Marine Designs
We have boat plans (both yacht designs, catamaran designs and power designs) for all sizes. From the 12ft Mushulu Dinghy stitch & glue yacht tender to the Oceansky 57 catamaran. We design timber boats, plywood boats, strip plank boats, fibreglass composite boats, steel and aluminum boats to very modern styling for both monohull designs or multihull designs, powerboat or sailboat and in round bilge, multi-chine or radius chine hull forms.
Power Boat Chine Flat Proportions
G'day Everyone,
Just a quick article about Spray knockers or Chine flats and how to design one for your own boat.
Typically, there should be a spray knocker at the chine. The spray knocker can be built into the hull shape as a chine flat. In this case, it can be a bit wider, from midships aft, than if it is a simple spray knocker on a wood hull screwed and glued into place. Chine flats or spray knockers increase stability at low speed and at rest, reducing "flop roll": increase dynamic lift slightly: and make for a drier boat.
Generally, the chine flat should be roughly 3% to 5% of maximum chine beam from midships aft, tapering narrower forward to the stem., where it goes to zero width.
The chine flat should be dead flat athwartships or angled down slightly as it goes outboard in the section view, but do not angle down more than 5 degrees. More down angle will deflect the water from the chine too hard so it strikes the water surface with enough force to kick up extra spray, making the boat wetter.
This does not apply to "tunnel boats" as the angle chine flat is not exposed to the outside of the vessel, but only within the tunnel.Therefore any spray which is created is confined within the tunnel and forced out the back of the boat.
You can design a fine planing boat without a chine flat at all. This reduces wetted surface slightly and so is a slight advantage for very fast boats, but at the cost of less comfort in roll (particularly at lower speeds.), very slightly more "hump" getting up on the plane, and a somewhat wetter boat. Really fast offshore boats may elect to have the chine itself (with no intergal chine flat) at or just barely above the DWL at rest. This minimizes wetted surface even further, but such craft tend to flop roll at lower speeds.
Have fun !
regards
Mark Bowdidge (MRINA)
Bowdidge Marine Designs
