Glen-L.com

Hi All
After building the Squirt with the 750 Kawasiki in it I really have a feaver for this type of power. It is so much simpler than the big chevy with prop and rudder. So I have purchased the study plan for the Barrell Back here. I'd like some input on placing a jet system in this boat.
I am looking on Ebay for a Kawasiki 1200 before 2006 as they seem resonable. and put out quite a bit of horse power. Not sure this will be enough to push this size boat.
what do you all think?

Thanks

David Streeter

here's a link to the Squirt Build
http://picasaweb.google.com/streeter.da ... directlink

IMHO, the barrel back hull is too flat to work well as a jet.

But I've been wrong before

Exactly my thought.

That pump is going to be more of an air compressor than a water pump!

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

I am aware that there is a pretty flat bottom on the plan for the boat. The Squirt has the same flat bottom yet I have built it with a jet ski bottom grafted right into it and it pumps very well. Hell it goes 50 mph. That's the whole thing. You build a real light weight hull and it doesn't take that much to power it. If the last two feet of the boat is on the water it's going to suck it in and blow it out. Seems to me all I need is to be sure I have enough power to push it fast enough.

Thanks

David Streeter

based on the info on the Glen-l site the squirt hull is aprox 120lbs while the barrel back hull is aprox 875lbs. Thats just the bare hull. How much HP does the motor you are thinking about have? What speed are you hoping to get with the barrel back?

based on the info on the Glen-l site the squirt hull is aprox 120lbs while the barrel back hull is aprox 875lbs. Thats just the bare hull. How much HP does the motor you are thinking about have? What speed are you hoping to get with the barrel back?

That's the same info I am looking at.
I figure that the Squirt is well overpowered as TM here has I belive a 550 or maybe even less in his Squirt and it performs quite well.
Now I am no engineer so how much HP I need to push the Barrell Back, I don't know. That's the reason for my post here. I have been serching for a damaged jet sky with a 1200 to 1500 cc in it. I am leaning toward the 1500 as more is always better in my mind.
I have noticed that after 2006 models the turbos are installed on these engins and they are really powerfull but also real expensive.
So I am looking for earlier than 2006 mainly because of the cost.
Rambleing here a little as you can tell, but I hope I answered the question.

Thanks

David Streeter

David, I think it could be a really cool project. Are you thinking Jet ski or one of the Jet boat drives for the boat?

David, I think it could be a really cool project. Are you thinking Jet ski or one of the Jet boat drives for the boat?

I'am thinking Jet Ski. These things are well powered for their size and It is not unusual for them to weigh 900 to 1200 pounds and go 60 MPH.

45 or 50 MPH is enough for me and my wife and if it's up to her 25 would be tops.
The thing that I like is the ease that the jet ski hull can be molded into a wood hull and with it comes all the properly aligned muonting hardware, engine, pump etc. Another prime interest is the facr that I live on Charlotte Harbor. Now this is a beautifull place and has large expanses of open water but an awfully lot of it is extreamly shallow. My first year here I don't even want to tell you how many props I bought.

I was out in a Yahama 230 jet boat the other day that weighs over 3,500 pounds.
It had twin 1500 cc motors it it and it screemed.
That being the case I am looking for some one to confirm my thoughts on using this power option.

Thanks

David Streeter

The effective thrust of a jet drive can be decieving, and, well, a complicated mess to calculate. Without knowing the swept area of the impeller you are looking at, it's virtually impossible to give you a decent answer. With any given boat the basic static thrust numbers mean, well, basically nothing. That being what it is, you can see the advantage of a FSJ's larger impeller over a PWC's whimpy 140-155 mm impeller by looking at the formula for BST.

. ((water density * impeller efficiency)*(Flow Rate squared))
Bst=--------------------------------------------------------------------- * (Choke Ratio-1)
. Inlet area in Sq In

A small change in impeller flow rate makes a large change in thrust. The Yamaha's dual 155mm impellers and 320 hp are about what it takes to move that sort of weight in the 48-51 mph range.

In the case of a single pump, I don't see how the 155mm impeller can move enough water to get 1/2 ton of boat moving well. With waterjet drive, mass(volume) equals acceleration, velocity of the waterstream equals speed. Again, without some reliable data on the impeller flow rate, or at least something to make an educated guess from (like swept area), it is impossible for me to come up with good data. There is bloody little info of PWC impellers!

1200# jet skis doing a GPS 60 MPH are not all that common, at least under 10,000$ The kid's Kaw ultra 260x just nudges 66 gps with me and a border collie on it. (Don't ask, dog likes to go everywhere with me.) The 260x generates right at 1600 lbs of peak thrust. By comparison, the example FSJ with 320 HP in a C impeller is going to be in the 9330 lb range, all as a result of the increased volume.

I guess if this exercise in A.D.D. saturated rambling has a point, it would be that IMNHO the PWC pump doesn't have the MFE to propel a 1000# hull at much beyond displacement speeds. The Barrel back's bottom could easily be modified to accommodate a FSJ, but I am not sure where one would begin trying to reestablish a proper Cg. Without moving the motor forward to the original location, the weight of a pump, and small v8 would make her stern heavy.

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

I'm thinking about a jet ski powered Klondike. Any thoughts?

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Isn't it amazing!! The person that never has the fortitude to pursue his own dreams, will be the first to try and discourage you from pursuing yours.

well all I can say is it sure would be slow

Maybe for loiter propulsion... or a firehose pump.

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

David,

I haven't posted in a while, but I saw your thread and thought I'd throw in my 2 cents worth...

While there are all kinds of ways to predict performance, (and things like bottom configuration have a lot to do with top speed) a simple way to make a SWAG (what us engineers call a "scientific wild ass guess") on performance is the ratio of LOADED weight (not hull weight) to shaft horsepower. You are correct, my jet squirt is also scary fast, and using her as a data point, my hull, engine, drive train, battery and fuel (the big players in the weigth game) come out to around 400 pounds, compared to the 120 lb hull weight. With a 250 lb passenger load (me at 165 and a couple of ~50 lb kids) this gives me a total displacement of somewhere around 650 lb. My Kawa 550 puts out 36 hp. This gives a ratio of 650/36 or around 18 lb/hp. The boat will do about 45 MPH with this loading. As a second data point, my big cruiser (a 27 ft Regal) has a loaded weight of about 6800 lb, with a 340 HP Volvo Duoprop IO drive. She will top out at right around 50 MPH at a weight to power ratio of 20. Same ball park.

OK, the barrelback has a hull weight of 875 (lets' call it 900 for round numbers). Engine and drive train will probably be around a couple of hundred pounds. Figure 50 lb for a battery, 30 gallons of fuel at 6 pounds/gallon adds a couple of hundred more, and you will want a passenger and gear loading of at least 600 lb. Call it a total displacement of 2000 lb. Using that 20 lb/hp number says you will need at least 100 HP to get decent performance. Given the "back of the envelope" nature of this calculation, I'd give that at least a 40% margin. If I was doing this project, I'd look for something in the 150HP range...

Peace,

TRM

after a certain point performance is not linear in nature. The more weight you have to move or the faster you want to go the more power you need exponentially.

I'm not so sure he will get 50mph out of a barrel back with only 150HP. Mark Bronkalla's Riviera(not the same baot but simular) has something in the neighbourhood of 300+ ponies and it can barely do 50mph (if I memory is correct) Everything I have always read put jets as being less efficient then prop driven boats. So again that would lead me to think 150HP might be a tad low to get 50mph out of it.

I get 39 mph from about 115 shaft hp. You need about twice the hp to get to 50. Jets are not as efficient as a prop. So, probably at least 250 hp.

Bill

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