gas/electric lobsterboat?

[gschuld]

I hope you all will indulge me as I would like to explore the feasability of using a combination of a gas v8 engine with an electric drive system tied into it as a secondary propulsion system.

I am interested in using a 30-34 ft. lobster boat hull with a traditional underbody. Round chine, deeper hull section forward, nearly flat deadrise aft about 10" below waterline. These boats were developed over many years to be driven easily and economically in displacement speeds yet were cabable of planing easily with fairly modest power with the ability to comfortably cruise at 20kts. I am interested in powering the boat with a fully rebuilt maranized AMC 401 gas engine that is carefully modified towards strong low rpm torque (I am an AMC car nut, and I already have these parts on hand). I would be interested in using a modified AMC bellhousing pattern th-400 (heavy duty automatic car transmission) with the ability to use 2nd gear as the planing gear and 3rd gear (1:1) as a cruising gear for lowering engine rpms. I realize that this will require a seperate thrust bearing to control shaft position among other things to accomplish. Oddly enough, I have owned a boat with a similar driveline. I owned a 1928 45' Dawn twin engine "commuter" for about 5 years. The second owner of the boat was an accomplished mechanic and engineer working for the Army during WWII installing 346 Cadillac engines and Hydro Matic 3 speed transmissions into M-24 light tanks for the war. After the war was over, he was given 2 sets of never run engines/trannies right off the assembly line. He bought the 45' dawn (whose original 6cyl engines were all but destroyed by the Coast Cuard Auxiliary who commandered the vessel for patrol duty searching for German subs off the New Jersey coast. Anyway, he installed the 2 engines and transmissions into the Dawn(with seperate thrust bearings) and hand built a pair of custom shifters with 2 fwd speed positions. The system worked perfectly. Marine water cooled exhaust manifolds were produced in those days for Cadillac engines as were other marinazation parts, so they were well done. The performance was great. In second gear, the boat was perfectly geared to get all 20,000lbs up on plane and steady at about 15 kts. When in displacement mode, setting the shifters into the second position(3rd gear, 1:1) I could reach around 9 kts at around 1000rpms easily and quietly. I really loved that boat, but I sold it to buy my first house years ago.

Sorry for running on... So my new interest is to use a similar setup in a single engine boat and be able to accomplish the same thing. Plus, I am interested in being able to use an electric drive system to run the boat for limited periods of time. To do this, I would think that the electric drive motor would need to be belt driven(or similar) from the driveshaft between the thrust bearing and the rear of the transmission. I thought about the idea of simply mounting the electric motor inline between the main shaft and transmission, but the typical shaft diameter for an application such as this for a 401 cube v8 turning a fairly large propeller would be 1 1/4" or so, far too big for the shafts of any electric motor I know that would be otherwise correctly sized for this application. The next hurdle would be disconnecting the shaft from the transmission so the shaft spins independently from the transmission. This would both free up a noticable amount of friction and be required as I believe that having the tailshaft of an automobile based automatic transmission run for an extended period would be harmful to the tranny. If it was a v-drive application, using a Casale V-drive with an in-and-out unit would probably work fine. Preferring a straight inboard installation leaves me with a small challenge. I have spoken with the head engineer of Casale engineering and he seems to think that one of there in-and-out units could be modified to replace the actual tailhousing of the th-400, thoeretically giving me what I would need.
I would not expect to get an exceedingly long range with such a boat when powered by an electric motor. At an assumed gross weight of around 14,000lbs. and a fairly large propeller, it would need a significant amount of electrical power to get it going to say 5kts. I was figuring something in the range of a 3-5hp equivalent 48volt electric motor and a respectable amount of lead acid batteries to accompany it. Both my wife and I enjoy quiet evening cruises up bay a bit and back, maybe 4 miles tops. She has allergies and is fairly unhappy with typical engine exhaust smells and noise at slow cruise speeds (3-6kts). Plus she leans towards being green in moderation. I would likely be installing some sort of underwater exhaust for when the engine is on to help out, but we both like the electric idea if it is feasible. I have spent more than 10 years as a custom wooden boat builder, have renovated 4 houses completely(including moving one house 2 blocks down the road) and like to work of old cars, so I am fairly handy. I know just enough to be dangerous!

Any thoughts...thanks in advance

George

[Tim R Jones]

Hello, I've been working on something similar for some years and getting close to launching the boat.

It's a 31 foot Skagit Saratogan built in 1959. All fiberglass. This was the first big fiberglass cruiser manufactured in the US. I have installed a new pair of Volvo Penta diesels in place of the twin Chrysler V-8's. Between the two engines is the electric propulsion system.

The traction motor is a WWII aircraft generator, 400 amp/ 30 volt. Supposed to make about 10 horsepower on 24 volts. There is a 2:1 reduction gear and variable pitch two blade 13 inch propeller. The variable pitch and motor field control will allow me to dial in perfect amperage for any given hull speed.

Still looking at batteries. I think the lithium Ion batteries aren't developed enough for me to take a chance on them at this time. One of the problems with them is thermal runaway which can result in fire which you are all probably aware.

I've found a new set of Northstar AGM batteries I might get. 600 amp hours worth at 24 volts. I'm hoping for a 4 to 6 knot speed and perhaps 20-25 mile range. Don't have a launch date yet.

Tim Jones
Friday Harbor

[FAST FRED]

For a slow speed application I would install a simple OB bracket.

With a borrowed gas engine , you will find out if 2hp, 4hp , 6 hp worth of thrust is needed.

Then look at the newer high thrust DC motors that will simply replace the outboard.

No muss , no fuss , no big expense or staggering machinery bill.

You will get as far as with a FANTASTICALLY EXPENSIVE drive system , as the limit will be the battery bank.

Thrust is thrust , cheap thrust pushes just as well as complex thrust.

FF

[Kay9]

FF Where do you find electric motors to replace the power head in outboards? I have an old 35 HP OMC that I would like to do this too.

Thanks.

K9

[FAST FRED]

Most of the electric motor outboards are far weaker than 35 hp, most are down in the 100lbs thrust , same as a 5 hp gas engine.

To run 35HP on DC would require 100's of pounds of batteries, huge wires , an e$pensive controller as used in electric cars and have a very short range , and long recharge time.

FF

[Guest625101138]

Originally Posted by Kay9

FF Where do you find electric motors to replace the power head in outboards? I have an old 35 HP OMC that I would like to do this too.

Thanks.

K9

These are the best priced motors and controllers I have found:
http://www.kellycontroller.com/shop/?mod=cat&cat_id=16

The bigger brushed Etek on 72V would be a good fit for the 35HP leg but it will only be good for around 12HP:
http://www.kellycontroller.com/shop/...product_id=125
It may need to be repropped. It could go to 20HP for short duration but you really would not want to design for this.

You can get bigger motors from places like EV Parts but the require higher voltage systems that are not ideally suited to an outboard application.

Rick W.

[Kay9]

So basically I would be as well off, with an 8hp trolling motor, and maby buy a briggs and straton power head to repower my 35hp.

Ok thanks guys.

K9

[Guest625101138]

Originally Posted by Kay9

So basically I would be as well off, with an 8hp trolling motor, and maby buy a briggs and straton power head to repower my 35hp.

Ok thanks guys.

K9

K9
I am not unimpressed with electric drives just that you have to be realistic. People see numbers like a 10HP electric motor is the same as a 30HP IC engine. This comes from traction applications and is about right. In constant power applications like a boat a 10HP electric motor and a 10HP IC motor are not a lot different. The significant different is that the 10HP electric can probably get 25HP for a short period. So if you have an emergency for a short period you can really crank it out of an electric motor. They do not die like an IC engine but just keep taking more power.

Not sure if you have seen my electric outboard test. It is a 3Mb video so will take a bit of time to load:
http://boatdesign.net/forums/attachm...6&d=1209288392
This has the smaller MARS brushless DC motor and Kelly controller. I was testing on 2 small batteries as you can see. They were good for 300W before they were dying enough for the controller low voltage control to kick in. The motor will take 48V and 200A so something like 30 times more than I was using for the test. The motor and controller cost USD600 and there is a gearbox worth AUD400 down the bottom that I already had. I am swinging a 14" prop. The hardest part in making this prototype outboard was fiddling with the tiny control plug on the controller.

The 35HP outboard leg would NOT be a silly fit for an electric motor because it allows you to fit a large diameter low pitch prop. This will give lots of thrust if that is what you want. So it all depends on the application.

Rick W.