Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 12-06-2013, 11:47   #1
Registered User
 
Gboy's Avatar

Join Date: Mar 2011
Location: Georgia
Boat: Conser 47 performance CAT
Posts: 108
Mast Rake 40-50 ft Catamarans

Hi all..

I would like some opinions (not too many) on mast rake, related to sail plan and hull shape as much as possible.

My CAT (Conser 47) is a more performance CAT with narrow hulls, 14,000 Ibs deplacement and wing mast..so not your regular cruising CAT.
Have 625/329 sqft sail plan, mast is 20 ft from bow on this 47 ft CAT..

Just replaced the composite rigging and have a 3 ft rake on a 58 ft mast (actual mast length). I read everything from 1-4 deg rake..

Presently I have 3 deg, which is a 3 ft rake, measured at mast base.

As one may expect good upwind performance...but seem to have more weather helm.

Is it possible to calculate the recommended rake angle, given some factors/measurements ??

Or is this a sail and play type of correction ?

If anyone really know their stuff, I can supply all info required....



Thanks for advice
__________________

__________________
Gboy is offline   Reply With Quote
Old 12-06-2013, 11:57   #2
Registered User
 
caradow's Avatar

Join Date: Mar 2011
Location: Connecticut/Caribbean
Boat: Voyage 440 Owners Version
Posts: 472
Re: Mast Rake 40-50 ft Catamarans

so......if you have too much weather helm just keep reducing it until the helm feels right.
at the point you are at why all the complicated measurements?
in my 40 years of racing I always thought boats were tuned best by feel.
even in one design classes the sailmaker numbers only get you in the ballpark.
sounds like a fun boat
good luck
__________________

__________________
caradow is offline   Reply With Quote
Old 12-06-2013, 12:01   #3
CF Adviser

Cruisers Forum Supporter

Join Date: Dec 2007
Location: Wherever our boat is; Playa Zaragoza, Isla Margarita
Boat: 1994 Solaris Sunstream 40
Posts: 2,439
Re: Mast Rake 40-50 ft Catamarans

I agree totally with caradow - as you move the truck of the mast forward, you will reduce weather helm. There are so many variables on any boat that effect weather/lee helm, it really is a matter of trial and error.

Brad
__________________
Southern Star is offline   Reply With Quote
Old 12-06-2013, 12:18   #4
Registered User
 
salticrak's Avatar

Join Date: Jul 2011
Location: palmwoods qld australia
Boat: wharram tiki 26
Posts: 739
Re: Mast Rake 40-50 ft Catamarans

The mast rake for my wharram tiki 26 is 4 deg. Naturally it is not a performance boat but does have narrow hulls.

I am not sure but i think the rake is the same for the larger Wharrams.
__________________
salticrak is offline   Reply With Quote
Old 12-06-2013, 13:06   #5
Registered User
 
Gboy's Avatar

Join Date: Mar 2011
Location: Georgia
Boat: Conser 47 performance CAT
Posts: 108
Re: Mast Rake 40-50 ft Catamarans

Thanks for the initial feed back..I agree it has to be want feels right in the end.

This is my first real CAT (only charters previous)..

I also realize there are so many variables in the boat design details (and even hull condition, etc..) that can effect any such advice or initial considerations..

Just trying to get a general experienced view point. One problem I have is the hydraulic steering design, that gives very little feel. I can only really go by rudder in dictator ...

The initial discussion came from slower speeds than expected with this CAT, that has history of achieving near apparent wind speed (in certain conditions of course)..and if the rudders were adding too much drag.

I have to state as well, I am new to sailing (2 yrs)...but learning fast.

Can I asume that anything between 1 - 4 degrees would be normal range and I just need to find where works the best for current boat design and condition.

Thanks again.
__________________
Gboy is offline   Reply With Quote
Old 12-06-2013, 13:31   #6
Registered User
 
caradow's Avatar

Join Date: Mar 2011
Location: Connecticut/Caribbean
Boat: Voyage 440 Owners Version
Posts: 472
Re: Mast Rake 40-50 ft Catamarans

yes those numbers are fine
just dial out the excess rudder by getting rid of some rake.
hydraulic steering is problematic in that sense but if you have a rudder indicator then that will work.
I personally am not a fan of hydraulic steering for that reason although I had it on my 50 foot ketch for over 12 years and it never failed me but sort of "sailing blind" when it comes to feel.
again I would not get too hung up on numbers other than reducing sail by numbers and not feel!
a lot of factors/forces will be affecting your boat at any one time.
__________________
caradow is offline   Reply With Quote
Old 12-06-2013, 13:45   #7
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Mast Rake 40-50 ft Catamarans

Before doing any rig work, check to make sure the rudders are aligned properly. Hydraulic steering can creep over time and one rudder could be misaligned to the other.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 12-06-2013, 18:41   #8
Registered User

Join Date: Jun 2010
Location: Sailing the Caribbean
Boat: Switch 51
Posts: 1,498
Re: Mast Rake 40-50 ft Catamarans

Switch 51 calls for 4 degrees. You can check by doing the math on the triangle a halyard makes dropped to the deck.
__________________
SVNeko is offline   Reply With Quote
Old 05-08-2015, 07:18   #9
Marine Service Provider
 
beiland's Avatar

Join Date: Aug 2007
Location: St Augustine, FL, Thailand
Boat: 65 Sailing/Fishing catamaran
Posts: 1,142
Re: Mast Rake 40-50 ft Catamarans

Quote:
Originally Posted by Gboy View Post
Hi all..

I would like some opinions (not too many) on mast rake, related to sail plan and hull shape as much as possible.

My CAT (Conser 47) is a more performance CAT with narrow hulls, 14,000 Ibs deplacement and wing mast..so not your regular cruising CAT.
Have 625/329 sqft sail plan, mast is 20 ft from bow on this 47 ft CAT..

Just replaced the composite rigging and have a 3 ft rake on a 58 ft mast (actual mast length). I read everything from 1-4 deg rake..

Presently I have 3 deg, which is a 3 ft rake, measured at mast base.

As one may expect good upwind performance...but seem to have more weather helm.

Is it possible to calculate the recommended rake angle, given some factors/measurements ??

Or is this a sail and play type of correction ?

If anyone really know their stuff, I can supply all info required....
Thanks for advice
Happen across this subject thread while looking for something else.

Wondering if you still have the boat, and if you ever solved your problem?
__________________
Brian Eiland
distinctive exploration yachts
beiland is offline   Reply With Quote
Old 23-02-2016, 02:45   #10
Registered User
 
Gboy's Avatar

Join Date: Mar 2011
Location: Georgia
Boat: Conser 47 performance CAT
Posts: 108
Re: Mast Rake 40-50 ft Catamarans

Yes, but don't have much of a problem, just trying to optimize and learn..

Thankd


Sent from my iPhone using Cruisers Sailing Forum
__________________
Gboy is offline   Reply With Quote
Old 23-02-2016, 09:39   #11
Marine Service Provider

Join Date: May 2012
Location: New Orleans
Boat: We have a problem... A serious addiction issue.
Posts: 3,940
Re: Mast Rake 40-50 ft Catamarans

I don't know of any way to calculate rig settings. There is the designers original plan, and then racers get ahold of the boat and throw the book out of the window. Just as an example, the original J-35 tuning guide called for 2 degrees of rake and no prebend. This was right up until a boat named Big-J showed up at worlds with 0 rake and 16" of prebend and almost lapped the fleet.

I would think that 1-4 degrees is a pretty conservative place to start. My A-Cat for instance starts at 6.5 degrees prebend, and rakes back to 9 degrees as the wind picks up.
__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.
Stumble is offline   Reply With Quote
Old 23-02-2016, 11:13   #12
cruiser

Join Date: Oct 2015
Posts: 285
Re: Mast Rake 40-50 ft Catamarans

Quote:
Originally Posted by Stumble View Post
My A-Cat for instance starts at 6.5 degrees prebend, and rakes back to 9 degrees as the wind picks up.
Are you talking about prebend, which is mast bend or curve within the mast itself, or rake, which is mast angle, or the mast's relationship as a whole to the deck/level of the boat? Two different things.
__________________
AD28 is offline   Reply With Quote
Old 23-02-2016, 12:36   #13
Writing Full-Time Since 2014
 
thinwater's Avatar

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 4,332
Re: Mast Rake 40-50 ft Catamarans

All about rudder angle and the relative size of keel and rudders.

High rake is relatively common on beach cats, particularly Hobbie 16s, as the sailors learned that the best foils were the rudders (no dagger board). Thus, if they rake the mast, it keeps the bows up reaching and places lateral load on the rudders, which they can handle at speed as they are relatively deep. Even better on the Prindle 16/18.

However, this exaggerated rake does NOT apply to most larger cats. The rudders are small by comparison, the keel/dagger is better, and the lee bow does not dive on a reach.

Because cats have little helm feel, it is useful to know how far off center on the wheel corresponds to 4 degrees of rudder; lets you know when the balance is off.
__________________
Gear Testing--Engineering--Sailing

Writing full-time since 2014.
Bookstore:http://sail-delmarva.blogspot.com/20...ook-store.html
thinwater is offline   Reply With Quote
Old 23-02-2016, 13:20   #14
Marine Service Provider

Join Date: May 2012
Location: New Orleans
Boat: We have a problem... A serious addiction issue.
Posts: 3,940
Re: Mast Rake 40-50 ft Catamarans

Quote:
Originally Posted by AD28 View Post
Are you talking about prebend, which is mast bend or curve within the mast itself, or rake, which is mast angle, or the mast's relationship as a whole to the deck/level of the boat? Two different things.
Sorry I should have been more clear. My neutral rake setting is 6.5 degrees for 8-10kn of breeze. As the wind lightens the mast is raked forward to about 5.5 degrees at 0-3kn. In heavy air I pull the mast back to 9 degrees at 20+kn.

The boat has almost zero prebend at rest, rig tensions aren't high enough to induce much. But as the mast rotates it indices side bend, so where a normal rig is bend backwards on the A-Cats the rig bends to the side.
__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.
Stumble is offline   Reply With Quote
Old 23-02-2016, 14:51   #15
cruiser

Join Date: Oct 2015
Posts: 285
Re: Mast Rake 40-50 ft Catamarans

Quote:
Originally Posted by Stumble View Post
But as the mast rotates it indices side bend, so where a normal rig is bend backwards on the A-Cats the rig bends to the side.
Actually, if you care for some history, the original 'normal' is what we used to call 'bendy' rigs (what you have) ergo the mast had no prebend/tightened diamond wires, but was flexy enough with loose diamonds such that when we'd (over)rotate the rig the mast would bend on the minor axis. Back in the old 18 Square days, there was quite a contention between 'bendy' and 'prebent'.

The bendy rigs lose a bit of sail efficiency, in that the bent mast creates a bit of a shadow into the luff of the main. The advantage of prebend is that one doesn't have to over-rotate, in that the mast camber is induced in line with the foil shape.

I was under the impression that the A guys these days are all messing with diamonds that tighten on the fly to induce bend for ambient conditions... but then my high-tech was the 18 Square
__________________

__________________
AD28 is offline   Reply With Quote
Reply

Tags
mast

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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 04:48.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.