Jetski vs outboard hp per liter

[Mark75H]

PWC guys are always asking why outboards have less hp per liter ... shouldn't they be asking why 250 hp doesn't go 80 mph? :D

[VernG]

Actually for a lot of us, 250+ hp does go 80 mph. My RXP goes 81+ on GPS like many other friends, and my engine is only 1.5 liters. But it is a 4 stroke supercharged engine with 13 lbs boost and a big air to water intercooler. There are quite a few GPRs with 1.3 - 1.4 liter two strokes that are going over 80 mph too ... some with triple pipes are going 85 - 88 mph. Then there are the guys running 18 - 30 lbs boost using big superchargers or turbos and are running in the 90 mph range. There are a few skis that have hit the magic 100 mph mark as well, still using the inefficient jet drive ... one was recorded on video at the Riva Racing sponsored Hydrodrags, and there are a few others. The 100 mph skis are typically GPR hulls with turbocharged Rotax (Sea Doo) 1.5 liter 3 cylinder engines with turbochargers and 20 - 30 lbs boost.

On the other extreme is a basically stock GPR with 1.3 liter two stroke 3 cylinder, 170 hp that went 70 mph ... the owner (David Bunn of NC I think) then pulled the pump off and set it up with a prop and rudder ... and went 104 mph after some fine tuning, gaining 30+ mph by switching to a propeller from a jet pump. There are YouTube videos of all the above if people are interested.

[engineermike]

Hey, Vern!

I, too, have both. I had a turbo RXP producing around 300 hp from a 1.5 liter 4-stroke that ran 83 mph. That was with no hull mods, which are usually worth 2-4 mph (set-back pump and modified rideplate).

I recently purchased a Checkmate Pulsare 2100 with a 300 hp Yamaha with over double the displacement. While the boat, which weighs over 3 times what the ski does, goes 85-87 mph with the same hp, the acceleration is night and day. The PWC jumps out the water and accelerates to 60 mph in under 4 seconds. The boat takes over 4 seconds just to get on plane. The acceleration of the boat is truly yawn-inspiring compared to the ski.

The jet pump is horribly inefficient at speed, but produces tremendous thrust at low speeds because recirculation is non-existent.

Mike

[VernG]

Hey Mike!

Good to see you on here ... my brother had a Pulsare too, although with only a 225 Merc. Ran low 70s and was a very fun boat ... a bit white knuckle at full up trim. Within the family we have had 4 jetboats, 3 bass boats, a Mastercraft, Donzi and Checkmate stern drives, and a 80 mph Eliminator 234 Edge. All fun boats ... the Eliminator was my sister's, great boat ... once up on plane it would run 55 mph with the drive tucked in tight, but as you trimmed out, the hull would lift a lot, and shoot up to 75+, then creep up to 80 mph if you had the water. But my RXP would destroy all of them out of the hole ... I had a little fun with my friend Jerry's STV and Skater, both ran over 100 mph but I would have to do circles in the lake waiting for them to get up to 60 mph. From 60 mph it was a good race until 80 ... then I was done!

[mackeral5]

what do those guys do about a water pump when they convert from jet to prop? transom pickup??

[Mark75H]

OK, make it 85 then :reddevil:

[VernG]

Good question since stock cooling usually uses a bleed off the jet pump. I am not sure what David did, my guess would be the same as yours. He also has run/owned a lot of fast tunnel hull boats and I am sure he is a member here, but don't know his S&F screen name ... he is very open and helpful, if he sees this I am sure he would explain what he did for cooling.

I always thought it would be fun to create a sleeper ... take a good single engine small 'mini jetboat' (15 ft) like a Sea Doo or Tango or whatever, that has 200 - 250 hp motor and jet drive. They typically run 55 - 58 mph stock ... dump the jet drive, install a prop and shaft setup, would likely run 80++ mph and be a huge surprise to a lot of people.

[VernG]

OK, make it 85 then :reddevil:

:cheers::cheers: I get it ... but I have owned and liked two smokes, 4 strokes, boats, skis, etc. No question a tunnel hull outboard is usually the most efficient hp vs speed setup, but its all mechanics. Good hull + most efficient drive system will win every time. Jets are the least efficient, stern drives are better, outboards better yet, and theoretically Arneson/direct drive/surface piercing drive should be the most efficient of all. But not all can be effectively used on different hull types either, so compromises are made. Best use of hp in a boat IMO are the 17 ft hydros that use a simple PWC engine coupled with a shaft/prop setup and will go over 100 mph with 150 hp two stroke engines ... but they only seat one and don't like waves much.

[DoktorC]

OK, make it 85 then :reddevil:

My 1.2L 155hp GPR does 73mph...my 2.6L 225hp SRV runs 93. The funny thing is one is 20' and one is 11' and they are close on weight lol.

The SRV can't do this though:

http://i46.tinypic.com/2mpdk3q.jpg

[Mark75H]

I always thought it would be fun to create a sleeper ... take a good single engine small 'mini jetboat' (15 ft) like a Sea Doo or Tango or whatever, that has 200 - 250 hp motor and jet drive. They typically run 55 - 58 mph stock ... dump the jet drive, install a prop and shaft setup, would likely run 80++ mph and be a huge surprise to a lot of people.

A couple guys have done that. Maybe someone can supply the links to there here on Screamandfly

[mackeral5]

the old school rotax 2 strokes still amaze me from a weight to hp perspective. we've got 2 older skis, the 96gts has a 85hp 717cc runs in the upper 40's, the 97xp has the 110hp 787cc and runs in the mid 50's. these are nothing compared to the newer skis, but I just couldn't see sinking more than a couple thousand in something I have little or no interest in. the wife loves them.....they are fun to play on every once in a while, but burn way more fuel than our boat does....

[VernG]

what do those guys do about a water pump when they convert from jet to prop? transom pickup??

Found this from his thread on Green Hulk (full thread here, its huge 833 posts): http://greenhulk.net/forums/showthread.php?t=47449&highlight=propski

Good day on water... finally got cooling system figured out. It took an electric pump for idle and slow speeds. Now it will pee like this (see pic) even with engine cut off but water pump on. At high speeds, my ram tubes take over and pump auto shuts off at 34 psi (at inlet to manifold).

I think later he switched to a tube on/in the rudder that was mounted behind the propeller and no longer needed the electric pump at idle/low speeds. But the thread is huge and I am not sure of his final cooling setup ...

[powerabout]

The average jet ski operation cant be overloaded like a whole boat so hence the engine can be tuned to a higher state, same goes for a skidoo
Check out the BRP's Etec twin cyl skidoo, more powerful than a larger 3 cyl Etec outboard.
I havn't seen a jet ski with 2 or 3 people skiing behind it and 2 or 3 more on it with eskys...
Jets re for Boeings, rivers in New Zealand and England to France cross channel ferries

[tinker060]

OK, I will line my 153 CUI OB up with a PWC................:D

PWCs and boats are apples and pineapples!

Jon Wright

[baja200merk]

OK, I will line my 153 CUI OB up with a PWC................:D

PWCs and boats are apples and pineapples!

Jon Wright

i only opened this thread because i saw you responded:D:thumbsup:

[JR IN JAX]

The PWC pumps are not very efficient but the PWC engines are. The new Turbo Hondas with their 1500CC powerplants are turning out 250 HP with just a few settings/tweaks and their gas mileage with the inefficient pumps is still 7+ MPG at 50 MPH cruise speed.The powerplant could easily turn out 350 HP with some work.
The same engine with a prop would be hard to beat, efficiency or speed wise.

[DoktorC]

OK, I will line my 153 CUI OB up with a PWC................:D

PWCs and boats are apples and pineapples!

Jon Wright


I'd line my PWC up with your 153cuber any day...as long as I get to pick the location (and duration of the race) :)....see post #9 lol

Comparing your boat to a pwc is more like apples and pine trees!!

[hydrostream1]

Only problem I have with modifiying jet skis is EXPENSIVE.Ive owned several different models and those triple pipes are pricey!I found a 17ft action marine boat with a stock 200 merc and a cheap 28p chopper prop ran 85mph!I found the rig in a local salvage yard years ago.To me, it costs alot of money to modify not to mention questionable reliability,plus the costs of the jetski some 10,000 or more.

[JR IN JAX]

I like my jetski [Honda turbo] like I do my boat. It only needs to modded to be fast enough for it to be fun but relaible enough to go 100 miles from the ramp and back. 60+ on my 'ski is the same as 90+ in my boat and is better than the boat on a winding tight creek.

There are few things as fun as much fun as a good PWC on a warm sunny day.

It is a shame the jet drives aren't more efficient, but they are fun in shallow stumpy water.

[David]

I've lined my 150 HP XR4 SS2000 up against my brother's Yamaha 1100 155 HP Waverunner a couple of times.

Rolling starts from 40+ mph are best for me. Standing starts are embarrassing, but I catch him. Like Doc says, if the distance is short enough, the PWC can't be caught.

[tj309]

A Jet is inherently less efficient than an OB. 2 examples:

1. California jet boats - typically a low profile 18-20' with big ass 454's cranking out like 500HP are lucky to see 80 MPH

2. Mercury makes jet OB motors and if you look at the specs they use a 115 powerhead to get an 80 hp jet.

Anytime you make a conversion like a prop in water turning rotating energy into thrust you are going to loose something. If you restrict that conversion with an intake and extra plumbing like a jet you loose even more. My 2 examples lay it out in real life scenarios - if you really want to go fast jet is not the way to do it.

Another reason is quite evident here - why is there so little talk about jets on a go-fast boat forum?

Case closed.

[VernG]

Jets are inefficient, no question, but I will line up with any single outboard in a race to 80 mph ... the other side to jets is they are quick out of the hole, and on a very small hull (PWC) with 250+ hp, good intake grate and good impeller, they are very hard to beat to 60+ mph. Plus my ski is only 90 cubic inch ...

[Mark75H]

Jets are inefficient, no question, but I will line up with any single outboard in a race to 80 mph ... the other side to jets is they are quick out of the hole, and on a very small hull (PWC) with 250+ hp, good intake grate and good impeller, they are very hard to beat to 60+ mph. Plus my ski is only 90 cubic inch ...

you are on for a race ... I think I can take you with just 60 cubic inches :cheers:

[engineermike]

Sure, there are a few quick accelerating boats out there, but the fact is that 90% of stock 1.2+ liter PWC's will out accelerate 90% of the prop-driven boats. Now, if you want to compare a specially prepared drag boat to a PWC, it would only be fair to compare it to a specially prepared drag ski which have gone 0-60 mph in 2.5 seconds.

Sea-Doo, itself, lists their jet pump efficiency at ~48%, while I believe prop drives can reach 80+%. No one is arguing that jets are more efficient, but the holeshot is where they shine.

[VernG]

Pyro, I boat in Grand Haven, MI area, Spring Lake, Grand River, occasionally Lake MI. The Jerry I mentioned is a friend who lives on Spring Lake, last name is Enten.

I know there are some boats that would beat me to 80 mph ... but they are few and far between. I did not say I would beat every single outboard ... just that I would happily race any of them. I have not been beat yet, but I have not gone to Hardy Dam or other places where the really fast boats hang out. Its funny ... win or lose I usually meet new people and make new friends, EXCEPT for guys in bass boats ... they seem to lack any sense of humor about a jetski outrunning them. I have taken on 100 mph boats from a 60 mph cruise just to see/hear them crank up and outrun me ... but we always meet later to talk boats.

Like Mike said, it depends how each boat/ski is setup. Mine is just an average all-around pump gas setup, but there are some that are setup for drag, and run insane 0 - 60 times and still top out over 80 mph. I would like to see acceleration graphs from some of the fast outboards that show 0 - 80 mph times. All I know is I have not raced a boat that could stay close from idle to 60+ mph, but I would love to run into one that could. No shame in losing, I respect anything that outruns me ...

[WATERWINGS]

On the other extreme is a basically stock GPR with 1.3 liter two stroke 3 cylinder, 170 hp that went 70 mph ... the owner (David Bunn of NC I think) then pulled the pump off and set it up with a prop and rudder ... and went 104 mph after some fine tuning, gaining 30+ mph by switching to a propeller from a jet pump. There are YouTube videos of all the above if people are interested.

David actually went 107 MPH with a little more left, (he thinks maybe 109 MPH)

This was with a STOCK motor NO NITROS.......PROP ONLY.....(I have pics of the set up)

He ran 93 MPH (?) with nitros and the pump.

[VernG]

David actually went 107 MPH with a little more left, (he thinks maybe 109 MPH)

This was with a STOCK motor NO NITROS.......PROP ONLY.....(I have pics of the set up)

He ran 93 MPH (?) with nitros and the pump.

Thanks for the correction, I wanted to make sure I did not exaggerate the speed he achieved. Does David post on S&F? Anything new with the propski? He has not posted on www.greenhulk.net (http://www.greenhulk.net) for awhile.

[WATERWINGS]

Yea, David used to post on here, same screen name as on the green hulk site.

"RUNWME" is his screen name.

I have pics of the setup, and a few videos of it running when he was in the testing stages.

I don't have any of his 100 MPH plus runs but I have seen a few on Utube.

[specboatops]

100 mph on a jet ski :eek::eek::eek::eek: that takes a set of balls i'd assume...........

Chris

[VernG]

Just put 'propski' in the search bar on YouTube and you will find some videos of David's ski ...

Chris, I agree ... 100 mph in a boat is fun, on a jet ski is different ... I am comfortable with 80 - 85, but not sure I would want to go faster on a jet ski either.

Also check out videos from stvdrag225 ... Kenny put a warmed over Merc 2.5 powerhead in his GSXL ... just the sound of the 2.5 coming out of dual exhausts on the jet ski is amazing.

[JR IN JAX]

The water definitely does get harder. I have been tossed from a tube behind my Hydrostream with the boat traveling 80 MPH in a "spin" on a hundred foot kevlar rope. You are over 100 and spend a long time bouncing and skipping. We tore the shoulders out of dozens of the impact-rated waterskiing vests. You always get the breath knocked out of you and sometimes break ribs. It is hard to get back in the boat,,,, but then it is your turn to pull the boat driver on the tube for revenge....I can not believe I never got sued by having someone get injured. We were young and tough.

[allstock]

You certainly wouldn't want to fall off a pwc with a surface drive prop!!:eek:

[WATERWINGS]

You always get the breath knocked out of you and sometimes break ribs. It is hard to get back in the boat,,,, but then it is your turn to pull the boat driver on the tube for revenge.....

We used to do that too, (but not THAT fast), the tube was called a "Ski Buiscuit"....but because how we used it.....we called it.....THE DEATH BISCUIT:eek:

[JR IN JAX]

We used to do that too, (but not THAT fast), the tube was called a "Ski Buiscuit"....but because how we used it.....we called it.....THE DEATH BISCUIT:eek:We used a 16" superheavy wall truck tube. They were expensive/hard to come by but could be inflated as hard as a basketball. The G force in the spin would stretch the tube into a canoe-shape. The death blow was when you made a figure 8 spin and the tube crossed the wake just as it hit max velocity.
I have old film pictures that show the unfortunate tubers skipping for over a hundred feet. The splash is still in the air where he first came off.
It is a shame there was no youtube back then.

[Forkin' Crazy]

Other than white water jet boat racing, this is the best application I have seen for a jet! ;)

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[Forkin' Crazy]

Jets are inefficient, no question, but I will line up with any single outboard in a race to 80 mph ... the other side to jets is they are quick out of the hole, and on a very small hull (PWC) with 250+ hp, good intake grate and good impeller, they are very hard to beat to 60+ mph. Plus my ski is only 90 cubic inch ...

I have a buddy with a light weight 16' hull with a lil' old 2 liter on it that will give you a run for your money. My money will be on the boat. ;)

[VernG]

I have a buddy with a light weight 16' hull with a lil' old 2 liter on it that will give you a run for your money. My money will be on the boat. ;)

I would love to try, but never trailer my ski out of MI. There are a lot of very fast jetskis in Morgan, LA though ... the guy who runs greenhulk.net lives there in case you want to find some fast local skis. Below is an acceleration graph from two pump gas skis racing.

http://greenhulk.net/forums/attachment.php?attachmentid=148377&d=1251764324


http://www.youtube.com/watch?v=epfarOubFEQ Link to a 2.5 second 0 to 60 mph RXP.

[WATERWINGS]

Other than white water jet boat racing, this is the best application I have seen for a jet! ;)

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Hmmm...that RXP sounded very turboee:D


The video above is a new one to me, I have the old one on my Myspace page.

Looks like they learned a few more tricks in the new vid.

Can you imagine relaxin, crusin down the river and this guy passes you 15 feet in the air........:eek:

Looks like fun to me:D

[VernG]

Supposedly that RXP is only running a B kit SC, which puts out about 13 lbs boost, so not much boost really compared to the 20+ that the turbo guys are running.

The jet lev thing basically takes a good running jetski, changes the top deck a bit and runs the thrust venturi into the yellow fire hose, then up into the jet pack itself, which controls and redirects the thrust. The jetski powers the jet lev and is just dragged along for the ride ... and for only $100,000 :eek::eek::eek: you can buy one too!

[engineermike]

Something else worth noting is that PWC's don't chine walk. I ASSumed it would be easier to drive a boat 80+ than a PWC, but I was wrong. I had no problem piloting my turbo RXP to 83 mph, but the 21' Checkmate chinewalks like crazy over 70.

[JonnyRXT]

Well owning both a power boat and a jet ski with high power mods the Powerboat is much more fun for the family but would never replace the feeling u get at 80mph only 3 inches from the water, My Sunsation is a blast with its 540 big block and pro charger setup up and at 26 foot gets scary around 90 mph for sure.

[Duke 1]

Pretty calm debate from what I expected.:cheers:

A decent set up PWC can easily smoke a prop boat to 60 without issue. Pumps start to lose effeciency around 70 and downhill from there. Acceleration is hard to beat though. Don't get me wrong, I own a Checkmate and my friends have Hydros and Allisons.

I've built 2 turbo PWCs that run over 100mph with pumps and my supercharged pump drag ski will hit 95 in a few seconds. Would love to line up with a few of the fast prop guys in Fl to see how we really tally up.:D

[WATERWINGS]

First off welcome to Scream and Fly!:thumbsup:

Most of us race 1/4 mile, and the boats are set up for that.....That IS the race.

I don't race, I just play hard.

I rode a guy's stock, wimpy 215 HP supercharged ski, and it pulled like crazy to 69-70 (GPS)......so I can't imagine what you guys are sittin on, and how hard they must pull.

There is a boat on this site that has run 151 MPH in an all out run, and I know of a member here that has run 139.44 in the 1/4 mile with a V-6!

[Duke 1]

First off welcome to Scream and Fly!:thumbsup:

Most of us race 1/4 mile, and the boats are set up for that.....That IS the race.

I don't race, I just play hard.

I rode a stock, wimpy 215 HP supercharged ski, and it pulled like crazy to 69-70 (GPS)......so I can't imagine what you guys are sittin on, and how hard they must pull.

There have been boats on this site that have run 151 MPH in an all out run, and I know of a member here that has run 139.44 in the 1/4 mile with a V-6!

Thanks for the welcome!!

Most of us just play hard on the St Johns every weekend. We ride between SR 46 and SR 520 and usually put close to 100 miles on the GPS every weekend.

Most of our skis are between 350 to 400 HP and are supercharged 4strokes. Jetpumps limit our speed but not our acceleration. Its a complete thrill to no end!!

David Bunn is a friend and believe he is one of those guys running over 130.

[WATERWINGS]

I rode with David in his Cougar, (with twins), and his STV.

Not sure of the speed we went with the twins, but I remember 117 with three of us in the STV.......:eek:

I told him, "Remember, I have a wife and child at home"

I watched his start with the "blender", (or did ya'll name it the "shredder"?), and I have some pics and vids of some of the things he tried along the way.

David is a Mad Scientist without a doubt.......I think he had his hands in almost everything that is fast land or sea........(and thats all I got to say about that):D

[JonnyRXT]

Still nothing better then blowing pass the guy doing 75mph in his 100g boat on my 12g ski with my woman on the back giving the thumbs down with a big smile on her face.

[WATERWINGS]

The welcome was for your too Jonny:thumbsup:

Man, I couldn't afford to boat ride if it cost as much as either of the two you just mentioned.

I got lucky and for just under $6000, and a few little things like a different jack plate and a different prop, and a little set up, I got up to 96......(OK I lied)........95.9 GPS, with an old 2.4 200.

How many more of ya'll are experimenting with props on the skis?

[JonnyRXT]

thanks for the welcome,

I have a **** old seadoo 2 smoke i might try it with once my new shed is built, its to cold to do **** till then, I am right now doing new heads on my 540 with much better flow for the blower to work better.

[Forkin' Crazy]

Now, if you want to compare a specially prepared drag boat to a PWC, it would only be fair to compare it to a specially prepared drag ski which have gone 0-60 mph in 2.5 seconds.

I'm sure there are a few drag OBs that can do that.


Something else worth noting is that PWC's don't chine walk. I ASSumed it would be easier to drive a boat 80+ than a PWC, but I was wrong. I had no problem piloting my turbo RXP to 83 mph, but the 21' Checkmate chinewalks like crazy over 70.

That is because of the flat ride plate, shoe, grate, etc holding it to the water. You get a prop, half the prop pushing the boat, it will cause yaw issues, chining, and all kinds of crazy things until you move the motor around or beat on the prop in the right places to get it better. Balance, slack in the steering, loose motor mounts all can cause handling issues.

I can run my Allison like it is on a string. I can't keep up with you guys on the take off the way it is set up, but give me 1' to 1.5' of chop, and lets race across the lake. ;)