Engine noise reduction

[amytom]

I did a search and found several people talked about noise reduction for the 9.9 engines but I didn't see any after results. Has anybody had any luck with this? I was considering a vibration mount under the brackets and some soundproofing lining the engine pod.

[thinwater]

The difficulty is that most of the noise is nice guitar frequencies that the cored construction picks up wonderfully. Unless you can come up with a mount that will damp the correct frequencies - and that is complex and not simply a matter of rubber pads - I doubt it.

The engine compartment foam aproach is for high-frequency noise. I think the combination of outboard cowl and seat get most of that , anyway, but it would help some. However, I would be concerened about anything that might hold water - greater harm theory.

[amytom]

I should have known is wasn't going to be that easy. If it was, others would have written it up long ago.

[thinwater]

My stiletto was even more of a guitar box than the PDQ - Nomex honey comb with little bracing structure. It was deafening down below when sailing in rough conditions. Yet the engine tones were not bad. The engine is not mounted to the boat directly - it is on a metal bracket cantilevered off the rear tube. Thus, it is mounted on a long leaf spring that damps the critical frequency range.

Which means there is a way, but it may be complex... or not. Perhaps a "shoe" that would fit over the FRP mount, lined either with springs or softer foam. The shoe in turn, would have to be well secured to the boat.

The thing is, a clever solution might be easy to duplicate, but perhaps we should look further than PDQ sites. It is an outboard/cored construction problem... although that really does sound like the sail drive on a cat.

[amytom]

I'll try Multihulls4us, lots of good advice coming out of there.

thanks

[Page 83]

I think that most of the noise is transmitted through the structure. I base that on the fact that the engines are remarkably quieter running on a work stand with a water hose. Perhaps replacing the 'transoms' on the boat with something on isolations dampers would do the trick. For example, see
http://www.vibrasystems.com/?EC=Product&ProductID=11
but I have no idea how they would survive in this environment.

engine damper 2.jpg (40.13 KiB) Viewed 11827 times

[thinwater]

Though your sketch makes more sense. But the surgery would be frightening!

It is not engine noise exactly, it vibration transfered to the cored structure of the boat.

The Seawind, for example, does not use the engine tilt - it has a bracket that goes up-an-down. That would solve 2 problems: noise and latch failure....

Which leads to Saturday's misadventure. The latch failed while backing into the slip, causing me to lose steering. Though it did not go up into the bridge deck, it did wind up the tilt line. I hope the hub is OK. The water was too cold to give it a good look!

[Page 83]

Congratulations: you have experienced initiation ordeal #1. As the current record holder for the number of Initiation #1 experiences, I urge you not to try for the record. It frequently involves buying a new prop!

[thinwater]

Congratulations: you have experienced initiation ordeal #1. As the current record holder for the number of Initiation #1 experiences, I urge you not to try for the record. It frequently involves buying a new prop!

I think I told you that I lost a prop on the delivery trip (just spun...PO had replaced the other) and the carb on the other engine within hours. Ended up sailing into the slip. Luck on my side. Any other wind direction and I would have been cooked.

So far, between accumulated "might needs" and what I can build in my shop, I think I have not yet spent 1 "boat buck," assuming that internationally recognized standard of 1:1,000 is still applicable in these times. I need to sail her for at least 1 year before major surgery can be justified.

I've been smearing the $$$ VERY thinly.

[amytom]

Sandy,

Until my hold-down modification I may have given you a run for your money on kick-ups. Aside from a broken cavitation plate on the port engine my most common damage is the exhaust delflector mounted with the prop. (do you happen to have any in the pile of parts?)

Your idea for a vibration isolation mount looks very interesting but , like Thinwater, I'm not sure I'm up to the surgery right now.
Tom