Ganging Outboards - Does it work?

Could you adapt to an outboard with the powerhead removed ? I don't think you'd want a replica of the relic described above, it has straight-cut gears which would whine nicely, you'd think, and no capability to tilt.

 

I suppose, but they have the wrong props available. Also, I don't know where to source the legs. I need a 1:1 gearing to work with a diesel and transmission. Outboards are all 3:1 or so.

No need for my leg to tilt in the setup I've worked out. Just need a z shaped drive leg.

 

There is quite a bit of variation in outboard gearboxes ratios, say 1.6 to 2.8/1 roughly, and the prop pitch range is very wide for most engines. Outboards with blown powerheads are not that expensive, sourced from wreckers, but it would not be easy to make it all work reliably.

 

I agree. If the drive leg isn't plug and play, I'm not sure there is enough time to rig it all up. I'll just stick with the gas/petrol outboards for now. I have to get this boat into service so I can start earning money again.

The custom Hvac system will keep me busy enough.

 

If you'd scrolled that page up to post 107....
Its Cats thread, if he asks questions and if it wanders off and offends you well then too bad for you-don't read it then.

Anyways,all your refer needs run on solar? That's great!

I know you're on the minimal drag kick,but are folding props or CPP on a regular shaft such a bad thing?

 

Ah, I missed my friend Tunnels' post somehow. ha ha ha

Mr Tunnels, outboards, drive legs, propulsion in general, have everything to do with refrigeration and HVAC systems on a boat.

How could that be?

Each and every system on a boat is inter-related as one derives power from the other or depends in some way on the other.

Designing the systems aboard a bare hull (or hull in need of a refit) is an exercise in interdependency. All the systems are dependent on each other in some way or another.

West: Yes, I need my refers to run on solar because I can't stand doing daily generator (or engine) runs. You are literally a prisoner on your own boat if that is the case. At any given time, I will have $500 worth of food in the freezer. This means you don't just up and leave the boat saying, "who cares" about the daily generator run. See, I've had boats with it both ways. I had a diesel generator based boat and a solar based boat. I much prefer to just look into that ice box and notice everything is nice and cold as I'm getting some food out, over managing systems. A generator failure in the past used to be quite a panic aboard our 2nd to last boat because $500 in food would weigh in the balance of my being able to fix the generator within 24 hours. Not fun! That's why I am strongly for 12V (or 24V) refrigeration, powered by the sun. It just works better to protect our valuable food.

Nothing to monitor and do, just open up the icebox and it's cold - every day.

About the folding props on a regular shaft, yes, I can't do it. I have a sailing machine coming together here. Any junk dragging below the boat will hurt my light air performance and it's not something I'm willing to compromise on. These are auxiliary engines, to get me into and out of port, basically. They are also in case there is actually zero wind or a perfect headwind and my guests need to get somewhere.

Other than that, this boat is optimized in every way for using the sails as main propulsion. It's not a motorsailer like most boats. It's a thoroughbred sailing machine with some motors to get it through those spots that are impractical to sail through.

A lot of people are willing to sacrifice some light air performance to have props below the boat. I'm really striving for that light air performance on this boat, so I'm not willing to make that kind of compromise.

Having done this stuff for many years now (chartering guests around and living aboard 24/7/365), I know that the most annoying part of a boat is having to motor it in light air. My choice of this boat and the strong stance I have against any "junk" dragging below her is borne of many years of frustration.

There aren't really many times in my life I'd wished for less wind (maybe at anchor). I've always wished for more wind. Not having junk below the waterline will help us sail in 6 knots of wind while other boats are motoring. That's the real goal. Light air performance.

 

CatBuilder, are you going with outboard power now? All the high thrust yamahas are geared to 2.33 to 1 except for the smallest and they get extra bucks for them. Tohutsu
makes a 75 hp with that gearing standard and I've spotted other outboards with various hp that had the 2.33 to 1 set-up and no extra charge. Props are always extra so you can get the correct prop. Just info.

 

Yes, there is no choice. Everything else weighs too much. Diesel engines plus generator is too heavy, inboard diesels have drag, diesel electric inboard systems weigh as much or more than diesel inboards, etc... etc...

I had been thinking about ganging Torqueedos when opening this thead, but they are not, apparently, up to task to produce enough power without getting 6 of them.

Evinrudes are also geared nicely (2.3 to 1 or similar).

I'll select the right ones once I get there in about another half a year or so.

I'm going 60HP and 9.9HP. That way, the total weight for 70HP of thrust is 373lbs, assuming Yamaha high thrust. More than the HP of a pair of Yanmar YM30's at half the weight. Of course, they also retract.

The key is two different size engines though. Keeps the weight way down and allows me to run as follows:

Fast: 70HP total thrust available - use lots of fuel
Standard Speed: 60HP - use a little less fuel
Slow: 9.9HP, plodding along - sip fuel and go forever if I'm not in a hurry

Still has the dual props needed for maneuvering in marinas too.

 

Cat have you checked out this neat little unit? much $$$ but I priced out just the engine through a dealer here at $ 2,400.00 That 60hp yahama will cost more then the 75hp tohutsu
http://www.aquamarineinc.net/minigen.html

 

Hey rasor I've suggested those to him already..

Fair enough..thanks for the explanation...makes a lot of sense trying to stay out of the weight/power loop.

I wish I could do that solar refer method,but not worth it for me as I'm in a cool climate.Have an engine drive holding plate for my fish freezer with 12V to hold it longer.
It could run off 12v solo as well.

I start up every couple days at anchor for an hour or two to charge batteries and the freezer plate..and as it'll run 4 hours on a gallon of diesel,it costs me very little in diesel.

If I'm running then the house batteries get charged off the mains of course.

You've probably already thought of this..how about a storage spot in the sugar scoops for the outboards..maybe a levered bracket that holds the outboards,and swivels out when needed?

 

Rasor: Wow! That's exactly what I'm building, except that I will be using a fresh water cooled Kubota to keep the noise down (charter guests). I think I'll need a bigger engine too, since I need a pair of auto compressors, not just one.

Yeah, the exact outboard wasn't really my point above, just the setup of having one large and one 9.9 makes the boat much lighter with lots of powering options to suit the conditions. I like Tohatsus as well. Had one for about 6 years before my utter neglect finally killed it. It started and ran perfectly for that entire time - and I bought it used too.

West: Exactly! I am going to do the outboards like this, in the sugar scoop.

 

I also like the idea of one big and one small.
Like you say,if you are motoring so rarely wth is the point of heavy diesels/shafts/etc etc

In the pic,I can envision a powered ram lifting it out and tilting it back on a track and a step covering to hide when not in use...but that's just me,I like uncluttered things.

 

Ok, don't let me wife see this post!

Seriously, we are looking for ways to minimize the visibility of the outboards, so could you explain the idea for the ram and tilt?

Where would the ram go?

Where would the tilted motor go?

How would that cover work?

I was going to do it this way (like the pictures) because it seemed to be the most practical (props won't breach too badly) and most protected (no spray shooting down between the hulls can hit them).

If they can be better hidden, I'm all for it.

Could you explain your idea for hiding them better?

 

A lot of posts today, you must be waiting for epoxy to cure!

400w solar will work good for a freezer (200w is the min) (WestVan: heat doesn't matter for solar - sunlight, even weak sunlight, does, so in the PNW with summers of 16hr sun and no clouds every day solar makes more sense than in the often cloudy tropics with 12 hrs of night)

Not sure about the 9.9 plus 60 idea. Will the 9.9 do anything useful apart from help when manouvering when the 60 is running full speed?

And very unsure about the Tomcat (I think) engine in wells idea. I wouldn't do it. I doubt if you can make the bomb doors (for lack of a better phrase) fully watertight.

If you cannot then I think you'll have more drag than with a prop shaft. And if you have the prop behind the rudder then in reverse you'll have massive loads onto the rudder. At best it will be difficult to steer

IIRC the Volvo race boats have conventional prop shafts that fold up flush into the hull. Most of the 60ft racing trimarans have exposed shafts.

Richard Woods of Woods Designs

www.sailingcatamarans.com

Online and not sailing as its raining

 

Thank you, Richard, for the post. Yes, I'm in for the evening, just going over things for the build and waiting to start in again in the morning. Too many posts...


Some thoughts in response in green...