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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 07-25-2007
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jet drive

I know that most sailors seem to lean toward diesel for power for its reliability but I think that there might be a better solution growing up as a powerboat guy and then seeing the light of sailing I have been thinking of an idea that I have nor the financial means nor the boat worth experimenting on but a good idea non the less I think and I am sure that you good sailnet folk will be more than happy to let me know if I am way off base. But here is the idea with the new small jet boats on the market most used by incompetent boaters their musts be a fair amount of them out there for parts. The new four stroke motors are lightweight and reliable. So my thought Is retrofit one into a sailboat to eliminate prop drag and the dreaded side stepping effect seen in reverse on standard inboard setups I know that there is 20 to 35 percent power loss in a jet drive but I think it would be worth it to have a lot less drag no prop to wrap up lines with and a true reverse that works.
Let me know what you think when I am ready to start my life as a cruiser I will be looking for the boat with a seized motor for this reason.
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Old 07-25-2007
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A jet drive on a sailboat? Hmmm... Well, yeah, you'd eliminate the prop in the water and substitute for it the jet drive in the water. Plus, I would guess all that impeller, housing, stuff hanging off the bottom of the transom, etc. probably weighs a good deal more than a traditional prop, shaft and transmission.

But if you find a jet drive boat and a sailboat you want to sacrifice in the name of experimentation and discovery, do let us know.

The name of the resulting boat would be easy: Frankenstein

Jim
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Old 07-25-2007
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You say you've seen the light, but you seem like someone who's quit smoking but still gets cravings. You should get your mind out of the gutter. Think about sails and sailing not motors and motoring. Spend your time, money and ingenuity there.
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Old 07-25-2007
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If I'm not mistaken, jet drives are also gas guzzlers. Why trade a diesel and prop, sipping less than a gallon an hour at cruising speed, for a jet drive? Sailors only use their motors for close-quarters manuevering or when the wind has died (or to make time against a headwind or tide), so it seems to me to be a bit of overkill.

Personally, I'm much more interested in electric motors, whether straight battery or diesel/electric applications.
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Old 07-25-2007
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Installing a PWC gas jetdrive on a sailboat is analogous to attempting to play rap music with a Stradivarius.
Quote:
. . . with the new small jet boats on the market most used by incompetent boaters their musts be a fair amount of them out there for parts. The new four stroke motors are lightweight and reliable. So my thought Is retrofit one into a sailboat . . .
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Old 07-25-2007
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I think he is just talking about replacing the prop with a jet drive pump.

Big advantage - There is no transmission. Motion is controlled by a gate at the pump exit.

It is an interesting idea. They did turn efficiently at low speeds and they would back in the direction you wanted to go. If the pump was efficient enough...maybe

I don't think anybody with a jet drive checked the fuel consumption at low speeds. I could tell you how may gallons it took go 10 miles to the marina, where I had to make sure I had enough gas for the trip back to the house. I could be back before you got your sails trimmed.

However......

Jet drives are gas guzzlers. And I mean guzzle. I have had 2 jet boats - 455cu in with berkeley drives. They would go about 80mph, outrun everything on the lake except those high performance bass boats. My dad had one with 2 - 4 barrel carbs and over hull exhaust, would run over 90. They were fun, could turn around with very little forward or backward movement, could wet the rails. When they were being driven away from the dock you could hear it at least a mile away and these had the thru-hull exhaust.

And we also just sold 2 PWC's. No we were not idoit PWC'ers.

Let me just say diving to untangle a rope from a prop would be better than pulling rope out of the jet pump. We had a ski rope get sucked up in the 455. Only took a second. Took 4 hours of reaching in the pump from the access on the top with a knfe, cutting rope that has been pulled tight around the shaft. Not to mention if the rope gets in the seal (between the pump and the bilge) you have a big problem.

It is an interesting idea. Would depend on the efficiency of the jet pump. It would not be a retrofit without major work. The intake grate is designed to be in the bottom of the hull and the pump is out the back of the hull usually hidden by a swim platform. A jet pump pod put in place of the prop would probably create more drag than the prop.
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Old 07-25-2007
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From an engineering perspective it is interesting, not sure if it would be practical for most boats because of inefficiencies inherent to jet drives. I could see die hard racers being interested in it; no prop =no drag, and they probably wouldn't be worried about an increase in fuel consumption. I can't see it being practical for cruising even mated to a diesel, too complicated and inefficient, but for smaller boats(daysailors, pocket cruisers) it might be OK, but there would be a million bugs to work out I'm sure.
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Old 07-25-2007
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ok guys I know that a lot of you think this is a bad Idea but as far as more drag from a jet pump you are way off the standard jet pump has a inlet grate that mounts flush to the bottom of the boat and the nosle is in the stern only a few inches below the waterline where the water is airated and turblent undersail where as a prop is in deep thick water. also a pwc motor and jet drive has one more big advantage 85 hp weighs about 130 lbs and fits in a mid sized duffle bag

I monted a 900cc pwc setup in a 14ft johnboat that worked very well and with no real test is seemed to be a little less thirsty than the 25 hp two stroke outboard it replaced

my thoughs were geared more to race boats where drag and weight are more of a concern
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Old 07-25-2007
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Now we're getting somewhere. My boat came with either a Saildrive or an outboard. I have the outboard, but there is a nice little well under the cockpit for the optional Saildrive. If I took an old jetski and modified it to fit.......oh never mind.
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Quote:
Originally Posted by rewell6 View Post
I have had 2 jet boats - 455cu in with berkeley drives. They would go about 80mph, outrun everything on the lake except those high performance bass boats.
Yeah, had a buddy with a "California something-or-other" with a 455 in it and a Berkeley drive. And another with I-don't-recall-what, but ISTR it had tri-power carbs and over-the-transom exhaust. Oh yeah, jet boats are fast, all right . Can turn and stop on a dime, too. Loads of fun. Loads of expensive to feed, too.

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Originally Posted by rewell6 View Post
Let me just say diving to untangle a rope from a prop would be better than pulling rope out of the jet pump.
Tell me about it. The one with the 455 was during my skiing days. (He once pulled seven skiers up at once with that boat--with at least four of 'em were on one ski, IIRC. They all stayed up, too.) More than once we had to get a ski rope out of that pump. And weeds. A jet pump will basically suck up anything that gets w/in range of that grate and will fit through. But ropes are the worst.

Jim
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