View Full Version : centre boards
Would it be advantageous to make a center board out of 1/4" steel plate instead of 3/4 mahogany ply with lead "plug" for the Joel White Shearwater? Would this not provide balast in a boat that doesn't have any?
07-18-2001, 08:46 PM
Interesting question. From what I've seen, heard, read, you won't gain a great deal of righting moment from such a move. A little, but not as much as you might think. I think the reason is that we aren't talking about that much mass.
Factor in the hassle of fabricating the steel, and the galvanizing, and I think I'd stick with the wood.
[This message has been edited by ishmael (edited 07-18-2001).]
You'd gain a little because the board would be heavier. You'd lose some because the board would be too thin (and more because it wouldn't be shaped as well as you could the wooden one.)
I think you'd be ahead with the wooden one.
07-19-2001, 02:57 AM
"...You'd lose some because the board would be too thin ..."
For a minute there,HTOM, I thought that you were a shipfitter! The only people I know who regard 1/4 inch steel as thin.
Gert, look at it this way, 1/4 inch thick steel plate weights 10.2 pounds per square foot. At that rate, a steel centerboard is likely to comprise a substantial increase in the boats weight. Also, as steel rusts (and it will) it expands so you'll have to be more careful you don't cause the steel centerboard to jamb in the trunk while the boat sits on the trailer. In addition, you would have to substantially beef up the centerboard support structure.
Your benefits would be minimal. Joel White really did know what he was doing. Stick with the established design, you'll be glad you did.
By the way, in a boat of this size, the weight of the crew makes up a major part of any ballast. If you are concerned about stability, then just lower the seats by an inch or two. You'll be pleasantly surprised by the increased stability (not to mention it is alot cheaper and more variable than a steel plate).
[This message has been edited by PugetSound (edited 07-19-2001).]
Gert I've sailed and rowed the boat and she does both well ,with stability in the low normal range . Course I own a Deleware Ducker which also has low initial stability (like alot of boats that are fast under sail And oar).I think that by simply spending time in her you'll quikly come to terms with her motion . I found that adding Interlux Polymeric Nonskid Compound ( plastic sand )to the interior paint when I refinished helped tremendously in handeling my Ducker - less helpless groveling in the bottom of the boat .
I sailed Shearwater in a good breeze with another adult and we sat on the bottom , one on each side of the center thwart,leaning against the side of the boat very comfortably. While comeing about in a chop , I put wieght on the offset tiller , which bore apon the gunnel in a certian way at that moment and levered the rudder up and off ! I don't like that setup .
The lightness of the boat is a huge asset on the beach and at the ramp , I don't think you want to build in more wieght. If you're a light person ,I can imagine experimenting with a couple of bags of beach sand for inside ballast when rowing ,and perhaps sailing , alone . I think a set of reef points in the sail would also be a good idea .
07-19-2001, 10:59 AM
I wouldn't. I've got a boat that was originally built with a steel centerboard (or centreplate, for our British friends). It seems to make very little difference to stablity, and is really more trouble than it's worth. It rusts, it rattles and bangs in the case, it isn't very efficient hydrodynamically, it vibrates under certain conditions and sounds like an outboard motor in the distance, and you can bend it if you hit something the wrong way.
BTW, if you don't want to bother with melting lead, lead shot in epoxy makes a good CB weight. It takes up a it more space than solid lead, but is very easy to do.
07-19-2001, 11:03 AM
Pardon me a minute while I hijack this thread while mining for a little more info. In fact, I suspect that Gert won't mind.
[Begin hijack mode.]
Will, I understand from your post that you've sailed Shearwater at least in a stiff breeze. Do you have any experience with it in light air? I'm curious how she does.
My impression of Shearwater is that the hull shape is a lot like the old canoe yawls from the late 1800s, and that a certain amount of tenderness is to be expected. But I've also heard some comments that she's primarily a pulling boat and is not a very good sailer. Care to comment further on that?
Just sittin' here with the plans in hand, debatin'.
We now return you to your regularly scheduled thread.
[End hijack mode]
I did get a chance to sail her in light air .She was slower than a round bottomed boat , but perfectly acceptable I thought . The beauty of a boat like that is if you become at all dissatisfied with your rate of progress under sail in a light or dieing breeze ,just douse the rig ,or better yet brail it up some way , and start rowing .
You could make the rig bigger ( the plans show 69 sq. ft.), but you'd want a set of reef points ,and you would have to reef when it was windy . In fact I think this is what I'll do if I get my act together and build this boat .Seems to me that the point of useing the lugsail on this boat would be so the sail could be sized for light air and reefed down as required .She does want to dip her rail. I bet the balance of the enlarged rig would be O.K. or at worst could be delt with by a minor tweaking of the masts location or rake .
The boat seems to be derived from John Atkins' Valderda ,which in turn was a close copy of a Norwegian work boat .The Atkins draweings show two deep reefs on the standing lug .For me there would be no point in adopting the rig to the smaller Shearwater without the reef points . Might as well use a spritsail of 69 ft. sq. ft.
I believe I would also saw off the projection of the stern post , if that's the right term , and rig a regular tiller . The offset tiller seems like a work boat affectation on this little craft .It's good if your deploying a pile of seine net off the stern that you need to clear , but on the Shearwater I think it solves a problem that doesn't need to exist . I also suspect that on the bigger , beamier work boats the helmsman didn' t change station on opposeing tacks , while on the Shearwater you definetly have to shift to the windward side . When the short steering arm is pointed to leeward ,and the helmsman is sitting to windward ,the mechanical advantage of the tiller is reduced ,not that it's ever great .Plus the tiller crosses the gunnel at the lee quarter on this tack and I've found , as I,ve said ,that it's possible for me at least to lose my balance ,press down on the tiller ,and lever the rudder up and off its pintles.
[This message has been edited by Will (edited 07-19-2001).]
07-19-2001, 06:39 PM
I might be dateing myself with this one, but I recall the second boat I built called for a metal board. It was a snipe. Lightings also had a metal board. The case can be narrow and a with a neat little slot that can be "gasketed", preventing water sloshing around when under sail. But in any case do what the design calls for.
Come to think of it the "lighting" had a winch for getting the board up.
07-20-2001, 09:37 AM
Ian Oughtred gives the option of a 5/8" 80lb.
steel center plate in his Whillyboat. That is roughly equal to 50% of the hull weight and seem massive to me. But is it massive enough to be effective as ballast?
Powered by vBulletin® Version 4.2.1 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.