2 "B" motors in offshore boat?

[cjohnson]

A buddy of mine is looking to get an offshore boat sometime in the next few years. Probably in the range of 33 to 38 feet. I turned him on to the Cummins in the Dodge a few years ago and he has been a believer ever since( his 01 is now bombed). Anyway, I told him if he really wants to have something cool, he needs to build his boat with dual, twin turboed, 12 valve cummins'. What a perfect platform for those motors. We know they are capable of suviving the marine environment with their history in this type of service. I figure it is pretty reasonable to shoot for 600-650 bhp for each motor. He will achieve unbelievable mileage compared to the standard BB Chevy's found in these boats.



A few of his concerns are 1) Finding Diesel at lakes. This boat will definately be used in fresh water quite a bit, (ie lake Havasu). I figure they shoud have diesel at the marinas of big lakes, surely some of the larger cruisers use diesel. If not, I figured with the improved mileage, he could probably fill that bad boy up and be good to go for the weekend. Diesel obviously won't be a problem at marinas in the ocean.



A few things I'm worried about. I wonder if mounting the cummins' would present an issue, I wouldn't think so, appears to be lots of room in the engine compartments of those boats. But what about weight, Probably looking at 500 lbs. or so more than what two BB Chevy's would weigh.



Also, I'm wondering if the "B's" operating rpm would be too limited for a sporty boat. I know the motors would make great power and have tons of torque, but in order to be responsive and get the top end out of the boat, I wonder if it would require more rpm than the "B's" can offer. With no gearbox in the boat, rpm becomes a factor.



Also, what would be the best way to go about getting and building the engines. Would one go straight to Cummins and buy two marine engines, and send them to Enterprise (or the like) to have the motors built (twins, fueling, etc. ). What do you think?



Anyway, I just think this would be something cool. It would actually be different and very unique compared to everything else on the water, but it would have to work. And it would need to uphold the Cummins name in style. What do you guys think?



Craig

 

[KLockliear]

Diesels in boats isn't a faux-pas, but it seems to have been in the performance arena. True, I don't remember seeing diesel at the pump at any of the Havasu marinas, or even Topock for that matter, but you should be able to carry enough for a day easily.



Look in Hot Boat about 2-3 months ago... there was a 50'er with 4 Yanmar's in it. You would have to couple them to at least a 2-speed transmission to get the input RPM up, but most drives have low ratios 1. 36:1 or so. To withstand the torque, he'd likely have to look into the Merc #6 (which requires a trans anyway) or the new Imco 4x4 drives.



Power is easy, especially with those big (water) intercoolers. Should be plenty of room in a boat that size for a pair. I know I saw a 36-38 footer at SEMA last year with a pair of 8. 3 6CT's in it.

 

[dpetre]

I have a boat with 280hp Cummins diesels 12 valve. The marine engines are designed to put out a rated horse power and bombing them like you would do your truck engine will wear them out quick. Take a look at the Cummins sight and you will see the ratings on the engines the B series goes up to 370 HP but is rated for pleasure use. To go up in HP you will need to go to a C series which adds more weight. If you go stern drive you would be looking at a Konrad that would cost about $11000. You could try Bravo III but they do not seem to take the torque a diesel puts out. So you will need a trans cost $5000 for that kind of HP

Good luck with your project all it takes time and money.

 

[cjohnson]

Thanks for the replies guys.



I know there is a lot to consider here, thats why I called on all of you. As for bombing these things and getting a lot of power out of them. dpetre, I know you say the marine engines are designed to be run at a rated hp - no doubt. For commercial use, I can see that they wouldn't ask the little b to perform in the 500+ HP range. But for performance, pleasure, is it really any different than what they do with the BB chev's. Marine use is hard on any engine, regardless of gas or diesel - right? I just figure it can't be any worse on an engine like the B to be bombed than it is to build a high performance BB chevy. I don't know, what do you think? As for finding drives that would handle the torque, that I know very little about. Explain, is the transmission something seperate from the drives? So you would install the trans. (2 speed I assume?), and then hook it up to the drives of your choice? How exactly does that work?



Thanks again,



Craig

 

[dan_gilson]

Marine engines take a more constant and higher load than a highway engine. You are typically running them at a most constant RPM and the load is more toward the higher end of the range. This is because you are pushing the weight of the boat through water. There is no coasting for a stop sign or going down a grade. On the highway you can be using as little a say 30HP to keep things moving. This is not the case for a boat where you might be constant at 100 or 120HP for crusing.



One of the old tricks that used to be done is to put a marine crank shaft in a high performance gaser for street. The bottom end would last longer and be more reliable and take a lot more abuse.



Diesels do perform on the water. There are offshore racing boats (few in number) that use them. The only comment that I have heard is that they do not accelerate as fast. They also do not over tach as easy either.

 

[hammersley]

Look at the 2nd Used Bentz

Check out the second Bentz with twin Cummins... . http://www.bentzboats.com/usedboats.htm BTW - these are the best jetboats made for large use. Also look at these - some with Cummins... http://www.bentzboats.com/sample.htm

 

[dpetre]

The marine transmissions come in different ratio's to match the prop size, shaft size,to the boats weight and hull type. They usually reduce the engine speed to a usable RPM. ZF makes a 2 speed trans but most boats are powered by single speed trans. Like I said earlier boat diesel has a web site that has a prop and shaft calculator. Some of the faster diesels are Yanmar and Volvo. The engines are setup to run a higher RPM. One of my charter boats was set up with Yamaha stern drives which where rated at 245 hp. My cruise at 3000 RPM was 30Knots I had a top end of 48 Knots. I converted my boat to Volvo 32KDPE diesels rated at 170HP My cruise was 26Kt top end 30Kt. The difference in fuel use was the Yamaha got 2 miles per gallon the Volvo 2. 25 per gallon. The Volvo's cost me $34,000. If I had to do it again I would have stayed with gas. I took one of my Volvo's that was running to a dealer for repairs. The dealer tore the engine apart and said it would cost $9000 for parts. I picked my engine up which is in a box in pieces and took it home. I was so mad at the dealer and Volvo that I have since went back to gas engines and Bravo III out drives. Marine diesels cost a lot of money and require a lot of maintenance. Unless you have a large boat 12000 pounds or larger and you are going use it alot stay away from marine diesels. Stick a couple of 502's in your boat and you will have all the speed you need. Good luck with your project

 

[MD500E]

Ever consider a turbine conversion? I have been looking to get into a turbine powered boat myself for the past year. You can take 30+ foot boat, pull 2 gas motors, and Drop in one T53 gas turbine from an old Huey helicopter. Now you have a boat that lost 600+ pounds and has 1200-1500Hp in a single engine that was designed to produce its max HP for thousands of hours!

I love our little cummins motors dearly, but when it comes to putting them in a performance boat, I am a little concerned about the weight. Just think one 500LB turbine can put out 1500HP. or to be a little more conservative you could put in two allison 250 C-18's that weigh 135lbs each and make 320-350HP each. These engine sell for about 12,000 each for military surplus and can be connected to a standard out-drive.



Kevin

 

[hammersley]

Oh Oh

We're trying to make a flying boat - no only kidding. Can you get the noise down to yelling levels with these chopper rigs? I haven't been around one that's working that doesn't sound like you're on the flight line. And what about fuel consumption - yet alone type of fuel. AND I'll bet the insurance guys would go Crazy over this - but would be fun.

 

[MD500E]

Turbine engines can be run on jet fuel, diesel, kero, and even gasoline depending on the engine. Fuel burn is high but the lighter weight of the engine more than makes up for the extra fuel required. As for noise level, it depends on the installation. With an enclosed engine compartment and rear facing exhaust carrying on a conversation should not be a problem.

 

[cjohnson]

Oh man, this is getting serious, wait till I tell my buddy to scrap the twin cummins idea and throw in a pair of turbine engines out of a Huey. In all seriousness, the way it sounds, I don't think the dual, twin turboed, bombed cummins idea is going to work. I (actually my buddy who is getting the boat) can't afford for this project not to be successful. If we got this whole thing together and it didn't perform or work properly - that would not be good. Unless someone can convince me this thing would work . . . ?

 

[KLockliear]

The motors will make the power, live long and get good mileage, but it will be costly to make whatever you put behind them, reliable. An Arneson drive would be great, as there is almost nothing to break, but they are expensive and don't maneuver well at slow speeds. For a high-perf application, the Merc #6 drives are the way to go.

 

[cjohnson]

So what is the deal with the Merc #6 drives? Do you think they would work or not? Wouldn't they need a trans in front of them? Anything from Bravo that would be an option? I'm just throwing things out here. My experience with boats is limited to 18ft squirters. I've got a 73 Nordic with a tunnel rammed, dual carbed 429 super cobra jet, blueprinted pump, place diverter etc. . . just little stuff. Even though its a dorf, it runs pretty hard. Anyway, back to bigger things. . .

 

[KLockliear]

The Merc #6 drive is the baddest of the bad out there right now. It's Merc top of the line drive. It will take pretty much whatever is currently available power wise. They are pricey though, at about $30k per drive/standoff box/trans. They do come with a trans though (the main drive is direct only, so the shifting happens in this trans in the boat).



Now, the new Imco 4x4 drive is supposed to be released shortly and directly compete with the #6. Another option that should take the power.

 

[KLockliear]

You can look to these places for more info on diesel packages:



http://www.arneson-industries.com/Yanmar Engine Packages.htm



http://www.twindisc.com/plma_main.html

 

[cjohnson]

Interesting stuff Keith. Now, assuming we could put together some drives that we were relatively confident would hold the power, what would your reccomendation be for building motors. And what reasonable estimate or expectation on what they would cost. Do you think it is possible to put together a pair of b's with twins for say 35k - total for the 2 that is? And how would you do it? Get some marine motors from Cummins and have someone build them? Or would that be a waste because they woud be totally torn down and rebuilt anyway. Seems to me, it would be ideal if you could pick up some crate marine motors, leave the bottom ends alone, o ring the blocks, maybe a camshaft or something, maybe some mild head work, some trick water intercoolers and intakes, a tricked out p pump, some fire nozzles, and a nice set of twins. I can't see why we couldn't get in the 600 + hp range with that . . oh man, if I only had the money. That would probably be at least 20k a piece huh. I don't know, could this work? I'm still not sure. Seems to me if you could get the drives geared to spin those screws fast enough, without tearing things apart with the torque, just maybe.

 

[dpetre]

The Mercury #6 outdrivers are they the ones Bam is selling that are rated at 1000hp and 1000pounds of torque? The gas turbine is the way to go. The American Eagle Gentry was powered by gas turbines and set the US to Europe speed record. Average speed 65 mph.

 

[KLockliear]

I think the #6's would handle it. Power wise, a marine 370 could easily be turned up to the 600hp level (or more). A good pump, twins (or even a big single as lag isn't that much of an issue), injectors, etc.



I'd say the cost of the motors plus, maybe $12k each would get that power reliably. That would be twins, pump, injectors, lines, cam, etc.

 

[cjohnson]

dpetre,



The gas turbine idea is interesting, just not sure how feasible. Who the heck would maintinence that thing?



Keith,



As for the series 6 drives, assuming they would handle the torque, do you think they could be geared to get the top end out of the boat. We can't have this thing top out at 60mph, that wouldn't be unacceptable. Also, about how much are those marine crate motors? Any idea?



Thanks guys,



Craig

 

[KLockliear]

I think the transmissions can be geared for whatever you want. I also believe a stock, crate motor 370 marine would run around $12k from Cummins, new, with a pump, turbo, everything.