Backup Hydraulic Drive

Yeah i agree about the stairs but with 25ft beam and fairly slim hulls a pair of outboards hanging off the aft beam are still far enough apart to give a decent turning couple. Outboards are probably always going to be the least expensive and lightest option but its worth exploring other options.

Steve

 

So what your saying is the aft beam is 25 feet long *inside* the hulls?

Or is the overall beam gunnel to gunnel 25ft?

Makes a big difference to the turning circle a pair of beam slung outboards can manage....

 

No,no, no, the overall beam is 25ft but the hulls are slim so motors mounted on the aft beam are still spaced pretty far apart, probably not much different to a pair of diesels in a 20ft wide cat, one of the many advantages of outboards of course is you can cruise on either one with the other out of the water. one of the disadvantages of inboards is the need for either inefficient folding props or very expensive feathering props, less expensive, most efficient fixed blade props are not an option.

Steve.

 

Yeah, the whole 'saildrive' thing is a total con. Stern drives are a better option as you can at least lift them mostly out of the water and thus reduce drag under sail, but, as you say, fixed props are no good, and the feathering and folding kind are exxy.

Outboards are still looking good, but even with them mounted as far outboard as possible on the aft beam, I'd stil be inclined to add bow thrusters, especially if you will be in and out of marinas often, as manouvering in any sort of wind in a marina, in a cat, is a PITA.

My mate is always stressed, even with the hydraulic drives that can be switched back and forth (forward/reverse) without any gearbox or neutral position to slow them down.

Having seen what bow thursters can do, I am amazed more people with cats don't fit them automatically.

I predict (crystal ball out on a very thin limb) that trailered power boats will have them as 'optional extras' within a few years and within 10 years they'll be the norm, and the electronics to couple them to the engine controls will be standardised and probably available for Arduino...if they aren't already!

 

I agree the thrusters do work very well, we have installed a few over the years and stern thrusters are becoming commonplace with powerboats but with sailing cats i dunno. For the most part larger cats already have the expense and complexity of twin diesels on top of the expense of the sailing rig and then to add the considerable expense of thrusters i think would be getting a bit much. Another issue may be that it is always a challenge to find a place to install the things, they need to be immersed deep enough to work well and a lot of cats may not have the depth although they now have surface mount ones that just bolt up to the bottom. Also on planning powerboats that big hole is out of the water once you are up on plane. Another point is twin engines on a monohull are just not as effective as the widely spaced props on a cat.
Here's a thought ive had for a while, its a little outside the box but could be the best of all worlds, retractable pod drives with one mounted aft in one hull and the other forward in the other hull. A clever guy could make his own using either hydraulic drives from a single cockpit mounted engine or perhaps electric with a good sized cockpit mounted generator. It would be somewhat comlex mainly because of the need to have controls running to it while it has to be able to rotate at least 180 degrees and also retract to provide a smooth bottom for sailing. There is no reason i can think of why the props would have to be in the same fore and aft locations for forward propulsion and on a sailing cat and i would be retracting one anyway when motoring out in open water. I don't see a problem with mounting, rotating for steering or retracting but you need either hoses or large cables going to it without getting twisted up when rotating it.
Hell, you could use stripped down outboards if you could figure out how to shift gears and operate the throttles.

Steve.

 

Yeah, I take your point about the hole in the boat, causing drag, and of course you're right about the spacing of cat motors relative to planing hull monos.

Dunno about the retractable pod drives - what are they displacing when retracted? The shower? A bunk?

On balance I think the twin outboards is still the most economical solution, and provided the space *they* occupy is well designed (pod lids incorporated into cockpit seating for example, they can be virtually invisible and silent if insulated properly.

Here's a thought - how about using twin pod drives that fully retract into the bridgedeck as for outboards, by pivoting the leg up, rather than rising vertically. They could then spin 360 degrees which, as we should know, is far more effective than reversing one of the props (which don't work as well in reverse thrust as they do forwards due to prop shape).

Now there's an artistic solution.....

 

Don't worry, ive thought about home grown pod drives that rotate 360 degrees but the problem as i see it is how to connect the controls to the unit while still allowing it to rotate all the way around. I don't think, if the pods were mounted through the hulls they would be too much in the way as long as they were hydraulic or electric legs driven from a cockpit mounted engine. The aft one could be as far aft as you want as they would be relatively light compared to even an outboard and well aft of the accomodations and the forward one in the other hull could also be well forward, also ahead of the accomodations. It would be fun to do a scale test with a pair of small 360 degree rotating outboards on a beach cat.

Steve.