A Different Perspective on a Keel

Discussion in 'Sailboats' started by gfusch, Apr 15, 2016.

  1. gfusch
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    gfusch Cruising thru Retirement

    I am new to this list and have a discussion question/topic about a different perspective on keels and ballast. I built an overhead winch crane in my shop using two steel W I-beams that weigh 96 pounds per linear foot and will lift 10-tons. I have been reading other forums about wing keels but most of them are short fin keels with a wing. I am thinking that it might be interesting to mount a heavier wide (i.e., 18" - 20" wide) i-beam as a full wing keel that could offer a shoal draft as well as ballast. A thicker 20-22 foot long i-beam could weigh up to 250 or 300 pounds per foot, be very sturdy and offer a very stout stand for beaching and a ballast alternative to concrete.

    That being suggested, there are those that will likely argue about getting stuck in the mud or poor pointing with a full wing keel. I bring this too the list as a new member introducing a home boat building topic--this is definitely an off the wall concept for an offshore cruising boat. Your thoughts?
  2. upchurchmr
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    upchurchmr Senior Member

    Make a sketch, I can't understand the configuration you are proposing.
    Right off the bat it sounds like something with so much drag the boat will never be used.
  3. gggGuest
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    gggGuest ...

    Am I right in thinking you're talking about a wing keel with a large span, maybe approaching beam of boat?
    The 1987 Americas Cup was the time for that sort of thing, with the rule at the time mandating relatively modest draft but allowing all sorts of exotic attachments, this being an example.


    So yes, it can be made to work. But...

    Take a good look at that thing. They were, I think, cast and then machined to shape, and what a complex shape it is. The hydrodynamics of the design were right up there in rocket science territory and the whole affair was ferociously expensive, and also needed a lot of care in handling. imagine if you caught one of those wingtips on something solid. I believe every wing keel that's been made to work well has been extraordinarily complex in design and execution.

    So yes, with sufficient money and design expertise something on the same lines can be done today, but its a lot of trouble, and the consensus is there are easier and better solutions . I've also heard that if you sail in a soft mud area such keels anchor you comprehensively to the mud, and they are also a problem with kelp.
  4. Skyak
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    Skyak Senior Member

    As you get advice be sure to get to the numbers. I am pretty sure you are suggesting something 'simple' but lower performance than common practice.

    There are two functions -lowering the center of gravity, and resisting leeway. The cost for performance is drag and there are two big components that are easy to measure -aspect ratio (for induced drag) and surface area. Horizontal wings on keels are for the most part trying to reduce induced drag by effectively increasing aspect ratio. The rule to know here is that no matter how great your wing, it will not provide as much benefit as adding the same wing downward, so even with a great hydrodynamic design all you can achieve is shallower draft than a fin.

    I am no sure what you are proposing (sketch) but the characteristics of flat plates are well known, so if you propose to use an extrusion performance can be figured.
  5. PAR
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    PAR Yacht Designer/Builder

    The only real advantage of a wing keel is you can employ shallower draft with similar effectiveness as a deeper fin. Wing keels always have considerably more drag than deeper fins or similar area. You're not getting any reductions, just a shallower appendage, that acts much like a deeper one, abet with more drag, which is why it was employed on Australia II. They were willing to pay the drag penalty, knowing they got an appendage that met the appendage depth rule, but acted as if it was deeper. The wing keel was an effective rule beating approuch, but not so in terms of drag to a standard fin of similar area.

    Both concrete and steel beams are poor ballast materials. Concrete at best will be in the 150 pounds per cubic foot range and though steel is considerably heavier, as a solid hunk of material, much harder to shape well and has serious corrosion issues.

    As a rule, in ballasted shoal draft craft, you need as dense and as low a casting as you can develop. Using relatively light materials such as concrete, is self defeating in this regard. Additionally, using difficult to work materials, such as steel beams, just doesn't offer the necessary advantages of lead, which is easy to cast and work.
  6. Waterwitch
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    Waterwitch Senior Member

    I believe the OP is proposing the idea of bolting a large I beam to the bottom of a hull, with the web of the beam in a vertical orientation and the flange of the beam on a horizontal plane to act as a full length ballast keel.
  7. gonzo
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    gonzo Senior Member

    The first time I sailed a boat with a large wing keel, it surprised me how little it heaved compared to a traditional keel design. The horizontal surface acts as a large damper. It was a Sadler.
  8. gfusch
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    gfusch Cruising thru Retirement

    Thank you for the responses and I offered this as a discussion that I thought of one night and it has left me wondering. I agree that steel would need special treatment. My thought was to use a W-Beam/wide I-Beam as a full length keel. The weight of the I-Beam that I referenced was 96# per foot but one could get a W-Beam that is 300# per foot or one like I have and weld a thick plate on the bottom adding weight lower. The narrow 1"-3" web on an I-Beam should not cause additional resistance from the typical 6" wide lead keel. Thinking that the lower flange could act a an 18-20" tool width wing inspired my query.

    In my area, full keels are more popular that fin keels for rough weather cruising. Thoughts? Thank you, gfusch

    Attached Files:

  9. PAR
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    PAR Yacht Designer/Builder

    With an I beam up against the hull, mostly in the boundary layer, it's effectiveness as an appendage would be next to nothing.
  10. sharpii2
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    sharpii2 Senior Member

    My guess is that it would work as well as a long, shallow keel, which has a depth of one quarter flange width greater.

    It would work well as a leeway preventor, but would not provide the lift of a deeper, airfoil section fin keel. Your windward ability would reflect this fact, as the fin keel boats sail past you to windward.

    Your tacks will probably be more like glorified close reaches.

    That's on the negative side.

    On the positive side, it would add great strength to the hull, and would be quite durable, as long as it's protected from corrosion.

    It would also be very likely to provide much better roll dampening than a shorter, deeper fin keel.

    And, yes, you would be able to sail to windward, if you have sufficient keel area to sail area and you have proper alignment of the the Center of Area (CA) of the sails, and the Center of Lateral Area (CLA) of the "I" beam keel.

    The effective CLA of the "I" Beam is likely to be about 3/8 its length from the leading edge.

    A lot of these factors are dependent on hull and rig design.

    For instance, if the hull is initially tender and has a tall rig, The CA may have to be moved forward of the CLA by as much as 20% of the Length Water Line (LWL).

    If the hull is stiff with hard bilges, and has a short rig, such as a ketch or Schooner, the CA will be closer to The CLA.

    Best to make a scale model and test it.
    Last edited: Apr 18, 2016
  11. gfusch
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    gfusch Cruising thru Retirement


    Thank you for your insight on the pros and cons of using an wide I-Beam (W-Beam) for a keel. My thoughts were that with a 20-22" hight I-Beam/W-B weighing 200-300# per linear foot plus another 6" of wood above the keel before the frames and floors, the draft could be just a little over 4' and provide ballast, strength, a solid foot for beaching (avoiding the cost of haul outs), and some protection against hitting rocks/solid objects (which I hope not to experience).

    Do you think that the I-beam would be better or worse for tacking than a full keel with the same height/depth?

    My thoughts were that the wide I-Beam (20-22" high, 20-22" wide) could be about the same as a full keel at the same depth. However, I may be missing something such as the straight thin web (2-3" thick) versus a curved full keel with a thickness of 6-8" in places. I also may be missing the impact of the wing (base of the I-Beam/W-Beam) and welcome input from others (good, bad, or ugly).

    Thank you,

  12. PAR
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    PAR Yacht Designer/Builder

    No, an appropriately shaped fin of the same general dimensions will easily outperform the I beam approuch, hydrodynamically. If this fin also incorporated a lead shoe, as ballast, you have better impact protection, as it absorbs energy much better than steel. It also could be shaped to permit standing on it. What boat (make, model and year) would this new appendage be going on?
  13. gfusch
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    gfusch Cruising thru Retirement


    Thank you for the feedback. There are a lot of different and good perspectives out there. My perspective comes from having sailed with both fin keels and full keels in rough weather, I would never take a fin keel boat offshore for extended cruises. That being said, there are a lot of people that have enjoyed successful cruises off shore with fin keels.

    I will share that although you made some good points for a fin keel, I hope to never be in a position to have to stand on my keel. :)

    My post does not relate to any particular boat plan and was just a query. I currently have a 40 LOD Spray modified replica with a full keel (Gitane des Mers) that I sail as well as several projects in my shop.

    I will be building a smaller easier boat to handle offshore in the Pacific as I cruise through retirement. I like the tracking and stability of a full keel for rough weather sailing. I do not expect to be entering or winning any races.

    What type of boat am I planning: perhaps a Colin Archer type 32-36 LOD ketch or V-bottom schooner with a heavy full keel (aging often requires one to scale down boat and sail size). I am currently exploring the options for my retirement boat.

    For comparison, I am curious how a W-beam may perform compared to a full keel with the same depth and weight. The wing on a W-Beam (wide I-Beam) could be 20-22" wide for perhaps 20' in length with a 2-3" thick web versus a 6-8" thick full keel keel. I suspect that there will be more bad and ugly issues using a W-beam than good but wanted to ask.
  14. PAR
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    PAR Yacht Designer/Builder

    So, you're looking to decrease the sailing ability of a built down style of hull form, which is limited in it's abilities, because of it's shape choices?

    Your terms "full keel" and possibly how they relate to a fin need to be refined. The hull form examples you've listed have a lot of wetted surface associated with them, which limits what they can do, particularly in terms of quickness in maneuvering, pointing ability and of course speed potential. For the most part, these are antique shapes, long since replaced with more refined ones. It's a bit like saying I wouldn't go on the interstate without a '53 Buick under me.

    Well, the '53 Buick will have a nice soft ride and is built like a tank, but it's also slow, handles poorly, gets lousy gas mileage and generally is a mere shadow, of what's currently possible in this venue. What can also be said about the beloved '53 Buick metaphor is that it hasn't any seatbelts, a full metal dashboard to bounce your head off of in a crash, no antilock brakes (in fact crappy drums to stop this monolithic beast) and generally doesn't have any of the standard conveniences we now take for granted in modern cars.

    The same is true of yachts. Yeah, there's something about an old pilot cutter that's charming, but once the charm wears off, you're still stuck with a slug of a boat. A modern cutter of similar dimensions will sail rings around it in every regard. It will get away from the dock in lighter air, it will point higher, turn crisper, go faster and be easier to handle too, possibly at the push of a button. Not wanting to go to sea in anything but a built down hull is pretty subjective, especially considering off all the yachts that'll take to sea this year, a small fraction will be built down, while all the rest are fin keelers.

    As to the I beam idea, well you can ignore the hydrodynamics and physics aspects or belly up to reality. In terms of a built down hull benefiting, well you can't really "improve" these hull forms, without taking a chainsaw to their undersides, so an I beam isn't going to hurt much. This said, most built downs have a fair bit of "drag" associated to the keel profile and an I beam would just present a bigger, wider and much more resistance generating appendage. Now, if you cut the deadwood and mounted the I beam parallel to the LWL, you'd decrease much of this (until the boat pitches), but again it'll still make a lot of resistance. An appendage operates in more than the flow moving aft environment. Flow also goes up and down it's length and depth. Picture this I beam plunging down, as the boat climbs over a swell. Now picture the opposite, the boat is surging forward and up. How much resistance do you think the long flat blade of the lower flange is going to make as it tries to carry half the ocean with it on the upward acceleration element of the dynamic? Simply put a foil, be this a shallow, low aspect one or a deep fin will "penetrate" the flow, regardless of the direction it's coming, making for less resistance.

    Look you seem married to the idea of doing something to the bottom of a well refined (if antiquated) hull form, so go for it. Personally, I'd probably consider a model first, as it's cheaper to return this back to it's original configuration, than full size.

  15. JSL
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    JSL Senior Member

    I have done this 'I' beam or 'WF' ballast keel idea on larger (75' to 140') steel fishboats to improve stability but it is closed in with plates each side to keep it 'clean'. In one case ballast was fitted in the voids and hull internal ballast was removed thereby lowering the VCG
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