Too old, you're right. I believe the new ASD 6 can be run with up to 750hp but again it's more a question of torque than anything else. I mentioned around 700hp in my first post, saying that with this sort of power you should really run a SSM6 unless you like trouble. So in those cases, ASD 6 can advantageously replace the Speedmaster both in terms of cost and performance. Many people are actually running around 700hp because this is a number which can be obtained from a blown big block while keeping it reasonably reliable by running tame boost pressures. However, if you have more power, say 1000s, then you would need to step up to the ASD 8. They are much more expensive but I believe Twin Disc are working on a new version (like they did with the ASD 6) which will be simplified as a replacement for the Speedmaster and much cheaper.
Sutphen30, the Trimax is a fantastic drive, the most reliable of them all because it has the smallest number of moving parts. Its simplicity is truly beautiful and if you look at the photo, only stainless steel is in contact with water. All hydraulics and steering is inside the hull and accessible from inside for servicing. If you look at trim tabs, only the SS piston comes out while the hydraulic cylinder and lines are inside the hull as well. No leaks, no electrolysis, no galvanic corrosion... However, the big problem is that the transom needs to be configured for Trimax and that platform is necessary. It is actually very practical but it forces the manufacturers to tool up differently and modify their molds and this is why so few manufacturers are using Trimax. Even though the drive itself, once you've tooled up, is cheaper than a Bravo XR. This drive is manufactured and marketed by ZF Marine so go to
www.zf-marine.com and look for trimax under their propulsion heading...
bouyhunter, glassdave is right. those are ventilation ducts which bring air to the props when the boat is accelerating from standstill. This cavitates the props or "breaks" the prop which allows you to pick RPMs up faster and thus accelerate faster. As props start to turn faster, there is a pressure-sensitive flap in the duct which is shut down as the back pressure increases. This means that the amount of air is regulated at high speeds to increase efficiency. This is one of the advantages of Trimax over Arneson in terms of performance. Arneson has the props sitting relatively deep in water at standstill with no air being channeled to them which makes it difficult to "break" the prop and accelerate fast. Then, at high speeds Arneson has props on the surface which causes too much air to be sucked in and it looses in efficiency. In other words, with Arneson, props are being well aerated when they do not necessarily need it and are starved of air when they need it, a thing Trimax has corrected and put the right way around. Another thing about that boat on the photo is the fact that it has underwater exhausts which come out under the hull and forward of the drives. This means that when the Trimax ducts are closed off at speed and drives covered by that platform, props are still aerated by exhaust gases. In addition, this provides extra transom lift and hides any smoke you may get from those diesel engines.
Finally glassdave, that boat is the new Hustler "Esprit de Soleil". It is 50' by just over 10', powered by 4 Yanmar 440hp diesels running through ZF 2-speed trannies. It is approx. 23 000lb dry and it will run close to 80 mph and accelerate to 60 in 10 seconds. It gets on plane in 3 to 4 seconds, as soon as the turbos kick in. It's a tank and it's what you need for endurance runs.
