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Mast rake

Posted: 10 Oct 2005, 13:00
by Andy Stevenson
Afternoon folks, me again :)

Plans for the new rig continue to fill out. I’m now thinking about mast rake adjustment. Having read Lester’s ideas on making a mast & rig, I have to admit being tempted to head in the direction of a fixed length jib stay & adjustable positioning to give the desired rake. But just what range will cover the likely desired rake?

Keeping the rig as close to the deck as possible (60mm) would seem to limit me to about 2deg forward rake before hitting the upper limit mark, so that one’s easy. But how far back might one need to go? I haven’t really sailed this boat in all weathers but I’ve not yet been passed 2deg aft rake before I’m happy with the balance. Am I likely to need to go further than that? Lester’s mast for the A rig looks like it’ll go back to 6deg.

I know each boat’s going to be different, but is there a rule on thumb that’ll get me started?


Re: Mast rake

Posted: 11 Oct 2005, 09:19
by awallin
andy111 wrote: I know each boat’s going to be different, but is there a rule on thumb that’ll get me started?
1rig: 0 to 2 deg back (more forward in heavy weather, back in light)
2rig: 1 to 3 deg back
3rig: 2 to 4 deg back

it will ofcourse be different for each hull...


Posted: 12 Oct 2005, 05:41
by Steve Landeau
Hello, Roy.
I have always used rake as a regular adjustment. I have also asked many other top skippers about it, and it's about a split as to whether it is moved or not once the "right" balance has been acheived. In other words, there are some that find the "correct" rake, and then never adjust it in any conditions. This "correct" rake will obviously be very different depending on design. The way I set up my boat is with a series of holes (usually 5) about 3-4mm apart. The top hole is right at the mid-band, and drill down from there. Then, set up your forestay to be in the middle hole while the mast is in the center of the mast trunk (assuming it is keel stepped). I generally will not take the mast ram pressure into consideration, cause if you are raking all the way back in the trunk, it is very light air, and you'll be using minimal backstay.
If you are one that uses mast rake, the series of holes is good, because you know right where you are simply by looking at which hole you are in. Using a bowsie is not as consistent, and will require that you take regular measurements with a rule.

Posted: 12 Oct 2005, 10:04
by Lester
Steve Landeau wrote:The way I set up my boat is with a series of holes (usually 5) about 3-4mm apart
Hi Steve

Playing with a little math, it seems that we shorten the jibstay by around 5.7 or 5.8 mm for every degree of rake of the mast if we use a bowsie on the stay. If we are not shortening the stay but are instead hooking it into holes in the mast, they need to be correspondingly spaced by about 6 mm instead... So to cover the range of rake from, say, -1 degrees to 5 degrees, 7 holes at 6 mm intervals.

Posted: 12 Oct 2005, 12:56
by Andy Stevenson
Thank you all for your views.

It strikes me that I might be getting a little too fussy with this. As Lester points out, I can do the sums to get hole spacings (I made it 6mm, 5mm & 4mm per degree for A,B & C rigs respectivley). It's just a case of deciding the range after that, the jibstay limit sorts out how far forward I can go & I'm now reasonably sure that if I go up, er down, to 6 degrees aft I'll cover all I'm going to need.

At worst I'm going to end up with a hole or two I don't use.

Marvelous, thanks folks, I think I've got my head round it now.

Posted: 12 Oct 2005, 15:00
by peter spence
why not initially use a bowsie (I do and freely admit I rarely adjust it once I have found a happy medium setting) and then once you have found the correct length for your hull shape/fin position etc if you want to you can make yourself a permanent forestay the required length and use the existing hole



Posted: 12 Oct 2005, 15:13
by Lester
peter spence wrote:I rarely adjust it once I have found a happy medium setting
Hi Peter

Maybe you aren't sailing the IOM designs I am, or maybe my skill level is really as bad as I think it is (smile), but I *definitely* have to adjust rake if I am to get anything like an acceptable touch of weather helm all the way from drifting conditions to overpowered in any rig... And then finding that setting again with a bowsie is a difficult task. Some sailors I know put waterproof pen marks (spaced at 10.5 mm, natch!) on the part of the stay line that runs back through the bowsie, so I guess this gives them some kind of clue.

Posted: 12 Oct 2005, 16:55
by peter spence
I'm just a simple boy at heart and try not to make things more coplicated than they need to be - I just aim to get a boat that is all-round competitive and then the hard and most important bit of all... try to point it in the right direction - and equally important, try to keep clear of trouble !!!!!!

the last thing I want or need is to have a IOM out on the racecourse optimised for a drifter only to find the sea breeze arriving and it suddenly becomes top of rig conditions

im my view better to have an all-round setting and then learrn how to make it perform in all conditions - practice makes perfect

of course in a 'real' boat when you can alter things on-board during a race then it is obviously a different matter - back in the days of my Five-oh racing it was a joy to yank the rig back during a race as the wind blew up - the more rake you have, the quicker you seem to go - it was the same in my Contender - only problem with that is you can only rake it back so far before you cant physically get under the boom during a tack :)