Nice looking!   ( Not sure where this came from please let me know and I'll give credit.)

Here's part of a email "conversation" that Mr. Motorman had with a sailing boat owner who is interested in electric drive.

Hi Mr Motorman:  I have been looking at the information you sent me and doing a great deal of research as well. It has been a long road of learning, but I am
more interested in having you design a motor than ever. I have decided to take your advice on some design points and have decided to change the system voltage to 144VDC. This should let us use smaller gage wire and cable, but I am interested in your advice about system safety and optional safety equipment for a marine environment. It looks more probable that we would contract to have you do the complete motor and controller design as well as fabricate two prototypes. As part of the contract we would need to get complete
design drawings, parts lists, as well as motor specification and performance sheets. As I mentioned before, I am particularly interested in finding a means by which to build this size motor in the most cost effective manner possible. Can you show me the design drawings for a similar motor so that I will know what to expect of the deliverables and t o help me plan more for the development task of turning the prototype systems into commercial products? To ensure that we are both on the same page as far as motor specifications are concerned, I will reiterate my design requirement:
Motor Power: 35HP continuous @ 1500rpm
50HP peak at max. 2200rpm (max. 10 minutes)
10HP peak efficiency
Motor Voltage: 144VDC
Peak Efficiency: 88% min
Motor Type: 3 ph brushless PM motor
Motor Gearing: None,  direct drive
Magnet type: Ferrite w/ option of using NdFeB
Controller: 4 quadrant with regenerative charging from prop while sailing

Motorman answers:

The motor specs are a good choice for the application and would be my choiuce too for a boat upto 50 ft. The voltage is  high enough so that the current doesn't get too high and still reasonable for safety. Also for your safety I would suggest that you use batteries with no free acid , I use the AGM by Concord  the acid is contained in a fiber glass mat and they have much longer life and can be discharged down better. The 3 phase DC motor is wound like a three phase AC motor but the rotor is a permanent magnet array. I suggested ferrite because
unlike the high-tech motor I usually build the motor weight on a boat isn't critical and ferrite is about 1/30 of the cost of NeDyFe magnets. Ferrite is also totally corrosion resistant. I can provide a rare earth motor if you want but the cost will be much higher with no better performance just lighter weight.The motor efficiency is a trade off between size , weight and cost and RPM. The higher the RPM the lighter a motor will be ( all the other features constant ), diameter helps too as the torque can increase more than the weight.
Hope this helps

Dear motorman.
I'm a dreamer, not an engineer. The dream is an electric auxiliary drive system for a sailboat.
Performance parameters are roughly:
1) 7HP max for up to 30 minutes.
2) 2-3HP cruise mode for at least 2 hours, preferably closer to 4.
3) System weight of 800 to 1000 lbs., excludes shoreside charger.
4) Cost limit of $7000.

Motorman answers:

7  HP for 30 minutes? is this actual HP or are you just asking for same performance as a "7HP" gas engine? Again for 2-3 HP gas or actual?
Here's some useful data: a battery the size of a car battery can store about 1/2 HP-hr, so if you had 20 batteries you'd have about 20 x
0.5=10 HP-hrs of energy available between charges. A battery will weigh about 50 pounds so you get 1/2 HP-hr for 50 pounds or for the
same 20 batteries the weight would be 20 x 50-=1000 pounds. With your weight limit you'd have 10 HP-hrs for the 1000 pounds of
batteries. This is about what you seem to need so it looks OK to me. The cost of the batteries would be about $2000 and the motor and
controller and charger about $5000, so your budget looks ok too. The motor size would be about 10" diameter and 15" long and could
deliver 7 HP at 500 RPMs so you could direct drive the propeller, this is a nice and quiet way to do it! You could also use a smaller
motor with a gear box but the noise would be much more, also the gears wear out and need lubrication so this IS NOT my first choice.
Let me now how I can help you further.

? Mr Motorman,
I am seeking both brushed and brushless. This is for a sailboat to replace a diesel. A "washdown" motor would be too good to be true. Almost all DC motors over 3HP I've found are not permanent magnet types...

Motorman answers:
Good idea! you are the third sailor to ask these questions this month. The size you mention is a larger motor than most would want or could expect to have batteries to power. Recharging while sailing is a great idea and the controller for a brushless DC motor can be designed to do this automatically. A solar cell backup might be useful if you spend a lot of time in a harbor. It would be almost noiseless just the prop noise and I would keep the RPMS low by using a large prop.
Let me know how serious you are and what is your budget?

? Mr Motorman,
Anyway, I'm into boatbuilding (sailboat in particular) and I'm interested in exploring the possibility of using an electric motor as aux power on a large sailboat. Weight of batteries/motor are not a big factor as ballast is needed. I wonder if it's possible to have a 60hp or so electric motor that can be recharged by sun/wind/electrolosys while under power and additionally propeller action (act as a generator) while under sail. What do you think? My philosophy is that I like quiet, so why put a diesel in a quiet boat??

Mr Motorman answers:
First 60 HP is much too much for an electrci A 10 HP will do all you need.  My offer to the other sailing / aux applications is that I will  supply an efficient brushless motor continuous rated at 10 HP with a controller for $9,500. This will have all the connections for a battery auto recharge, solar power etc , and is intended for direct drive, no gears needed. Efficiency at 10 HP and 1000 RPM will be at least 90%. The motor will have sealed bearings and a 1.0 diameter shaft for connection to the prop shaft. Brushless motor are the only way to go in a yacht as there is no brush friction, sparks ( propane worries! ) and a life that is only dependent on the bearings. BTW; I don't like cast aluminum on an ocean going design as the aluminum has a tendency to corrode badly in salt air. Our construction will be epoxy coated steel or stainless steel for shaft etc. We only make motors to order and so each motor is customized for the user.

Here's a group of questions and each contains some useful insights to questions in sail boaters minds...

? Mr Motorman:
About prices: Solomon Technologies wants at least $3500 for a (very promising) cast aluminum motor which is not even available yet, and Elco (Electric Launch Company...also very
good) is asking upwards of $10,000 for a complete system. Browsing an industrial catalog I see motors in the 2-5 HP range for more like $900. I know its probably too much to ask for a motor that price to perform properly in this application, but still I think one should be able to do better than $3500. We sailors are sometimes independently
wealthy, but more often we're just the working class, as in my case. If we cant find a way for Joe Sixpack to buy and use this technology,
then its just so much hot air. It has to be cheap. And believe me, every sailor I know would gladly sell those diesels for scrap if you
could show them an electric drive they could afford. I want to build this cheap because its all I can afford, and also to prove it will
work without getting NASA involved. I think we're a lot closer to making it work on boats than on cars. Especially sailboats, cause a
sailboat drags around several thousand pounds of ballast anyway, so the batteries make great ballast if you install them in the right
place, down low in the hull. The heavier the better. As to power required: Im still looking for the equations for required
power for a given hull shape, but the Solomon motor is supposed to cruise at 1200 watts (about 1 or 2 HP???), and other electric examples
mention up to 10 HP. A typical 33ft sailboat usually has a diesel of 15 to 30 HP, but apparently there are differences in the way power is
specified for diesels and electrics. I am still doing homework on this, but this is what I have so far.

HI Mr Motorman:
I am an electrician and I have worked both with ships and generator sets like those used in mining equipment. I seem to remember that you could use
considerably smaller horsepower electric motors of all kinds in place of internal combustion types because of their much higher starting torques.
In my case I want to replace a 150 hp out board with a generator  ( for all power needs plus recharging batteries on longer trips) and put an electric
motor in place of the regular motor. Then have a bank of batteries for short trips and on long trips the generator could charge as you go. I believe this
to be a "hybrid" set up. Please your thoughts? I know that variable frequency set-ups are both expensive and vibration sensitive (they did terrible at the mine in mobile equipment.
Rectification drives do better but they aren't cheap either. And I don't know what has come about recently so maybe you can help to fill in the gaps?
First of all, great web site. It has a lot of very helpful information. I read thru the FAQ's, but didn't get everything I was looking for, so I am hoping you can point me in the right direction on the following.
 

And this from another Ultimate Motor seeker ........
 

 Mr Motorman: I am designing a sailboat to be refit with an electric motor, but I confess I know little to nothing about motors. I need an electric motor that can produce up to 35 hp to drive a propeller shaft (3500 RPM max), and survive in a marine environment. This motor will be powered by batteries that will be trickle charged from wind generators and photo electric cells. My objective is to have enough battery power to run the electric motor for 10+ hours at continuous 25 hp with no concurrent charging. In ideal conditions (e.g.. lots of sun and wind), this configuration would allow for perpetual power output.
Can you recommend a motor and battery configuration to satisfy the above objectives? If you cannot satisfy the above with your inventory, can you point me in another direction? Your help is appreciated. I am happy to call you to discuss further if you prefer.

Mr Motorman Answers:
I am working some sailing boat owners who want an in board electric, so you may have the same needs.The motor size depends on what performance you want . About 1/4 of
the power in an electric will do the same as a gas engine. The hybrid has one main advantage in that you can put the gas generator where it makes less noise. The cost will be fairly high
as the generator for a 40 HP motor will need to put out 50 KW or you will be running on batteries and at 40 HP the battery pack will be huge. ( A car battery has only about 1/2 a HP-hrs of energy available! ) You can rectify the AC from the generator ( alternator really ) with a cheap rectifier bridge so going form AC to DC is easy. A 40 HP electric motor and controller will run about $500 - 10,000 depending on the exact set up. A simple and cheap way to go would be to use an AC motor to drive a fixed speed prop. with a variable pitch. This way you won't need any conversion. For low speed motoring  you could use a low power DC motor off  the batteries. The batteries can still be charged off the alternator.
Hope this helps and doesn't confuse...

? HI Mr Motorman: Could you point me to some reference material on diesel electric that brings it down to a layman's level? I like the way you've explained
things in your FAQ. The object of the exercise is to utilize electric motors on an outboard type leg, either driving gears or submerged at the end of the leg,
driven by a single diesel generator. The legs would be retractable for the underwing of a catamaran thus would be able to be brought up into
the cockpit area allowing them to be cleaned et cetera. The generator could be located anywhere on the vessel where the weight would least
affect the performance/livability.

Motorman's Answer:

I do not have any references to a source for such information. My thoughts are that I don't like diesels, they have an unpleasant noise and smell. It might be possible to put the generator set down in the bilges and somehow smother the noise but the vibration would still bother me.
Other than that your idea would be fine. The electric motor can work well underwater, there are good sealing methods to keep all the sea water away from the electricals. Cost for the motor as a custom by me would run about $8000 depending on power needs etc.