Sail/helm Balance and Mast Rake

[Toxophilite]

Lately I've been thinking of the rake of my Gartside 130's mast. It probably has a good 7-9 degrees more rake than the sail plan.
As such I've been able to fly small jibs off a removable sprit and have good helm balance (or so I was told by an Olympic small boat sailor) and it seemed it to me too.


Lately I've been sailing in some stronger conditions where using just the main has been much more comfortable ( 8 knts and up) However I've noticed that the boat has a fair amount of weather helm.


To sort this all out in my head I figured out the centre of effort of my mainsail and then the centre of lateral resistance of my hull
I used this resource
https://www.diy-wood-boat.com/sail-balance.html
No affiliation of course
I found it all quite interesting and enjoyed delving into it.
I also figured out what the COE effort would be while flying a jib off the sprit (of roughly the size I use)
Comparing this o the sailplan one can see the COE with the jib is pretty well exactly where it is on the sailplan which would account for the good helm balance.

The sailplan has about 3 degrees of rake


It also had some info at the bottom of the page that suggested a good amount of lead for a centreboard type hull is 12-14% of the hull length. On my boat this is about 18-19 inches. Not sure of this is right

I set the boat up on a level keel (it has a dead straight keel..or should at least) using a 4 ft level and also levelled it side to side.
Then using a framing square and the 4 ft level I made some right angle triangle measurements to determine the rake measurements.

I also took some straight on sideview pictures and made measurements on those pictures.
Interestingly the two don't match up. I'm missing something
The pictures measure the rake at around 11.5 degrees.(HUGE! and it looks it) while the square and level measurements suggest it's more like 6.5 degrees
I angled my mast as far forward as it would go in the partners(raising the tenon out of the step and made the same sort of measurements.
Same sort of discrepancy
I get about 8 degrees on the picture and about 3.5 using the level and square measurements
Not sure why that is.

Any insight on this?? What am I doing wrong?

A side benefit of doing this is that I discovered my mast has a slight lean to starboard that I can correct at the step

I was contemplating building a new step for my mast (it notches onto two little floors and is fastened by 3 large bronze bolts and is thus removable.) copy the original and build another with a longer mortise for the rectangular mast tenon.
I have the wood and it would be pretty easy. I would build out the mast tenon to be full mast width fore and aft and then I could use a large hardwood wedge either in front or behind the mast to achieve both positions. There is JUST enough play in the partners to accomplish this though a little shaping top, fore bottom aft would maybe give me another degree of forward rake.

I think it would be nice to have the rake adjustable so that I could achieve good helm balance with or without the jib. Not sure if it's possible


Here is my calculations regarding the COE CLR and COE with the jib

Sailplan (not eCOE mark at front of daggerboard)

Here's the rake with the mast moved forwards as much as the partners will allow(shows right angle measurement)


Here's my nutty measuring of the COE of my sail

[AJZimm]

Regarding the difference in mast rake measured on the boat vs measured from the photo, I suspect what you are dealing with in the photo is vertical distortion caused by the camera lens. This is a common problem in architectural photography. It is caused by the plane of the camera’s image sensor not being the same as the plane of the vertical objects in the picture. If you look at pictures of tall buildings taken from ground level, the sides of the building will seem to converge at the top. This is a vertical perspective distortion. While to some degree this a real thing, like the apparent vanishing point you see when looking at railway tracks, a building or boat plan is not drawn with vanishing points or perspectives in mind. Instead, everything you see on a boat sail plan is drawn as if all points are the same distance from your eye. This is necessary for the scale to work but it is not what the camera captures.

The more you have to tilt the camera up to get the whole subject in the viewfinder, the worse the distortion is, and the closer you are and the wider the angle of the lens you use the worse it is, too. In this case, if the mast was absolutely vertical, it still would appear to be slanted or raked in the photo, just the way that building sides look slanted. You can try to overcome this effect by taking the picture from about the mid-point of the height of the mast and from further back, but you’d still have some distortion.

There are specialized architectural cameras that correct for that optically with tilt and shift mechanisms, and some software packages also can partially correct for it after you have taken the picture (Lightroom comes to mind) but both seem to me to be not worth the effort.

I’d trust the measurements on the boat more.

On the correct amount of lead, others who know far more than me will chime in about what goes into determining actual COE and CLR when you are sailing, both of which are somewhat dynamic, but 12-14% as measured on a static plan seems like a lot to design for. I would expect a starting number to be something less than half that.

[pvg]

Agree with Alex regarding the distortion induced by the camera/lens; look at the buildings in the background...

[Hugh MacD]

Is there another dock farther away you could shoot from to minimize the parallax? If you can achieve more distance you can get more of the rig into the "sweet spot" on your lens, then enlarge that image for measurements.

[Toxophilite]

Hey thanks! I can actually use my neighbours dock and if we have a few dry hours today I'll give that a try too

[stromborg]

Chock the boat level to the waterline, hang a plumb bob from the sheave at the top of the mast and you'll know exactly how much rake you've got. None of this faffing about with lenses and parallax distortions.

[Toxophilite]

That's sound advice, thanks, I'll try that . Might save me the 200 steps up and down to take pictures. That or launching a canoe..

However my waterline is a smoothed out copy of the one that was on the boat when I bought it. So it might not be the most accurate reference. It's pretty good but a little high actually. I was going to address that this summer, when I touch up the bottom and finish the interior brightwork. I didn't have a laser level to redo it before. I might borrow one.
Looking at the sail plan the boat is sitting on it's flat keel and the waterline depicted is parallel to that.
Is it bad to use the keel as a reference for level?

[stromborg]

Depends on what the plans indicate. If it is calm enough you could put the boat in the water and mark the "true" waterline, or at least where it is at rest. You might even be able to use the plumb bob.

[Toxophilite]

Sadly I don't have the full plans, just the sail plan and a light scan of one of the construction plans that Paul Gartside generously sent me when I was building the missing stern sheets and floorboards.
Might be a future purchase though. Now I have to acquire a plumb bob. I lost my ubiquitous high school later project one (Almost 40 years ago), Might be at my folks. I was just going to use a small appropriately shaped weighty object.

[John Meachen]

I think you may be causing yourself more anguish than is required.The plans show more sail forward of the mast than the real thing seems to have.Is it a major task to attach the halyard and downhaul a few inches further aft?

[stromborg]

I've been known to use an eyebolt

[Toxophilite]

Well in this case most everyone is right except me. However I am not necessarily causing myself anguish, as much as basically geeking out with the rig and trying to learn things. It's true I do have it rigged more like a conventional standing lug than the plan depicts. Being able to slide my downhaul back might achieve the same object as having an adjustable step when sailing with just the main.

I used an oarlock as a plumb bob and setting my keel rollers dead level I measured about 5 degrees of rake.erp so much closer to my on the boat measurements.Tilting the mast in the partners I could easily achieve the designed rake if desired by adjusting the step.
This is about 2.5 degrees more than the actual sailplan which is about 2.5 degrees (just checked it.)
and to prove that my initial faffing was mistaken as was suggested I got onto my neighbours dock and took a photo which much more like the sail plan and pretty well exactly matches the angle measured with my improv plumb bob.

I feel a little silly about my picture goof but it certainly won't be the first time , nor the last
fucked.jpg

[Clinton B Chase]

I haven't read every word of this thread, but thought it was important to add that
Lugsails have one advantage in that the location of the CE can be adjusted by changing where the halyard ties off to the yard. Move the tie off point up the yard and your CE shifts forward a touch. Small ,but can make a difference.
This is one reason I am not a fan of a fixed lashing point on the yard - much better to do a cow hitch or prusik there allowing for movement.

[AJZimm]

Clinton has a good point. There may, however, depending on the height of your mast and the location of the halyard beehole/sheeve, be a limit to how much you can shift the sail forward. This is because the halyard lift point moves up when move it aft on the yard. The total length of hoist can increase pretty quickly, especially if the yard is peaked high. While it looks like you have enough room to experiment with your rig, it can be a problem if the mast isn’t tall enough. Don’t ask me how I know this.

[Toxophilite]

I have an extra 2' of mast provided by a previous owner. My first reef so to speak.

I am still of two minds regarding the mast traveller. My Shellback didn't have one, just a topsail halyard bend. Not a lot of thinking to do.

I liked the idea of the traveller (the boat came with it) and there are some advantages to being able to remove the rig from the mast, however it creates problems with the downhaul and reefing. You need a lot of travel on your downhaul setup to allow the spars to move far enough forward to hook the yard on the traveller and then be able to provide enough downhaul tension. It was pretty finicky to get operational. Getting the balance right between the two extremes has been difficult.