Prop to jet question

Discussion in 'Jet Drives' started by skiguygeetz, Oct 3, 2010.

  1. skiguygeetz
    Joined: Mar 2010
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Chandler, Tx.

    skiguygeetz New Member

    I have a '92 procraft, glass bassboat with a 60hp mariner on it. It has tilt and trim and plains out easily at 3800rpm. Everything is just fine on the local lake here in Texas. However, I'm moving to Idaho and would like to put a jet pump on this 60hp. I understand there is a loss of about 40% hp when switching to a jet pump. Opinions, and suggestions please.
     
  2. tunnels

    tunnels Previous Member

    why do you want to swap to a pump? what is you reasoning and logic to do that ??
    :confused:
     
  3. Submarine Tom

    Submarine Tom Previous Member

    Opinion: Shouldn't be necessary

    Suggestion: Don't do it.

    -Tom
     
    Last edited: Oct 4, 2010
  4. skiguygeetz
    Joined: Mar 2010
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Chandler, Tx.

    skiguygeetz New Member

    I'm moving to the lewiston area and want to run the rivers.
     
  5. apex1

    apex1 Guest

    My experience with bboth systems told me, that the outboard is not worse in shallow waters than the jet. In fact I ruined two impellers in shallows but no prop.

    Regards
    Richard
     
  6. Rampager
    Joined: Mar 2004
    Posts: 24
    Likes: 1, Points: 0, Legacy Rep: 33
    Location: Canada

    Rampager Junior Member

    finding it hard to agree with that statement. Where we boat a prop would last about 2 minutes, if you could even get the boat off the trailer and thats debatable.

    Whether its worth it depends on the waters you will be running. Have you been on any of them yet?

    A 60 hp prop is gonna be like a 40 with a jet on it. Id suggest looking for something thats more specifically designed for shallow waters if thats your intent because your hull likely isnt up to the task either if you happen to "encounter" the bottom.

    Cheers
     
  7. apex1

    apex1 Guest

    Of course I don´t know where you go boating. But I did use my tenders all around the world and had 9 years to compare these two. One was a 17ft Boston Whaler with a OB, the other a 20ft Castoldi jet RIB. The outboard has a tilt function which can help to save the prop btw. The jet does not!
    On a pebble beach the jet got killed in seconds, the prop was not harmed.
    On the Amazon river the other jet was killed by debris.

    The statement is wholeheartedly agreed by the entire megayacht world, where you rarely find jets anymore.

    Don´t know about trailers, never had a trailer boat.
     
  8. anthony goodson
    Joined: Mar 2007
    Posts: 422
    Likes: 17, Points: 18, Legacy Rep: 256
    Location: Dorset UK & Murcia Spain

    anthony goodson Senior Member

    Tell that to the marines
     
  9. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 146, Points: 0, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member

    Simply put: If you're running in waters where you're afraid of banging the prop, you also need to be afraid of banging the hull. A deep-V fibreglass bassboat is not the appropriate hull for shallow river running.
    My suggestion would be to look at trading in the Procraft for something like a Duckworth that is designed from the outset for shallow, rocky rivers.
     
  10. mark775

    mark775 Guest

    My experience says that a jet can often get your boat stuck further up the bar, it wears out as well, and a prop gives an "early warning system". Of course there are some streams rocky and just the right depth for a jet. The marines use a jet for safety of dropping off a moving skiff - otherwise, of course they wud use props as they are better in every way for beach landings and such.
     
  11. anthony goodson
    Joined: Mar 2007
    Posts: 422
    Likes: 17, Points: 18, Legacy Rep: 256
    Location: Dorset UK & Murcia Spain

    anthony goodson Senior Member

    Well Mark, our marines are obviously not as safety conscious as yours ,which under certain circumstances I suppose could be considered an asset .Their base is just around the corner from here ,and jets now appear to be the choice for beach landing craft ,although they do sometimes use twin outboards on RIBS for high speed recovery of parachutists. Apex gave the right answer for the wrong reasons the answer is no no no ,because of inefficiency ,the outboards fitted with jets use the wrong design of pump for propulsion ,and there are major problems with maintaining the correct ride height, an extremelly ill conceived device ,never to be confused with a proper jet pump installation. Incidentally ,jets don't wear out easily ,they are more likely to corrode away slowly, and I suppose the early warning a prop gives is when a blade falls off. Knock jets for their faults by all means ,but not in the areas where they excel.
     
  12. Rampager
    Joined: Mar 2004
    Posts: 24
    Likes: 1, Points: 0, Legacy Rep: 33
    Location: Canada

    Rampager Junior Member

    This forum never ceases to amaze me.....

    I suppose had the original poster asked what style drive system to use in his tender to get to his mega yacht your post would be highly relevant
    However since he asked about converting the engine on what a quick google search seems to reveals to be a fishing/bass boat which he intends to use in shallow rivers in Oregon I'd say its completely irrelevant to the topic

    If the water is shallow enough to warrant a jet it likely also warrants the RIGHT jet setup and that almost certainly precludes a rock grate which solves most of the issues you describe

    Cheers
     
  13. speedboats
    Joined: Jun 2006
    Posts: 139
    Likes: 11, Points: 0, Legacy Rep: 127
    Location: New Zealand

    speedboats Senior Member

    As has been posted, if you need to use jet due to impact hazzards in the river, then consider the right tool for the job. A vessel with wear strips or impact resistance built into their structure is going to be far better than tearing your glass boat to shreds, osmossis, etc.

    Putting a jet onto the bottom of an outdrive is a seriously bad idea. In a nutshell, they are ****. As has been mentioned they suffer from mount height issues, internal component wear (particularly if pumping silt, grit or pebbles), and breakages due to impact.

    A purpose built pump is designed to be mounted in such a manner that minimises risk of direct impact. Internal impellers are made of harder materials to minimise wear when pumping aggregates, water off-takes usually have some sort of trap to limit the amount of silt entering the motor, and steering nozzles are now being fitted with the ability to trim the vessel.

    As has been widely discussed, saying there is an x% of drive loss from going to a jet iover a props hard to back up. There are people who will tell of the ineffiencies of the jet, and how a slow turning large prop is far better. Or how a 200hp outboard will go faster than a 350hp jet. But I've compared similarly built boats with both drives at similar speeds and both have comparable fuel consumption rates. Fuel consumption is directly related to energy (or power) use. Ever measured the bollard pull on a jet? Compare that to an out-drive?

    If you want to run the rivers, sell your rig and get the right tool for the job, else you might end up trying to drive a 9" nail with a 2oz hammer...
     
    1 person likes this.
  14. ondarvr
    Joined: Dec 2005
    Posts: 2,030
    Likes: 153, Points: 63, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    I'm getting into this late, but being the owner of outboard jet boats and prop boats of similar size, plus living on a river and knowing the water he wants to venture into (been there), I feel I may have some relevant advise.

    Don't do it, its a waste of time and money. You would need to buy a much larger motor to even get it up on plane and it would still be a terrible hull for a jet.

    Outboard jets are very inefficient, they suck fuel much faster than you can imagine, combine that with the HP loss it makes for what would seem to be a miserable package...but....for some types of boating (actually fishing) they work very well, even taking into consideration these shortcomings.

    In Idaho inboard jets are much more common, mainly because the rivers are large, but you could use an OB jet if you wanted to. Depending on which river you plan to fish and where in that river, a prop could work on many of them.

    As for using a prop or pump in shallow water, I would need to replace my lower unit within a 100' of the launch every trip out with a prop, I'm going on ten years with the current pump. There is very little maintenance on an OB pump, just a grease fitting, it takes about 2 minutes to pump some grease in.

    If you suck up rocks and gravel you can damage the impeller and wear ring, but the impeller can be sharpened and if you need to replace the wear ring they don't cost much. Like I said, my wear ring and impeller are about ten years old. On outboards if the intake becomes plugged you just raise the motor and pull the stuff out, leaves and grass are the worst, in the fall when the leaves drop I've gone as little as 1/2 mile before it would plug.

    Inboards are much more efficient, but when they plug it can be a little more difficult to clean the intake. You can get a stomp great and keep a rake in the boat to pull leaves and other debris off the intake, but you may need to get a little wet.

    If the water is deep enough I would never use an OB jet, but I have boats for that purpose and most of my fishing is done rivers with very shallow areas (6" deep), so to fish them, the jet is required.
     
    1 person likes this.

  15. Akgramps
    Joined: Aug 2008
    Posts: 34
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Alaska

    Akgramps Junior Member

    You may have plyed the waters of the world with your "Tenders", but its blatantly obvious you have never jet boated in Idaho or Montana or Alaska or Bc.........or ever anywhere...............
    Also most of the people that run boats there have trailers.........AMAZING....

    It never ceases to amaze me people with no knowledge of what the poster is asking will respond........and in a manner as if they actually know something........Geeeezzzzz

    Rarely find jets....ever hear of Hamilton? Scott? Jazuzzi? American Turbine?????

    Outboard with a jet still tilts just fine...............!
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.