CB extra weight

[Crikey]

I completely forgot the argument of why the factory chose fragility over robustness. There must surely have been some point in the design process where cost benefits were applied to a dagger board design to resist an impact versus outright replacement. That of course would have to involve the incorporation of the strength of the holding channel into the maximum weight allowance, for the whole finished package. Beer and all! That same argument could be applied to a swing keel as well.
To increase the weight of an intelligently designed component, of this type, clearly pushes the built in failure margin towards its limits.

That said, providing you don't over exceed the flexibility/strength capabilities of the existing fiberglass layup, and pack it full of depleted uranium, there should be some wiggle room for at least a modest percentage increase in the amount of lower, located mass. I don't hear too many horror stories about stock keels running amok!

Ross

[seahouse]

Hi All!

I made several changes in this area before Boat of Us first hit the water.

1- I placed 4 adhesive-backed neoprene (foam wet suit type) strips, ¼” X 1” X about 12” vertically at the bottom of the dagger board trunk. It totally eliminated the rattle issue, and it has to have reduced side play somewhat.

My only experience with the annoying DB rattle was while we were sitting in the boat on the trailer at the dealer’s when we picked it up. That put it near the top of the priority list (after barrier coat, anti-foul, and rudder bushings), although I’m not sure if others around us at a marina would have been able to hear it, let alone be bothered by it.

2- I glassed a piece of slotted ½” PEX tubing on the top 12” of the trailing (sharp) edge of the DB, and extended it about 1” past the top. This greatly strengthens the area, reduces the side and fore-aft play, and distributes any instantaneous shock forces (striking an obstacle) over a larger surface area both for the DB trunk, and the DB itself. The PEX is slippery, so it's a good bearing surface and also reduces friction when the extending and retracting the DB. Since it is just the top 12”, it does not extend into the free stream, so no drag is induced. Still, I faired it for both strength and appearance. Others here have done a similar mod.

3- I made a clamp mechanism for holding a 12” piece of insulating pipe wrap over the leading (blunt) edge of the top of the DB. This did not hold up, but I want to revisit and have another try at this. (I just was anxious to get the boat into the water and sailing at that point). In the short-term it served the purpose of further reducing free play, and distributing shock loading, which is less important at the blunt edge, than the sharp edge of the DB.

The DB was covered in barrier coat, then anti-foul, so after the first season it is easy to see where the contact points with the DB trunk are.

It’s a small thing, but in the interest of good form I cut a (~1”) piece of bicycle inner tube and placed it over the end of the hinging “hasp” that holds the roller above the DB. I saw this as an area where the gelcoat could become damaged from friction. Looks like it should be there.

- Brian.

[Crikey]

Brian, excellent! I really needed to hear this!
Any possibility of a couple of pictures? - I know, if your boat is now wrapped this will have to wait until next spring. Can you give any knowledge of how much play you encountered before you made the 'adjustments'? Or was it simply something you did after you heard the rattling while retracted.... also what is PEX? And, finally, could the DB be twisted left or right before these fixes (like a rudder)?
Was there any noticeable improvement in pointing under sail, and heeling stability? (lots of questions here!)

Ross

[Divecoz]

WOW! This is turning into a Very Informative thread!.. Mastreb! Thanks for the Physics/Math.. I knew I could count on YOU!
Excellent job of turning Formulas into the written word... For me most often now, being willing to sail with the DB only about 28" deployed, I am not all that sure I would see any real benefit of weighting my DB.. I just don't have what it takes to Sail Empty ballast.
Seahorse.. have you got pictures?? Slotted PEX ? I am just not positive I am sure of what your describing..( I think I do, but I want to be sure)
Neoprene? Dang never thought of that ... That might work for a Trunk gasket as well..How well is that holding up to the wear and tear / sliding up and down of the DB? I assume fabric one side?? Are you seeing any issues from water saturation of that material. Humm My Brother is and has been for a very long time..... The Manufacturer of Custom One Off Dive Suits.. I will ask him if he can sew or vulcanize some of his Kevlar Knee-pad material to my Closed cell Neoprene strips for the trunk..
I have a piece of thin S.S. Plate I want to use,with a gasket, for the DB to slide through, and maybe reduce water turbulence at the trunk opening.. Maybe Closed cell Neoprene as the gasket, that the D.B slides up and down through would work?

[Crikey]

Matt, thanks (like Divecoz said) for some excellent math research! Too long ago for my brain to resurrect moments and pivot arms properly!

It occurs to me your CAD/physics software could take the mass (increased) of the DB, per your manual calculations, and give some descriptive data of the daggerboard moment - around the center of buoyancy. Similar to your kind of funky 'mast raising the dagger board' animation. Only, instead, it would be diagrammed looking through the stern of the hull with righting forces calculated by the physics software as different angles of rotation are dialed in. (Just forget about the mast connection.)

Dive, my original question still remains - how much does this dang thing move around (in any axis) when fully extended, before, and after shimming is deployed? Unless you're running, I'm not sure I understand why you'd have the dagger board partially retracted?
As for extra weight, as I said earlier, surely there'd be some extra wiggle room in the design before you really jeopardized things. Moreover, this design - modified or not - is intended to break upon impact and doesn't vary that much from a keelboat in the sense of 'Don't hit anything, regardless!'.

Ross

[Divecoz]

Crikey... The less DB you can get away with while sailing ? The Faster your boat will be..
DB Rattle? I have it at anchor.. Not always but enough to bother me.. I am anchored and sound asleep and some big stink pot goes by .. maybe a mile or more away and when his waves hit me.. I rock , but my board Knocks.. and I am Up and out.. or at least awake wondering whose boarded my boat.. or wondering / preparing a gift... at least ...until my mind begins to work and says........it just that @#$%^& DB again..

[Crikey]

[mastreb]

Ross, when I get a minute I'll work up a simulation of a weighted daggerboard's effect on tenderness and heel, comparing it to unweighted. The math tells me exactly what's going to happen, but a picture speaks a thousand operands and a simulation speaks a million.

[Divecoz]

Very cool .. I know its a Holiday and you have children ... But I will be waiting and watching for that POST!

Ross, when I get a minute I'll work up a simulation of a weighted daggerboard's effect on tenderness and heel, comparing it to unweighted. The math tells me exactly what's going to happen, but a picture speaks a thousand operands and a simulation speaks a million.

[Crikey]

Still waiting for someone to pipe in with how much the dagger board moves around, in the stock slot, when fully deployed?

All quiet on the western front! ....... chirp

[Divecoz]

Sorry Crikey... Basically... Not at all.. Not while Under Power or Sail.. BUT I am never down stairs during either of those two situation or at least seldom and for verrrrrrrrrry short periods.. Mine and I believes " others " Issues are when we are , at anchor.. or slipped....

[arknoah]

Ross, when I get a minute I'll work up a simulation of a weighted daggerboard's effect on tenderness and heel, comparing it to unweighted. The math tells me exactly what's going to happen, but a picture speaks a thousand operands and a simulation speaks a million.

Cool!

[Highlander]

Here's Jack Sparrows mod

http://www.macgregorsailors.com/modt/in ... ?view=1109

Most of my sailing is with 1/2-1/3 - 1/4 D/B down . Up-Wind fully down

My boat is heavily laden so my idea of having a weighted D/B is not necc. for less heel more for less tenderness when none sailors are aboard

The plastic pipe mod for the rear trailing top end of the D/B is on my agenda also I already have the materail just no time

Winged D/B is also on my agenda no time

I have alot of unfinished mods no time

I have alot of scheduled mods with parts sitting in the basement for a yr or more no time

I have suggested using sand as a substance for weight in the D/B cheap non hazardous can be dumped out for a long haul on the road & replaced @ the next beach for free , if forbid you should ever hit something as long as you do not overly strengthen the D/B that section thats below the hull it will break-off or break-away as designed the sand is a non solid even when wet its not going to harm anything it'll just wash away
winged & weighted I think would improve handling & sailing ability
Lead pellets left loose inside the D/B would also not harm the boat
J