Heard a loud "bump"

[jonelli]

I was just motor sailing about 6knts on one of the calmest days I've ever seen in a awhile and after about 3.5 hours we heard and felt a large "bump" and thought we might have hit something. Never saw anything in the water but a little while later we heard it twice again but less intense. I didn't feel anything wrong with the steering or the normal prop vibrations, but my wife who was sitting on top of the engine compartment made a comment that she felt the engine was vibrating a lot.

I had to quickly pack up the boat and leave to catch a flight so I couldn't inspect anything, but I'm wondering what it could be. Does anyone have any guesses? Could a bad motor mount do something as I described?

I'm planning a 9 day cruise in a few weeks and it's got me worried now.

 

[SFS]

I'd get a diver in the water to inspect the strut, shaft, cutlass bearing, and prop.

 

[jonelli]

I will call my bottom diver tomorrow. But what would you suspect?

 

[SFS]

I don't want to speculate, especially without more info. When you heard the first noise, was it forward or aft? Did it sound like the hull hit something, or was it more metallic? How did the later two noises compare, in terms of location and character? Had your wife sat upon the engine box before, so she had experienced a "normal" amount of vibration, enough to know that what she felt was an "increase" in the amount of vibration after the "thump" noise? Lots to think about. I assume the boat was not (and is not) taking on water.

I have been aboard a 30 foot sailboat motoring when a strut failed (sheared fore and aft). The symptoms were: an impact-type noise (a "thunk", as I recall, followed immediately by a change in the character of engine noise, and an enormous increase in vibration felt throughout the fiberglass hull. Hence my suggestions related to inspections of the running gear.

 

[jonelli]

To me, it sounded centrally located, not necessarily aft, and would be hard to tell if was forward. I would have described it as a hull type thump rather than a metallic bang. I only heard one of the other two noises myself, and it sounded similar just less intense, maybe 25% of the loud one.
Exactly what you asked is why I can't really decide if my wife's comments are relevant, but she has been on the boat a lot, and it's interesting that she said that out of the blue (she didn't know we were concerned about a noise).
The boat did not appear to be taking on water (we checked the bilge while underway) and since we heard the noise more than once, we were sort of confident that we didn't hit something.
I was at the helm for the last hour (no auto pirate) when the last quieter noise happened and I did not feel anything else out of the ordinary.

 

[justsomeguy]

I can't really decide if my wife's comments are relevant, but she has been on the boat a lot, and it's interesting that she said that out of the blue (she didn't know we were concerned about a noise).

Was she sitting there on the engine compartment when said bump occurred?

 

[seadaddler]

Could be anything but would check under boat by diver cutless bearing strut and check drive train like shaft and coupling and motor mounts , had some bolts on my coupling fall out once.
Nick

 

[LeslieTroyer]

I have an action camera and waterproof light so I can put it on a boat hook to look at the bottom. I got it incase I wrapped an anchor line or pickup a crab pot. Used camera + lights is cheaper than one diver. Good for checking zincs also

 

[jonelli]

Was she sitting there on the engine compartment when said bump occurred?

No, not at that moment.

@LeslieTroyer Great idea. I will get the diver this time, but great plan for the future.

 

[jonelli]

I just heard from the diver who checked everything below the water line and they tell me everything looks good down there from the shaft to the cutlass bearing, etc.
when I get home from being out of town I'll check everything around the engine.

 

[salishmermaid]

Might want to check the shaft coupling bolts just aft of the transmission. I found one of mine out laying in the bilge and the other three loose on one trip last year.

 

[Mark Maulden]

I have an action camera and waterproof light so I can put it on a boat hook to look at the bottom. I got it incase I wrapped an anchor line or pickup a crab pot. Used camera + lights is cheaper than one diver. Good for checking zincs also

Les, what are you using for lights?

 

[LeslieTroyer]

Something like the following.

https://www.amazon.com/Suptig-Divin...65&sr=8-4&keywords=Underwater+led+hero+Camera

 

[jonelli]

I just got home and went to check the boat this morning. The motormounts look fine, and from what I can tell the tranny coupling looks good, no missing bolts, and checked the fluid, also good. I put it in reverse at the dock and ran the motor at different RPM's with all the panels open below and checked it several times and could not see anything abnormal.
I'm stumped.

 

[JamesG161]

I'm stumped.

Well a least you eliminated Pirates!!

I was at the helm for the last hour (no auto pirate) when the last quieter noise happened

Sorry I couldn't help myself.
______
Same thing happened to me, after I eliminated the pirates, I think we hit a submerged Crab Trap and the vibrations quit after the pick up rope was cut away from the prop.
Look at your propeller for damage.
Jim...

 

[LeslieTroyer]

Could be a chunk of wood. The 3/4 waterlogged ones dive despite after being hit. Can sound like a shotgun going off inside the cabin

Les

 

[jonelli]

I would have totally wrote it off as a piece of wood if I didn't hear the same noise about 15 min later, it was less intense though.

 

[Ned Ludd]

Must have been the crew member you keel hauled still kicking.

 

[Ron20324]

...we heard and felt a large "bump" and thought we might have hit something.

I had that happen once. Thunk, then the engine and boat shook considerably, so shut it off ASAP and hoisted sail in unfavorable conditions. I saw a crab pot float- well, half of it- falling away astern, still on its line. I figured I could sail into Solomons Island Harbor then try to motor into a slip. Motor ran okay! I figured the float hit the folding prop and partially closed it, making the vibrations. All was okay.

 

[jonelli]

I had that happen once. Thunk, then the engine and boat shook considerably

Yah, that didn't quite happen to me. I just got the "thunk" and no vibrations. I know what it feels like to foul a prop, I've done it in kelp and had to dive down to cut it away.
Honestly, I've checked everything I can think of, and maybe we did hit something or someone... We'll never know! (unless it happens again....)