adding a keel to a boat.

Discussion in 'Boat Design' started by gentleman, Oct 25, 2011.

  1. gentleman
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    gentleman Junior Member

    if we build a boat thats not designed with a keel, how much will it slow it down and what effect will it have far as turning when we add a keel to it?
     
  2. gonzo
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    gonzo Senior Member

    It depends on how long a string is. Can you post more information about the boat? For example: power, sail or rowing, dimension, the lines plans, etc.
     
  3. gentleman
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    gentleman Junior Member

    gentleman's racer, 30ft long 6ft wide, fiberglass haul, 750hp. the keel can be no shorter then 8 ft in length, it can be longer but most all our race boat have 8ft keels. the keel has to be 8 inchs or more in depth at it's deepest point, also from the end of the stern to where the shaft comes out of the keel has the be 40 inchs no shorter or longer. we were just wonder how much it would slow the boat down, or will it? being where the G'Rer was designed with no keel.
     
  4. gonzo
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    gonzo Senior Member

    I think you have other threads on a similar subject. There are no gentleman's racers. It is something like "tall ship", means nothing from a technical point of view. Can you post a lines plans with the intended modification? Also, some analysis of the design, like CG,etc. would help.
     
  5. viking north
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    viking north VINLAND

    I'm no designer or architect (a builder) but it's not that simple. Example if you make the keel too short, your shaft angle becomes greater in a low deadrise craft. The result could be, as power is applied you end up with not only forward but excessive downward motion of the stern(squatting) creating excessive drag which would far exceed the small amout of extra wetted surface drag caused by any length of keel. With that amount of horsepower adding a properly engineered keel/optimum shaft angle you would have some but little effect on overall average straight line speed. (key word straight line) As for the effect on turning, an added keel will greatly reduce the ability to slide her *** around (remember a boat turns by transverse movement of the stern) As i prev. stated i'm a builder not a qualified engineer so I can only offer these generalities from boat operational experience---Geo.
     
  6. tunnels

    tunnels Previous Member

    A keel could serve the purpose of a fin and used to make the boat turn really quickly and possitively . No keel past where the shaft comes out from under the hull so you could make the keel act as a pivot point and make the steering very responsive and responsive . With all 750 horses pulling there weight would be nice to steer but would deffinitely look at Hydraulic steering and do a nice shaped rudder that wouldnt do silly things and maybe let go when steering a hard turn !
     
    Last edited: Oct 27, 2011
  7. viking north
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    viking north VINLAND

    The problem is by regulation, the end of the keel has to be 40in. from the transom/stern. 40inches in on 30ft(360in) LOA places the aft end of the keel and the aft section of the keel essentially at the very point to hinder "sliding her stern around" for quick turns. On second thought a shallow keel with that much HP might just prevent excessive sliding out on a turn by creating some bite. Thus the keeled boat could possibly turn inside it's non keeled competitor. The question here is how much would the speed drop off as your are re orienting the hull in the desired direction. It would be interesting to compare a strut verses a keel setup on two identical hulls. My gut feeling is the keel version would lose out speed wise as a result of handling the turn. (bite verses roll over)
     
  8. gentleman
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    gentleman Junior Member

    thanks for the advice guy's, as for the boats that race down home here has alway's had trouble turning in one way or other, the course is set up to make U-turn, straight down, U-turn and straight back. whats the guy's haven't learned yet is if they'd just slow down more then they do going into the corner, the boats would come around quicker, but the fear of losing the race make them try to take the corner's to quick.
     
  9. gentleman
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    gentleman Junior Member

    stepped bottom

    we have contacted a guy who can make the plan's-blueprints of the boat (el lagarto) she is a hacker designed gold cup racer from the 20's and 30's. the reason we want one of these style boats is because they are very very close to the style boat's that we race, we don't want anything that look's really out of place so we figured why not one of these style boats. but anyway's, these's guy can blue-print the boat to exact measurements or so he claims, here's the thing, it's a (stepped bottom) there are 5 individual steps, each step is maybe 5-6ft long, each step starts from 0 inchs and ends up to be 3/4 inches in depth. are there pro's and con's with a stepped bottom? what do ya think, go with the stepped bottom? are they faster?
     
  10. viking north
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    viking north VINLAND

    Wow! outta my knowledge other than steps are suppose to help get her upon a plane faster, maybe one of the designers could respond .
     
  11. gonzo
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    gonzo Senior Member

    Stepped bottoms, called "shingle bottom" at the time, were banned because they were too fast.
     
  12. viking north
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    viking north VINLAND

    GONZO- as a racing man he's hooked on steps now --TOO FAST-- My bet GENTLEMAN you're gonna incorporate steps :D --Geo.
     
  13. itchy1finger
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    itchy1finger Junior Member

    here are our boats
     

    Attached Files:

  14. viking north
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    viking north VINLAND

    That white/blue underwater profile looks like a mover. Why is the engine so small in that yellow Stinger :p
     

  15. gonzo
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    gonzo Senior Member

    It looks like a shallow vee skiff. That boat has nothing in common with the racers of the early 20th century. Is the skeg for directional stability or for a tighter turning radius?
     
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