Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 25-11-2019, 08:48   #16
Registered User

Join Date: Dec 2013
Posts: 119
Re: Emergency turn under engine

Almost everyone here avoided answering your question. Years ago in a class I ask the instructor almost the same question and he said he had no idea. I can think of two ways of going. One is to find someone with access to a good simulator. Probably a more practical solution is to try it. Probably in less than an hour you could try each scenario several times. If you do or someone else does please post your answers here. Also be sure to mention the boat, speed, and other pertinent data about the Keel and props such as if they are counter-rotating.
lvictorlucas is offline   Reply With Quote
Old 25-11-2019, 09:15   #17
Registered User
 
OS2Dude's Avatar

Join Date: Nov 2014
Location: Atlanta, GA
Boat: Catalina 30
Posts: 659
Images: 5
Re: Emergency turn under engine

Quote:
Originally Posted by S/V Adeline View Post
In THE Titanic situation the vessel was traveling too fast to turn within its field of vision.
An interesting aside: I saw a show that said atmospheric conditions created a 'mirror' that hid the iceberg until it was too late. It was also stated that it caused a mirage of the ship over itself, which is why the other ship (California?) did not think they were looking at a cruise ship when they. got the S.O.S.

Something about the difference in air density over the waters of the Labador Current and the Gulf Stream.
OS2Dude is offline   Reply With Quote
Old 25-11-2019, 10:12   #18
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 10,208
Re: Emergency turn under engine

Quote:
Originally Posted by nfbr View Post
Assume you are motoring, both engines, 3/4 ish throttle, 7knts ish

You see, dead ahead, a log / whale / shipping container / kraken, and want to turn to avoid.

This is the titanic problem. Will the boat turn better with propwash.

What is actually more effective

Rudder Hard Over, Both Full Fwd
Rudder Hard Over, One Full Fwd, One Full Rev (Hopefully the right ones)
Rudder Hard Over, Both Full Rev
Rudder Hard Over, One Full Rev, One Neutral.
Don't Turn. Both full rev. (Titanic might not have sunk if hit head on)
Some other combination.

Now - here is the tough bit - it's not only how quickly the boat rotates heading, but how quickly the vector changes.
It will sideslip. And yes, daggerboards down would help. Assume no time for that. You are motoring with daggerboards up.

Comments?
Leave the rudders amidships.
Cadence is offline   Reply With Quote
Old 25-11-2019, 10:28   #19
Registered User

Join Date: Oct 2007
Posts: 387
Re: Emergency turn under engine

Motoring on a twin engined cat with the daggerboards up, the only thing the hull has to pivot on is the rocker of the hulls. I know that my cat mostly goes sideways with daggerboards up when trying to make a tight turn. The hull needs something to pivot around. When motoring, no sail up, I have both daggerboards down about one-third so I can manoeuvre as desired. All cats are different, but if you have a cat with shallow rocker, narrow (underwater) hulls, with no fins or other underwater protrusions other than small rudders, then you need some daggerboard for directional stability.

With daggerboards up and slamming one engine in reverse and the other in neutral (or in reverse) will turn the boat sideways, but the direction of forward movement is not predictable.
Keep some daggerboard down at all times when motoring.
The least daggerboard I have down when underway is running downwind with the spinnaker, and even then I keep one board down a bit.
Paul Howard is offline   Reply With Quote
Old 25-11-2019, 11:01   #20
Marine Service Provider

Join Date: Dec 2011
Posts: 1,539
Re: Emergency turn under engine

Need to know the type of boat (cat ?) distance to obsticle when sighted, beam and distance between shafts and engine, sea state and prop type for starters to guestimate the corrective action. Also brain, eye, hand coordination of helmsman. Check the video of the cat crashing on the rocks at Kona Hawaii. First item failed the skipper.

You are correct about the Titanic, actions from the bridge and the engine room served to kick the stern out to starboard and the glancing blow ripped open the hull several compartment aft of the collision bulkhead. The intermediate bulkheads didn't extend all the way up to the main deck. Sea water spilled over the top of enough of the intermediates to sink her. She may have survived a head-on. Same with the Costa Concordia (stern kicked out to port by steering command) but the collision with the rock allow the water ingress to kill all engine power. Luckily the wind was such that she drifted on shore. On the chart the water there was probably deep enough that by maintaining course and speed she would have missed the rock or slightly grazed it.
jmschmidt is offline   Reply With Quote
Old 25-11-2019, 11:02   #21
Registered User
 
Shrew's Avatar

Join Date: Aug 2010
Posts: 3,101
Re: Emergency turn under engine

Quote:
Originally Posted by Bycrick View Post
Back to the original question. "You see an object dead ahead ...."

When you move the rudder to one side, it causes the STERN to move in the opposite direction from where you want to go. So turning "away" from the object actually moves your stern towards the object, exposing the side of the boat.
This would be similar to what I would attempt. Things are rarely truely 'dead-ahead'. In most cases it will be either slightly to port or stbd of center.

If it's slightly to port...

turn hard to stbd 45 degrees.
Straighten wheel and hold for at least 1/2 to 1 boat length.
Turn back to port 45 degrees.

The last turn should kick the stern away and hopefully you avoided the object.
Shrew is offline   Reply With Quote
Old 25-11-2019, 12:40   #22
Registered User

Join Date: Oct 2019
Posts: 756
Re: Emergency turn under engine

Engine in neutral until the prop stops to avoid damaging the clutch, then full astern to lessen the impact. Turn the wheel in the hope that you miss the object.
Stewie12 is offline   Reply With Quote
Old 25-11-2019, 15:36   #23
Registered User
 
Juho's Avatar

Join Date: Apr 2015
Location: Finland
Boat: Nauticat 32
Posts: 974
Re: Emergency turn under engine

I think it depends. If your vessel is a hovercraft, your best option might be both full rev. If your boat is a deep fin keel sailboat with an efficient rudder and weak engines, your best option might be to turn it sideways. The boat would not move an inch (maybe a foot ) sideways (former forward) after it has quickly turned. Keeping both engines running forward or idle would keep the water flow good at both(?) rudders, making the quick turn possible.

Paul Howard already mentioned having the daggerboards up or down in a catamaran. Similar differences there. A dagger keel monohull might turn faster (since most of the weight is in the middle). Catamaran daggerboards could stay fully vertical during the turn, which would keep them efficient.
Juho is offline   Reply With Quote
Old 25-11-2019, 15:40   #24
Registered User

Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,233
Re: Emergency turn under engine

Thinking about it, in a cat you'd definitely want to keep the power on regardless of rudder effectiveness. That way even with some side slip, you'll have plenty of thrust to help get you moving in the new direction as you finish the turn.
rslifkin is offline   Reply With Quote
Old 25-11-2019, 15:45   #25
Registered User
 
Stu Jackson's Avatar

Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 9,705
Re: Emergency turn under engine

Quote:
Originally Posted by redneckrob View Post
The big most people forget to do because it's counterintuitive is to turn into the obstacle as it comes abeam your pivot point (somewhere amidships) which will kick your stern away from it. Continuing to turn away could actually cause you to hit something you would otherwise clear.

^^^^VERY important. Some joker hit me last year because he got too close then turned away but his starboard quarter hit my port gunwale because of this^^^.
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, SR/FK, M25, Rocna 10 (22#) (NZ model)
Stu Jackson is offline   Reply With Quote
Old 25-11-2019, 15:48   #26
Registered User

Join Date: Oct 2015
Location: Summerstown Ontario Canada
Posts: 457
Re: Emergency turn under engine

Quote:
Originally Posted by nfbr View Post
Titanic situation
Flat calm, poor viz, autopilot on
it's a judgement call... how fast can you turn or stop and how you can maneuver to avoid an obstacle. Only you can answer that as per your vessel and crew... I personally would turn hard over and shift to neutral. Stop, assess, and plan.... quickly and again....
seabreez is offline   Reply With Quote
Old 25-11-2019, 16:03   #27
Registered User
 
StuM's Avatar

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,891
Re: Emergency turn under engine

Quote:
Originally Posted by Juho View Post
I think it depends. If your vessel is a hovercraft, your best option might be both full rev. If your boat is a deep fin keel sailboat with an efficient rudder and weak engines, your best option might be to turn it sideways. The boat would not move an inch (maybe a foot ) sideways (former forward) after it has quickly turned. Keeping both engines running forward or idle would keep the water flow good at both(?) rudders, making the quick turn possible.

Paul Howard already mentioned having the daggerboards up or down in a catamaran. Similar differences there. A dagger keel monohull might turn faster (since most of the weight is in the middle). Catamaran daggerboards could stay fully vertical during the turn, which would keep them efficient.

This thread is in the multihull sailboats area of CF, so I assume the OP is talking about a performance sailing cat (the daggerboards suggest "performance").


Hovercraft and keelboats are irrelevant.


And to add my 2c worth - those who say "it depends" have it right. Take your own boat out and try it a few times with a beachball in the water. The best solution will depend on the characteristics of your vessel.
StuM is offline   Reply With Quote
Old 25-11-2019, 18:39   #28
Registered User

Join Date: Mar 2016
Location: North of San Francisco, Bodega Bay
Boat: 44' Custom Aluminum Cutter, & Pearson 30
Posts: 608
Re: Emergency turn under engine

Why not go out and test your boat. When I first take out a new to me boat I get it up to speed and do a few hard turns and doughnuts just to see how it behaves. In forward and reverse too.
NorthCoastJoe is offline   Reply With Quote
Old 25-11-2019, 20:32   #29
Writing Full-Time Since 2014
 
thinwater's Avatar

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 9,588
Re: Emergency turn under engine

You don't motor boards up as a rule. A little board down makes it MUCH easier for the auto pilot.


So, a trick question.
__________________
Gear Testing--Engineering--Sailing
https://sail-delmarva.blogspot.com/
thinwater is offline   Reply With Quote
Old 25-11-2019, 23:32   #30
Registered User

Join Date: Apr 2013
Posts: 11,002
Re: Emergency turn under engine

Quote:
Originally Posted by thinwater View Post
You don't motor boards up as a rule. A little board down makes it MUCH easier for the auto pilot.


So, a trick question.
Yep, unless we are trying to sneak into somewhere really shallow, usually put at least a foot of board down. Makes a big difference in maneuverability.
valhalla360 is offline   Reply With Quote
Reply

Tags
emergency, enc, engine

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Want To Buy: Turn Key Cruising Sailboat under 30K in Florida tommycook Boats For Sale and Wanted 20 27-08-2019 13:43
Yanmar engine starts but power buzzer does not turn off/ no tacho gstent Electrical: Batteries, Generators & Solar 20 19-08-2019 04:18
Coolmatic cu 55 under performing under way. unbusted67 Electrical: Batteries, Generators & Solar 1 16-12-2014 13:22
Engine Won't Turn Over Cap Engines and Propulsion Systems 8 02-05-2014 03:17
New Solenoid, Perkins 4-108 / Engine Will Not Turn Over EC Sailor Engines and Propulsion Systems 1 23-08-2011 17:44

Advertise Here


All times are GMT -7. The time now is 22:51.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.