Wednesday Rant: Mast Ram Geometry?

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Craig Thompson

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Mar 10, 2021, 4:14:01 AM3/10/21
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One of my pet peeves has always been people comparing/discussing mast ram adjustment based on distance at the track, which is dependent on having the same tube length to be a relevant comparison. Ethan Bixby proposed measuring position at the gate which is a much more universal comparison, but harder to see when sailing. Position of the forward ram pivot point relative to mast step/boat is the other variable but my experience is this is more consistent between boats than the tube length.

Waterat has two standard length ram tubes; 22" (21.25" pin-to-pin) and 20.5" (19.75" pin-to-pin). Holger and P&B tend to use shorter/lower ram tubes closer to 18-19" pin-to-pin range.

I've just made up a 22" ram tube to the Waterat standard spec. The forward ram pivot point is 1520 mm from the pin CL to the forward edge of the deck/bow. This is looking pretty long to me and perhaps a bit too high on the mast in the neutral position. 

Does anyone else have a 22" ram tube in use with the auto-ram down control. I'm curious to know how the ratio of rake/ram works this tube length?

Any info you can share would be helpful. Thanks in advance.
___

Craig Thompson
+44 7387 023 608 (UK mobile)
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Parker Shinn

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Mar 10, 2021, 8:49:30 AM3/10/21
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Eric and I calculated the differences between our ram and Howie and Mike’s boats. Hope this helps. 

Double check this, but if my memory is correct:

A = distance from deck pin to the front of the mast
B = distance from deck to pin on the ram car
C = tube length




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Parker Shinn

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Mar 10, 2021, 9:02:20 AM3/10/21
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Whoops, looked more closely and I got A and B switched. 

Craig Thompson

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Mar 10, 2021, 9:04:27 AM3/10/21
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 Parker,

Thanks so much for this data. Makes sense to me now.

So if the measurements at A1/B1 are at rake= 25'-8", does that mean A2/B2 are at rake= 25'-7",  A3/B3 are at rake= 25'-6" ....and so on?

Also, what are the numbers on the right-hand side of the sheet? 
___

Craig Thompson
+44 7387 023 608 (UK mobile)

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Ryan Cox

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Mar 10, 2021, 1:49:41 PM3/10/21
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Calibrating Rams always bothered me too.  Ram numbers are inconsistent unless the tube length and angle are pretty similar.  A ram nearly parallel to the deck doesn’t move the mast much but a steep angle moves it a ton.  It would be a smaller range but maybe ram measurement should be along the deck, how far back the mast moves at deck level.  Distance the car moves isn’t a good indicator.

Ryan Cox

On Mar 10, 2021, at 6:04 AM, Craig Thompson <iqc...@gmail.com> wrote:


 Parker,

Thanks so much for this data. Makes sense to me now.

So if the measurements at A1/B1 are at rake= 25'-8", does that mean A2/B2 are at rake= 25'-7",  A3/B3 are at rake= 25'-6" ....and so on?

Also, what are the numbers on the right-hand side of the sheet? 
___

Craig Thompson
+44 7387 023 608 (UK mobile)


On Wed, Mar 10, 2021 at 2:02 PM Parker Shinn <parke...@gmail.com> wrote:
Whoops, looked more closely and I got A and B switched. 
On Wed, Mar 10, 2021 at 8:49 AM Parker Shinn <parke...@gmail.com> wrote:
Eric and I calculated the differences between our ram and Howie and Mike’s boats. Hope this helps. 

Double check this, but if my memory is correct:

A = distance from deck pin to the front of the mast
B = distance from deck to pin on the ram car
C = tube length

<image_6487327.JPG>

Miller, Jeff

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Mar 10, 2021, 1:55:36 PM3/10/21
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Welcome back, Ryan!


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Mike Holt

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Mar 10, 2021, 1:58:31 PM3/10/21
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Ryan who?

 

We us the numbers as a sanity check. But our goal is even bend as the basis, too many other things effect that, spreaders, shroud tension vang.

 

So, going upwind, the crew will check and call more high or low or even. Based on that I will fine tune ram.

Parker Shinn

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Mar 10, 2021, 3:28:18 PM3/10/21
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Craig, we didn’t take mast rake into account aside from making sure all the masts started at 25’8” (B1). What we were looking for was how much the mast moved backwards at the deck given at .5” movement in mast ram. 

Column F was the delta between B1 and B’. 

Column G = Column C - Column B. It shows how much Mike’s mast moves relative to our mast through out the range. Notice is only changes by .1” throughout the ram range. Column H is the same thing except for Howie. 


Antoine Laussu

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Mar 10, 2021, 7:52:53 PM3/10/21
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The distance of the mast base to the deck will also impact the rake geometry.

Antoine

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Craig Thompson

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Mar 11, 2021, 5:15:07 AM3/11/21
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Parker,

OK, I see what you have done now. Thanks for sharing your data; very helpful. This data set disproves by initial thinking that tube length is the only critical issue. It is clear that the variation in the "B" dimension and the angle of the tube at the datum point are critical in determining the overall travel.

If you are curious, I have put this into a bit different format to help my understanding of it: https://docs.google.com/spreadsheets/d/1UbsZD107UKjxynaGAaQZIbUpTkWEYpaVCrRshxyF3-U/edit?usp=sharing
___

Craig Thompson
+44 7387 023 608 (UK mobile)

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