quad keels on cat??

Discussion in 'Multihulls' started by massandspace, Dec 23, 2017.

  1. massandspace
    Joined: Sep 2017
    Posts: 33
    Likes: 0, Points: 6
    Location: Salt Chuck

    massandspace Junior Member

    Building a 27' mini cruising cat and designing/thinking about the keel(s). Considering both fixed and sliding boards at this juncture.

    Brainstorm question on fixed (LAR) keels:

    Since the main issue with LAR keels seems to be there relatively inefficient share, why not build and fit 4 fixed keels (instead of 2)? Two on each hull....about a third of the way in from each end? You could then make them quite a bit less "LAR" in shape (i.e. more draft per length) and thus higher aspect, which I think would help quite a bit in performance. Will the flow coming off the back of the front set of keels disrupt the ability of the rear keels to "work"?

    The main issue, I am thinking, would be maneuvering at slow speeds in a tight marina, as the keels would tend to prevent this. But we never go to marinas (unless to get fuel)...the boat is stored dry...and the docks there are very wide and easy to get into. And you sail 99.9% of the time anyway...build the boat for that, no? The boat will also have a steerable outboard so that will at least give some directionality to the trust vectors. Finally, we live in an area of the country where "drying out on the keels" is not really an option (huge tides and huge rocks)....although I would argue that it would still be possible with 4 keels resting into softer sand or mud...(why not, as long as the loads are spread amongst all 4 and they are properly built?)

    It seems the amount of extra work would not be that bad as you would still have to buy, measure and cut accurate materials for 2 keels anyway , so 4 just means use the templates twice more before chucking them. Material cost also not that much more as each of the 4 would be about 1/2 the size of the full LARs...more work, yes, of course....but that is all relative in the end.....

    Thanks for any advice/opinions....
     

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  2. rwatson
    Joined: Aug 2007
    Posts: 5,818
    Likes: 269, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    "Will the flow coming off the back of the front set of keels disrupt the ability of the rear keels to "work"?"

    Maybe. It will certainly muck up your steering with the rudders, making turning ( tight marinas or out on the water) really awkward.

    If you want level ground support, at least put the sternmost skeg where you can hang the rudder off it.
     
  3. outside the box

    outside the box Previous Member

    Ron Given's Split Enz had a forward dagger well forward of the main beam/mast position and the balancing board near or in the cockpit. He did this setup in the early 1980's but the crew found the shifting the four boards to be too much of a problem and changed to a more conventional setup. But Ron was proud of his four boards/two rudders approach because by careful positioning, Split Enz would sail herself. QUOTE="massandspace, post: 820804, member: 62755"]Building a 27' mini cruising cat and designing/thinking about the keel(s). Considering both fixed and sliding boards at this juncture.

    Brainstorm question on fixed (LAR) keels:

    Since the main issue with LAR keels seems to be there relatively inefficient share, why not build and fit 4 fixed keels (instead of 2)? Two on each hull....about a third of the way in from each end? You could then make them quite a bit less "LAR" in shape (i.e. more draft per length) and thus higher aspect, which I think would help quite a bit in performance. Will the flow coming off the back of the front set of keels disrupt the ability of the rear keels to "work"?

    The main issue, I am thinking, would be maneuvering at slow speeds in a tight marina, as the keels would tend to prevent this. But we never go to marinas (unless to get fuel)...the boat is stored dry...and the docks there are very wide and easy to get into. And you sail 99.9% of the time anyway...build the boat for that, no? The boat will also have a steerable outboard so that will at least give some directionality to the trust vectors. Finally, we live in an area of the country where "drying out on the keels" is not really an option (huge tides and huge rocks)....although I would argue that it would still be possible with 4 keels resting into softer sand or mud...(why not, as long as the loads are spread amongst all 4 and they are properly built?)

    It seems the amount of extra work would not be that bad as you would still have to buy, measure and cut accurate materials for 2 keels anyway , so 4 just means use the templates twice more before chucking them. Material cost also not that much more as each of the 4 would be about 1/2 the size of the full LARs...more work, yes, of course....but that is all relative in the end.....

    Thanks for any advice/opinions....[/QUOTE]
     

  4. pogo
    Joined: Mar 2010
    Posts: 342
    Likes: 9, Points: 18, Legacy Rep: 73
    Location: Germany Northsea

    pogo ingenious dilletante

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