Reverse bows on cruising cats pros and cons

Discussion in 'Multihulls' started by DennisRB, Mar 1, 2013.

  1. DennisRB
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    DennisRB Senior Member

    This seems to be all the rage right now and I have to say it looks cool. How do reverse bows affect the performance of the boat? I guess there are 2 scenarios you need to look at. My thoughts.

    Imagine a 40 foot cat with plumb bows as a base example.

    1: Say you design that 40 foot cat with reverse bows with LOA still 40 foot. Compared to a plumb bow you are loosing buoyancy above the water line. But also loosing weight and windage up the front. So yeah it should be faster with less weight and windage.

    2: Instead of loosing a couple of feet of deck area and buoyancy at the bow, you then extend the bows a couple of feet at the waterline and fair the lines up to the top of the original stem. This would give more buoyancy and a longer water line for the minimum amount of weight. So in most conditions it will be faster as it has a longer water line and a better length to beam ratio by way of adding the minimum amount of weight.

    Nose diving. Which of these 3 cats would be have the most tendency to nose dive or pitch pole? I would say cat 2 would be the least likely with more waterline and extra buoyancy. Cat one has less buoyancy but the shape of the bows do not lend them selves to burying themselves as the reverse bow has the perfect shape for "cutting" its way back up. Once the deck of the plumb bow version goes under the deck will act kind of like a foil which will be hydrodynamically opposed to coming back up due to the weight and force of the water pressing down on it.

    Thoughts?
     
    Last edited: Mar 3, 2013
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  2. Submarine Tom

    Submarine Tom Previous Member

    Pictures?
     
  3. Doug Lord
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    Doug Lord Flight Ready

    Here is a cruising boat with reversed bow-has curved daggerboards too. Read what they say about it: http://www.catana.com/en/catana59/speed.html

    Speed

    With more than 26 years of experience and the help of several established firms of naval architects, the Catana drawing office has taken a fresh look at what makes the perfect catamaran.

    All this has culminated in the new Catana 59. A Catana with incredibly streamlined hulls, classically elegant, and offering astounding performance. The sail plan is borrowed from racing vessels, with a short mainsail that is easy to manage and a larger foresail. Moving away from the legendary daggerboards that made the Catana shipyard's name, this catamaran is fitted with revolutionary curved daggerboards, to create a hydrofoil effect. The result is an extremely safe and comfortable boat that achieves astonishing acceleration and an extraordinary cruising speed.
     

    Attached Files:

  4. warwick
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    warwick Senior Member

    Another part of the equation you would have to consider is the deck camber and edge.

    A plumb bow could be thought of as a neutral bow buoyancy wise, from what I read recently (Australia Sailing had an article a couple of months ago).
     
  5. jamez
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    jamez Senior Member

    Some of the older multis have extremely forward raked bows, presumably the thinking being as the bow was depressed the buoyancy would increase to compensate. A number of older designs here - I can think of a bunch of GBE's - have had their bows plumbed to address a lack of buoyancy forward. They still go over from time to time.

    Reverse bows can look cool and are no doubt functional on some boats eg. Gary Baigents Sid, A class etc.
    Yet, I do wonder how much of a fashion thing this is, with full bodied cruising boats and whether they actually benefit from having them to any great degree.

    If anyone has an older boat with a forward raked bow, that has had the bows plumbed or reversed I'd be interested in a report on the before and after.
     
  6. warwick
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    warwick Senior Member

    Thanks Jamez for your question as to reversing a forward raked bow back to plumb, as most input at present appears focus on moving the water line forward.
     
  7. Richard Woods
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    Richard Woods Woods Designs

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  8. Gary Baigent
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    Gary Baigent Senior Member

    Jim Young doesn't like vertical or ram bows purely because of the anchoring lowering and retrieving problem, fair enough, seems to be Richard's disagreement too ... but imo, there are important advantages with the reverse bow in the areas of sailing performance, more important than noisy/scratchy anchor problem (which occurs say a couple of minutes during your normal long sailing time) - and that is full waterline length for speed and the safety of not tripping/slowing when the bow(s) is/are driven down by sail power or burying into wave backs - the water is shedded quickly from the rounded and fine deck/s.
    I'll live with the anchoring problem, thanks.
     
  9. DennisRB
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    DennisRB Senior Member

    Thanks guys.

    Great article Richard. Seems you make a good argument against reverse and plumb bows for cruising, and its hard not to agree with that. I must say I thought I read most of your website years ago. Looks like I need to spend a few more hours reading some more of your articles. They are very informative.

    After spending last year cruising from the USA to Australia in a mono. I am looking forward to the day I build a high performance cruising cat to live on, which is my 5-7 year plan. My preference will be high speed with acceptable living areas and payload. Think the opposite of a lagoon. Something like an Oram 44C. Racing will be on the cards as will a lot of time spent sailing.

    I would have thought a plumb/reverse bow on a mono/tri would be very bad for anchoring, but on a cat which does not tend to sail at anchor, and the anchor lines originate from inbetween the hulls may not be an issue? I did see a few trees out in the ocean, presumed washed from rivers in floods. I think hitting one of these with a reverse bow at speed might scoop the tree up and lead to some nasty damage.
     
  10. Alik
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    Alik Senior Member

    The advantage of reverse bow is less pitching on steep waves, thus less speed loss. We have done simulations and yes it works, though the effect is more pronounced for slender demihulls and there is almost none for wider/heavier demihulls. As to practicality of such bows, I am not convinced is they are practical both for operation and build. It is more a fashion thing than a necessity.

    Recently, we have developed few powercats with such bows, the 12m one is now in build so will see how it works in reality.
    [​IMG]
    [​IMG]
     
  11. masalai
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    masalai masalai

    Hi Dennis,
    You may be a bit late in seeking one of Bob Oram's excellent designs, but he has "retired" - - Last known he is living at "River Head" -25.418762°S and 152.916599°E I built a 39C with approved modifications via Bob's drawing board, and I am mightily pleased with the performance, motoring on 2 x 900cc kubota diesel saildrives (Nanni) doing 2500rpm for 7 knots and with both running getting around 2 N Miles/litre and with about 80square meters of hitch-hiker sails should be a good tropical cruising boat. http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-138.html#post606997 & http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-138.html#post607395 - 'CNO' is now in Cairns - I drove it up solo daysailing and visiting places as I went, 450 odd litres for 910 N Miles...
     
  12. Richard Woods
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    Richard Woods Woods Designs

    I have just come back from racing on a 26ft monohull. The winds were rather higher than we had hoped, especially with two green crew on board. Getting back into our downwind berth was challenging for my skipper and me.

    It ended up with me saving the day by jumping off over the long overhanging bow just seconds before it would have run into the dock. I could not have done that with a reverse bow, we would have hit the dock hard for sure. They are not called "ram bows" without reason!

    I assume that you do not want a flat front on your reverse bow. So the deck HAS to be narrower and the buoyancy and interior space much reduced. Imagine a conventional overhanging bow. Then cut the bow back to a reverse bow. The only way to get the two hull sides to touch at the bow is to pull them together.

    As I have said many times, a day racing boat (whether 18ft or 72ft long) only needs to be designed for speed. Those who have different boats have extra design parameters that often will take precedence over speed.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  13. michael pierzga
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    michael pierzga Senior Member

    Form and function should dictate design.
    The stem handles anchors , mooring lines , downwind sails and humans . Plumb stems are inferior and you end up with junk hanging over the stem , an ugly, rust bleeding, ss stem chafe plate, you loose surface area on deck and volume inside the bowpulpit. Plumb bows on cruisers are a fashion statement .

    choose form and function. Its always the most elegant solution
     
  14. Corley
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    Corley epoxy coated

    I cant see the issue for cats that deploy their anchor from the centre or offset on the front beam with a bridle from the inside corners of the front beam. It's been a long time since I've seen a bow mounted anchor on a cat in Australia. Most screechers, spinnakers etc are set off a bow prod from the centre of the beam and most mooring cleats are some distance from the bow. Even picking up a mooring should be done from the centre of the front beam not from the bow of one of the hulls.
     
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  15. DennisRB
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    DennisRB Senior Member

    Micheal. Your points do apply to monohulls, but you obviously missed that this was about catamarans. I have always thought on a mono the best solution would be the smallest amount of rake needed to prevent the anchor damaging the hull on the way down. This changes a lot with a cat, since there are no anchors launched from the bow.

    "So the deck HAS to be narrower and the buoyancy and interior space much reduced."

    That would be true when applied to example 1 in my first post (shortening the deck with same water line). To me it would appear with example 2 all those points would be false (lengthening WL with reverse bow). There would be more interior space and more buoyancy with little extra cost when building? The deck would be the same size. The shear panels and hull would be longer at the bottom. Where the old stem was would now we opened up down low in hull allowing more room forward in the hulls.

    I have never had to jump from the bow of boat (yet ;) )when docking, but I agree this would be a bad idea if you had a reverse bow!
     
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