Pocket cruising boats

Discussion in 'Sailboats' started by Guillermo, Apr 30, 2006.

  1. Guillermo
    Joined: Mar 2005
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    Guillermo Ingeniero Naval

    OK! Go ahead! :)

    Not exagerated design and quite good from the point of safety, but probably umcomfortable, as roll period is quite low. But we've seen in this thread many other 'modern' designs with similar or worse numbers.

    LH = 7,63 m
    Lwl = 7,27 m
    Bmax = 2,54 m
    Draught = 1,53 m (keel down)
    HD = 0,3 m (guessed)
    Disp = 2773 kg (2045 kg light)
    Ballast = 1136 kg
    Ballast/Disp = 0,41
    Sail area = 31,6 m2
    Power = 15 HP

    Displacement /Length Ratio D/L = 201,29
    Sail Area /Disp. Ratio SA/D = 16,27
    Power / Disp. Ratio 6*HP/D = 14,71
    Hull speed HSPD = 6,54 Kn
    Potential Maximum Speed PMS = 7,23 Kn
    Velocity Ratio VR = 1,11
    Capsize Safety Factor CSF = 1,82
    Motion Comfort Ratio MCR = 23,02
    Screening Stability Value SSV = 46,14
    Angle of Vanishing Stability AVS = 121,07 º

    Roll Period T = 1,79 Sec
    Roll Acceleration Acc = 0,18 G's
    Stability Index SI = 0,7

    From the pages of the designer:
    "The seaworthiness may come as a surprise to beginners or to those who have never sailed a shallow draft boat but experienced seamen know that the shallow draft boat is more seaworthy than a hull with a deep keel.
    Unlike the deep boat, a centerboarder will not resist the sea. Instead of tripping on it's keel, it will dodge the waves or lift over them. Properly designed, a keel centerboarder will have the same ultimate stability than a boat with a conventional keel. All over the world, lifeboats are shallow draft. Slocum sailed around the world in a shallow draft boat, my daughter's Presto style sharpie was 55' long but had less than 4' draft and sailed 2-1/2 times around the world and I sailed half around the world in a 41 footer with 3' draft.
    But there is more to it than safety at sea. In case of real bad weather like a hurricane, a shallow draft boat can take refuge deep inland or in very protected coves inaccessible to deep boats. The centerboarder can, with only a small tide, be beached for repairs or to clean and paint the bottom. It can go on anchor where nobody else can and save on marina fees.
    Altogether, shallow draft is the way to go for a serious cruising boat.
    "

    Well, I have some disagreement here. I think using lifeboats to justify shallow draft for an all around cruiser doesn't seem quite correct to me. Also I do not find correct the statement that a shallow draft hull is seaworthier than a deep keeled one, because it depends also on other important factors.

    Ballast/Disp ratio of 0,41 is quite high, probably due to the combination of inside ballast and leaded centerboard, so designer ends losing around 200 kg of payload by choosing this option, being this against his claims of a high load carrying capacity. Also fractional rig for a cruiser is not my favourite.

    Interesting to note calculated AVS is 121,07º, against designer's data of 137º as by the posted GZ curve. For sure calculated data is only a rough approximation and should be taken with care. The volume of the deckhouse is probably producing the hump in the curve at 75º, so increasing AVS from around 125º+ to 137º. To be noted that it is not specified the load condition for that stability curve (As a matter of fact there's something strange to me with that curve: I find it too steep and pointy for an inside ballasted boat....)

    Most strange thing is that designer, when comparing with other boats, states the following:
    D/L ratio = 251,56
    Roll period 2,16 sec
    AVS = 118,06º (!!!)

    Am I understanding well?
     
  2. Vega
    Joined: Apr 2005
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    Vega Senior Member

    I agree so much with Jacques Mertens that what he says is the reason that has made me abandon the design I have been modifying, of what would be my retirement cruising boat, a good seaworthy keel boat. Instead I am working in the modification and adaptation of an existing boat design with a retractable keel, exactly by the same reasons that Mertens points out, just to get a more seaworthy boat.

    I owe to Milan the beginning of my understanding on this matter, when he pointed out that the OVNIS are very seaworthy boats, even with a not satisfactory final stability.

    Further investigations led me to find that manufacturers of retractable ballasted keel boats, like Southerlies, advise the owners to partially put the keel up in gale conditions, giving the boat more seaworthiness.

    This confirms, as Mertens says, that “experienced seamen know that the shallow draft boat is more seaworthy than a hull with a deep keel”. Who can be more experienced in a boat than the ones that have made it and test-sailed it for more than 20 years, I mean the Southerlies?

    The boat with a ballasted keel up will have worse final stability and a lower AVS (all negative things) but can compensate that and better its seaworthiness by the ability of “gliding” on the face of the waves.

    A deep keel would not permit the “gliding” and the force of the wave on the boat instead of being transformed into a linear movement, would be transformed also in movement, but this time in a rotational one, that would lead to a capsize.

    Another sailor that has understood that is Eric Tabarlay . In his book “Guide practique de manoeuvre” he talks about the problem and these drawings (from the book) illustrate why a boat with a smaller keel area is a more seaworthy boat, regarding capsizing.
     

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  3. Guillermo
    Joined: Mar 2005
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    Guillermo Ingeniero Naval

    As I've said it's not only a matter of deepness. Probably Mertens wanted to say area and deepness, instead of only deepness.

    But capsizing has also to see with mass and inertia of the boat, among other thigs, so we cannot make things very simple. I would like to point out that a deeper analysis taking into account other factors should be made. Seaworthiness is more than just resisting capsizing, but also winward going ability, running ability, hoving to ability, kind motions, structural and rig resistance, sail handling characteristics, watertightness, self-righting ability, steering ability, etc, etc. And, on top of all that: the crew's preparedness, resistance, knowdledge and good criteria.

    Now, going on talking about off-shore small boats design criteria, here the opinion from Stephen Baker, of Stephen Baker Yacht Design

    "In rough order of importance:
    1.Unsinkable - using solid flotation if possible, such as thick foam core.
    2. Fixed keel
    3. Easily reefed
    4. Fully watertight companionway
    5. Enclosed cockpit (i.e. full lifelines)
    6. Full height lifelines (27")
    7. The ability to self-right from at least 125 degrees of roll (180 preferable but hard to achieve)
    9. Sealed mast with external halyards (to help with self-righting ability)
    10. Enough headroom to at least sit upright while on the head (an under-rated characteristic).
    11. Sailable (and preferably sailed) by 3 or 4 maximum.
    12. Fast enough to get out of trouble (also an under-rated characteristic)
    13. Open accommodations to avoid claustrophobia
    14. Large enough berths (6'4" minimum) for all crew.
    15. Real head with holding tank, chemical toilets just don't hack it in a storm
    16. Watermaker
    17. SSB
    18. All items required for a Class I Offshore race as defined by ORC, if not already included. A life raft is a really comfortable thing to have around, but difficult in 25ft. I realize I would probably have to work very hard to get all this into 25ft, but I'd love to try."

    More interesting stuff about small boats at:
    http://www.smallcraftadvisor.com/

    Interesting to read there their page on Seaworthiness:
    http://www.smallcraftadvisor.com/content/seaworthiness/index.htm
     
  4. sailaweigh
    Joined: Feb 2006
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    sailaweigh Junior Member

    "The seaworthiness may come as a surprise to beginners or to those who have never sailed a shallow draft boat but experienced seamen know that the shallow draft boat is more seaworthy than a hull with a deep keel.
    Unlike the deep boat, a centerboarder will not resist the sea. Instead of tripping on it's keel, it will dodge the waves or lift over them. Properly designed, a keel centerboarder will have the same ultimate stability than a boat with a conventional keel.


    What a bunch of crap. Been there, done that. It's bull.
    Mike
     
  5. Vega
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    Vega Senior Member

    Interesting post Mike...You mean you have been in bad weather in a shallow draft boat?
    Tell us about it;)
     
  6. Vega
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    Vega Senior Member


    Some more information about this one, coming from the first test data from the specialized press.

    In this month edition of “Voile Magazine” it is published a sail test of the new Etap 28ft.

    They went out for testing the boat with 25k winds and when they returned it was blowing 35k and gusting, with an already formed sea.

    They have said (translated):

    “It is difficult to imagine a more seaworthy and faster boat, offering so much comfort”....
    “ We have surfed downwind at more than 10k without too much rolling.”
    About the quality – “Superb finish at all stages and a high quality construction, as in all Etaps..”


    Well, I am impressed Frede.;)
     

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  7. frede
    Joined: May 2006
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    frede New Member

    Thanks, I will look for the review in Voile. I too am impressed with the 28s.
     
  8. Guillermo
    Joined: Mar 2005
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    Guillermo Ingeniero Naval

    Another Light & Fast one:
    http://www.rodgermartindesign.com/

    QUEST 30

    Lh = 9.15 m
    Lwl = 8.4 m
    Bmax = 3.45 m3
    Bwl = 2.76 m (guessed)
    Draught = 2.1 m
    HD = 0.3 m (guessed)
    Disp = 2720 kg (probably lightship)
    Ballast = 793 kg
    Sail area = 62 m2

    Ballast/Disp Ratio W/Disp =0,29
    Displacement/Length Ratio D/L = 128
    Sail Area/Disp. Ratio SA/D = 32,33
    Hull speed HSPD = 7,03Kn
    Potential Maximum Speed PMS = 9,78Kn
    Velocity Ratio VR =1,39
    Comfort Safety Factor CSF = 2,49
    Motion Comfort Ratio MCR = 12,84
    Screening Stability Value SSV = 119,67
    Angle of Vanishing Stability AVS = 113,65º
    Heft Ratio HF =0,49
    Roll Period T =1,6 Sec
    Roll Acceleration Acc =0,35G's
    Stability Index SI = 0,46
    Roll Period/Beam Ratio T/Bcorr =0,52 (Comfort: 1 – 1,1)
    Righting arm 10º RA10 =0,36m
    Initial Metacentric height GMo =2,09m
     
  9. Seafarer24
    Joined: May 2005
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    Seafarer24 Sunset Chaser

    I've been gone for a month so I haven't quite kept up with this thread but wanted to comment on the pictures of waves breaking over the boats a few posts back.

    That first boat with the long, full keel, would be more likely to create the "slick" (turbulent wake extending to windward) which causes waves to break before reaching the boat when lying a-hull. The shape of the keel would allow the boat to lie sideways to the waves without slipping forwards out of this protective zone. This is one area that modern underbodies lose out. When lying a-hull they still want to move forwards as the waves aproach, drifting out of their protective "slick". A drogue towed astern can help pin the boat in place.
     
  10. Vega
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    Vega Senior Member

    Seafarer, this thread is not about seaworthiness, dynamic stability and type of underbody so I will not go any further on it.

    But let me tell you that those pictures represent the opinion of one of the greatest sailors of all times about the behavior of those hulls in that situation. He knew those two hulls very well. He loved both boats, and has probably made hundreds of thousands of miles in each one of them and endured countless storms.

    I am inclined to think he knows what he is talking about.
     
  11. Guillermo
    Joined: Mar 2005
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    Guillermo Ingeniero Naval

    A well known and reputed one:

    VARNE 27 (http://www.varne.co.uk/)

    Lh = 8,45 m
    Lwl = 6,4 m
    Bmax = 2,7 m
    Bwl = 2,43 m (0.9*Bmax)
    Draught = 1,3 m
    HD = 0,5 m (Guess)
    Disp = 2812 kg (Light?)
    Ballast = 1177 kg
    Sail area = 31,94 m2
    Power = 12 HP
    Heeling Arm = 5,2 m (Guess)

    Length/Beam ratio (Lfl+Lh)/2B = 2,75
    Ballast/Disp Ratio Ball/Disp = 0,42
    Displacement/Length Ratio D/L = 299,2
    Sail Area/Disp. Ratio SA/D = 16,29
    Power/ Disp. Ratio HP/D = 1,93 HP/ton
    Hull speed HSPD = 6,14 Kn
    Potential Maximum Speed PMS = 6,79 Kn
    Velocity Ratio VR = 1,11
    Capsize Safety Factor CSF = 1,93 (OK under 2)
    Motion Comfort Ratio MCR = 22,63

    Angle of Vanishing Stability AVS = 129 º
    Heft Ratio HF = 0,89 (OK over 1)
    Roll Period T = 2,28 Sec
    Roll Acceleration Acc = 0,12 G's (Malaise 0.1+)
    Stability Index SI = 0,85 (Comfort: 1 – 1,1)

    Upright Heeling Moment UHM = 5865,34 Ft*pound
    Heeling Moment at 1º HM1º = 281,9 Ft*pound
    Dellenbaugh Angle DA = 20,81 º


    To be taken with care:

    Righting Arm 10º RA10 = 0,45 Ft
    Righting Arm 20º RA20 = 0,82 Ft
    Righting Arm 30º RA30 = 1,11 Ft
    Initial Metacentric height GMo = 2,6 Ft
    CG height to floatation GF = -0,05 Ft
    CG from bottom of Keel KG = 3,71 Ft

    I have to find out about displacement, probably being the one used the correspondent to lighship condition. A full load displacement of around 3520 kg makes mores sense to me, bringing comfort and safety numbers to what is perceived by owners as a boat having "...a motion that could rock you to sleep"
     

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  12. Guillermo
    Joined: Mar 2005
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    Guillermo Ingeniero Naval

    And here what has been said to be the best cruiser in its range ever built:

    GREAT DANE 28
    (data taken here and there, but mainly from a Yachtworld ad. More accurate info will be greatly appreciated)

    Lh = 8,54 m
    Lwl = 6,4 m
    Bmax = 2,44 m
    Bwl = 2,2 m (0.9*Bmax)
    Draught = 1,45 m
    HD = 0,5 m (Guess)
    Disp = 4195 kg
    Ballast = 1798 kg
    Sail area = 36,7 m2
    Power = 18 HP

    Length/Beam ratio (Lfl+Lh)/2B = 3,06
    Ballast/Disp Ratio Ball/Disp = 0,43
    Displacement/Length Ratio D/L = 446,35
    Sail Area/Disp. Ratio SA/D = 14,34
    Power/ Disp. Ratio HP/D = 1,94 HP/ton
    Hull speed HSPD = 6,14 Kn
    Potential Maximum Speed PMS = 6,43 Kn
    Velocity Ratio VR = 1,05
    Capsize Safety Factor CSF = 1,53 (OK under 2)
    Motion Comfort Ratio MCR = 38,49

    Angle of Vanishing Stability AVS = 138 º
    Heft Ratio HF = 1,61 (OK over 1)
    Roll Period T = 3,77 Sec
    Roll Acceleration Acc = 0,04 G's (Malaise 0.1+)
    Stability Index SI = 1,54 (Comfort: 1 – 1,1)
     

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  13. VadimGo
    Joined: Aug 2006
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    Location: USA

    VadimGo Junior Member

    Puma 23 question

    I find your comment by searching the forum, Apology if bothering you.
    I just got myself an old Puma 23 sailboat, a bit neglected for some years. The hull is in great condition, rig is OK, interior is in need of reconstruction/modernization. I would like to make it sailable again. I was not able to find any info about this boat – apparently there are very few of them in the USA. I would greatly appreciate if you could help me in any way – comments, pics, links etc.

    Thank you
     
  14. Guillermo
    Joined: Mar 2005
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    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    VladimGo,
    My father owned a Puma 23 for several years, when I was young. Unluckily I haven't kept any kind of data. Building boatyard (INERGA) is not working either, since a long time ago. Anyhow I'll try to do some search for you in Spain and if I find something I'll let you know. A friend of mine has just got an old one from the Spanish Navy (They bought 6 units at the same time my father bought his), so maybe he has some info. Let's see...
    In the mean time here you have a link to a selling ad in Spain, where you can find several interior photographs:
    http://www.cosasdebarcos.com/barco_37668050061548665250546853544570.html
    And here a better maintained unit:
    http://www.marktplaats.nl/index.php.../kajuitzeilboten_en_zeiljachten/43526029.html
    You may find some info on the Puma 23 at CDboats: http://www.cdboats.com/boats.html (But you'll have to buy the CD, which maybe doesn't worth while, just for this info. It's up to you)
    Cheers.
     

  15. Guillermo
    Joined: Mar 2005
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    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

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