How to avoid hull slap on plane

Marco Flamingo

Active member
I don't know how useful this will be. First, it may only apply to the CD 16. Second, it may only be practical when solo. But here goes.

On a recent trip, I was on plane several hours at about 18 knots. Sea conditions were generally calm, but there were slight swells and occasional wakes from other boats. We all know the feeling where the swell lifts the bow, and again, and again. By the fourth time we can predict that the hull is going to slap into the next swell, sometimes making the hull shiver and us wish that we had throttled back. If you don't slow down, it goes SLAM, Slam, slam, slap and then you can continue on until the timing syncs up and you go through the same thing again. Or, you could throttle down to 12 knots when that starts and throttle back up. Or just leave it at 12 knots.

I thought, what if I could change the angle of my deadrise? Instead of going flat on plane into the next swell when the synchronization started, what if I turned and the boat heeled? It felt a lot like skiing through moguls, if you've had that experience. When I felt that I was going to "launch" over the swell and smack the next swell, I turned sharply to one side as I was at the top of the swell. The boat heeled over and I didn't present such a flat surface to the next swell. It felt more like I sliced into it rather than slapping it. As I went up that one, I reversed helm and did the same thing to the next swell. The sync was broken and I went on at 18 knots until I had to do it again.

The "turns" were short and fast, just enough to heel the boat, and I remained surprisingly true to course. Again, like skiing, you can throw your skis right and left and still remain in the fall line. That's sort of what I was doing. I was staying on course enough that it didn't effect my GPS speed. When I checked my wake, I couldn't tell I had been turning back and forth.

After a while, it became routine and I didn't really have to think about it. The timing of the swells indicated when I needed to turn to slice the next swell. I just felt like, okay, here we go again, turn this way, that way, and back, and continue on. Kind of like dancing.

I was solo, and like when driving, if you've got the wheel in your hand, you don't get car sick. I'm not sure what a passenger would think of this technique. And on the 16, getting bounced around is standard procedure. Just thought I'd put this out for anybody who wants to try it. Be sure to get permission from the Admiral, if that's applicable.

Mark
 
Hey Mark,

Yep, know what you're talking about. It will work on other powered boats of various hull designs as well. I'd accomplished it with my CD 16 as well as my 16' McKee Craft, center console. However, there were times I'd "miscalculate" with a resounding slap and spilt drinks.

My father-in-law taught me; he was one of those people that could take any boat, get in it and a few minutes later do anything you'd want with it. For him operating a boat was as natural as breathing. Me? I have had to learn everything and sometimes it was rather, well, let's say interesting... fun though :lol:

Thanks for the thread! Take care and be safe out there.
Spuncopper
 
Interesting and makes sense. How about rapid shift of weight, or trim tabs to induce a quick heel to one side?

In most of the C Dorys, we tend to put the bow down when we get into these type of conditions, but trimming with trim tabs, or the motor with a Permatrim.
 
I've done the same thing, and slanting over waves works. And I've also done some swerving to avoid weed beds. But one caveat or caution: Once I was dodging waves on the Mississippi, and suddenly, seemingly out of nowhere, a bass boat passed me only 20 feet to my port at about 70 mph, with no horn to warn me. I was unaware he was behind me, and if I'd dodged some weeds at just the wrong time he would've t-boned me.
 
Good point. I had some idiot do the same thing to me west of Key West. With the whole Atlantic ocean to run in, this idiot passed me 10 yards to port. I added a rear view camera and monitor and now can keep a watch aft.
 
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