Modification of SkiKing design

Designs for inboard or outboard power

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slowcarguy
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Modification of SkiKing design

Postby slowcarguy » Wed May 09, 2007 9:27 am

I've bought the plans, I love the look and I know I can build it.
I want to change 2 things about the design. I want to purchase a 2.5l opposing 4 from a 1998+ Legacy/Forrester. They have about 160 hp and tq and they're compact. Wider than they are tall...It'll fit nicely under the "motor box" I plan on using a stand alone FI unit from www.sdsefi.com and run a pressurized fuel system. I've had experience with FI and would love to have the power and fuel economy of such.

Secondly, I realize its original design was an I/O but I'd love to run a jet drive. I've helped a friend fully rebuild his 79 jetboat and had a blast on it. I feel the lack of a prop will be beneficial to us in the water(safety from no prop) and it'll do well when I go out on the Colorado in more shallow waters.

Imput on such a swap? I think mid-ship engine and a driveshaft to jet drive will work out nicely but I was hoping to have some imput from some seasoned builders. I don't see it compromising the structural integrity of the transom.


Thanks in advance

~Alex Jones
I'm on my first boat! Ski King with the economy of a 4cyl Sooby motor.

slowcarguy
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Will a biger jet-ski work

Postby slowcarguy » Wed May 09, 2007 11:53 am

I am referring to the jetdrive itself from say a Kawasaki 750 or larger.(I don't know how big those olfer ones come) I'd guess that they're designed to run at higher RPMs similar to the Subaru motor but the newer motor may have 75 more HP. Will this be enough to move a 15' boat?

~Alex Jones
I'm on my first boat! Ski King with the economy of a 4cyl Sooby motor.

Nova SS
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Postby Nova SS » Wed May 09, 2007 12:42 pm

you need to find out if the motor you want to convert to marine use actually has items such as marine exhaust manifolds etc avialable for it...if not all of the parts will need to be custom fabricated and of course will then have a custom price... :D

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Caber-Feidh
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Postby Caber-Feidh » Wed May 09, 2007 2:06 pm

Great engine!

My bro built a Universal uh-18spw using the EJ22 subaru motor. The pwr/weight is spectacular!

Marinize what? There is nothing to marinize!

The starter is a sealed unit on late EFi engines.
Fuel pump is in tank.
EFI eliminates the carb, no vapor probs.
Exh is tubular steel, not a cast manifold; cut, patch, and weld to fit. Inject water past y pipe, or setup for dry tubes.
Discrete multicoil coil ignition eliminates distributor.

Cooling would take some work, the ECU wouldn't like the engine running cold. Likely it would be better to setup a closed system.

A Delco marine unit in a home made mount fixes the alternator.

Only real difficulties would be in coupling the engine to the pump, and finding a pump that worked properly in the proper powerband.

jake1.11
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Postby jake1.11 » Thu May 10, 2007 5:30 pm

Alex,

Why not go with a jet ski conversion. There are some fairly high horsepower jet skis on the market now that should push a boat like the ski king.

Jake

slowcarguy
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yes

Postby slowcarguy » Thu May 10, 2007 10:02 pm

I was thinking the same thing. I don't know how much power lets say a 750cc 2-stroke jetski has but i assume it's in the low 100's. I was reading about how one of the members even picked up a manual for the 1980's jetski and saw it produced 350lbs of thrust. Is that enough to move a hull rated at 700lbs?

Thanks for the imput, I think it can work in the budget because those used berkleys and the like seem to be a little pricey.

~Alex Jones
I'm on my first boat! Ski King with the economy of a 4cyl Sooby motor.

Dwain the ski king
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Postby Dwain the ski king » Thu May 10, 2007 10:21 pm

Yes you can use a jet...An aquaitence near the Grand Coulee dam has an Audeen(16', almost the same size as the Ski King) with a pump in it and it's powered by a 318 Chrysler(2 bbl.180hp) motor. Don't know if the Soobie can make the torque required by a jet pump, but the pump Manufacturers could probably help you out there. I have some where in my pictures the installation of that pump the fellow sent to me. If interested I'll try to send them to you.....Dwain, the Ski King....at---dbcolton@ccwebster.net.....or call BR-549-chuckle-snork.....

terrymc
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Postby terrymc » Fri May 11, 2007 7:24 am

Alex,

I'm Terry, the guy with the Kawasaki manual, and well along on a jet powered squirt.

My 1987 Kawa 550 puts out 36 HP, and its associated pump generates 350 lb of thrust. I don't have the specs for a 750, but just scaling up on displacement tells me it would be in the 55-60 HP range. Low end of the Ski King range, but certainly do-able.

Old Kawa's are 2-strokes. Nothing wrong with that, but be advised that many lakes no longer allow 2-stroke motors. If you go the jet-ski engine route, I'd look to find a newer 4-stroke variety - they put out on the order of 100 HP+, of course they will be more expensive. Inboards, unlike outboards, do not have a max HP rating set by the USCG. Thus you can legally go higher that the Glen-l recommended engine range.

Newer jet skis also have made provision for a reverse "gear" - actually a bucket that rotates down behind the jet nozzle, much like the arrangement is jet aircraft. Older models (like what is in my Jet Squirt) are direct drive. With the engine running you go forward, to stop you turn off the mill! When the engine is not running, you have no steering capability.

Here's a photo of the pump arrangement in my Squirt:
Image
The pump is on a bracket on the transom. With the longer length of the Ski King this could probably be built into the boat itself. In the Kawa 550, the total drive length is 56 inches from the front of the engine to the jet nozzle. A 750 is a 3 cylinder engine (the 550 is a twin) so I'd add 6" or so in that case. Here's what the overall machinery layout looks like:
Image

Hope this helps. Take a look at your plans, and see if you can come up with an approximate arrangment. Let me know what you come up with.

Peace,

TRM

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Caber-Feidh
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Postby Caber-Feidh » Sat May 12, 2007 6:30 am

Nice work on the squirt! looks like you have a well thought out mechanical config.

I am not too familiar with the squirt design, but from a full size jet standpoint, the pump would need a shoe! Is it just not mounted yet?

slowcarguy
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Found a place

Postby slowcarguy » Wed May 16, 2007 5:56 am

I was in CA this weekend and stopped by a place called Jet Boat Performance and they were very helpful. Upon telling him my engine plan he mentioned that he'd seen some Wankel powered jet boats in his day. One thing to consider is the impeller. For such a relatively low torque motor and high RPM I'd need to have a stock impeller reworked. Most big block jet boats have an A or B cut but he mentioned I'd be looking for one more like a D. It'll allow the engine to reach the higher RPMs necessary to create the power.
Also, they'd be able to machine a PTO for the motor if I was to present a template(Flywheel!)
Recommendations to my design would to move the engine as far back in the boat as possible as opposed to the mid engine design called for in the plans.... I suppose I'll have to rearrange the rear seating.

~just an update
-I think I will order my lumber this week.

~Alex
I'm on my first boat! Ski King with the economy of a 4cyl Sooby motor.

Dwain the ski king
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Postby Dwain the ski king » Fri May 18, 2007 8:49 pm

Don't move the engine back to far, it will upset the balance of the hull. They are designed for mid engine, with weight of the pump at the back I'd say keep the engine in it's proper spot. Otherwise it will take off nose high like an I/O setup....The best part about using a pump is you set the motor level, instead of a 14-16 degree angle...Like I said E-M Rux and get his views.......Dwain, the Ski King..........


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