Measuring mast rake
Posted: 02 Dec 12 17:24
Message ID: 2271
What is the 'proper' way to measure mast rake?
I'm asking as I'm trying to setup my boat using one of the tuning guides - however I'm a bit confused as there seems to be be various methods from the top of the mast to the top of the transom, or is it to the inside bottom of the transom / floor joint? - I have seen both ways discussed here.
Also I have seen mentioned that you set the tape to 19ft at the goose neck, then measure to the transom. I found this this took off 90mm from the measurements...compared with the tape hoisted to the one to the very top of the mast.
My boat is a Parker mk2 by the way...
Thanks in advance.
Posted: 03 Dec 12 13:07
Reply ID: 6384
I'd measure to the top of the transom as it is easier. You don't need to set the tape to 19ft at the goose neck; this can be a fiddle. Just pull it to the top and take the reading at the goose neck. Then subtract that reading from the "rake" reading (at the top of transom). This will give you a repeatable number. Measure with the boat upright in a windless area, not on its side or in a blow, to minimise tape sag.
Someone else better qualified than me can remind us whether the ram is left on or off.
Posted: 03 Dec 12 18:57
Reply ID: 6385
On Parkers you need to measure to the join of the floor with the transom, that was the standard when the Parker guides were written as the transom tops were not consistent.
I've never bothered with a gooseneck "verification" measurement, I just look to make sure the tape has pulled right up to the masthead.
Measurement should be taken with the rig tension on.
It isn't a measurement that matters to be millimeter perfect, too many other things that could affect it are potentially variable by a few mm (like centreboard bolt position for instance). The guides are a good starting point and then try SMALL changes and see if it gets better or worse.
Posted: 04 Dec 12 22:11
Reply ID: 6386
Thanks for the replies.
I've now set the rake to approx 6830mm from top of mast to transom / floor joint. I'll give this a go at the weekend to see if it improves things - I think the mast was too upright (original measurement was 6950mm) as there was a lack of any weather-helm, maybe actually verging toward lee-helm!
Around 6800mm seems to be what the set-up guides recommend.
Posted: 12 Dec 12 17:43
Reply ID: 6387
I would disagree with not taking a measurement to the gooseneck. I donít believe it is possible to get an accurate measurement without some sort of calibration. There are too many variables when simply pulling it to the top of the mast such as shackle length and how the tape measure is tied on to the halyard (i.e. at the end or beginning of the shackle or some may use a bobble on a rope halyard) and then whether it has slipped or not on the way up to the top.
In my short time sailing larks the sail plans from different sailmakers and settings from one boat to another appear to vary a lot, which is something I really like about the class. However, because of this I would suggest having a standard way to measure your rake is important when starting to build your own set of settings as I would imagine the settings from one sailmaker to another should vary.
For example, I am currently working off the following figures, using HD sails:
Measurement to top of gooseneck - 5560mm
Upright setting - 6685
Raked setting - 6640
Pre-bend Ė 30mm
Rake is measured to the top of the transom on an ovi.