Centerboard optimization opportunity.

[baggywrinkle]

The Thistle CB is heavy. Probably some form of lead in it. I wonder if I can find a way to cut out the needed shape and retain enough of its structural integrity. Otherwise might have to cut it a little small, then rebuild/reinforce the perimeter, up to the desired size.

...and when Dream Board is built, I imagine vacuum bagging after skinning will be the way to get resin to encapsulate the interior components. Surely have to drill some holes where needed for the resin to go where it should.

[baggywrinkle]

Pic below of the Thistle CB.

The Thistle CB has no pin, and no pin-hole in trunk. Instead it has rollers on the pointy end of the CB, which roll on the curved trunk top. Tackle assisted fore and aft rolling raises and lowers the board.

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rsz_thistle_cb__and_trunk.jpg (125.09 KiB) Viewed 25599 times

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I like the Thistle CB system. I like its looks. I've always admired Thistles. I was about to acquire this very Thistle. That could be why I convinced myself it would be just as easy to simply transplant the entire Thistle trunk with CB into my yellow boat. No need to modify the Thistle board!! Hence the whole job would probably even be easier!!! I came to my senses, after a little while.

To make the Thistle CB fit my yellow sloop, I will cut some off that pointy end and shape that end to match my trunk. Then it will be 51" X 13.5". Close enough for me. Saint Rudy's new DS boards are 50" X 14.5" . They weigh 51-55 pounds.

This Thistle board weighs in at 73 pounds. It's heavy. It will weigh a bit less after the pointy end is trimmed. A square hole fitting for it is being fabricated in stainless steel. A square tube was welded up today. It is a snug fit on the old bronze handle's slightly worn square lug. Flanges will be welded to the square tube. Pics later. Baby zincs shall be embedded in the board near the SS.

I was going to remove and re-use the bronze square hole fitting from the old board. Then I realized that board is luckily almost perfect as it is for the new rudder needed. Less work, leaving it as is, I decided. Another reason to leave it as is is that it may yet be needed to serve as the 'dream board'.

I'm with you if you're thinking 70 pounds might be too much for the old handle to lift without hurting itself or the trunk/fittings. Rather than find out the hard way, I guess I'll have to devise a lifting system near the after end of the trunk. I'm thinking a new hole in the trunk top, some short SS tubing with a fairlead on each end, and a chain or wire rope attached to the board in some clever fashion.

Chain would be good for pinning at any board depth desired, and a pile of chain seems easier to live with than a length of wire rope, when it is all up. However wire rope could fit tightly in a small hole, piercing a sturdy rubber cap placed atop the fairlead to discourage unwanted seagushers. Since I like the chain idea, maybe I can devise a rubber seal for it too. I guess lifting will be done with a handle, rather than with tackle, until I realize/admit tackle would be smarter/better. Maybe. Not sure. I will start with just a handle on the chain or wire rope.

I suppose that once I grow weary of swimming underneath to clear seaweed from the chain so I can raise the CB, I may get around to building the aforementioned new 50 LB 'dream board' stuffed with Mr Okuda's lead slabs. For now, this Thistle CB seems to be my quickest acceptable route to sailing. It does have a foil shape, and single handing should be easier with 70 pounds down there, as long as it doesn't break something.

Thoughts? Suggestions?

Thanks !!!

[baggywrinkle]

Pic, location of proposed board lifting system.....Through the teak cap, or avoid that, and install it in the glass below/aft close to the teak cap ? I guess maybe it needs to be thru the teak, since aft/below the teak may not allow raising CB all the way ?

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CB Trunk aft end.jpg (75.96 KiB) Viewed 25595 times

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Most recent Centerboard, now destined for glory as new rudder..jpg (118.54 KiB) Viewed 25595 times

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[GreenLake]

Before you commit to a lifting system, please read all (and I mean all ) the long threads about the DS2...

Here's the lifting system you want: Near the top of the trunk, put an axle though the trunk on which you can wind up 4 or 5mm Dyneema (such as Amsteel).That's your lifting "wire". On the outside, of the same axle, you mount a drum, big enough to give you a good ratio of inner/outer radius. 6-8" should do, or even a bit less given the lightweight board. On that you wrap some nice grippy line. As you pull on the outer line, the inner line gets wound up on the axle and lifts the CB with some mechanical advantage over straight pull.

Since you are already overweight compared to class rules, put a bit of lead in the tip to bring the board to 70+ pounds again. That is probably enough to keep it down, so you don't need a downhaul.

You do not want chain - it would kink into a mess inside the trunk and wedge itself god knows where.

You don't want to copy the DS2 system - every owner is unhappy with it

So, go with the system I've tried to describe (it's used on the O'Day mariner - that CB is bigger, but also much heavier yet, so I know you won't have trouble raising a lighter board with it. As long as the board is heavy enough to stay down when you go fast, you don't need a downhaul (one less line to get wedged).

If you go for this, don't overdo the mechanical advantage. Figure out what's comfortable to pull when making an adjustment underway, and go from there.

[baggywrinkle]

Thanks GreenLake !!

I've been reading those great threads. So much good info therein !

Another project ! ? Well, OK, good point, I will use Amsteel instead of chain. Thanks! But initially I will try brute force instead of the proven, sensible efficient axle and drum you described. It is just that time is running out over here. The yard (and others) are being evicted by the state, as parking is needed for increasing numbers of shipping containers. Axle and drum later, if needed. Someone else said just leave the "!%#**@X&$" board down. But I want to be able to raise it.

Pics:

Blue tape indicating, (like a blueprint?) (sorry) the 1st rough cut of Thistle CB. The SS square tube is there too.


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rsz_cb_blueprint_2.jpg (14.26 KiB) Viewed 25590 times

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Pointy end with rollers cut off, revealing lightweight foam core construction of CB head area. It would need major reinforcement if the square hole is to be used to raise the board. Not gonna happen. Too heavy for the fittings and CB head, I think. The hole and handle will now serve as pivot only. Even that requires reinforcement.

For reinforcing the square, maybe insert a 6" (or bigger) plywood disc or square, epoxy/glassed, with the SS square mounted in it ? Or maybe just a glass & epoxy insert would be better, instead of plywood ? Thickness cannot increase so the insert needs to be edge joined, or maybe 'scarfed in' ? I need to talk to a 'foam joinery' expert.

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rsz_1cb_rollers_cut_off.jpg (224.47 KiB) Viewed 25590 times

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[baggywrinkle]

Maybe should enhance load distribution surface area by adding larger SS square(s) around the first one, then put it in the plywood or glass insert.

Whoa, places for the zincs could be made by enlarging the SS square. Maybe easiest way to enlarge it is to surround it with more square tubes welded on, and then those can be stuffed with zincs.... Two birds... Wait, instead of additional costly fabricated squares, pieces of SS pipe, or pipe fittings welded on would do the job for less.

I wonder if such a contraption, if big enough, and well joined to the foam/glass head of the Thistle CB....could suffice for raising/lowering the 70 LB CB. Then no need other lifting system. Maybe a project trade off benefit there.

Maybe the old bronze handle would then need to be replaced with an SS version for more strength, I'm thinking.

More crazy? Probably. Oh yeah, might need a handle about ten feet long, or a seagoing gorilla for operating the CB handle ! Maybe should stick with the other lifting system....?

[baggywrinkle]

Low ground in rainy season. Not much going on there today.

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[GreenLake]

time to go sailing

[baggywrinkle]

time to go sailing

Thanks GreenLake.

Sailing season starts in 2 weeks.

[baggywrinkle]

Old Yeller is a U. S. Marine Corps vessel (retired). Beginning in the fifties, she served at U. S. Marine Corps Air Station Kaneohe Bay, Oahu, Hawaii (MCAS Kaneohe Bay) . I reckon this means she is a DS1. She was one of a fleet of Daysailers, used for recreation. Good thing she wasn't there earlier, say Dec 7 1941. That place got strafed, then bombed.

Today I met the guy that modified her. He got her from the guy that picked her up when she retired from the Corps, after the USMC Aviators enjoyed her for decades. She was tired. To stiffen her, he added the white cockpit "boxes", and the cuddy bulkhead which are all made of foam covered with Knytex Biaxial FG. It worked well.

He also faired the bottom and topsides with microballoons in epoxy resin, for more stiffening, and for perking up her tired soft and saggy old curves. No wonder she feels solid underfoot in the cockpit. I asked if he made a double layered cockpit sole with foam and glass. Nope. Just the original bottom, with fairing added. He said before stiffening she sailed like a floppy wet sponge. Also added a stiffer mast. Performance after stiffening is like night vs day, we are told. Fairing was done by handsanding with longboards. A pro job, he did. Good to know. No wonder she looks so good.

I'm in love.

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[baggywrinkle]

Maybe (it seems) the marines replaced Daysailers with American 18s...

http://mccshawaii.com/sailing/
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[TIM WEBB]

Wow ... her (very) interesting past finally revealed! And it all makes so much sense now ...

When our boats can't tell their stories, it's nice to have PO's who can! ;-P

[baggywrinkle]

Thanks Tim !

Yep its great to know the history, and its sort of a unique history at that. I'm really glad to know about all the improvement the prior owner did. Although he added some weight, the stiffening made it faster.

[baggywrinkle]

Note:

The boat's history, above, was more appropriately posted on page 3 of the thread about the boat in general.
Link to page 3 of that thread:

viewtopic.php?f=2&t=5641&start=30

[baggywrinkle]

Getting back to CB project....

Ooops, wait....posted this too soon because must get explanatory pics and re-post it.

Sorry. Later.