Why aren't sharpies/flat bottom yachts more common as offshore cruisers?

Discussion in 'Boat Design' started by SoonTBC, Jun 24, 2016.

  1. SoonTBC
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    SoonTBC New Member

    I have been doing some research on alternative cruising boats, and am starting to like the more outside the box cruisers like Bolger's AS39, Chris Morejohn's hogfish and hogfish maximus, Norwalk island sharpies and the like. From what I've read, they sound like pretty good boats. Generally pretty cheap, fast and easy to build, decent downwind performance, don't roll much at anchor, and the capability of extreme shoal draft. So why aren't they more common? Is it that they are too unusual for most people's likings or are there some serious issues with these types of boats?
     
  2. SoonTBC
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    SoonTBC New Member

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  3. rwatson
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    rwatson Senior Member

    There has been a bit of discussion on that in older threads.

    Seems opinions acknowledge ease of build and extra room, but for heavy weather you have potential problems - eg. Pounding in incoming waves, and stability side on to waves. With a flat bottom, you get the hull goign right over in sideways waves
     
  4. PAR
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    PAR Yacht Designer/Builder

    The problem with all flat bottoms, unless they have an unusual amount of rocker, is stability. It takes a bigass sharpie to get standing headroom and if you want to kill the stability curve on this hull form, just stick a standing headroom cabin on too small of one. If you do put enough rocker in the bottom, you pick up a huge amount of wetted surface and drag.

    A flat bottom boat isn't much easier than a V bottom (4 panels) or a 5 panel (flat bottom panel) build and there are many advantages to the multi chine approuch, fixing many of the issues of a flat bottom. Now a 15' jon boat is a pretty easy thing to assemble, compared to a V or 5 panel, but the actual hull build is a fairly small part of the complete project, once you get over the small day boat sizes. So, it's generally wiser to build a more efficient and stable hull form (V or multi chine) then save 5% - 10% of the build cost differences in a flat bottom.
     
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  5. upchurchmr
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    upchurchmr Senior Member

    When people get in trouble its mostly not due to good downwind performance.
    Its from poor upwind performance.

    All the reports I've seen on slab sided, flat bottomed, light weight boats are that they will not go to weather well. Same as the old square rigged tall ships. Many died on a lee shore, because they could not go to weather well.

    Not what I would want for a "safe" cruising boat.

    IMHO, they are ugly too.
     
  6. philSweet
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    philSweet Senior Member

    Compared to a production boat, they will have to be heavier because large flat panels are weak compared to compound curves. So they take more framing, which eats up even more space. And yes, they can pound terribly off shore, and are noisy at anchor. If you go by equal performance, they aren't much cheaper to build, and probably cost more to operate and maintain. But, they are within the ability of a lot more people to build in reasonable time. I happen to like HF Maximus a lot. But it is a 20 ton boat. Sharpie types, counter to popular notions, are not very good light boats. They are wonderful at carrying a load, though. If you are used to small boats, you have to get your head around the idea that the boat has to provide all of the righting moment. Crew weight doesn't do much on a couple's cruiser. With the wonderful little diesels we have now, the low-power designs don't make that much sense. You just don't design boats to sail well at 2 knots anymore.
     
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  7. SoonTBC
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    SoonTBC New Member

    Thanks for the replies, here are a few more questions. PAR said that putting a standing headroom cabin on a small sharpie without much rocker will kill the stability, but the nis 31 does that and has an AVS of 140 degrees. Not trying to challenge anyone's knowledge, but doesn't that contradict what PAR said? Upchurchmr, you commented on the upwind performance, but from what I've read about hogfish maximus, it has pretty decent performance. Can someone please clear this up for me?
     
  8. PAR
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    It's a lot more complex a set of subjects, than this venue permits describing easily. As to Kirby's "sharpie" designs, well they're not really sharpies and he's used most of the tricks in the book, to get accommodations and stability in these designs. For example, nearly 1/2 of the hull's freeboard is also used in cabin roof crown, which effectively does a couple of things, first is to hide the huge box like structure that would be there, if a conventional roof crown was employed and second to make the boat quite unstable when upside down. The hull is cleverly shaped and draws 18" with the board up, about 1/3rd of the ballast is in the board and in general Kirby is what his reputation suggests, but this isn't the general rule for flat bottom, sharpie type hulls. Hogfish Maximus uses some of the same shapes as the NIS series, though a lot more rocker and several other major differences, most way too subtle for the average person to notice.

    Simply put, you can design a flat bottom boat to take on deep water, but there's a big price to pay in terms of performance, compaired to boats of different hull configuration. It's easy to see once you run some comparative numbers on similar hulls (flat, V, multi chine and round bilge). It takes a lot of understanding to make a sharpie like hull do well and the typical changes you need to make, on a blue water version, usual turns them into something other than a sharpie, though the term sharpie, will sell more plans or boats, compaired to the flat bottom skiff like hull, that they actually become.

    Lastly, the hull being flat bottomed increases immersed volume (dramatically), which is why real sharpies are quite narrow and have modest rocker. There's no such thing as a small sharpie for this reason, though again, some will use the term anyway. Sharpies were used much like dories and in this role did very well. Half their displacement was in the fish hold, but if you take away this capacity to suit a yacht, then the qualities of both types disappear, so you either have a burdened down boat, to regain the qualities or a corky boat that's nothing like what the original variants were. Again, it's not as big an impact of the full scope on a 40' project, being a flat or V bottom (even multi chine), so the disadvantages and cost savings are difficult to quantify, when viewing the whole project. On a 40' yacht, the hull shell is what 10% of the total project effort, so your take you knocks when developing up the SOR and this dictates the hull form you'll employ, not the meager material and labor savings, that a flat bottom might bring to the table, comparatively.
     
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  9. CT249
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    CT249 Senior Member

    May I ask where the evidence is that HF has "pretty decent performance" upwind? Her owner writes that "the Hogfish Maximus is not a boat fast enough for racing in that her weak point is in going to weather she is a bit slower than needed to be competitive". I'm not attacking HF for that - in fact you've got to respect and trust an owner who is prepared to admit that his boat isn't perfect.

    Also what is "pretty decent performance"? What is "pretty decent" to one person could be dog slow to another and vice versa. There are even some people out there who have said that boats like the Bolger Martha Jane and Light Schooner are "fast", which is a pretty odd claim since they are rated much slower than middle-of-the-road 1970s cruiser/racers of similar length. Much as I like the Norwalk Islands and Bruce Kirby, the ratings we have for them down here indicate that they are slower than a normal local '80s cruiser/racer, and the ones I have raced against were distinctly slow upwind. I could try to give some PHRF numbers for comparison, but they would be rather vague.
     
  10. mydauphin
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    mydauphin Senior Member

    The problem is called flipping... IF you don't have a deep enough keel, you will get flipped, and like the poor turtle or catamaran, you won't get back up very easily. If you want to play in the big water, you have to be willing to take a tumble.
     
  11. gonzo
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    gonzo Senior Member

    That is not necessarily true. Lifeboats have no deep keel and are self-righting. Deep keel boats can capsize and roll over also.
     
  12. PAR
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    PAR Yacht Designer/Builder

    Gonzo caught it before I could reply. There are some advantages to shallow hulls in deep water, such as not tripping over their deep appendages, but generally it's a much more complex set of issues to homogenize than it would initially appear.
     

  13. gonzo
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    gonzo Senior Member

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