Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 12-07-2008, 13:26   #1
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,077
Images: 69
Hydraulic Steering in Multihulls

I've been trying to pin down exactly what my requirements are for a hydraulic system. The steering manufacturers, IMHO, seem to be overspecifying by incredible amounts.

Hydrive reckon I will need a system capable of exerting 300kg/m of torque for my boat! Frankly I think this is ridiculous.

For one thing, tillers are an option on my boat (the tillers would be under 2m long) how on Earth would anyone exert 300kg/m of torque on tillers? I think a maximum of around 30kg/m is more realistic.

There's a similar size, weight and speed cat called "McMoggy" which is tiller steered, and reportedly the steering effort is very light, barely a kilo or two on the tillers, which are also less than 2m long.

I suspect the steering manufacturers are covering their backsides, and also think they are basing a lot of their calculations on monohulls, which do tend to have higher steering loads.

Any thoughts?
__________________

__________________
44'cruisingcat is offline   Reply With Quote
Old 12-07-2008, 14:15   #2
Senior Cruiser
 
mikereed100's Avatar

Cruisers Forum Supporter

Join Date: Dec 2005
Location: Santa Barbara
Boat: 46' custom cat
Posts: 1,056
Images: 2
44,

I too will be looking at hydraulics soon so this interests me. If I remember from physics, torque = force x length of lever arm. If my math is correct, and I have no reason to believe that it is, then, using Hydrive's guidelines, a 2m tiller would be expected to exert 150kg of force. A 30cm tiller arm, as I have on my boat could expect 1000kg of force. I agree with you that that seems excessive. Your buddies boat, with 2kg on a 2m tiller would be equivalent to 13.3kg on a 30cm arm. Granted, there will be times when the boat is harder to steer but still...I will be interested to see what the more knowledgeable have to say. Good topic.

Mike
__________________

__________________
mikereed100 is online now   Reply With Quote
Old 12-07-2008, 14:50   #3
Registered User

Join Date: Feb 2008
Location: Kauai, Hawaii
Posts: 44
It is when going backwards that the load grows quickly. The rudder is no longer balanced, or semi balanced. Once the hydraulic system is grossly overloaded it entirely fails and you are in trouble.

The other problem with hydraulic steering with cats is trying th keep the rudders lined up. Tiny amounts of fluid bypassing the seals in the rams will get the rudders out of line quickly.
__________________
drewke07 is offline   Reply With Quote
Old 12-07-2008, 14:58   #4
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,077
Images: 69
Really, hydraulic steering is just a different method of gaining mechanical advantage. It's just a different kind of reduction gear.

There's a mechanically steered Schionning, "Cheetah" which is very similar in spec to my boat, and he has just one turn from lock to lock. Steering effort is very acceptable according to the owner.

I see no reason why I couldn't have a hydraulic system with around two turns lock to lock. The system Hydrive are specifying, apart from weighing a ton, would give me between 5 and 7 turns L/L, which is far too slow.

Dave (Catmando) put me on to Ultraflex, who seem to be a bit more reasonable with their steering torque expectations. prices seem reasonable too.
__________________
44'cruisingcat is offline   Reply With Quote
Old 12-07-2008, 15:01   #5
cruiser

Join Date: Nov 2004
Posts: 4,525
Quote:
Originally Posted by drewke07 View Post
It is when going backwards that the load grows quickly. The rudder is no longer balanced, or semi balanced. Once the hydraulic system is grossly overloaded it entirely fails and you are in trouble.

The other problem with hydraulic steering with cats is trying th keep the rudders lined up. Tiny amounts of fluid bypassing the seals in the rams will get the rudders out of line quickly.
I don't know about the rudders coming out of alignment...

I've put something like 2400 miles on my cat since I got her a few months back. Nothing like that has happened to my hydraulic steering.

Not saying it doesn't, but maybe it isn't a common problem - or I'm lucky....

PS: 44'Cat - I have 5 turns, lock to lock on my system, if that's of any help. Can get you some specifics to see what a smaller cruising cat has, if it helps.
__________________
ssullivan is offline   Reply With Quote
Old 12-07-2008, 15:06   #6
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,077
Images: 69
Quote:
Originally Posted by drewke07 View Post
It is when going backwards that the load grows quickly. The rudder is no longer balanced, or semi balanced. Once the hydraulic system is grossly overloaded it entirely fails and you are in trouble.

The other problem with hydraulic steering with cats is trying th keep the rudders lined up. Tiny amounts of fluid bypassing the seals in the rams will get the rudders out of line quickly.
You can fit a bypass round one cylinder (or both) to re-align the rudders. The method is to motor along in a straight line, and just open the bypass valve. The rudder is straightened by the water flow. This shouldn't need to be done all that often.

I understand that loads could potentially be greater when going backwards, but will they be in reality? I mean I could very likely be seeing 20+ knots forwards, certainly high teens will be regular. I doubt if I will ever be going backwards at those kinds of speeds. (I hope) Also, most hydraulic steering pumps have a pressure relief valve fitted.
__________________
44'cruisingcat is offline   Reply With Quote
Old 12-07-2008, 15:11   #7
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,077
Images: 69
Quote:
Originally Posted by ssullivan View Post
I don't know about the rudders coming out of alignment...

I've put something like 2400 miles on my cat since I got her a few months back. Nothing like that has happened to my hydraulic steering.

Not saying it doesn't, but maybe it isn't a common problem - or I'm lucky....

PS: 44'Cat - I have 5 turns, lock to lock on my system, if that's of any help. Can get you some specifics to see what a smaller cruising cat has, if it helps.
G'day Sean, thanks for the input. How do you find 5 turn L/L? I'm hoping to get somewhere between 2 and 3 turns. (preferably closer to 2) Your steering must be very light with that kind of reduction.
__________________
44'cruisingcat is offline   Reply With Quote
Old 12-07-2008, 15:28   #8
cruiser

Join Date: Nov 2004
Posts: 4,525
Quote:
Originally Posted by 44'cruisingcat View Post
G'day Sean, thanks for the input. How do you find 5 turn L/L? I'm hoping to get somewhere between 2 and 3 turns. (preferably closer to 2) Your steering must be very light with that kind of reduction.
Considering I displace just 6 tons (with no gear), the steering is extremely light. The only time it gets stiffer is when she's backing down in reverse and you turn the helm.

Still, very light - like a luxury car with power steering!

But, you can feel the rudders through even this system. You can feel if they are well centered or not by a very slight pressure back on your steering.

I would say there is nothing wrong with having an extra turn or two. Keeps fatigue down. This boat is a dream for making passages... very easy on you. Might be something to consider....
__________________
ssullivan is offline   Reply With Quote
Old 12-07-2008, 15:50   #9
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 4,077
Images: 69
Thanks Sean. Food for thought. It's good to know you still get some feel. I expect on passage the autopilot will be doing almost all the work, the hand steering will be mainly for when I'm "just out for a sail" or maybe if I enter the odd race. Which is why I'd like it to be responsive.

I'm probably going to fit a third helm station inside, which would be mostly for if the A/P has failed and the weather is crappy enough that you'd rather steer from inside. I could install a smaller volume pump there, for lighter/slower steering, to reduce fatigue, as you suggest.
__________________
44'cruisingcat is offline   Reply With Quote
Old 12-07-2008, 16:40   #10
Registered User
 
cat man do's Avatar

Join Date: Aug 2006
Location: Brisbane Australia [until the boats launched]
Boat: 50ft powercat, light,long and low powered
Posts: 4,411
Images: 36
I also had a bit of mild panic when doing my steering, especially as it is truly a one off so no other to refer to.

In you're instance 44cc, what does Bob say? There would be others that have been done before.

I spoke to Rob New at home - marine castings & manufacturers as he has done shafts and head stock for mine and we compared my ruddershape to what he sells as stock and then to what he supplies for most of the other Brisbane cat manufacturers.

He felt it amusing when I told him what I had got as he thought it was overkill.


As far as extra load when backing down, well I always planned on centering the rudders and using the engines which are 22 ft apart.


Dave
__________________
"Money can't buy you happiness but it can buy you a yacht large enough to pull up right alongside it"...............David Lee Roth
Long Distance Motorboat Cruising – It Is Possible on a Small Budget
cat man do is offline   Reply With Quote
Old 12-07-2008, 18:08   #11
Registered User

Join Date: May 2007
Location: Isle des Saintes, Guadeloupe
Boat: Voyage 38 Catamaran
Posts: 165
My experience with hydraulic steering is that it is not responsive. On my PDQ 32 and on various charters that had hydraulics there was no feedback of weather or lee helm. To my pleasant surprise, the mechanical cable steering in my Voyage 38 cat has almost the same feedback as a monohull.
__________________
Billyehh
billyehh is offline   Reply With Quote
Old 12-07-2008, 22:15   #12
Registered User

Join Date: Apr 2008
Posts: 12
Quote:
Originally Posted by billyehh View Post
My experience with hydraulic steering is that it is not responsive. On my PDQ 32 and on various charters that had hydraulics there was no feedback of weather or lee helm. To my pleasant surprise, the mechanical cable steering in my Voyage 38 cat has almost the same feedback as a monohull.
Billyehh,

What material is your steering cable? metal?, synthetic fibre?

44' cruisin cat,

As has been mentioned, the reason the rudders see greater load when backing is that the moment arm about the stock is much greater as the force balance is reversed.

As for the design of the steering system, would it not make sense to design for failure of the least expensive component? Which would you have break first, rudder/stock, or hydraulic system? And besides, why not design the hydraulics to incorporate a relief valve so the system never sees force near the breaking point of the rudders (or whatever component of the system you may choose)?
__________________
sailrjim is offline   Reply With Quote
Old 12-07-2008, 22:29   #13
Registered User

Join Date: Nov 2006
Location: Vancouver, Can.
Boat: Woods 40' catamaran
Posts: 277
I disagree that the highest loads are seen in reverse. The forces are proportional to Velocity squared. Given that a typical cat might see speeds of 15 knots in the ahead condition, that's the sort of speed you have to design to.

Yes, in reverse, the Center of pressure might be twice as far back from the rudder stock, but the much lower astern speeds more than make up for it.

Yes, the suggested hydraulic system is over the top.

I have a 40' cat with both tillers and a rope drum / wheel setup that connects to the tillers. The tillers are 4' long or so, and I have steered with just tillers, beam reaching at 15 knots with full sail in 25 knots of wind, windward hull lifting up about 1/3 - 1/2. Very little helm loads where I would have expected tons on a monohull.

The rope drum/wheel gives an additional 3:1 or 4:1 mechanical advantage, and there is never any appreciable helm load on the wheel. About 3-1/2 turns.

Hydraulic systems on cats can get out of alignment, but if the seals are in good condition, it can take many months before re-alignment is required.
__________________
Evan is offline   Reply With Quote
Old 13-07-2008, 02:00   #14
Registered User
 
fastcat435's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Amstelveen Netherlands
Boat: FastCat 445 Green Motion
Posts: 1,649
Images: 10
Send a message via Skype™ to fastcat435
On our cats we advice to check the alignment once every month un less lots of sailing is done and realigning the rudders takes 5 seconds , we have made a open circuit valve and when moving forward at 8 knots plus under power the rudders align themselves when the valve is opened for a couple of seconds

Greetings
Gideon
__________________
fastcat435 is offline   Reply With Quote
Old 13-07-2008, 03:39   #15
cruiser

Join Date: Nov 2004
Posts: 4,525
Quote:
Originally Posted by Evan View Post
I disagree that the highest loads are seen in reverse. The forces are proportional to Velocity squared. Given that a typical cat might see speeds of 15 knots in the ahead condition, that's the sort of speed you have to design to.

Yes, in reverse, the Center of pressure might be twice as far back from the rudder stock, but the much lower astern speeds more than make up for it.

Try it out. Put her in reverse with the engines at 3/4 max rpm. Go hard over to port or starboard. Compare this pressure you feel at the helm to the pressure you feel moving forward. Should be greater...


but may depend on rudder configuration. Mine are "barn door" type hung from skegs like a cruising mono would have. Well, come to think of it, every mono I've owned with balanced spade rudders behaved the same way with any speed on in reverse, so not sure how your boat doesn't.
__________________

__________________
ssullivan is offline   Reply With Quote
Reply

Tags
hydraulic steering

Thread Tools
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
Hydraulic Steering NoTies Propellers & Drive Systems 38 19-10-2011 09:23
Hydraulic Self-Steering dana-tenacity Auxiliary Equipment & Dinghy 12 30-12-2009 13:37
converting tiller steering to wheel steering hooked on water Construction, Maintenance & Refit 4 09-04-2008 22:13
hydraulic steering and rudder? turkish6 General Sailing Forum 14 16-01-2008 21:13
Worm-gear steering - any experience with this type of steering? sneuman Monohull Sailboats 2 12-04-2007 11:52


Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

RV & Travel Trailer Communities

Our RV & Travel Trailer sites encompasses virtually all types of Recreational Vehicles, from brand-specific to general RV communities.

» More about our RV Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities


Copyright 2002-2012 Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 07:28.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2014, vBulletin Solutions, Inc.

Sailing News Delivered to your Email!

Stay up-to-date with the latest cruising news.

unsusbcribe at anytime with one click

Close [X]


ShowCase vBulletin Plugins by Drive Thru Online, Inc.