Brainstorming Retractable Drives

No matter if I go with an inboard diesel, an outboard or diesel electric system, my one main requirements is a retractable drive for each hull.

Anyone have any thoughts on the best possible design for a retractable drive?

The boat is a 45', performance cruising catamaran.

The sterns are set up with a balanced spade rudder in a kick-up cassette, which complicates inventive drive ideas.

Any thoughts?

Free and open discussion. No prejudice at all, except if I notice something that won't work within the parameters of the boat.

Anybody?

 

Outboards are pretty good as they include so much in the one neat package, all engineered & assembled by the manufacturer at low cost. Dont know if the sonic drives are still made but you might be interested, one was fitted to a Beach Marine cat I worked on http://www.sillette.co.uk/pdf/sillette_mk_2_cat_drive_manual.pdf All the best.

 

Ah, man... I know I said I wouldn't have any prejudice... ha ha ha

But... I did get a quote on the Sillette drives. Over $10K just for the legs. Completely insane and way outside my budget just for legs when I still have to buy engines.

I know what you mean about the outboards though. I just wish they came with larger props. I have educated myself a bit more on props and the high thrust outboard props are just so-so in efficiency. The engines are also pretty heavy, coming in close to 300lbs each for anything over 25HP.

Plus, you have to find ways to keep the outboards from going underwater or coming up out of the water in rough conditions.

What do you make of those issues with the outboards?

The market is really hungry for a good, lighter weight, high thrust outboard that runs on diesel. Well, at least I am.

 

Yanmah made diesel outboards, dunno if they still do but Aus defence forces used them & they'd come up for auction sometimes, pretty noisy though & not sure of the weights. As for petrol outboards the Yamaha 9.9 4 strokes were good but not enough hp for your vessel, I heard they changed them to make them not so good, there was "ring" props & shrouds available too.
The petrol outboards are most affordable & for well inside the price of diesel options you can have a standby engine or two or even size your tender engine to match the main vessels', this adds a great deal to reliability for charters.

I thought the Sonic drive might be exxy, also the guy that had it experienced a failure, from distant memory an input shaft or something- but fixed at no $ cost......! it looked a bit "frosty" after a few years too.

As for ventilation & dunking there's differing strategies. Outboards fitted to "wells" in front of the rudders & generally on a track system mounted to the rear connective bulkhead seem to go OK on the Shionning vessels, I'm sure they have a baffle or seal for when down though, our survey/inspection- for comercial/passenger use authorities here dont like the wells due to vapour issue, although I've seen one that had passed but had a "ladder" like set of vents through the inboard hull side. For through underwing mounting, fore & aft positioning is important in regards to about the center of pitching, along with immersion of the prop & proximity to the hulls so the props mostly stay as immersed as the hull its near, the slots the leg comes through vent & drain the engine space, possibly a set of rubber sheet "lips" might seal some splash out. Regards from Jeff.

 

Make your own? of composites? pivot the foil shaped leg using a long tube mounted high under the bridge-deck running fore/aft either a shaft and gears or a "silent chain" will deliver thrust to the short propeller shaft at the bottom of the foil-shaped leg, The long tube is the swing point and will allow the leg to swing up under the bridge-deck where a hole/inspection hatch will give access to the propellers near midships Depending on separation of the hulls, depth of the legs etc... The legs are either swung by hydraulic means or lever... The legs are NOT steerable - no need as varying thrust and direction should give excellent control... Check on the engineering as considerable thrust will be delivered...

Does that make sense? I am not real good at freehand drawing and haven't used cad for years & years...

 

how about a coupla these...................... http://www.********.net/

 

Huh ??? on a SAILING cat...

 

Brainstorming.........................http://www.youtube.com/watch?v=eHCKLwXq0e0

Mas, its a conceptual thing, adjust the propping, no need to steer in the cat application, fwd/neutral/reverse box & x 2 & CB is good to go.

Some Wharram cats have these kind of thing.

All the best from Jeff

 

you must have something planned considering propulsion on the drawings dont you? have a link or wanna show your hulls
becouse the hulls sort of dictate what to use, if kano hulls below than perhaps -foldable- props behind the keels..

 

I would keep it simple, use an outboard. There is a simple set-up used on the old Thunderbird 26, it has an aft compartment that completely encloses the engine, and when it is kicked up, most builders install a door that closes like the landing gear door on an aircraft. It keeps the outboard secure from theft and it looks clean on the boat, gives an unbroken hull with the engine retracted. And to have it serviced you just remove the engine and take it to a shop.

 

What if you built like an internal outboard engine mounting and box and you had a hydralic or electrical transom mount in your hold that could raise the outbord and tilt it so it clears the water. A box 18" wide by 48" with the sides higher than the water line and a top to close it off when engine up and tilted. A single Hi Thrust outboard should move you at a good clip. I know what a 9.9 hi thrust will do and it is amazing. Just an idea for you. You could also adapt a cat track (rubber belt with paddles) to go up and down and I've seen some of these go like a bat out of hell. Use an electric engine and your gen set.
Raise and lower at will. I once saw a jeep 4 wheel drive with paddle tires and it was going over 50 mph on a river.

 

I am really appreciating all the brainstorming, guys. Thanks! This thread is going well.

Yipster: Here is a link to my hull form...

http://multihulldesigns.com/designs_stock/45bdcat.html

**Note: I have kick up rudders in a cassette at the aft most part of the transoms on each hull. I also have dagger boards.

 

I said Huh? - because CatBuilder said his transoms had a kick up cassette for his rudder on his SAILING cat so where does said monstrosity fit?

 

http://www.youtube.com/watch?v=0jB6uKa_PjE&feature=player_detailpage

http://www.youtube.com/watch?v=xFz5i0RFSuw&feature=related

It seems to me that with rudder cassettes ,any drives you choose would have to be mounted outside your hulls.

 

This is what I was thinking....... but then looking at your layout plan, not very accommodating for alternate engine placement? - This fetish for an abundance of toilet facilities is a bit of a waste of space... but,,, 'thems-be-the-demands-of-tourists' ?

Maybe a matched pair 48V gensets aft in the engine bays that could be hoisted out for servicing, batteries, water-maker in the chamfer panel running from the aft cross-beam forward to the mast beam, then tapering off to the bows (similar to my boat)... The legs could then swing out from a section of that chamfer panel under the bridge-deck so that the propellers could be accessible under the aft cockpit... returning again to electric drive???
each engine needs to deliver sufficient to run one leg at full power or both at "half" power... batteries there to give boost, and for quiet when at anchor?