35' cat concept for the inside passage.

I suppose if I'm going with two kubota engines then I'll need two transmissions. I hear you on the junk yard wars thing but really a v drive reduction set up is no big deal and its bound to be a lot lighter than some big heavy chunk of cast iron trany. I'm open to ideas if you folks have something in mind but a simple shaft with a few pulley's on it is kinda hard to beat in terms of both price and weight. I'll still need a clutch or two but reverse isn't that big a deal either. I've gotta work that stuff out as well before I can complete me preliminary weight calcs

 

Ok so I went with a 36" beam/hul and about 14"~16" draft which gives me 6.4 tons displacement and leaves me room under the bridge deck to be slightly overweight when I've got full tanks. I increased the length 2' for a new total of 37'. I'm not so sure about that boxy looking aft end now though. Although I liked the parapet walls around aft deck in the previous rendition, they don't quite look right now that I've lengthened the hull. The forward view reflects the simple rocker bottom with the stem submerged.

I've designed a drive unit a while back that might just go perfectly with this application I'll post it in a bit.





oops I shouldn't have those two vertical stem lines extending all the way down to the bottoms of the hulls like that, I'll fix that in a moment.

 

Look forward to some pictures Boston

 

I kinda liked the looks of the shorter version of the hulls better but its a minor issue

 

Thinking a bit about the single diesel. Even at 500lb its gonna be dwarfed by the weight of the fuel/water you're wanting to carry, so I don't see a major issue with having it on the bridge-deck.

But don't put it out back. Put it in the salon (above COB) with the dining table on top of it, transverse as you were thinking. Easy then to get a transverse shaft over to each hull. Perhaps use an ex:agriculture right-angle gearbox with reduction (reverse possible?) to then get longitudinal shafts.

If current diesels can be made almost inaudible in a car, soundproofing (and appropriate venting) in a cat should be achievable. It's going to run at 1800-2000 rpm in cruise anyway, not be screaming at WOT all the time.

 

I like the look of the extended stern. Just wanted to pipe in with the downside of putting an engine in the living space. It's hot, could be loud since it's a power cat and will always run, there are possible CO issues and worst of all, it smells bad (fuel, oil leaks and breathers, belt dust, etc)

I'd say do yourself a favor and have a real engine room, separate from the main cabin. It's a much better life.

 

I'm feeling inclined to isolate the engines in there own sound proofed and ventilated areas, The smell as well as the risk of fire I believe needs to be isolated from the rest of the vehicle, and its easier to use a CO2 suppression system in a small space, the stuff sinks in air or at least it does at first when its still cold from decompression. Works better if its at the bottom of the structure. Also gives the boat better balance. I suppose its a preference in the end but I want those engines out of the way and down low. I hear you guys on the risk of electrical fire being greatest but I want to address both as thoroughly as possible

Brian I'm not going to be fully loaded all the time, I just want the option of loading up on fuel and making a dash for Hawaii. The PNW is about the rainiest place I could have picked so 50 gallons of fresh water storage will be more than adequate. I'll collect it off the roof as well as have a small water maker. Very small water maker. I might even DIY that as well using the heat off the headers

I think a basic reduction gear is bound to be pretty easy, a simple chain set up would work fine and its been done a thousand times before. You guys forget I grew up in a pretty rural setting and we built or rebuilt just about everything we ever hooked up to our old POS tractor. Even a basic PTO reduction gear would work just fine with out modifications, most even come with a u joint yoke already on it. I haven't figured out what I'm going to use yet, but I can't picture spending a fortune on a pair of marine transmissions when a little ingenuity should do the trick

Reverse is a piece of cake but I know I'd take some flak for reinventing the wheel so I'm going to hold off on how I want to handle that one for now. Hmmmm think I'll go look up PTO reduction boxes

 

oh and thanks for the input on the aesthetics Cat, I'm pretty picky about the way I like stuff to look even small changes can make a big difference. In this case I don't think lengthening the hulls really detracts from the overall appearance but it did accentuate the square look aft. Might have to put an angle in there somewhere not sure yet.

just what I thought, Hyspecs agro gear boxes 2:1 reduction 1 3/8 shaft, 6 t spline, 130ft/lb capable is about $600 new and every ranch supply house has ten of em used for a couple hundred. I'm thinking unless trany's are say 1k each with reverse + reduction + clutch its worth it to just piece it together. Also makes replacing faulty components a lot easier rather than having to lift out an entire transmission box.

OK so I"m going to spec out that particular gear box for the sake of the preliminary weight calcs
http://www.google.com/url?sa=t&rct=...ANEWEf7NXsO6BfTVg&sig2=Qd0e-_lIUxkY02WUHGRKaw

weighs under 20 lbs is about 7 x 12 x 3 long not including the spline. and I need two of them

in order to make that work I need a class 1 pto shaft adapter for the Kubota if all else fails I can weld on up, I'm going to estimate it at ~5lbs

I need two pto clutch brakes that will act as my clutches, cost is about $300 each weight <20lbs 12v

I also need two over run clutches cost about $70 each and weigh about <10lbs

now for a clutch and here's where I start getting tricky, I want a PTO over run clutch so if I hit something my drive line can disengage from the motor. Gotta spec one out and get its weight and dimensions, then I want a PTO clutch brake that will act as my clutch. http://www.ogura-clutch.com/products.html?category=1&product=9 Issue with those guys is they don't use a class 1 shaft size so lets just use this as an example, the same guys sell the over run clutch. I might put the over run clutch last in the system so the jarring force of hitting something won't damage all the other stuff or the motors. The over run clutches are these things ( this one is exactly the model I would need ) http://www.hoyetractor.com/mm5/merchant.mvc?Screen=PROD&Store_Code=HTE&Product_Code=OR-660

 

Bos, the CoG of the shell is gonna be roughly 50%, i can tell just by dead reckoning and by playing with all the computer models ive done and assuming your materials are fairly consistent throughout the shell... the CoB can be anywhere between 50% and as far back as about 60% max, the hulls i modelled earlier had the CoB right back @ 4m from the stern... so you can be a bit stern heavy and the balance still wont be a problem... i managed to balance my cat with 300kg of outboards hanging off the transoms in a 3.5 tonnes dispalcement design. Although you may have a higher than ideal prismatic coefficient for your typical speed like this, the difference in resistance is pretty small...
6.4 tonnes displacement = 540mm draft - by the same model.

 

pardon my ignorance but in what way would I modify that prismatic coefficient to obtain a more efficient hull, ( waves pencil in the air ) I got this here eraser and I'm getting pretty good with it.

I'm happy with a cruise of 8 knots for efficiency sakes, although that might have gone up a tad when I lengthened it. Max can be whatever that 70 or so total HP gets me which obviously depends on how fully loaded I am.

Something else I thought of doing was to instead of stretch the hull in the middles I could have simply extended the sheer line further aft and saved some weight. But that would leave the aft area with little reserve buoyancy

as far as reverse goes on that drive train I was assembling, in the words of one or our best

So I gotta look into what lower unit might work best and then see about what size prop I can squeeze onto it. I'm thinking a honda 50 but thats just a guess. Maybe something larger so I can run it slow but with a big prop.

Anyway my drive trains are so far new costing about 1k each and weigh in at just about nothing, not bad if you ask me but I still need the shaft and the coupling to the lower units.

one thing I've been wondering about is how badly do I really need reverse in this thing. I could use a small electric drive kinda like a Torquito and run it off the house bank when I'm in a tight spot in port.

 

Just a couple a thoughts....

As a sailing multihull owner, I've learned that running on one engine in a multihull is just fine. Give me a bow thruster to compensate and I would be just as happy maneuvering in a marina with only one engine in one hull. ( I do like the redundancy of two engines but I do not like the expense/fuel consumption of two engines)

If I had the option, I wouldn't to the saildrive thing again. Potential damage, electrolysis, leaky seals, small seawater intakes that can plug with marine growth and the need to haul out to change oil in the lower unit all are potential factors that make me less than happy with that solution. That said, in 6 years I have yet to experience most of these issues. Fingers crossed.

 

You need real reverse. Don't even think about skimping there. (slap on wrist)

Reverse thrust is used all the time on a boat.

 

reverse it is then

 

yes mate, you definately need reverse... dont worry about the prismatic coefficient Bos, in fact dont worry about the hulls at all - your going to be fine... you bigggest challenge is bringing it all together fully loaded and sail away under 6.5 tonnes....

hows that floor plan going?

 

I'll add up the bare bones mechanical, then decide what luxuries there I'd like to have. Whats left is my home weight budget, I'll bring it in under 6 tons and use whats left for fuel.