Re: Micro with plate centerboard
- Nice, Mason,
sounds like a really interesting experiment. Maybe the thing to do to have a second look at it would be to find a day with a steady breeze, sail a three point course with the board and then take it off and do it again.
--- In firstname.lastname@example.org, "mason smith" <masonsmith@...> wrote:
> Dear gang---Last fall some of us were talking here about the notion of a device to give the Micro a boost in windward performance and I threatened to try it. Well, before launching this year I have done what I had in mind. I have hung a quarter-inch brass plate, shaped to fit in the shadow of the ballast keel, on a bolt through the keel almost vertically below the forward end of the cockpit.
> I made it out of a piece of brass plate somebody gave me years ago, and was limited in length by that piece ov brass. It could not be as long as I might have wished, but, on the other hand, I thought it would do for a test, and perhaps it was as long and large as it could be in brass without bending in use. If it bent over the edge of the keel, it might not lift up, and I would be in a nasty situation come retrieval onto the trailer. And even a square foot of added lateral plane, below the keel at the right location (guessed at) should be enough to test the concept.
> So I guessed at the location, apporoximately under the cabin/cockpit bulkhead, and sawed my piece of brass to fit the keel and bottom aft of that pivot point, with as much bearing surface against the keel, when the board is down, as possible.
> I notched the trailing edge so it could come tight up to the bottom around a cheek blick screwed to the shoe keel from which the ballast keel hangs. The pendant is attached at the bottom of this cutout, by a small shackle. For trials, I simiply used a piece of nylon small-stuff tied to the shackle, shifting to 3/8" braid partway back along the bottom to the hole alongside the rudderpost where it turns up into the sternwell. It passes through a hole in the rudder yoke, over a roller, to a clam-cleat just forward.
> I'll put photos of this thing on the group site in a Micro Centerboard album.
> I put something on the trailer to hold this plate board up beside the keel when trailering, rather than have its jiggling weight on the pendant. Conveniently this support lifts the board as you load the boat onto the trailer if you forget to raise it, and then to relax the pendant.
> Well, I've just come back from testing this thing over a four-day trip to Lake Champlain. Maggie, 14, won a scholarship to a young writers conference at Champlain College. She had a championship softball game at Crown Point Thursdy PM, and so I trailered over to watch the game (lost) and pick her up and head north to Willsboro Bay. We motored over to Buirlington, VT and tied up at the Boathouse docks for $1.75 per foot. Nice showers. After hauling her duffel up to Champlain College, I skipped back down to the dock and shoved off, to beat north against a north wind of 10 to 15 mph according to NOAA atop Mt. Mansfield. The test, at last.
> Well, I think she's more boat this way but iti's pretty unscientific rreporting I am about to do. She's had two other changes since last used at Gloucester for Phil's Memorial: her repaired mast is raked more nearly to the plans rake. And she has a full-length rudder, with an end-plate. (She originally was only an outboard cruiser and had a skeg with a rudderpost and rudder about 5" shorter than plans show. When I put on her ballast keel with a full length rudderpost, I didn't right away add to the rudder.) So I would expect her to do a little better even without the plate cb.
> She certainly does beautifully now. I'm not sure she points higher but she makes much less leeway and it's my impression that she's faster, which I think goes with less leeway. With the end of her boom brought just above the bulwarks, she heads 45 degrees off the wind and almost seems to be making that heading good; but the gps track shows that she is by no means really sailing her tacks within 90 degrees. In general I find that she sails, on a tack like this, at about half the wind speed. 4 mph in an 8 mph breeze, almost 5 in 10, and a bit more at times in stronger winds, but not much. On a reach in winds of 10 she will sail at 6 and a little over (mph, not knots) steadily. With the new underwater features she tacks more surely, indeed very quickly and surely.
> Still better, she does this without my attention. I sailed upwind for 7 or 8 hours Friday in winds of around 8, and 7 hours Saturday against stronger winds, sometimes up to 15 or 18, I think, and almost all the time she steered herself. I had only to put the tiller over about a foot at the end of each tack and she quickly passed through stays and off. I let go and the rudder found its own position on the new tack without any adjustment of the mizzen. I never lashed the tiller. Don't yet have a system for holding it, but will soon, to see if she will sail herself on a reach with the rudder held amidships and so turned into more lateral plane aft. I could not make her do this on the return to Willsboro across the wind yesterday, a sweet, fast sail and very comfortable.
> Upwind, by the way, the boat was addictively comfortable in the 2' waves that had built up in the long fetch on Champlain. Once in a while she pounded and one felt the plywood bottom flexing, but mostly she notched into these waves comfortably. Better when I sat to leeward, as I did when that was the sunny side. These were hot days on land, but Champlain water is at 54 degrees, and I wore long pants and a windbreaker to stay warm.
> So, in the end, I am highly pleased with the addition. If one were to make a bit longer board, I think it could be good, but my sense is that my board is large enough for effect and any longer, in brass, it might bend. Better make any longer ones of steel.
> Hope Susanne comments, as well as vous autres. I am on record as advising caution in modifying a PCB design, the tradeoffs being likely to bite you; but this seemed a harmless experiment. What's a 3/8" hole through the keel? What's the drag of a quarter-inch plate beside it (with UHMW plastic on the bearing portion ot the plate, and a strip of the same where the pendant-shackle will run up and down the keel)? Nothing ventured, nothing gained. So I confess, I did it, and am satisfied that the gain is considerable. The boat is no longer for sale.
> Best to you all, especially the dear designer's dear friend. ---Mason
- I go away to Asia for a few weeks and miss out on my favorite topic (Micro/LMs)? What luck. Mason, great report on the centerboard mod. I'd love to see a comparison of GPS tracklogs.
I have been "knocked down" once in my LM, on Lake Erie. There are two ways I can see it happen. The first happens when running, with sharp and high waves coming from abeam. The flat bottom of the M/LM rides the swells easily, but also heels considerably, and if the waves are steep enough and spaced close-enough together, that long boom can dig into a passing wave. When this happens, the mainsail sheets in tighter (no matter how much you ease the main sheet), as the boom digs into the wave. The boat heels further, the boom digs deeper into the wave, and so on. I recall Phil Bolger wrote something about this in regards to a vice of cat boats with long booms? Anyway, I had it happen to me a few times on Lake Erie, but it was never serious enough to result in a knockdown, although I could see it happening.
My knockdown occurred when a sudden gust of wind blew me over (again on Lake Erie). I usually sit with my back to the wind on the windward side and I did not see the approaching gust. Before I could ease the mainsheet I was heeled at least 70 degrees- not enough to put the mast head into the water, but enough that I was standing on the gunwale, looking down into the depths of the lake. Time slowed like cold molasses. She popped up almost instantly and I reefed.
I cannot speak of the M, but my LM plans show 11 cu feet of foam total. I recall that one cubic foot will float approx. 62 lbs, so the flotation from the plans will float 682 lbs. The estimated weight of my LM (with .5 inch thick sides and top deck, and the added structure of the self bailing cockpit) without the outboard is 1870 lbs. The plywood(26 cubic feet) will float an additional 1612 lbs. In total, a stock LM should float 2,294 lbs. That's not bad. A heavily laden boat would sink, a lightly loaded one might stay awash.
I altered my LM by adding more foam (and floatation space) under the cockpit sole. I now have a little over 20 cubic feet of floatation space which gives me 1240 lbs of floatation, along with the 1612 lbs in ply. I feel more comfortable with this margin of error (2852 lbs of floatation for a ~1900 lb boat). Regardless, I don't think a Micro or LM would sink as quickly as some plastic boats (such as J24's, which seem to sink with some frequency).
Love these discussions.
Bill, in Texas
Long Micro Pugnacious
--- In email@example.com, Bruce Hallman <hallman@...> wrote:
> On Thu, May 27, 2010 at 10:33 AM, John Bell <yonderman@...> wrote:
> > A long time ago I heard a story from Texas that a Micro got knocked down, flooded, and sank. I'm not sure there is 450 lbs of positive bouyancy in the wood structure alone to keep a Micro afloat.
> > I don't know if it's true, though.
> (I have the Chinese Gaff Micro Navigator design rig, not the basic
> Micro rig.) But with my sail rig, the few times I have got caught in
> overpowering winds, the way the boat behaved was to lean over a bit,
> and then then quickly dump the wind out of the mainsail while rapidly
> spinning around to point directly up into the wind. That is why I say
> I cannot imagine getting knocked down, because the boat naturally
> spins and heads up into the wind automatically and seemingly idiot
> The only way I could imagine turning over would be if one got caught
> in a big surf break, and even then I am not sure how she would behave.
> My guess is that she would lean over about 60 degrees, (which would
> lift the fin keel up to a point that it wouldn't have any grab on the
> water), and then she would skitter along like a cork.