Page 1 of 2 12 LastLast
Results 1 to 20 of 23

Thread: Jet/prop questions?

  1. #1
    Member
    Join Date
    Feb 2007
    Location
    Anchorage, Alaska
    Posts
    137

    Default Jet/prop questions?

    I,m buying a 16- 18 ft jon boat soon. I want to power it with a Yamaha tiller outboard. That being said would you buy the motor with the jet on from the factory then convert to a lower end unit later or the reverse as in with a lower end then buy the jet to convert.I will have a riser built from aluminum and also a extension from the bottom of the boat to run good water to the foot. Been there and done this but how would you start out motor wise with a jet foot or lower end unit and why?I started with lower end units and then switched but would it be better the other way? Might even be interested in a 5 inch lower unit extension so as to leave motor mounted the same on the transom.Please give me your thoughts. Thanks

  2. #2

    Default

    I bought my Yamah tiller with a prop lower unit and ordered the jet seperately and am able to switch back and forth no problems, but have no experience with a "factory" jet. A few years ago I looked at getting an extension added for a Honda to extend the shaft length from 20" to 25" and unfortunately it was not economically feasable of practical. You have to change out a number of shafts, rods and other pieces. I asked my mechanic at the time to price it out and stop at $1000 but he found it was going to be way over $1000 and changing out the mid section of the motor was not a process that I would want to repeat on a regular basis. Good Luck!

  3. #3
    Moderator stid2677's Avatar
    Join Date
    Apr 2006
    Location
    Fairbanks Area
    Posts
    7,274

    Default

    Buy the factory jet, there are more lower units on the market with props. Most folks buy with the Jet installed, this leaves many TAKE OFF lower prop units in stock at the boat shops. That is how I got mine, I prices jet units and they cost way more than the prop units.

    Steve

  4. #4
    Member
    Join Date
    Apr 2006
    Location
    Tennessee
    Posts
    3,568

    Default

    The jet unit runs about $2100-2,200 new. So the best answer for you depends on the price of the new motor with prop or the jet and then compare it against what it would cost to add either the jet or to find a nice lower unit on the used market.
    For best performance you may also need a jackplate.
    A quick search shows that Yamaha charges about $1,000 more for the motor with the factory jet. I am pretty sure you can find a new take off lower unit for less than that.

    What I am doing for my Wooldridge is installing a 25 inch shaft length motor with the Power Tran jackplate. Motor will be mounted in the correct position to run the prop. Then next year as my finances permit I plan to add the jet. Then Power Tran jackplate has 7.5 inches of lift which will permit the jet to be positioned at the optimal running height. I dont have an option to purchase a factory jet since Optimax doesnt offer one.
    Tennessee

  5. #5
    Member Akgramps's Avatar
    Join Date
    Apr 2008
    Location
    Last civilized place on the planet
    Posts
    2,079

    Default

    I would do as Steve suggested and buy the motor with a jet on it, as he pointed out you could probably come up with a prop lower unit if you really wanted one.
    I dont know if its worth the trouble switching back and forth from prop to jet, it may make some sense on a bigger- heavier boat where you are running a prop most of the time or making long trips on the Yukon and then switch to jet when you hit the shallows. Some fuel economy in doing that.
    The problem is the setup to convert from prop to jet, if you use a lift plate you will move the motor back about 4", while this is not much of a detriment with a prop, it will compromise your jet preformance somewhat.
    You have already lost 30% just converting to a jet, and you really want the jet foot tucked in tight to the tunnel or transom, 1/4" off on jet height can make a difference.
    If you dont run a lift plate, you will have to dismount and remount the motor to correct the height. You have got to be tough to want to do that very often!
    In my opinion (particuarily on a 16-18 foot jon) stick the jet on it and use it! a new 4 stroke is a pretty efficent setup on a light boat.
    Simple can be better, lighter and less messing around.

    By the way........................
    What size motor are you looking at? I have a 2007 Yamaha 115/80 with 40 hours and still under warranty that I am planning on selling.

    Akgramps

  6. #6
    Member
    Join Date
    Apr 2006
    Location
    Tennessee
    Posts
    3,568

    Default

    Akgramps,
    You made some good points. Some of the guys I talked to who convert back and forth add an extension under the boat using that heavy pastic material to allow water to feed to the jet better.
    Of course every compromise is a give a take situation. But in some cases (like mine) I plan on using the jet all summer long playing in the rivers and then will only use the prop when we run up the Yukon and Koyukuk for moose. I would hate to switch it out more than once a year.
    And a good jackplate can help the boat achieve higher fuel economy even while running the prop.
    Tennessee

  7. #7
    Member
    Join Date
    Feb 2007
    Location
    Anchorage, Alaska
    Posts
    137

    Default

    I had a new 94 Wooldridge 17.5 Alaskan with 115 hp Evinrude and CMC manuel lift jet/ prop setup by Wooldridge and it worked perfect.Late summer I would switch to jet for moose and leave the jet on all winter(in storage)and run it in the spring low water then change to prop for summer high water. So better to buy with the jet seems to be the go. Thanks for the ideas.

  8. #8
    Member AKBassking's Avatar
    Join Date
    Oct 2006
    Location
    SE Alaska-Summer Columbia River-Winter
    Posts
    2,007

    Default Besides

    all jet units come from the same and only manufacture. Buy the engine w/jet unit and then find a lower unit. Cheaper and you end up with the most up-to-date jet unit.

    ALASKAN SEA-DUCTION
    1988 M/Y Camargue YachtFisher
    MMSI# 338131469
    Blog: http://alaskanseaduction.blogspot.com/

  9. #9

    Default Question

    Quote Originally Posted by J-FRAME View Post
    I,m buying a 16- 18 ft jon boat soon. I want to power it with a Yamaha tiller outboard. That being said would you buy the motor with the jet on from the factory then convert to a lower end unit later or the reverse as in with a lower end then buy the jet to convert.I will have a riser built from aluminum and also a extension from the bottom of the boat to run good water to the foot. Been there and done this but how would you start out motor wise with a jet foot or lower end unit and why?I started with lower end units and then switched but would it be better the other way? Might even be interested in a 5 inch lower unit extension so as to leave motor mounted the same on the transom.Please give me your thoughts. Thanks
    I realize this is sacrilegious to the jet guys, but it has to be said. Stop worrying about converting and still go shallow with your 18 foot jon boat. Get a GoDevil Surface Drive You'll double your fuel economy at the same time.

  10. #10
    Member
    Join Date
    Feb 2007
    Location
    Anchorage, Alaska
    Posts
    137

    Default

    No its ok with me. I never had no love for a jet just where it would take me. I had a Go Devil in the early 90,s before the Wooldrige. It worked ok but was pretty slow. It had a Honda motor which is good.Yes I will go the their website and do a look see. Thanks

  11. #11

    Default Question

    I run a 35 hp Surface Drive on an 18' X 48" jon boat. It will do between 18 and 20 mph upstream in the Tanana and 25 to 30 mph downstream. That is with 2 people,24 gallons of fuel, and gear for a weeks fishing. 24 gallons gives me an easy 190 miles, down and back, on a river. Full throttle burn is 2.5 to 3.0 gph. Google "godevil alaska" I think there is a dealer around Fairbanks.

  12. #12
    Member
    Join Date
    Feb 2007
    Location
    Anchorage, Alaska
    Posts
    137

    Default

    So how would it work for trolling the Kenai ??

  13. #13

    Default trolling the Kenai

    I've never fished the Kenai so I can't really answer your question. I can tell you that, in a lake, the trolling speed is pretty fast... about 4 mph. Also there is no reverse if you are into backtrolling. The Prodrive does have a reverse, but it is an entirely different design of mudmotor. I like the GoDevil for the interior rivers because of its reliability and simplicity.

  14. #14
    New member
    Join Date
    Nov 2007
    Posts
    5

    Default

    I believe it is entirely up to you, which way you want to buy your motor. All jets come from the same jet company. When you buy a Yamaha (jet motor) it comes in the crate without the jet on. Then the mechanic at the shop grabs a jet in a box and slaps it on. You can buy your motor in a jet model but if you are going to buy a prop later don't look to the retailer. You are better off trying to find a used prop or someone who has a new one and has no use for it. Retailer price for a prop lower unit might cost upwards of $1500. I am not sure what a jet unit would cost, but if its cheaper than a prop (lower unit) I would buy with the prop and then switch it later. One control cable and a couple of bolts, pretty easy to swap.

  15. #15
    Member Akgramps's Avatar
    Join Date
    Apr 2008
    Location
    Last civilized place on the planet
    Posts
    2,079

    Default Jet unit

    Typically a new jet unit is about $2100.00.
    Depending on which brand you are dealing with can affect the cost of a (prop) lower unit, deals can be had, yamaha lower units are reasonable, johnsons however can get spendy.
    Craiglist can be a great resource for parts or the swap and sell on this site.

  16. #16
    Member
    Join Date
    Jan 2007
    Location
    Juneau
    Posts
    2,127

    Default

    Quote Originally Posted by Akgramps View Post
    I would do as Steve suggested and buy the motor with a jet on it, as he pointed out you could probably come up with a prop lower unit if you really wanted one.
    I dont know if its worth the trouble switching back and forth from prop to jet, it may make some sense on a bigger- heavier boat where you are running a prop most of the time or making long trips on the Yukon and then switch to jet when you hit the shallows. Some fuel economy in doing that.
    The problem is the setup to convert from prop to jet, if you use a lift plate you will move the motor back about 4", while this is not much of a detriment with a prop, it will compromise your jet preformance somewhat.
    You have already lost 30% just converting to a jet, and you really want the jet foot tucked in tight to the tunnel or transom, 1/4" off on jet height can make a difference.
    If you dont run a lift plate, you will have to dismount and remount the motor to correct the height. You have got to be tough to want to do that very often!
    In my opinion (particuarily on a 16-18 foot jon) stick the jet on it and use it! a new 4 stroke is a pretty efficent setup on a light boat.
    Simple can be better, lighter and less messing around.

    By the way........................
    What size motor are you looking at? I have a 2007 Yamaha 115/80 with 40 hours and still under warranty that I am planning on selling.

    Akgramps
    Folks I have talked to on this say that setting your motor back actually feeds cleaner water to the jet thus increasing your efficiency, although it does sound counterintuitive. I've even seen plates mounted to river boats that intentionally set their motors back even though the riser plates don't go up or down.

    Anyhoo, I had the same question a few years ago and I got the jet. It goes everywhere and unless you are making some severely long runs or plan on hitting alot of big lakes (jets in a good chop suck) it will take forever to recoup the cost of buying a prop lower unit. I run a 60/40 yammer jet and it burns 4 gallons an hour full out...that ain't bad.

    If you can have only one...get the jet.

  17. #17
    Member Akgramps's Avatar
    Join Date
    Apr 2008
    Location
    Last civilized place on the planet
    Posts
    2,079

    Default jet placement

    Catch it,
    I have read some articles on the web that recomend setting the jet back from the transom and the use of a jack plate for adjusting motor heicht, be it manual or power it still moves the motor back.
    So I called Specialty Jets and asked them, lo and behold Dick stalman (the orginator of outboard jets) answered the phone and said most emphatically not to use a jack plate, unless of course you absoultley have to have one?
    Probably the biggest problem with jets is overcoming cavitation, boat manufactures have largely overcome, I suspect that is why you see a lot of tunnel hull type boats (OB) with the tunnel actually extended past the hull some 4"6". Then the foot just tucks right into the tunnel. What you want going to the jet intake is a good solid stream of dense water, if the jet sets back, as soon as the water leaves the tunnel the water starts to spread out, introducing air, not unlike shot leaving the barrel of a shotgun. I suppose its a high pressure/ low pressure thing like lift on a aircraft wing.
    On non adjustable transom extensions, proably what you have seen is some aluminum angle to extend the transom for supporting a jet motor.

  18. #18
    Moderator stid2677's Avatar
    Join Date
    Apr 2006
    Location
    Fairbanks Area
    Posts
    7,274

    Default

    What I did to make sure I had clean water to the jet, was install a longer piece of Plastic from the hull to the pickup. All you are doing is extending the hull tunnel. You loose 30% power with a pump, my boat uses about 45% more fuel. The entire mod cost me 2500.00, this covered the welding and the lower unit and prop. With gas getting close to 4 bucks it was worth it for me. I have been using less than half the fuel I used to running out of Valdez.

    Steve

  19. #19
    Member
    Join Date
    Jan 2007
    Location
    Juneau
    Posts
    2,127

    Default David and Goliath

    What it comes down to for the question posed by J Frame is the size of the boat involved. In Stid's situation, having both units and the jack plate etc. is much more worthwhile considering that the boat is worthy of sea running etc. and is in the end, a very nice and big and expensive boat (read investment). The problem with trying this on a smaller rig, is that it almost becomes a turd polishing event. Since this rig at 16 to 18 foot, with a smaller motor on it, with limited big water capabilities and range, and it will cost nearly as much to set it up for the conversion as it did for Stid's sled despite being worth 30 to 40 percent fiscally. To me, it's an investment that will take forever to pay off economically considering how little fuel a four stroke of that size will burn compared to the 100hp plus models. I feel that this smaller sized boat is best set up as a river runner and to try and stretch it's capabilities will take more than a second lower unit. Then again, if J frame is made of cash and wants an interesting project...go for it.

    The way I look at it is if you get the prop lower unit, what does it exactly do for you and does it do it enough to make it worth the hassle and expense. Switching out lower units on smaller boats isn't that hard but it's no fun to do on the fly (which I've done) and in many situations inland, a jet is required but a prop is optional.

    My only other thought is to make sure you get a big enough motor. A forty jet (30 at the pump) is great on a lighter 18 foot jon but a dog if it's a heavier welded version. Even then, you are limited on cargo if you intend to hunt with it and want to be able to take gobs of gas, buddies, equipment etc. I am very very very pleased with the performance of the 60/40 jet on my 18 foot boat (it's a lund, but the principle stands) I get great cargo capacity and range and never feel underpowered, unless I am ridiculously loaded. When I got started with buying motorized toys up here five years ago. I got a 340 snowgo, and after getting left behind and buried as everybody else zoomed on ahead in the hills I swore to never be underpowered again, thus the larger jet motor. I realize this will limit you legally on places like the Kenai and that needs to be taken into consideration. But on an 18 foot boat, the 60/40 is a beauty, it's not necessarily that much faster, but the increased torque and capacity means you can take whoever and whatever you want without losing as much performance.

  20. #20
    Moderator stid2677's Avatar
    Join Date
    Apr 2006
    Location
    Fairbanks Area
    Posts
    7,274

    Default Great Post

    Catch It, nailed it. Figure out want you want to do and where you plan on doing it. Then buy a boat to do that mission. Will save you a ton.

    Steve

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •