35' cat concept for the inside passage.

Fuel and long range capability... That is what led me to go from 10M loa to 12M loa... FUEL capacity... I guess I can carry up to 1500kg but currently feel 2 x 500/600 litre bladders midships and the 450 litres presently in the forward holds... (1650 litres = 1320kg) and I am around 4500kg empty but with full supplies... You will note that the hulls project beyond the bridgedeck by 4 ft forward plus 3 ft of deck then 2 ft raised forward hold - - and 4 ft aft... Note the inked in modification for the front windows...

 

I meant to ask you earlier what Cp you are using. After length and displacement it's probably the most important coefficient in boat design. And I don't see how you can get a displacement figure without knowing it (or vice versa)

For what its worth, the attached are the hydrostatics for the 36ft semi displacement power cat I am working on now. Still subject to major change though

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

If you're still on the belt idea,how about toothed ones?

I worked in a mill, right on the ocean,and the 250 hp electric motors ran the boom lifts (3' from the ocean,with a roof over them only) via 4 or 5" toothed belts. 16 hours a day,they'd last a couple years IIRC.

Reverse? Disengage the toothed and have reverse like the rototillers.

Have you thought about using dog clutches? Once off the dock it'll stay in FWD 99% of the time....

 

I'm going to wait with great interest to see how he solves the transmission problem.

I went through something similar, determined not to pay the money etc. I've got a complete metalworking machine shop so can make pretty much anything I put my mind to.

In the end I decided I only had a finite amount of time I wanted to use up on building stuff rather than having time to use it. So I bought a new marine engine with transmission. Then again I'm building a monohull so I only need 1.

Adapting an outboard lower leg might be a good way to go, though, never had any reason to look into that. Screwing about with tractor stuff is going to get tricky when you deal with the need to go from fwd to reverse when coming to a dock etc. Not saying it can't be done, but personally I'd be checking out the price of marine transmissions. I've got 2 Chinese made ones sitting in my shed that I've picked up over time, 1 of them fitted to a single cylinder horizontal diesel, nice & compact, so the stuff is out there.

PDW

 

Richard, i havnt done any optimization on the hull as it was just to get a rough starting point for boston, the prismatic coefficient is very high because the stern is very full - it was thought Bostons boat would be stern heavy, but im not so sure thats going to be the case anymore... we shall have to wait and see his floor plan/GA...
Im not so sure i agree with the typical "ideal" Cp vs SLR... ill get back to you on that once ive played around some more...

Heres the hydros on it anyway;

 

Nope, i cant get it much better than it already was... reducing the Cp created more wave resistance and the negative interference wave drag (from the 2 hulls as a cat) peaked right on 8.7kts... just the interference drag alone was 0.45kN at this speed...

The high Cp shape im using has some interesting wave cancellation characteristics... together with a rearward CoB, its use in powercats is very well suited... or so the computer says anyway...

 

As am I..if it were me I'd throw in a transmission as I don't have the patience,but he seems to love fiddling about and inventing different things so I'm just giving him more ammo.

Seen the oil burner unit he made for his truck?

 

In general terms a high Cp is needed for an efficient hull at speed. But it can be lowered if the SLR is lower

However if you have a high Cp the buoyancy has to come from somewhere. So for a given WL beam either that means very fine bows, or a very fat stern or reduced rocker

All of those have implications when considering the overall design and so the optimum Cp may get modified. And of course all those factors mean the CofG needs determining before drawing the hull.

And we don't know that, and nor, it seems, does Boston, so no one can go much further with discussing the hull shape (and by implication the engine hp) until more is known about the GA etc.

It seems we maybe going round in circles here

Fortunately power boat design is easier than sailboats in part as the speed is known and there's no heeling.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

I agree, but I'm sure the vast majority of every topic here is a rehash of one that's been done and beat to death months and years before.

I don't mind putting in posts,because Boston takes the time and effort to draw things and figure things out.

Unlike many,who on their first time here take the minutest effort in a 20 word post, while demanding enough technical details to build the thing.

 

Agreed, and that's why I've carried on posting

Richard Woods

 

Hey Bos, my design is getting closer to finish Btw; check this out

Speed = 20kts in 45deg randomized head seas with 4m swell...

This is what i was referring to earlier... but according to my resistance simulations, the resistance got worse, not better, when i lowered the Cp by either increasing rocker, reducing beam at stern or a combination of both - All combinations used identical bow section. The speed i was doing the comparisons was at 8.7kts - which i dont consider high speed for a cat... so this doesnt agree with "ideal Cp and SLR" ive been hearing about... the biggest difference i can see in the resistance components, is the significantly increased transverse waves generated by a constantly changing hull section as opposed to a straight or constant volume section. Any theories on this Richard?

 

What software do you use for that groper?

 

No I must have missed that.

I like building stuff too but there is a limit. I built my own steering gear because I wasn't paying the asking price from Edson and I had the machinery to do it. If I hadn't a big lathe & mill I would have used a different method.

Frankly if the prop thrust is taken care of via an o/b leg then I'd be tempted to hook up a 4 speed manual transmission from a small truck or similar. Reverse is going to be way too big a reduction though, not sure if there's a fix for that. Going the PTO/override clutch then some form of reverse is going to be messy & bulky. Dog clutches aren't going to work IMO, going to be brutal engaging them. Cone clutches will but now you need to design/build or buy ones capable of transferring maybe 80 HP from fwd to reverse in 10 seconds or less. Good luck with that, there's already stuff you can buy off the shelf or off of Ebay if you start early enough.

An industrial 1:1 fwd-neutral-reverse g/box mounted to the engine would be the way to go if you can find one. Then put that PTO speed reducer on to get the reduction needed.

Or you can look into hydraulics or electrics. Ask catbuilder all about it....

PDW

 

I converted an old international 7.3 diesel to run on used motor oil. Ran so well I decided to rebuild the whole truck. It was kinda an experiment to check the viability of running an old diesel on alternative fuels in the build. Seemed to work great, so now to develop a boat that does the same.

this series of flickers is me tuning the build, it smoked like a ***** when I first started out, but I got it tuned enough that it quit that **** and runs fine now on nothing but pure used motor oil, filtered of course but still. Free fuel. OH used motor oil has a higher potential energy than diesel, 140k btu/gal vs 120 btu/gal for diesel. and 90k btu for veggie oil. Its hands down the best fuel if you can get it, and I've got an exemption to carry up to 502 gallons. So ya, no reason not to run on WMO.

http://s29.photobucket.com/albums/c262/bostonpyramidbuilder/?action=view&current=DSCN0249.mp4

http://s29.photobucket.com/albums/c262/bostonpyramidbuilder/?action=view&current=DSCN0256.mp4

http://s29.photobucket.com/albums/c262/bostonpyramidbuilder/?action=view&current=DSCN0257.mp4

by the way, there is no limit to building my own stuff, its half the fun. Other half is making it work, cheaper than the other guy.

 

westy I'm off the belt plan, and onto the PTO accessories. I've got everything imaginable except a reverse so far and its just a mater of time before I find a PTO trany with reverse. That or just use the gears in a outboard lower unit as Par said.