8V92 TI / Twin Disc info wanted

A 55 footer with Arnesons? Sounds like a Magnum.

I can tell you the drives are darn near bullet proof, although there was some tweaking with early production releases. Low speed steering lacks good deflection, making maneuvering or docking a little challenging.

Great engines, great gears, and great drives. But you better get a lot of practice driving before you try maneuvering in close quarters. Arnesons love going forward, but there is almost no reverse... you really have to get on the throttles to stop or make way astern, and it takes practice to learn how to split the sticks and get a desired result. Think of them like driving outboards.

Arneson Drives

Based on what I have read, sometimes the problem with "no reverse" on Arneson boats is attributed to those using agressive, "cleaver" type props, which do not have much of a bite in reverse. And, depending on the configuration of the vessel bottom, and the drive position, the back wash can hit the transom, negating the effectiveness of the reverse thrust.

I understand that not all Arneson boats react in this manner, though.

Personally, I like Arneson Drives, they have a niche application to be sure, but I think they are well engineered and can deliver great performance if applied properly.

You are absolutely correct...

I've got a little experience with surface piercing drives, although they were not Arnesons. They were were one-off prototypes we mated to a pair of Lamborghini V-12's. This was the propulsion system that drove an all-aluminum, 38 foot, 24 degree deadrise, no pad Deep-V.

While the hull was generic (except it was alloy), the remainder of the boat was state-of-the-art, featuring a servo-driven, gyro-controlled active canard at the bow that adjusted the angle of attack several times a second. This effectively controlled pitch (or porpoising) at high rates of speed in rough conditions. This system was developed to enhance guidance system accuracy for weapon's deployment.

Among other features were 12 seperate fuel cell bladders, incase one or more were ruptured, G-Load captains chairs and armrests (to sustain the punishment of 100 mph + speeds in rough conditions, while sitting down). There were a couple of other unique attributes, but it's probably best not to discuss those.

During our sea trials, I remember hearing about Steve Stepp (Velocity) breaking the 100 mph mark in a Deep-V, claiming to be the world's fastest Deep-V. Sure wish we could have run up against him! We had eclipsed 130 mph and there was more room in that number.

Anyhow, back to surface drives...

In a Deep-V configuration, the drives have to placed as close to centerline as possible. This is where the least disrupted and ventilated flow of water occurs in a Deep-V at high speeds. The further you place the drives closer to the chines, the less effective they become. Due to speed, lift and surface irregularities, drives must be placed in the most effective position to maintain thrust... which is as close to centerline as possible. Essentially...keep the prop hooked-up!

Due to this, closely spaced drives do not lend themselves well to low-speed maneuverability. Because the drives are surface piercing, the "X" placement of the thrust line is typically on the same plane with the bottom of the hull, to achieve maximum RPM's and reduced drag. Hence, the reverse backwash scenerio Patrick is referring to, which is further compounded by the depth of the hull at centerline. This becomes a wall that deflects reverse thrust.

Cleaver's have always been the choice in a surfacing environment, but they are not an effective prop for reverse propulsion. The straight (blunt) trailing edge of the ears greatly disrupts laminar flow over the propeller, producing almost instant cavitation. Again, Patrick was right-on with his statement.

The most effective application of surfacing drives is generally in a catamaran, as drive locations are seperated to create sufficient leverage against the hull for maneuvering. In addition, because catamaran sponsons are a generally narrow hull form, reversed thrust can flow around each sponson with limited resistance.

Ultimately, the surface piercing drive is favorable because there are very few moving parts. It is, for all practical purposes, a direct drive system that has proven to be very reliable. As usual, Howard Arneson was ahead of his time.

Arneson Drive Boat

The ultimate oxymoron... a high speed trawler! Love it!

I have experience

with both arnessons and the new zealand sea fury system in commercial lobster boat fleet situation.

I'd pick the Sea Fury over Arnesson but both are excellent.

Arnesson - are fine - except they have more moving parts (universal / gimball joints & hydraulic rams) and as described - the flat transom and cleaver style surface piercing props basically negates reverse thrust.

The 45 degree cutaway transom on the sea fury means they back up much better - they are a straight line drive system so no uni joints to replace.

Ohh, and I'd pick ZF boxes over twin disc! (but both are good)

Yes Arnesson was (still is?) a genius, and his drives still cut the mustard - but sea fury will give em a run for their money.

http://www.seafury.com/

Cheers!

Ohh - we can do pictures?

Here goes then.

First two photo's show Sea Fury during construction and in the water - last one shows aresson equipped vessel. (If this upoad thing worked!).

Cheers!

Brilliance lies in simplicity! Overcome the obstacle and function is restored. Leave it to the boys from down under! The Aussies have made significant contributions to hull designs and propulsion systems over the years.

This is an excellent example of combining a straight forward propulsion system to the right transom configuration. All too often, propulsion systems are developed to work on a variety of boats, but few boats possess the proper design to capitalize on certain drives.

Harry Schoell's "Pulse Drive" addresses similar issues. Harry is easily one of the greatest minds in the marine industry, with a number of patents to his name. Harry's stock system is more of a bolt-on configuration, but many of the same design elements of the Pulse Drive are being adapted to larger vessels, where the hull shape is configured to accomodate the drive.

Thanks for sharing Trouty! You're always informative!

OK, this thread got a little too technical for my brain matter at this particular moment. I just drive the boats... and fix 'em when dey be broken.
Put arnesons down when manuevering and bring them up as you bring the rev's up.... that's all I have to say about that. Oh - and use your noggin' before believing a repairman. I know a skipper that was taken for ten-bigguns for some baloney-pony story about an o-ring. turns out it was a $500 job. ooops!

Arnesons

I do not have any experience or opinion with the 8V92TI, or that transmission, I do feel that the ASD 12 should be a problem free unit, if it has been maintained properly and has not suffered any damage from collisions etc.
What is the horsepower and torque rating of that motor? And the reduction ratio on the gearing?

Like any purchase, you shoud have a good surveyor, and I can pass along the name of an excellent Arneson Drive technician to you if you like... PM me if so.