Centreboard alignment

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SAS
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Centreboard alignment

Post by SAS » Wed May 01, 2013 4:22 pm

Hi All,

I am replacing the centreboard on my Morrison 11 with a high aspect ratio one. I have built a new carbon case to bond into the boat (it fits inside the existing case), however I need some advice on how to set up the new case in the boat.

The issue I have is not so much the side to side alignment, but fore/aft alignment. The existing case is not much help, as the opening is some 20mm longer at the top (floor) than the bottom (hull)....????.

I assume the board should be perpendicular to the waterline, but how is this measured and is there any tricks to establish this position while the boat is upside down with board in position to bond the case in place.

Thanks
Sean

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Shu
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Re: Centreboard alignment

Post by Shu » Wed May 01, 2013 5:06 pm

Here's one way: If you're confident that the gunwales are symmetrical, run a true (perfectly straight) board or (my choice) long carpenter's level under the gunwales. Measure outward from the boat's centerline an equal distance and mark the board or level. With the centerboard in the cassette and positioned, measure from the marks to the centerboard tip. Adjust the centerboard until the measurements are equal and bond the cassette in place. This will require some jigs to hold everything in place, and (like most of my projects) lots of clamps :D
Steve Shumaker
USA 1183

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Shu
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Re: Centreboard alignment

Post by Shu » Wed May 01, 2013 5:18 pm

Oops, I saw fore and aft as the critical alignment issue after I posted. Basically you want to establish the waterline postion. Barring any design drawings, I would guess it's about 1" to 1.5" up from the bottom of the transom, and at the top of the curve of the knuclke at the bow ("up" and "top" as when the boat is upright). Set up some sort of solid frame both at the bow and stern, and stretch a line parallel and sufficiently far above these marks to clear the bottom of the hull ("above" as when the boat is upside down). This is the line you can make your board perpendicular too.

Does anyone here know if the Morrison 11 board is truly vertical in profile?
Steve Shumaker
USA 1183

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Re: Centreboard alignment

Post by Dan H » Sat May 04, 2013 11:55 am

If you are happy to assume that the angle of the board f/a was good with the bigger board, my advice would be to chock the whole arrangement at equal distances from the fwd part of the original hole top and bottom. I've done that job twice and it all went fine. Although I used packing bog rather than making a new case - this meant that I release coated my chocks, removed them when the bog was cured then back filled the holes left before removing the dagger (which had a good few rounds of parcel tapes round it)
Hope that helps or you can do something similar.
Dan

SAS
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Re: Centreboard alignment

Post by SAS » Tue May 07, 2013 12:10 pm

Thanks All,

Dan - I am not happy that the existing angle of the board is good. Both the front and back angles of the existing case look a fair way out to me. It is for this reason I am looking to re-establish that the new board/case is vertical.

I have no idea why the top of the case is this much larger than the bottom on what was essentialy a production boat. No wonder I had variable upwind speed.

Sean

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Re: Centreboard alignment

Post by Dan H » Wed May 08, 2013 11:43 am

You sail an RMW M11 right? Haven't looked at one in a while, but if the M12 is much to go by (one of the more productiony i14s ever made) the intent is generally for a bit more "gape" on the deck to allow some packing material, and a more low drag tigh fit on the hull exit. Both hull and deck gaps are moulded in on plants on the mould, the case is a seperate moulding with lots of nice release, which is bonded onto the plant on the hull as part of the join process, and a big healthy flange on the top to fit around the outside of the lip for the dagger hole.
I'm not 100% convinced that many i14 daggers are vert w.r.t the load wl, when you see pics with them up they tend to look a bit aft raked. Big variance of course.
If you see the .pdfs of bieker's designs on his website, the leading edges do look vertical, but its tricky to know whether this was Morrison's intent with the M11.
Probably muddies the waters, sorry!

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