Ride comfort question...

Hi there, yet another newbie! (Sorry in advance!)

I was wondering if any work has done in the past on the NVH (Noise, vibration and harshness) on boats? I am currently doing NVH as a module on an automotive course where the equations are applied to land vehicles, I am also involved with a project to install a hydrofoil system onto a trimaran (length 10m, width 4.5m, exact dimensions unknown at present, mass 3-4 T unloaded, 7 T fuelled).

I'd like to try and model the boat's amplitudes and displacement of the system on a sinusoidal wave of varying heights. Can the automotive equations be applied directly to boats? Or are there specific marine equations? I know they won't behave the same with the boat lacking the damping of a suspension system...

Many thanks to anyone who can answer this question!

 

Chris;

There is a rather large but somewhat disjointed body of knowledge and criteria for 'ride quality' and comfort on marine vehicles. Probably the best source for a coherent compilation of comfort criteria is international standard ISO 2631.

As for modeling of the motions of a hydrofoil?..there are no off-the-shelf tools that I am aware of. It is a complex problem and, unlike the road vehicle, the dyanamics of bouyant support and, in the case of foils, dynamic lift in a viscous media, add quite a few variables to the mix..even if you limit the modeling exercise to only vertical-plane motions as many simulations do.

We never attempted to simulate the motions or attitude control of the trimaran hydrofoil we built as a 1/4-scale model (only slightly larger than the one you describe in fact..). In fact, that was one of the main reasons it was built..because of the lack of credible analytic tools to predict virtually any aspect of the performance of the design.

 

This book may be of use to you:

http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521845687&ss=exc

Cheers.

 

Oh, Boy! Are you going to learn a lot.

yes vessels do have "suspension systems" and it is possible to tune them ( actually you de-tune them, but it is the same idea). The big problem with marine vessels is the inability to separate propulsion, speed, and seaway motions and vibrations. Complicating this is the fact that slamming (i.e. your "harshness") is a stochastic function, not a regular one.

As well as Hydrodynamics of High-Speed Marine Vehicles, try to get a copy of Theory of Seakeeping for the initial basic maths of vessel response and Dynamics of Marine Vehicles for the basic stochastics.

 

well, if this question is NOT for the trimaran on hydrofoils (since you said you were ALSO working on it), Ted Brewer gave a reasonable equation on his yacht design site for figuring a "comfort rating," that figures displacement & LWL as the main contributing factors to a smooth ride. (don't have the link handy, but if you look up "Ted Brewer Yacht Design" on google, it should be right up near the top)

 

Size does count