Sailboat: Beneteau first 35S5GT, moored in Barcelona.
2 ELLEBOGEN 75 (Ref. 128270-08341) and 2 ELLEBOGEN 100 (Ref. 128377-08351)
The aim of this report is to explain the case of who had a Yanmar 3YM30 engine that presented high levels of vibration on a Beneteau first 35S5GT sailboat and the steps that were followed to solve the vibration problem.
We will start first describing the details of the Sailboat. The boat is 10.80 meters (35,42ft) long ,and a beam of 3.61m (11,83ft) giving it a total displacement of 5198Kg. (11.460lbs)
Designed by Jean Berret/ Philippe Starck and built by Beneteau Shipyard in Saint Hilaire de Riez, FRANCE.
INITIAL SITUATION OF THE ENGINE.
|The owner of the Sailboat complains about excessive vibration and noise on his 3YM30 Yanmar engine. The Sailboat owner contacts Sergi Castelló from Bricolaje Nautico Youtube Channel to explain his case.-The mount that he is using has the below design.|
|Fig 1. The mount that he is using has this design|
This Sailboat well maintained and properly stowed can accommodate up to 5 people in comfort.
The mount is coming from a good reputation engine mount manufacturer based in Australia. The stiffness of the mount is high, this type of mount is designed to provide little mobility to the engine.
The stiffness has a role on the resonant frequency (also called natural or fundamental frequency) of the engine defined by the below formula:
Where “k” is the stiffness of the marine engine mount, and the “m” is the mass of the marine engine.
The relationship between the fundamental frequency and the idle speed of the engine (also called disturbing frequency) is defined by the transmissibility curve below.
In the graph below, Iddle speed would be represented by the yellow line and the dark blue line represents the potential impact of this (also called a Transmissibility curve). The worst case scenario would be if the yellow line matched the dark blue peak, at which point the system wouldgo into a resonance which could damage engine components, mounts, transmissions etc… so clearly something to be avoided.
If the mount has a higher stiffness the fundamental frequency of the engine also increases, as indicated on the below formula:
If the Fundamental frequency is increasing, we will be closer from the disturbing frequency, having a case of resonance. Therefore, the way to avoid this phenomenon is to increase the idle speed, as it can be seen in the graph below.
Having a high iddle speed may be harsh for the clutch when enganging the gears. Due to this reason and with the aim of avoiding transmission problems the sailboat owner decides to change the flexible engine mounts of this Yanmar engine.
CHANGING THE STIFFNESS TO THE CORRECT VALUE.
The stiffness of the mount plays a key role on the resonant frequency of the engine. The Ellebogen engine mounts have lower stiffness than the preiously used engine mounts by the user. This allows to have a lower resonant frequency of the engine. (Also called Fundamental frequency)
When the stiffness is lower, the engine provides a higher vibration isolation. This allows to decrease the idle speed to the normal conditions (around 850rpm) that Yanmar recommends.
|On the below video we can see the new Ellebogen engine mounts on the Yanmar 3YM30 marine engine at work from 820 rpm to 1000rpm.|
The customer is impressed with the level of vibration isolation that his engine has now. He also indicates that it is hard to notice when the engine is on.
The position of the Ellebogen marine engine mounts follow the diagram as shown below.
Our special thanks to Sergi Castello from Bricolaje Nautico for the identification and dedication to the solution of this sailboat owner.
Bricolage Nautico youtube channel provides interesting content for Sailboat owners. Here are some examples.
How to adjust the idle speed you the engine. 3 possible alternatives.