designing a boat that doesnt broach

Discussion in 'Boat Design' started by nzboy, Apr 16, 2013.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    The double ender would probably be less likely to broach, but more likely to tip over if it did, all else being equal, imo. Going in through barred entrances is problematical in boats that don't have the speed to stay with the wave train, I recall an old timer telling me that when he traversed a bar in a slow displacement launch, he would be constantly looking behind him to watch for a big swell or set looming up, and turn the boat immediately 180 degrees if he sensed trouble, sometimes it was three steps forward and two steps back, and took a while to clear the bar. But that is how he managed it. Needless to stay a boat that responded well to the helm would help, too slow could have put him broadside to a break.
     
  2. MikeJohns
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    MikeJohns Senior Member

    I thought there might be some interest in the long keel, deep forefoot as a broach resistant design. Marchaj was always bemoaning that hard won knowledge of out forefathers was replaced by fashion and fad too often. I've even heard yacht designers propose that a deep forefoot would induce a broach from nothing more than a gut feeling because it differs so much from current trends. But this is contrary to seaworthy design evolution and contrary to wave tank model testing.


    Pete Goss a fairly famous sailor and a racer of ULDB mono and multihulls built a Cornish lugger and sailed her to Australia. He was surprised how docile the vessel was to handle downwind in heavy seas.

    look at the forefoot and then look at the video in the southern ocean.

    http://lloydimagesgallery.photoshel...-of-Mystery/G0000L8n7M6rbfqM/I0000UWgBfiGzYFI

    http://www.youtube.com/watch?v=t1sq-mgnO6k

    Note that although this is a double ender, transom types are just as shure footed. One downside of a double ender is if they are too narrow and angle aft they tend to invite a following wave aboard ( prone to being pooped) the transom improves this as it adds a lot of reserve buoyancy aft. A lot of double enders are so built in timber because it's a stronger way to build a boat than adopting a transom.
     
  3. JSL
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    JSL Senior Member

    Displacement hulls don't 'surf' well. Planing hulls can be better unless they have the 'double wedge' underwater shape and then watch out. Especially if a large full length keel is fitted.
    During a north Pacific gale on a 64' steel cruising ketch we towed a 'ball' of 1 1/2" line (like a drogue) and it steadied the boat very nicely while surfing up to 14 knots in 30' swells.
     
  4. MLC
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    MLC Junior Member

    I would guess that is the case in trawlers, seiners, crabbers, or most other types of vessels. The old double end trollers that I was speaking of did not have any heavy deck gear to pack around, so they might have been able get away with the smaller water-plane since their center of gravity was relatively low. But then again that is just my speculation.

    It does make sense that a deep forefoot and long keel could help the situation since the greater the depth, the smaller the effect the waves should have on the water flow.

    A sea-anchor like device might be a winning idea to reduce broaching, provided that it doesn't fly out of the water at the critical moment, end up in the prop, or cause anything else unpleasant. Towing such a device should not be a big issue for a trawler.
     
  5. JosephT
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    JosephT Senior Member

    I've always been impressed with the varous coast guards around the world. They do a good job overall teaching anti-broach techniques. Here's a video of what NOT to do.

    https://www.youtube.com/watch?v=knz51leymyc
     
  6. MikeJohns
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    MikeJohns Senior Member

    . I have a 45 footer medium displacment sailboat that drives like a car when surfing and we have clocked 15 knots for several minutes in heavy weather on the faces of large waves. The faster it goes the more control you get.

    I also have a 40 ton 65' steel ketch that is very hard to get to surf since the waves just don't get quite big enough for it to get the momentum up.
     
  7. micah719
    Joined: Jul 2012
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    micah719 Plotting Dreamer

    Some junks and sampans have a freeflooding well at the stern, the idea being that the sudden increase in stern ballast just at the right time slows the stern. I'm playing around with the idea and thought about an added bonus: when that water flows out again, direct it through vents aimed at the rudder, perhaps it might contribute to rudder bite just at that moment when you need it most, when the flow over the rudder is disturbed and the attitude of the boat is critical.

    The junk hullform is ideal...windage at the stern, daggerboard forward: left alone, the crew cowers below deck with their buckets while the boat lies head to wind. In case one has to run, the stern well helps, along with the versatile rig; one can show a bit of sail forward or aft, depending on what is needed.

    Another anti broach solution I want to have available is a JSD. The modification I'd make for bar crossings would be a float at the end to prevent the weight (not an anchor...) sinking to the bottom.

    However, if there were any sensible way of avoiding a bar crossing or being in danger of a broach, I'd take it.

    The stern well would come in handy for a bait well or live holding tank when things aren't so bumpy. Or how about a seawater jacuzzi?
     

  8. jonr
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    jonr Senior Member

    A drogue to a) resist accelerating down the face of a wave and b) help maintain direction makes sense to me for any boat that can't power faster than the waves.
     
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