paired diesels?

[hinemoa]

just a query , if one was to have twin diesels in a catamaran, and for example i used one isuzu diesel at 145hp and another brand of diesel of 145hp could this be done as i am having trouble finding the same motor but have other brands around the same hp available??

anyone had any problems etc with seperate brands of motors, ofcourse these will be individually operated via remote morse operation

[CDK]

More important than peak horsepower is the engine torque at various rpm.
If you find another diesel with peak power in the same rpm range and roughly the same weight you can use it.

[FAST FRED]

If you chose unmatched engines , I would mount a simple pair of shaft tachometers to keep the boat going straight.

Unless identical trannies are used (2-1 may not be exactally 2-1 on every brand,) there might be a hassle with the engines operating at slightly different rpm's and making really awful resonant noises.

Sorta like a piston airplane with engines out of sync.

For displacement cruise you will probably be at 12-1500 rpm , but it will be a annoying.

I wudn't have thot to consider it but the owner of the Glacier Bay molds is making cats with one inboard to great success. As I thot, counter-intuitive but the things are super-efficient (a single is almost always a better choice than twins in this regard) and don't turn circles like a skiff with one oar. I now believe that displacement, hull speed cats shud be single-engine!

[Easy Rider]

Mark,
I think the single engine cats are a bit like an outrigger w the engine off CL toward the outer hull. In quartering seas I can't imagine that single engine cats would be 100% good.
What are the reasons you think single engines are more efficient? That's what most people say but I've never been convinced. I think there's so many variables a flat statement cannot be made.
Re: Dissimilar engines: Maint and spare parts would be a minus. Having different looking instruments on the bridge would be a conversation maker. Good way to decide what engine's best. No V types w inline. No DD. Main thing may be (as CDK says) torque curves should be very very similar. And like FF says a 2-1 gear may be 1.96-1. I agree w FF. Harmonic vibration is worse than vibration!

Easy

[hinemoa]

thanks for the replies guys, i have a paired set of gearboxs, twin disc mg506's one l/h and one r/h that i can get for $2750 for the pair that are advertised as 2000hrs gearboxes and have been replaced by outboards, so if i brought these pairs i would have matching rations, and for the noise , yes i have actually hurd this on larger comercial boats when like a main engine is running and the genset or auxilary is running together, would a good water muffler help that? as engines are quit a way away from cabin area
for the instruments, i have a pair of cummins panels complete so was hoping to mate these to the engines, and all the controling is done by electric remote control

Well, Easy, first off, I am no fan of small cats to begin with as I have just seen too many attempts end in disaster (slamming trampoline and resulting breaking apart in seas larger than design height, i.e., sharp enuf seas that they hit the tramp and have nowhere to go but a direct route to passenger organs and dental work) and weird handling (hobby-horsing, burying a hull in bad folling seas and subsequent broach, and mal-de-mer inducing drunken roll) in mean seas also, the designers of these things often seem intent on ultimate efficiency thru surface drives or jets that will always lose waterflow in rough water sporadically, and slowing down in rough water negates any speed advantage and causes the engine to run in an inefficient and often over-taxing range, but displacement cats seem to be the ones that the benefits outweigh the oddities.
The efficiency of single engine is simply that there is less stuff hanging in the water. I prefer a single because I like an engine room with maximum space for a given size boat (in fact, if an engine space is ever not the nicest space on my boats, I am doing something wrong) and because far fewer things go wrong with a single (for example, try to have a piece of wood hit your prop on a keeled, 7°+ deadrise monohull - it almost cannot be done. I once hit a house floating just at the surface and once a big male otter and these are the only times I have dinged a prop since 1984 when I bought this boat). The efficiency is a perk to me but I do carry more passengers for less fuel spent than any other boat that I know. Doin' my part for the environment!

I have not personally seen the Glacier Bay guy's boats with one engine but have heard very positive reviews. I thot that they were inboard but don't know. If it is as you said, then my single engine cat idea makes no sense.

[FAST FRED]

The efficiency of single engine is simply that there is less stuff hanging in the water.


There is also the reality that just to spin the motor over and make no power will take more fuel to do it 2x than just once.

The internal losses are half for the single , and with one engine the maint is usually higher.

Fear of a failure, half the work , and of course half the PM , oil filters belts and all the rest.

I am no cat fan but have seen center line pod mounted engines that would seem the simplest.

The drive can be lifted for no drag , turned to assist docking , and the noise stench and vibration are well away from the hulls.

Any really nice pod engined cats out there?

FF

I sure don't want to turn it into a single vs. twin debate but why do you feel that "maintenance is higher" with a single? I agree, "maintenance is better"..but "higher"? I am the only passenger vessel in Homer that never breaks down mid-summer. True, I am not a turn-key driver but Gold-Streaking parts in July and four days off for a Saturday afternoon broken shaft are not part of my usual repertoire (A-L-I-G-N the shaft with a safety factor of at least four and you almost can't break it - at least I never have).
An aside - I towed a fifty foot twin-engine boat with the screws tied together by a rope 22 miles the other day - one of his trannies was shattered and that's not low maintenance!.

[Easy Rider]

Fred,
Wev'e been through this before. The friction of 2 100hp engines is about the same as the friction of one 200hp engine ..friction same for both. So the "internal losses" are equal for both.
Mark,
I think Fred is saying maint costs will be higher ... but I say not much. Two smaller oil filters v/s one large, 2 small V belts v/s one large, 2 small oil changes ..7 qts each v/s one large oil change ..14qts. The cost of buying and maintaining 2 100hp engines v/s one 200hp engine is not the same more like 30% more .. not anywhere near double. I don't want to get into the single v/s twin either but I want to step on the concept that twins are double the maint costs.

Easy

I concur. And the debate is so subjective, so personal, that nothing ever comes of it!

[marshmat]

Regarding the Aspen single-engine cat (proa): I haven't seen the thing in person yet, but the photos and technical information I've found suggests that its hulls are, in fact, asymmetrical and are shaped so that the unpowered hull pushes inboard just enough to counteract the off-axis thrust from the engine in the powered hull. It can't have been easy to design, but all reports so far are that it works quite well throughout the thing's speed range. IIRC, it carries a single inboard diesel.

Regarding different engines in each hull: It's doable, yes. Fred's point about harmonic vibration could turn very nasty, very quickly- and there isn't any easy way to predict how bad it'll be. You also have the issue EasyRider mentioned about spare parts: tracking and carrying spares for two different engines, etc. I wouldn't do it, personally, but to each his own.

[hinemoa]

so for pairing diesels etc, how do you know if they are compatible, is this found out via torque curves or engine revs at rated hp
also, do you run both engines at identical revs or till the boat goes in a strait line so to say , as i have never had a twin engines craft
for my liking with the twin engines, i am going to run second hand engines, so to me if i have twin engines, and something goes amiss out at the water, i will get home, as she is 16 metres long and not many boats could tow me home....hehe
it is all set up , shafts, mounting , remotes, electrics etc are all there, as the original engines were removed when she went into the finance companies recievership and was sold of and seperated

Get two identical ones and don´t bother.

All the drama is not worth talking. You definetively find two similar engines if you want.

Regards
Richard