Slight centerboard vibration under sail

gsr977

gsr977

Apr1977-Sunfish
Mostly occurs at higher speeds. At times acts like a speed brake. I positioned my wooden centerboard with the eyelet forward. At this position the center board sweeps aft, do I have it in backwards?
 
Re: Sleight centerboard vibration under sail

The longer side of the blade should be forward. It could be a few things. THe board will vibrate if you have it too far down when sailing on a reach/broad reach or run. If you are not close hauled, try raising it a bit until is stops vibrating.

You might also try putting some carpet strips or velcro strips in the trunk to make the fit more snug
 
Re: Sleight centerboard vibration under sail

Sounds like I had it in backwards. I'll flip it around and see if the condition is remedied. Thanks!
 
I've also discovered the same condition when I have an accumulation of sea weed. It's easily resolved by raising and lowering the centerboard. PLEASE, when raising & lowering, be prepared to adjust your trim based on conditions!
 
gsr977 said:
I positioned my wooden centerboard with the eyelet forward. At this position the center board sweeps aft, do I have it in backwards?
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This is a source of debate. The composite "racing" board, now standard, goes in oriented the opposite way from how the wood board instructions show. Some wood board owners, especially those with the "Shadow" profile from the 1970s swear flipping the wood board long edge forward performs best for them. Try it both ways and see how it performs for your sailing style.

Vibration can also develop from the play in the daggerboard trunk. Thin strips of I/O carpet or the soft side of wide peel & stick Velcro have been stuck vertically in the trunk to dampen vibration.


From a 1992 Sunfish/Laser setup manual

4609349035_e6c140b5ab_b.jpg
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The profile of the board should be a foil, with one end more sharp and the other more blunt. Like a wing, or sail for that matter the blunt end goes first. While this shape is obvious in the new boards, it's less defined in the old wood boards.

Regardless, if you have vibrations with the board in the correct orientation it is important to understand the cause. While I would recommend padding the trunk, this only masks the problem.

Vibrations are caused turbulence off the trailing edge. This is similar to how a whistle works.

Imperfections in the trailing edge make this problem show up a much lower speeds. A perfectly shaped trailing edge would not hum unless superman were sailing it at some amazing speed. This is why my new board is quiet, and my practice board screams at me.

Solution: Reshape your trailing edge. Sand away imperfections to get a crisp, smooth trailing edge.
 
The diagram that Wayne showed (from 1992) might confuse those with newer boards. The current version has the curved, shorter edge facing aft. Regardless, as fbjru says, the blunt edge always goes forward. I noticed the same thing when changing from a mid-80's wood board to a new composite one (with no imperfections on the trailing edge that I could find). I've found that proper depth in the trunk (and a little soft Velcro) takes care of the problem pretty well.
 
Having an older wooden centerboard, according to the schematic provided, I positioned the board correctly with the curvature sweeping aft. As far as my centerboard is concerned (circa. 1977) the leading and trailing edges seem to be identical. I'll try reversing it once I can get back to the lake and see if things are remedied or worsened by doing the switch around. Thank you all for providing more insight into this. I'll report my findings.

EDIT: I may very well need to look into the carpet mod.

P.S. Does the newer style centerboard drop right in and work well with an older hull, and does it float?

Thanks.
 
gsr977 said:
As far as my centerboard is concerned (circa. 1977) the leading and trailing edges seem to be identical.
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If your board is the "old style", they were pretty nondescript unless someone reworked them. Straight from the Sunfish shop both edges were rounded the same and had equal thickness. The changing arc at the tip was subtle at best. Racers would often feather one edge making it the trailing edge. Racing Class rules set limits on how much the edges could be modified and still be allowed in class events. Today many variations are found, the result of all the customization people did.


4610523531_15b2dc6dfe_o.jpg


gsr977 said:
P.S. Does the newer style centerboard drop right in and work well with an older hull, and does it float?
Click to expand...
The composite board does drop right in and IMHO adds to performance.

No it does not float..., tether it.

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Composite looks appealing, I wonder if intensity sails composite copy is worth a darn. Price seems reasonable.
 
Wayne, unless my board is special, the new boards do float. I've "tested" it and the results saved me $260 that would have otherwise been a gift for Davy Jones.
 
fbjru said:
Wayne, unless my board is special, the new boards do float. I've "tested" it and the results saved me $260 that would have otherwise been a gift for Davy Jones.
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I wonder what's changed. I bought mine in the late '90s and thought I remembered it sinking like a rock. I don't think I've dropped it in the lake since then..., always tethered.

Could the urethane foam core to outer shell ratio vary enough to see a range of
buoyancy? Did they switch from steel rod reinforcement to aluminum?

I'm gonna put re-check float test on the to do list ... thanks for the heads-up
 
That's really strange.

As far as i know nothing has changed in the rods. I have four of them. At least two of them show rust from where the steel rods meet the surface.

All of mine where built between 99 and 06. They all have the built in handle. I'm tempted to go test all of them to see which ones float.

It seems like there should be no reason for them to sink. They are,after all, constructed similarly to surfboards with a foam core and ?epoxy? outer coating.
 
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