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Thread: Wavepiercing Bows on Catamarans

  1. #41
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    Default Re: Wavepiercing Bows on Catamarans

    I made a thread on reverse bows on boatdesign.net which went for 13 pages. In short its a cheap and effective way to increase waterline length with the least weight and windage. But this does not come without some negatives such as a wetter boat, docking difficulties, possible difficulties with snagging anchor rodes, more marina fees without much extra space etc etc.

    http://www.boatdesign.net/forums/mul...ons-46412.html

  2. #42
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    Default Sailing Machines.com

    Quote Originally Posted by sailingmachines View Post
    Hello, Im Doug Prince (President and Founder of sailingmachines.com)
    I was involved w/ the Victorinox Project- from the design to the final delivery... Even had her up to 23knts... what do you need to know???
    Strange that this fellow offered to contribute, then never did,...only one post??

  3. #43
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    Default Re: Wavepiercing Bows on Journey 46 LR

    Quote Originally Posted by brian eiland View Post
    It will be interesting to see how these bows work...in heavy conditions.

    http://www.multihulls4us.com/forums/...3&postcount=46
    Haven't seen any full size test/reports on how these bows worked out?

    Overall, the vessel is really nicely finished out. Hope they make a go of it in this really tough boat market.

  4. #44
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    Default Pacific Harmony bow change

    Big power cat had a bit of a change in bow shape since originally launched.
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    Last edited by brian eiland; 17th December 2013 at 02:28 PM.

  5. #45

    Default Re: Wavepiercing Bows on Journey 46 LR

    Quote Originally Posted by brian eiland View Post
    Haven't seen any full size test/reports on how these bows worked out?

    Overall, the vessel is really nicely finished out. Hope they make a go of it in this really tough boat market.
    Can't work out why a long range cruiser needs 500+ hp, or why at 47ft and only 18ft wide has a loaded displacement of a whopping 17 ton with a fuel load of only 2 tons.

  6. #46
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    Default Re: Wavepiercing Bows on Catamarans

    Gregor Tarjan has a discussion on the subject at the aeroyacht web site.

    http://www.aeroyacht.com/catamaran-l...piercing-bows/

    Probably a good read for the non-engineers among us.

    Marshall
    "People sail for fun and no one has yet convinced me that it's more fun to go slow than it is to go fast." -- Dick Newick

  7. #47

    Default Re: Wavepiercing Bows on Catamarans

    NEEL Trimarans have incorporated this design element in their NEEL 45. There is a video of the 45 sailing in a moderate chop both at their website and a different video on youtube. It is a short segment from SAIL Magazine with several interior shots and a few seconds of it sailing.


    It should be noted that Gregor Tarjan is the NEEL rep in the states so certainly is a fan of wave piercing bows.

    http://www.neel-trimarans.com/nos-tr...eel-45/videos/

    https://www.youtube.com/watch?v=oydcwPqXDxY

  8. #48
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    Default Re: Wavepiercing Bows on Catamarans

    "Wavepiercing Bow" is perhaps the wrong name,...or wrong connotation. Yes, they do pierce the wave, but its not as though they are there to pierce thru the wave. There are better bow shapes for this 'piercing action'.

    These 'bulb type bows' were originally developed for tanker ships to reduce the size of the bow wave that built up at their front. It was felt that this would make it easier to push thru the water rather than 'climbing' their own bow wave. They had to be shaped and sized for a specific length, and hull speed, of each singular vessel to be most effective.

    What I was most attracted to about them was if properly shaped they would really cut the height of the bow wave created by the vessel virtually in half. It would lessen that water that tried to climb up the bows and get blown back over us on the decks, etc.

    Couple of problems on sailing craft though.
    1) First off we are often lifting our bows in and out of the water much more often than a long hull-speed tanker/freighter, so effectiveness can be marginalized.
    2) Secondly, particular attention must be paid to the shape of the bottom of this 'bulb bow' or it will slam the water upon re-entry in any kind of seaway.
    3) And thirdly, our sailing ships are very often not 'steady-state', constant-velocity machines, so designing to any particular speed range is marginalized.

  9. #49
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    Default Re: Wavepiercing Bows on Catamarans

    Brian,

    Not being a marine architect or engineer, I am not sure about your post, or where you really want to go with it. The bulb on the ships does improve the flow of water and therefore the size of the bow wave on a displacement ship, however I believe the speed of the ship helps determine the efficiency of it. Not having the scientific background to fully understand it, my guess the "bulb" is most effective on displacement hulls.

    My rudimentary guess is that most modern multihulls, while not planing, probably do not "displace" enough water or go fast enough to make a "bulb" work efficiently, or are already efficient enough. I am sure better minds than mine have probably worked on this issue for recreational sailing craft. The "wave piercing" hulls of today's modern catamarans and tri's are probably somewhat of a "hybrid" or evolution of the bulb in that they get the hull "out in front."



    I do think that some of these fast ferries might have a protrusion below the water line. It appears the Morrelli & Melvin Cabo 100 power cat might have one as well, though slightly above the water. http://www.morrellimelvin.com/cabopowercat/

    I admit, I am way out of my field in this discussion, but it is snowing out, Searenity was hauled yesterday and is on the hard for the winter, and I didn't have much else to do!

    Marshall
    "People sail for fun and no one has yet convinced me that it's more fun to go slow than it is to go fast." -- Dick Newick

  10. #50
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    Default Re: Wavepiercing Bows on Catamarans

    Marshall,

    Not sure that the traditional wave piercing bows are in vogue any more.

    Crowther seemed to start the trend and moved away from them.

    The fast ferry pictured seems just to be using the techinique to increase waterline length.

    Bob Oram before he retired desgined several powerboats with what I think he called called axe blade entry similar the recent M& M and Tarjay cats.

    Picture on left should not be there and could not be deleted , by your friendly Mod.
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  11. #51
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    Default Re: Wavepiercing Bows on Catamarans

    Another Oram axe, the Upolo 10m powercat.
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  12. #52
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    Default Re: Wavepiercing Bows on Catamarans

    Downunder,

    Interesting.

    Gregor Tarjan's Alpha 42 hull.

    Marshall
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    "People sail for fun and no one has yet convinced me that it's more fun to go slow than it is to go fast." -- Dick Newick

  13. #53
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    Default Re: Wavepiercing Bows on Catamarans

    Quote Originally Posted by searenitysail View Post
    Downunder,

    Interesting.

    Gregor Tarjan's Alpha 42 hull.

    Marshall
    Clearly this is a fashion statement similar to curved boards on the catana.

  14. #54
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    Default Re: Wavepiercing Bows on Catamarans

    I think its more than a fashion statement as clearly it works as a means of both maximizing WL and progressive buoyancy to bows on both power and sail.

    M7M have been using the concept for a while.
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  15. #55
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    Default Re: Wavepiercing Bows on Catamarans

    Check this one out on M& M site

    http://www.morrellimelvin.com/agility/gallery.html
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  16. #56
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    Default Re: Wavepiercing Bows on Catamarans

    Quote Originally Posted by downunder View Post
    Hmmmm . . . looks pretty. But impractical.

    How would the skipper have proper visibility? Where could you park it? Marinas aren't built for that sort of boat.

    Mike
    Nothing works on an old boat, except the skipper.

  17. #57
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    Default Re: Wavepiercing Bows on Catamarans

    Quote Originally Posted by dennisail View Post
    Clearly this is a fashion statement similar to curved boards on the catana.
    Somehow I think this concept in hull design has gone beyond a fashion statement!

    "People sail for fun and no one has yet convinced me that it's more fun to go slow than it is to go fast." -- Dick Newick

  18. #58

    Default Re: Wavepiercing Bows on Catamarans

    Quote Originally Posted by dmmbruce View Post
    Hmmmm . . . looks pretty. But impractical.

    How would the skipper have proper visibility? Where could you park it? Marinas aren't built for that sort of boat.

    Mike

    Visibility has always been a concern and there are ways to address that problem. Just yesterday I noticed "wireless back up cameras" on sale for $45. I have used one of these on my Vixen motorhome and I think that there would be an application for the same device on the bows of a boat that has limited visibility to the helmsman.

    One could simply hard wire into the nav lights and have two little screens at the helm to monitor clearances to the dock.

  19. #59
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    Default Re: Wavepiercing Bows on Catamarans

    Quote Originally Posted by dmmbruce View Post
    Hmmmm . . . looks pretty. But impractical.

    How would the skipper have proper visibility? Where could you park it? Marinas aren't built for that sort of boat.

    Mike
    I make no comment on its practicalities or my views just drawing the reference. Don't think it has been built yet.

    Anchoring could pose bigger issues that marinas. where dollars solve most.

    Cheers

  20. #60
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    Default Bulb bows vs Wave Piercing bows

    In the first place we should differentiate bulb bows from wave piercing bows.


    Bulb Bows
    As I said before bulb bows really originated on ocean tankers to try and cut down on the size of the bow wave they would generate without the bulb. This was thought to create a little increase in their efficiency to move at speed. It was found that the bulb needed to be designed in size and shape to fit a narrow speed range of the particular ship, or they could be counter productive.

    Here is a good explanation of the bulb bow.
    http://en.wikipedia.org/wiki/Bulbous_bow

    Bulb bows are NOT really wave piercing bows. Lock Crowther never did a wave piercing bow to my recollection. He did do some small bulb bows in the hopes that they might help reduce pitching motions, and likely to add a little more buoyancy to his newer, slimmer bow designs. I believe they were referred to as 'tulip bows', ...shaped like a tulip.




    Wave Piercing Bows
    These bows are a best attempt to punch straight thru a wave rather than have the bow get displaced in an upward motion. But on sailing boats (particularly catamarans) we all realize that we need SOME buoyancy in our bows to prevent burying them when off the wind (sails driving the bows down).

    NACRA catamarans was really a pioneer here. (do you remember these?) They were the first (I believe) to have a plumb bow, and in addition a deck surface that was smaller in area than the waterline plane. In other words the bows of their hulls were more narrow at deck level than at the waterline. This allowed then to retain some needed buoyancy in their bows, but when the whole hull got pressed under upon fast sailing off the wind, the smaller deck area would not contribute as much downward force. Hobie cats and Prindle cats, on the contrary had much bigger deck area that would contribute more down force on the bows upon 'stuffing'

    http://www.nacra17class.com/history/
    NACRA cats (images)




    Reverse Bows
    In my opinion they are just another evolutionary step to create the smaller deck area even further aft than was the case with NACRA. They make sense on RACING boats.

    But I have yet to justify there feasibility on cruising boats. Who wants to try and navigated those slim little bows in docking situations, fending off another vessel, dock-line handling, anchoring retrieval situations, or handling a sea anchor parachute, etc ? How often is a cruising cat driven that hard that she needs these reverse bows?? To me they are just a 'fashion statement of the times'.

    Brian
    Last edited by brian eiland; 18th December 2013 at 10:12 PM.

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