The Dark Knight

Removing the IOR bump

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Are there many old IOR boats that have had the infamous IOR bump removed and how was it done?

I was just looking on the "Police car" FB page https://www.facebook.com/police.car.sailing/ and someone had posted photos of work they had done to remove the bump from a Davidson 39

It's not structural work, so probably not so "expensive" to do. I wonder if the change has tamed the boat's down wind manners.    

 

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It would have to help some but that bustle and pinch was only a contributor to the "Death Roll".

The real problem was the boats were full displacement hulls and the racers would run them up to the hull speed wall and keep piling on sail - tall, skinny spinnakers in 25 or 30 knots of wind are going to broach any boat that can't break out of the displacement wave train. It just digs a bigger & bigger hole and rolls around in it.

People just didn't do that sort of shit on Westsails or Taiwan Teakies or they'd roll the decks under too.

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2 hours ago, The Dark Knight said:

It's not structural work, so probably not so "expensive" to do. I wonder if the change has tamed the boat's down wind manners.    

 

47341214_10216213371634567_6185163230235

 

 

 

 

yeah, you're right,  that doesn't look expensive...    to some billionaire

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1 minute ago, Grande Mastere Dreade said:

 

yeah, you're right,  that doesn't look expensive...    to some billionaire

It will be cheaper to put on a false bottom to smooth out the bump than it would to make a structural change to achieve the same goal. 

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Quite a few old half tonner & quarter tonners have been 'IRC Optimised' here in the UK. Which does sometimes involve removing the bump. 
Some good info & pics here: http://www.corby-yachts.com/refits.html

I've no idea how much it makes a difference because its usually combined with new keel, new rudder & new rig. 
I can't imagine it being a cheap job though.  

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Interesting looking at some of the mods done by Corby.

They take the same approach as in the photos I posted earlier. Add some external ribs and fill with hard foam, then put a skin over.

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Wonder why all the ribs? Probably just to get the shape right. But I'd treat the existing hull as the structural/watertight hull, and just add a foam layer + very light glass exterior skin.

If you wanted to it right you would laser scan the hull (< $2k), bring it into a CAD program, add the foam layer in 3D, and then CNC cut foam blocks that would perfectly create the shape you want. No upside down glassing of ribs and fairing. It would all just be very fair from the start.

Police car ribs look like plywood (shudder)

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Would add considerable flotation, no? What is the result? Insignificant?

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The wood ribs are used for fairing in the Davidson crease on a Davidson 39 - not Police Car, which was an alloy Dubois.  The Davidson mod photos got mixed in with the Police Car posting.  The Davidson crease is fairly evident in the photo below of Waverider

Not really removing the bump (crease) on the Davo per se.  I suspect more extending/fairing it to increase the sailing length.

Waverider shipping.jpg

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Apples and oranges. Those photos show an egg crated bump removal, not added surface area, thereby shoaling the hull. Most bumps, as in the Dubois example cited, are molded in, cutting out part of the hull and adding a new piece ain't easy. Neither is adding foam and glassing upside down and achieving a fair result. Nb the keel stub showing after the ribs are removed. Some IOR boats had U shaped bows, adding a bustle to such a boat might help. Or not, here's an intelligent article about shape.

http://www.oceannavigator.com/January-February-2003/Shaping-an-offshore-hull/

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Then there were the IOR local measurement point bumps that looked like a grapefruit was stuck to the hull and glassed over. At least they would be easy to fix. 

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Are you going remove lumps while you are doing the bumps? Our 1982 32’ IOR had all of the maxed out measuring points and duck tail. It was one of Brit Chance’s last IOR efforts. The mathematically optimised hull was a sight to behold out of the water. She was susceptible to broaching above 25 knots going downwind

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Are you going to remove her lumps while you are doing the bumps? Will this be a full liposuction reduction?

Our 1982 32’ IOR had all of the maxed out measuring points and duck tail. It was one of Brit Chance’s last IOR efforts. The mathematically optimised hull was a sight to behold out of the water. She was susceptible to broaching above 25 knots going downwind.

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18 hours ago, Zonker said:

Police car ribs look like plywood (shudder)

Not Police Car. It was photos from someone else's bump job mod that they shared on the PC page.

 

Police Car is getting the bottom paint finalised, bump and all, ready to get wet.

 

The owner is keen to sell but no one wants to buy a project on the hard, so he is trying to get it ready for the water to make it a more attractive proposition for buyers. 

 

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Unfortunately it seem that the sellers budget will not cover the full on PC paint job or vinyl wrap

 

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https://www.facebook.com/police.car.sailing/

 

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I wonder what the deck is like? It had holes in it 20 years ago! Was only 3mm plate to begin with...

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Regardless (N/M 1 ton) version, had the stern IOR whoopties evened out and the bow reshaped in the early 90s.   OH Rodgers engineered that project.   I was part of the sanding/fart-rock crew that faired the hull.

As far as I know, the boat is still up in the Great Lakes.

- Stumbling

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