Question on deeper deadrise on a light hull

Discussion in 'Boat Design' started by Wayne Grabow, Jul 24, 2011.

  1. Wayne Grabow
    Joined: Aug 2003
    Posts: 251
    Likes: 17, Points: 18, Legacy Rep: 297
    Location: Colorado

    Wayne Grabow Senior Member

    Question: How important is it to have the chine well-imersed in a power runabout?
    Background: I just built a 18' variable deadrise hull with a fine entry transitioning to 6 degrees of deadrise at the transom. It performs as you might expect; planes easily with low power, fast (for 50 hp) in flat water, but the bow rises enough when planing that we get wave slap about 1/3 back from the bow when going upwind in a chop. The hull is rather light; bonded West system with no fasteners. With a monocoque hull, the "slap" resonates like a violin.

    So now I am thinking of a new design with 14 degrees of deadrise at the transom maintaining constant deadrise for the aft 50-60% of the length then transitioning into a fine entry. This should keep the bow down and present more of a "V" aft to cleave the waves with less hull slap Problem is that with deeper deadrise on a light hull, the projected weight is less than the displacement when the chine is immersed. With two people aboard the chine will be slightly exposed; with four people it will be slightly immersed. Is this a problem? I don't want to reduce the beam due to accomodations and static stability concerns. I already plan chine flats so that the"V" deadrise is less than the chine beam. Maybe I am overly concerned, but it is better to ask questions than to make mistakes.
     
  2. gonzo
    Joined: Aug 2002
    Posts: 13,378
    Likes: 329, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    You will have very little initial stability. Also, it will probably chine walk or even worse, trip on the chines making the boat get out of control.
     
  3. Wayne Grabow
    Joined: Aug 2003
    Posts: 251
    Likes: 17, Points: 18, Legacy Rep: 297
    Location: Colorado

    Wayne Grabow Senior Member

    Thank you, Gonzo; just what I needed to know. I had considered initial stability, but, with little powerboat experience, hadn't considered the likelihood of chine tripping. So the deep V monohull by definition must be a fairly heavy boat. I need to either add some weight or reduce deadrise slightly.
     
  4. gonzo
    Joined: Aug 2002
    Posts: 13,378
    Likes: 329, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Deep vee fast boats are normally narrow.
     
  5. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 470, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Match your immersed volume with the anticipated weights you'll encounter and draw up a hull shape to conform to the SOR.

    Slapping and pounding will happen on any hull form and the faster you go, the more likely you'll experience it. If you over drive a warped bottom, you run into this issue pretty quickly. You'll need more speed to see the same affect on a deeper V hull form, but you'll eventually run into to it on them as well.
     
  6. anthony goodson
    Joined: Mar 2007
    Posts: 421
    Likes: 17, Points: 18, Legacy Rep: 256
    Location: Dorset UK & Murcia Spain

    anthony goodson Senior Member

    Wasn't there a detailed discussion about this idea a few months ago ? I can't find it ,does anyone else remember?
     

  7. Wayne Grabow
    Joined: Aug 2003
    Posts: 251
    Likes: 17, Points: 18, Legacy Rep: 297
    Location: Colorado

    Wayne Grabow Senior Member

    Thanks all. I reduced the deadrise to 11.75 degrees which better matches the anticipated weight of the hull with minimal crew and equipment. Should be fine now. Although I don't plan on high speeds, I can understand (after Gonzo brought it to my attention) why it would be better to have the chine consistently immersed and engaged, rather than catching unpredictable waves, for predictable performance.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.