Crowther 40 cat

Discussion in 'Multihulls' started by Contorta, Mar 31, 2011.

  1. Contorta
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    Contorta Junior Member

    I am building this boat with a cedar core, so it is already very stiff. When I came to set the hulls for final measurements I discovered they had 60mm less rocker (fore & aft) than the design asks for. Any suggestions regarding adjustments or complications down the line would be appreciated.
     
  2. Gary Baigent
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    Gary Baigent Senior Member

    You should be faster than the correct version - but tacking may be a little slower. I used to race against a Crowther 40 here in Auckland named Whiplash, owned by Tony Lawson, always a good boat. Anyone know where it is now?
     
  3. Contorta
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    Contorta Junior Member

    Thank you Gary, your reply is encouraging. The question remains,just how important is this 60mm discrepancy and what can I plan to do to compensate for the slow tacking or other related problems?
     
  4. Gary Baigent
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    Gary Baigent Senior Member

    It won't be slow to tack, maybe 2 seconds more. If I remember there was considerable rocker in Whiplash - your serendipitous "mistake" will be no problem.
     
  5. Hangtime
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    Hangtime Junior Member

    Crowther 40?

    Hello contorta.
    Which Crowther 40 design are you Building? I may be able to help.
     
  6. Contorta
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    Contorta Junior Member

    Hello Hangtime,
    She is a design 274. Thank you for your interest.
     
  7. Hangtime
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    Hangtime Junior Member

    Built one of those, its my current home. Sitting on it right now.Too much rocker in it so the mod will dampen hobbyhorsing.:)
     
  8. Contorta
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    Contorta Junior Member

    Hello Hangtime,
    Good to hear.:) Problem is I can't use the baseline measurements from the plans anymore accept at midship. I have decided to keep the design baseline to waterline 'ratios' and use the bulkhead pattern to form the sheer lines more or less but with some weight given to eye pleasure. I'm afraid this decision might cost me big time for something I have not yet considered. What do you think? Did you find the plan scale and numerical values often did not bare much relationship to each other? (for example: stated value for baseline to underwing intersection is 1200mm, measure to scale from plan is 1240mm)
     
  9. catsketcher
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    catsketcher Senior Member

    Gday

    Are you building the hulls now or are you dealing with a built set of hulls? Is this the first hull?

    If I was you I would look through to find a datum line and measure from it. trouble is that normal plans will not have the accuracy to produce great measurements from.

    Normally one of Lock's draftsmen would have lofted the design nice and big and then scaled down the design for the builder. You may have a set of offsets so that you can do the same. I can't see the 274 in my Crowther design book. Is it the SP 40 by Brett Crowther? This will have been drawn on the computer. My concern would be why the design lost the 60mm. Was the strongback bent, mold frames incorrectly set up or is it a design fault?

    Hopefully all of the bulkheads are set up on a certain waterline. If you set the middle ones slightly lower and the end ones higher then they should be approximately the same.

    Gary - Whiplash was a Spindrift wasn't she? About 15 years ago she was in Sydney, up the Georges river. She used to drop her mast to go sailing. Don't know where she is now. Did Tony ever finish his Newick?

    cheers

    Phil
     
  10. Gary Baigent
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    Gary Baigent Senior Member

    Catsketcher Phil, yes, Whiplash was a Spindrift.
    I remember Tony and family were doing a crossing: Fiji/Auckland, I think, and were actually rammed by a whale which tore open one of the hulls - and they struggled along after that with a monohull list. Trying to remember his wife's name; she was a strong, outspoken woman - and she was not impressed.
    Last time I saw Tony he was building a Farr Admirals Cup design for someone - and that was many years ago. Didn't know he was building a Newick. He would have seen Mokihi in those days and that boat was an impressive performer. Outgunned today of course.
     
  11. Hangtime
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    Hangtime Junior Member

    Contorta
    When i purchased the plans I didnt get a table of offsets, Instead i got full size mylar paper with hull lines computer printed on them. Being an amatuer boat builder i was happy with the ease of this and i drew the Design waterline straight from the printout to the frame and then to the hull via a light tap with a chisel to leave a 1mm indentation in the Cedar, filled with white epoxy bog the mark is there forever whereas a pencil mark would have dissapeared long ago. Reference is made to these marks reguarly and if i didnt have them i'd be in trouble .
    Do you have DWL datum marks in your hull?
    My boat has been on the water since 2002 and sails well but one bad problem it has is excessive hobbyhorsing when heading into a sea, Its real bad! This has nothing to do with sailing performance or the rig, Its a design thing. The bows are plumb with a big flare at the top, Very blunt on the leading edge and everytime they dip on a wave the boat loses half of its forward momentum. In a chop created by any wind greater than 12 knots the Hobby horsing gets too much.
    Now to rectify the problem Brett Crowther says to add bulbs. I say no to this as the bows ride high all the time and the bulbs need to be under water.
    My own thoughts are to add a meter to the sterns (sugar scoop style) and add probably 50mm of foam to the bottom at the back, Tapering out as it runs forward about 3 mters, in effect I'll be reducing rocker by 50mm and this is the situation that YOU have by some sort of mistake? I say stick with it.
    I'll also sharpen the bows a little which will add about 200-300mm to the waterline
    There are not too many of these boats on the water but all of them seem to be "Bow high". Keep this in mind as you build, Keeping weight out of the rear and moving it forward.
    Mine was actualy lighter than the design weight when launched as i used lighter material than specified, (duflex rather than durakore And outboards rather than Diesels) This may have an impact on the Hobbyhorsing problem as the boat was designed to be a heavyload carrying liveaboard cruiser, And carry weight it does very well!!!!!.
    If i could recommend you do one improvement at the build stage it is add a metre at the back! it will be a minimum of cost and labor at this stage and the alternative is where im at right now - A costly 6 weeks on the hardstand to make the modification. Im happy to pass my ph no on in a PM if you like as id be happy to pass on any help with your build in the future, My plans were the first one sold so i got all the problems and had to work close with the Crowther office to solve these.
    Philip - Hows it going This is Wazza here from Woy woy if you remember?
    Dont see you out there cruising, Do you still have your cat?
     
  12. Contorta
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    Contorta Junior Member

    Hi Hangtime & Phil,
    This design would be Bret's SP40. There was a considerable time lag between laying up the hulls and installing the keelson and bulkheads. I suspect sitting upside down with minimal support may have allowed the centre to 'settle'. I am situated inland so bulkheads 2,4,5,&6 don't get installed permanently until all the pieces get trucked to the coast. Bulkheads 3,7,8,&9 are installed in one hull and I intend to twin these in the other hull soon. I have already lengthened the stern 300mm for a gentler stern line and wider steps. Also I intend to install a diesel DC geny frwd of #6 along with a 48V battery bank and have electric drives in each hull aft. This should move a fair amount of weight to the centre. I hope this makes her quicker in stays but it may not improve the hobbyhorseing. Sharpen the bows, you say? Kind of thought that bluntness was different from most designs I'd seen. I appreciate all your input. Indecision is a big waste of time.
     
  13. catsketcher
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    catsketcher Senior Member

    Gday all

    Gary - Yeah Tony did build a Newick (at least the hulls) in the 90s
    Warren - great to hear from you. The kids are in school and uni. Deb and I are working and living at the top of Lake Mac. Ph 49465290. Still have Kankama and a couple more little cats. Going cruising again on Kankama in 2.5 years, this time with some money!

    Contorta - the settling is a bit of an issue. I am worried that the two hulls won't settle the same. Saying that there will not be that much of an issue if the hulls aren't exactly the same but it will make things harder for you. Try and support the hulls as well as you can. Make extra cradle supports and keep them true.

    Warren (Hangtime) and I built our boats at the same time and I got a lot out of talking to him. Make sure you get his email and start getting right into the ins and outs of the design. Some things you will agree with and some you won't but it will be hugely faster if you have others to bounce off. Warren and I (along with a team of others) formed a loose agglomeration of amateur boatbuilders who visited and helped each other. It is SO important to have contacts. In this age they can be virtual as well.

    I would seriously consider adding the extra metre Warren suggests. If I was in your shoes I would go "Oh no not extra work" but the SP 40 is a pretty fat boat and altering it now is so much easier than later. The big rig and tall deck makes for a high CG which may explain the hobby horsing. You also may like to ensure that all of your tankage is low and under floor in the middle. A smaller rig with a lighter mast section also will help.

    What stage are you up to? Building second hull?

    Cheers

    Phil

    Warren - give me a call. See lots of Red Ducs and think of your ride.
     
  14. Hangtime
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    Hangtime Junior Member

    Contorta
    I have several pics of the boat on facebook if you'd like to see what it looks like on the water, Look up Wazza Innes (if youre on FB of course) , There is a great story of what happened a few days ago in a lightening storm on there thats really good reading, Phil - I'll give you a ring tommorrow. Be good to catch up.
    The hobbyhorsing was a problem before the rig went on. I motored around for 2 years until i could afford a rig and sails and whenever i motored into a mild sea it would rock like a b#$ch, this tells me its a hull design problem.
    At all points of sail including pointing the boat excells, Downwind is exciting and the bows NEVER dig in.
    I love the boat and the lifestyle and dont want to ever do anything other than the cruising life!
     
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  15. Contorta
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    Contorta Junior Member

    Hi everyone,
    Warren, Linda Flewelling will ask Wazza Innes to link on FB as a friend. I would much like to see those pics.
    Please correct me if you think I'm wrong about this but I think as long as I keep the baseline to hull distance at station 9.75 in the bow 0.727 times the baseline to hull distance at station 0.0, stern, and the top of the bulkheads lined up with the design sheerline height I should be OK.
    Yes Phil both hulls are built but after doing more jacking and remeasuring I have less difference. 20mm low on the strb & port bow and 25mm low on the port stern. The design calls for heavy items,(water, genset, chainlocker) to be stored on the wingdeck fwd of #6 bulkhead. Do you think this raises the centre of gravity too much?
    Warren, if I copy the horizontal bow angle from the main hull of my Brown 25 it would translate to an additional 400mm to the cat bows and the bows would cease to be anywhere near plumb. I read somewhere that plumb bows are overrated anyway, more of a fashion fad than an advance at least on a cruising boat. The plumb bow does have an elegant soft sexy appeal to it though. Very much like a tall woman's leg.
    Did you guys opt for the fixed minikeel or the daggerboards? If you installed a horizontal wing (think stiff whale tail) on the bottom of the minikeel wouldn't it dampen hobbyhorsing? (The minikeel being strong enough of course)
     
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