Broken Mercury 250HP EFI Swivel Bracket

[Tim Worrall]

I am looking into how a Mercury 250HP EFI outboard engine swivel bracket broke whilst being used. The engine was one of two (P/S)onboard a RIB that was proceeding at 42kts in a sea state of 5. The engine had completed 450 operational hours and was due to undergo major overhaul at 500hrs as it has done since purchased. ( Note that during major overhauls the brackets are examined but not replaced )The engine is checked prior to each period of use. At the time of the accident the vessel was being operated by a highly skilled coxswain with many years of experience in handling fast craft in off shore conditions. The vessel was not engaged in a turn and the steering system appears to have been in good condition. The load carried by the vessel at the time was well within its operational loading capacity. I am considering whether the engine was over trimmed at the time and would appreciate views from others. Many thanks.

 

[WillyBWright]

Re: Broken Mercury 250HP EFI Swivel Bracket

Welcome to iboats.<br /><br />In order to give a proper evaluation we'd have to see the parts. But we can give you some good educated guesses. I personally would doubt the trim angle would cause such a failure. More likely it was an impact with an underwater obstruction and since you mention no other apparent damage, I'd suspect a collision with a submerged log. It might have been sitting on the bottom if the boat was in shallow water. If it was in deep water, it is possible for a log or tree to float close to but under the surface. I was out one day and saw a gull standing on the water amid a dozen other swimming gulls. Naturally that one got my attention. When I got close enough I saw the tree trunk beneath him. Had he not been standing on it, I never would've seen it. I towed it ashore to prevent an accident.<br /><br />You can frequently determine if the lower unit has struck a wooden object by wood fibers plugging the speedometer pick-up on the leading edge of the gearcase. Other than that, a log strike can leave no other obvious damage and if it hits below the speedometer pickup it won't even leave that. The hydraulics are supposed to disengage enough to absorb the shock and allow the motor to tilt at impact and come back into position, but an impact is an impact and sometimes things break. It might've broken on impact, or when it slammed back down.<br /><br />I should also mention that when the motor is beyond the trim range, forward thrust will overcome the hydraulics and the motor will come to rest on the trim rams. The motor cannot be operated under much thrust in the tilt range. Once in the trim range, there are supports that prevent lateral movement. In the tilt range that support isn't there and I can see where one would deduce that such a failure could occur if the motor was up there at the time. The design of the hydraulics makes that impossible.