Have you also watched the engine mounts while in low rpm to see if it's just excess vibration making the noise?
If you want to check the prop for snags without going for a cold water swim, a GoPro on an extension stick works well. I've used this method before to check the zincs. -Patrick 1984 C&C Landfall 38 Seattle, WA On Mon, May 9, 2016 at 9:00 AM, <cnc-list-requ...@cnc-list.com> wrote: > From: Andrew Means <andrew.cnc...@gmail.com> > To: cnc-list@cnc-list.com > Cc: > Date: Sun, 8 May 2016 15:40:53 -0700 > Subject: Stus-List Soft thumping/banging when in gear at low-rpm? > *Boat*: 1977 C&C 34 > *Engine*: Yanmar 3GM30 (F) > *Prop*: 3 Blade Max Prop > > Recently I noticed that when engaged in forward-drive, at low RPM, it > almost feels like something is banging against the bottom of the hull, like > a piece of kelp or rope tangled in the prop. Once the RPMs get above 1400 > or so the roughness goes away completely and everything feels very smooth. > > Additional info: > > + Looking at the propshaft and listening for knocks coming from the engine > doesn’t reveal anything obvious. > + We ran aground recently, but just the keel in soft sand. Bottom was > painted between now and then and yard didn’t report anything amiss. > + In reverse at the same RPMs everything feels pretty smooth. > > I’m waiting for the next 80° day to dive under the boat and see what I can > see, but was wondering if that’s even where I should be looking. Does this > sound familiar to anybody else? > > Andrew > > -- > Andrew Means > S.V. Safari - 1977 C&C 34 Mk I > Seattle, WA >
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