Weighted Keel

[baldbaby2000]

The sand idea sounds interesting. If you don't like it you could probably get it out. I wonder how dense sand is compared to say lead?

I think a longer board would be a problem because it would stick out the bottom when raised.

BB

[Richard O'Brien]

The sand idea sounds interesting. If you don't like it you could probably get it out. I wonder how dense sand is compared to say lead?

I think a longer board would be a problem because it would stick out the bottom when raised.

BB

Sand is not very dense compared to lead. a 2' x 14'" x1" piece of bronze or even steel is approx. 100 lbs, My thought is someday to chop the bottom off a daggerboard, and see how hollow it is. then cast or weld a plate of metal to slide inside a couple feet. Next it has to be secured at the top, new blocks, and additional winch. finally a couple of 1/4" or? sacrificial pins to break and allow the cast section to hinge back if it struck something. I've got nothing if it strikes something laterally? The whole business lowers to 67", catches an edge, and then the center slides down an additional 18". The main concern is not to damage the exising dagger trunk? When raised it occupies the same real estate as the current design.

[delevi]

I have found it difficult to find a shop which would take on a dagger board modification to fill it with lead or lead shot. I made a call to MacGregor, and the person I spoke with told me that he would highly advise against such a a mod. He doesn't think there is enough strength in the DB and possibly the trunk to support the additonal weight. Thoughts?

[Chip Hindes]

Okay, so if you really want opinions, here's mine: It's a bad idea. Let it go.

In order for this to work without self destructing or at least doing damage, you're betting there's a substantial design margin built into the board and trunk support structure. After observing the design margin built into many of the other systems on this boat, I don't think it's a safe bet.

If you don't want your Mac to heel, put your "rail meat" as far to windward as possible where it will do the most good. You can do that without risking damage to the boat. If it still heels too much for you, reduce sail.

Heeling is a characteristic of monohull sailboats. Learn to live with it or trade it in on a cat.

[Frank C]

Leon,

OTOH ... we both know where you're sailing & what you're feeling. We also know that your risk of touching bottom there is nil. Considering that you've actually gone out to inquire about modifying the board, this topic is clearly important to you ... in view thereof, I may need to edit an earlier-expressed opinion. The 50-pound board we discussed earlier, in lieu of an empty 25# board, seemed it would add little benefit.

But, a few guys have partly-filled their 26X centerboards with lead shot. Hanging from a weak, pivoting hanger, it makes a way more complex change than yours (albeit, a pivot that provides an inate safety feature). Since E.Hardtle's CB gained 113 lbs. when filled with lead, the lower one-third of your board might hold ~40 lbs. (?) of shot. So ... if a daggerboard suspends an extra 40 lbs. concentrated in the lower board ... hmmm

• - fill the lower 2 ft. of board;
  - extra wt. now hangs from 3.5 to 5.5 feet below the hull;
  - 40# @ 4.5 ft. ~ 180# additional righting moment

So recognizing that it's relatively important to you .... you could try filling the lower one-third of your DB with lead shot. When extended, your dagger-mod might equal or exceed the ballast value of a crew-member on the rail. You need to SWAG a few considerations ...

• * prerequisite - you're willing to experiment with your current board
  * when retracted, your weighted DB simply hangs in space, with no special stress on the boat.
  * The hanger should be okay, but judge for yourself.
  * make sure the lifting line, the safety line and the cleat are adequate ....
  (dock lines prob. absorb similar stress)
  * make sure the lifting line is long enough to use the winch
  * judge for yourself any increased risk to the hull and board-trunk from a bottom-strike
  * consider that a "factory spokesman" suggests the DB trunk is at risk

I doubt the factory's "engineering assessments" are ever much deeper than a SWAG, so you're in good company! Todd's 400# pendulum seems at vastly greater risk than your weighted dagger would be.
YMMV

If you're serious, I think I know a muffler shop in Dublin who'd help you. This guy has a long beard, he looks like a pirate, and has a nasty parrot guarding the front door - couldn't be more perfect ... Arrrrrgh!

[Chip Hindes]

-extra wt. now hangs from 3.5 to 5.5 feet below the hull;
- 40# @ 4.5 ft. ~ 180# additional righting moment

OTOH...

The calculations are right but the assumptions are misleading. Righting moment varies by the sine of heeling angle, so (for instance) at zero degrees, righting moment is zero, etcetera.

It's 40# at 4.5' only when the "keel" is at 90 degrees to vertical, i.e., the mast is in the water (sin 90=1).

That's why the big, new, high tech boats have hydraulic, canting, bulb keels.

So let's redo the calculation at a more usable heeling angle, say, max 15 degrees, beyond which the book says not to go because neither the hull nor the rig is working effectively. The additional righting moment is 40*4.5*sin15, or about 47 lb-ft. I still say, not worth it.

Since we're supposing that the design strength of the board and trunk are in error on the favorable direction, let me just throw out a few thoughts,. I'm not saying this is the way thinkgs are, I'm just asking you to consider:

The side loads involved are fairly easily calculated, using standard, simple formulae, by someone who is even mildly acquainted with boat design. It's boat design 101. Roger has quite an impressive history of successful boat design in sized from 14 to 65 feet. You're going to look a long ways before you'll find anyone else accuse him of overdesign. Even if it's only seat of the pants calculations, Roger has about the largest floating database of any manufacturer from which to draw conclusions.

Discounting all of the above, for the sake of argument, lets say the strength of the centerboard and trunk are only a swag. They're as likely to have erred on the wrong side of the equation as the right side.

This summer in Bimini my office mate dove on his 26X and discovered his CB had broken off almost as if it had been sawn straight across, leaving about a one foot long stump when fully extended. He has no recollection of a collision which might have caused this "phenomenon". He had no lead shot, steel or sand in the bottom of his centerboard.

[Frank C]

Hmmm - I'm pleased to even remember two-thirds of the basic formula, Chip!

But if the sine function bears on the moment effect of the weighted board ... same must be true of the crew member. And my dim recall of algebra tells me that, since the angle of heel is constant, I could eliminate that function from both equations?

But there's a question yet unanswered in there ... how many foot-pounds are gained by moving my arse from the windward cockpit seat onto the windward coaming? And, uncertain if moving my arse effects the same benefit ... does that moment-delta indeed operate at the same sine function? Novice intuition makes me suspect that shifting my weight "up-more-than-out" has maybe less than 47 ft.lbs. on righting moment?

Risks of mods are to the owner's perogative, of course, but this mod is within my threshhold of risk for a 26X CB. YMMV.

Oops, Moe, you caught me mid-edit!

[Moe]

how many foot-pounds are gained by moving a crew member from cockpit seat to coaming? Novice intuition makes me suspect it's no more than (maybe less than) the 40 pounds added to the lower-board?

If the crew member weighs 150 lbs, it's about 3 times as much (2.5' vs 3.5') as the 40 lbs of shot.

[Chip Hindes]

It obviously depends on the weight and how far out the person hikes. & BTW, the righting moment arm is measured from the cg of the boat, which is located pretty much on the boat centerline and my guess is about a foot above the the bottom.

Based on my guess on the cg, I believe your estimated 40 lbs weight in the centerboard is worth the same as about 85-90 lbs of rail meat with their back against the cockpit seat.

An interesting additional factor though; note that for relatively small angles righting moment of rail meat varies approximately by the cosine of heel angle (cos 0=1, cos 90=0), so as heel angle increases, the relative value of centerboard weight goes up, while that of rail meat goes down.

[Frank C]

Thanks for the lessons ... I'd need to do some reading to understand the cosine twist, but just realized that my board weight is (4.5 + 1 feet) from CG. Also, I'm pretty sure that a crew member cannot pragmatically attain an offset-angle equivalent to that of the board ... but overall, I can buy an equivalence SWAG that one board-pound can replace three crew-pounds.

But I don't need to coordinate departure or return times with the board ... and the board consumes no beer and less gas. So maybe its 'intangible equivalence' is almost 1-to-4!

IMO a weighted board is worth pondering but the LazyJacks & traveler are definitely higher on the to-do list.

[Don T]

OK,
I just can't resist...............the X centerboard fills with water thus increasing it's mass. Should not this extra mass be considered in your formula?

[Catigale]

Don - it does, but my SWAG is there is maybe 1/2 gallon at most in the board, and so its only an extra 4 pounds or so.

[Jim Bunnell]

Wouldn't the water in the board be weight neutral as long as the board is below waterline?

[DLT]

Jim makes a very good point. But, let's extend the thought...

The proposal was to put 40lbs of lead in the center/dagger board. That 40 lbs is displacing something, maybe water. So, you are not truely adding 40 lbs. Rather, you are adding 40 lbs minus the weight of whatever you are displacing...

The end result is that you won't even get the full 47ft-lbs additional righting moment...

[Catigale]

Correct - your actual righting moment change by adding lead would be 47 pounds less the 4 pounds (my SWAG) of water displaced by lead.

The water in the CB has mass, and hence has righting moment no matter where is it with respect to the water line.

If it didnt, then the water ballast system wouldnt work - the water in the ballast tank is pretty much all below the waterline.