Ed Kelly wrote: > I hesitate to say a discouraging word about Chris > and Debbie's boat, but as all boats are compromises, > so are their engines. Chris did not use the boat as a > full time cruiser and on the only long cruise that > Chris took after leaving the marina (he was going > to head for Bermuda) his plans were hampered by > losing the electric engine before getting out of the > Chesapeake.
REPLY It has been my observation that many new designs - especially DIY built boats often lack sufficient cooling capacity of vital machinery and equipment components. This not meant to disparage Chris and Debbie's boat in particular. Nor is this an observation limited to any one class of boat, design type or propulsion method ( except sails) or even just power electronics and electrical equipment. Short test runs of only a few hours duration or even a single overnight run often fail to reveal the considerable amount of heat build up psustained when run day ofter day and round the clock. In the Island packet website I see Reuben Trane in the back ground of one photo. Three years ago when I met him at the Seattle boat show he spent considerable time asking me about high power inverter use to drive large sustained loads. He said he was just getting started on a new design back them. You can bet Island Packet has spent more than a few months just working on solving the engineering issues of heat build up. Given their engineering capability, I would expect this boat to do well. Realistically, how many regular mono-hulls could carry that amount of photo voltaic panels topside? It may be possible for a catamaran hull design to create sufficient deck space or rather canopy area. As Ed writes, every boat becomes a compromise. Monohulls are likely to require a diesel -electric combination setup. Ken James approach is right on target. A smaller than normal horse power genset provides steady charging of a battery bank. The battery bank serves as a reserve for surge loads of very short duration such as during acceleration. In reality; after a while the battery bank is going to deplete and then your only source of continuing power will be the power from the genset. so then you must have sufficient power to provide steady propulsion in nearly flat water conditions. If we are talking about sailboats that rely primarily on sails for motive power and the propeller for only auxilliary power entering or leaving harbor, we have additional issues to deal with. If the engine is sized large enough to move the hull at hull speed in nearly flat water, it will be very much oversized for normal generating jobs for just lighting, possibly cooking electrically and what have you. Running a genset at light loading has always been problematic.. The problem has been called "wet stacking." It may not over heat but will require frequent service. If we are talking about a pure power boat applications such as the Island Packet, then the electric propulsion motors is going to develop a lot of heat. Even a 95% efficiency equates to a 5% of full power loss as waste heat. This heat has to be disspated. In tropical conditions in a poorly ventilated engine compartment, how hot does this get? You either blow air through the electric motor or get a motor with liquid cooling jackets. Liquid cooling requires heat exchangers and piping not to mention circulation pumps. This is where costs increase a great deal over air cooling. However air cooling imposes some restrictions on hul land deck design. Either way costs are involved, and my experienc with builders is that this is where short cuts are often tried. Builders are not happy about spending more money than absolutely necessary. Builders are not always designers, or engineers. They simply do not see the need to add these expensive extras just to cool down the equipment. DIY experimenters who build their own boat often lack the deep pockets needed to speed the extra money to over desing things just to be sure. They will go with the minimum theoretical parameters that looks like it will work. Arild _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard To subscribe send an email to [EMAIL PROTECTED] To unsubscribe send an email to [EMAIL PROTECTED] The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
