I’ve a 1984 NS22 and recently sailed on a NS30. The difference in engine noise is tremendous. Perhaps it’s a function of the 22’s engine compartment being the entire below cockpit area with zero insulation. Other than replacing the diesel with electric; anyone been successful in deadening the engine noise? Thanks.
John Gialanella
Tourmaline NS22
Bolles Harbor, Lake Erie, MI
Most of the 30s came with 3 or four cylinder engines. The 22s with 2 cylinders. Some of the 30s had sail drives. More cylinders and sail drive transmit less vibrations to the hull and are therefore quieter. Two cylinders vibrate more and create more noise. A bit open engine room acts like a sound box on a guitar. Adding sound deadening insulation to the engine compartment should help. A Sigma drive is not cheap but should make a significant difference. I installed one on my boat, 20 hp 3 cylinder Beta and the sound level in the cockpit dropped by 7 to 10 db.
Mark Powers
Mark,
What is a Sigma drive?
Thanks,
Mike
Mariposa
NS30U Hull#272
Dutch Harbor, RI
It is a coupler made by Brenton’s. It is a type of constant velocity joint that does not require a separate thrust bearing unlike the Aqua Drive. On a straight drive system it simply replaces the existing coupler. The Westerbeke V drive requires an extra part.
I can’t get my system to paste the link but if you Google search Sigma Drive Coupler you can find more info on them.
Mark Powers
In case the question was more basic, the next simpler answer is that it’s a device that compensates for a certain amount of motor/shaft misalignment, and thus serves to reduce noise and vibration. It’s one of several devices on the market (some of which replace the connection between the engine transmission and the prop shaft and some of which serve as, in effect, pads between them).
In addition to the Sigma (https://bruntonspropellers.com/sigmadrive/), another example is sold by PYI: https://www.pyiinc.com/flexible-shaft-couplings.html
As Mark said, sound deadening insulation may also help. The original foam with a metallic covering insulation that many of our boats have in the engine compartments often has deteriorated to the point of uselessness.
– Bob
Me Gusta
Nonsuch e26U #233
Marina del Rey, California