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Conference unifix::sailing

Title:SAILING
Notice:Please read Note 2.* before participating in this conference
Moderator:UNIFIX::BERENS
Created:Wed Jul 01 1992
Last Modified:Mon Jun 02 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2299
Total number of notes:20724

1792.0. "Twin Rudders For Monohulls" by NZOMIS::MITCHELL (Glen M. - The Kiwi Connection) Tue Sep 17 1991 06:58

    I am an enthusiastic Trailer Sailer owner in New Zealand and currently
    own an EXPLORER 770, designed by Val Chubb. In NZ a Trailer Yacht is
    loosely defined as a monohull of 8' maximum beam, trailerable, with
    Cabin, and must conform to a small number of criteria mainly safety
    related. The EXPLORER is 25' LOA, is a fractionally rigged sloop with
    swept spreaders, no backstay or runners, 31'6" mast height, large sail
    area with generous roach, full Battened loose footed Main, 200lb centre
    plate with 200lb bulb.... we carry two spinakers and two headsails and
    compete in various regattas around the country including class and open
    events controlled by a National Rating system.
    
    The EXPLORER is of traditional fibreglass construction and approx 15
    were built in the early 1980's. (I understand 2 were exported to the
    United States).
    
    As an avid EXPLORER owner I am in the process of building a new
    EXPLORER using CEDAR strip construction and incorporating some Hull
    and Deck design "enhancements" plus rigging improvemewnts with a view
    to establishing a new EXPLORER SPORT class in this country..
    
    I am working with the designer and we are incorporating a lot of
    radical thinking that he has experimented with in recent years with
    considerable success on his own prototype!
    
    One area of interest is the possibility of using 2 rudders.. we have
    seen some pictures of 2 rudder designs (mainly French I think) and
    think the two rudder concept will have some advantage with the EXPLORER
    which has a very Flat aft section, and needs plenty of heel upwind to
    reduce wetted surface.
    
    Does anyone have any views on the merits of twin rudders on monohulls,
    and in particular any performance benefit/loss for my type of craft
    that will primarilarly be used for round the bouy racing?
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1792.1Unlinked maybe...MILKWY::WAGNERScottTue Sep 17 1991 14:0611
    
    	My fear would be the `upper' rudder stalling while the lower
    steered... unless you could unlink them or flip one up a'la catamarans.
    Hunter's Child, a good sized (70'?) creation of Warren Luhrs, had a
    manual pivoting rudder. I'd have put that to good use in my last boat-
    heeling actually pulled the rudder out of the water!
    
    	Have fun with the cedar... how are you treating it? Any oils in the
    wood that screw things up?
    
    	Scott. 
1792.2Cedar constructionNZOMIS::MITCHELLGlen M. - The Kiwi ConnectionWed Sep 18 1991 07:376
    re the Cedar; we are using a fairly common practice in NZ with the
    Cedar Strips being a core material which provide fore and aft strength,
    a laminate of 6oz "S" Glass inside and out laid perpendicular to the
    planked cedar, using expoxy resin...
    
    
1792.3I like it.MILKWY::WAGNERScottWed Sep 18 1991 12:425
    
    Neat & easy, huh? The cedar soaks up the epoxy well, then? Is the epoxy
    akin to acetone- thinned West System, or...?
    
    Curious_Scott, who has ingested too much West and System 3.
1792.4Am I crazy or is this the norm?NZOMIS::MITCHELLGlen M. - The Kiwi ConnectionThu Sep 19 1991 07:3133
    We're using unthinned West System Epoxy and get good penetration
    through the cedar resulting in excelent bond...
    
    Through the experience of others using Epoxies we are well protected...
    rubber gloves and chemical filtered breathing masks are standard
    equipment!
    
    As a matter of interest we finished the exterior hull surface last
    week, turned it over last weekend, and removed the frames in order to
    attack the inside surface... this week we (my crew/partner is currently
    working on it full time) has sanded and glassed the inside (6oz "S"
    glass again with West System Epoxy) and we are about to start making
    and inserting the bulkheads etc...
    
    We are extremely pleased with the stiffness and apparant strength so
    far, and the weight (or lack of) we have achieved... the hull can be
    lifted at the bow, with only the transom supported, using one arm
    only!!
    
    We are not working off plans.... they dont exist for the original 
    explorer... and used the original mould to get the basic hull shape
    which we have modified slightly to improve light air performance
    (introduced some rocker into the otherwise flat section aft of the
    centreplate).. we built new custom wood frames from taking 9 stations
    working from the centre-line of the original mould...
    
    We have also made the stem more plumb to increase the waterline length,
    and have reduced the sheerline slightly...
    
    Do you guys up on the East Coast do these crazy things.. or is just us
    mad KIWIS???
    
    
1792.5There are'nt many...MILKWY::WAGNERScottThu Sep 19 1991 12:2030
    
    There are a few cold-molded boats around; mostly racers. I helped a
    little on the one (and only... too bad) Dresser 30. Same basic
    construction technique and crew-on-fulltime, but a unique design- kind
    of a 30' Laser/Flying Scot with a lift-producing lead bulb way out on
    the end of a flat wood/carbon blade, allowing LOTS of sail. Some cherry
    and other wood veneers for looks on the outside, all the glass inside.
    Also scary-light, but no stress fractures yet- tho the rig was a
    dissapointment, for the price...
    
    	I also considered buying a very successful IMS coldmold out of
    Chicago- forget the designer- some known name- the price on such boats
    is ridiculous reasonable, since people think they'll implode or
    something in a puff.
    
    	My own home-project experience is more to the Light Cabin Furniture
    domain since I haven't a clue how to design or loft a boat... but a
    dinghy might be realizable. 
    
    	One of these days!
    
    	Let us know how you get on.
    
    	Oh yeah, is that cedar peculiar to NZ, or do you think my
    neighborhood veneer dealer's cedar would be the same stuff?
    
    	Have fun- turn that exhaust fan on (wish we woulda thought of
    that!)
    
    	Scott
1792.6less is better...ROMOIS::DEANGELIAbbasso tutte le diete!!!Mon Oct 21 1991 08:1315
    Hey, downunder!
    
    I've seen a photo on a magazine lots of time ago of an ULDB
    that had a very strange rudder pivoting on it's vertical
    axis i.e. always vertical with the boat healing. Could it
    be a suggestion in order to avoid the problems related to
    the twin rudders? I found it very interesting even if proba-
    bly less stiff than a fixed one.
    
    Let me know about your cedar construction, it's quite 
    interesting.
    
    Ciao from Italy.
    Arrigo
    
1792.7How about a boom made of Cedar?NZOMIS::MITCHELLGlen M. - The Kiwi ConnectionTue Oct 22 1991 06:5732
    Hi Arrigo,
    
    Thanks for the suggestion!  At this stage we are committed to the twin
    rudder concept.. our hull is very flat and wide at the transom, so we
    think rudders at the outside will have more "bite" when heeling, and
    close to the Broach situation.
    
    Most of the BOC Single handed yachts seem to have twin rudders.. In our
    case they will be on a pivot, thus the winward rudder can be "swung up"
    if neccessary!!   If it doesn't work we will simply revert to the more
    conventional.
    
    Construction of the boat proceeds at pace... the deck, cabin, and
    cockpit are nearly complete.. its all 4mm ply, and strengthened by
    having most flat sections actually curved to provide "intrinsic"
    stiffness.
    
    The Cedar and "S" glass hull looks good... its really stiff, and
    light... I can actually pick the boat up at the transom without too
    much trouble.
    
    We are seriously thinking about building a boom out of 4mm ply and
    cedar with an "s" glass laminate... we understand that the Kiwi
    Americas Cup yachts are doing booms in a similair fashion... we cant
    see why it wouldn't work... theres plenty of strength in a good box
    "jumbo" style section, and it'll be light... our main is loose footed,
    so your only looking for a system to carry the outhaul..  what do you
    reckon about this... I'll keep some of the other crazxy ideas for
    later!
    
    Glen.