Re: [bolger] Jet drive, engines
On Jan 5, 2004, at 11:55 AM, Don Tyson wrote:
the pump would fit between the tails.
Next a jetski motor and pump at the stern with the
accomodations moved forward. Come to think about it
the space occupied by the motor well and between
the tails might be enough to save you from moving
the cockpit.
Next a jetski pump at the stern connected by a
long drive shaft to the motor ahead of the cockpit.
There are pumps, Berkeley for one, that attach aft
of the transom. These would not eat so much
interior space but I'm not sure they are available
in Sneakeasy size.
hal
> Hal, What type of jet? Outboard are steerable but would they damageA jet outboard would be the simplest but I'm not sure
> the aft end of the sneakeasy?
the pump would fit between the tails.
Next a jetski motor and pump at the stern with the
accomodations moved forward. Come to think about it
the space occupied by the motor well and between
the tails might be enough to save you from moving
the cockpit.
Next a jetski pump at the stern connected by a
long drive shaft to the motor ahead of the cockpit.
There are pumps, Berkeley for one, that attach aft
of the transom. These would not eat so much
interior space but I'm not sure they are available
in Sneakeasy size.
hal
Sigh this is one of those times when a picture would be
worth a thousand words.
I think that if you want truly a truly shallow draft
Sneakeasy a jet is the way to go.
Hal, What type of jet? Outboard are steerable but would they damage the aft end of the sneakeasy?
How 'bout a sketch.
Don
[Non-text portions of this message have been removed]
worth a thousand words.
I think that if you want truly a truly shallow draft
Sneakeasy a jet is the way to go.
Hal, What type of jet? Outboard are steerable but would they damage the aft end of the sneakeasy?
How 'bout a sketch.
Don
[Non-text portions of this message have been removed]
In my research for tunnels on planing boats, the best info I got was that the tunnel should be a minimum 7 times it depth, 10 preferred, and about 50% larger than the prop. If you have a 5 inch tall tunnel the length should be at least 35 inches and tapered gradually to the last 12 inches which allows the stream to solidify and change directions to straight aft. Using a 15 inch diameter prop, use a minimum tunnel width of 22 or 23 inches.
Also, you can sneak the outboard or sterndrive another inch or two higher by narrowing the exit sides of the tunnel slightly, say about 1/4 inch and taper the top of the tunnel exit upwards. This in effect squirts the water upwards to small rooster tail which enables the prop and cooling inlet to run in a solid stream.
Obviously the disadvantage of the last paragraph is potential overheating at slow speeds depending on the outboard's water intake and for sure you would have poor reverse thrust.
The Sneakeasy could probably benefit from a 4" tunnel as you can push the tunnel depth about 1 inch above the water line. Running a outboard jet drive in this environment would allow it to run shallower than the hull though reverse might require an push pole depending on how far you push the envelope.
In some waters and rivers, that would way cool!
Jeff
[Non-text portions of this message have been removed]
Also, you can sneak the outboard or sterndrive another inch or two higher by narrowing the exit sides of the tunnel slightly, say about 1/4 inch and taper the top of the tunnel exit upwards. This in effect squirts the water upwards to small rooster tail which enables the prop and cooling inlet to run in a solid stream.
Obviously the disadvantage of the last paragraph is potential overheating at slow speeds depending on the outboard's water intake and for sure you would have poor reverse thrust.
The Sneakeasy could probably benefit from a 4" tunnel as you can push the tunnel depth about 1 inch above the water line. Running a outboard jet drive in this environment would allow it to run shallower than the hull though reverse might require an push pole depending on how far you push the envelope.
In some waters and rivers, that would way cool!
Jeff
[Non-text portions of this message have been removed]
On Jan 4, 2004, at 6:50 AM, johnfader wrote:
or outboard. The tunnel is just different than what
is found on displacement boats.
The idea of a tunnel on a planing boat is to permit
raising the outdrive to minimize drag. The front wall
of the tunnel is roughly perpendicular to the bottom so
the the water will break free of the bottom and not
-stick- to the front wall and top of the tunnel. This
will reduce drag at planing speeds. Also the tunnel is
very short more of a box shape than tunnel. Since
the bottom of the boat is below the surface, the water
immediately begins to rise as it breaks free of the
front edge of the tunnel. This area of -higher- water
right in front of the drive is what permits the drive
leg to be raised thus reducing drag from the drive leg.
BTW the water should not reach the top of the tunnel
before exiting the stern of the boat.
Sigh this is one of those times when a picture would be
worth a thousand words.
The draft of the Sneakeasy is little enough that I wonder
if a tunnel in front of the outboard would make a
difference.
I think that if you want truly a truly shallow draft
Sneakeasy a jet is the way to go. I got into this
discussion late and haven't seen all of the responses,
but I think the low speed manuverability thing is mostly
a bad rap. The thing to remember is that if water is
not flowing through the nozzle you won't have control.
Just turn the nozzle and blip the throttle, the boat
will turn. Same for reverse.
Sorry for the verbosity. Sorry if I repeated anyone.
hal
> John,Tunnels work well on planing boats with an outdrive
>
> for the Sneakeasy, I don't want to lose either the shallow draft nor
> the
> planing ability. I don't mind losing a bit of room inside that an
> inboard engine might take up. I didn't realize that a tunnel hull
> wasn't
> good for a planing boat; thoughtthey used them on racing hydros. Is
> there a difference in types of tunnel hull for those?... oh, you said
> below "tunnel stern" rather than tunnel hull. Maybe that's the
> difference.
or outboard. The tunnel is just different than what
is found on displacement boats.
The idea of a tunnel on a planing boat is to permit
raising the outdrive to minimize drag. The front wall
of the tunnel is roughly perpendicular to the bottom so
the the water will break free of the bottom and not
-stick- to the front wall and top of the tunnel. This
will reduce drag at planing speeds. Also the tunnel is
very short more of a box shape than tunnel. Since
the bottom of the boat is below the surface, the water
immediately begins to rise as it breaks free of the
front edge of the tunnel. This area of -higher- water
right in front of the drive is what permits the drive
leg to be raised thus reducing drag from the drive leg.
BTW the water should not reach the top of the tunnel
before exiting the stern of the boat.
Sigh this is one of those times when a picture would be
worth a thousand words.
The draft of the Sneakeasy is little enough that I wonder
if a tunnel in front of the outboard would make a
difference.
I think that if you want truly a truly shallow draft
Sneakeasy a jet is the way to go. I got into this
discussion late and haven't seen all of the responses,
but I think the low speed manuverability thing is mostly
a bad rap. The thing to remember is that if water is
not flowing through the nozzle you won't have control.
Just turn the nozzle and blip the throttle, the boat
will turn. Same for reverse.
Sorry for the verbosity. Sorry if I repeated anyone.
hal
What seems to be the sped limitations of these hulls. Was lack of speed the cause od their lack of popularity in recent years.
Seems like this configuration of tunnel and box stear would be perfect on the Flat bottomed sharpies.
jhkohnen@...wrote:
A planing boat with a tunnel stern hull should work. The Atkin tunnel-stern
Seabright skiff utilities in the current catalog are designed to go 17-18
mph. It's just that high-velocity jet drives aren't any good at slow speeds,
while tunnel-sterns work fine when going slow.
Seems like this configuration of tunnel and box stear would be perfect on the Flat bottomed sharpies.
jhkohnen@...wrote:
A planing boat with a tunnel stern hull should work. The Atkin tunnel-stern
Seabright skiff utilities in the current catalog are designed to go 17-18
mph. It's just that high-velocity jet drives aren't any good at slow speeds,
while tunnel-sterns work fine when going slow.
On Sun, 04 Jan 2004 08:50:45 -0500, John Fader wrote:
> ...
> I didn't realize that a tunnel hull wasn't
> good for a planing boat; thoughtthey used them on racing hydros. Is
> there a difference in types of tunnel hull for those?... oh, you said
> below "tunnel stern" rather than tunnel hull. Maybe that's the difference.
> ...
--
John
http://www.boat-links.com/
Never board a ship without an onion, is sound doctrine.
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[Non-text portions of this message have been removed]
I remember reading a book from our local library on the hisory of the seabright skiff. In the book low speed handling was praised because of its value to fisherman. Also the hulls plane easily apparently without a forceful transition from displacement mode to full planing mode. Rum runners liked them because they were fast in their time.
The Dave Gerr Design I was thinking about was featured either in Small Boat Jurnal or Wooden Boat some years ago and was called "Summer Kyle" (41') and had a draft of less than 2' as I recall.
Don
jhkohnen@...wrote:
A planing boat with a tunnel stern hull should work. The Atkin tunnel-stern
Seabright skiff utilities in the current catalog are designed to go 17-18
mph. It's just that high-velocity jet drives aren't any good at slow speeds,
while tunnel-sterns work fine when going slow.
The Dave Gerr Design I was thinking about was featured either in Small Boat Jurnal or Wooden Boat some years ago and was called "Summer Kyle" (41') and had a draft of less than 2' as I recall.
Don
jhkohnen@...wrote:
A planing boat with a tunnel stern hull should work. The Atkin tunnel-stern
Seabright skiff utilities in the current catalog are designed to go 17-18
mph. It's just that high-velocity jet drives aren't any good at slow speeds,
while tunnel-sterns work fine when going slow.
On Sun, 04 Jan 2004 08:50:45 -0500, John Fader wrote:
> ...
> I didn't realize that a tunnel hull wasn't
> good for a planing boat; thoughtthey used them on racing hydros. Is
> there a difference in types of tunnel hull for those?... oh, you said
> below "tunnel stern" rather than tunnel hull. Maybe that's the difference.
> ...
--
John
http://www.boat-links.com/
Never board a ship without an onion, is sound doctrine.
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:
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To unsubscribe from this group, send an email to:
bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to:
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[Non-text portions of this message have been removed]
A planing boat with a tunnel stern hull should work. The Atkin tunnel-stern
Seabright skiff utilities in the current catalog are designed to go 17-18
mph. It's just that high-velocity jet drives aren't any good at slow speeds,
while tunnel-sterns work fine when going slow.
Seabright skiff utilities in the current catalog are designed to go 17-18
mph. It's just that high-velocity jet drives aren't any good at slow speeds,
while tunnel-sterns work fine when going slow.
On Sun, 04 Jan 2004 08:50:45 -0500, John Fader wrote:
> ...
> I didn't realize that a tunnel hull wasn't
> good for a planing boat; thoughtthey used them on racing hydros. Is
> there a difference in types of tunnel hull for those?... oh, you said
> below "tunnel stern" rather than tunnel hull. Maybe that's the difference.
> ...
--
John <jkohnen@...>
http://www.boat-links.com/
Never board a ship without an onion, is sound doctrine.
<H. W. Tilman>
John,
for the Sneakeasy, I don't want to lose either the shallow draft nor the
planing ability. I don't mind losing a bit of room inside that an
inboard engine might take up. I didn't realize that a tunnel hull wasn't
good for a planing boat; thoughtthey used them on racing hydros. Is
there a difference in types of tunnel hull for those?... oh, you said
below "tunnel stern" rather than tunnel hull. Maybe that's the difference.
I wish I could come up with some sort of dispro arrangement as I have a
14hp Kohler single w/hydraulic drive that I'd sacrifice. I expect that
it would give me planing speed with the correct prop and would be dang
nice at 6-8 mph.
Cheers/The Fader
Jkohnen sez:
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:
for the Sneakeasy, I don't want to lose either the shallow draft nor the
planing ability. I don't mind losing a bit of room inside that an
inboard engine might take up. I didn't realize that a tunnel hull wasn't
good for a planing boat; thoughtthey used them on racing hydros. Is
there a difference in types of tunnel hull for those?... oh, you said
below "tunnel stern" rather than tunnel hull. Maybe that's the difference.
I wish I could come up with some sort of dispro arrangement as I have a
14hp Kohler single w/hydraulic drive that I'd sacrifice. I expect that
it would give me planing speed with the correct prop and would be dang
nice at 6-8 mph.
Cheers/The Fader
Jkohnen sez:
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: