How do you account for more HP with a jet?

[ZmOz]

I'm in the market for a different boat...and I'll most likely be getting something from the '70s that has a big V8. I'm leaning more towards jets because there are no gears to crap out. I know that if you have a boat with a prop...you can just change the prop if you are making more HP to keep the RPMs where they should be. How do you do it with a jet? Do they make different impellers or something?

 

[Link]

Re: How do you account for more HP with a jet?

All Jets are a compermize..just depends on what<br />you are looking for.. SS Impellers add to performance. but won't even compare to a prop! With the same HP on the motor!<br />Link

 

[Hasbeen]

Re: How do you account for more HP with a jet?

Id like to hear the people with big motors and jets tell about how much fuel they burn in a weekend with the family towing tubes and skiing! How about maybe 50 gals.<br /><br />Hasbeen

 

[Link]

Re: How do you account for more HP with a jet?

Hasbeen <br />I think most people really don't know how bad<br />pumps perform! I run a pump because it fits my<br />boating needs. How ever I have the lower unit<br />for my small 90HP also and have done the math!<br />They say that you only lose about 1/3 of the power<br />but that is just plain crapola! It's closer to<br />50% Right at 49% Top in speed is the biggest factor. Now I've been told this summer that they<br />have a new pump out that they claim only has a<br />12% loss in power.. I would double that to 25%<br />at least. But I haven't seen it<br />50 gallons for a 17ft sled pulling tubes for two<br />days ... on a good weekend

 

[kev_alaska]

Re: How do you account for more HP with a jet?

People who choose to go to a jet for wakeboarding or skiing are doing so for a couple reasons. 1. You can travel in as little as 6" of water. 2. There is no prop to avoid while picking someone up or to get a rope wrapped around. Most people using a jet here are owners of multiuse boats. Occasional lake or salt water use with the majority of use coming on shallow rivers and streams. Your useable range for your boat is about doubled with a jet unit, either inboard or outboard. <br /><br />It is not often that you pull someone at 70 MPH, so the horsepower that you lose is not a major issue. Inboard jets get better gas mileage than a comparable outboard, so lots of time it is a wash. Different configurations for different uses. My riverboat will run a steady 50 MPH, do I go that fast? Very rarely, and then only on a major river where my visabity around the next corner is unobstructed. <br /><br />You can change impellers on a jet to change your max RPM, but most people just use the throttle to adjust speed. If you want a jet, and it fits your useage, don't let others' predjuices get in your way.

 

[ZmOz]

Re: How do you account for more HP with a jet?

I know there are some disadvantages to a jet...but because I'm going for an old boat I think that is going to be the most reliable for me. As for gas mileage...with my old outboard I easily used 20 gallons of gas in one day - that's without pulling anyone, just rides up and down the river, and I was parked most of the time! Even if the mileage was the same, with the outboard gas works out to about $2.50 a gallon (premium with oil) and with an inboard I can use $1.95 regular and nothing else. Jet's may need alot of work and HP to get up to high speeds...but for the 50-70mph range I'm looking for they can do that just fine with a stock 454 or 460. (the engine I am looking for)

 

[Hasbeen]

Re: How do you account for more HP with a jet?

Like I said in a previous post, no one can influence you much when it comes to buying a boat, a car or much of anything else, You just eye over what you read in the forums, look at boats, find what you like for your needs and buy it! I think we mostly learn buy our own mistakes then do something different the next time! I probably wouldnt like what you would buy, and you wouldnt like my choice1 Thats what makes the world turn! Like I said before, We have an 18' dual console bass boat, (Its esentually an 18' two seater boat) most of our family thinks we are nuts as we really cant take many people comfortably for a boat ride, but we like the boat and we are the people that use it! Our car is a two seater also, (Mazda RX/7) We just like sporty things, So sue me!!!<br />If you like it, BUY IT!!!!<br /><br />Hasbeen

 

[chris in va]

Re: How do you account for more HP with a jet?

I watched a hopped-up older jetboat get on it the other day from a dead stop. The thing that suprised me the most was how slow it was, even with that huge 100' rooster tail and 454 V8 roaring. In comparison, a guy with what sounded like a 350 and sterndrive was much quicker up to speed.<br /><br />Not as dramatic, but more practical?

 

[kev_alaska]

Re: How do you account for more HP with a jet?

Chris in Va, you must have seen a jet boat that is set up for show and not to use. My aluminum jet boat can go from a dead stop to full step in about two boat lengths. No rooster tail though, we prefer to have the energy go into the water, rather than spraying sightseers...

 

[vidar]

Re: How do you account for more HP with a jet?

it does not matter were the water goes after it has left the nozzel....the pushing force is created by the accelration of water in the nozzel..we mfg passenger cats w 2 6000 hp gas turbines and the water was ejected 9 feet above the sea. they had underwater foils 23meters long and top speed of 50 miles fully loaded...cool stuff...

 

[chilifriedpork]

Re: How do you account for more HP with a jet?

I never knew that it was the speed at which the water exits the nozzle that determains the "power". Would it not help at all if the jet of water produced, was directed towards the water and would be like a backing?<br /><br />I'm just wondering because I have seen boats that I thought were all trimmed wrong, but still went fairly good, and have seen the boats with very little ruste. (jet boats I mean)

 

[Hasbeen]

Re: How do you account for more HP with a jet?

Here on the lake where I live There are some river racing jet boats that throw rooster tails I would guess to be 50 to 75 yards! They do close to 100 MPH! From up on the hill where I live Its an awesome sight!! Would make a great picture!<br /><br />Hasbeen

 

[vidar]

Re: How do you account for more HP with a jet?

you can see it like a "recoil" force...like a rifle pushing out a bullit (of water) after it has left the muzzel the bullit (water) contains energy (kinetic) iin same amount as recoil (pushing force. the lower effiency of jet iis caused by friction of water in pump/nozzel..

 

[chilifriedpork]

Re: How do you account for more HP with a jet?

I am amazed! I thought it had something to do with it hitting the water. <br /><br />What about the watter being sucked in(impeller intake)? Does that create a negative force? or do you need a nozzle that increases water velocity to get some actual force happening?<br /><br />What about a jet airplain? I assume it uses the velocity of the air being propelled from the turbine to fly. <br /><br />Could it be true that with water being heavier and all, it will produce more of a force with the same RPM's at the impeller compared to air?<br /><br />Boy, physics all over again (I still gotta take Ph.12!)

 

[rodbolt]

Re: How do you account for more HP with a jet?

Hello<br /> 50 galoons on a weekend??. my friend Kirby, his jet boat had a lightly modified 454 with a berkly pump on a 19 ft checkmate. we could burn 24 gallons of gas in about 45 minutes max time at playing speed was 2 hours for both 12 gallon tanks.we found out that a 454 in a boat that only had 24 gallons of gas is almost useless. we spent a lot of time heading back to the fuel docks. but the advice you have been given is sound. look at what you intend to do with the boat and buy what fits you not what is popular .<br /> Good luck and keep posting

 

[fishguy]

Re: How do you account for more HP with a jet?

Going back up a couple posts... To the "how do you move forward if you're not thrusting 'against' anything" thing...<br /><br />It's kind of like a firehose, or garden hose for that matter. It doesn't matter it the hose is spraying against anything, it's that the water being forced out one way causes the hose nozzle to be forced the opposite direction.<br />I remember my son asking me a long time ago....What good does a rocket engine do, if there's no air to push against in space? Umm...Uhhh....Thank God for the Internet

 

[Mike NZ]

Re: How do you account for more HP with a jet?

I switched from a 19' Maxum to a 16' Jet and I'm totally in love with Jets. We take on a river bar that has claimed a lot of lives and after grounding the Maxum a few times went to a jet. We also contend with hard breaking surf so we have to stop at times in the breakers to get in time with the waves then back on to full power when the light goes green. On my last trip I was cruising in at 24 kts and the bar sucked dry 15 ft in front of us, a small wave moistened the sand and bang, the boat hit the dry, skimmed over and kept going. Jets are amazing and are the 4WDs of the water.