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Old 10-06-2018, 11:23 PM   #1
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small jet ski engine?

I am looking for specs for the smallest jet ski propulsion system I can find to use in a 10' dinghy for my trawler. Lightest possible weight. the dighy will carry two people plus groceries. Hopefully. from a model no longer in favor that I can pick up as junk.
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Old 10-07-2018, 02:11 AM   #2
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Also, for your information, SBT carries a huge selection of remanufactured jet ski engines and systems.

Will be interested in seeing how your conversion works as we are strong proponents of jet RIBS.
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Old 10-07-2018, 07:33 AM   #3
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10' will not accommodate any jet ski or rib-jet engine/drive combinations that we are aware of. It lacks both size and weight capacity for the units but perhaps a smaller unit with less hp from the newer surfskis might work.

https://www.amazon.com/Motorized-sur.../dp/B078K4D9X4

IMHO - a jet drive is more complicated, heavier, less efficient and has less control than an outboard.
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Old 10-07-2018, 07:51 AM   #4
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Jet propulsion systems are a narrow-market product so they tend to be expensive and limited in availability.

I’ve thought of having a less than 15 hp jet unit for years but I think 25-40hp is where they bail out. Like diesel engines. Nobody put them in cars because they wern’t suitable ... until they were. Or are they? Hmm

Of course you could always find/get a water pump remembering that “jets” are just specialized water pumps and rig it up in you’re boat. This would be much much easier to do if you didn’t need it very light. Just any water pump w it’s discharge over the stern would be a “jet” but much sophisticated design and materials is usually necessary. Water-jet propulsion is expensive and inefficient so not the ideal DIY thing

But like me you like thinking out of the box so I’ll be looking for where this goes. One thing will probably be a given and that’s noise. So let the experiment begin.
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Old 10-07-2018, 08:17 AM   #5
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Old 10-07-2018, 08:28 AM   #6
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Old 10-07-2018, 08:46 AM   #7
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I think the Kawasaki Jet Ski likely has the smallest engine/pump. Noisy, though as exhaust comes out the side of the ski.
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Old 10-07-2018, 09:04 AM   #8
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The smallest jet drive readily available will be way too much power for a 10' dinghy, and much heavier than a comparable outboard.

For example here's a 9' jet RIB, 90 HP and the whole rig 550lbs. Keep in mind this is an inflatable designed for 90HP, not the same as dropping 90HP into an existing dinghy designed for 10HP

Aqua 9 | Aquascan Ribs

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Old 10-07-2018, 10:09 AM   #9
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Taking Ski's advice I checked out Kawasaki's jet skis on line. The smallest has a 1.5 liter, 4 cylinder engine. No way is that going to work with an RIB, it has to weigh 250 lbs.


Neither do I think that the 125 cc powered surfboard will work. Due to the inefficiency of a jet drive you will need more power than the typical 200 cc 9.9 hp outboard if you want to plane. So you will probably need 350 ccs which is typical of 15-20 hp outboards.


A 20 hp Yamaha outboard weighs about 110 lbs, so a jet drive built around the same engine should weigh approximately the same, maybe more.


So are there any 20 hp 350 CC jet skis on the market? In googling this subject I found a 7 hp powered kayak- Tech Specs β€” Mokai. The engine and pump weighs 50 lbs and is based on a 211 cc engine. But it sure wouldn't plane a 10' RIB.



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Old 10-07-2018, 10:13 AM   #10
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Also, for your information, SBT carries a huge selection of remanufactured jet ski engines and systems.

Will be interested in seeing how your conversion works as we are strong proponents of jet RIBS.

Who or what is SBT
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Old 10-07-2018, 10:43 AM   #11
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Kawasaki used to make their "stand-up" skis that were much smaller than modern skis. I think they were two cylinder two strokes. Probably not in production anymore, but nowhere near 1.5liter.

Look up old stuff.
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Old 10-07-2018, 10:46 AM   #12
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I really want one of these tiny 10’ mini aluminum jet boats. Looks like so much fun!


https://youtu.be/4n3PJqsXHKE
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Old 10-07-2018, 11:03 AM   #13
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I really want one of these tiny 10’ mini aluminum jet boats. Looks like so much fun!


https://youtu.be/4n3PJqsXHKE

What could possibly go wrong? Hopefully natural selection which seems inevitable, will be quick.

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Old 10-07-2018, 11:17 AM   #14
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Why not an outboard like tens of thousands of workhorse dinghies all over the world?


There were jet pump based RIBs built but I think they were all over 10 ft.
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Old 10-07-2018, 11:35 AM   #15
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In the early 90's there was a 10' Yamaha powered jet "boat" called Jet n Cat. You can google the name to see photos. They worked well but were ahead of their time. I had one of the 2 original Yamaha built units that were imported for market research. The design is heavy, 3 person capable, with storage. They had a removable transom board that allowed for wet or dry operator / passenger area.
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Old 10-07-2018, 12:07 PM   #16
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The smallest jet drive readily available will be way too much power for a 10' dinghy, and much heavier than a comparable outboard.
People put built up V-8s in old VW Beetles.
My son put a juiced up Cummins 6BT in a Chevy s-10 pickup.
What about the Hellcat?
There is always the quest for more power.
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Old 10-07-2018, 12:17 PM   #17
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People put built up V-8s in old VW Beetles.
My son put a juiced up Cummins 6BT in a Chevy s-10 pickup.
What about the Hellcat?
There is always the quest for more power.
A 6BT in an S10? I have got to see that. I have a 6BT in a 99 F350 and absolutely love it.

I agree, no such thing as too much power.
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Old 10-07-2018, 12:57 PM   #18
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Bayliner used to make a little jet boat called the JAZZ
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Old 10-07-2018, 01:01 PM   #19
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Ski, you are right. Apparently Kawasaki invented the term stand up jet ski and sold them with 300-400 cc engines in the late 70s and 80s. That would be a good choice to find a junker and rebuild the drive to use on a RIB. Will be heavy though.



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Old 10-07-2018, 01:02 PM   #20
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I love my WhisperJet, but truly hated a Nautica RibJet I had previously. Squirrelly low speed handling, 1000 rpm just to maneuver, noisy as hell - this is not a good application for that type of propulsion.
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