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Thread: Are outboard jets really that much heavier than props???

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    Member BluNosDav's Avatar
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    Question Are outboard jets really that much heavier than props???

    Looking for a small outboard jet to power my new-to-me inflatable.
    But, I'm getting different numbers when it comes to weight claims.
    Some of the factory jet outboards show the following weight differences:

    Yamaha 40 prop = 223# / Yamaha 40(30) jet = 221# (so the jet is a little bit lighter)
    Mercury 25 prop = 157# / Mercury 25(18) jet = 186# (so the jet is much heavier)
    Mercury 40 prop = #260 / Mercury 40(30) jet = 267# (so the jet is only a bit heavier)

    When I talked to Jet Outboards, Inc. that makes jet units for manufacturers, as well as conversion kits for other makes of motors, they said that their jet-pumps only add about 8# to a standard prop outboard.

    Why three different outcomes: less weight, more weight, and much more weight?

    Thanx, Dave.

    PS - I've also heard that Evinrude E-TEC's have heavier lower-units than other makes, so converting one to a jet shouldn't change the total weight?
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    The jet pump housings typicaly cover/fit a range of rated prop HP per outboard/manufacturer and are then fitted with an impeller designed operate within the rated HP range, example; a jet pump housing that fits a 50HP powerhead may work up to 70HP-the difference is the liner and the diameter and pitch of the impeller fitted to the housing and HP able to turn the impeller effectively, so on the lighter, lower HP powerhead, the weight of the jet pump assembly may add weight overall where on the 70HP powerhead the weight difference may negligible to less than the prop lower unit.

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    Unless you have an inflatable specifically designed to use a jet there is the real possibility you will have cavitation problems. Just a heads up.

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    Member BluNosDav's Avatar
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    338 - Didn't know that about the different impellers inside similar housings, Thanx!

    Koda - There were some cavitation issues with early models, but, then owners made modifications and solved those problems.

    Due to the demise of most 2-strokes in the 20-40hp range, it's getting harder to find a smaller sized jet outboard that doesn't weigh almost or over 200 pounds!
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    I've heard/been told that some outbaord manufacturers will add steering, linkages, cables to the weight of the engine; therefore making some weights seem much more than you'd think. You wouldn't think that an impellor diameter or a small thickness difference in a sleeve makes up for that 29 pound overall weight gain for the Merc 25hp... I could be misinformed though, food for thought.

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    Member BluNosDav's Avatar
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    Swamp,

    I just wish that I could find out how much each component weighs, and then I could do my own math. The guy at Jet Outboards wouldn't give exact numbers and just kept saying that the jet pumps "didn't add very much weight". Finally, when I pressed him for a number, he said "only about 8#". But, maufacturers usually like to advertise how light their motors are. Yet, a lot of the factory jets are listed as quite a bit heavier that the same motors with a prop. What's confusing is the lack of consistency, when it comes to how much more the jet-drives are.

    Here's an example; Mercury still sells a 2-stroke 25hp motor in countries other than the USA. It's actually manufactured for Mercury by Tohatsu. As a prop motor, it weighs 114#. Tohatsu markets the same 25hp motor as a factory jet, and claims that it weighs 130#. That's a 16# increase.

    Compare that to the 29# increase for Mercury's 4-stroke 25hp prop VS jet drive referenced above?
    That's nearly twice as much weight change, between what are all basically the same size (25hp) motors?

    Thanx, Dave.
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    Member broncoformudv's Avatar
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    .338wm brought up some of the differences and the others are the fact it is a different person using a different scale weighing different products.

    Generally speaking a jet unit does weigh a few lbs more than a prop unit for the same engine.

    I am surprised that jet Outboards could not or would not give you an exact weight since there are only so many lower units and they ship them all out and I am sure whatever shipping system they use goes by weight and dimensions.

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    Member Colby Jack's Avatar
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    BluNos,
    I found you on the e-tec owners board while looking for info on my power traveler. Seems you and I are in the same boat (pun intended). I am also looking to put the best outboard jet possible on my PT. I'm really leaning toward the e-tec 30 short shaft manual start/tilt with a jet. The only other I'm really considering is the Tohatsu 30 4-stroke. I was told by Tracy Harmon and others that the PT is rated for a 40hp jet, but the power to weight ratio is a big jump at 40hp. What have you been shopping for? Any new info you care to pass along?
    Colby Jack

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    One thing to consider is that a jet is less efficient than a prop so if a motor is rated at 30hp with a jet the same motor with a prop is rated at 40hp.

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    Your chart is comparing apples to oranges. Compare a 40 prop to a 40 jet weight.

    Vietnam - June 70 - Feb. 72
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    His comparison is spot on. He's looking at what should be the same powerheads with different drives. Why the 25 Merc has such a variation is curious. Electric start and power trim/tilt could sway the numbers if the two motors weren't equally equipped. The 8# average weight gain for a jet sounds about right to me. I never weighed mine when I changed them but the difference seemed similar to that.

    I ran a Zodiac MkIIGR for years with a 15hp prop. That was a great combo because of the motor weight. I still have a brand new/never started 15hp Yamaha 2-stroke prop in the shed. Maybe I should buy another little rubber boat for that motor.

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    Moderator Daveinthebush's Avatar
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    Probably confuses me because if the desire is a certain hp motor to push a certain load, then to get the same hp as a 40 hp prop motor, the jet unit is going to have to be probably 55 hp to get the same hp coming out of the work end. Henceforth the 55 has to weigh a lot more. Does that make sense.

    Or is the comparison just to find two motors that weigh the same reguardless of output? I would think you would match the hp output to the desired level of preformance. Just thinking!

    Vietnam - June 70 - Feb. 72
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    Member BluNosDav's Avatar
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    Thanx to everyone for bumping this thread back up with new information & discussion.

    First, let me clarify my original question. I'm well aware that when a motor is converted from propeller to jet drive, there is a loss of efficiency and therefore horsepower. The best approximation for this loss is 30%. So, a 50hp prop'd motor would become a 35hp jet, etc. I accept this fact, and not trying to achieve EQUAL hp/performance. I'm primarily concerned with the change in weight associated with the conversion from prop to jet. Since, I'm gonna have to lift and carry this portable motor from the truck/plane, and hand-mount it onto my inflatable boat at the water's edge. I may have to accept that the heaviest motor that I can physically carry with my arms, might not be the most powerful motor that my boat can carry on it's transom. But, unlike the accepted 30% reduction in hp, the change in weight seems to be completely random and arbitrary. Some manufacturers claim: no change, or a little change, or a lot of change, when they advertise the SAME powerhead as a prop and a jet ???

    Thanx again, Dave.
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    Member BluNosDav's Avatar
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    Jack,

    Are you sure we have the same boat? Mine's a prototype sportboat made by AIRE in 2005, called a "Panga" (here's a photo):

    Attachment 63723


    Here's a full-production canoe that AIRE now calls a "Traveler-Transom", and some folks refer to as a "Power Traveler":

    http://www.aire.com/aire/products/default.aspx?id=234

    I've also heard that some other folks called the Panga by the name Power Traveler, back during the design stage?

    Don't want to get even more confused than I already am!
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    Moderator Daveinthebush's Avatar
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    Quote Originally Posted by BluNosDav View Post
    Since, I'm gonna have to lift and carry this portable motor from the truck/plane, and hand-mount it onto my inflatable boat at the water's edge. I may have to accept that the heaviest motor that I can physically carry with my arms, might not be the most powerful motor that my boat can carry on it's transom.
    Carrying a 180-230 pound motor by yourself you are a mighter man than I. :-)

    Vietnam - June 70 - Feb. 72
    Cancer from Agent Orange - Aug. 25th 2012
    Cancer Survivor - Dec. 14th 2012

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    Member BluNosDav's Avatar
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    Nah, that's why I'm trying to find a jet motor that weighs less than 150, and preferably a lot less!
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    Just because you can lift it doesn't mean you can get it in and out of an airplane. I've carried my 15hp 2-stroke Yamaha prop and a 25hp 2-stroke Yamaha jet (25hp powerhead) in airplanes. The 15 is fairly simple to get in and out of a C180 without damaging airplane or engine. The 25 is more difficult and represents my limit for a one guy operation. When I needed to fly a Yamaha F40 jet, that's a 4-stroke 60hp powerhead with factory jet, I had to have a Beaver take it and it took three guys to get it in and out of the plane. If you're intending to fly it? There's more to it that knowing how much it weighs.

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    Member Colby Jack's Avatar
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    BluNos--
    Yes, I'm sure we have the same boat. Mine's name is the Kung Fu Panga! As I understand it, I got one of the last to be made. It was still on the show room floor in 2007 as a demo boat. I have been extending the frame, improving the seating, and adjusting the rowing system to work best for my family and I. Now I want more POWER!!! haha. I have dipnetted the Kenai in it for 3 years, but now the Big boat got a new 50hp Honda from Storm Chasers (Awesome pricing! Awesome to deal with! Even from Eagle River.), so I am ready to gear this boat to what it was made for-- fly-in, float out adventures, and minimalistic jet boating into remote areas ( again, thinking jet-up, float out). I would love to get together sometime (Alehouse) and compare notes. I have been tweaking this thing for awhile, but fresh eyes and ideas are always welcome!
    Colby Jack

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    Member BluNosDav's Avatar
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    Excellent boat name! Nice to hear there's another Panga in Eagle River. That make's three that I know of. (The other guy is named Jack, too.) I'd enjoy getting together this winter and comparing ideas. We could even have a Panga river regatta in the spring!
    "Luckily, enforcement reads these forums, and likely will peruse this one...Especially after a link of it is forwarded to them....." - AlaskaHippie.

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    Member Colby Jack's Avatar
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    My name is actually Colby. Nickname is cheese. Colby Jack just kinda fit. I met Jack (lefty) a few years ago when I first got my Panga. Hellova nice guy. I'll be in touch. So what jet are you really looking at??????
    Colby

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