Ever Refit a Sailboat with an Electric Water Jet ?

[BSV2]

I'd like to remove the Diesel engine and replace it with an electric water jet? I found that USCG and other boats use jet propulsion for their vessels, but I have not seen a sailboat.
Am I insane?

[Tristan]

Yes !!!

[sarafina]

but that isn't always a bad thing!

And it still may be a good idea for a little sail boat... interesting if nothing else!

[boatman61]

Also... you may not have noticed... USCG boats don't have sails....

As we say in the UK.... "Barking..."

[cabo_sailor]

Replacing a diesel with a waterjet has some other ramifications. Basically, you are trying to change the sailboat into a PWC. The boats that the coasties have propelled by waterjet are planing hulls, your sailboat is not, its a displacement hull. Add all the power you want and it won't go any faster. Second, waterjet boats, as I understand them, do not maneuver well at low speed. Of course that has always been something of a problem for sailboats.

Finally, if it was a really viable good idea, dontcha think there would be a few out there by now?? Waterjet powered boats were around in Viet Nam.

If you got the time and the money to play with it, then go for it and let us know how that worked out.

Have fun,

Rich

[boatman61]

Originally Posted by cabo_sailor

Replacing a diesel with a waterjet has some other ramifications. Basically, you are trying to change the sailboat into a PWC. The boats that the coasties have propelled by waterjet are planing hulls, your sailboat is not, its a displacement hull. Add all the power you want and it won't go any faster. Second, waterjet boats, as I understand them, do not maneuver well at low speed. Of course that has always been something of a problem for sailboats.

Finally, if it was a really viable good idea, dontcha think there would be a few out there by now?? Waterjet powered boats were around in Viet Nam.

If you got the time and the money to play with it, then go for it and let us know how that worked out.

Have fun,

Rich

Rich.... sorry to contradict you mate... but actually if you've twin water jets they're amazing.....
I skippered a drilling cat back in the 80's for an oil exploration company and it was fitted with water jets... the precision with which I could park that over the proposed drilling co-ordinates was awesome... top speed was 6kts but at 1/4 knot I could make that baby dance...

[JRM]

Originally Posted by cabo_sailor

Second, waterjet boats, as I understand them, do not maneuver well at low speed. Of course that has always been something of a problem for sailboats.

Heh. A waterjet only maneuvers under power. We use RWCs (jetskis) for surf rescue work, and I just underwent recertification last week. Nothing like trying to operate in waves in close quarters with people in the water to cement in the concepts...

Your biggest problem is going to be a lack of reverse. Yes, you can drop a hood over the jet and pretend it's reverse, but it really isn't. What it does is stop you from idling forward. Personally, I find the ability to reverse rather useful, and would be loath to give it up. We can get it to move a few feet backwards by giving it full throttle with the hood down, but there is no directional control.

Second, water jets are really not that efficient as implemented, and electric propulsion is all about efficiency. They're great at going fast. Our primary surf boat is a 1200 cc death machine, basically a marinized Honda Civic engine in a 750 pound boat. It *accelerates* like a dream. Great when you're trying to avoid getting smashed by a plunging wave, less so when you're trying to pick up someone and need to turn (see above) next to them.

If you'd like to talk electric propulsion, my Catalina 30 is electric. I'll be finishing the throttle on Wednesday, and she'll be headed out for her maiden electric voyage that afternoon. There are several folks here with conversions in various stages of finish, if that's a conversation you'd be interested in...

JRM

[SaltyMonkey]

boaty...and others...do knot water jets need plenty of space...e.g. tunnel drafts and hulls in teh way make em inneefficient

[SaltyMonkey]

i wanna know about elektrik and how peeeple power em?

[boatman61]

Yup... common problem with novice jetbikers... see something ahead and decelerate to turn and avoid... standard car practice... only it don't work on water..
You need to accelerate and turn hard and she'll pivot near on the spot... you'll then dive the nose and bounce back out... facing away from the hazard...
but who cares...??
The swimmer that you just avoided running down and taking their head off...
Jet Bikes should be treated the same as on road bikes... mandatory tuition

[smallyachts]

No, however I did the reverse several years ago. I bought an Erik Manners trimaran that was fitted with a 48 volt electric motor running a water jet.

Yes it moved the boat, but not into headwinds that were much over 10 knots, and this was on a trimaran that could easily achieve 20+ kts under sail.

Very heavy battery bank needed to power it, and the range was very small. It was functional to get out of the slip and out to the mouth of the bay, but that was about it.

Yes, I could bring the boat into very shallow water (around 18"), but I would not trust it, so I replaced the single water propulsion design with two 9.9 hp yamaha 4 strokes.

Reverse was accomplished by rotating the out thrust nozzle, it was mounted on a sealed ring that allowed it to be rotated 360 degrees by means of an auxilary "steering wheel" that was separate from the rudder.

If I had it to do over again, I would have replaced it with a single small diesel, or with the advances that have been made, with a single prop powered off of the electric motor.

[BSV2]

Yes, I am interested to hearing about your Catalina 30. I have a 41' Ta Chaio with the displacement of 20,000 lbs. Of course, she will displace more with some added daily use items, and possibly a dinghy.
I read that there are several problems I need to consider, but honestly, I have considered them.. I figure if the thrust from a three blade prop can move my boat forward at about 7 knots, so can a jet propulsion. Given that a sailboat is a V hull, there is a mathmatical conversion as to how fast she can move. I am only looking for up to 7 knots of forward movement. If I use a second propulsion source (bow thruster or even a dedicated reverse thruster) could I get the reverse I need? As for the battery bank needed, I have ideas there as well. I have two stowage compartments port and starboard of the helm, which will do nicely. There are several ways of recharding the batteries. There is wind, solar and yes, hydro. Hydro works kind of like the alternator on a car + the gyro used on some knotmeters on the bottom. If she is moving forward, she can generate electricity! At least that is the hypothesis. What do you think?


If you'd like to talk electric propulsion, my Catalina 30 is electric. I'll be finishing the throttle on Wednesday, and she'll be headed out for her maiden electric voyage that afternoon. There are several folks here with conversions in various stages of finish, if that's a conversation you'd be interested in...

JRM[/QUOTE]

[Juniper]

If you do this your biggest issue will be about efficiency. A propeller is quite efficent if used properly, a good waterjet can be better then a bad prop. I like the idea of having jets facing in different directions. Two ways of figuring it out, study up of try it out.

[smallyachts]

Propellors are more efficient at slow speeds than waterjets.

At high speed the waterjet wins.

So on a typical monohull I do not believe the waterjet would be more efficient.

[BSV2]

I'm really not looking for effeciency as much as I am trying to make the boat more "Green". I want to get away from Diesel, and the issues that come along with an internal combustion engine.

Originally Posted by smallyachts

Propellors are more efficient at slow speeds than waterjets.

At high speed the waterjet wins.

So on a typical monohull I do not believe the waterjet would be more efficient.