the lesser the resistance to capsize (side to side stability), but the greater the resistance to pitchpoling (for/aft stability).

    Don't worry mate - she is safe and the track record to which you allude confirms that. Of greater concern, IMO, is pounding due to the low bridgedeck clearance and yes, there will be times when you will want to bear off to minimize the impact. The good news is that, once again, your boat was very solidly constructed and will not suffer any ill-effects structurally from what pounding does occur. Your nerves, on the other hand......

    Cheers!

    Brad
    Last edited by Southern Star; 27th October 2010 at 06:44 PM. Reason: sp

  3. #23
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    While we are on the topic of beam versus capsize resistance in general, I have an idea that I would appreciate some imput/debate on. It strikes me that while increased beam increases resistance to lifting a hull, once the windward hull is lifted it might actually increase the risk of the boat actually capsizing.

    Consider the lever principle. Once the windward hull is lifted, the beam would operate as a lever, with the leeward hull being the fulcrum. The longer the lever, the less force required to lift a given weight. (Admittedly, as regards the force of the wind on the sails, the length of the lever would be 1/2 BWL as the mast is stepped at mid-beam; nevertheless, the greater the BOA the greater the length of the lever).

    Furthermore, once the hull is lifted, the wind will not only continue to provide lateral force on the sails, but also lateral force from underneath the boat; the greater the area of the bridgedeck, the greater the forces that will be generated. Furthermore, the force of the wind on the now rasied windward hull will also operate in accordance with the lever principle - i.e., the further it is from the fulcrum, the less force that will be required on it to raise a given weight.

    Anyway, food for thought. I suspect that while varous formulas are helpful in determining base parameters with respect to capsize resistance, there are various other factors that come into play. Another is obviously the lateral resistance of the hulls. One suspects that a rounded bottom with minimal or no keels, would tend to be pushed sideways and hence, not operate terribly well as a fulcrum. I know, such a design would be useless when sailing to windward - but we are speaking here only about capsize resistance. This may, however, be another way in which a boat such as the Solaris 42, while not very effective to windward, is nevertheless more effective at resisting capsize.

    Brad
    Last edited by Southern Star; 27th October 2010 at 02:18 PM. Reason: sp/2 signatures

  4. #24
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    Quote Originally Posted by Southern Star View Post
    Consider the lever principle. Once the windward hull is lifted, the beam would operate as a lever, with the leeward hull being the fulcrum. The longer the lever, the less force required to lift a given weight. (Admittedly, as regards the force of the wind on the sails, the length of the lever would be 1/2 BWL as the mast is stepped at mid-beam; nevertheless, the greater the BOA the greater the length of the lever).
    Brad,

    True, the lever arm is longer on a wider boat but the fulcrum point is moved further from the center of force as well which would increase the force needed to lift the hull further. Did I say that right?

    I agree with your point about wider boats having greater underdeck windage which may contribute to capsie. This is why Jim Brown preferred open wings to closed on his Searunner designs. I wonder if the wind under the bridgedeck contributed to Anna's capsize? The crew said at one point the boat seemed to hang at about 45 degrees and they felt it was going to come back down, but then it continued over.

    Mike

  5. #25
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    Good points Mike. In terms of the lever with respect to the force on the sails, I suspect that you are correct that while the lever arm is longer, the 'weight' (in effect, placed at the CG of the boat) also moves further out along the lever arm, counteracting that effect.

    Of course, as the windward hull lifts even higher, the CG (placement of the weight) also moves in towards the fulcrum, and hence the force of the wind on the underside of the windward hull (and the additional width of the bridgedeck windward of the CG) would operate pursuant to the lever principle. In this case, increased BWL and bridgedeck width will in fact increase the risk of capsize.

    Furthermore, even disregarding the forces on the underside of the boat, once the CE of the sailplan is beyond the fulcrum (and this will happen prior to heeling 90 degrees), then capsize is a certainty. This is where shorter rigs with lower CE's (as typically carried on narrower cats) have a distinct advantage.

    If the CE of the sailplan is 30 feet above the static waterline (I suspect that it must be close to that on the Lagoon 44, for example), then that point will be reached much sooner than on a boat with a CE that is only 20 feet above the static waterline; furthermore, this is true even though the Lagoon has additional beam (as only half of that is relevant to the equation since the mast is stepped at the centerline). Clear as mud?

    Anyway, I think we can all agree that the higher the CE of the sailplan and the CG of the boat, the greater the forces that will be generated towards capsize. Where there is debate is whether, after heeling to a certain point, additional beam not only cannot compensate for a significantly higher CE and CG, but may even make things worse.

    Brad
    Last edited by Southern Star; 27th October 2010 at 05:06 PM. Reason: sp

  6. #26
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    I (seriously) have the deepest respect for people like you who quite obviously KNOW what they are talking about - but as it so frequently happens in situations like this, the level you are communicating on, and the level I am just about able to follow are WAYS apart! :-)

    [ http://www.diy-wood-boat.com/Junk_Rig.html ]

    Also it would be interesting to learn why those unusual rigs - which according to your site offer a lot of advantages over a conventional rig, dont find the acceptance on the market they seem to deserve?

    [Most people buy stock boats, which have an economic incentive to offer 'the usual.' Here's some information about the parts of a junk rig. My wingsail rig is a modified junk rig, and has fewer lines. The front half of my junk rig wraps around the mast in a foil section. With the sail up, you don't see the mast from either side, because it's inside the sail - so there are none of those lines that you see at the front of the junk sail.]

    I also looked at that one website with the many pictures and found the 8 reefing lines led into the cockpit, per bow, VERY confusing, even so it said: "It's simple!"

    [They all come together as one tail. What you are seeing is much like a sheet that attaches along the boom at multiple points, yet which has only one tail. Attaching the sheet along the leach helps stay the sail, and takes up shock loads very nicely. In some sheet configurations, you have complete twist control. In other configurations, you have multiple purchases, such that you don't need sheet winches. By overlapping the mast, you get low sheet loads for the same reason you get less pressure on the helm from balanced rudders.]

    Especially those wing/-- rigs would be nice to see in action aka on a real boat, pref. out at sea in real conditions. Hard to believe that they would offer less resistance than a conv. marconi?

    [Foil shaped fairings have much less resistance than other shapes. If you google "Tystie" and "junk rig" you will see one, and if you google "Pha" and 'junk rig' you will see another. They have both made ocean voyages.]

    ....and, of course, I still am searching for an answer if that 42' x 17.2' cat of mine would have to be considered "too narrow" to be safe?


    [Do you know how high the center of effort is for your boat? If not, can you contact the designer?]
    Currently concentrating on http://earthnurture.com .

  7. #27
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    Bigcat is, of course, correct that the CE of the sailplan is a huge factor in determining capsize resistance. Without knowing the actual numbers, I am confident that it is very low in relation to most current cats, as:

    1. it is mounted much lower to the water due to lower freeboard and bridgedeck clearance.
    2. the rig is much shorter, in part because it is a ketch rig (and has the SA distributed more fore/aft); in part because the SA itself is lower than on most modern cats of comparable displacement.
    3. the mainsail has very little roach (let alone being a flat-top main that carries much of the sail area up quite high).

    Can this compensate for beam that is substantially narrower - say 3'9" (at 50% BOA/LOA) to 5'10" (at 55 % BOA/LOA) narrower than most current cats of your LOA or displacement? Yes, especially if this substantially lower CE is combined with a lower CG (and yours is very low due to the minimal bridgedeck clearance and galley down, etc.).

    However, to fit into any formula you would need the actual numbers and these we don't have.

    Brad

  8. #28
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    I am a strong believer in narrower cats, but with the following caveat. The design must be essentially lengthened hulls not expanded accommodations. We can all list the numerous cats that have been stretched. Seawind 1000 XL, Manta and many other production and custom cats. It seems that they all were improved boats.

    From a manufacturer's point of view folks will think of a 42 x 17 boat as narrow and a 42 x23' boat safe. They'll want the same number of bunks, engines,fuel, etc. The 42 x 17 may actually be the equivalent of a 34-35' cat. We know that they aren't the same but when someone starts looking at slips and paying for that extra 8', they begin to balk. Short sighted, true but a manufacturer's reality.

    These days when I doodle my 'next' boat, I draw what I want/need for cockpit, accomodations and rig and when I get it right, I add 3-4' on each end to get the performance and appearance that I want but I don't increase the rig. The other solemn warning to those of us who want this is the knowing discussion of increased wetted surface and it's resultant limitations especially in light airs. That usually dissuades but it's one that I can live with to get the aesthetics and performance in breeze and seaway that I want.

    Bob Oram has done a couple designs that he calls "Slims" that get me stirred up but I haven't been able to talk the Admiral into exchanging a perfectly good boat for one that is smaller all around. But it does real well on my Sea of Dreams.

  9. #29
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    Good points all! My boat, the Sunstream 40 started life as a Cherokee 35 and was lengthened by 4 1/2 feet aft. The waterline was increased, reverse transoms with steps were added, as were inboard rudders with partial skegs and some additional accomodation. Displacement was obviously increased and, in order to maintain performance without compromising stability, the SA was increased by converting to a cutter rig and increasing the length of the boom (rather than raising the mast). So yes, my BOA/LOA is relatively low, but there is no compromise to stability.

    Brad
    Last edited by Southern Star; 2nd November 2010 at 07:31 PM. Reason: sp

  10. #30
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    Brad, that sounds like a good way to deal with the increased length. I think too often there are two widely divergent design camps for cats: racing and chatering. Rracers want the slimmest possible hulls, tallest possible rigs, and lightest possible weight. This they handle with large crews. Charter companies, on the other hand want "cats for dummies", with lots of interior room, low sail plans for safety, and one head per stateroom. They also want lots of cockpit and tramp space, but with bridgedeck accomodations and lots of shade and space for stashing water toys. They only have to provision for two weeks or less, so storage isn't a priority. These two camps get two different types of boats. The racers are long and skinny, both as to individual hull shape and overall shape. They have large sailplans and tall rigs. The charter cats are square, with small, short sailplans and heavy construction so as to survive being sailed by those with little to no experience. Those of us who cruise/live aboard want something in between. We all make our compromises in different places.

  11. #31
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    Default Re: 15 foot Beam, on a 40 foot catamaran

    Amibon: I was very interested in a 42' catamaran Ketch listed with 2Hulls in Ft Lauderdale twenty years ago. It had a wonderfully crafted interior. So much for the good stuff.

    The rig was short, the sails had only stubby battens and virtually no roach. It was powered by two Mercedes diesels living in coal-black holes by virtue of liberal oil leaks, and the owner had cut 6" off the keels (!!?!) to get into skinnier water. It was heavier than a Sherman Tank and didn't sail much better. Under totally benign conditions it might actually tack without running an engine, given a truly skillful and extremely luck crew.

    Someone loved this boat, I'm sure. The alterations may have served a valid purpose. Given a sufficient means to refuel under way, this vessel might have been able to circumnavigate. If I was testifying in court and pressed by a cunning attorney I would also admit someone might survive a ride over Niagara Falls in it. I wouldn't get a chance to say how slim the chances would be in either case.

    If you now own this same vessel, I hope you can re-power her and restore the interior to its original glory. She would make a stunning residence in the right setting, and could easily cruise up and down a long coast following the seasons. I would place sailing her on an excitement level equal to listening to Debussy under the stars on a summer's eve, but nowhere near Flight of the Valkyries on a unicycle in an ice storm.

    Hmmm; I better go check the recommended dose on that pill bottle again.

  12. #32
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    Talking Re: 15 foot Beam, on a 40 foot catamaran

    Quote Originally Posted by Sandy Daugherty View Post
    If you now own this same vessel, I hope you can re-power her and restore the interior to its original glory. She would make a stunning residence in the right setting, and could easily cruise up and down a long coast following the seasons. I would place sailing her on an excitement level equal to listening to Debussy under the stars on a summer's eve, but nowhere near Flight of the Valkyries on a unicycle in an ice storm.

    Hmmm; I better go check the recommended dose on that pill bottle again.
    Funny!
    Currently concentrating on http://earthnurture.com .

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