# New guy with jet Jon ?



## Fordracing2105 (Dec 29, 2013)

Hey guys I have some questions about building a jet ski Jon boat. The boat I have now is a 1660 with a flat bottom. Will this haul work? Second is the boats only rated for a 40hp. Is there gonna be any problems with the dnr with it being over powered? I looked for awhile but didn't find anything about an over powered boat. I'm not doing this for it to be fast. I want to be able to jump up on plane in short distances and run shallow.


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## PSG-1 (Dec 29, 2013)

Horsepower ratings for outboards VS horsepower for inboard jet ski engines is comparing apples to oranges. For example, a 50 HP Mercury 2 stroke weighs 205 lbs. A 100 HP 2 stroke Tigershark jet ski engine weighs less than that. 

Also, HP ratings for outboards are taking into account that the weight is entirely on the transom, and they must also figure in the lateral forces and torque that would result from running that engine. With an inboard jet, the weight is farther forward, and there is virtually zero torque being applied to the transom.

One other thing, is that since a jet drive is less efficient at converting HP to torque, a to achieve the same amount of thrust/torque as a given HP outboard, with the inboard jet, you almost have to double the HP.

My boat is a Duracraft 1648, with a 160 HP Yamaha MR-1 engine. No problems with DNR, in fact, they think it's an awesome boat. Also, I went through a company in Florida "BUC" and had an evaluation done on the boat, and got it insured.

So, to sum it up, you shouldn't have any issues regarding power.

And if jumping on plane quickly in shallow water is your objective, check out this video:

https://www.youtube.com/watch?v=0510oeVQoLM


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## Fordracing2105 (Dec 29, 2013)

That's a pretty cool video. I knew that a prop compared to jet was fair amount different but I had no clue in board to outboard was that much.


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## PSG-1 (Dec 29, 2013)

Yeah, it's a considerable amount of difference. I will say that an inboard jet IS more efficient than an outboard jet. The OB jet has to draw the water up, then turn it 90 degrees. Any time you make a 90 degree bend in plumbing, you lose flow, and the OB jet is no different. The inboard jet draws it up at a slight angle, and the exit is in a straight line flow, which means it is somewhat more efficient than the OB jet, but I'm not sure by what percentage.


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## semojetman (Dec 29, 2013)

I seen the specifications on a website.
I dont know if it was set in stone but it was the typical 30% loss for the outboard jet and they stated 10% loss for the inboard jet. Not sure if these numbers are completley acurate but I feel they are close.


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## Ranchero50 (Dec 30, 2013)

What is your donor power coming from?

My '95 Seadoo Xp's 717 was rated at 85 hp, the pump is rated at 30 hp. My '92 1448MV hull as an outboard jon boat was rated for 25 hp on the data plate. 

Being that you reconfigured the hull for an I/B jet your data plate is null and void so you should be ok with any knowledgeable DNR guy. Of course I also recommend talking to you PA DNR and checking their online regulations. Laws don't always use common sense.

The Coast Guards HP guidelines also make for good reading.


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## Fordracing2105 (Dec 30, 2013)

Thanks for the info guys. I was thinking some where in the 1000cc engine size. I guess this isn't gonna have the hp I thought it was gonna have. Does any one know what the hp rating is at the pump on a 1000 or 1200 yamaha.


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## PSG-1 (Dec 30, 2013)

I'd say somewhere between 45-60 HP at the prop. No, it won't be the amount of horsepower you were hoping for, but it will definitely be equivalent performance to having the max size outboard for your boat.


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## Ranchero50 (Dec 30, 2013)

Ditto, you should be more than fine. I'm stretched out to 17'6" x 48" bottom running mid 40's at around 800 lbs loaded. A 60" bottom is going to take more umph to get it moving but it should also pop onto plane easier.


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## PSG-1 (Dec 30, 2013)

And will require less draft at static flow, meaning you can float over shallower areas that you could with a narrower boat of that same length.


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## Fordracing2105 (Dec 30, 2013)

Do you think there will be any problem with the haul of the boat being flat and 60" wide?


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## PSG-1 (Dec 30, 2013)

Is it a _completely_ flat bottom? Or is there a slight V? My boat has a 10 degree deadrise, and performs well on flat water to small chop, but in moderate to heavy chop, it cavitates. A completely flat bottom would tend to cavitate a lot more.

Ranchero50 built a 'spoon' into the hull of his boat to eliminate the issue of cavitation with a flat bottom, and the spoon does work, if you look at most jetboats, they will have this incorporated into their hull.


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## Fordracing2105 (Dec 30, 2013)

There isn't any v. It's completely flat except for the ribs that run front to back.


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## PSG-1 (Dec 31, 2013)

Then you will either need to incorporate a spoon into your hull, or form a 'delta pad' to sit the pump lower in the water. 



Also, take out the center strake for at least 3 ft in front of the pump, because this will most assuredly cause issues with cavitation. 
Cut along either side of that center "V" and replace it with a piece of 1/4" aluminum flat bar, wide, and long enough to cover the cut-out area and weld a continuous seam around that piece.


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## Ranchero50 (Dec 31, 2013)

Ditto, you'll need to spoon it or it'll only go about 15 mph before it sucks air.

Post up some pics of you hull and what you want it to do.

Here's mine:







And a shot of the spoon for reference.


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## Fordracing2105 (Dec 31, 2013)

Ok I'll get some pics up tomorrow. As for what I want to do with it or lay it out not really sure yet. Still in the planning stage yet I guess.


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## PSG-1 (Dec 31, 2013)

It's good that you're in the planning stage, as it's much easier to build something correctly to begin with, rather than having to go back and modify it later, that can really be a PITA. Take it from someone who's dealt with enough PITA, I should be running a bread factory, not a welding shop! LOL


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## Fordracing2105 (Jan 2, 2014)

Well I didn't have time to get pics and post and this is the only one I have right now.


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## PSG-1 (Jan 2, 2014)

It's definitely a 'blank canvas' so to speak!

I think if you do some reading on Ranchero's build, and some reading on my build, you should be able to gather enough info to help you through your project with minimal headaches.


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## Fordracing2105 (Jan 2, 2014)

I have been reading up on Rancheros build and it's pretty awsome. Still not through it yet though. Right now all my boat really has is a side console and a diamond tread floor it's pretty plain and I want to keep it that way. It I change this boat around ill probly go with a center console up against the front deck. The two seats in the back will stay depending in where the motor falls. There will be a hatch or two in the front deck for life vest and what not.


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## Ranchero50 (Jan 3, 2014)

Sounds good. If you are going to play on the Susky I'd also recommend looking into the UHMW for the bottom.


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## Fordracing2105 (Jan 4, 2014)

I have been thinking about the UHMW. Well I have some more builds to read and a lot to think about till next winter. I have to finish another boat before I start this one. Thanks for all the help guys. I'm sure there will be a lot of questions to come.


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## airbornemike (Jan 13, 2014)

I wish a manufacturer would start producing a boat like this, love these builds.


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## PSG-1 (Jan 14, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=338587#p338587 said:


> airbornemike » Yesterday, 20:13[/url]"]I wish a manufacturer would start producing a boat like this, love these builds.



*
I wish there were some people willing to spend the money to have these boats built, because that's what I'd be doing right now, sending jetboats out the door, and putting people on the water!*

I just can't figure out why this potential business seems so hard to get off the ground, and get something going. There's a market where people with more money than sense are willing to spend $100K on a customized chopper from Jesse James, or that arrogant, abusive, loud-mouthed walrus-looking POS Paul Sr from OCC. 

But, when people hear a price of $2K for labor to install the engine and pump, or a price of $5K for labor to have it turn-key ready, they start hemming and hawing about "my pockets aren't that deep" To which, my sarcastic response is "this boat can run in water shallower than the average pants pocket, so your pockets ARE that deep, you just don't know it" (Hey, I can be arrogant, too, especially when people jerk me around like they're dealing with some schmuck at a used car dealership)

Seems that people just don't understand that performance costs money. It's 100 dollars per horsepower. Anyone who doesn't think so, go price an outboard motor, and see if that isn't just about right. Also, when you have custom work done, it costs money to have a job done right.

Had one guy that wanted a price, and I gave him a price. Then he said he found somebody local to do it for 600 dollars labor. Yeah, good luck with that one, pal! Can't wait to see how THAT works out for him! There will probably be a maiden voyage, and that's all we'll see. Then he will likely have issues with the cheap, substandard work. And if he contacts me back, there will be no need for me to say "I told you so" When you're as right as I am, there's no need to say a word, just feel vindicated when your prediction turns out correctly. And I can predict that a jetboat built for 600 dollars labor is going to have more issues than a publisher's clearing house lifetime subscription.

Sorry, but I didn't get an AWS certification to work for crackhead prices, or to do sub-standard half-a$$ work for someone who wants something for nothing, and is willing to cut corners. If they hire me to build a jetboat, it WILL be built to NMMA/ABYC/USCG standards, or they can take it somewhere else and have goober the drunken mechanic slap some chicken-crap together for them. Then, when it tears up, they can both stand around and scratch their rear end in confusion like a couple of chimpanzees, trying to figure out why JB welding an engine into a boat, or gluing the pump in with chewed bubble gum, isn't working out for them.

Anyhow, out of the 50 or so people who have contacted me about having a jetboat built, there's about 3 or 4 right now that did NOT balk at my prices. Obviously, they understand that performance and quality cost money, and in a case like that, I'm more than willing to work with them any way I can. Over the past month, these 3 or 4 people have said they're ready to have one built, and I'm hoping to hear from them soon. 

If I DO get lucky enough to take on one or more of these projects, I will definitely post them here on the forum, so people can see the progress.

Holding out hope........


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## gotasquirt (Jan 15, 2014)

it sure is funny the guys that say its easy to build one and they do it and use one the river once and then you see on craigs list the next week for sale and you them about the performance and they tell you it works ok if you know what I mean lol will


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## PSG-1 (Jan 15, 2014)

That's EXACTLY what I was referring to, gotasquirt! (And BTW, I really, really, like that little 10' jetboat of yours, this is what I want to build for my next jetboat.)

As for building a jet john, anybody can slap some parts together and make something run for an hour or two. But the REAL test is the test of time. How many of these boats are still running 2 or 3 years later? 

I know there's several of us on this board who have built jet johns that have stood the test of time, such as you, Ranchero, Scubapro, Painlesstom, and myself. And if you look through some of our threads, we've all had our own issues with trial and error, finding out what works and what doesn't. You only gain that through experience and testing.

So, some shadetree goober that has never built one, that says they can do it for a case of beer and some cigs for labor costs, be my guest LMFAO!! If I see 'em broke down, I'll give them a tow back to the hill with my jetboat...on plane (I have done this before with towing, particularly across shallow areas, my boat has enough power to do it, too)


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## Ranchero50 (Jan 15, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=338704#p338704 said:


> PSG-1 » Today, 09:02[/url]"]As for building a jet john, anybody can slap some parts together and make something run for an hour or two. But the REAL test is the test of time. How many of these boats are still running 2 or 3 years later?



Mine's still ticking although I'll be honest and admit that I welded most of the tunnel with mud dobber nests in the argon hose. #-o


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## PSG-1 (Jan 16, 2014)

LOL @ the obstructed argon hose! I bet you played hell trying to keep the puddle shielded with argon, trying to weld. :shock: 

That said, your build is a fine example of a jetboat that was properly built, and has stood the test of time. And like me, you also went through a little trial and error to get everything fine-tuned. All of us that have built these boats have been there, done that. I probably have as much time in testing/trial/error/back to the drawing board, as I do for the actual build!

But if the time should come for me to build a boat for someone else, I know there is no room for trial and error, it has to be done right, the first time. Knowing that, if I were to do a build, as I said before, it would be done using my boat as a prototype, and built to the same type of specs, because this setup has proven itself to be reliable and durable. It's the only way I would be able to do it and be able to send it out the door with confidence.


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## zacksimpson (Jan 25, 2014)

PSG-1, when my VA disability comes through, I might have to take you up on a turn key rig. I'd even help out with it just so when it's done I'll have a better idea of how to fix it if it ever has trouble. I'm very intrigued by these jet jons, I think they'd be an awesome solution for me and my buddies where we fish and hunt (plus they're just plain cool).


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## PSG-1 (Jan 25, 2014)

Zack, that sounds like a plan to me! 8) By all means, if you want to get your hands dirty and take part in the build, that would definitely help reduce labor costs. Not to mention giving you a chance to see some of the idiosyncrasies involved, so you would know how to tackle any problems that may aries in the future. 

99.99% guarantee that any future issue that may arise, wouldn't involve any kind of structural failure, most likely it'll be mechanical issues, like having to replace an impeller or something like that.


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## Fordracing2105 (Jan 9, 2015)

Well it's been cold out and I have been thinking about this boat again. I have another question about it again. I was wondering if I would still have to make a spoon to run an outboard jet.


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## PSG-1 (Jan 9, 2015)

As far as I know, you don't need any kind of spoon to run an outboard jet. Some boats have a tunnel modification which allows you to set the engine a little higher to guarantee clearance of the jet unit as the boat goes across rocks, etc. But again, from my understanding, you can run a jet outboard with a flat bottom with no problems. 

Inboards are different because the water is being drawn in from underneath the boat, where it still has the tendency to form air bubbles, especially from the chines under the hull. As such, they need a spoon to displace the air so that the water flows more efficiently to the intake.


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## dhoganjr (Jan 9, 2015)

Fordracing2105 said:


> Well it's been cold out and I have been thinking about this boat again. I have another question about it again. I was wondering if I would still have to make a spoon to run an outboard jet.



All that is required to run an outboard jet is a clean apron of water coming off the bottom of the hull.

To get the height correct put a straight edge on the bottom of the hull extending out to where it hits the front pin of the shoe (the one that holds the intake grates in). If it cavitates drop it an 1/8 inch and retest it. Most boats can run at this height and should be near the optimal setup. 

The leading edge of the shoe should be higher than the bottom of the hull or it will drag in the water, cutting performance, reducing speed, and causing backspray.


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## Fordracing2105 (Jan 10, 2015)

What about the boat being so wide and flat. The boat has a 60" bottom. I'm also thinking about adding a tunnel and flote pods.


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## dhoganjr (Jan 10, 2015)

I run an 1860 flat bottom, the boat in my sig. If you are going with an outboard I would go max hp and keep it light. The wide bottom will put it on plane faster and keep it on plane a bit longer than a narrower bottom, but will run a bit slower than the narrower bottoms. 

I would try running it without the add-ons first and then decide if you want to add them. A tunnel will provide some protection to the shoe, but will also increase the draft adding the need for float pods. The tunnel also must be designed correctly to feed the pump, so research extensively before cutting.


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## Fordracing2105 (Jan 11, 2015)

Well that makes me feel alittle better about this. I really didn't want to get a different boat I like this one. There won't be much added so it should stay light. I really only wanted a tunnel to help save the jet. The bad is the boat is still only rated for a 40 hp. My old 35 prop does ok I'm hoping a newer 60/40 will do just as good maybe alittle better. That 35hp merc got to be getting tired.


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## dhoganjr (Jan 11, 2015)

A 60/40 should get you 28-30mph with proper setup. They are about the most common size used in Southern Missouri due to the hp restrictions on the Current River. semojetman on here runs one on an 1856 Blazer. They run good as long as you don't overload them.

You will need to build a riser on the transom to get the proper height.


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## Fordracing2105 (Jan 11, 2015)

If I would get in the high 20 for speed that would be great. I think if I do this I'm going to rebuild the transom anyway right now it's just light aluminum sheet and some plywood. I want to get rid of the wood and beef it up alittle.


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