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Figuring out torque vs hp, and more...

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Old 10-03-2011, 09:18 PM
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Default Put down the calculator and go boating.

It's not reinventing the wheel, it's already being done. A lot of new yachts will come out yielding the advantages of diesel electric.

Project? Yes. But a project that will get done, and be very satisfying. The electric motor side is still at conception, but I do find good feedback and resources online. I have found large working electric motors at scrap cost. I saw two today, one at 100 VDC and the other 240 / 480 3 PH

EPA is shutting down industry, everything must go.

I may very well get a mild 350 back in there for the time being. That is still months away, however, as I'm am getting my topside work done. I don't think I'll even refer to it as a Sea Ray when I'm done, she'll be a Carter Craft.

Now, should I have just flushed with diesel, thrown rebuilt heads on there, and go fishing? I don't think so. So far, my project has revealed a transom rotted thru at the drain plug, and under port engine mount (all repaired), Also, that "killer" bait tank had standing water in the foam all the way around it. It was only separated by plywood from the fuel tank. The fuel tank was exposed to wet foam, it's been drained, flushed with argon, and pressure tested. It failed. It has to come out. I do not regret any of the progress I have made up to date.

-Tony

Last edited by funkyonion; 10-04-2011 at 01:06 AM.
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Old 10-03-2011, 10:19 PM
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Old 10-04-2011, 11:14 AM
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Tony,

Sounds like you have made a lot of progress already on the hull. I'm sure it needed it and it's good you are taking the time to repair it properly. While I have seen some of the diesel electric technology and I agree it is going to become more commonplace in the industry, just remember that there are no free lunches...

It takes energy to move a heavy object through the water. On a boat the size of your sea-ray (Carter Craft ) I would think the weight gain and space required to install a functional hybrid electric diesel propulsion system would be very prohibitive. When you consider the cost of the conversion, time, and the potential to actually loose performance over a tried and true 350, you could pay a LOT of gas dock bills.

I admire your ambition to take on a project of this size, but make sure you think long and hard about the resources you are going to dump into this boat. You have to be prepared to keep it forever!

There is a ton of great knowledge on this site, but I would say very few of us are very worried about fuel economy, so you may not get much in the way of responses.

There are guys on here with 50' boats that seat 6, have no cabin, and burn diesel at an astonoshing rate through a pair of turbines, all in the name of fun.

Best of luck with your project.
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Old 10-04-2011, 11:46 AM
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Take an electric lawn mower, extend the blade shaft and bolt it so it goes thru the transom. Polish the cutting blade for performance purposes, plug it in and give it hell..... So what if your range is restricted by a elec cord?? Its all good...

Seriously good luck sounds like quite the project, exhausting just reading about it
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Old 10-04-2011, 09:28 PM
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Default Thanks Artie

I picked up some motors from a liquidator, and some 10 gauge wire. The 150 HP motor is too big, but I'm hoping to barter for a 100 HP at 1780 rpm. It should weigh about 1200 lbs. for the motor. A dressed merc 260 is about 650 lbs. The same hull can have twin engines, the combined 1300 lbs. narrows the gap. I can probably get a controller from the same source. The genset can mount sideways wherever is balanced best.

Here's a pic of what I got today:

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Old 10-05-2011, 09:57 AM
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So you are going to DOUBLE the weight of a single 260 Merc, for much less than half of the HP? doesnt seem to make sense to me. This doesnt even factor in the weight of your genset.

Now I am very familiar with diesel electrics, as the drillship I work on has 6 7MW diesels running 6 4.5MW thrusters. They are very efficient and all, but on your scale, you are going to have trouble getting enough power to actually move your boat.
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Old 10-05-2011, 11:09 AM
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Put a 350 back in it please and save us all the headache of "I told you so"
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Old 10-05-2011, 06:06 PM
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Originally Posted by Philm View Post
So you are going to DOUBLE the weight of a single 260 Merc, for much less than half of the HP? doesnt seem to make sense to me. This doesnt even factor in the weight of your genset.

Now I am very familiar with diesel electrics, as the drillship I work on has 6 7MW diesels running 6 4.5MW thrusters. They are very efficient and all, but on your scale, you are going to have trouble getting enough power to actually move your boat.
HP doesn't matter. The torque is more with the 100 HP electric than the 260 HP merc, and also, the electric motor's torque is throughout the rpm cycle. A direct power drive cannot utilize an optimum prop size for their HP, it would just stall at idle.

The generator will use the original merc 260 installed backwards, with the output side facing the bow. The manifolds can be flipped, and still dumped out the original collector. The small block will turn the generator. The largest pto generator I found from Onan was 40kw, I would need 57 kw for the 100 HP (which still beats the merc 260 in torque) I hardly think the motor will ever be able to provide max torque, or full amp load, as the prop can only be so aggressive on the out drive itself.


I can achieve low rpm, high rpm, whatever I want, with an optimized constant rpm (but still adjustable for generator demand) from the motor itself.

I realized I misinterpreted "Offshore Only" when I came to this site. I was thinking of a different kind of offshore boat.

Last edited by funkyonion; 10-07-2011 at 10:57 AM.
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