15th June 2012, 01:34 PM #1
replacing a TS16 centreboard with bilgeboards
I've got this TS16 which I am wanting to turn into (my) ideal cruising boat.
One of the things I'm toying with is replacing the large and intrusive steel
centreboard with a couple of swinging bilge boards, set up something like
B&B's Bellhaven 19' or Selway Fisher's Lynx 16.
The new cases would sit along the second stringer, not too far from
centreline so as to be hopelessly out of parallel water flow, but wide enough
to take the ground flat. This would give unobstructed foot / portapotti /
standing-up room midships.
They would butt to frame 3 at the forward end, and past frame 4 at rear,
tying to cabin wall, bunk tops & cockpit floor. Coupled with suitable logs &
reinstating the hole at the back of the cabin where the centrecase exits,
I think they would be well enough supported.
They would protrude maybe 4" below the bottom, level with the keel.
The pivot bolt would move into this protrusion - external to the cabin -
eliminating a common leak/weep point.
The total wet area of the two boards would be about 10% greater than the
existing centreboard, and move CLR in fully down position about 8" forward.
This would be offset by the ability to independently vary the board angles,
plus the likely moving the sail COE forward by changing the rig to cat ketch.
I would expect some slight loss of performance, but I'm not racing so not
Question - what (if anything) am I missing?
Why would this not be a good idea?
Last edited by b.o.a.t.; 15th June 2012 at 01:44 PM. Reason: add pics
15th June 2012 01:34 PM # ADSGoogle Adsense Advertisement
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16th June 2012, 05:36 PM #2
Well AJ my first thought was you have been watching too much KTL and Mr. Winter has brain washed you.
Then I thought hmm......seems like a lot of work for a potti but one must not underestimate the importance of these items.
So without any concern to performance from a practical point of view seems like a worthwhile project.
As for the impact on how she'll sail think I'll leave that to one of our regular knowlegable types.
"Working to a rigidly defined method of doubt and uncertainty"
17th June 2012, 03:50 PM #3Senior Member
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- Dec 2004
- Rushworth, Victoria
If you seal the board pivot well it doesnt leak, I had a pivot bolt with head/nut cut off and two sealed and screwed covers over the ends. And the centrecase makes for a very good place to brace ones foot when the wind gets up."World's oldest kid"
17th June 2012, 08:00 PM #4
I have just built a pivoting center board, into a sailing canoe, this was not sealed at the pivot bolt.
Fro what you are doing , I would counter sink the bolt hole with a speed bore( both sides), by 3mm, seal the timber with epxoy resin, then cut washers from gasket rubber, with a slightly undersize hole for the bolt.
Fit a s/steel washer under the bolt head, and under the nut , then just nip the nut , does not need to be over tight .
Just a suggestion,
17th June 2012, 08:35 PM #5Senior Member
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- Dec 2004
- Rushworth, Victoria
I just thought of something else too Alan, having looked at your drawings again.
Your bilge boards dont project very far up into their cases so the sideways leverage would soon wrench them out I'm afraid. The standard centerboard projects the full height of the case and that is in turn braced by the bulkhead."World's oldest kid"
18th June 2012, 03:20 AM #6
These are 30 second concept sketches, not final plans.
The pivot would be somewhat further aft to give a goodly amount of board
still in the case to resist twist & lateral loads. Most important seems to flow
as an extension of a comment PAR made a few weeks ago, about transferring
loads to the keel. The bottom isn't strong enough to handle the sort of loads
that drying out & bumping into things would impose. Also, given a bit of
shape, the downward case extensions should contribute to lift.
Still thinking through control line arrangements to keep their exit above water
line when heeled.
Jeff, there are a number of ways of creating a reliable seal on the pivot bolt.
I like John Welsford's pivot tube with sealing rings each end the best. The
attraction of moving it outside is that I don't have to worry about any of them !
Also still thinking through sail plan, mast location & tabernacle design.
Solo, including installing the outboard, it used to take me about an hour from
arrival at the ramp to sailing away. Same in retrieval. I want to halve that,
or better. At this stage, a cat ketch keeps all the bits relatively small & low-
stress - therefore light & cheap - without sacrificing sail area from Hartley's
original. (Unfortunately, Richard Hartley is long deceased, so I can't waste
his time with this stuff.)
regards from a daft & incorrigible fiddler
18th June 2012, 03:34 AM #7
I guess I'm trying to turn a TS16 into a de facto Murray Isles Chestnut Teal.
I've seen nothing else that comes close to what I'm trying to achieve in cabin
head-room, stability, sail plan & user-friendliness.
Why not just build a Chestnut Teal ?... Simple.
I got the TS on a trailer for under $1K .. less than the price of a trailer,
let alone building the Teal.
By the same token, I'm not quite willing to turn a perfectly good TS16, albeit
one which hasn't been in the water for almost a quarter century, into unsailable
& unsaleable firewood. If I am not reasonably confident that what I'm thinking
will 'work', I'll either do the boat up as standard & flog it (or just flog it as-is),
and build/buy something else.
18th June 2012, 03:41 AM #8
18th June 2012, 05:18 AM #9
You'd be better off placing the case inside the furniture, so you can gain free triangulation with the rest of the boats structure. The most important portion of the case is the top, directly above the pivot point. This is where the case will be tested.
The lanyard can be enclosed, not dangling in the water and the case top can also be sealed tight, so no water spurts out of a slot. I've been using a board and lanyard design that I stole from a S&S design years ago. It eliminates the usual lever arm on the back of the board and keeps the lanyard out of the water. It also permits a tackle (weighted boards) to be employed easily.
Shown is the setup I usually use, though in this case it's a modification to a popular home build, which had an open slot and lever arm (shown in pale blue). The board on this boat had a 15 pound weight, which caused it to sink with authority, so a whip tackle (2:1) was used to make the hoist easy. The tackle lands on a cam cleat under a midship thwart.
The difference with my versions and this one, are I'd have a lower pivot point, to gain a slight leverage advantage and make the pivot easily replace, being "let" into the bottom planks. When at all possible, I try to keep the pivot out of the boat, placing it in the planking.
The other image is one of my designs with better detail about the pivot arrangement. It still has an internal pivot, mostly because the bottom planking is too thin to bury one outside. Note the cross bracing at the top of the case at the pivot pin location. This is where the case will try to twist itself out of the boat.
I should add that I never make an internal pivot pin, accessible with removable covers. I glue them on and they become part of the case sides. Removable covers eventually leak. If you need to access the pin, then a chisel and a few swats with a hammer will get you in, grind it smooth again and glue on new pin plates. It's simpler and leak free.
18th June 2012, 02:07 PM #10
Snap! on most items, including building the cases into the furniture.
They would become the bunk faces. Tying the inner face at the pivot to the
structure will probably have to be accomplished via the top cap & bunk framing.
Will probably have to lead the lifting lanyard aft & up through a tube, as I think
the case top would be at or below water line at 20degree or greater heel.
Intending to significantly weight the boards to offset loss of the steel plate, so
I'll also need to support the boards to de-load the lanyard whilst trailering.
18th June 2012, 06:41 PM #11Senior Member
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- Jun 2011
In other news, What do our fellow TS16 owners think about modifying the current standard centreplate in a similar fashion as PAR's examples- eg. Fully enclosed case, lanyard over rounded top, instead of the lever arm it has now? I'm not worried about the class certificate so would there be any major issue doing it?
19th June 2012, 02:01 AM #12Senior Member
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- Aug 2008
19th June 2012, 06:01 AM #13
19th June 2012, 09:25 PM #14I should note that this setup is reserved for small, light weight, non-ballasted craft. Larger boats, with ballasted boards use a different setup, though more purchases can be employed. I have a 23' ketch that lifts a 600 pound (272 kilo) board, using a similar system, except a winch is used, instead of tackle. The winch has a small powerboat destroyer style wheel (my idea to prevent fouled lines), instead of a crank. It's 10 turns from full up to full down and a clutch permits it to stop anywhere along the way.
There are many ways to skin a cat folks. With the above arrangement I was hoping to solve some common issues such as; an open top case, that likes to spit water, a lever arm sticking up through the case, further intruding into living spaces, eliminating the lanyard dragging in the water causing turbulence, complicated hoisting arrangements and a lower profile case. I've seen some clever case arrangements over the years, but none addressing small craft for the home builder have been particularly impressive or innovative, simple yes, but often contrived.
One case designed by Phil Rhodes, uses a very clever hydraulic ram arrangement. Very simple, few moving parts, quite robust, no leak points, nothing dragging in the water or sticking out of the case. I've blatantly stolen this design for use on large craft.
This is a S&S tackle arrangement, similar to mine, though done vertically. The board is narrow and mostly under the sole on this boat, except for this triangular shaped tower inside, with the lanyard tube, that goes up to a winch. The pivot pin isn't visable, but is located just out of frame on the left, in this view. The lanyard, just drops the puppy down on a whip tackle. The triangular portion of the board provide leverage.
Get out your sketch pads and dream one up. There's all sorts of ways to approach them, so don't let convention hold you back.
25th June 2012, 12:08 AM #15
I mentioned I like using an external pivot pin arrangement, so I dug up a drawing for an 18'er of mine. The board is lightly ballasted (30 lbs./13.6 kilo), uses the same rounded top/lanyard arrangement and places the pin in the planking, outside the hull.
What isn't shown is the epoxy block this pin and related support is buried in. The armature inside the board and the angle steel pin holders are buried in thickened epoxy, within the planking. This seals up the exposed end grain and protects the steel too. Naturally, all the hull penetrations (bolts) are set in epoxy bonded holes too, so no moisture can get at the wood.
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