Keel design advice please

Discussion in 'Boat Design' started by geoleo, Dec 25, 2013.

  1. geoleo
    Joined: Dec 2011
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    geoleo Junior Member

    Dear friends, I just purchased a 1983 Brewer 12.8 cutter/sloop. Similar to the WHtiby 42 but with a centerboard.. The former owner got mad at the centerboard and dropped it in a Bay in DR. Slot in keel still there. Now I want to close up slot next time in yard as I know it s causing drag. Its 3.5in wide X 6ft long x 2ft deep. I plan to just put about 5/8 thk FG over opening. Now here is my question: What, if anything , could I put in place that would make boat more stable and reduce lee way- I really don't care much about pointing ability. I was thinking of a sort of modified LARS keel like on some catamarans. Or even a bolted stainless steel 'L' maybe with a shape say 8X8x 3/4 Help please :)
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Contact Brewer, as the board was ballasted and you'll need to replace this weight.

    As to reducing leeway, well this requires lateral area, which with the board removed has been dramatically reduced (not good). Your boat also carries a healthy ballast/displacement ratio, of which the board was a significant portion, so you're screwed in the area as well.

    If you want more stability, you need weight down low. A bulb on the end of the fin will help, but not as well as a deeper fin or the old weighted board, both of which place the weight lower.

    The logical solution is a replacement board, as nothing has to change. If you want a board fee boat add a minimum of 6" to your current keel, though a foot would be better. Make the keel extension all lead and fill the forward portion of the slot with lead as well. The after portion of the slot can just be foamed.

    The Whitby 42 carried a full length keel of 5' draft. It wasn't known to be a great pointing boat, but it didn't skid off much either. She tracked well, but backing down she was nearly imposable to steer and helm response in maneuvers weren't described as sparkling. Your boat has much better appendages and does everything better as a result. It wasn't an upwind screamer, but without the board is much more disadvantaged.
     
  3. geoleo
    Joined: Dec 2011
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    geoleo Junior Member

    Centerboard gone. Brewer 12.8

    Brewer was contacted before board was dropped. He said it should be fine without it. He said most Brewer 12.8 boards have been removed . aA yacht Club in NY directed him to include them in the design. Former owner said board weighed 300 lbs. and slowed boat 0.5 kn when lowered and improved upwind ability only 10 degrees. He also said several owners used cavity as another fuel or water tank(which boat doesn't need). He had boat 12 years and cruised a lot and that board worked poorly in its up/down mechanism and had a wire that vibrated over 6kn -wire was to keep board from going forward . Im just searching for a way to improve the leeway without going nuts. Adding weight to the cavity wouldn't take too much work but the boat is quite stable now and I wouldn't think 300# weight will improve leeway. I had a R Woods open bridgedeck 36 ft Catamaran before and rebuilt the daggerboards of foam and epoxy and Kevlar/Fg mix but that boat was fast and light. I was thinking maybe a modified LARS appendage as the bottom of the brewer is straight and fair in the old centerboard area. The current performance is close to my previous Island Packet 44 --maybe a little slower-they are almost the samesize. :p
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    10 degrees is a huge difference in pointing ability. The Whitby used the aft portion of the keel as a tank, though also had more volume to play with.

    I didn't realize the weight was only 300 pounds. I'd just stuff a 300 pound slug at the very bottom of the forward portion of the slot and seal the after portion. You do lose a significant amount of upwind ability, but this boat (again) never was a killer upwind anyway. Personally, I wouldn't want to kiss off 10 degrees, but it is a simple fix.

    Pointing ability can be improved without the board, but you'll need some draft. The 300 pound lead slug could be dangling below the slot, which will help and offer additional lateral area to help with leeward slip too. You could design some end plate effect into this slight addition to the bottom of the keel if you wanted, though I don't think it'll be a big improvement, maybe a few more degrees of windward ability. Maybe a 6" thick bulb and beaver tail, dangling below the slot, but I'll bet this will require a lot more then 300 pounds of lead. The forward end could be lead, with a foam cored after section faired in. I guess it depends on how much trouble you're willing to spank this issue with.
     
  5. LCrosby
    Joined: Dec 2013
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    LCrosby Junior Member

    I agree with PAR, 10 degrees is a huge loss.
    All of the reasons you have given (including Brewer's), don't come close to justifying
    a 10 degree loss.
    How well did she point to begin with?
     
  6. FAST FRED
    Joined: Oct 2002
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    FAST FRED Senior Member

    Maurice Griffiths was a Brit designer that solved most of the problems with centerboards (hatches too).

    Perhaps installing a better built and shaped board of a better design would be easier than simply plugging the slot.

    You would keep the windward ability , and not have to hassle with stoopid board weights that will change the righting moment by .001% at best.
     
  7. geoleo
    Joined: Dec 2011
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    geoleo Junior Member

    centerboard

    Yes true, I was thinking of a thinner lighter board with a weighted end without the damned wire that was there to prevent board from going forward and hitting forward end of opening. This wire vibrated at speeds over 6kn. The board "thunked" and itself vibrated a lot too. Maybe a foam/Kevlar/epoxy 2 inch thick board with lead weights on the end and some sort of a cushion stop at the forward end of opening will be an answer. Slot/board clearance needs to be tight say 1/8".
     

  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Board hoist inventiveness is all over the place. I've seen dozens of various approaches. The one I like best is a Phillip Rhodes design, that I've been blatantly sealing and using for years. It has no lanyard in the water and the mechanism stays above the board. The actual hoist can be just tackle or sent to a winch on bigger craft or the coolest setup is a hydraulic ram, which is used on bigger boats.

    This arrangement is an "over center" pull setup, so you will need room forward of the pivot pin, inside the case, but like I said, this setup is as simple and reliable as it gets. S&S also has some clever approach to board hoist setups.

    As I mentioned earlier, just replacing the board would be the simple solution. The slot can be sealed to a degree and a better appendage design could also benefit. Getting the damned hoist lanyard out of the water just has to be addressed. I can't imagine why designers still do this.
     
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