Hi Keith,
Our typical rule of thumb to convert boats to electric is 1kW of power for each ton of displacement. But most of our boats are pointy at the ends and fairly low profile. That's why I would recommend more power for a houseboat, exactly how much, I don't know. I don't know of any successful houseboat conversions in your size range, so requirements are mostly conjecture for now.
I don't know if the Parsuns are as efficient at turning energy into thrust as a Torqeedo, personally I might start with two Torqeedo Cruise 4.0 motors, pricy but a good value from my perspective (I own a Travel 801). As a houseboat pilot, you know the advantages of twin motors for steering.
Another alternative for dealing with crosswinds and such would be a trolling motor mounted near the bow to act as a thruster of sorts. There are remote steering units for trolling motors that would make the front motor very effective.
I tend towards inboard installations because I think that they are easier to find the right motor/ratio/prop combination and to change them if needed. Bigger, more agressive props are more efficient, generally the hull limits your overall prop size. I would run a skeg to add directional stability and to protect the prop. Once you know the maximum prop that you can fit, then the gearing can be worked out from there. On the other hand, outboards also have the advantage of steerable thrust, so they may be more appropriate/safer. Outboards just don't have nearly as many options when it comes to props and gearing.
Bottom line is that your boat should be operable with 6kW and everything extra goes towards your safety margins. If you go with the outboard route, you might want to build the boat and do your proof of concept trials with used ICE outboard(s). That will give you time to get most of your other systems operating without the up front investment in an electric drive. You'll collect good data concerning your actual power requirements and the used outboards should be able to be sold for close to what you paid for them when you do take the plunge into electric drive. Unfortunately, used electric drives rarely get 50 cents on the dollar if you don't nail the requirements the first time. So starting with ICE should be lower risk.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Keith Jacko <nrixez@...> wrote:
>
> Hi Eric, thanks much for the reply. The barge front end would definitely be an issue if the water entry of the hull wasn't so gentle. It is a very shallow angle though, so I don't anticipate a problem as long as the waves are 1.5' or less. Somewhere between 1' and 2' wave height I'll start knocking the "bow transom" into oncoming waves, greatly hampering forward progress. Large boat wakes aside, 2' waves on the rivers I'm talking about are not the norm. In the types of conditions I'm going to be operating in, < 1' waves are to be expected.
>
> As far as the boat settling fore and aft, we should discuss that because it's been a theme of the feedback so far this morning since posting the pics. By my calculations, at 12k displacement and perfect COG, if I (a touch more than 200 lbs) were to move from the center of the boat and go stand on the rear transom, the stern would settle < 1/3". I'm quite willing to accept that. Stepping out onto the bow would cause the front to settle a little more because the COG is about 2.5' aft of the center of the boat, but it wouldn't be much more. Less than 1/2", I believe (though I didn't run the numbers on that yet, so it could be a bit more... but *definitely* less than 1").
>
> All that being said, it's difficult to know how wave action will set the boat to pitching, or how quickly she'll settle down once started. That's definitely a bit of a gamble on my part, but so far I haven't heard anything that makes me want to avoid that gamble enough to redesign the boat. :)
>
> Side winds are indeed a real possible issue. I do have some experience piloting larger houseboats, and side winds really, er, "blow". ;) The height of this one is a compromise, higher than I'd like for exactly the side wind reason, but lower than I'd like for living concerns. Note that one will be forced to duck no matter how they enter this boat. In this particular case I'll probably just have to pick my weather window and go out when the wind is fairly calm. Fortunately it's not overly windy here, and for me just being on the boat is a lot of fun, even if I'm not moving it around on the river.
>
> I'm still interested in hearing someone's thoughts about the ideal power, prop size, prop rpm, and prop pitch for this boat. 27' waterline. 12k lbs. Fairly easily driven in calm conditions, but heavy.
>
> Still hoping for a 48v system, too.
>
> Thanks,
> -keith
>
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