Catamaran Single Engine One Hull

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Why not mount the outboard on the vessels centre line on the aft deck. This way there is no "out of balance" aspects to consider. If your layout/arrangement allows it, everything else is straight forward.

We designed a large passenger cat like this many years again, to keep costs down. But the client eventually pulled out, so didn't get to build it. But mounting the engine on the centre line is an obvious solution.

 

Thanks, Phil, I was trying to avoid naming him as he is not on this forum....

What with spambots and what not crawling all over everything, it's best to keep a little bit of privacy - especially that of others..!!

But he does contribute to The Coastal Passage, so is kind of 'out' anyways, and he's got broad shoulders so I guess he won't mind......

 

Didn't realise the privacy issues. My mistake

Phil

 

Like Steve W, I owned a MacGregor 36 which came standard with a motor bracket on ONLY the starboard hull. Mine had remote controls and except when there was a strong wind from starboard I had no issues underway. Sometimes a wave would push the boat to port ( along with a strong wind from port) and she just would not turn back to starboard, but those conditions were very few as when there were waves like that there was usually wind and we would sail except in a very narrow range of circumstances. Slow speed maneuvering needed to be planned accordingly.

For various reasons, none of which had to do with maneuverability, I added a bracket to the port hull and had 2 x 9.9 Yamaha hi thrust motors, was awesome power for such a light boat.

Steve

 

If I were looking to use my auxiliary engine in a strictly aux manner, rather than in a motor/sailing demand, I would seriously consider a single engine installation. This engine would be conveniently mounted in a 'box' enclosure on the cockpit deck and would belt drive an out-drive leg that would be incorporated into the rear portion of the central nacelle structure. Maybe this rear nacelle might appear as on "Earthling's pod" (attached photo)

This saves the cost and weight of the second engine, trans, shafting, prop, etc, and opens up the rears of the hulls for a nice master bath, or whatever
Easy access to the motor for maintence, etc. Box enclosure could be another seat or table top.

If you are handy you might just adopt a used outboard outdrive to the arrangement that would pivot up, or with more considerations you might made it a 'steerable' situation, although with this small of a vessel I'd be tempted to leave it straight drive with steerable rudders.

With more thought you might make use of these relatively simple but strong chain drives,.....outdrive leg might be constructed using a 'silent chain belt drive'.
http://www.ramseychain.com/prod_sc.asp

Then again look thru these Thai longtail designs for some ideas:
http://www.boatdesign.net/forums/powerboats/thai-boat-plans-needed-20398-3.html

Have you looked over here:
http://www.boatdesign.net/forums/propulsion/brainstorming-retractable-drives-39922.html


You might need some different 'U-joints'
http://www.boatdesign.net/forums/propulsion/u-joint-cv-joint-thompson-coupling-16397.html

 

In my experience (primarily with a bridgedeck mounted generator, noise and vibration are accentuated with a bridgedeck mount. Also, great care must be taken with cooling water pump location and impellers on the bridgedeck. My generator cooling water pump was severely challenged with a long suction hose and by being significantly higher above the waterline than is normal in most marine engine installations. It resulted in 10-50 hour impeller life. I've recently moved the gen to the engine room. Time will tell about the impeller but noise/vibration reduction is significant. A bilge mounted cooling pump might alleviate some of the issues but then you probably need to eliminate the normal engine mounted pump. Putting two in line could be problematic. It was easier for me to relocate the genset and also gain the sound advantage.

 

Yes it can be done but-- ist second hand value is nothing, its noisy and gets wet. The manuvering capability of a twin and having a back up is surely worth something not to mention all the ugliness.

It will be frowned upon by other cat owners and no way will you be given a slip near the yacht club.

 

These are the guys with the asymmetrical hulls/1 engine power cats:

http://www.aspenpowercatamarans.com/pages/technology.html

Brilliant idea.

Mike

 

I had a Yanmar YSE12 diesel under the aft bunk in one hull without any problems whatsoever. Phil is right - as usual - the fuel efficiency is better than 2 engines.

When moving forward, it was impossible to tell there was only one engine - no helm correction was necessary. Only in reverse was there any "problem" because the boat would not run straight back, but started to swing. Actually, when one got used to this, it became a benefit, because it made it easy to turn the vessel into tight spaces by simply judging the approach angle

Alan

 

Sent you a PM Bushman with a few other questions.

Cheers,
Jeff

 

Hi Fellas,

Dealing with a central pod at the moment in post 29 of this thread. Sea anchor

The current situation I have is a nicely faired fibreglass pod with a small transom on which the outboard is mounted, and the OB is tilted to the horizontal when under sail. The "pod" hits the waves and the bigger the wave the larger the disruption.

It was OKish in the harbour, but once we got out in a seaway, any higher and the outboard would have been lifted out of the water too frequently, and where it is, it slows the boat (especially under sail) pretty dramatically, like you can feel the boat stopping and there is a tremendous amount of water disruption in the central section of the wash. (think a 10 inch fixed propeller dangling in water as an equivalent hold up!!!)

Whatever happens I need to fix it as a matter of urgency.

Looking forward to some potential solutions in this thread

Cheers

 

These are problems easily addressed with the proper insulation / isolation plans.

Steve

 

Steve

I had the same problem with a 15 HP outboard mounted centrally on the bridgedeck of a 30foot cat because the prop lifted too much when there was a lot of chop - usually caused by Sh$theads in their power boats.

The solution might be an extra-long shaft to get the prop lower into the water, but a better (if more complex and expensive) alternative could be to fit one or two sliding mounts (like heavy sailtrack) between the transom of the pod and the outboard bracket, so the whole unit can slide up and down maybe 200 mm or so. It could be lowered and raised manually with a block and tackle but a better option might be a hydraulic cylinder and pump for remote control.

If you post some pictures, I'll see if I can produce a sketch of a possible solution

Regards

Alan

 

Go the pivoting nacelle

Gday Brett

Kankama originally had a pivoting nacelle made from ply which we used when cruising. It was great and got the powerhead way up out of the way sailing and down low when motoring. Then some scumbag stole my motor - they couldn't get the outboard off the nacelle so too the whole thing - nacelle included.

I then made a nice foam fixed nacelle that was deep enough for the new Yammie 25 which doesn't get its prop very low due to the big transom mount. It was a drag - literally. I couldn't hack it. Okay in the lake but terrible outside - constantly banging and making waves.

When I put the new cabin I made this nacelle pivoting too. Its really quite easy. I put some glass tube made from glassing stainless tube at the front and glassed heaps of uni and DB around it. Then I did the same for the bridgedeck bottom. I cut a bigger hole in the cockpit floor and put a nice big seat/table over it. You need a set of ears at the back to stop the nacelle at the right height. Lovely quiet sailing with no nacelle noise.

It's so much better than before and protects the engine well. With a well made seat the whole thing is unobtrusive. The nacelle works nicely so I would recommend it. Better sailing and better motoring. I will take some shots on Sunday if you want.

cheers

Phil