Electrical Propulsion vs Diesel Propulsion

[mcarling]

Originally Posted by senormechanico

All boat designers I have heard about agree:
Keep the heavy stuff centered in the boat as much as possible for best seakeeping and the boat's safety.

I don't know which model Dragonfly for which you are proposing this.
I hope it's at least a DF35 you are talking about with the above.

Think how much the polar moment of inertia is going to punish the rigging, waterstays and akas during a spirited sail in rough conditions! Yikes!
With that much weight out on the lateral ends of the boat, imho you are asking for trouble.

If I did that to my DF1000, it would probably break apart in any elevated seaway.

I've thought about the polar moment of inertia. Increasing the polar moment of inertia results in slower rolls of greater amplitude, but a trimaran with high buoyancy amas would have insignificantly greater roll amplitude -- assuming we won't be flying the vaka.

Even with fully loaded fuel tanks, that's a maximum of 300kg in each ama. The leeward ama would be 250-300kg less loaded than with empty amas; it's the windward (flying) ama that would suffer a load for which it may not have been designed. Have you any information from Quorning Boats about the maximum payload for an ama?

[senormechanico]

Originally Posted by mcarling

I've thought about the polar moment of inertia. Increasing the polar moment of inertia results in slower rolls of greater amplitude, but a trimaran with high buoyancy amas would have insignificantly greater roll amplitude -- assuming we won't be flying the vaka.

Even with fully loaded fuel tanks, that's a maximum of 300kg in each ama. The leeward ama would be 250-300kg less loaded than with empty amas; it's the windward (flying) ama that would suffer a load for which it may not have been designed. Have you any information from Quorning Boats about the maximum payload for an ama?

The manual that came with my boat said to keep the weight centered as much as possible and to store only lightweight things in the amas.

I put fenders, cruising spinnaker, screecher in forward compartments in the amas, and fenders and an inflatable kayak with oars in each aft locker.
Total weight in each ama, under 50 lbs.

Oh, and a HAM automatic tuner on one side driving a cap shroud with a homemade KISS ground plane running foreward at the bottom of that ama, another 7 lbs? That's all.

The rest of the things we take on the boat go in the main hull.

[susswein]

I can't envision a likely situation where having the extra power available for a short period of time would make much of a difference, but the incremental cost for the larger electric motor is pretty minimal, so why not.

I didn't realize you were going to have 1000 watts of solar, so the battery bank size makes more sense now, but still seems like overkill, especially on a weight-critical multihull. You didn't mention where you plan to sail or your usage of the boat (long periods at anchor vs moving most days), but it seems to me that sizing the battery bank based on consumption (vs. solar input potential) makes more sense. I sized my battery bank to have a useful capacity equal to 2 days of usage. Even on overcast days I get at least some solar gain, so I actually have enough capacity to last 3 cloudy days before I have to fire up the generator. Since 3 cloudy days in a row only happens about once a month where/when I cruise this seemed like the sweet spot in the cost curve. The incremental cost of having to occasionally run a generator to top off the batteries is minimal.

A couple of other questions:

1) What kind of solar panels are you planning to mount on the Amas? Framed, or flexible/glue down? I've got flexible glue down panels on my camper van and it seems like they would make the most sense for mounting on Amas, but the energy density is lower. fitting the 3 (or 4) panels you talk about on each Ama seems like a challenge.

2) Why are the battery packs going in the Amas instead of in the center hull? Your biggest amperage draw is the motor in the main hull, so I would think that that's where you would want the batteries, in order to minimize wire size and voltage drop, not to mention keeping the weight out of the Amas. With the batteries in the main hull the the wires running to each ama would only have to be sized to accomodate the 4 KW output of each generator, not the 18KW of the engine.

3) I'm amazed that you can do a system like this for 20-30K. I would have guessed more like 60K. I guess prices have really come down since the last time I looked, when even DIY lithium battery packs were in the $0.50 to $1/Wh range.

4) Apologies if it sounds like I'm trying to challenge you; I'm really just trying to understand your design decisions since I might try to design a similar system in the future myself.

[deckofficer]

Originally Posted by susswein

I guess prices have really come down since the last time I looked, when even DIY lithium battery packs were in the $0.50 to $1/Wh range.

Clearance sale at Balqon has them down to $0.19 per watt. Even the regular price is only $0.29 per watt. Lithium is now very affordable and cheaper when considering cycle life.

[senormechanico]

These

Balqon - Advanced Transportation Solution

than these

Balqon - Advanced Transportation Solution

By the time my FLA batteries in my home's backup system are shot, I'll definitely replace them with the above.

[Ocean Girl]

Don't know if this has been posted yet, great site with great insight
Torqeeedo, scroll down a bit
KatieKat 2011/2012 PostCruise Chapter

Main page, lots of great info, updated every few years of cruising( hindsight ).
Welcome to Siudzinski KatieKat


Erika

[sparau]

i haven't spotted anyone mentioning this boat, it certainly comes into the category of being primarily a sailing vessel.
Current Sunshine
if i was cashed up i'd find a way to deal with the 36' beam (ah, and hire someone to teach me how to pilot such a beast without hitting 25k and pitchpoling it) and report how well the electric systems worked

[GrowleyMonster]

http://www.cruisersforum.com/forums/...on-129944.html

I recently converted, for a net cost of about $2500 after selling the old Atomic for $300. I am quite happy and I will grow happier as I tweak things More Toward My needs.

Lithium is getting cheaper but when weight is not an issue, lead acid flooded cell is still the biggest bang for buck. But not biggest bang for pound, by any means. My 220ah 6v Batts were $85/ea at Sams Club. My 48v bank cost me peanuts. My motor was $375 with free shipping. My controller I don't remember but direct from Kelly it was cheap. EP is becoming viable for an increasingly large market and user group.

Hybrid really comes into its own when you incorporate at least 500w of solar, wind, regen, or a combination, to reduce reliance on the generator. Without renewable power, on a small scale, straight diesel is still king. For day sailing, you simply can't beat just charging from shore power.

EP works. And it is getting better for users who once would have been terrible candidates for EP. Some day it will most definitely be more important to our community than internal combustion propulsion.