My new electric sail drive

[Skipperdan]

The weekend started out pretty good. I just put a rack and pinion in my wife's car so I thought I would test drive it to Bismark 100 miles away. I was looking to go to an outboard engine shop that specializes in rebuilds. I was going to by a lower unit from him for my sail drive. when I got there the shop was closed with a note that said they were at the boat show another 100 miles away. A quick phone call and he told me he would not be back, but I was welcome to go through his pile of scrap and take what I wanted. He also mentioned a Yamaha complete outboard that he was not going to use and I could have that. SO I DID. All for free. I think I can sell some of the good parts off the top end on ebay to pay for gas. The only holes in the boat will be four small bolt holes and the small hole for the shaft. I will have to build a platform to rest it on, but that should not be a big deal. I already have the motor and controller picked out, Total cost of the project should be less than $1,500.00 with 4 marine batteries. A generator to charge the batteries on longer runs and also for house supply when needed. I am going all 120 vlt for the house side and 48 for the motor.

 

[weinie]

 

[Skipperdan]

Pulley on the shaft, pulley on the motor, belt to connect them. If that is what you are asking. The shaft is not pictured because it was too long and I could not get the unit close enough to the hull.

 

[Jackdaw]

You are going to bolt (couple) that unit directly to the hull? Not a great idea.

 

[Skipperdan]

Why not?

 

[Skipperdan]

Itgoes through the hull the bolts go through also to a plate on the inside. The hull is sandwiched inbetween

 

[kloudie1]

Not throwing stones, but how are ya gonna seal the shaft penetration reliably? The water intake and exhaust passages in the lower unit will have seawater (lake water?) in 'em.

 

[Jackdaw]

Itgoes through the hull the bolts go through also to a plate on the inside. The hull is sandwiched inbetween

As long as you can isolate it from vibration you should be OK. Otherwise that interface will be very hard on the hull.

On another front, will the prop match the RPMs of the electric motor?

 

[Skipperdan]

Not throwing stones, but how are ya gonna seal the shaft penetration reliably? The water intake and exhaust passages in the lower unit will have seawater (lake water?) in 'em.

There is one intake on the bottom for the water intake just replace the screen with a blank. There are two other small holes that need to Be welded shut.

 

[Skipperdan]

As long as you can isolate it from vibration you should be OK. Otherwise that interface will be very hard on the hull.

On another front, will the prop match the RPMs of the electric motor?

This is not a new idea there are a lot of sail drive add-ons, they just use a $9,000.00 unit that is basically the same thing.
The exterior will have a sizable block fared in to match the hull shape to the lower unit. The inside will have layers of laminate wood to spread out the force about one foot by two feet. The shaft is only turning about 1000 RPMs, it can go to 30 hp for one minute at something like 3000 RPM's. Everything is calculated a head of time to get 6 knots at max. so you arrange your pulley's accordingly. I used a similar engine as an outboard on my Triton which is twice as heavy and never had a problem on the Mississippi. Figure just a nice average 2 or 3 knots is not hard on anything. Plus this is a sailboat and the unit will get used very little.

 

[Jackdaw]

This is not a new idea there are a lot of sail drive add-ons, they just use a $9,000.00 unit that is basically the same thing.

Well that's not true. Those units contain the electric motor, attached directly to the prop.

I'm not saying it cannot be done. I'm saying that any unit that has to deal with vibration (like traditional saildrives) are not hard-fixed to the hull, but on a dampened mounting that can vibrate along with the source.

 

[Skipperdan]

Well I guess it is not really hard fixed to the hull. The hull is sandwiched between the drive and the plate on the inside.

 

[Skipperdan]

Well that's not true. Those units contain the electric motor, attached directly to the prop.

I'm not saying it cannot be done. I'm saying that any unit that has to deal with vibration (like traditional saildrives) are not hard-fixed to the hull, but on a dampened mounting that can vibrate along with the source.

http://saildrive.com/ same thing only I am attaching an electric motor instead of a vibrating diesel.

 

[Jackdaw]

http://saildrive.com/ same thing only I am attaching an electric motor instead of a vibrating diesel.

Again sorry, but you're not understanding how these work.

Look at the pictures. The sail drive lower unit is NOT attached to the hull. It is isolated via a rubber gasket, and is a part of the upper unit. and is is allowed to vibrate with the drive source.

I have a saildrive on one of my boats, and if you push the lower unit the motor moves.

If you bond the lower unit to the hull (with bolts) it will have to deal with the vibration and the harmonics.

 

[Skipperdan]

Well I guess two rubber gaskets will help. I am quite sure electric is not going to create much in the way of vibration. It will be a good experiment anyway. Thanks for the help

 

[Skipperdan]

I found a nice piece of 3/4" thick rubber that I think will work. I also remember seeing a thicker 2" piece at Mac's. This might also work well to make the transition point if I can mold it. Just got to keep the brain working.

 

[Skipperdan]

That sure looks like it is sandwiched between the hull. At any rate using a rubber mounting is not a problem.

 

[Meriachee]

Hopefully you are considering some form of mechanical seal with this rubber being an internal, isolated structure as part of the drive.

 

[Gunni]

Remember SkipperDan, that Pennsylvania dude who successfully built what had been known as Fulton's Folly and those Ohio bike mechanics who invented manned flight all carefully studied the methods and mistakes of those who had failed before them! They shared your willingness to dismiss conventional wisdom and ignore the negative nay-Bob's of Negativism. Carry on.

 

[Skipperdan]

I have a request in at VoltSport (the above picture showing a retro fit). They are mounting it direct to the fiberglass no isolation at all. I still think I will use the 3/4" rubber mounted to the hull and the Drive mounted to that. It will make forming the attach point rather easy. Very close to how Yanmar is doing it, using rubber instead of Fiberglass.