Jet Pump Efficiency

[Redneck]

Alright you jet pump experts...i've heard that mercury sportjet/optimax pumps have only a 10% power loss. I've heard that all the other pumps out there (hamilton, kodiak, outboard jets, etc.) have a 30%ish power loss. Anyone know why the sportjets/optimax have such better efficiency than the other pumps? And why don't the other pump manufacturers go to the sportjet style? I'm thinking there must be some disadvantages of the sportjet style pump that keep the other manufacturers to do their own thing.
Thanks,
Redneck

[jimh]

The 30% number is attributed to older style outboard jets. I've heard the newer ones are more efficient. Inboard jets like hamilton, american turbine, kodiak, etc have approximately the same characteristics of the sportjets.

[HOOKUP]

If you have ever been in both a Sportjet and a V8 boat, you have probably seen the rpm at close to 5500 rpm where the pump was absorbing 175 hp, however it is highly unlikely that you have ever been in a 310 HP boat operating at 5500 rpm and supposedly putting out 310 HP. Furthermore, even if you were, the pump would not be absorbing 310 HP.
What does this mean? Well, first of all there are some games being played. Shaft horsepower is not the same as powerhead HP. Mainstream engine manufacturers who sell integrated engine/drive packages must rate their packages power a prop or jet drive. Thus a 200 HP outboard powerhead is typically rated only 140 at the jet. When you buy an integrated unit such as a Mercury Sportjet 175 you get 175 HP at the jet at 5500 rpm, whereas the powerhead itself maybe generating 200 HP.
Contrast this to a V8. Typically when you buy a 350/351 V8 and a Berkeley/Legend/Kodiak/American Turbine/Jacuzzi you will hear that a person bought a 350 310 HP engine. This is not a comparable rating to the packaged drives.
The 310 rating is at the powerhead and not the jet nozzle. Moreover, you need to read the fine print as to how the 310 HP is measured. Usually this is on a test bed with no exhaust, load etc on the engine. Secondly, there is a 5 -15% HP loss due to friction, gears etc as power is transmitted to the drive. Powerhead HP is not shaft horsepower. An example of the differences was in 1972 when the auto manufacturers moved to NET ratings of their engines. The previously rated 300 HP engine ended up being 180 HP at the rear wheels. Or look at a Mercury or Volvo V8 stern drive which uses the same powerheads from Detroit as the 310 HP jet drive engines you are looking at purchasing. What are their net ratings? Around 260 HP. These are the same engines – it is just that Mercury and Volvo must NET rate or measure their HP at the prop or jet.
So how do we get to apples and apples rating with a jet rated Mercury 175 Sportjet and a 310HP V8?
click the below link and scroll down to the comp chart
http://www.marathonmarine.com/docs/stpb_jetboats.html#power_plants

[HOOKUP]

marathon marine has the most informative info I have ever seen. I hope this clears up some of your queations. Lots of good info in there

[jimh]

There story is misleading and is slanted to the advantages of the sportjet. Sportjets definitely have some advantages but considering HP independently as the "measure" doesn't explain the true advantages. I'm not going to try to explain all of the differences, but I'll mention some below.

Volume of the pump, durability of the pump, ability to handle whitewater/dirty water, and load carrying capacity are other factors to consider that aren't meantioned in their comments. NOTE: All automotive style pumps are also not created equal. My point, it isn't as simple as rated HP even if you are only worried about top speed with a light load. "Even a sportjet" has to be able to make their top RPM to develop 5500 RPM. Putting a load in the boat can dramatically impact the ability of any engine either prop or jet to reach maximum RPM. They are also making an assumption that the HP rating is at 5500 RPM for both sportjets and inboards, but that isn't the case. Aerated water also impacts the efficiency of different pumps.

Their page seems to suggest that top speed is where it is at. There is some good information on their page, but it doesn't tell the whole story about why you choose automotive style engine vs sportjet.

Do most of us care what HP our motor really is? I suggest not. We are concerned about whether our boat/jet combination works for us for our intended uses.

[WaterDog]

Jimh is spot on. You really need to consider the intended use and what your loading is going to be. The SJ I had, had a great hole shot and was fast with light to medium load. A heavy load and I could see a performance loss. The v-8 and hami I have now, while it's a bit slower out of the hole,(it's no slouch tho) it will pack whatever I can get in the hull.

[Regular Joe]

To keep it simple..........The SJ pump is like a garden hose
and the Hamilton 212 and others are like a fireman's hose.
Therefore these bigger pumps coupled to a V8 move a much higher volume of water at the same speed as the Merc SJ.
Think of a water fight one person with a garden hose verses the other with the fireman's hose. The bigger pumps are for
20 ft hulls or bigger and SJ are for 19 ft or less..my $0.02
:dance:

[Mikeymoto]

To keep it simple..........The SJ pump is like a garden hose
and the Hamilton 212 and others are like a fireman's hose.
Therefore these bigger pumps coupled to a V8 move a much higher volume of water at the same speed as the Merc SJ.
Think of a water fight one person with a garden hose verses the other with the fireman's hose. The bigger pumps are for
20 ft hulls or bigger and SJ are for 19 ft or less..my $0.02
:dance:


Aren't they 2 different types of pumps? 1 is a High Volume pump and the other is a High Velocity pump.
MM

[Regular Joe]

Hey Mickey,

In Your opinion which pump would be better for most application? The 312 c/w inducer or the 212 turbo. The 312 will work without the inducer in most water conditions but the 212 without the turbo is a no go! :lurk:

[HOOKUP]

Aren't they 2 different types of pumps? 1 is a High Volume pump and the other is a High Velocity pump.
MM

[/quote]


Hamiltons are volume pumps thats why they have the best control. The others like american turbine, kodiak etc are mixed flow pumps, sort of a hybrid between volume and pressure. The sportjet is a pressure pump meaning the voilume is low but the pressure is high. High speeds good control, lower speed worse control. It is due to the small amount of water in the pump. This also is key when running rapids. In real white water a SJ may run out of water if the pump is out of the water for any amount of time, meanwhile the Hamilton 212 will maintain control because of the large amount of volume of water in the pump.

I hope this makes sense, I have had a few beers tonight.

[Regular Joe]

Snagfish,

The Kodiak is a good volume pump as well and one of the first. It's an axial flow not a mixed flow. Good trash eating pump and handles very well in reverse and at low speed. The Kodiak 3 stage is good up to a 21 ft boat. Can go on a 22' with the 496 V8 and can handle a diesel engine as well. They are loud so plug your ears. Get to think of it the SJ 175 is loud to............ :smash:

[Redneck]

thanks everyone, that marathon marine site was very helpful.
redneck

[Green Machine]

The Kodiak is the volume pump. 3 stages of water sucking power!! It actually is the old Hamilton 773. The Hamilton 212 is the hybrid, hence the turbo inducer. Without the inducer, it's a dog turd. I have the Kodiak and it is loud, a little slower than the 212, but still have plenty of power.

Green Machine

[fishingls]

If you have a Kodiak pump and want the performance of a 212, contact Kokiak. They have a replacement grate and a newer impeller. Installing them will do marvels for performance. I did it and I'm faster on the hole shot, able to run at lower rpms and faster at top end.

[Regular Joe]

If you have a Kodiak pump and want the performance of a 212, contact Kokiak. They have a replacement grate and a newer impeller. Installing them will do marvels for performance. I did it and I'm faster on the hole shot, able to run at lower rpms and faster at top end.



What size is your boat? Hull type delta pad, radius? I understand that this pump is the loudiest but in a well design hull it could come close to the 212 in sound. :cheers:

[weekender]

fishingls - More info please...

Tell us about your boat and this grate/impeller(s) upgrade. Who did the install for you and about how much cash are we talking?

Shoot me a PM if you would prefer, but I am sure others are interested.

[weekender]

If you have a Kodiak pump and want the performance of a 212, contact Kokiak. They have a replacement grate and a newer impeller. Installing them will do marvels for performance. I did it and I'm faster on the hole shot, able to run at lower rpms and faster at top end.



I checked this out on KEM's webpage and found the following information.

Impeller Chart ::

ENGINE : 3 STAGE : 2 STAGE : IMPELLER :
262 X 1/5-92
305 X 2/4-92
350 X 5/5/4-92
350 X 1/4-92
454 X 1/2/4-92
502HO X 1/2/4-92
496 X 1/3/4-92
496HO X 1/3/4-92

For best performance to an old 3 stage pump, change the intake grate to the new style, and change the back impeller to a #4. This will drop the rpm. And increase performance.

Then I called Kodiak Direct. They told me this basically equates to adding an Over Drive. They said RPM's would drop 100-150 and you would pick up a couple MPH. Your looking at $850 for both parts.

I figured I would post what I learned incase anyone else was interested.