With regards to the Nortec; if they have a vibration issue either they did not align the engines or whose ever propellers they used were out of balance to cause the vibration. If you are confusing a harmonics noise for vibration then welcome to the world of cats. They resonate any noise anywhere in the boat. Think of them like two large drums. Same for rides, the hull is the hull, not every problem with a boat is related to the drives. Maybe it is just not going fast enough for the cat to air out properly? Cats do ride differently than Vís and the slower speeds you are experiencing are not doing respect to the capabilities of boat itself.
As to what to do when you hit a tree. Try avoiding all trees in the water would be my first thought. If you hit something like a tree and cause damage, then you will have to address the damage once you get back out of the water. I really do not have an answer for running over trees.
Question has to be how many of the Merc drives were in front of a diesel engine? I think you are comparing apples to oranges in the setup and associated side effects. Diesels vibrate a lot more than a gas engine.
Once again are you comparing speeds on the non stepped hulls with a gas engine to a diesel engine setup. We have the majority of our applications non stepped hulls and yes for the most part non stepped bottoms are not as fast as the stepped bottom design boats. All of the Magnumís, Pershings and such are non stepped and run very well though.
As for the older 12 M Fountain, (this is a 36í V bottom with twin Yanmar 480ís) the boat is simply to heavy for the engine weight. Once again not really anyoneís fault but what was the owner expecting for speed when a 36í boat weighs some 5,500 Ė 6,000 kg? With a small bottom and all that weight the boat is actually running well. Take the weight of those 480ís with the marine gears (1.800 lbs each) out of the equation and put a lighter more power gas engine in the boat and then look at the speeds. We have several 12 M fountains with Arnesonís and gas engines that run over 100 mph. Once again someone has over reached the expectations from a 20 yr old boat design with heavy diesel engines.
As for propellers, for a diesel application or a gas application. Mercury and Hering both offer differing degrees of rake in their cleaver propellers and this translates to differing amounts of bow lift from degrees of rake.
What you have to look at is where the CG of the boat lies with the diesel engines in comparison to the gas engines. This changes a lot in the performance of the boat especially when you add an additional 727 kg and them move it forward in the hull by half a meter in comparison to the gas engine setup.
As to your original comments (which is in regards to the Ilmor Fountain package) you would not be using the same drives as what you have seen on the Nortec Cat, not the triple 48í Fountain with Diesels. Rather you would be using a smaller drive unit that has a normal mechanical tie bar assembly and uses standard Mercury or Hering propellers.
The boat will get on plane and run reliably wit the Arnesons that are made for that setup. (http://www.arneson-industries.com/pa...ducts&id=asd7m) Please remember the boat you originally addressed is not a 20 + yr old hull and is not under powered and over weighted. Itís a modern designed efficient hull with a light weight powerful engine.