Eliminating Hull Slap

We spend a lot of time at anchor and the resounding slap of the water against the hull is unacceptable to us. When the boat was hauled for the winter of 2006-07, I studied the configuration of the hull toward the bow to determine the best way to fill in the area and, hopefully, eliminate most, if not all, of the slap.

jb_chinefill1Photo 1 shows the completed project.

On my 32, I filled in the chine starting 33″ from the bow and going back 47″. At the point where the waterline meets the chine, I filled 9″ aft and 38″ forward of that point. After grinding out the gelcoat in the area to be filled, I filled under the chine with pieces of 3/8″ CoreCell foam, bound with West System 404 bonding compound. This area was then covered with a 6″ foam panel. This follows a line directly under the chine to the hull. The area about 6″ before and aft of the filled area is tapered up into the chine.

jb_foam1The foam section was covered with 2 layers of West 3″ unidirectional carbon tape, with the first layer running vertical and the second running horizontal. The entire area was fared with West 410 fairing compound. From an inch above the waterline and below, I covered with 2 layers of epoxy resin. Above the waterline, I used factory gelcoat to finish that off.

The work was done in 2 sessions, first in April and then in June. Photos 2-4 show work done in June.

jb_foam2Photo 2 shows a 3″ foam section laid up under the chine. I used double-cut 3/8″ thick CoreCell panels. The longitudinal cut allows the foam panel to wedge up in the chine. The foam is bonded to the hull with the West Systems epoxy resin and 404 bonding compound. To the left of this new work, you can see the 24″ section filled in initially in April. As I mentioned, I found that I needed to fill in a 47″ section of chine.

Photo 3 shows the area covered with a 6″ foam panel, bonded directly below the chine and down to the hull. The area is filled and smoothed forward into the chine.

ijb.foam3Photo 4 shows the area covered with 2 layers of 3″ unidirectional carbon tape. The first layer was laid in vertically, the 2nd layer horizontally. The entire area was fared with West Systems 410 fairing compound, covered with 2 layers of epoxy resin, and gel coat above the water line (as seen in Photo 1).

The bulk of the area filled in is below the waterline.

My changes have eliminated about 95% of the hull slap and all of the internal resonance associated with hull slap. I’ve taken pictures before and after the changes, and I see no negative effects in performance or wave deflection. Most of the area filled is out of the water at or above 7 knots. A one-piece shaped foam block would simplify the process. I discovered a method to shape a foam block, but only after I started my changes. With the hull molds, Nordic Tugs could easily provide foam blocks to those customers wanting them.

I’m very satisfied with the changes I’ve made. This winter, I may fill the forward chine in an additional small wedge-shaped area (no more than 6″) to eliminate any remaining slap when anchored in high winds and short chop (the cause of the other 5% of my current hull slap).

John & Doris Baczek
Puffin – NT 32-266