Engine insulation

I completed a project that has been going on for a while: completely replace and improve the noise insulation of the engine. Going at 2000 rpm has been stress so far both in the cockpit and the cabin. Using modern material, engine noise is now not gone, but bearable, and in the cockpit really ok. I used 10mm material in the box, since the engine is large, and 25mm in the engine housing and under the floor boards in the aft cabin. An area that can still be improved, maybe with foam, is under the pantry sink, where most tubes exit the engine housing.

Much of the remaining noise now comes from the drive train (when the clutch is engaged), and not from the engine itself. The engine has been aligned recently and is very smooth, so not sure if there is further potential with reasonable effort. I understand a game changer here would be an arrangement of the drive train that allows the engine to use soft silent blocks.

I already noticed for a while that a lot of noise in the cockpit comes through the place where the engine throttle is installed (see photo). That piece of GRP is much thinner than the structure of the cockpit. I put a thin layer of heavy insultation material at the back of it, without disturbing the throttle mechanism, and it did the trick and reduced noise in the cockpit noticeably. This may be specific to our 411, but you can easily check that on your boat, by comparing noise levels to both sides of the wheel. 

Christian 411/028 IF

Dear Christian

Some of the reduction gears have spiral cut teeth in forward and straight cut in reverse, this causes a big difference in noise level, and it should be checked that you use the correct direction of rotation. It is not unheard of that the reduction gear is run in the wrong direction

Thank you Lars!

I have verified the turning direction of engine/gearbox, no issue here :-). One of the things I learned from sailing and boat maintenance is that what can go wrong will go wrong, and punishment for lack of diligence is sometimes immediate and most of the times shortly after the mistake. In a way this is a school for life; some reminiscence to Zen and the art of motorcycle maintenance.

The cables behind the control panel are fine, it was really just more noise pentrating from the aft of the boat into the cockpit through the thin control panel. There is no insulation along the shaft, so noise can freely go under the floor boards of the aft cabin and from there following the draining canal into that aft of the boat. The exhaust system is also not insulated, so another source of noise in the aft of the boat. 

Nevertheless, the noise level is now really ok, and at least from what I hear in the harbour, similar to other more recent boats.

Christian

Dear Christian