Re: engines; jet drives
I know of two Atkins tunnel drives built recently, both documented
extensively in MAIB: Robb White's Rescue Minor, which IIRC is about 20'x5',
with a small deisel, and a 34' deisel cruiser built by Alex Hadden - took
more than 2 years, in a professional shop with 2-3 guys working. Both are
reported to be remarkable . But don't try to design one yourself, or to
modify a Sneakeasy to this shape.
The JetJon site is a bunch of guys who are actively experimenting with old
jetski drives, stuck into various hull shapes. I suspect that the Sneakeasy
would be perfect for this, perhaps with some slight modifications, or using
the "step sharpie" variation to limit ventilation (NOT 'cavitation'). Draft
might increase a couple inches, but still, a boat that would plane at 20mph
in less than 6".... For low speed, consider a pair of trolling motors,
foreward and aft, as "thrusters"
One of the big jet mfrs used to make a small unit, for up to 20hp, iirc. It
was inexpensive, for toys and projects. I seem to remember they sold it
with no warranty.
To get a couple inches less draft in my Diablo, I cut a notch, or "tunnel"
2-3" up into the transom. The transom was 20", now it's effectively 17",
which works fine with a short shaft 25. Doing it again, I'd cut much more
out, and raise the transom...
Best regards
Curtis
extensively in MAIB: Robb White's Rescue Minor, which IIRC is about 20'x5',
with a small deisel, and a 34' deisel cruiser built by Alex Hadden - took
more than 2 years, in a professional shop with 2-3 guys working. Both are
reported to be remarkable . But don't try to design one yourself, or to
modify a Sneakeasy to this shape.
The JetJon site is a bunch of guys who are actively experimenting with old
jetski drives, stuck into various hull shapes. I suspect that the Sneakeasy
would be perfect for this, perhaps with some slight modifications, or using
the "step sharpie" variation to limit ventilation (NOT 'cavitation'). Draft
might increase a couple inches, but still, a boat that would plane at 20mph
in less than 6".... For low speed, consider a pair of trolling motors,
foreward and aft, as "thrusters"
One of the big jet mfrs used to make a small unit, for up to 20hp, iirc. It
was inexpensive, for toys and projects. I seem to remember they sold it
with no warranty.
To get a couple inches less draft in my Diablo, I cut a notch, or "tunnel"
2-3" up into the transom. The transom was 20", now it's effectively 17",
which works fine with a short shaft 25. Doing it again, I'd cut much more
out, and raise the transom...
Best regards
Curtis
On Jan 3, 2004, at 4:35 PM, someone wrote:
to the type of pump used. Outboards us a centrifugal
pump, where inboard jets such as berkeley, Panther, and
jetski/wave runners use axial flow pumps.
hal
>I believe the inefficiencies of outboard jets are due
> Seriously, how much power do you need? From what I've read about
> outboard jets, they are really inefficient... as I remember, they are
> about as effective as a screw-driven outbaard one-third the size. Max,
> correct me please if I'm misremembering. Of course, with that goes 3X
> the fuel consumption for a given thrust, Compared to a prop.
to the type of pump used. Outboards us a centrifugal
pump, where inboard jets such as berkeley, Panther, and
jetski/wave runners use axial flow pumps.
hal
On Jan 3, 2004, at 4:49 PM, Hugo Tyson wrote:
of the nozzle, among other things. A high speed jet
will have a -small- diameter nozzle to increase the
velocity of the stream, and will be inefficient at low
speeds because not much water will be flowing. A low
speed jet will have a -large- diameter nozzle so a lot
of water will flow at low speeds, but it won't go fast.
Most commercial jet makers allow you to choose nozzle
diameter based partly on the weight of the boat and
desired speed. And of course the power of the engine.
hal
> Jet drives are best at speeds above 25 Knots where they are moreThe efficiency of a jet drive is related to the diameter
> efficient than propellers. Speeds under 25 Kts the're really
> inefficient as the motor is still working relatively hard to drive
> them.
of the nozzle, among other things. A high speed jet
will have a -small- diameter nozzle to increase the
velocity of the stream, and will be inefficient at low
speeds because not much water will be flowing. A low
speed jet will have a -large- diameter nozzle so a lot
of water will flow at low speeds, but it won't go fast.
Most commercial jet makers allow you to choose nozzle
diameter based partly on the weight of the boat and
desired speed. And of course the power of the engine.
hal
It was William Atkin who first modified the Seabright skiff with reverse
deadrise aft, forming a tunnel. He also mated the Seabright skiff box
deadwood with a V-bottom, both with tunnel sterns and without. Most of us
think of Billy Atkin as a designer of Good Boats, but not as much of an
innovator, but his V-bottom and tunnel stern Seabright skiffs were truly
innovative. His gift to the boat design world, as he put it. Dave Gerr has
done some tunnel-stern boats, but I don't recall if he was inspired by the
Atkin designs. Here are some Atkin tunnel-stern Seabrights:
http://www.boat-links.com/Atkinco/Utilities/Everhope.html
http://www.boat-links.com/Atkinco/Utilities/ShoalsRunner.html
http://www.boat-links.com/Atkinco/Cruisers/NanukIII.html
And a non-tunnel-stern V-bottom Seabright skiff:
http://www.boat-links.com/Atkinco/Cruisers/NanukIII.html
deadrise aft, forming a tunnel. He also mated the Seabright skiff box
deadwood with a V-bottom, both with tunnel sterns and without. Most of us
think of Billy Atkin as a designer of Good Boats, but not as much of an
innovator, but his V-bottom and tunnel stern Seabright skiffs were truly
innovative. His gift to the boat design world, as he put it. Dave Gerr has
done some tunnel-stern boats, but I don't recall if he was inspired by the
Atkin designs. Here are some Atkin tunnel-stern Seabrights:
http://www.boat-links.com/Atkinco/Utilities/Everhope.html
http://www.boat-links.com/Atkinco/Utilities/ShoalsRunner.html
http://www.boat-links.com/Atkinco/Cruisers/NanukIII.html
And a non-tunnel-stern V-bottom Seabright skiff:
http://www.boat-links.com/Atkinco/Cruisers/NanukIII.html
On Sun, 4 Jan 2004 12:51:27 -0800 (PST), Don Tyson wrote:
> Jeff, I could be wrong but I think Dave Gerr ( Well known east coast
designer/author) did some designs with this concept which is essentially the
same as the historic Seabright Skiff. The seabright skiff is uniqe in that
it was launched from unprotected sand beaches directly into the rough
Atlantic off the NJ coast. Having the prop up in like that alowed the hulls
to be dragged up the beach at the end of the day. As long as the two bladed
prop was horizontal dragging the hulls didn't cause any damage.
> ...
--
John <jkohnen@...>
http://www.boat-links.com/
In this world of sin and sorrow there is always something to be thankful
for; as for me, I rejoice that I am not a Republican. <H. L. Mencken>
The prop I intend to use is a 15" prop and with the cavitation plate about
an inch below the top of the tunnel at rest, I would estimate that only the
top three inches of the prop will actually be running in the tunnel itself.
Without a drive to test fit, I can only estimate that even in the full up
position, the bottom of the fin may still drag in the mud but the prop
should be clear. Either way I was only after the ability to have the drive
lift clear of the water and to remove the drive unit without pulling the
boat. I don't plan on motoring the Wyo in real shallows except to nose up
to a beach.
Jeff
an inch below the top of the tunnel at rest, I would estimate that only the
top three inches of the prop will actually be running in the tunnel itself.
Without a drive to test fit, I can only estimate that even in the full up
position, the bottom of the fin may still drag in the mud but the prop
should be clear. Either way I was only after the ability to have the drive
lift clear of the water and to remove the drive unit without pulling the
boat. I don't plan on motoring the Wyo in real shallows except to nose up
to a beach.
Jeff
----- Original Message -----
From: "Don Tyson" <tysond99@...>
To: <bolger@yahoogroups.com>
Sent: Sunday, January 04, 2004 1:51 PM
Subject: Re: [bolger] Re: engines; jet drives
> Jeff, I could be wrong but I think Dave Gerr ( Well known east coast
designer/author) did some designs with this concept which is essentially the
same as the historic Seabright Skiff. The seabright skiff is uniqe in that
it was launched from unprotected sand beaches directly into the rough
Atlantic off the NJ coast. Having the prop up in like that alowed the hulls
to be dragged up the beach at the end of the day. As long as the two bladed
prop was horizontal dragging the hulls didn't cause any damage. I havent
seen anyone enploy a stern drive to this bottom but it sounds inexpensive as
there are many used 3.0 units out there for a song.
> Keep me posted.
> Don Tyson
>
> Jeff Blunck <boatbuilding@...> wrote:
> Actually I have adapted the Wyo to something similar though it's untested
> yet. I put a 28" inch wide by 5" deep tunnel running 42 inches long at the
> stern. You can just see it on some of my pictures showing me move the
stern
> section with a trailer.
>
> The key here is that the tunnel is still under the designed water line so
> there should be no problems with reversing or cooling. It was not
installed
> to get into shallows with a stern drive but it does reduce the overall
> operating depth by 5 inches. Theory here is to have a tunnel allowing me
to
> raise the Sterndrive high enough that it's mostly out of the water for
> corrosion problems plus it can be removed with out shipping water into the
> engine compartment so repairs can be made without pulling the 50 foot
boat.
>
> This tunnel will not be very effective at the top end speeds of the Wyo
and
> in fact may cause some cavitations, that's still to be determined.
>
> Jeff
>
>http://www.4dw.net/cosailor/
>
>
> ----- Original Message -----
> From:
> To:
> Sent: Saturday, January 03, 2004 11:14 PM
> Subject: Re: [bolger] Re: engines; jet drives
>
>
> > For a low-speed boat you might consider a tunnel stern, which is
> essentially
> > a high-volume, low-velocity jet drive. In ascending order of
construction
> > complexity and propulsion efficiency, here are some examples from
Chester
> > Nedwidek and the Atkin catalog:
> >
> >http://www.boat-links.com/images/Skeeter.gif
> >
> >http://www.boat-links.com/Atkinco/Utilities/Twinkle.html
> >
> >http://www.boat-links.com/Atkinco/Utilities/RescueMinor.html
> >
> > On Sat, 3 Jan 2004 09:31:28 -0700, Jeff wrote:
> > > ...
> > > They also expressed that the efficiency of jet drives are not realized
> > until
> > > the boat exceeds planing speeds so if I was to travel at hull speeds
> most
> > of
> > > the time, my fuel consumption would be excessive compared to a
> propeller.
> > > ...
> >
> > --
> > John
> >http://www.boat-links.com/
> > Distrust any enterprise that requires new clothes.
> >
> >
> >
> >
> >
> > Bolger rules!!!
> > - no cursing, flaming, trolling, spamming, or flogging dead horses
> > - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
> > - Pls add your comments at the TOP, SIGN your posts, and snip away
> > - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930,
Fax:
> (978) 282-1349
> > - Unsubscribe:bolger-unsubscribe@yahoogroups.com
> > - Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
> >
> > Yahoo! Groups Links
> >
> > To visit your group on the web, go to:
> >http://groups.yahoo.com/group/bolger/
> >
> > To unsubscribe from this group, send an email to:
> >bolger-unsubscribe@yahoogroups.com
> >
> > Your use of Yahoo! Groups is subject to:
> >http://docs.yahoo.com/info/terms/
> >
> >
>
>
> Bolger rules!!!
> - no cursing, flaming, trolling, spamming, or flogging dead horses
> - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
> - Pls add your comments at the TOP, SIGN your posts, and snip away
> - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
(978) 282-1349
> - Unsubscribe:bolger-unsubscribe@yahoogroups.com
> - Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
>
>
> Yahoo! Groups Links
>
> To visit your group on the web, go to:
>http://groups.yahoo.com/group/bolger/
>
> To unsubscribe from this group, send an email to:
>bolger-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject to:
>http://docs.yahoo.com/info/terms/
>
>
>
> [Non-text portions of this message have been removed]
>
>
> Bolger rules!!!
> - no cursing, flaming, trolling, spamming, or flogging dead horses
> - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
> - Pls add your comments at the TOP, SIGN your posts, and snip away
> - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
(978) 282-1349
> - Unsubscribe:bolger-unsubscribe@yahoogroups.com
> - Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
>
> Yahoo! Groups Links
>
> To visit your group on the web, go to:
>http://groups.yahoo.com/group/bolger/
>
> To unsubscribe from this group, send an email to:
>bolger-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject to:
>http://docs.yahoo.com/info/terms/
>
>
>
Jeff, I could be wrong but I think Dave Gerr ( Well known east coast designer/author) did some designs with this concept which is essentially the same as the historic Seabright Skiff. The seabright skiff is uniqe in that it was launched from unprotected sand beaches directly into the rough Atlantic off the NJ coast. Having the prop up in like that alowed the hulls to be dragged up the beach at the end of the day. As long as the two bladed prop was horizontal dragging the hulls didn't cause any damage. I havent seen anyone enploy a stern drive to this bottom but it sounds inexpensive as there are many used 3.0 units out there for a song.
Keep me posted.
Don Tyson
Jeff Blunck <boatbuilding@...> wrote:
Actually I have adapted the Wyo to something similar though it's untested
yet. I put a 28" inch wide by 5" deep tunnel running 42 inches long at the
stern. You can just see it on some of my pictures showing me move the stern
section with a trailer.
The key here is that the tunnel is still under the designed water line so
there should be no problems with reversing or cooling. It was not installed
to get into shallows with a stern drive but it does reduce the overall
operating depth by 5 inches. Theory here is to have a tunnel allowing me to
raise the Sterndrive high enough that it's mostly out of the water for
corrosion problems plus it can be removed with out shipping water into the
engine compartment so repairs can be made without pulling the 50 foot boat.
This tunnel will not be very effective at the top end speeds of the Wyo and
in fact may cause some cavitations, that's still to be determined.
Jeff
http://www.4dw.net/cosailor/
Keep me posted.
Don Tyson
Jeff Blunck <boatbuilding@...> wrote:
Actually I have adapted the Wyo to something similar though it's untested
yet. I put a 28" inch wide by 5" deep tunnel running 42 inches long at the
stern. You can just see it on some of my pictures showing me move the stern
section with a trailer.
The key here is that the tunnel is still under the designed water line so
there should be no problems with reversing or cooling. It was not installed
to get into shallows with a stern drive but it does reduce the overall
operating depth by 5 inches. Theory here is to have a tunnel allowing me to
raise the Sterndrive high enough that it's mostly out of the water for
corrosion problems plus it can be removed with out shipping water into the
engine compartment so repairs can be made without pulling the 50 foot boat.
This tunnel will not be very effective at the top end speeds of the Wyo and
in fact may cause some cavitations, that's still to be determined.
Jeff
http://www.4dw.net/cosailor/
----- Original Message -----
From:
To:
Sent: Saturday, January 03, 2004 11:14 PM
Subject: Re: [bolger] Re: engines; jet drives
> For a low-speed boat you might consider a tunnel stern, which is
essentially
> a high-volume, low-velocity jet drive. In ascending order of construction
> complexity and propulsion efficiency, here are some examples from Chester
> Nedwidek and the Atkin catalog:
>
>http://www.boat-links.com/images/Skeeter.gif
>
>http://www.boat-links.com/Atkinco/Utilities/Twinkle.html
>
>http://www.boat-links.com/Atkinco/Utilities/RescueMinor.html
>
> On Sat, 3 Jan 2004 09:31:28 -0700, Jeff wrote:
> > ...
> > They also expressed that the efficiency of jet drives are not realized
> until
> > the boat exceeds planing speeds so if I was to travel at hull speeds
most
> of
> > the time, my fuel consumption would be excessive compared to a
propeller.
> > ...
>
> --
> John
>http://www.boat-links.com/
> Distrust any enterprise that requires new clothes.
>
>
>
>
>
> Bolger rules!!!
> - no cursing, flaming, trolling, spamming, or flogging dead horses
> - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
> - Pls add your comments at the TOP, SIGN your posts, and snip away
> - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
(978) 282-1349
> - Unsubscribe:bolger-unsubscribe@yahoogroups.com
> - Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
>
> Yahoo! Groups Links
>
> To visit your group on the web, go to:
>http://groups.yahoo.com/group/bolger/
>
> To unsubscribe from this group, send an email to:
>bolger-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject to:
>http://docs.yahoo.com/info/terms/
>
>
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
- Pls add your comments at the TOP, SIGN your posts, and snip away
- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
Yahoo! Groups Links
To visit your group on the web, go to:
http://groups.yahoo.com/group/bolger/
To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
[Non-text portions of this message have been removed]
Actually I have adapted the Wyo to something similar though it's untested
yet. I put a 28" inch wide by 5" deep tunnel running 42 inches long at the
stern. You can just see it on some of my pictures showing me move the stern
section with a trailer.
The key here is that the tunnel is still under the designed water line so
there should be no problems with reversing or cooling. It was not installed
to get into shallows with a stern drive but it does reduce the overall
operating depth by 5 inches. Theory here is to have a tunnel allowing me to
raise the Sterndrive high enough that it's mostly out of the water for
corrosion problems plus it can be removed with out shipping water into the
engine compartment so repairs can be made without pulling the 50 foot boat.
This tunnel will not be very effective at the top end speeds of the Wyo and
in fact may cause some cavitations, that's still to be determined.
Jeff
http://www.4dw.net/cosailor/
yet. I put a 28" inch wide by 5" deep tunnel running 42 inches long at the
stern. You can just see it on some of my pictures showing me move the stern
section with a trailer.
The key here is that the tunnel is still under the designed water line so
there should be no problems with reversing or cooling. It was not installed
to get into shallows with a stern drive but it does reduce the overall
operating depth by 5 inches. Theory here is to have a tunnel allowing me to
raise the Sterndrive high enough that it's mostly out of the water for
corrosion problems plus it can be removed with out shipping water into the
engine compartment so repairs can be made without pulling the 50 foot boat.
This tunnel will not be very effective at the top end speeds of the Wyo and
in fact may cause some cavitations, that's still to be determined.
Jeff
http://www.4dw.net/cosailor/
----- Original Message -----
From: <jhkohnen@...>
To: <bolger@yahoogroups.com>
Sent: Saturday, January 03, 2004 11:14 PM
Subject: Re: [bolger] Re: engines; jet drives
> For a low-speed boat you might consider a tunnel stern, which is
essentially
> a high-volume, low-velocity jet drive. In ascending order of construction
> complexity and propulsion efficiency, here are some examples from Chester
> Nedwidek and the Atkin catalog:
>
>http://www.boat-links.com/images/Skeeter.gif
>
>http://www.boat-links.com/Atkinco/Utilities/Twinkle.html
>
>http://www.boat-links.com/Atkinco/Utilities/RescueMinor.html
>
> On Sat, 3 Jan 2004 09:31:28 -0700, Jeff wrote:
> > ...
> > They also expressed that the efficiency of jet drives are not realized
> until
> > the boat exceeds planing speeds so if I was to travel at hull speeds
most
> of
> > the time, my fuel consumption would be excessive compared to a
propeller.
> > ...
>
> --
> John <jkohnen@...>
>http://www.boat-links.com/
> Distrust any enterprise that requires new clothes.
> <Henry David Thoreau>
>
>
>
>
> Bolger rules!!!
> - no cursing, flaming, trolling, spamming, or flogging dead horses
> - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
> - Pls add your comments at the TOP, SIGN your posts, and snip away
> - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
(978) 282-1349
> - Unsubscribe:bolger-unsubscribe@yahoogroups.com
> - Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
>
> Yahoo! Groups Links
>
> To visit your group on the web, go to:
>http://groups.yahoo.com/group/bolger/
>
> To unsubscribe from this group, send an email to:
>bolger-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject to:
>http://docs.yahoo.com/info/terms/
>
>
For a low-speed boat you might consider a tunnel stern, which is essentially
a high-volume, low-velocity jet drive. In ascending order of construction
complexity and propulsion efficiency, here are some examples from Chester
Nedwidek and the Atkin catalog:
http://www.boat-links.com/images/Skeeter.gif
http://www.boat-links.com/Atkinco/Utilities/Twinkle.html
http://www.boat-links.com/Atkinco/Utilities/RescueMinor.html
a high-volume, low-velocity jet drive. In ascending order of construction
complexity and propulsion efficiency, here are some examples from Chester
Nedwidek and the Atkin catalog:
http://www.boat-links.com/images/Skeeter.gif
http://www.boat-links.com/Atkinco/Utilities/Twinkle.html
http://www.boat-links.com/Atkinco/Utilities/RescueMinor.html
On Sat, 3 Jan 2004 09:31:28 -0700, Jeff wrote:
> ...
> They also expressed that the efficiency of jet drives are not realized
until
> the boat exceeds planing speeds so if I was to travel at hull speeds most
of
> the time, my fuel consumption would be excessive compared to a propeller.
> ...
--
John <jkohnen@...>
http://www.boat-links.com/
Distrust any enterprise that requires new clothes.
<Henry David Thoreau>
> Yamaha used to make a 25hp outboard which when converted to a jet wasrated as an 18hp, perfect for a Sneakeasy.
> I would like to see a jet powered Wyo and since the Sneakeasy is supposedto be scaled down from that why not experment on the smaller cheaper boat?
> The other problem I have been wondering about is braking power. Iunderstand that reverse is poor on jets. Any thoughts anyone? Jeff Blunck,
What are you oing to use?
> DonDropping the transom a bit on a Sneakeasy for the Jet would probably be
ideal and work just fine. Seeing a Sneakeasy scooting along on a morning
dew would be something to watch!
I'm current built out to fit a 3.0L Mercruiser Stern Drive on my Wyoming.
Bolger calls for a max of 150 HP on the Wyo for safety sake so the 130 HP
Sterndrive should be ideal. I expect to cruise around 10 knts on 1/3
throttle with a WOT range of about 22 knts. Who wants to bounce a Wyo and
rattle the dishes going faster? At least in crusing mode with all the gear.
:>)
Jeff
Jet drives are best at speeds above 25 Knots where they are more efficient than propellers. Speeds under 25 Kts the're really inefficient as the motor is still working relatively hard to drive them. The propulsion is directed by the "bucket" on the nozzle, so the engine needs no gearbox in most cases. You adjust the thrust, therefore speed and direction with a lever.You can go from full speed ahead to full astern with just the pull of the lever. Motors are not stressed in these jet applications as they run at a constant load driving the impeller. One must realise that the major strain on a boat's hull is on the bottom, where the jet drive is mounted, not the transom in the case of OB motors or the engine bearers,gearbox in a inboard . I've heard at lower speeds they can be a bit tricky to steer.
As to Outboard jet drives they aren't as bad as you make out, (being only a third of the hp.) Apparently a 115HP Outboard Jet drive is equivilent to a 90 hp outboard. So you do lose a bit of hp, but not 2/3rds!!.but gain lots of advantages as long as you're aware of the jet drive's limitations also. Remember most 115HP outboards are the same size and weight as the 90HP models.Only the rev. range,prop.dimensions and fuel injection/carburettion differ between most brands of 75,90 & 115 HP outboards..
Of course the smaller the HP the greater the difference in output between jet and prop. I'm not sure what the smallest HP jet drive OB is but I don't think I've seen anything under 40hp which would be approximately equivilent to a 25-30hp outboard with prop. drive.
Hugo Tyson, Tasmania Australia.
johnfader <johnfader@...> wrote:
Don:
syncronicity? Just yesterday I was thinking about the jet drive for use in my planned Sneakeasy.
From what I've read about outboard jets, they are really inefficient... as I remember, they are about as effective as a screw-driven outbaard one-third the size. Max, correct me please if I'm misremembering.
Anyone have any idea whether jets work well at low speeds? I'd guess their efficiency increases, but don't know for sure.
Cheers/The Fader
Don Sez:
Happy Hollidays,
I wonder if anyone in this group has experience with outboard
jet drives. I have talked to designers who say that it is hard to
make an inboard/jet drive work smoothly because alot of air
(bubbles) are trapped under the hull and consequently fed to the jet
pump with a poor result in propulsion. I wonder if outboard jets
would work better since they can be adjusted for depth independent
of the hull.
On the Upper Delaware River where I live I see Carolina skiffs
going though 6" deep water at 20-30 MPH with 100/+- HP engines on
their transoms. Imagine how nice this might work on some of the PCB
sharpie boats.
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
- Pls add your comments at the TOP, SIGN your posts, and snip away
- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
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[Non-text portions of this message have been removed]
As to Outboard jet drives they aren't as bad as you make out, (being only a third of the hp.) Apparently a 115HP Outboard Jet drive is equivilent to a 90 hp outboard. So you do lose a bit of hp, but not 2/3rds!!.but gain lots of advantages as long as you're aware of the jet drive's limitations also. Remember most 115HP outboards are the same size and weight as the 90HP models.Only the rev. range,prop.dimensions and fuel injection/carburettion differ between most brands of 75,90 & 115 HP outboards..
Of course the smaller the HP the greater the difference in output between jet and prop. I'm not sure what the smallest HP jet drive OB is but I don't think I've seen anything under 40hp which would be approximately equivilent to a 25-30hp outboard with prop. drive.
Hugo Tyson, Tasmania Australia.
johnfader <johnfader@...> wrote:
Don:
syncronicity? Just yesterday I was thinking about the jet drive for use in my planned Sneakeasy.
From what I've read about outboard jets, they are really inefficient... as I remember, they are about as effective as a screw-driven outbaard one-third the size. Max, correct me please if I'm misremembering.
Anyone have any idea whether jets work well at low speeds? I'd guess their efficiency increases, but don't know for sure.
Cheers/The Fader
Don Sez:
Happy Hollidays,
I wonder if anyone in this group has experience with outboard
jet drives. I have talked to designers who say that it is hard to
make an inboard/jet drive work smoothly because alot of air
(bubbles) are trapped under the hull and consequently fed to the jet
pump with a poor result in propulsion. I wonder if outboard jets
would work better since they can be adjusted for depth independent
of the hull.
On the Upper Delaware River where I live I see Carolina skiffs
going though 6" deep water at 20-30 MPH with 100/+- HP engines on
their transoms. Imagine how nice this might work on some of the PCB
sharpie boats.
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
- Pls add your comments at the TOP, SIGN your posts, and snip away
- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
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---------------------------------
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To visit your group on the web, go to:
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Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
---------------------------------
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[Non-text portions of this message have been removed]
John,
The outboard Jet I was on was very efficient once the owner got it adjusted well enough to keep the intake full of water and not air. This was a original flat bottom Carolina Skiff 19'. I heard that the impellers don't last long if their fed alot of air. If entrained air under flat bottom boats (i.e.Sneakeasy) is a serious problem then I was wonder if the pickup unit on an outboard jet could be lowered several inches further than normal to get away from or , in other words, below this area of entrained air? Said another way: I wonder if lowering the intake would alow the jet to be fed pure water?
Yamaha used to make a 25hp outboard which when converted to a jet was rated as an 18hp, perfect for a Sneakeasy.
I would like to see a jet powered Wyo and since the Sneakeasy is supposed to be scaled down from that why not experment on the smaller cheaper boat?
The other problem I have been wondering about is braking power. I understand that reverse is poor on jets. Any thoughts anyone? Jeff Blunck, What are you oing to use?
Don
johnfader <johnfader@...> wrote:
Don:
syncronicity? Just yesterday I was thinking about the jet drive for use in my planned Sneakeasy. I was thinking about a complete drive from a jet-ski machine. These are far more powerful than I need for this boat, as it will be primarily a river cruiser used ad displacement speeds. I have been planning to use an outboard in the 15-20 hp range.
I have a cousin with a Berkely jet and 455 CID Olds engine that I could have... guess that might be a bit much for a Sneakeasy :-)
As for your application, maybe you shouldn't worry about air bubbles, eh? The drives work; no need worrying about whether there is some theoretical better arrangement. I see folks charging about the lakes all the time before these things, without a worry line on thier brows :-)
Seriously, how much power do you need? From what I've read about outboard jets, they are really inefficient... as I remember, they are about as effective as a screw-driven outbaard one-third the size. Max, correct me please if I'm misremembering. Of course, with that goes 3X the fuel consumption for a given thrust, Compared to a prop.
Anyone have any idea whether jets work well at low speeds? I'd guess their efficiency increases, but don't know for sure.
Cheers/The Fader
Don Sez:
Happy Hollidays,
I wonder if anyone in this group has experience with outboard
jet drives. I have talked to designers who say that it is hard to
make an inboard/jet drive work smoothly because alot of air
(bubbles) are trapped under the hull and consequently fed to the jet
pump with a poor result in propulsion. I wonder if outboard jets
would work better since they can be adjusted for depth independent
of the hull.
On the Upper Delaware River where I live I see Carolina skiffs
going though 6" deep water at 20-30 MPH with 100/+- HP engines on
their transoms. Imagine how nice this might work on some of the PCB
sharpie boats.
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
- Pls add your comments at the TOP, SIGN your posts, and snip away
- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
Yahoo! Groups Links
To visit your group on the web, go to:
http://groups.yahoo.com/group/bolger/
To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
[Non-text portions of this message have been removed]
The outboard Jet I was on was very efficient once the owner got it adjusted well enough to keep the intake full of water and not air. This was a original flat bottom Carolina Skiff 19'. I heard that the impellers don't last long if their fed alot of air. If entrained air under flat bottom boats (i.e.Sneakeasy) is a serious problem then I was wonder if the pickup unit on an outboard jet could be lowered several inches further than normal to get away from or , in other words, below this area of entrained air? Said another way: I wonder if lowering the intake would alow the jet to be fed pure water?
Yamaha used to make a 25hp outboard which when converted to a jet was rated as an 18hp, perfect for a Sneakeasy.
I would like to see a jet powered Wyo and since the Sneakeasy is supposed to be scaled down from that why not experment on the smaller cheaper boat?
The other problem I have been wondering about is braking power. I understand that reverse is poor on jets. Any thoughts anyone? Jeff Blunck, What are you oing to use?
Don
johnfader <johnfader@...> wrote:
Don:
syncronicity? Just yesterday I was thinking about the jet drive for use in my planned Sneakeasy. I was thinking about a complete drive from a jet-ski machine. These are far more powerful than I need for this boat, as it will be primarily a river cruiser used ad displacement speeds. I have been planning to use an outboard in the 15-20 hp range.
I have a cousin with a Berkely jet and 455 CID Olds engine that I could have... guess that might be a bit much for a Sneakeasy :-)
As for your application, maybe you shouldn't worry about air bubbles, eh? The drives work; no need worrying about whether there is some theoretical better arrangement. I see folks charging about the lakes all the time before these things, without a worry line on thier brows :-)
Seriously, how much power do you need? From what I've read about outboard jets, they are really inefficient... as I remember, they are about as effective as a screw-driven outbaard one-third the size. Max, correct me please if I'm misremembering. Of course, with that goes 3X the fuel consumption for a given thrust, Compared to a prop.
Anyone have any idea whether jets work well at low speeds? I'd guess their efficiency increases, but don't know for sure.
Cheers/The Fader
Don Sez:
Happy Hollidays,
I wonder if anyone in this group has experience with outboard
jet drives. I have talked to designers who say that it is hard to
make an inboard/jet drive work smoothly because alot of air
(bubbles) are trapped under the hull and consequently fed to the jet
pump with a poor result in propulsion. I wonder if outboard jets
would work better since they can be adjusted for depth independent
of the hull.
On the Upper Delaware River where I live I see Carolina skiffs
going though 6" deep water at 20-30 MPH with 100/+- HP engines on
their transoms. Imagine how nice this might work on some of the PCB
sharpie boats.
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
- Pls add your comments at the TOP, SIGN your posts, and snip away
- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
Yahoo! Groups Links
To visit your group on the web, go to:
http://groups.yahoo.com/group/bolger/
To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
[Non-text portions of this message have been removed]
According to Mercury, their outboard jet drives are 25% - 30% less
efficient. The advantages are strictly for very shallow running where
debris can impact on propellers and ruin the standard outboard.
I did a fair amount of research on inboard jet drives for my Wyoming and all
the manufacturers that I visited with expressed concern with an inboard jet
drive on a flat bottom boat.
Essentially flatties have to many air bubbles in the water following the
underside of the hull. This has a great advantage in reduced power needed
to get them moving and planing up to the point where the turbulence counters
the power and they hit a wall where much more power is needed to go faster.
This is why flatties where popular in the era of lower HP engines of the
20's and 30's. Now all planing boats are designed with a vee hull which is
usually constant from amidships to the stern.
On an inboard jet drive, these air bubbles impacting on the turbine blades
cause some loss of power and cavitations which can be deadly to an impeller.
They like to see some vee in the hull design where the water pressure is
equal across the bottom and sides, especially when the boat gets up on
plane.
They also expressed that the efficiency of jet drives are not realized until
the boat exceeds planing speeds so if I was to travel at hull speeds most of
the time, my fuel consumption would be excessive compared to a propeller.
The Berkley jet people where very helpful and against their desire to sell
me a drive, convinced me otherwise.
Jeff
efficient. The advantages are strictly for very shallow running where
debris can impact on propellers and ruin the standard outboard.
I did a fair amount of research on inboard jet drives for my Wyoming and all
the manufacturers that I visited with expressed concern with an inboard jet
drive on a flat bottom boat.
Essentially flatties have to many air bubbles in the water following the
underside of the hull. This has a great advantage in reduced power needed
to get them moving and planing up to the point where the turbulence counters
the power and they hit a wall where much more power is needed to go faster.
This is why flatties where popular in the era of lower HP engines of the
20's and 30's. Now all planing boats are designed with a vee hull which is
usually constant from amidships to the stern.
On an inboard jet drive, these air bubbles impacting on the turbine blades
cause some loss of power and cavitations which can be deadly to an impeller.
They like to see some vee in the hull design where the water pressure is
equal across the bottom and sides, especially when the boat gets up on
plane.
They also expressed that the efficiency of jet drives are not realized until
the boat exceeds planing speeds so if I was to travel at hull speeds most of
the time, my fuel consumption would be excessive compared to a propeller.
The Berkley jet people where very helpful and against their desire to sell
me a drive, convinced me otherwise.
Jeff
Don:
syncronicity? Just yesterday I was thinking about the jet drive for use in my planned Sneakeasy. I was thinking about a complete drive from a jet-ski machine. These are far more powerful than I need for this boat, as it will be primarily a river cruiser used ad displacement speeds. I have been planning to use an outboard in the 15-20 hp range.
I have a cousin with a Berkely jet and 455 CID Olds engine that I could have... guess that might be a bit much for a Sneakeasy :-)
As for your application, maybe you shouldn't worry about air bubbles, eh? The drives work; no need worrying about whether there is some theoretical better arrangement. I see folks charging about the lakes all the time before these things, without a worry line on thier brows :-)
Seriously, how much power do you need? From what I've read about outboard jets, they are really inefficient... as I remember, they are about as effective as a screw-driven outbaard one-third the size. Max, correct me please if I'm misremembering. Of course, with that goes 3X the fuel consumption for a given thrust, Compared to a prop.
Anyone have any idea whether jets work well at low speeds? I'd guess their efficiency increases, but don't know for sure.
Cheers/The Fader
Don Sez:
Happy Hollidays,
I wonder if anyone in this group has experience with outboard
jet drives. I have talked to designers who say that it is hard to
make an inboard/jet drive work smoothly because alot of air
(bubbles) are trapped under the hull and consequently fed to the jet
pump with a poor result in propulsion. I wonder if outboard jets
would work better since they can be adjusted for depth independent
of the hull.
On the Upper Delaware River where I live I see Carolina skiffs
going though 6" deep water at 20-30 MPH with 100/+- HP engines on
their transoms. Imagine how nice this might work on some of the PCB
sharpie boats.
syncronicity? Just yesterday I was thinking about the jet drive for use in my planned Sneakeasy. I was thinking about a complete drive from a jet-ski machine. These are far more powerful than I need for this boat, as it will be primarily a river cruiser used ad displacement speeds. I have been planning to use an outboard in the 15-20 hp range.
I have a cousin with a Berkely jet and 455 CID Olds engine that I could have... guess that might be a bit much for a Sneakeasy :-)
As for your application, maybe you shouldn't worry about air bubbles, eh? The drives work; no need worrying about whether there is some theoretical better arrangement. I see folks charging about the lakes all the time before these things, without a worry line on thier brows :-)
Seriously, how much power do you need? From what I've read about outboard jets, they are really inefficient... as I remember, they are about as effective as a screw-driven outbaard one-third the size. Max, correct me please if I'm misremembering. Of course, with that goes 3X the fuel consumption for a given thrust, Compared to a prop.
Anyone have any idea whether jets work well at low speeds? I'd guess their efficiency increases, but don't know for sure.
Cheers/The Fader
Don Sez:
Happy Hollidays,
I wonder if anyone in this group has experience with outboard
jet drives. I have talked to designers who say that it is hard to
make an inboard/jet drive work smoothly because alot of air
(bubbles) are trapped under the hull and consequently fed to the jet
pump with a poor result in propulsion. I wonder if outboard jets
would work better since they can be adjusted for depth independent
of the hull.
On the Upper Delaware River where I live I see Carolina skiffs
going though 6" deep water at 20-30 MPH with 100/+- HP engines on
their transoms. Imagine how nice this might work on some of the PCB
sharpie boats.