Engines

Steve

I bought a HT27 a month ago which has a 30HP outboard mounted on the transom. This doesn’t seem like a very good idea to me at all, turns the boat into a bit of a rocking horse, so I’ve been looking into repowering options. I came across electric motors and they definitely peaked my interest.
There are a few good groups with a wealth of information on the subject (albeit a bit disjointed):
http://groups.yahoo.com/group/electricboats/
http://groups.yahoo.com/group/ElectricBoating/
I have quite a few more links on the subject if you’re interested.

The electric solution appeals to me for a number of reasons:
Environmental (more economical as the generator runs at optimum speed), noise, diesel smell, lower maintenance, longer life span, more componentized for better weight distribution, but mainly I’m too lazy haul in two diesel engines, sounds like serious work to me, and of course I’m to cheep to pay someone to do it. This is probably why the US navy uses this option.

Most people start looking at a complete solutions like Solomon technologies which is super expensive. But if you read some of the posts on the groups you’ll see that some have got away with far cheaper solutions. Considering the cost of the diesel engine is generally a 1/3 of the price of an installation I think it may be comparable cost wise.
That said, it’s certainly not as easy as wiring up a few components. There are many variables to worry about:
• The difference between electric motors and ICE’s (internal combustion engines). Motors apparently have a higher and constant torque across the range and this affects the size of the propeller and reduction ratio. With props, bigger and slower is better, as with an ICE engine but apparently more important in this case.
• Apparently this difference in torque if used correctly makes a motor more powerful when you compare it to a ICE engine HP to HP. How much difference I’ve never been able to get a clear answer but it seems to be a 5.5HP motor will give about 9HP ICE. Also a electric motor has some serious peak HP but this can only be used for a short time, so you’ll find motor rating with continuous, one hour and peak. Which one you use depends on your motoring needs I guess.
• There are a myriad of bits and bobs that come between the motor and the batteries I haven’t figured all these out yet.
• The motors themselves seem to be progressing and you get some powerful highly efficient brushless DC motors that are low to no maintenance and last for a very long time, longer than a diesels lifespan (eteck, lynch etc.)
• There is a tradeoff with the number of batteries and the generator. We all know by now that keeping the HT as light as possible is a good idea so we don’t want to pack her with batteries. These motors typically run at 48-72 VDC and chew up amps when you push them. Some recommended that I install 10 12V batteries which is way too much weight but you can of course compensate by running the generator.
• My guess so far is that a 7.7kw generator for this size boat should be sufficient. (the PMG132 runs at a continuous rating of 7.2KW @ 9.7HP (electric HP ??15.8HP ICE??)
• DC motors are apparently a better option than AC cause of the conversion inefficiencies from DC to AC but then if your running directly off a DC genset as opposed to running through the batteries, I guess it’s ok.

I am currently considering a few solutions:
1. Use a trim tab solution with submersible electric motors (like trolling motors) that can be raised from the cockpit. Take a look at http://www.lencomarine.com site for an example of these.
The disadvantages are
• The motors would be mounted on the transom, although they are not nearly as heavy an ICE, might add to rocking.
• They would need to lowered enough to not come out/cavitate when the boat rocks. (still figuring how to do this)
• A custom Kort nozzle would need to be built for best performance. Although you can buy electric outboards with these on.
The advantages are:
• You can raise them whist sailing with the touch of a button.
• No through hulls, stuffing boxes and drive train stuff.
• Pretty easy to install.
1. Inboard installation
This would entail two eteck type VDC motors, but besides the hoisting of diesel engines, and the space, comes with all the installation issues you get with inboards. With this option you could have two motors for better steering and put the generator in the cockpit.

2. Outboard installation in the cockpit.
I initially discarded this idea cause I was looking at ICE engines and didn’t want that much weight that high up and all that noise in the cockpit but now that I’m typing this I’m realizing that with an electric motor this may well be a viable option. There are some powerful electric outboards out there with Kort nozzles and all the bit’s and bobs in-between out of the box it (about $4K will find the link if you need it) http://www.outboardelectric.org.
According to the manufacturer this motor will push a 26ft sailboat (displacement hull) of 8000lb 7.5mph. They don’t say what type of boat, I assume it’s a mono hull.
9HP does not seem like enough power to me. Some people have taken ICE outboards, taken the engine off and added one or two VDC motors inline to get a bigger engine.
Disadvantages:
• Where to put the generator?
• Only one motor so you lose steering ability unless the cockpit motor can pivot.
• The biggest electric outboard I can find so far is 5.5HP = 9HP-ICE which is too small for my requirements.
Advantages:
• Easy to install.
• Can raise the prop whilst sailing.
• No holes in the hulls etc.
• Less wiring cause there are no remote controls, can adjust it manually from the cockpit.

All that said it is considerably cheaper to mount a outboard ICE in the cockpit well. This is a MUCH more affordable option, the disadvantages being noise and petrol storage.

Regards
Ryan

Model electric flight is causing some wonderful outrunner brushless motors to be manufactured such as this rather nice 20kW one! see:- http://www.rcgroups.com/forums/showthread.php?t=571975

I understand it weighs only 3kg 😎

I am currently doing some sums to see what 'off the peg' e-flight motors and controllers would do in this application. One of the big advantages is that e-flight systems are designed to run typically from 10 cell LiPo packs (i.e. 38v) so would run quite conservatively from 28v. Keeping below 50v has the advantage of avoiding all the 'fun' of the EU 'high voltage' directive which I believe applies to nominal 48v systems as they exceed the magic 50v when on charge.

As a quick sum I have looked at what could be achieved with 4 off EFLM4160A motors clustered around a 5.3:1 gearbox. These motors are continuously rated at 60amps and with about 90% efficiency would give almost exactly 6kW output. The motors would turn at 6860 rpm on 28v so the 5.3:1 box would drop this to 1295rpm almost exactly matching the continuously rated output and speed of a Yanmar 1GM10 with a 2.64:1 gearbox. The best price I can find on these motors is 163 US dollars each. Brushless controllers run out about the same price so the total for 4 motors and controllers would be about 1300 US dollars. Brushless motors can be reversed by the controller so there is no need for a gear reverse and no heavy switchgear.