Small inboard gas engine

Gray Marine Sea Scout 25

We are currently in the process of parting out our 1966 Ted Hood designed hand layed fiberglass mast head sloop which was powered by this fine gas inboard which still has only a little over 750 hrs. it should still offer good service for the lucky sailor who finds our sound hulll and restores this little yacht to fit condition. more info contact:thebarrys@camphost.us

 

jeez tahia - talk about off topic - jeez this is a bit more than a language barrier

 

Yeah, I know that on other forums people go kookoo about zombie threads, but I think you all are smart enough to know that it's useful to have further thought/experience added to an existing conversation rather than rehash it all over again.

I came upon this discussion while searching myself for small inboard engines/transmissions. But it happens I have an electric vehicle running a 15hp Mars Permanent Magnet Motor and since this thread had taken a turn to electric motors I figured that I'd weigh in....

Yes, these motors are quite strong, LOTS of torque. It's difficult to compare electric to gas because they are apples/oranges.

The torque they can generate is near instantaneous in comparison, so in my vehicle I have worried about breaking the driveline if the throttle is used carelessly.

I have the Mars 0709, and an ALLTRAX 12/24V Controller running at 24V. I think it's 100A continuous and 400A short-term. 4 deep cycle batteries in series-parallel, and a motorcycle-style "throttle" potentiometer.

While it's true, that the no load RPM is like 72 RPM/volt, it's silly to say that "it produces too much RPM"..... No matter what the voltage of your pack (whether it's 12V max or 72V max) your throttle dictates how many volts you're using. It's not a simple on/off scenario....

In a non-planing hull, you're not going to be trying to produce that kind of RPM anyway. Not being a gas engine, you don't need to run it at full RPM to get max torque.

Throttle control is very sensitive and linear. In my vehicle, you can make it move at an absolute crawl, that you could not duplicate with a gas engine without stalling it.

No, you can't use these kind of motors without batteries. I think it would be possible to run direct genny to motor with other kinds of motor/genny setups, but certainly NOT with this type of motor and controller.

The constant generator idea is a great idea.... But bear in mind, that a Honda 2000 max charge DC at 12V is paltry.... Like 8 amps DC. You need to use the 120V section of the genny's power into a battery charger. Based on some research on the web, it looks like when you account for losses in heat and efficiency you can reliably pull about 55 amps charging from a Honda 2000 .

These are not commercial generators either. I would not attempt to run a Honda genny hard day in/day out. Splash sump motor and need to change the oil every 60 hours of runtime or something like that. I have a friend who lives off the grid, and while these gennys are awesome for what they are, they are not heavy continuous duty machines. He's been thru 3 of them in several years due to attempting continuous use and not following the maintenance schedule.

But, as a weekend craft, occasional fishing, or use on a sailboat for maneuvor and docking, would work fine.

The Mars 0709 is about 40 pounds, and well-built. A set of brushes is about $75. The shaft is 7/8" so it's really beefy. This is the kind of motor, that when run at 72V and Li-ion batts (lighter) can make a golf cart stand on end in a wheelie!! The 15hp rating just doesn't do it justice.

This is important, of course, because you need torque in a boat application.

Here's some facts on my application:

I'm running 24V with 4 - Trojan lead-acid batts with 105 Ah each, for a total of 420 Ah. Yes, that's a fair amount of weight. If I was running a genset for continuous operation, I could get away with two batteries.

I have them hooked together in series parallel, with a "crossover" switch that allows me to change the output from 24 to 12V for charging. I had a Magnum Energy 2000W continuous inverter, with max charging capacity of 150A, and didn't want to shell out $500 for a comparable 24V unit.

This led me to selecting the 12-24V alltrax controller. It runs on 12/24, the 12V obviously limits the top speed, but you still have all the battery capacity.

If you are using 12V batteries in a "low speed application" then you really have no need to go 36, 48, 72V. From my research 5 years ago or so, the batteries and chargers needed for the higher voltages are much more expensive since they aren't common. 12 and 24V chargers are relatively common and in line with automotive and marine applications.

24V at 72rpm/volt is 1728 rpm, which is probably more than enough prop rpm for any displacement hull application.

A continuous duty solenoid is used to turn the system off. Flip a switch, solenoid closes and you're ready to go.

Reverse can easily be handled by a reverse switch. I didn't use one due to expense. There are both mechanical versions (think golf cart) as well as solenoid-operated switches. It simply reverses polarity.

My application was a chinese rickshaw. Think of it as a fun "parade" or "pit" vehicle. Originally a pedal rickshaw, I wanted to haul more than 2 people. So I wanted to haul a wagon behind the rickshaw. I settled on a large 2000lb capacity wagon used in tree nurseries and landscaping. The batteries are in the wagon, with cables running up to the rickshaw, and then people sit on top of the wagon on cushioned seats.

Rickshaw has 26" wheels, so I didn't need the full 1700 rpm either! I also wanted to be able to pull alot of weight, so I designed a 7:1 gear reduction, for a top speed of about 20mph which is faster than that rickshaw probably should ever go.

The most people I ever had on it was 11. Handled that load easily. It would run several hours at 5-10 and occasional 20 mph blast on those batteries.

NOT inexpensive, but I went the electric route for two reasons:

First, the rules of the location we were using allowed us to avoid a required inspection process if vehicle wasn't running a gas motor, and two, we had an abundance of electricity for charging.

Summary

In summary, I hope I have left some useful information to someone considering using a permanent magnet motor for a boat application. They are simple, in that you don't need a transmission which these days seems a rare thing for a small motor application.

They are strong, and tuneable. One thing to consider in a boat application, is that if you wanted to do continuous motoring, you would have to limit your current consumption to whatever your genny can comfortably put out. You'd have reserve power for short-term high-throttle needs, but you'd need to plan to motor on what you can sustain. Should be totally doable in any situation but a "performance boat" situation.

Housing of motor is I believe unfinished aluminum, or some kind of light plating. No idea if this is suitable for a marine environment. Should be able to disassemble motor though and have the case plated.

C. Monk