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Bulb Keel

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WK 727
1st Mate

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USA
72 Posts

Initially Posted - 06/16/2023 : 15:15:08

I modified my keel by cutting off the wings and then adding back a bulb keel. The keel now weighs 1,250 pounds instead of the original weight of 1,050 pounds. I basically added 200 pounds at the lowest point possible and added the appropriate amount of fiberglass layers in the bilge under the keel bolts for the increased stress. More images are in the photo gallery. This was a fun/challenging project to undertake.

Regards, John
Westlawn Institute graduate
Yacht Design and Naval Architecture
04 Catalina 250 WK
Standard rig w/wheel steering
Yanmar 9hp diesel

Edited by - WK 727 on 06/16/2023 15:17:49

islander
Master Marine Consultant

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USA
4013 Posts

Response Posted - 06/16/2023 : 17:50:37

Challenging is an understatement. Beautiful workmanship. Have you had a chance to sail the boat with this modification?

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Voyager
Master Marine Consultant

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USA
5320 Posts

Response Posted - 06/18/2023 : 07:31:26

The new design looks really cool. Nice work!
Looking at the numbers, however, comparing a 1050# and 1250# keel weight to my fir keel at 1700#, I originally assumed that my boat would feel stiffer in a heel. But, the idea of using a bulb keel is that you put the weight where you need it - at the end of the lever arm - instead of distributing it generally around the keel.
The righting force is equal to the weight multiplied by the distance from the rotation point of the boat that matters. So if your 200# is located say 4 ft from the axis point, it�s righting moment is 800 lb-ft, not counting the moment from the keel fin. The math for calculating the exact moment is beyond this post, but you�ll know it when you feel it.
Like Scott �Islander�, I�d be interested to learn how the boat sails and how much less �tender� it is on heel in strong winds.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Buzz Maring
Master Marine Consultant

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USA
1764 Posts

Response Posted - 06/18/2023 : 07:37:27

VERY COOL!!

Buzz Maring

~~Freya~~
C-25 SK/SR #68
Lake Dallas, TX

zeil
Master Marine Consultant

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Canada
1311 Posts

Response Posted - 06/26/2023 : 15:50:39

Wow... did not hold it for possible. Great job, hard to follow!!

Just wondering what the effect of having the weight of the new beautifully shaped bulb spread further forward and aft would have versus the discarded central located "wings".

Would it decrease Hobby-Horsing?
Would "wings", placed far aft help?

Henk & Johanna
"Floating", a few off your "barnacles".
"Someday Lady" '95 C250WB #151 ('03 - 2016)
"Sea ya" 30ft Bayliner (04-2018 - 09-2018)
"Mariah" '96 C250WB #191 (05-2019 - 15-05-2023)
"Lady J" '00 C250WK #499 (05-2021 - 09-2022)

Edited by - zeil on 06/26/2023 16:18:35

WK 727
1st Mate

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USA
72 Posts

Response Posted - 06/27/2023 : 15:03:54

Thanks for the kind comments everyone. The forward location of the bulb in relation to the keel is to correct the squatting of the stern. The wings were 86 pounds each (with lead shavings). By removing the 172 pounds near the aft section of the keel and adding 372 pounds with the lead center closer to the front of the keel, the boat now sits on its lines with no ballast needed to level it out. Zeil, my gut is that the more we can move weight forward, the better the performance, but I am not really sure. Hobby horsing? Great question. The length is needed to create the most efficient bulb for the design weight. I wasn't concerned about catching crab pots, this is all about performance!

Regards, John
Westlawn Institute graduate
Yacht Design and Naval Architecture
04 Catalina 250 WK
Standard rig w/wheel steering
Yanmar 9hp diesel

Edited by - WK 727 on 06/27/2023 15:41:22

zeil
Master Marine Consultant

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Canada
1311 Posts

Response Posted - 06/27/2023 : 18:33:22

Just love your design incorporating forward weight consideration thereby correcting forward ballast and with absolutely beautiful lines and execution work. Your design and work is totally professional. Thank you for sharing this

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.