Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 21-01-2013, 16:13   #1
Registered User

Join Date: Nov 2010
Posts: 830
Images: 27
Excessive Rake

Hello, I noticed this whilst browsing second hand cats.

Am I dreaming or is this a ridiculous amount of rake? Surely it would have some major affects on performance?



From:

Catamarans for sale
__________________

__________________
ausaviator is offline   Reply With Quote
Old 21-01-2013, 17:40   #2
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,152
Re: Excessive Rake

With their higher speeds than monohulls the longitudinal hydrodynamic resistance on the hull is greater causing the sail to want to rake forward. Raked aft they are less prone to have the sails center of effort shift forward of the hulls center of lateral resistance causing lee helm.

At high speeds, imagine the wind pushing the top of the mast forward and the hulls resistance pushing the base of the mast aft causing the bow to pitch down, shifting the sails center of effort further forward.

You especially see a good amount of rake on lightweight racing catamarans whose hydrodynamic resistance on the hull compared to its sail area to displacement ratio is much higher. On larger cats not as much rake is needed because of the reduced sail area to displacement ratio and reduced righting moment for the amount of displacement.
__________________

__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 21-01-2013, 17:51   #3
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 19,371
Re: Excessive Rake

Looks pretty excessive to me. Maybe he has a lee helm problem! Or maybe he thinks he's a pirate!
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Old 21-01-2013, 18:02   #4
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,152
Re: Excessive Rake

Ok, I just saw the picture. That is excessive even if it were a racing catamaran
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 21-01-2013, 18:07   #5
Registered User

Join Date: Nov 2008
Posts: 407
Re: Excessive Rake

It's a dean cat. I find them unsightly with that ridiculous racked mast.
__________________
Overlord is offline   Reply With Quote
Old 21-01-2013, 18:14   #6
Head in a locker
 
Cavalier's Avatar

Cruisers Forum Supporter

Join Date: Dec 2010
Location: Houston, TX
Boat: Beneteau 461 47'
Posts: 879
Images: 1
Quote:
Originally Posted by Cheechako View Post
Looks pretty excessive to me. Maybe he has a lee helm problem! Or maybe he thinks he's a pirate!
... maybe it's not a mast at all, just a very manly VHF antenna!
__________________
"By day the hot sun fermented us; and we were dizzied by the beating wind. At night we were stained by dew, and shamed into pettiness by the innumerable silences of stars."
Cavalier is online now   Reply With Quote
Old 21-01-2013, 18:32   #7
Registered User

Join Date: Nov 2010
Posts: 830
Images: 27
Re: Excessive Rake

Ok, so it's not an isolated instance! This one looks worse!

__________________
ausaviator is offline   Reply With Quote
Old 21-01-2013, 19:04   #8
Registered User

Join Date: Dec 2010
Location: W Carib
Boat: Wildcat 35, Hobie 33
Posts: 7,965
Re: Excessive Rake

Not sure why Dean's are built with such an extreme rake. It's not like it is a one-off build issue.

Any Dean owners out there who know the rationale?
__________________
belizesailor is offline   Reply With Quote
Old 21-01-2013, 19:25   #9
Registered User

Join Date: Nov 2010
Posts: 830
Images: 27
Re: Excessive Rake



Even their 44 model has a similar set-up.

__________________
ausaviator is offline   Reply With Quote
Old 21-01-2013, 19:41   #10
Marine Service Provider
 
Factor's Avatar

Join Date: Dec 2006
Location: Brisbane Australia
Boat: Corsair Dash MKII
Posts: 4,087
Re: Excessive Rake

Yep - way too much. Moving Finger, a very very fast racing tri with canting and variable rake mast doesnt have that much.

As I understand the Dean Company design reasoning - the mast is proportionally further forward than most and the rake moves the centre of effort to a balanced position, but that is just what I was told when inquiring, I haven't done any analysis myself.
__________________
Factor is offline   Reply With Quote
Old 21-01-2013, 20:24   #11
Senior Cruiser
 
Roy M's Avatar

Cruisers Forum Supporter

Join Date: Feb 2007
Location: Southwestern Yacht Club, San Diego, CA
Boat: Searunner 40 trimaran, WILDERNESS
Posts: 3,042
Images: 4
Re: Excessive Rake

These bring to mind the old Delta rigs. I haven't seen one in San Diego for at least 25 years.
__________________
Roy M is offline   Reply With Quote
Old 21-01-2013, 21:33   #12
Writing Full-Time Since 2014
 
thinwater's Avatar

Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 4,352
Re: Excessive Rake

If the rake helped, performance classes would have gone there. They do some, but not so much and for reasons not relevant here (lift and loading up the rudders on cats without boards).

Could it have been to get the mast base out of the salon? Not a good enough reason.

Hmm....
__________________
Gear Testing--Engineering--Sailing

Writing full-time since 2014.
Bookstore:http://sail-delmarva.blogspot.com/20...ook-store.html
thinwater is online now   Reply With Quote
Old 21-01-2013, 21:33   #13
Registered User
 
eliems's Avatar

Join Date: Jan 2011
Location: Vancouver BC
Boat: 1993 Hunter H28
Posts: 152
Re: Excessive Rake

I think I read somewhere it is to compensate for not having a backstay. It does look odd but the Deans have a good reputaion as a tough sturdy but comfortable Blue Water cat that makes pretty good speed for it's class.

I have been thinking about a Dean 400 currently for sale.
__________________
eliems is offline   Reply With Quote
Old 21-01-2013, 21:34   #14
Registered User
 
cwyckham's Avatar

Join Date: Apr 2011
Location: Vancouver, BC
Boat: Niagara 35
Posts: 1,870
Re: Excessive Rake

Looks like it hit a bridge! I guess they wanted to have more unobstructed area in the Salon, so they pushed the base of the mast forward. Just silly, IMHO
__________________
cwyckham is offline   Reply With Quote
Old 21-01-2013, 21:43   #15
Senior Cruiser

Cruisers Forum Supporter

Join Date: Dec 2006
Location: Seattle
Boat: Cal 40
Posts: 2,401
Images: 7
Re: Excessive Rake

Quote:
Originally Posted by David M View Post
With their higher speeds than monohulls the longitudinal hydrodynamic resistance on the hull is greater causing the sail to want to rake forward. Raked aft they are less prone to have the sails center of effort shift forward of the hulls center of lateral resistance causing lee helm.

At high speeds, imagine the wind pushing the top of the mast forward and the hulls resistance pushing the base of the mast aft causing the bow to pitch down, shifting the sails center of effort further forward.

You especially see a good amount of rake on lightweight racing catamarans whose hydrodynamic resistance on the hull compared to its sail area to displacement ratio is much higher. On larger cats not as much rake is needed because of the reduced sail area to displacement ratio and reduced righting moment for the amount of displacement.
I would argue that it is a lack of buoyancy in the bows that allow a cat to pitch bow down more than a keelboat. More an issue on beach cats than cruising cats. And while the CE is moving forward as you pitch bow down, at least on all the beach cats I have sailed the CLR moves forward much faster and farther due to more bow in the water and less stern in resulting in weather helm, not lee helm.

Top racing beach cat sailors change rake for the conditions. Hobie 16s with no daggerboard have a different reason. Boats with daggerboards will sail with a more upright mast in lighter conditions and will rake back for stronger winds. I haven't seen an explanation that I like yet but talk to any racing sailor and they will tell you that raking the mast aft will depower the rig and allow you to point higher, this is for cats, planing dinghies and keelboats. The beach cat sailors also like to point out that the weight of mast is further aft, but that seems a minor point to me.

The first cat I chartered, a Privilege 39 had a lot of rake, it did not look like other Privilege 39s. On one day we had a nice wind and on a broad reach we had to reef the main because the weather helm was so bad the steering system was binding and locking up. At first I thought we had the rudder hard over, but a lull unloaded the gear and then I could turn it farther.

I like the other explanation better that it was designed with the mast base forward and the mast raked to balance the boat.

JOhn
__________________

__________________
cal40john is offline   Reply With Quote
Reply

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 04:23.


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.