2-3m Sit in Performance orientated yacht

Discussion in 'Sailboats' started by Sailingkid, Mar 20, 2012.

  1. CutOnce

    CutOnce Previous Member

    History is changing again!

    This is a specific example of proof by Internet anecdote. The little boat being discussed is a Firebug - a boat designed for use by children.

    Just because one person claims on the Internet that a Firebug planes with 90 kilograms in it in 12 knots wind, this is not sufficient "proof" that this can be used to validate a proposed design.

    There are huge problems with this. What does "plane" mean to the original poster? Does it mean a turbulence-free wake? Does it mean the boat has climbed out of the hole in the water and moved forward on the bow wave to dramatically exceed displacement hull speed? Without a common frame of reference this citation is doubtful at best.

    I'm not disputing the original poster's sincerity or enthusiasm. Perhaps he has GPS tracks showing 16 knots, video with witnesses and I'm full of fecal matter. But without establishing a common vocabulary, this is not enough information to quote as a fact.

    Much of the following is a freshly edited personal attack and new to the discussion. Got to love how history changes here.

    --
    CutOnce
     
    Last edited: Mar 22, 2012
  2. Doug Lord
    Joined: May 2009
    Posts: 16,679
    Likes: 349, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    ========================
    Don't like the Firebug example? Well, how about an 8' windsurfer which even you would have to agree planes-carrying larger SA than a windsurfer! If a small boat has enough sail area, enough RM and light enough weight it will plane. An 8-10 "Little 60" could be designed to plane off the wind using DSS . A 12 footer is a better length for higher speed but would require some ballast in a sit-in configuration.
    DSS is ideal for these little boats particularly off the wind. DSS adds RM w/o any appreciable weight gain. Even in the example of the 12(12.75' LWL) footer upwind(158ft.lb) at "hull speed"(1.34X sq.rt. of lwl-just for reference ) is nothing to sneer at-50lb three feet to windward! And around 4 times that off the wind. Basic physics and science( the formula for lift) shows that the foil will work-it is not speculation! And there are more benefits than just RM-including substantial wetted surface reduction off the wind and improved handling with less pitching upwind and downwind. These are proven facts with a DSS foil.
    --
    Foil 3' X .5'= 1.5sq.ft. area
    L=V^2 X S X Cl where L=lift, V= speed in ft.per second, S= area, Cl=.6
    sq.rt. 12.75 X 1.34 = 4.78 knots=5.5mph X 1.47=8.085 ftper second; squared =65.36
    so,
    65.36 X 1.5 X .6= 58.8lb. lift at 4.78 knots. Lift is centered 2.6875' from heeled CB =58.8 X 2.6875= 158ft.lb RM upwind in a 12.75' waterline boat.
    At 6.95 knots(8mph) RM= 334.6 ft.lb.
    At 8.69 knots(10mph) RM= 521.4 ft.lb.
    At 10 knots(11.5mph) RM= 690.7 ft.lb.
    Quite substantial.......
     
  3. CutOnce

    CutOnce Previous Member

    Wow. This just keeps on getting weirder. No one has disputed that small boats can plane. I can't understand why you think a windsurfer is relevant to the current conversation. You keep on getting further and further from the thread we are discussing.

    I fully agree that a 8-10 foot boat of the right design could plane - even without DSS if it was helmed by a lightweight person, a raccoon, or some other thing that keeps weight down. I do however think a 200 plus pound human being in an 8-10 foot monohull boat will have a much harder time. Especially if they can't move laterally from the boat centerline. These conditions are set in the first post of the thread, not my imagination. The Minuet example pointed out by Sailing Kid isn't close to a windsurfer.

    Adding DSS to an 8-10 foot boat so it can support more rig to generate more power at 300+ pounds displacement (including the helm sitting on centerline) doesn't seem to help, in my opinion. More power may solve equations for planing, but it makes the whole thing more precarious, less sail-able and further from the original poster's desire for a relaxed, fun, non-intense ride.

    I came to the conclusion a long time ago that you and I would not agree on many things, so I'll have to agree to disagree.

    No one has sneered anywhere except in your imagination. Until something is demonstrated, it IS speculation. Until something is measured, it IS speculation.

    Somewhere in my education I guess I missed the day they told everyone that third party information, randomly assembled by someone not connected with the original project is adequate proof to claim something as fact. My bad. As I've stated many times before, people have to share a common understanding of language for a discussion to have any value.

    Don't bother responding with more Internet forum "proof". Just build one and show me. Or get Mr. Welbourne to read this thread in it's unmodified entirety and set me straight. I'm perfectly willing to accept his opinion - but I'm sure he has much better things to do than mediate a playground dispute you have created out of thin air because you don't want to read anyone else's opinions.

    --
    CutOnce
     
  4. Doug Lord
    Joined: May 2009
    Posts: 16,679
    Likes: 349, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    From the Minuet thread -detailed calculations and comparison with a Laser using various ratios for the 9.5' version of the Little 60. These represent PROVEN facts when discussing the feasibility of DSS on a small boat-based on the SCIENCE of small boat design-not small boat design speculation. Of course, since it hasn't been built we can have no actual results between a Laser and Little 60. The Laser is likely to be much faster upwind. Downwind not so much. But the Little 60 will probably be very high performance for its length using the best of modern technology. Like Minuet, the Little 60 would be able to capsize-thats where a slightly larger boat(12-14') carrying a sealed sliding ballast wing(or even a fixed,retractable keel) would have a significant advantage with much greater resistance to capsize. But if you don't mind getting wet every now and then the 9.5 would be a blast.....


    ------------------------------
    Comparison with a Laser:


    rough sketches of 9.5' "Little 60" :
     

    Attached Files:

  5. Perm Stress
    Joined: Sep 2009
    Posts: 554
    Likes: 24, Points: 0, Legacy Rep: 323
    Location: Lithuania

    Perm Stress Senior Member

    Back to the roots.

    Lets take the Optimist dingy.
    In Force 5-6, an adult person can bring her on plane even closehauled, if chop is not too short and steep (I tried this. It was not sit-in affair however :) ). Other vise, Optimist have plenty of initial stability to be "sit-in" boat for most normal wheather conditions, if the crew is an adult person instead of a kid.
    Now:
    * if we add to her fore transom some lengthening to make the bow sort of pointed or rounded (and add longitudinal stability she lack in stronger breeze)
    * install sealed side compartments and side decks leaving the cockpit wide enough to sit in in reasonable comfort and arrange a simple linkage from the tiller to some lever in front of the helmsman
    * plant in a little more decent rig
    * bolt the bulb to the bottom of (reinforced) daggerboard to offset weight of that rig when heeled 90 degrees + some margin
    we have a not-so-expensive sit-in boat for single person to play in sheltered (and so sheltered) waters.
    That's basically. Some fiddling with rig details, proper trim and balance will be of course necessary.
     
  6. CutOnce

    CutOnce Previous Member

    Finally, common sense that brings this wandering train wreck back to something resembling the tracks.

    I'd make things a little simpler. First, I'd not bother with the bulb and just build a second daggerboard that has a fair amount of lead embedded on the lower end - kind of like what Meade Gougeon did on his i550. That way the boat could be sailed in "detuned" mode when needed without having to deal with an unremove-able bulb, complex launching etc. When the wind is down, you could sail with the "normal" daggerboard and not pay the penalty of the extra 50 pounds of the lead.

    Boat wise, I'd look hard at a homebuild design like a Sabre. This is a boat that is the right size, great performance, nice rig, Aussie roots (like SailingKid) and a good first build with help all around him. With a good daggerboard tie down/retention strap, a heavy board Sabre would be perfect for this SOR. And it would have resale value so the effort would not be put into a weird Frankenorphan.

    --
    CutOnce
     
  7. Doug Lord
    Joined: May 2009
    Posts: 16,679
    Likes: 349, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    The problem with the Sabre or Optimist is that they are both singlehanded boats. And SK wants a "sit-it" boat. Why is that important? Because in order for the boat to meet the SOR below ballast would have to be added. And since ,from another thread, SK is 180lb, either the Sabre or Optimist would be severely overloaded to meet these requirements-especially with a bulb keel. Thats why unique solutions such as sliding on-deck ballast were considered in the first place: sliding on-deck ballast(proven to work originally in the 1800's) allows two to three times the RM of a bulb keel@ 30degrees or the same RM with much less weight and no heel. All this is why the design considerations of these requirements have to be looked at very carefully and why a two person boat like SK's Cherub is the best route to take for a conversion that meets the stated requirements.
    One may not like what SK wanted, nor understand the potential solutions directed toward fullfilling this SOR- but his requirements should not be forgotten....
    From post #1:

     
    Last edited: Mar 31, 2012
  8. WhiteDwarf
    Joined: Jun 2011
    Posts: 131
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Sydney

    WhiteDwarf White Dwarf

    Reply to Cutonce re Firebugs

    Cutonce, Doug was referring to my 'Bug. I do weigh 90kg and I do get the boat to plane in a reasonable breeze. Recently I completed a 6 nautical mile figure of 8 course (two laps) in 70 minutes. Do the mathematics. Allowing extra distance for tacks and stemming a tide in one direction maximum displacement speed was exceeded for the whole course and no I didn't plane on the works!

    Various participants have remarked upon their experience and authority. Cutonce please accept I have well over 50 years experience, I have raced International
    Moths and on up to 300 ton topsail schooner.

    Thank you, I can tell when a boat is on the plane; even an 8 footer.

    Why then do I sail "silly little 8 footer? "Because its fun and the people are great.
     
    1 person likes this.
  9. WhiteDwarf
    Joined: Jun 2011
    Posts: 131
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Sydney

    WhiteDwarf White Dwarf

    Further response to Cutonce post #16

    The link below shows a Firebug in less than 12kts (no white caps) and close to, if not occassionally planing. The sailor weighs 85 kg.

    http://www.youtube.com/watch?v=FFnrHCSLFNo

    I absolutely agree that planing performance for a sit-in boat of this length is problematic, perhaps improbable. DSS may provide righting moment, but at the cost of complexity (therefore cost) and weight. If extra cost, a longer hull?...

    Wide flat bottomed hulls become unstable fore and aft if they are too short. A 'Bug, and I am sure this applies to Optis, etc. will nosedive if run in excessive winds. Solution, reach and when you get to the gibe, do it quickly and fingers crossed until established on the new board.
     
  10. CutOnce

    CutOnce Previous Member

    Thanks for posting this. My original post has been completely validated - we obviously have different interpretations of exactly what qualifies as planing. Here's a boat that used to reside at my club (well after it's competitive days). It is planing according to my interpretation - and really flying as it turns the corner at the top mark and set's the kite.

    There is nothing wrong with your interpretation of planing - but the 'Bug wasn't able to climb on top of it's bow wave, wasn't accelerating way past it's hull speed and certainly wasn't close to or exceeding wind speed. It did get the point where the wake was cleaned up and it was moving along smartly, but from a skiff sailor's perspective it wasn't planing. Get out on a 49er, a I-14 - there is a world of difference.

    Herein lies the point I was making - we do not share the same understanding of what basic sailing terminology means, therefore we can't use each other's statements as foundation for discussion.

    I wasn't arguing with your original statement that a Firebug can plane - I know quite well that many people interpret a clean turbulence free wake and a little surfing each wave cycle as planing. I don't. But that's okay.

    --
    CutOnce
     
  11. WhiteDwarf
    Joined: Jun 2011
    Posts: 131
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Sydney

    WhiteDwarf White Dwarf

    Response to Cutonce - Post 25

    Thank you for that.

    From Wikipedia... "Planing is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydrodynamic lift, rather than hydrostatic lift (buoyancy)."

    May I respectively submit that; if your wake is peeking several feet behind your transom, you are planing, and that is what a 'bug will do.

    The wind in the video was clearly under 12 kts, Beaufort force 3, presumably. You will note that I was very careful to minimise the performance of the 'bug in the video - "close to, if not occassionally planing." Move up to Beaufort 4 and she'll plane.

    You seek to make the comparison Sydney Hbr 18 footer. Not a fair!
     
  12. Doug Lord
    Joined: May 2009
    Posts: 16,679
    Likes: 349, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Planing

    From the Minuet thread. We know that small "craft" can plane with enough sail and RM. There is NO QUESTION whatsoever that an 8-10' dinghy can plane with the right power. A small boat like the Little 60 with a large asy spin would definitely plane by any definition. So would a 7' windsurfer. The Little 60 at 9' has 115 sq.ft. of sail downwind and would definitely plane off the wind.

     

    Attached Files:

  13. CutOnce

    CutOnce Previous Member

    I absolutely did choose an example to provide the greatest possible contrast. I agree with the Wikipedia definition as well. Where we differ is in our interpretation of how the hydrodynamic lift manifests itself. My interpretation is founded on the visible evidence presented in "my" video example where the boat has climbed up AND forward on it's own bow wave, with only the back 1/3 or less of the hull touching the water. This results in a major drop in drag and subsequent major increase in speed. Yes, in this case the stern wave is also far behind the boat.

    Your interpretation of planing where the stern wave is several feet behind the transom and the wake turbulence-free is a more generous definition. The effect of the hydrodynamic lift is not visibly apparent as most of the waterline of the boat is still immersed, and the speed difference is not dramatically higher than maximum displacement hull speed. This doesn't mean the Firebug isn't fun and more people would enjoy a 'Bug than getting punished in an 18. I don't doubt that a Firebug can plane (by my definition) in the right (lightweight) hands and (wind and sea) conditions.

    I've absolutely planed singlehanded in a Mirror dinghy under spinnaker in 25+ knots of wind when I was 15 years old. I had that pram faced 10' dinghy absolutely blasting. It was more memorable fun than I've had going two or three times the speed in much faster boats. But getting the Mirror on a plane was highly dependent on light weight (140 pounds at the time), large sail area for singlehanded sailing and major hiking in a lot of wind. It was just about as hard as someone could push that boat design.

    Given this thread was posted by someone who was inquiring about a slightly upsized sit-in Minuet style boat (notice I'm not calling it a dinghy), I feel all the diversions into miniature Open 60's and other things like DSS foils are far off topic. Personally, I think the emphasis on planing is far off-topic. Like many discussions here once someone sees "high performance" in a sentence, they spin out of control and forget the rest of the stated requirements. You don't have to plane (using my interpretation) to have fun. You don't have to jump waves, be faster than other boats or even as fast as anything else. Fun is an opinion, not an absolute.

    I'm sure there will be another self-promotional response to this as my good friend from Florida MUST have the last word in every discussion.

    Cheers,

    --
    CutOnce
     
  14. ancient kayaker
    Joined: Aug 2006
    Posts: 3,497
    Likes: 147, Points: 0, Legacy Rep: 2291
    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    The hypothetical boat will have to do one of two things to get 6k from a 2.4m length in anything less than a half-gale:-

    Either 1) it will plane, in which case it will have a substantially flat bottom and substantial beam -

    Or 2) it will be extremely narrow like a kayak in which case it will have minimal stability and very little space.

    - and then there’s multihulls . . .

    Either will do the job. Anything involving the words “deep” or "displacement" won’t achieve the objective at this size. See -
    http://www.boatdesign.net/forums/bo...ulation-implications-30857-18.html#post353422
     

  15. CutOnce

    CutOnce Previous Member

    Or 3) It will be on the roof rack of a car.

    Terry, many people just don't want to concede physics is real and established benchmarks exist. At 2.4 meters in length, a rig powerful enough to satisfy planing "equations" will be a horror show to sail, with the bow constantly trying to go down the mine and submarine. People can't just tweak one or two variables in an equation to arrive at the results you want.

    At the end of the day, the Minuet appears to deliver the feeling of performance, as it's small scale and low to the water design make 4 knots feel like 12. It is the feeling that counts, not the display on the GPS.

    --
    CutOnce
     
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.