Marinizing automotive diesel engine and transmission.

[hinemoa]

some great feed back people, ok
the current situation is that the engine were obviously in the hulls , has heaps of venting ducting etc, the old engines(cummins 120hp) went straight from the turbo did a 90degree bend and out the side of the hull in a down pipe, so i gather the setup is already there to reuse, secondly the props and shafts are still in there, the thing that worries me is the shaft is one and three quarter in diameter and the prop is like 400 mm in diameter, and i was hoping to use a nissan td27 turbo engine out of a pathfinder 4x4 as i have worked with these engines a bit and find them very reliable and quite easily run all day at 90hp or in factory form intercooled at 108hp, my only worry is, is this enough to turn the eggbeaters at a disired speed?? obviously i dont have 50k for each engine plus box etc to spend so was hoping to run the diesel and auto trans to find if the thing would turn it. i was hoping that it would go to the plane stage but i might be dreaming as i figured the boat was 11 ton plus gear and now only 8 ton max, its a 16.5 metre hull and aprox 350mm draft and 700mm width of water contact, i have tried to look it up but cant figure the calculation??and i dont know what pitch the existing props are as i cant see anything stamped on them, i just measured the outside and it was 400mm diameter

[CDK]

And I thought I was an optimist......

Your props are 16", quite big wheels for a pathfinder engine, but usable if you strike planing from your wish list. If they were a match for the Cummins diesels, the prop rpm probably should be approx. 1600 for the Nissans.

9.5 knots hull speed and good fuel economy should be your target!

[hinemoa]

hmmm. ok been thinking bout it today, say i get my hands on a older perkins 6/354 and fit this to the boat(in pairs), would i need maual gearbox or the paragon hydraulic 1;1 or 1;2?as i understand it the shaft speed should not exceed 1800rpm? so this meaning if your engine has its peak power at say 3400rpm then i will ned a two to one reduction? am i thinking around the right lines
I think that the 6/354 engine is 180hp as i have found one and am pretty sure another will come up ??
thirdly, can you run just one engine in a cat or do you always need to use both?? and do i need left and right drive gearboxes, if so why is the counter rotating prop for?

[CDK]

Just like you can fly a Boeing 737 with just one engine you can also run one engine in a cat. You get home eventually, but it's not much fun.

The props are mirror images so there is no "wheel effect" and steering is neutral. It is better but not strictly necessary.
I use 2:1 gearboxes where one is running in reverse while going forward. You cannot do that with any gearbox, just the ones designed for it.

[DennisRB]

I have always wondered how a cat would go with one motor dead. I guess it would require a lot of rudder to keep straight creating a lot of drag. That combined with half the prop surface required for a boat of that particular size probably wouldn't add up to efficient motoring.

[FAST FRED]

I guess it would require a lot of rudder to keep straight creating a lot of drag. That combined with half the prop surface required for a boat of that particular size probably wouldn't add up to efficient motoring.

The motoring will only be half as bad as the sailing performance dragging a pair of 16 inch drogues since one will not be dragging.

Folding props (or simply removing the props at sea) will make a huge difference in the boats performance in all conditions less than a full gale.

FF

[hinemoa]

hi you say sae standard, what is that?
secondly, if i put a box behind it ,. what brand can be run in reverse for forward gear, as i need one going lh and one rh, and i presume now i need a 1;2 ratio and a hydrualic one??
as what im understanding is that the shaft shouldnt turn faster than 2000rpm?
so if my engine for example was a low reving perkins 6/354 than i would use a 1;1 ratio
and a fast revving diesel use a 1;2 ratio?
sorry may seem dumb but just trying to work out the way you guys work this out...hehehe
i have found a paragon hydraulic 1;1 ratio was fitted to a 4 cyl international for $450 nz , is this cheap or a lemon and are these reverseable to go fowards??

[CDK]

Hinemoa, I think you are mixing things up a bit, nobody mentioned SAE on this thread.

There is a relation between max. rpm and prop size. If you want to keep the 16" props, spinning much faster than 2000 rpm will result in the speed of the blade tips becoming to high, causing cavitation and less usable blade area.

Because of the counter rotating prop you need gearboxes with the same ratio in fwd and reverse. Many models have a lower reverse ratio, that's why they are not suitable. I used Technomarine gearboxes, now part of TwinDisc Inc.

Look here for a list of nearly all available gearboxes: http://www.lancingmarine.com

[Guest62110524]

hine
kia ora
forget it bros,
go to google search used diesel engines
as FF said dy stack, keel cool is an option, but at the end of the day, you put a heath robinson conversion into a baot , you just make the resale unappetising
NZ has the most liberal import regime in the world: so go look mate

[hinemoa]

very true, i guess at least i have looked at the options, went and talked to a hydraulic man about doing the job, but he also advised to stay with what i have as its a lot simpler to work with and end of the day will save a lot of headaches as new systems always have there deamons

i have found a pair of maranised hino 6cyl 2h diesel engines rated at 120hp so once i find out about my props and gearbox ratios i can make the decision on these engines as to wether they will do the job..

[FAST FRED]

"6cyl 2h diesel engines rated at 120hp "

With most folks using 3hp per ton at Flank speed as a rule of thumb ,

is your boat actually 120+120=240/3 = 80 tons?

WOW!!

[hinemoa]

yeh wow, no its only about 8 ton, but i am waiting for someone to tell me the formula as i have looked and looked to try and work out the catamaran mathmatics as i have just found the size and pitch of the props on my boat, and am waiting to hear back from anyone to let me know what ration box i will need, i have found out so far that my shaft speed should be max 2000rpm?
the hull was designed as a fast passenger ferry, but now its just a pleasure boat and would still like to get some speed out of her as she was designed for, but dont know what hp or box i need to match the props to maybe get the performance she is designed for
abviously as a ferry she would have carried some weight with 40 add passengers etc

if you know formula than please save my stresss.....hehehehe

[FAST FRED]

hull was designed as a fast passenger ferry, but now its just a pleasure boat and would still like to get some speed out of her as she was designed for, but dont know what hp or box i need to match the props to maybe get the performance she is designed for
abviously as a ferry she would have carried some weight with 40 add passengers etc

The formula of 3 hp per ton is for DISPLACEMENT boats and speeds.

If you need go fast , simply rebuild what ever the boat was fitted with.

1 Gallon per mile per engine will be the high speed cruise fuel bill,

Go for it!