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  1. #46
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    Quote Originally Posted by Timeless Timber View Post
    I guess being a blow boater means you need know nothing about vessel stability and meta centric height!

    That would make sense - because they often know nothing about the rules of the road on the water either - which is why as a rule us stink boaters give em a wide berth wherever possible.

    Why not google the terms "vessel stability" and "meta-centric height" and soak up a little vessel theory - you'd honestly be more stable in a bathtub than that sailboat (and I use the term sailboat judiciously - I'm not sure it really qualifies for the term boat even...)

    Let me guess - do you hand over your can of beer to a bystander when launching her and say words too the effect "here hold my beer and watch this"?

    Sorry I can't help but laugh at this whole thread - what scares me is we could share the same stretch of water one day.

    Cheers
    Howdy,

    You misinterpret the problem. Someone who knows sailing will be aware of what the thread is discussing in quite a different way.

    There are boats which measured by the standards of metacentric height and vessel stability should theoretically be a lot less stable than the boat being discussed here.

    But they are satisfactory sailing boats.

    So it becomes an interesting question to try to work out exactly why there are possibly specific problems with this boat or whether it can be changed by some detail or rigging or setup or sailing technique.

    For example, I wonder what you have to say about the metacentric height of this.



    This type of boat ended up with the final dimensions of 11ft long and about 12" wide. Later they sprouted hydrofoils, but that is another story.

    The people involved in this thread have the knowledge and ability to wrap their heads around this type of sailing with a bit of practice.

    So just maybe looking at what is being discussed here with an open mind is the best approach.

    Best wishes
    Michael Storer


    "Timeless Timber"s behaviour on the forum is subject to review by the moderators. There are several other questionable posts by him that have been reported.

    Members can report posts by clicking on the little red triangle with the exclamation mark inside - at the top of any post. This just means the moderators will review the post and decide if it needs an edit or a reminder about the terms and conditions of this forum (or no action at all) or something more.

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  3. #47
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    Thank you MIK,

    Hoping that discuss about boat's stability can be continued without obstacles ...

    There is an illustration of kayaks/sailing canoes stability (at sea and for my planed trip also).

    Kayaks which proveniences directly from eskimo umiak have low metacentric height (centre of weight positioned near waterline) and they are really stable at sea:

    [ame="http://www.youtube.com/watch?v=4ZYe0h3EypE"]YouTube - Flinders Island Sea Kayaking, Tasmania[/ame]

    There is a my BETH "YuanFen" - centre of weight is high that weight of spars and skipper are higher than previously. Than metacentric height is bigger. To this we add the power of the wind and the heeling moment that active hiking is needed:



    General dimensions of those boats are a bit similar - kayaks are longer and smoother, initial stability of BETH is better, but in the final analysis - thanks of bigger metacentric height - kayak is really more stable at sea.
    Aloha!
    Robert Hoffman
    http://robhosailor.blogspot.com/


  4. #48
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    Robert,
    If I contributed anything of value, it was from confused ignorance rather than informed wisdom.

    Now... my bouyancy bags (gave up on sourcing thick vinyl to glue up and am using car inner tubes) are in the pointy bits only... a capsize test in shallow water shows them being of use only when the canoe has a lot of water in it. e.g. when they are in the water.
    Side bouyancy is on my to do list, along with more practice on getting my 110kg in a bit more gracefully (think 'slide and wriggle' rather than muscling my way back in).

    BTW, I now know that I should have modified MIK's design to allow for stern/bow bouyancy tanks as that would be lighter than the car inner tubes. The benefit of tubes is that you can pick the inner tube size and blow them up to give the 'right' amount of bouyancy, whereas a deck tank is 'static' in dimensions.

    Benefit of hindsight I guess...

    apologies, this post is related to the thread, but could also go in the drop in sail or QC tips threads... I may be sidetracking things
    Cheers,
    Clinton

    "Use your third eye" - Watson

    http://www.flickr.com/photos/clinton_findlay/

  5. #49
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    Quote Originally Posted by Clinton1 View Post
    Robert,
    If I contributed anything of value, it was from confused ignorance rather than informed wisdom.

    Now... my bouyancy bags (gave up on sourcing thick vinyl to glue up and am using car inner tubes) are in the pointy bits only... a capsize test in shallow water shows them being of use only when the canoe has a lot of water in it. e.g. when they are in the water.
    Side bouyancy is on my to do list, along with more practice on getting my 110kg in a bit more gracefully (think 'slide and wriggle' rather than muscling my way back in).

    BTW, I now know that I should have modified MIK's design to allow for stern/bow bouyancy tanks as that would be lighter than the car inner tubes. The benefit of tubes is that you can pick the inner tube size and blow them up to give the 'right' amount of bouyancy, whereas a deck tank is 'static' in dimensions.

    Benefit of hindsight I guess...

    apologies, this post is related to the thread, but could also go in the drop in sail or QC tips threads... I may be sidetracking things
    Clinton,

    I'm not an expert
    As you've seen the video - side buoyancy are important for restoring the correct position - much less water is inside the boat.
    Once we (in my country) used motorcycle inner tubes as a side buoyancy - they are easier to use (inside the cockpit arrangement) than the automobile inner tubes.
    You can use styrofoam bloks also - they can be cut into appropriate shapes and fitted into the boat.
    BETH (Raid41 also) has built in air (buoyancy) chambers but no foam there (attachement - sorry for Polish description) - you can see them red hatched, and waterproof luggage compartments green hatched - so not much water remains inside the cockpit.

    ***
    For my planned sailing on the sea I consider adding air or styrofoam buoyancy in the cockpit to reduce the amount of water thrown by the waves.
    Aloha!
    Robert Hoffman
    http://robhosailor.blogspot.com/


  6. #50
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    so, returning to page 1 of this thread (which has wandered OT just a little...)

    As I understand it, the thinking is that R41 capsize was likely a combination of
    slab side of the fine bow 'tripping' on the water, multiplied by narrow bottom
    plus high crew weight, happening well forward of a really grippy centreboard.
    And probably some other factors like rudder lift opposing the broach vector,
    but actually assisting the capsize vector.

    Theory is then, using OH&S principles, eliminating one or more of the
    contributors is likely to reduce/eliminate the problem. Can't do much about
    the high crew weight due to needing dry sleeping space, so...

    Possibilities...
    1. A Rainbow scow style pram bow changes the bow dynamics - brings the
    tripping hazard aft to where it is negated by the centreboard, but keeps the
    simplicity of concept. Also increases stability forward. Penalty is a shorter
    waterline length, and a noisier, wetter ride in slop. Also noisier to sleep in but
    hey, if it doesn't fall over... Sleep-time noise-cancelling by warping a sheet of
    foam or carpet under the bow ?

    2. A fuller bow to float better, resisting diving, & hopefully less prone to tripping?

    3. A wider bottom increases static stability, and creates a fuller bow which
    -may- float rather than dig-in. BUT loses the ease of on-land handling. And
    does nothing to assist re-boarding, which IIRC is why the project was canned.

    4. A 45degree chine panel tapering from 0" near midships up to maybe 3-6"
    high at the bow complicates the build, but would make it vastly less likely to
    dig-in. Would need to make the bow above it fuller, and reduce rocker below
    it to compensate for loss of volume. Both of these might be good things?

    5. Bring the main mast aft a foot or two & aim for a more "balanced" balanced
    lug to reduce broaching thrust vectors ?

    6. A bigger rudder might resist a tripping bow better, but would also 'lift' the
    bottom in the direction of capsize... possibly the two cancel out completely
    yielding no benefit. so...

    7. taking a leaf out of Bolger's "Dart" and "Cartopper" desgns - move the CB
    forward & reduce its size, compensating for reduced 'lift' with a larger rudder.
    see attachments below.
    Result as noted by Bolger in the case of Dart, is a very unconventionally handling vessel.
    May not work without also applying one or more of opts 1, 2, 4 or 5,
    Which my gut feel are the best options anyway.

    Does any of this make sense regarding the actual capsize Brian?

    Do any of these (or combinations thereof) make sense to you Michael ?
    What would least harm the performance?
    You are the one who knows the numbers.
    I'm just feeling the 'vibe' of the thing... Mabo & The Castle & all that.

    Still got to figure out the re-boarding.

    cheers
    AJ

  7. #51
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    Quote Originally Posted by b.o.a.t. View Post
    this thread (which has wandered OT just a little...)
    Yes - that's why I like it

    In my opinion - The size of the centreboard and the rudder have no big relevance in this case.
    Aloha!
    Robert Hoffman
    http://robhosailor.blogspot.com/


  8. #52
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    Thanks so much for your post AJ. You pose questions, suggest answers , just what I was hoping for when I started this thread.

    I currently feel your suggestion No4, the chine panel sounds the most promising. I think that bow digging in is what I was getting at with my opening thread. I actually considered sawing the hard chine off and adding such a chine panel.

    Here's something that puzzles me about the RAID41 design.

    Normally a design is drawn and displacement calculated so the hull sits on the water in the way it is supposed to.

    With Raid41 the length is just less than 2 sheets long. Fixed.

    Her beam was just under 4' so she would fit one sheet width. Fixed per say.

    Sides are vertical so no way to slope hull sides inwards from the deck to reduce immersed hull volume.

    So, how do you design her to sit on her waterlines? Increase rocker, the only variable left.

    This ends up with the hull below the mast in the air, not even in the water at all. And if I go forward on a down wind run, just how high is the rudder out of the water.

    I think a PDR at 8' can be immersed by 90kg man and 40kg hull. Twice as long and 50kg and 90kg man cannot immerse her properly. She sat on the water like a leaf. Two people on board, or water ballast filled and she was completely different.

    PDR at 8' immerses and works, Beth being narrower immerses and works, Goat has angled sides and more load normally and works and does not have the rig in the bows.

    Poor Raid41, with such good bloodlines.

    Brian

  9. #53
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    G'day Brian

    As it stands, I think Raid's bow needs to be kept well clear of the water.
    As you describe her - the leaf sitting on rather than in the water.

    been drooling over videos of Welsford's Houdini (which I fully expect to be my next build,
    despite having 2 sets of foil blanks for Oz-Racer / Raid41, and plans for Eureka & outriggers...)

    [ame=http://www.youtube.com/watch?v=ZoFro_gzFi8]YouTube - Launch day 3[/ame]

    Houdini tends to run bow down, which may be ok with the huge rudder JW designed for it.
    Adding the chine panel on Raid41 would lose bow volume & tend to cause same, but I'm not
    sure Raid41s smaller rudder would cope. I think the chine panel would need to be complemented
    with a flattening of the rocker forward, and probably fuller bow sections.
    By comparison with that fiddle, turning it into a scow might be the simpler & more effective solution.

    Still got the re-boarding problem. For which the only solution I see is a ladder.
    And/or compartments which flood when capsized to keep it more docile for reboarding.

    If the above could be figured, I'd prefer to build it ahead of Houdini.
    Would be fun to give most of the Milang - Goolwa fleet a hiding in an "old-fashioned" boat.
    Anyway, MIK is the numbers man, & I'd love to hear his rough calculations on the matter.
    cheers
    AJ

  10. #54
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    Take a look at my recent video's over at: Texas-GIS:

    https://www.woodworkforums.com/f169/t...3/index30.html

    It shows a view from the stern of our GIS and you can watch the rudder just before and during the capsize.

    I would say that we had a bow down attitude because my daughter was way up front. With her behind the middle seat our bow would of been just above the water.

    "the leaf sitting on rather than in the water"

  11. #55
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    John, what a fantastic video.

    I have to say, I cannot believe how clean Goat's wake is. Unbelievable. No wonder she is so quick. I am astounded a boat can have such a clean wake.

    Wow.

    Will have to watch video loads of times. At 1.31 you are distracted by beginning the gybe, some extra heel and it all goes wrong from there on.

    Thanks, John. The camera on a stick has never been better applied.

    Brian

  12. #56
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    What Brian said.

    In common with Brian's Raid41 capsize, it didn't look like particularly strong wind.
    But I don't think this was the 'tripping' sensation that Brian experienced.
    Unfortunately, there are no landmarks visible to detect whether the boat slewed as it went over.

    To me it looks like you sheeted in to set up for the gybe, causing the wind flow to suddenly
    change from stalled in the run, to flowing "backwards" across the sail. Driving the mast to the
    left faster than you could react with weight or steering. I notice the rudder came clear of
    the water fairly early on, so there was loss of steerage at a time when it might potentially
    have still been recoverable.

    I wonder if maybe there's a different technique to be followed gybing these light narrow boats with big, powerful sails.
    Normally, one sheets in first to reduce the uncontrolled gybing arc, and allow a controlled finale onto the new tack.
    If the partially sheeted sail generates big by-the-lee lift, then there will be 2 periods during the gybe when there is
    strong heeling force opposite to what one would normally expect. So maybe Raid didn't 'trip' at all ?

    Watching vids of Lasers gybing, they seem to make a radical turn towards the sail to start the gybe,
    then an equally radical one the other way as the sail swings across. Little or no apparent effort made
    to soften the gybing boom. I'm guessing that this is, as MIK? commented earlier, to steer the boat under
    the mast & stay upright.
    Maybe GIS & Raid both need to be handled in this way ?

    just thinking out loud....
    AJ

  13. #57
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    IMHO all unballasted boats have a propensity for swimming because they all eventually fall over unless the skipper is able to balance the wind and wave forces. The only difference is in the compromises made in the design. fast boats fall or trip over more often. slow boats dont but are no fun.

    One other point needed to be remembered is that an unexpected swim at the gybe mark is a precurser to becoming a world champion. All champions will admit to having unexpected swims at one stage or another at the gybe mark. Its just that as they sail more and more their second sailing brain in their bum learns and gets better at telling them to take action and do something now to avoid a swim.

    The last point is that up until the above post we haven't really discussed the main sheet and the head of the sail. A lot of small wooden boats dont have stays, vangs or travellers. So if the mainsheet is loose the head of the sail and indeed the boom sometimesis able to lay off the wind. And as we all know the head of the sail also likes to initiate the swimming event and is able to get involved because of its leverage. The cause of many a learning event on the way to becoming a champion.

  14. #58
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    theory is, and as seen in the video, the balanced lug is self-vanging.
    In the light winds seen, sail twist -shouldn't- be a big issue.

    But these are narrow-bottommed boats without much in the way of hull form righting moment,
    so seem to be more sensitive to minor events. More akin to recreational riding on a racing bike
    than a Sunday drive in the Kingswood.

    I also note that the Lasers seem to get crew weight right aft for gybing.
    As seen in John's capsize, the rudder came out of the water at about 30deg of heel.
    With weight aft, there would have been more boat width in the water to aid stability,
    and more rudder immersed to control direction. And less bow in the water to trip over.
    So possibly gybe technique needs to be the same for Raid & GIS.

  15. #59
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    Yes thats another factor. Weight aft helps when sharp bowed, fat sterned, flat bottom especially chined hulls are in that uncontrolled round up position with the rudder losing traction. On a lot of sports boats when going downhill in breeze there is often an invisible line on the deck near the mast called the FBL. No fat boys are allowed forward of that line.

  16. #60
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    for me that line would be located somewhere just aft of the tiller handle...

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