Which drive?

[Guest]

Arneson, trimax, or outdrive?? all are very efficient, but which has the upper hand?? all fitted to new sealine C39, but only have figures for the outdrive version!! Does anyone know if you could fit arneson/trimax drives to flybridge boats, i know they do sportsboats, like flash 48 & S42, but was just wandering?

<hr width=100% size=1>

 

[Divemaster1]

This is a difficult one and could open up discussions along the line of the benefits of waterjets vs shafts etc....

Anyway, I have posted on the subject on surface drives before, so will attempt a short(ish) one here.

For the C39, the most efficient one seems to be the outdrive (30 something K with 2xKAD 300's), but if you want 40 + you need the surface drives...but engine power goes up, and so does weight.

Trimax - modified UW section in rear to accommodate 50% of prop in water etc. (previous post on how this stuff works), & have rudder section. (could also have built in Trim flaps to keep on plane at lower speed). Well proven design and used on Sunseekers XS2000.

Arneson - Articulated (steering ald trim) and no rudder section (less "drag"). Beautifully engineered and good performance.

Surface vs Sterndrive

Sterndrive transmitts power to back of boat allowing engine installations with "soft" mounts, which results in less engine vibration transmitted to hull.
Surface drives works more like shafts, so need firmer engine mounts.
Surface drives require gearbox (added weight), but can be two speed (good for speed and economy).
Surface drives have virtually no limitation on engine power, whilst sterndrive have up to 300 hp (on diesel)...... Discounting petrol stuff here.

So, which drive depends on your use, but personally I would not go for sterndrives on much larger boats than the C39. Below that size it depends on which operating speed you want.... discounting waterjets and shafts...

With respect to fitting on flybridge boats, this causes no real problem, but you need to think of Trimaxe's restrictions of the UW section.

On Std planning hull, the Arnesons or these

from PulseDrive could be OK. Other installations on planning / non planning hulls here <A target="_blank" HREF=http://www.pulsedrive.net/commercial.htm>http://www.pulsedrive.net/commercial.htm</A>

Will stop there, but would of course be happpy to contribute to further discussions....







<hr width=100% size=1>Alf

 

[Guest]

Another factor that could well affect the fitting of a tri-max or arneson to a flybridge is, most (not all I know) flybridges have thier motors amidships in a conventional shaft instalation, tri-max and arnies require the motor(s)/engine room to be at the transom- stern drive stylie.



<hr width=100% size=1>

 

[jfm]

Divemaster:
Have admired your posts on this subject, excellent stuff. Two thoughts though:

1. You say surface drives need a gearbox. But so do sterndrives!

2. You mention engine mounts and say sterndrives transmit thrust direct to transom, whereas you seem to imply surface drives and shaft drives dont. I dont think this is correct. Surface drives transmit the thrust to a thrust bearing at the transom. On a shaft drive boat, there is often a thrust bearing at the sterngland area so no thrust load is applied to gearbox or engine (though, perhaps some shaft drive boats are built without a thrust bearing, I dunno. If they are, it's not an intrinsic limitation of shaft drives.

In a sterndrive set up, the primary drive shaft is rigidly mounted as it comes through the transom up to the point where it connects to the engine, and so the possibility to fit soft engine mounts (with a flexible coupling, if needed) is surely no different from a shaft or surface drive set- up. Or am I missing something?

<hr width=100% size=1>

 

[Divemaster1]

Some mistakes there... too heavy night before....

1. Weight of Drive, rams, etc. + Box normally exceeds the weight of a sterndrive unit..... but large benefits with slower, larger rotating props for better efficiency.

2. Yup... you're right.... joint (double universal for articulated drives), and in some cases to a combination of joint and sternplate. As a sample, in the Trimax's case, thrust is totally discharged on a coupe of rolling bearings in oil bath in a thrust bowl fitted with a oil heat exchanger connected to a circulating pump.

There are also some geometric limitations on what a double universal joint driveline can and cannot do so more care is needed with alignment of the engine, gearbox and driveline, making the installation more complex than a sterndrive unit.

Of course with an Arneson like installation prop protection comes in...for close quarter manouvers care must be taken to not daage the props by getting too close to anything with the stern (Large swim platform is good stuff, but may cause vibration ... see SS 95 test...) It is also worth remembering that a surface propeller can be a substantial hazard to anything or anybody that falls off the stern of a vessel underway as it bears a striking resemblance to a giant food processor with similar effect to anything in it's way...


<hr width=100% size=1>Alf