Oday 25 mask rake

[Ritdog]

Oday 25 mast rake

I was looking at tabernacle mounts today on three 25 masts, and noticed that 2 had a separater between the mast and base plate that created about a 1/8th" differance between the fore and aft thicknesses, which would rake the mast slightly back, probably about 6+ inches at the top. Is this normal? What's the advantage?

MY mast didn't have this - should I?

 

[Brian S]

Rake is controlled by standing rigging tension. To determine the correct rake, you kinda need to tweak it as necessary. Take a look over at Don Guillette's forum, there is a discussion of weather helm, and how much is good, and how much is too much. http://forums.oday.sailboatowners.com/showthread.php?t=159303&#post1088405 Raking aft by loosening forestay and tightening shrouds and backstay increases weather helm, raking forward induces lee helm (very undesirable…) Seldén's "Hints and Advice" rig tuning guide is a good starting point: http://www.seldenmast.com/resources/hints_and_advices.html

On racing boats, and in particular dinghies with bendy masts, setting pre-bend in the mast is done routinely. A shim under the mast foot might accomplish this, but on masts that go up though a slot in the deck, shims are often used to induce or reduce pre-bend. Most active class racing boats like this will have a class sponsored tuning guide, or a manufacturer's tuning guide.

On my 192, there are no tuning guides, since 192 are day sailing cruising boats, and not a racing class. I had to go out 2 or 3 times to tweak the rig, and get that mast rake set so I felt I had a neutral helm with a trace of weather helm as Don points out. Having a Loos tension gauge helped keep uppers and lowers balanced as far as tension is concerned.

Hope this helps.

 

[Jackdaw]

ritdog,

Great question.

Mast rake on a masthead rig like yours moves the Center of Effort (CE) of the rig backwards and forwards. As Brian notes this is often done to deal with weather or lee helm.

It is important to note that mast rake and pre-bend are two totally different things. Rake tilts the entire mast at a angle. Bend does just that, bends the mast and is a sail trim control. Pre-bend is very difficult to do on most masthead rigs and is normally not done.

There are two schools of thought regarding how to set deck stepped masts for rake.

One is just to set the standing rigging to rake it and leave it be. But the problem is that the base of the mast tilts and all the compression forces and up of one end. This can (and has) spit masts at the base.

The other idea then is to wedge it at the rake angle, This spreads the load of entire base again. Sounds like what someone did to yours.

New masts often come with a rounded base to keep even pressure no matter the rake angle.

 

[Golden Road]

The 23 carrys a heavy weather helm when healed to a certain degree. I wouldn't doubt the 25 (similar hull design) has the same. I would not rake at all to begin with.

 

[Technodad]

My Seldon furler came with a new front stay that you cut to length and install the supplied wire fitting. This effectively sets the length (mast rake) as there is no adjustment.
I find the stock length gives me just the right amount of weather helm.
When I raise the mast, I use only one pin in the base, this prevents any back and forth strain on the cabin top mount plate.

GOLDEN ROAD... I really like the work you have done on your boat, you have a good album of pics.

 

[RichBone]

I was looking at tabernacle mounts today on three 25 masts, and noticed that 2 had a separater between the mast and base plate that created about a 1/8th" differance between the fore and aft thicknesses, which would rake the mast slightly back, probably about 6+ inches at the top. Is this normal? What's the advantage?

MY mast didn't have this - should I?

My tabernacle plate is flat on the cabintop. I don't know why any would have a tapered spacer underneath. I don't know if it was standard on some models or not. Difference between shoal keel and full keel? I removed the plate when I rebuilt my boat and noticed there was a difference of fore and aft placement if it was turned around. Probably enough to make a difference in the balancing of the rig. I guess only Rudy knows.
My boat balances out very nicely. A new main makes a difference in balance too. If your boat handles well now then you're fine.