mast rake?

Discussion about the building and sailing of the Iain Oughtred designed Caledonia Yawl

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mast rake?

Postby Rene » Tue Aug 22, 2017 4:27 am

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good morning all,

i have a caledonia yawl in a simple lug configuration, therefore the mast is located in the aft position.
in normal winds she moves perfect, however yesterday i was sailing her in very light wind and i noticed it was almost impossible to tack
i had the same experience with one reef in stronger winds.

looking at the boat in the harbour i noticed the mast was almost vertical
when i look at the drawing of the boats in Ian's catalogue, i see most of them with a noticeable mast rake
this mast rake seems to be in the area of 5 degrees
this effectively means that the top of the 6 meter mast is leaning almost 50 cm back, moving the CE of the sail aft with 25-30 cm.

does anyone have experience adding rake to the mast?
or could you advise on the amount of mast rake in Ian's plan?

thank you.
Rene
 
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Re: mast rake?

Postby Mike » Tue Aug 22, 2017 2:33 pm

Rene,

Oh, this is the aluminum boat with twin bilge boards that you posted last year. You may have some issues related to tuning the boards and tacking. Would you please post some information about the boards, such as location, angle, depth of the boards and maybe some photos? The boards may be the real issue.

I would recommend that before you tinker with the rake, that you take a good look at how your downhaul on the boom is rigged. You need to have to have it very tight. That said, the attached file shows the correct rake for both mast positions. Be sure that you have the boat leveled to the water line before measuring your rake :)

Good luck,
Mike

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Re: mast rake?

Postby Rene » Thu Aug 24, 2017 6:58 am

Thank u Mike for your quick response

this morning i made some pictures and indeed the mast has a 5-6 degrees rake, about half of the amount i measured from your drawing
for this picture i connected the halyard around the mast and to the front of the boom in order to get the sail a bit more aft
see picture boat
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boat
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now to answer your points.
the bilge boards are operated like regular Ducht leeboards are at the same location and are the same size as the original one, they are fully profiled and about 85 cm apart
you can see the construction and the boards on the picture construction
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construction
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when sailing in the wind the one on the lee side is fully lowered and the other one is fully raised
just before the tack i reverse the situation and in 3 bft wind this works quit well.
to me it seems in this position they are even more effective then the central board, the lee board is deeper, see picture board
in broad reach i use both and raise them partially till i have a fully neutral rudder.
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The downhaul is rather loose when there is little wind but tight to super tight in higher winds
the downhaul can be operated from behind and has a 3:1 reduction


i hope u can make something out the pictures

regards, rene
Rene
 
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Re: mast rake?

Postby Mike » Thu Aug 24, 2017 9:51 am

Rene,
The attached sail plan has three points for you to consider, 1) the tick mark on the water line abaft the centerboard (center of lateral resistance "COLR"), 2) the number "164" on the foresail (combined center of effort "CCOE"), and 3) the number "151" on the foresail (center of effort of the foresail "COE"). For your boat, you ideally want the location of "151" to be where the "164" is located. I.E.; for your boat, the CCOE and the foresail COE are identical and that COE needs to be located just in front of the COLR by about the same amount as in the drawing. If you can achieve that relationship, the actual rake of the mast is less important. Moving the yard attachment point AND the boom downhaul attachment point are the way to tune that location. You may want to physically verify the location of your "as built" COLR when determining the location.

Note: The optimal downhaul attachment location point may change as you add reefs to the sail. Again, the downhaul needs to be tight, even in light air.

Good Luck,
Mike

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Re: mast rake?

Postby Scott Mason » Thu Aug 24, 2017 2:26 pm

Hi Rene,

I second what Mike said about the halyard attachment location. A couple more thoughts for you to consider, based on what I learned with getting my lug yawl CY to tack better:
1) The bow of the CY has a lot of windage so it helps to back wind the sail until the bow swings through the wind. So rather than letting the boom just swing over after putting the tiller over, I often hold the aft end of the boom to windward until we are on the desired tack.
2) Weight forward - when I described my problems on the Woodenboat forum, John Welsford the boat designer responded and said that in his (ample) experience, tacking problems were usually the result of weight balance too far aft. I put a bit of ballast in front of the CB case and this does seem to help. It also helps to helm from the center thwart rather than the aft. Crew in front of the center thwart also helps.
3) Outhaul tension - it helps, especially when reefed, to adjust outhaul tension to suit wind strength, looser in light winds, tighter in higher wind.

Good luck!
Scott
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Re: mast rake?

Postby Rene » Thu Aug 24, 2017 4:22 pm

Gentlemen, thank you all for your advise

I will play around with the halyard and downhaul attachment points, to move the sail .
Without fixed boom and yard it is great what u can do with this type of sail.
Since i have very light balasted boards i will also move the ballast forward.

How to find the actual CLR is not clear to me, maybe Mike can elaborate a bit on this.
Probably just pulling the boat sidewards with a fixed rudder position and different attachment points might do the trick.

Next week the weather seems to be perfect for this type of exercise, in general i think i got some ideas for improvement.
Will let you know the results.

Regards, Rene
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Re: mast rake?

Postby Mike » Thu Aug 24, 2017 6:06 pm

The CLR is measured as 1/2 the distance from bow to stern along the waterline. Rudders and boards are ignored for the purpose of determining the CLR. Adding ballast forward (a very good idea) may increase your water line length by a few inches (not to worry).

I might add that in sailing borrowed CYs, I have been to known to ask a crew member to sit in front of the mast in order to get that particular boat in trim. It's one of those things you tend to do automatically and then forget to mention. The same for holding the boom when tacking, that is a common move. If you have a mizzen sail, pulling it in tight does thing same thing.

Sounds like you are well on the way to getting your boat tuned up.

Take care,
Mike
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