Electric motors

[Eleven]

'where they motor sail like that at ten knots in a 65 foot mono and achieve an extra 25 per cent or so range because of the mainsail.'
From other threads it is clear that many US cruisers use the motor frequently and accept poor sailing ability as a return for good accomodation.
The other group are the economy cruisers who can't afford diesel in green, red or carbon black shades. Sailing is the first option, survivial sailing is their safety net, not motoring out of situations. Electrical power from the sun or wind is still a high capital cost. Usefull for maintaining batteries and basic Nav systems but too expensive for kW's so diesel is carried. 3 days at a litre an hour and 2 kg a liter is 150 kg. Batteries for three days ? It just doesn't add up yet even with a trickle from solar/wind. If it's got to be green it's got to sail well, ask Gideon, then batteries can give a couple of hours at half throttle to get clear of harbour and traffic but using sails to charge the batteries? How many sailors waste wind by dragging brakes behind them? It doesn't add up again. BUT Diesel Electric really can provide more efficient drive as an Auxilliary not an alternative power source. Making four knots in a calm is a big bonus, adding a couple of knots in a light airs confined waters is a big bonus, but electrics alone are are not going to drag you away from a continent against a prolonged storm.

[fastcat435]

Originally Posted by Eleven

'where they motor sail like that at ten knots in a 65 foot mono and achieve an extra 25 per cent or so range because of the mainsail.'
From other threads it is clear that many US cruisers use the motor frequently and accept poor sailing ability as a return for good accomodation.
The other group are the economy cruisers who can't afford diesel in green, red or carbon black shades. Sailing is the first option, survivial sailing is their safety net, not motoring out of situations. Electrical power from the sun or wind is still a high capital cost. Usefull for maintaining batteries and basic Nav systems but too expensive for kW's so diesel is carried. 3 days at a litre an hour and 2 kg a liter is 150 kg. Batteries for three days ? It just doesn't add up yet even with a trickle from solar/wind. If it's got to be green it's got to sail well, ask Gideon, then batteries can give a couple of hours at half throttle to get clear of harbour and traffic but using sails to charge the batteries? How many sailors waste wind by dragging brakes behind them? It doesn't add up again. BUT Diesel Electric really can provide more efficient drive as an Auxilliary not an alternative power source. Making four knots in a calm is a big bonus, adding a couple of knots in a light airs confined waters is a big bonus, but electrics alone are are not going to drag you away from a continent against a prolonged storm.

Not trying to be a wise guy but diesel weights 800 grams per liter not 2 kilo,s so the weight for 3 days is 57.6 kilo,s , we do carry a emergency generator as part of the Multi Hybrid system , off course the other generators , solar , wind and hydro also contribute to keeping the battery full
We now install 4 x 280 watts solar panels in combination with 1 mast head mounted generator and the 2 hydro Motogens that can generate as much as 4 Kw each to recharge the batteries.When on shore we can use shore power to recharge the batteries.
You are right the cost is high for wind , solar and hydro power but the cost of fossil fuels is actually higher taking into account the cost to get the air clean again.
It is in a way a time bomb just like nuclear energy and cost of making all safe and clean again. This is off course my green mind thinking .

Greetings

Gideon

[Roy M]

Originally Posted by Gludy

Gideon
"t will be very hard to get your boat over the hull speed no matter if the motors are electric or diesel ,"

I am puzzled.
If sail power can push a boat well over hull speed why cannot engine power?

Remember the difference between displacement (most monohull sailboats) and planing hulls (most multihulls). You just need enough seahorse power to leap the bow wave, or else be submerged by it.

[44'cruisingcat]

Originally Posted by Gludy

Gideon
"t will be very hard to get your boat over the hull speed no matter if the motors are electric or diesel ,"

I am puzzled.
If sail power can push a boat well over hull speed why cannot engine power?

Engine power can. Even in a heavy displacement boat with a low length/beam ratio. But it will need a LOT of power to climb over its own bow wave.

Edmund Bruce researched hull length/beam ratios during the 1960's.

My understanding is he found that at higher L/B ratios, above around 8:1, the resistance due to wave making becomes greatly reduced. The higher the ratio, the less wave making. At around 11:1 it virtually dissapears. So boats with higher L/B ratios don't encounter the same hull speed "wall" as shorter, beamier boats.

There is a video here: Allura Marine | Welcome of a 55' power catamaran at 30 knots, clearly still in full displacement mode, not planing, where normally hull speed would said to be around 10 knots.

[ldrhawke]

I wonder why they don't build sailing cat hulls with the same long chime in them as they do the power boat cat in the movie? They appear very effective in keeping down spray. It appears that those chimes and a fine entry would go along way in keeping spray off the decks and cabin that we often see in high speed sailing cat movies.

[44'cruisingcat]

It does seem quite effective doesn't it. It might be noisy though, which wouldn't be as much of an issue with a power boat. Next time I see Bob Oram I'll ask him. (He's off delivering a boat to Darwin just now)

[decktapper]

Thank you Octopus

I wondered how people with actual experience viewed the electric systems.
decktapper.

[decktapper]

Originally Posted by fastcat435

In both cases with Diesel and with the electric motors we measured in no wind and flat water conditions however with wind on the nose with both , the drop in speed is considerable more with the diesels as it is with the electric motors.Force 7 on the nose gives
5.5 knots for the electric 2 x 4.5 kw version and 6.5 knots with the twin 29 hp diesel .
This probably has to do with the lower revving larger props on the electric version.
With the 2 x 9.6 Kw retractable electric version we expect better speeds with wind on the nose than with the diesels for the same reason.
I have not had 50 knots on the nose with the electric motors yet but with the 29 hp yanmars it is the same as with you , almost no headway with 50 knots

Greetings
Gideon

Hello Gideon:
I am not fool enough to argue with experimental data combined with real world experience. Do you have any information on the props, diameter, number of blades, pitch, RPM etc for the different test runs? I am floored to think that my diesel propulsion could be so poorly designed.
How do the diesels perform with variable pitch props?
Thanks for the information
decktapper.

[fastcat435]

Originally Posted by decktapper

Hello Gideon:
I am not fool enough to argue with experimental data combined with real world experience. Do you have any information on the props, diameter, number of blades, pitch, RPM etc for the different test runs? I am floored to think that my diesel propulsion could be so poorly designed.
How do the diesels perform with variable pitch props?
Thanks for the information
decktapper.

Hallo Deck tapper

we use 16 x 13 props 3 bladed and are still experimenting with different sizes.we use a 0.51 prop area or 25 % more blade surface than normal.
This is more like a tug boats prop.
Our motors turn out top rpm at 1320.
Variable pitch props are wonderful on a diesel and increase the efficiency dramatically .
If your diesel motor had these type of props it would stall if put into gear since the torque is very low at idle rpm

Greetings

Gideon

[Captain Bill]

A couple of years ago (2005 I think) at the Miami boat show there was a Diesel Electric cat (might have been a leopard but don't hold me to it). This thing had a sigle 40 HP Electric motor in the port hull and with a few batteries and a whole bunch of batteries in the starboard hull for balance. It had a bunch of solar panels (10x75w). It had a Generator mounted in a compartment on the bridgedeck. I talked to the captain who had just delivered it from South Africa. He said that it could charge the batteries off of the motor while under sail and it cost him about 1/2 a knot. In anycase he had come across with an identical boat that was conventionally powered and they stayed together for the whole trip. At the end of the trip the conventional boat had used 435 gallons of diesel, his boat had used 85.

[Eleven]

Just the sensible figures we all need, thanks Ctn Bill.
It's easy from that to do a cost assessment based on local prices. On an earlier post I see 4kW from a water genny for a half knot, that's useful cooking power for an hour a day. Hard to convert that into battery charge or is it a fairly high voltage system. Thats 40 Amps at 100 Volts. Heavy cables, risky voltages but still very useful and not as risky as Propane/butane.
It does suggest that a water driven wind generator type motor (Permanent Magnet Type (PMG's) seem the latest thing for cost v output) might be the way to go for domestic power.
Cptn Bill, any idea what the 85 litres of diesel was used for?
Also 435 litres of motoring is some 2 weeks under power? but the US cost of diesel (motoring) is lower than Europe.
I still think the time for solar electric is not yet, maybe in five years, a breakthrough in solar power would help but they are getting better all the time.
For a new boat that's going to last or twenty years that's about two years ago!
For an old boat adding a genny to the main motor and an electric drive leg might be the way to replace the gearbox and drive leg / propshafts.

[Eleven]

By the way that flying hydrofoil reminds me of a sixties scheme to fly passenger airplanes in the ground effect over the water of the italian lakes. Halves the fuel consumption. Shortens masts. Gets more yachts flying radar reflectors.

[Captain Bill]

Eleven, These were gallons of Diesel, not liters. My understanding was that virtually all of the diesel on the electric boat was for propulsion, the solar panels and Motor generator handled all of the house requirements. 10 Solar panels certainly should have. The conventional boat used it for house as well as propulsion. It was not clear to me that the conventional boat had any solar panels at all. I don't know the exact distance traveled but it must be about 8000+ miles from South Africa to Miami. These boats were in the 45 foot range and they were trying to make it in time for the show, so they were probably pushing a little harder than someone without a schedule, besides the captains weren't paying the fuel bill so they probably didn't have all that much incentive to conserve. I don't find it terribly hard to believe they could have used 435 gallons on a trip this long. My endeavourcat with twin 40 HP Yanmars burns about a gallon per hour on each engine at 7 knots when motoring in calm water. I burned about 200 gallons on a 6 week 2300 nautical mile trip to the bahamas from North Carolina this winter. I had a six week time limit on the trip so I had to motor quite a bit to keep the schedule. I suffered a lot from the Number 1 rule of sailing,"The wind was always coming from where I was going", or becalmed. I also had a couple of short weather windows where I had to motor sail to get ahead of a storm off of the Carolinas. In any case I used much more fuel than I wanted to.

[GreatKetch]

Originally Posted by Captain Bill

A couple of years ago (2005 I think) at the Miami boat show there was a Diesel Electric cat (might have been a leopard but don't hold me to it). This thing had a sigle 40 HP Electric motor in the port hull and with a few batteries and a whole bunch of batteries in the starboard hull for balance. It had a bunch of solar panels (10x75w). It had a Generator mounted in a compartment on the bridgedeck. I talked to the captain who had just delivered it from South Africa. He said that it could charge the batteries off of the motor while under sail and it cost him about 1/2 a knot. In anycase he had come across with an identical boat that was conventionally powered and they stayed together for the whole trip. At the end of the trip the conventional boat had used 435 gallons of diesel, his boat had used 85.

Catain Bill,

Nice story, but are you trying to tell me those two boats motored the same number of miles on the passage? There are pieces to that story that don't add up. For example: Have you every "buddy boated" across an ocean? If so you would be suspicious of the claim that they "stayed together for the whole trip". People shouldn't expect to use 1/5 the fuel when they switch to d/e units.

Let's be sure we are comparing apples and oranges.

By way of example, Two boats recently made a passage from Southern California to San Francisco. One boat motored the whole way and used over 100 gallons of fuel, a similar boat sailed the whole way and used less than 5. Neither one was electric.

Certainly D/E units can be somewhat more efficient than simple diesels, but not to that extent and anybody interested in passagemaking efficiency would be far better looking for a boat that SAILED well than in optimizing the fossil fuel power plant.

[sandy daugherty]

Great Catch: Its OK to express your surprise at Captain Bill's report, but perhaps you overstated your objection. After all, independance from petroleum based fuel has been the goal of well financed research for more than forty years, and progress is being made. Why can't we expect to see incremental breakthroughs and major accomplishments? In my mind they are LONG overdue. The time may not be far away when we are not PERMITTED to use this precious resource for recreation! Electric motors driven by batteries charged by a dockside plug or solar panels may be the ONLY way to get out of a harbor unless you're paying to ride public transportation. Lets hope and pray that the Gideons in this world get us to petroleum independance sooner rather than later.

Another point: as Richard Woods points out, multihullers frequently have to slow down for an enjoyable transit. THIS is the time to drop the motors down and recharge the batteries. In fact, it might be good to come up with another storage medium. Perhaps we could generate and store hydrogen and oxygen for those 'clawing your way off shore' moments or hours or days.