|Subject: Re: [harryproa] Electric Drive for Charter Proa|
|From: "Gardner Pomper" <firstname.lastname@example.org>|
|Date: 5/18/2008, 7:09 PM|
I have been following your posts on the forum and it is clear that you are much more knowledgeable in boat building than I am, but I am not sure that I agree that a hydraulic system is more complicated than the electric. This isn't so much from an engineering basis, but from living aboard a small (30') cat in the bahamas, and also owning a 37' one-tonne racing monohull with a hydraulic drive. So, take my comments for what they are worth.
All the systems on our cat were operated off electric (refrigeration, radar, etc) from 4 solar panels. We had gasoline outboards for mobility, but they were pretty useless for charging the batteries. It operated well, until we were hit by 3 rainy days in a row. We might have been ok if we had a wind generator, but there wasn't really all that much wind either. We had to go in to a marina to recharge. Since then, a generator to recharge the batteries has been right up at the top of the list of things to have one a boat. Running off solar/wind is great, but you know that you will run out of electricity at some point. If you are using the electric for motive power, you will have much greater reserves, but you will also use them up motoring (charter delivery dates, plane dates, etc). Were I to have an "all-electric" system, I would still need a genset, with its attendent fuel requirements. And I believe, that the charter harryproa will have a genset. So, could we not have an electric pump, pumping hydraulic to the submerged motor?
Perhaps that it too inefficient. My monohull sloop had a 60HP Perkings 4108 mounted under the V-berth (racing handicap, apparently) which ran back to a hydraulic box on the propellor shaft. It would push the 16,000 pound monohull at about 8 knots in flat water.
I am thinking that motoring a proa should not take that much power. If it can run at 8 knots, that should be satisfactory. One would almost expect that it could just be done with outboards (not that I approve of those; I would really want diesel for any sustained motoring).
Apart from fuel efficiency, (and lack of explosions), the main thing I would want from an engine is quiet. Electric would give me that for short periods, but I am worried about the genset right up on the deck. It would have to really ruin the serenity.
I guess what all this boils down to is that this proa design is a pretty radical new concept. Things are bound to go wrong. I would rather just keep the engine systems simple and use all the engineering brilliance on the sailing platform. After all, it is a sailboat. The motors are already a fallback. They need to just work.
I thought it a good idea to make a separate topic while Rob and Ron are
discussing drive options.
I agree the electric drives "in general" offer freedom of installtion
location. Electric can use battery power that is stored energy for
some duration depending on size of battery bank and speed desired.
Battery provides an extra level of safety as reliability is very high
and can be abused in emergency if genset doesn't start. I have
personally on my own charter boat twice to lose all engine power.
Problem is fuel in the tropics. Source in carib. is questionable,
while biocides and such do not seem to keep the sludge under control.
Charter fleets are not going to manage quality of fuel as you or me
will do it. Nor do they take time to purge tanks and thoroughly
clean. So batteries provide a very handy energy backup to keep charter
sailors going. Nothing worse than coming into a slip or crowded
mooring field undersail alone. I've done it, but not fun.
Recharging as a charter boat in the carib has a lot of input from the
Lagoon 420 thread in cruiser's forum. Bottom line, don't sail long
enough from point to point to give a full recharge. Going upwind is
full motor in most all situations for charter goers. Too much hassle
and schedules to get to next locale and beat the rest of the charter
gangs is prime concern. You might say that sailing is faster,.... The
charter bunch are a point and shoot type. So while it takes 3 or more
time to recharge than use you can see it is highly more likely the
genset will be needed to top off.
Aside from weight, I don't see a huge advantage to go with hydraulic.
Why add complexity and a system when not needed. I do agree
engineering will be needed for cable type, and protection on any
submerged motor. The 48V re-e-power type need bigger cables and
protection than the higher voltage types like from African cats.
In any event thought I would add this topic separate for everyone's
input on options, mounting, control, size and type,...etc.