Reply
 
Thread Tools Search this Thread Display Modes
 
Old 12-31-2019, 07:39 PM   #1
Member
 
stuarth44's Avatar
 
City: buderim
Country: australia
Join Date: Oct 2019
Posts: 7
tunnels in new build

i found this, which greatly encouraged me to redesign my bottom, maybe it is in wrong thread, it should be of great interest to designers and N.A.s
http://www.ayocol.itu.edu.tr/AYOCOL2...014_Samsul.pdf
this should kake 25knts cruise with 4btm cummins
Attached Thumbnails
Click image for larger version

Name:	Screenshot (41).jpg
Views:	51
Size:	96.4 KB
ID:	97960  
__________________
Advertisement

stuarth44 is offline   Reply With Quote
Old 01-01-2020, 12:10 AM   #2
TF Site Team
 
FlyWright's Avatar
 
City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 12,772
In my uneducated position, only if you want a protected prop at the expense of maneuverability.

I hear tunnels present a problem with maneuvering in some twins. Can't imagine how much worse it might be in a single.
__________________

__________________
My boat is my ark. It's my mobile treehouse and my floating fishing cabin. It's my retreat and my respite. Everyday I thank God I have a boat! -Al

@DeltaBridges - 25 Delta Bridges in 25 Days
FlyWright is offline   Reply With Quote
Old 01-01-2020, 01:45 AM   #3
Guru
 
Comodave's Avatar
 
City: Au Gres, MI
Country: US
Vessel Name: Never Say Never
Vessel Model: President 41 DC
Join Date: Jul 2015
Posts: 7,667
I think that Bayliner had tunnels in some of their motoryachts and then phased the tunnels out. Donít remember why they got rid of them.
__________________
Boat Nut:
If you are one there is no explanation necessary.
If you arenít one, there is no explanation possible.
Comodave is online now   Reply With Quote
Old 01-01-2020, 07:12 AM   #4
Enigma
 
RT Firefly's Avatar
 
City: Slicker?
Country: Bumpkin?
Join Date: Oct 2007
Posts: 14,063
Greetings,
Old, old news. Penn Yan boats patented their "Tunnel Drive" system in 1970. https://patentimages.storage.googlea.../US3515087.pdf


I've had a 23' single for 5 years and have experienced no problems with maneuverability. Photo is similar to my boat:


__________________
RTF
RT Firefly is offline   Reply With Quote
Old 01-01-2020, 08:52 AM   #5
Guru
 
CaptTom's Avatar
 
City: Southern Maine
Country: USA
Vessel Model: Prairie 36 Coastal Cruiser
Join Date: Dec 2012
Posts: 2,038
Hey RT, my buddy had an early '70s Penn Yan 23' with tunnel drive. Man we had fun with that thing. Drew about 18" of water. Didn't back up very well. Slow-speed maneuvering wasn't pretty, either. No bow thruster. He docked in on the back side of a face dock, just a few feet from the rocks, in a strong current. I guess we just learned to deal with it. I notice the extended rudder in that pic, probably helps a lot.
CaptTom is offline   Reply With Quote
Old 01-01-2020, 09:15 AM   #6
Enigma
 
RT Firefly's Avatar
 
City: Slicker?
Country: Bumpkin?
Join Date: Oct 2007
Posts: 14,063
Greetings,
Mr. CT. More fun than a basket of puppies on a ferris wheel. There ARE maneuvering "quirks" but once learned, moving the boat where you want is fairly simple. NO prop walk and a small rudder can pose problems to those that are used to the behavior of trawlers. I expect the poor low speed steering is symptomatic of any planing boat with a small rudder. One does have to think ahead.


The rudder pictured is not extended but "bent", on purpose. Evidently, over the years, Penn Yan made changes to both the size and shape of the tunnel AND the size, shape and placement of the rudder to gain better performance. Not unheard of for any manufacturer to "tweak" their design.


I think I draw about 18" as well, at rest but about 12" when on plane. She scoots right along but gets a bit "squirrely" above 30 mph. Light load @ 3000 RPM she's doing about 24 mph and burning 16 gph. Mercruiser 350. GREAT boat.


__________________
RTF
RT Firefly is offline   Reply With Quote
Old 01-01-2020, 09:31 AM   #7
Guru
 
City: Canaveral
Country: USA
Join Date: Jun 2012
Posts: 1,699
I suppose that a small tunnel acts like a partial Kort nozzle, which are known to reduce maneuverability
makobuilders is offline   Reply With Quote
Old 01-01-2020, 09:46 AM   #8
Guru
 
Pete Meisinger's Avatar
 
City: Oconto, WI
Country: USA
Vessel Name: Best Alternative
Vessel Model: 36 Albin Aft Cabin
Join Date: Oct 2012
Posts: 1,145
I also had a Penn Yan, 23 foot. It was a pretty high speed boat with a 383 Chrysler in it. I was absolutely mesmerizing to stick your head over the stern rail at high speed and watch the fury of the prop wash. Plus the dual exhaust roaring away.

pete
Pete Meisinger is offline   Reply With Quote
Old 01-01-2020, 10:06 AM   #9
Guru
 
City: gulf coast
Country: pinellas
Join Date: Jun 2014
Posts: 2,953
There wont be any prop walk to aid manouverability
bayview is offline   Reply With Quote
Old 01-01-2020, 10:14 AM   #10
Enigma
 
RT Firefly's Avatar
 
City: Slicker?
Country: Bumpkin?
Join Date: Oct 2007
Posts: 14,063
Greetings,
Mr. b. Agreed. NO prop walk in my case but since Mr. 44 is contemplating a new build it should be no problem to incorporate thrusters to compensate, I would think.
__________________
RTF
RT Firefly is offline   Reply With Quote
Old 01-01-2020, 10:56 AM   #11
Guru
 
City: Anacortes
Country: USA
Join Date: Nov 2012
Posts: 846
+1 on the 23 Penn Yan!!!

Great maneuverability on that boat. At least as compared to other single screw inboards.

However, searching for the right prop took talking with the owner of PY, at least 6 prop shop experts, 7 props and 8 or 9 adjustments. It was quite the science project. Costly, but also a lot of fun.

The advantages of the tunnel were primarily low draft, and a shallow shaft angle that put the engine very low and centered in the small boat, ideal for the center of gravity.

I eventually got fairly decent performance on a new higher hp engine, but it took a LOT of experimentation. The tunnel was very finicky on how it responded. Since the prop diameter was essentially fixed, you had to play with blade number, rake, cup to get the tunnel to flow more water. Off even by a little and efficiency would tank.

My buddy had a twin tunnel screw 33 but he only drafted a couple inches more than I did. We traversed some shallow rocky water together at speed! I once went clean over a hiding tree with no damage to the prop at all.

Iím left with mixed feelings. It was really fun on a small boat for someone who loved to tinker, but could become prohibitively expensive on a vessel with larger, expensive props. Lots of guys in the PY community ran around with some pretty horrible perf, large rooster tails, slow speed and just lived with it as normal. I hear some pretty bad reputations on larger boats with pockets and canít help but to wonder whether the problem is really just non ideal props and too expensive to troubleshoot coupled with few people who know how to make it work.

First question/principle if I went with prop tunnels would be to get very clear on what my goals were and in what order. To get something, you will need to give something else.
ghost is offline   Reply With Quote
Old 01-01-2020, 11:02 AM   #12
Guru
 
Codger2's Avatar
 
City: San Diego
Country: US
Vessel Name: "Sandpiper"
Vessel Model: 2006 42' Ocean Alexander Sedan
Join Date: Oct 2007
Posts: 6,260
Quote:
Originally Posted by bayview View Post
There wont be any prop walk to aid manouverability
Not 100% true! If the prop(s) are High up in the tunnel there won't be hardly any prop walk. With about half the prop(s) diameter below the tunnel(s) bottom, prop walk is excellent! Ocean Alexander was fully aware of this and positioned the props correctly
Attached Thumbnails
Click image for larger version

Name:	Sandpiper's bottom.jpg
Views:	24
Size:	147.3 KB
ID:	97966   Click image for larger version

Name:	Sandpiper's Bottom 2.jpg
Views:	22
Size:	117.2 KB
ID:	97967   Click image for larger version

Name:	Sandpiper's bottom 3.jpg
Views:	23
Size:	95.4 KB
ID:	97968  
__________________
Codger 1941.. Constant pursuit of the ultimate SoCal Cruising boat.
Codger2 is offline   Reply With Quote
Old 01-01-2020, 11:03 AM   #13
Guru
 
City: Rochester, NY
Country: USA
Vessel Name: Hour Glass
Vessel Model: Chris Craft Catalina 381
Join Date: Aug 2019
Posts: 1,498
Looking at how small those tunnels force the trim tabs to be, I wonder if that costs some of the efficiency the tunnels are trying to gain on a planing hull?
rslifkin is offline   Reply With Quote
Old 01-01-2020, 11:13 AM   #14
Guru
 
Codger2's Avatar
 
City: San Diego
Country: US
Vessel Name: "Sandpiper"
Vessel Model: 2006 42' Ocean Alexander Sedan
Join Date: Oct 2007
Posts: 6,260
Quote:
Originally Posted by rslifkin View Post
Looking at how small those tunnels force the trim tabs to be, I wonder if that costs some of the efficiency the tunnels are trying to gain on a planing hull?
I can't answer that as there is really no need for trim tabs n my boat. I never use them.
__________________
Codger 1941.. Constant pursuit of the ultimate SoCal Cruising boat.
Codger2 is offline   Reply With Quote
Old 01-01-2020, 12:52 PM   #15
Guru
 
City: gulf coast
Country: pinellas
Join Date: Jun 2014
Posts: 2,953
Those are some very shallow "tunnels"
bayview is offline   Reply With Quote
Old 01-01-2020, 01:11 PM   #16
Guru
 
MurrayM's Avatar
 
City: Kitimat, North Coast BC
Country: Canada
Vessel Name: Badger
Vessel Model: 30' Sundowner Tug
Join Date: Jul 2012
Posts: 5,896
Dave Gerr's single tunnel protected prop coupled with a box keel opens up skinny water and beaching opportunities: https://www.gerrmarine.com/Beachable_Boats.html
__________________

__________________
"The most interesting path between two points is not a straight line" Murray Minchin
MurrayM is online now   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 11:47 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×