Through bolts for centerboard case?

[D Gobby]

I asked this question in another thread no response so I will try again. My plans for the 15' daysailor I'm building call for the centerboard case to be screwed and through bolted. I'm assuming that this means screw the centerboard case to the keel through the case logs but where does the through bolting come in? Through the case logs and the keel or through the centerboard case head logs and the keel. The case logs are 7/8" x 7/8" and the case head logs are 1 1/2" x 1". I don't see much point in screwing and bolting the case logs. If I through bolt from the top of the center board case down thru the case head logs through the keel what would be the best size of bolts or threaded rod to use? 1/4" or 5/16". The case head logs are only 1" thick and go through the keel with a half tenon joint. Am I on the right track with this thinking? I could use a carriage bolt on one end but the other would have to be all thread or solid rod threaded at the ends because of the length.

Any Help!!!!
Darrel

[B. Burnside]

Can you ask the designer what he had in mind? You will probably get lots of opinions here, but the designer would have thought through the process already, and would probably give you the most reliable and informed advice.

Good luck!

Barb

[Paul Scheuer]

I saw the other thread. and I'm not sure I am seeing the problem. I think that all of the through-bolting should be done at the bottom of the case. (case logs to keel (?). The screws are to help provide the waterproof seal, and the bolts are for the necessary strength, in addition to some lateral bracing at the top. Bolts or rods all the way to the top (head logs ?), would not stay tight, trying to compress the entire vertical dimension of the case.

My plan for my Snipe project will be to bolt the bottom of the dagger board trunk. The top is braced by the deck structure.

[D Gobby]

Barb the Designer Al Mason is no longer with us. So I can't ask Him.

Paul sometimes I over think things. The centerboard case is approx 4' long where it meets the keel. Do you think that 4 bolts per side with an equal # of screws would be enough? There is no fastening schedule with the plans so I can't look at that to figure things out. There is a lateral support on each side that extends from the intersecting frame to the top of the case for support. What size Dia bolts? Would 1/4" be enough.

Thanks Darrel

[imported_Conrad]

I'd probably use 1/4" bolts every six inches and forget the screws. If you think about it, the bolts will be trying to compress the screws as the wood shrinks/swells, or trying to push them out the bottom. (I assume you intend to drive them through the bottom/keel into the logs, which I would make deeper) If the board is well braced at the forward end/top by a thwart, etc. you might get away with less, but why risk it when centerboard leaks are the most common problem with boats this size?

[B. Burnside]

Darrel, that's a realy good reason not to ask the designer!

Barb

[Ian McColgin]

Darryl, why not contact Anita?

[J. Dillon]

Darrel,

Use the bolts for all the reasons stated above.

It's not a place to skimp. Over built is better then under buillt. Look at some of the problems encountered by a few of the A. cup contenders. Of course they are trying to save weight but this is not your goal.

JD

[A. Mason]

Hi Darrel,

I'm at a loss as to how to advise you regarding the screw/through bolt issue. "Bart" was inspired/based on the Lightning/Blue Jay one design classes, so my first thought would be to ask how those two types are done.

Al had access to the plans for both of those designs [S&S/Rhodes], and my guess is he had planned to have "Bart" built by the same yard that was building either Lightnings or Blue Jays. This would explain the lack of a fastening schedule and more details.

As near as I can figure out, Al had not planned on adding "Bart" to his list of "how-to-build" designs, or to have it reviewed in a magazine, at least not until after the prototype was built, which as you know never happened.

When I get a chance this weekend, I'll check Al's 12-foot Swampscott Sailing Dory plans ["Ms. Peach"] to see if they contain any better information on how to install the centerboard and centerboard case, since this design has a similar shape centerboard.

Hope this helps,
Anita

[Bob Cleek]

Ahem... not to stir things up or anything, but centerboard cases on small boats may be one of those rare occasions when one might seriously consider the use of FIBREGLASS to fabricate the whole case! It can then easily be bedded and fastened to the keel assembly. Solves the leak problem pretty well, I'm told.

Pardon me if I just stand back and let the fur fly.

[ 01-02-2003, 01:54 PM: Message edited by: Bob Cleek ]

[shadow99]

Bob- How dare you mention the "F" word here, those pre-fab "fooey-glass" C/B cases are worth crap. I'd rather use duct tape and bubblegum to secure my C/B trunk before using a fooey-glass one. I had one on a Lark 12' it was made of 9oz cloth, and had the structural strength of tupperware.

Rick

[D Gobby]

Ohhh Nooo now you've gone and done it Bob. I think I'll just keep my head down for a little bit and wait for the dust to settle.

Darrel

[Ian McColgin]

My favorite approach to a centerboard trunk is lightish plywood sides, glassed and bottome painted on the inside surfaces before assembly, epoxied onto a kind of spacer and cap rail for the forward, top and afty edges, and epoxied to the bedlogs with some plysood sticking out far enough to come out the bottom of the boat. It also helps to have the forward part of the sides reinforced in the way of the pin and any place where the board will stick up into the trunk and need bracing against the side load of sailing.

Once in and nicely bedded and bolted in place, the ply of the trunk can be trimmed back to a bit so that it's in essence a tad countersunk and the ends sealed with epoxy.

Fairly easy, drip proof and repairable.

But in general, I'd follow the designer's notes. Some designers are actually smarter than I am . . .

[Scott Rosen]

I like Ian's general approach, but since I haven't built a centerboard boat, you can take my opinion for what it's worth.

WoodenBoat Magazine has published a number of articles on the construction of centerboard cases. In fact, WB 153 has some materials on a Lightning centerboard trunk. If you go the WB homepage and search the on-line index, you'll get a list of the articles. I remember reading some of them and thinking they were quite useful, with good pictures and illustrations, too. Here's some of what I found.

/Bray, Maynard, author:/"Replacing a Keel and Centerboard Trunk," 124:51

/Catboat, Beetle Cat:/stem and centerboard trunk installation, photos, 52:107

/Centerboard:/boring for fastenings/Greg Rossel, 128:32

/Centerboard:/construction method/Bud McIntosh, 78:41

/Centerboard:/design for small craft, 108:80

/Centerboard:/for Biscayne Bay 14 daysailer, 98:28

/Centerboard:/for Riverside sailing dinghy, 168:26

/Centerboard:/for sloop Grey Seal, 130:64

/Centerboard:/for Whitehall pulling boat, 24:58

/Centerboard trunk:/Catspaw dinghy (Herreshoff Columbia ), 27:63, 28:64

/Centerboard trunk:/comments, detail photo, 65:52

/Centerboard trunk:/construction method/Ray Speck, 152:30

/Centerboard trunk:/installation/Riverside sailing dinghy, 168:26

/Centerboard trunk:/Lightning class sloop, 153:60

/Dunbar, F. Spaulding, designer:/letter on centerboard design, 163:8

/Manning, Sam F., illustrator:/"Centerboards and Trunks," 78:41

/Speck, Ray, author:/"Another Kind of Centerboard Trunk," 152:30