Mast rake, tricky geometry

Lakesailor said:
I would suggest your headsail is cut too high. The sailplan in the drawings has a much lower foot and clew. You're losing a load of power ahead of the mast.
Get another headsail (borrow one?) and see if that changes your balance, (neutral or lee helm). Then you may have the room to manoeuvre in mast rake without making matters worse.
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+1 The jib is often raised to fit in the drum turnscrew etc on the forestay and under the jib tack. Ideally you want the drum for reefing right down as low as possible. You may be able to do without a turnscrew in the forestay. Even better is a drum under the deck level. probably too hard to manage.
A jib does work better if it is closer to the deck.
Also note however that as said weather helm increases with boat heel no a mount of sail ballance can overcome that. good luck olewill
 
As has been pointed out, increasing the mast rake will tend to increase weather helm, although yours does look a bit forward in the pics. There's a boat the same as yours at Port Ed (name escapes me for the moment but I will look it up) which you might want to study and measure for comparative purposes and which I can confirm sails very well. The cut of the genoa does look somewhat on the high side which may be part of the problem.

PS if you can't do the calculations how are you going to manage spherical trigonometry ;)
Cheers
 
The simplest way to calculate lengths is to get a large sheet of paper & do a scale drawing
When I wanted the rigger to rake my 31 ft boat mast forward I used a CAD programme & plotted the lengths.it was then easy to see what effect various lengths had on mast rake
I am sure a forumite can direct you to a simple free CAD programme on the web you could use
Finally one point not mentioned is hull trim fore & aft. On old gaffers with plum bows & long raked sterns this has a big effect. Not sure if this would apply to your boat but may be a factor worth considering
 
1st raking the mast by increasing the forestay will increase the weather helm,

2nd, by tighting the backstey you flatten you sails both main & jib, taking all the power out of the jib and increasing the weather helm.

3rd to redress the balance in the boat, ensure the jib is set correctly using tell tails, ensure the jib care are correct and you are not over twisting . once the jib is trimmed correctly, trim the main to ballance. try easing then kicker, to allow the main to twist off but keet the boon near the centre line to maintain pointing.
 
The forestay doesn't look too tight in the photo, so first guess is that that isn't the problem.

Weather helm can also be caused by too much belly in the mainsail. Flattening the main can help control it. How much pre-bend do you have? What does the luff of your mainsail look like when laid out flat on the lawn? Do they more or less match?

You could try adjusting the lowers to get a bit more bend in the mast. Do you have any means of adjusting the backstay underway?
 
Clive said:
1st raking the mast by increasing the forestay will increase the weather helm,

2nd, by tighting the backstey you flatten you sails both main & jib, taking all the power out of the jib and increasing the weather helm.

3rd to redress the balance in the boat, ensure the jib is set correctly using tell tails, ensure the jib care are correct and you are not over twisting . once the jib is trimmed correctly, trim the main to ballance. try easing then kicker, to allow the main to twist off but keet the boon near the centre line to maintain pointing.
Click to expand...

dt4134 said:
The forestay doesn't look too tight in the photo, so first guess is that that isn't the problem.

Weather helm can also be caused by too much belly in the mainsail. Flattening the main can help control it. How much pre-bend do you have? What does the luff of your mainsail look like when laid out flat on the lawn? Do they more or less match?

You could try adjusting the lowers to get a bit more bend in the mast. Do you have any means of adjusting the backstay underway?
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Thanks for the thoughtful replies

I have taken all the adjustment out of the backstay that the bottle screw allows and yes I would agree that the forestay is still not totally tight.

I also sail her to the tell tales but I suspect I am not helped by having an old and baggy mainsail and a genoa cut for the wrong boat.

When the mast goes back up in spring I'll try a shorter backstay and by then I should have new sails.
 
Clive said:
2nd, by tighting the backstey you flatten you sails both main & jib, taking all the power out of the jib and increasing the weather helm.
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Not necessarily so .tightening the forestay does change the shape of the jib but it normally pulls the flow forward. Flattening the main will reduce the pressure or at least help it to achieve the correct shape in higher winds. Baggy sails with the flow too far aft are often the cause of heavy helm. Changing the main & tightening the rig tension( thus the forestay) made a massive difference to my boats perfprmance
 
Lakesailor said:
Are the sails being made to plan or has he measured your boat?
If the latter you could be asking for trouble.
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I'm going to send the sailmaker the photos of the present set up along with this thread.

She (Diana Shellcock, Owen Sails) will also come and measure on the boat.

I have not yet had the conversation with her as to whether she is happy to measure the boat, the boom and the mast with them all in the yard or whether to wait until I have the mast up again and hopefully correctly raked next April.

As long as I will definitely get the sails by early June I think I would prefer to go the mast up route.
 
Ran it through AutoCAD for you. It is roughly 30mm of forestay and 50mm of backstay for each 100mm of mast rake:-

(Scaling the boat dimensions based on 26ft length on deck)

invicta-Model.jpg


Better pdf copy.
 
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Fascadale said:
I have not yet had the conversation with her as to whether she is happy to measure the boat, the boom and the mast with them all in the yard or whether to wait until I have the mast up again and hopefully correctly raked next April.

As long as I will definitely get the sails by early June I think I would prefer to go the mast up route.
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My worry would be that sails would be cut for the angle the mast and boom intersect at. Changing the rake afterwards would result in a droopy boom.
 
Fascadale said:
This is fantastic. Many thanks
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Before making permanent modifications my suggestion is still to put a shackle or 2 in as spacers and shorten back stay in similar manner.

Given the measurements I would say a Dyneema Lashing would do for few weeks till you are satisfied.

For all the pontification on here, the best way to find out is to do it. You will also be able to see and report back what effect it had.
 
I agree with Onesea, temporary lashings, extra toggles and shackles to play around with the rake until you are happy before buying new stays. The top photo in the OP looks like there is a kink in the forestay due to sheet tension on the rolled sail. This makes me think that the forestay isn't tight enough. A slack forestay won't help with sail shape and too full sails will increase heeling and weather helm. And temporary lashings aren't going to get the forestay tight enough for a good sail shape.
 
Musings

I'm surprised nobody has mentioned ballast. Aside from all the potential changes to the rig mentioned, the fore and aft trim of your boat is likely to affect the extent of weather helm. An increase in the displacement will also tend to affect it. Whether either of these is a contributory factor, or a significant one, in your case I don't know.

However, in the photos the boat looks lower in the water than in the drawing, though it's difficult to be sure because of the waves. Note that in the photo you can't see the rearward curve of the lower bow at all, but it's clearly visible in the drawing. If the boat is overladen and low in the water (even if trimmed level fore and aft), this will bring the centre of lateral resistance (?terminology?) forward (because of the difference in the bow and stern profiles) to some degree, and if that is the case if not causing the problem, it certainly isn't helping what you describe as excessive weather helm.

If I were you I would certainly move the mast back to upright, if only for aesthetics (it's a lovely looking boat, I think, but to my eyes the forward rake looks wrong), and then adjust your sails to suit around that. I can't think the boat needs that forward rake to work properly.

Good luck, anyway. Do report back on progress.
 
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LittleSister said:
I'm surprised nobody has mentioned ballast. Aside from all the potential changes to the rig mentioned, the fore and aft trim of your boat is likely to affect the extent of weather helm.

However, in the photos the boat looks lower in the water than in the drawing, though it's difficult to be sure because of the waves.

Good luck, anyway. Do report back on progress.
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Interesting point

I think she sits properly in the water, maybe a bit down at the stern.

Here's a photo taken when the boat was leaving, fully laden, for a six week Norway trip and another one soon after arriving, still well laden.

IMGP0443.jpg


IMGP0623.jpg
 
LittleSister said:
I'm surprised nobody has mentioned ballast. Aside from all the potential changes to the rig mentioned, the fore and aft trim of your boat is likely to affect the extent of weather helm. .
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Thought. i had!!!
However being down at the stern will cause the bow to pivot away from the wind not luff up, so apart from being a bit overloaded it should not be a contributory factor
 
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