It's time to cut the bottom of the hull for the dagger boards. Should I ? is the performance worth the holes. I'm not opposed to putting in a pie shaped center board if it's better. Any idea as to placement of pivot point if I do the center board. Thanks everyone.
Dagger and centerboards work about the same and offer similar results. Centerboards require a longer case, but can bounce over a bottom strike. Well designed, appropriately canted and toed daggers can outperform a centerboard, but need two cases and they have to be raised and deployed on each tack, which isn't necessary on a centerboard. In short they have good and bad things to consider.
If you're a novice sailor, just build to the plans. These boats don't have the performance envelop to take much advantage of fancy foil sections, canting duel daggers and all that. Personally I prefer centerboards, because they're simple, are less inclined to damage and can serve as a depth sounder of sort.
If changing to a single centerboard, they are some design considerations other than placement that should be examined. Placement should be pretty much with the boards center of area (CA) in the same relative location as the daggers in the stock plan. Because the centerboard rotates, instead of pulls straight up, the pivoting action might need the centerboard to be a tad farther forward than the daggers. What I do on this conversion is find out what the "lead" is on the daggerboard setup and try to nail this percentage of the LWL at 3/4's down on the centerboard's CA. What this permits is adjustments so light and heavy air settings can be used on the centerboard, that will help the boat balance. All the way down on very light air, 3/4's down in most instances and maybe 1/2 down on very heavy air days.
Notice I use an "over center" approuch to the board hoist arrangement. I find this permits more of the board to remain in the boat, helping with leverage. There are lots of ways to do this, though getting one that works every time takes some screwed up stuff, before you learn.
The pivot arrangement can mean the difference in an easy to retrieve and a difficult to hoist board. All my centerboards now employ a self contained pivot mechanism. This means no pivot pin hole to leak and the board and it's pivot assembly is lowered or removed from the case as a unit, making repairs and maintenance much easier, even if this is done in the water.
This is a typical arrangement on one of my centerboard designs. There's a lot of information here so look it over. This shows the conventional pivot pin arrangement and the updated version.
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attachment=1628]
This shows the pin arrangement I now use. It does require some metal fabrication, but is easy to make. The tabs at the top land on the top of the case, where I usually have at least a 1x2 running fore and aft to support the top edge. The board has this assembly attached, before getting inserted into the case.
I haven't figured out how to get rid of the extra text that is displayed after a post is edited, maybe Frank can help.
Thanks Paul. had to do a double read but i get it. Is any of it really necessary on this boat? I like the open interior but now I don't think the case would bother me, maybe a small folding table top would be nice. I'll spend some over nights but i don't think a second person will be there. Should it be a vertical board or does a pie shape also work, how deep should it go. Thanks.
(08-29-2017, 06:01 PM)bill s hunt Wrote: [ -> ]Thanks Paul. had to do a double read but i get it. Is any of it really necessary on this boat? I like the open interior but now I don't think the case would bother me, maybe a small folding table top would be nice. I'll spend some over nights but i don't think a second person will be there. Should it be a vertical board or does a pie shape also work, how deep should it go. Thanks.
not sure but i think there was an old thread here about wing keels on this boat instead of the daggerboards.
that would preserve the interior space, but paul would be the guy to tell you if they'd work
The PC is a fat little boat and was intended to be a sort of quick build "cat boat". The Cape Cod Cat model is a difficult model to get "right" and the PC doesn't really, no offense intended to owners, builders or the Stevenson's. Making a short, fat boat sail well is tough for the best of us. The Stevensons intended to kiss off some sailing ability and performance, in order to provide more interior volume, which this design does well, compaired to the Weekender. Given her keel, displacement, sail area, wetted surface, Cp, rig and other design parameters, she's just limited in what you can expect. So, in this regard, yep Bill, daggers and centerboards aren't going to help as much as you might think, without other additional, some wholesale changes.
She could benefit from a revised set of appendages, though her wetted surface and small rig, will not be able to take much advantage of it. The revised appendages would permit her to maneuver more crisply and accelerate slightly better, but these generally aren't things that most owners of a PC are all that worried about, or they'd have selected another design to begin with.
No Bob, I think this is a new thread that Bill has brought up. I vaguely remember a tongue in cheek set of remarks (mine of course) about putting foils on a Weekender, some years ago. I wasn't terribly serious, though with enough sail area (double?), several modifications and a really serious weight lightening program, you could get one to "fly" on foils.
Lastly, there's no such thing as daggers or centerboards being better than each other. There's good and bad things about both arrangements. Daggers are reserved mostly for very small craft where the case footprint is minimized and for racers, where every ounce of drag is reduced. Centerboards are much more common, mostly because they can do more, are handier and easier to live with. Which is a matter of personal preference and your needs. Twin daggers can save some interior space in the center of the boat, but tend to sacrifice it along the sides. If it was me, I'd go with a centerboard and hack off most of the deadwood assembly, which doesn't help performance and maneuverability at all, but this is a decision you need to make.
So, Paul, I am building a boat with bilge boards that are quite substantial as you know. Am I going to have to lift one or the other of them each time I tack? I thought that they would work quite a bit like twin keels such as the English are fond of. If not then I am going to have to design in a method to lift the keels that I had not considered.
Al
Typically, you raise the windward board and lower the "new" leeward board as you tack, but you don't have to. You can leave both down and just accept the additional drag the extra board and slot creates. The PC isn't a performance boat, so there's no real need to "tack" the boards, but she'll be ever so slightly faster, particularly in light wind strengths, if you do. The only reason I can see for twin daggers on a PC is to open up the interior a bit, moving the cases outboard in the process. On a boat like this, I consider this a bit of a contrivance and build complication. These are simply built boats, so any additional structure that doesn't really make much of an impact seems fruitless, in my way of looking at stuff.
If you'd like I can design a centerboard, that you can raise and lower as desired, one that will bounce over any bottom strikes you might encounter and still leave the interior of the boat free of a big case. Several of my smaller designs incorporate this feature and there's a few different ways to do it. One of the most common and one that several small boat designers have previously employed (like Phil Bolger) is to offset the case a few inches to one side, so it's hidden under a cabinet or in this case, part of a raised V berth. This leaves the center of the boat open and the case is out of sight. Another way is to partly or wholly hide the case, in the deadwood assembly. This makes the cabin completely (or nearly so) free of the case.
As you can see by the above drawing, I like to lightly ballast the board, so it can sink with authority, requiring only an "uphaul" tackle to lift it. It sinks all by itself and the last one I did (earlier this summer) I used lead bird shot, mixed with epoxy and poured into a hole cut in the bottom of the centerboard. No melting lead, no burned wood, just a neat and easy way to add weight fast and it can be formed to fit nicely. It was similar to the one above, except the weight formed part of the lower leading edge and the bottom most tip, so if it hits the bottom or an obnoxious mermaid, the board isn't easily damaged and the lead is easily repaired (just hammer it back into shape and add some putty). This is one of the nice things about using lead. First it's really dense, but it's also easy to beat into shapes you want and most importantly of all, it absorbs impact loads and disperses this energy across a large area quickly, saving the board itself from major damage. I've fixed big ass keels and bulbs on fins (5,000 pounders) with just a hammer and some putty for years.
Twin keels (what's usually called bilge keels) aren't the same as twin daggerboards. Boards are retractable and typically built fairly light. Bilge keels are keels, built to accept the weight of the boat, as it stands on a mudflat after the tide as left her high and dry. These are built much stouter, as you might imagine and usually don't retract. This might be a route for you if you'd like, but designing good working bilge keels is even harder than twin daggers. They usually cant inward at the leading edge a bit. They also need to be sized and positioned to keep the draft low, yet offer enough lateral area to prevent leeward skidding. With bilge keels, you wouldn't need, nor would it be desirable to have the bulk of the main, centerline keel assembly, so this would be removed or simply not installed. No need for the additional drag of the third keel. The cutwater can remain, for the look and a simple 1x4 batten down the centerline, outside the boat would replace the reinforcement lost by removing the stock deadwood.
So I do plan on some of the keel mods, I'm not really looking for speed gains just good performance for what the boat is. Do I need daggers or a centerboard at all? Does the chine provide enough lateral resistance and save me the hole cutting. I do plan on beaching a fair amount (almost always sand) so if I do a centerboard it does have to swing up. Any pocket cruiser guy's out there share some more stories.Thanks
The hull sides do offer some lateral area, but not enough. Chine runners are an option, which will permit windward efforts, but no substitute for real appendages. The PC's bottom rocker isn't ideally shaped for very effective chine runners. If you beach her a lot, bilge keels are the way to go, though certainly plenty of folks use daggers and centerboards the same way, with few issues. The PC's flat bottom will permit easy beaching, especially if the deadwood assembly is dramatically cut down and replaced with some sort of retractable appendage(s). I own several shoal draft boats, all have centerboards, but this is me and shallow water sailing is what I do.
Performance is just as much rig choices and weight related as it is keel design. Given the limitations of the build type, rig and hull form, big performance gains aren't going to happen, though modest improvements in certain elements of the performance envelop are possible.