Loss of stability while powering

[Spirit of the Wind]

Has anyone encountered this problem? I have a '96 I have seen it with both my old 50 HP Mercury and my new ETEC 90. In rare occasions while powering at 18 MPH or higher I lose directional stability. Ballast is empty, rudders are up and the centerboard is fully up (I have verified the latter.) Last weekend it occurred after I was passed from astern by two powerboats, one on each side of me. The wakes were quite small; maybe 12 to 18 inches. As the wakes hit my stern quarters, the bow started to wander and the boat started to heel back and forth from one side to another. These oscillations continued to increase in severity with each oscillation. It feels to me that if I were to continue high speed powering, the boat would quickly roll over on its side. It's not unlike what happens when you forger to bring the centerboard all the way up and try a high speed turn except that the boat oscillates from side to side instead of just heeling away from the turn. I've learned that the only way to recover is to immediately chop the power. This brings the boat back under control.

I'm speculating that the problem is related to the fact that at high speed, the forward section of the hull is out of the water and the boat is planing on the aft half of the hull. Would adjusting the motor mount to try and bring the bow down help? Has anyone else experienced this and/or found a solution?

Thanks is advance.

Bob Cameron
Spirit of the Wind

[edurbin]

Yeah I've had that feeling Bob. Running parallel with another boats wake. I look for it now and cut the power before it turns into a problem.

Craig

[David Clarke]

I have encountered similar situations under the conditions you described. (M) I tend to float off course each way about 15 degrees. It feels like the boat is surfing down the wave at an angle then has to climb the back side as it passes under the boat at an angle. I tend to counter steer as the wave passes under but if extreme conditions happen powering down seems like the best option that's left if out of control. I have found the more that this has happened to me the more I have started taking notice of crossing the wakes of the boats around me. If I see larger waves coming the best bet is to track at about a 45 degree angle into the waves and the Mac tracks like a champ and cuts right through. I don't know if there would be a better way to negotiate the situation. I don't enjoy following waves that are perpendicular to the stern either but they don't generate these problems to a high degree. I guess it's all about the angles.

[Rolf]

I have the tohatsu 90, and have reached speeds of up to 32 mph. The Mac is a very stable boat, but at higher planing speeds lightly loaded with no ballast the very flat aft bottom is very reactive to even small wake turbulance. With the Mac's light, long, narrow shape it is only logical these small waves can still have a scary affect, although I've never experienced it as bad as leaving the c/b down, which I have done. Loaded down and with ballast, these small wakes pretty much bounce off and under the Mac at highr speeds. Interesting note-- I've felt these small wakes just as bad in the harbor while cruising in my friend's 40 foot Sea Ray Sedan bridge deep v cruiser-- just never give it a second thought when you're sitting in a over 12000 pound boat.
Rolf

[awolfe]

I have had a lot of experience with small powerboats, less with sail boats. My '98 x was bought new with a Nissan 90. And I too have experienced the motion you describe.

I however never felt out of control as long as I have no passengers forward - on the v berth or on the bow. As long as most crew weight is in the cockpit, the boat will behave. IMHO, if you lower the bow, as someone suggested, the boat becomes more unstable.

I would suggest that the more you experience the feel of being pushed around by quartering waves while at high speed, the more confidence you will gain that the motion is normal. And (to a point) of little concern.

My experience has been that for some, especially sailors, the motion of the X at speed can be unnerving-even with ballast full. Its similar the the uncomfortable feeling non-sailors get while heeled over in a sailboat. But even powerboaters can feel uncomfortable sometimes on our boats. We sit up higher and our boats are narrow and long.(as previously stated) So any motion is amplified.

Having said all that. I still try to hit wakes and waves at 60 to 90 degrees. And cutting the power is always an option (unless you're towing a skier or wakeboarder). But I maintain that the Mac is a safe boat at planing speeds under most "normal" conditions.

I find that the boat will squat, wallow, roll a little, but will work itself through the wakes. If anyone finds that the mac is unstable in any sea condition that would be considered 'likely' to be encountered, we need to know about it. I just don't believe it is... I think its a matter of getting used to the natural motion of the hull under power.

Tom
Annie's Song
Denver

[Spirit of the Wind]

I've had Spirit of the Wind for 9 1/2 years now and while I seldom encounter the conditions I describe, I think I have learned when it is best to chop power. I previously had a Bayliner Contessa 28 powerboat and experienced similar behaviour, except that the boat always worked through it on its own without loss of control. I believe that every boat, being a compromise, has some part of its performance envelope where undesirable behaviour occurs.

My never loses control completely. However, with each oscillation, the rolling intensifies. The purpose of my post was not to knock the . Obviously if I've owned it for this length of time, I love it! However, I was interested in whether other owners have experienced this behaviour and how they dealt with it. I was gratified to find out that I shouldn't trim bow down. That is one of the things I might have tried.

I also appreciate the posts from other owners with 90 HP engines. I wondered if prop torgue was a factor, especially since the boat always seems to break to starboard.

I appreciate learning from other owners' expreiences.

Regards,

Bob Cameron
Spirit of the Wind

[Mark Prouty]

Bob,

I have experienced this with my boat. I was in a narrow channel with oncoming boat traffic and others passing me. I will reduce speed to below planing speed under this circumstance.

These are some negative experiences I've had with my 115 hp Mac.

* Forgetting to pull up centerboard and rudder when full powering.
** Sharp veering left.
** Rudder damage and pretzeled bracket.
** Bracket torn from transom.
** Sharp right heel.

* Snapped centerboard line when powering fast.
** Sharp veering left.
** Sharp right heel.

These are great powersailors with caveats.

note:

I have had experienced a similar loss of control when in a following sea under low speed - yaw. I should have followed advice from this board - filled ballast, and used the centerboard and rudders.

[Moe]

The X hull isn't a powerboat hull. The chines are very soft, which will reduce longitudinal stability. It also has more "rocker." Note how there's less hull depth under the waterline stripe at the transom than the center of the boat. While this helps reduce the amount of drag-causing flat transom in the water, it also encourages the boat to yaw about a vertical axis, reducing longitudinal stability.

With too much weight in the bow and/or the motor trimmed down, this "rocker" could also encourage "bow steering," a condition which causes a sudden, and sometimes sharp, uncommanded turn to one side. Powerboats with the motor trimmed down too far can experience this and actually throw passengers overboard.

[Jeff Ritsema]

Moe,
When you refer to the motor being trimmed down, is this in reference to pushing the bow down? Does this hull configuation function best and safest bow up? There have been numerous references in the forum to efforts to bring the bow down when powering, I presume for improved visibility, but doesn't this actually introduce a risk and loss of performance, having the bow down to an extreme?
Appreciate your thoughts.

[mgg4]

Moe,
When you refer to the motor being trimmed down, is this in reference to pushing the bow down? Does this hull configuation function best and safest bow up? There have been numerous references in the forum to efforts to bring the bow down when powering, I presume for improved visibility, but doesn't this actually introduce a risk and loss of performance, having the bow down to an extreme?
Appreciate your thoughts.

Jeff, you are exactly right. The loss of stability could be related to the bow being forced down which causes the bow to plow. Many Mac owners adjust the motor down (in) to the extreme in an effort to bring the bow down. At low speeds this is not a problem, but then you don't really need to bring the bow down at low speed. At high speed, the boat becomes unstable in any sort of wave or wake action if the bow is being forced down.

The best thing you can do is trim the motor out, letting the bow come up. Continue trimming the motor until the cavitation plate on the motor is parallel to the surface of the water coming out from behind the boat. Yes, the bow will rise, but the ride will smooth out, and there will be very little loss of stability when encountering wake or wave action.

I know this is counter to what most Mac owners do, but it is absolutely vital that you trim the motor properly to avoid loss of control. If you need to improve visibility, stand up, or sit on a tall cushion or a fender. Of course, you could always slow down to bring the bow down, but what fun is that?