Box? keel sailing hull

Discussion in 'Boat Design' started by lewisboats, Sep 20, 2007.

  1. kengrome
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    kengrome Senior Member

    Billy Atkin seems to have been motivated by the same arguments:

    http://www.boat-links.com/Atkinco/Sail/HeartsDesireII.html
     
  2. alan white
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    alan white Senior Member

    Yeah, that's it. I myself go back to that Atkins collection from time to time.
    A bit of recurve at the garboard, and it's just a wider than average shoal keel.

    A.
     
  3. lewisboats
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    lewisboats Obsessed Member

    So... disregarding the cabin and interior accomodations...if we took my existing (box keeled) hull and modified it to something like this there may be a decent compromise between excessive displacement, speed and possible standing headroom using the box keeled hull? Atkins design is nice but even I can see it is no Greyhound...more like a Bluetick hound on a hot and humid afternoon.

    Steve
     

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  4. alan white
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    alan white Senior Member

    The blade keel---- is this trailerable? Meaning, as a thing a couple could do alone at the ramp, in and out, within a half hour, etc.? The box keel looks like it might get you 18" below the water, 55" above, which is fine. But if trailering, no way to fold board up into the hull.
    why not bilge keels at this point?
     
  5. lewisboats
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    lewisboats Obsessed Member

    What are you...Psychic??? I had been thinking that bilge keels (I've always liked the idea) would be excellent at letting you ground on the level. The only reason I haven't said anything yet is that putting bilge keels on a hull in FreeShip is an excercise in patience...you have to build the keel along the centerline then work it to the right spot all by hand, rebuilding the hull in between. Takes a bunch of time to get right...which I haven't had to play with this past week or so.

    Steve.

    PS: The center keel wouldn't be all that hard to trailer...it is only about 17 inches deep (lowest point of hull to bottom of keel), maybe 20 with the pivoting keel protruding a bit.
     
  6. woodwind
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    woodwind Junior Member


    Alan,

    i couldn't disagree more on the bilge issue, having years of experience with both types of boats.

    I would rate having a deep (!!), not necessarily a large bilge a big, practical comfort and *safety* factor.

    a) While in theory you could make a boat completely watertight, in practise this is hardly ever the case. Even welded metal boats do have openings for cables, hatches, companionway, ventilation, etc.

    b) in rough conditions, especially on a small boat, the crew will carry lots of water down the companionway each time someone goes belowdecks.

    Having a flat bottomed boat without a bilge, even tiny amounts of fluids, like 1 or 2 litres will redistribute itself all along the inner hull, due to heeling from sailing, and due to violent movements in heavy sea.

    While with water this is merely an inconvenience, if the fluids in question happen to be diesel or motor oil, as can happen in any ship, the difference between the 2 designs would be a slight olefactory nuisance in the deep bilge boat, and a major damage (diesel soaked interior....) and security risk (slick floorboards, fire hazard) with the flat bottomed boat.


    After years of sailing modern boats, I now own a mid-sixties classical 35 ft sloop, and for all practical purposes the old, narrow and deep long keeled hull IMHO is superior in every single regard - except for speed when going downwind in a blow (or with a large kite). Talking cruising of course, not racing.

    I do like your 2nd revision of the boat - she looks fast.

    Just my 2 cents on bilges - I love mine! :)

    George
     
  7. alan white
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    alan white Senior Member

    I said "all hulls" once needed a bilge. Nowadays, SOME hulls do (offshore boats in particular)--------- but this is a trailerable boat.
    No disagreement. By the way, water finding its way below can certainly flow beneath the sole even if the sole is 3" above the bottom. It doesn't need more than an inch or two to carry normal water away to a shallow sump.
    And headroom, blessed headroom, is a comfort factor as well. To have to crouch when the hatch is necessarily closed tight in order to cook especially, but also to dress and undress foul weather gear, etc... well, it's a shame to be with a few short inches of a supremely more comfortable position.
    We should say, a "minimal" bilge is sometimes alright if it allows you to stand up straight and stretch.
    Steve's design, by the way, not mine.

    A.
     
  8. woodwind
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    woodwind Junior Member


    Alan,

    I must admit I kind of didn't grasp the size of the boat - somehow thought it to be a bit larger. Yes, lack of headroom can be terrible. Although when dressing/undressing foul weather gear, I have never managed (or attempted) to do that standing up - I don't like broken bones...;) Ok, there is, of course, rain...but still feels more comfortable sitting down.

    Would I trade off headroom vs. a good bilge? Possibly - mainly because a boat to me is a sailing machine first, a place to live in second. But obviously that is a question of personal preference.

    Steve,

    have you noticed that in the last design you posted there actually are elements from classic hulls reappearing? Namely the wineglass shaped cross section...:)

    If I would horizontally saw off everything below my bilge, it would almost look like that.

    Question: Does your software allow you to produce line plots rather than the shaded 3d model? I think the shape can be better visualized with the former...

    Happy sailing,

    George
     
  9. alan white
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    alan white Senior Member

    If you are accustomed to larger boats and offshore sailing, you will need more of a sailing machine. But since smaller inshore boats don't generally sail through gales at sea, the don't need to be designed as if they do.
    I have an open boat, and it is a very seaworthy design, but that's because it was never intended to sail offshore.
    Any boat I own is a sailing machine first too, but seaworthiness is a term that considers intended use. Inshore waters allow different itineraries, such as short sails with inexperienced crew. No gales at sea, but standing headroom is helpful and safer because when water does get rough, it's easier to keep one's balance when moving about if one can stand up fully.
    No boat should become incapacitated because of excessive tophamper. That's why the design that keeps the deck lower and still acheives headroom by elimination of the bilge is, in my view, a better design IF the hull iefficiency is not sacrificed in the bargain.
    At worst, an inshore crew will experience an odd storm and some water gets below and feet get wet. All they really need, to mimic the comfort of an offshore vessel, is a set of 3/8" plywood sections that drop into place and raise the floor level six inches. Would they go to the trouble of implementing this cheap and easy solution, knowing they might encounter wet conditions one day? That's the question, but let them have headroom in the meanwhile!
     
  10. alan white
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    alan white Senior Member

    There is an uncle... something to do with the heart... a problem... I see a doctor with a foreign-sounding name... does the uncle wear plaid shirts? I see a plaid shirt.

    A.
     
  11. woodwind
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    woodwind Junior Member

    Hm, I wouldn't define a *working* bilge as the measurement between the floorboards and the bottom of the boat. In order to function properly, a bilge has to have steep sides, and be reasonably deep. Only that way any fluid inside it can be retained at high heel angles and/or violent movement of the whole boat.

    The main probling with sloshing water is not the floor boards or the crew's feet, but the water (or diesel, etc) running 'up' the inside of the hull, to soak whatever ist there - bunk cushions, whatever you store there.

    I have had the nasty experience of a (chartered) 48 ft boat where the engine's oil filter broke, releasing about 6 litres of black engine oil into the non-existing bilge. We had to sail her back in rough conditions, against the wind. You won't believe what a total mess the inside was after that. Oil everywhere. I guess they had to rip half of the interior out afterwards.

    On my current boat, the bilge's bottom is about 80 cm (32 inches) below the floorboards, with near vertical sides for the bottom 2/3s. It contained a major diesel leak due to a failed solder joint on the tank very nicely - in fact we only noticed something was wrong when moored in the harbour due to the stink. Fortunately for the environment I hardly ever have the bilge pumps on automatic - this 40 yo wooden ship usually does not take more than a half-cup of water per day, and that through the propeller shaft bearing. ;)

    Happy sailing,

    George
     
  12. alan white
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    alan white Senior Member

    I think, George, that you are defining sailing through the lens of your offshore experience in big boats with diesel inboards, and if this dialogue were about offshore passages in large well-found and deep vessels, in other words, that 1% of boats that are involved in such enterprises, what you're saying would apply.
    The other 99% of all boats have design parameters too.
    Regarding the bilge-less boat with the oil filter leak---- the real design shortcoming wasn't the lack of bilge, but the single bilge that didn't seperate the engine compartment from the living quarters. But for the lack of a bulkhead, the damage to the interior would not have happened.
    One could also argue that the effect of having a deep bilge is that it makes it harder to determine where water is coming from (indeed, to know there's a problem in the first place).
    Not that I disagree with having a bilge just like, say, a deep full-keeler has. I am only saying inshore boats do not need bilges so much as in the olden days when wood planked boats leaked, and therefore they might benefit from exchanging the bilge for more headroom.
    Many have crossed oceans without bilges in any event, but that's not my point. This is about Steve's boat, it size, intended use, and the acceptable comprimises within the scope of that intended use.

    Alan
     
  13. woodwind
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    woodwind Junior Member

    Alan,

    is this the bilge wars? :) Who would have thought anybody could be passionate about bilges? But indeed, I kind of have gotten passionate about them, or rather that only after having sailed/owned a boat with a proper bilge I now understand what difference it makes compared to other, modern boats I have sailed.

    I understand that Steve's design has other constraints, and probably no intended inboard engine. So maybe this discussion would belong in another tread by itself....

    So what defines offshore sailing? Ocean crossing? I think that you narrow the field of boats that could benefit from a bilge a little too much. Of course, we are not talking about dingies here, right? So looking at any boat with a ballast keel and a closed cabin, each of those is capable to do more than harbour hopping or blasting around the local bay, and at least here in Europe, usually does so, too.

    Yes, the non-separation was a design flaw - on top of not having a real bilge. But the whole boat wasn't built with a lot of thought towards cruising capabilities or even safety, she was just fast.

    The latter, yes. So a bilge water alarm is a good idea with a deep bilge. The former -hmm I don't think so, unless the leak was within the bilge itself.

    Looking at some of your other posts I'd guess you are somewhere involved in yacht design professionally?

    I personally think that any cruising sailboat above 30 ft should have a proper bilge. But it appears that modern boats are introducing more and more characteristics directly from the racing front, with very dubious results for the average sailor.

    Among other things that has brought us things like extreme fin keels (that tend to fall off in cheaper productions), dinghy-like hulls that might be a little faster, but are much less forgiving in rough conditions, lightweight sandwich construction where just a fouled up mooring manouver can severly compromise the structure of the hull, open transoms that like to loose winch handles or crew members to the sea, flat bottomed forward hull sections that make beating upwind in a blow unnecessary hard both on the ship and the crew, and so on.

    But that is a much wider field, and, I am sure, one that has been discussed here before.
     
  14. alan white
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    alan white Senior Member

    George,

    Your bilge passion is duly noted. Let others consider pros and cons---- the food for thought has been brought to the table. I agree more than disagree with you, but what you and I value isn't as important as what each individual values, except to us.
    We've presented more facts by debate than by collaboration. But since I have no strong desire to be right, I'll let you have the last word if you like.

    A.
     

  15. woodwind
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    woodwind Junior Member

    Alan,

    as long as the debate is fruitful.... :) Looking at your own choice of boat, it appears that be both seem to lean towards classical designs, if not the underlying values that influence the design of any particular boat.

    Happy sailing,

    George
     
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