Weather Helm / Skeg and Rudder

[Cwens]

Originally Posted by rhubstuff

The CE cannot move to leeward or to weather. It can only move fore and aft.

To a reasonable degree, all of the aerodynamic forces acting on a sailplan can be approximated as a single force vector acting on a single point. That's the point to which I was referring to. It's pretty close to the geometric centroid of all the sailcloth, Whether or not CE is the correct term for that point depends upon which naval architect / sail designer you ask. But in any case, that point, whatever one wants to call it, moves to leeward as the boat heels. Consider a bird's eye view of a sailboat close hauled heeled over. Most of the sail area is well to leeward of the center of the submerged area of the hull.

[rhubstuff]

Originally Posted by ChrisOwens

To a reasonable degree, all of the aerodynamic forces acting on a sailplan can be approximated as a single force vector acting on a single point. That's the point to which I was referring to. It's pretty close to the geometric centroid of all the sailcloth, Whether or not CE is the correct term for that point depends upon which naval architect / sail designer you ask. But in any case, that point, whatever one wants to call it, moves to leeward as the boat heels. Consider a bird's eye view of a sailboat close hauled heeled over. Most of the sail area is well to leeward of the center of the submerged area of the hull.

I was thinking of the CE only in relation to the boat, not the boat heeled over. You are correct, of course, but I wonder if that makes a difference during actual sailing, since the CE and CLR remain in the same relative positions to eachi other and the hull.

[Cwens]

Originally Posted by rhubstuff

I was thinking of the CE only in relation to the boat, not the boat heeled over. You are correct, of course, but I wonder if that makes a difference during actual sailing, since the CE and CLR remain in the same relative positions to eachi other and the hull.

Both effects are significant -- CE moving fore and aft relative to CLR affects helm, but so does CE moving to leeward as the boat heels. On a typical cruising keelboat we have control over the former (by fiddling with sail trim and mast rake) and not so much the latter (indirectly by shortening sail and reducing heel). But the latter is very noticeable in a round-bottom dinghy. In a laser, on a beat, when I get tired of hiking and I lean in a bit to give my aging, sagging gut a break, the rudder loads up instantly, and I forlornly watch the fit young Viking in the next lane moving ahead of me.

[MicHughV]

My first boat had a full skeg hung rudder and it was a ketch so I could balance it pretty well, but it always had a touch of weather helm, which I prefer over a neutral helm. When I say weather helm, I mean about 1 spoke of wheel turn.

My next boat had a partial skeg hung rudder..it was a cutter rig, but it too had weather helm, much as above, about 1 spoke worth.

My last boat has a so-called balanced spade rudder, ie, a portion of the rudder is ahead of the rudder post. The rudder is also much deeper and bigger than the previous two and it too had weather helm, again, about 1 spoke's worth.

All three boats sailed just fine under autopilot...the autopilot, like me, seems to prefer a bit of pressure on the helm...

The point of sail is also a factor. Generally speaking, any wind forward of the beam will induce weather helm. Behind the beam, not so much, when the helm is relatively light and tends to wander a bit.

Just my perspective.....

[BAD ORCA]

Originally Posted by MicHughV

My first boat had a full skeg hung rudder and it was a ketch so I could balance it pretty well, but it always had a touch of weather helm, which I prefer over a neutral helm. When I say weather helm, I mean about 1 spoke of wheel turn.

My next boat had a partial skeg hung rudder..it was a cutter rig, but it too had weather helm, much as above, about 1 spoke worth.

My last boat has a so-called balanced spade rudder, ie, a portion of the rudder is ahead of the rudder post. The rudder is also much deeper and bigger than the previous two and it too had weather helm, again, about 1 spoke's worth.

All three boats sailed just fine under autopilot...the autopilot, like me, seems to prefer a bit of pressure on the helm...

The point of sail is also a factor. Generally speaking, any wind forward of the beam will induce weather helm. Behind the beam, not so much, when the helm is relatively light and tends to wander a bit.

Just my perspective.....

interesting. I would say thats probably about what mine is. I just ordered a CPT wheel pilot so was getting a little nervous my weather helm will be too much for it but i think im going to be just fine.

[Cheechako]

Originally Posted by BAD ORCA

Do sailboat designers when designing a new sailboat (monohull) always try to design with a very slight amount of weather helm or is the intended goal of the designer to always try and build a balanced sailing boat?

My gut feeling is that they might try to design in a very slight amount of weather helm with a 100% genoa since large 100+ genoas seem so popular but my thinking may be way off.

My second question is...is it possible that a skeg and rudder (fin keel monohull / dinghy type flattish bottom) could be too large for a particular sailboat and actually cause some weather helm as well, independent of the sails?

My understanding is they design for some weather helm, so the boat will round up if unattended, or head up well when beating. I hate it. I've had boats I could balance with some lee helm and it's great. The crowd here doesn't like that though!

Skeg and Rudder designs have a difficult helm though by nature and it seems to include weather helm. At least every one I've had has been that way. The water flows along the skeg then hits the angled rudder trying to force it back straight. There's a lot of power in that flowing water. No rudder balance ahead of the rudder shaft on most.

[Bill O]

Originally Posted by BAD ORCA

Hi Bill. Well i started reading 'Desirable and Undesirable Characteristics of Offshore Yachts'. Im in the third or fourth chapter where he starts to explain weather helm. I know what it is and have experienced with it sailing my boat and my friends boat, but i realize i still dont fully understand it.

I have a Peter Canning Mariner36. My sails are on the old side for sure. To give an example of its weather helm, when we take her out in the bay in 15ish kts of wind, with full genoa up (its a 130 or 150, overlaps mainmast), i can steer my boat with very little effort. If i take my hand off the wheel she will round up slowly into the wind within about 50ish yards. Assuming water is reasonably flat with genoa and mainsail sheeted in pretty tight. On my friends little Ranger 29, we can sail in the same conditions, maybe slightly furled in jib, and i can take my hand off the wheel and the boat will follow a strait course for 30 minutes unless large waves.

I really dont have much more experience than that. I'd like to swap out my large genoa for a 100% jib. If i do i'm assuming weather helm will get worse. In fairness to my boat, I havn't known how to properly trim to alleviate it. We always furled in the jib, which does help de-power the boat but simply letting out the main might have been all that was needed.

Im just trying to learn and sort of 'evaluate' my boat by comparison to try and asses where she falls. I dont know if what i described for my boat would be considered 'excessive' weather helm or pretty normal.

Sorry I missed your reply from a few days back. The Mariner 36 is a nice boat.

The line drawing for the Mariner 36 on sailboat data shows your boat should be fairly well balanced w/a full main and 150ish genoa.

Many people think their 30 yr old sails are in good condition, but really they are worn out. If you want better performance, buy a new main and you will notice the change. It is like putting a new motor in an old car. This is where I would start.

In general, if you go w/a smaller head sail than the 130/150 you will increase WH unless you reef the main.

After you get a new main, would then play with the head sail sheet leads to try to get the best shape in the head sail at different points of sail.

It sounds like a lot of work, but it does help you get to know your boat and how to tweak it for better performance.

[BAD ORCA]

Originally Posted by Bill O

Sorry I missed your reply from a few days back. The Mariner 36 is a nice boat.

The line drawing for the Mariner 36 on sailboat data shows your boat should be fairly well balanced w/a full main and 150ish genoa.

Many people think their 30 yr old sails are in good condition, but really they are worn out. If you want better performance, buy a new main and you will notice the change. It is like putting a new motor in an old car. This is where I would start.

In general, if you go w/a smaller head sail than the 130/150 you will increase WH unless you reef the main.

After you get a new main, would then play with the head sail sheet leads to try to get the best shape in the head sail at different points of sail.

It sounds like a lot of work, but it does help you get to know your boat and how to tweak it for better performance.

Thanks Bill. She is an absolute joy to sail. I hate to admit it, but i believe the main is the original 1980 mainsail. It does look a little stretched out. Unfortunately there have been many other needy projects to attend to as i restore her so sails keep getting pushed down the list. Since i have a genoa and jib it makes sense, and seems now like it would be more prudent to replace the main first...much thanks for your insight. Until i can replace the main it looks like i will need to learn to reef and trim the main as necessary.

[Bill O]

I totally understand the long list of projects and the $$ to distribute among them.

Not sure where you are located, but if you wait for a major boat show, they usually have several sail makers show up. This usually provides some nice discounts (20-25%) to the normal cost of a sail.

If it's just time to do the long list, the best part of a new main is they do most of the work. :-)

[BAD ORCA]

Originally Posted by Bill O

I totally understand the long list of projects and the $$ to distribute among them.

Not sure where you are located, but if you wait for a major boat show, they usually have several sail makers show up. This usually provides some nice discounts (20-25%) to the normal cost of a sail.

If it's just time to do the long list, the best part of a new main is they do most of the work. :-)

Interesting...good to know. I will have to look into that. I think there are several in southern california.

[BAD ORCA]

Originally Posted by Cheechako

My understanding is they design for some weather helm, so the boat will round up if unattended, or head up well when beating. I hate it. I've had boats I could balance with some lee helm and it's great. The crowd here doesn't like that though!

Skeg and Rudder designs have a difficult helm though by nature and it seems to include weather helm. At least every one I've had has been that way. The water flows along the skeg then hits the angled rudder trying to force it back straight. There's a lot of power in that flowing water. No rudder balance ahead of the rudder shaft on most.

I have to admit i do kind of like the idea. I dont know how realistic my thinking is , but it would be nice to know if i was day sailing in the bay, untethered, auto pilot off and i fell over, the boat would round up and i could swim back to it. Im not sure if that would still be feasible in very heavy weather though.

[Boston Blackie]

A slight amount of weather helm dramatically improves VMG going to weather. This is because the angled rudder exerts force pushing the stern to windward in balancing the tendency to turn into the wind. Conversely a lee helm rudder pulls the stern to leeward.

Adding a skeg, if it increases the overall area of the rudder, actually moves the CLR aft which would reduce weather helm or create lee helm.

When I removed the original scimitar spade rudder on Iteration, our Pearson 30, and built a new larger area semi-skeg rudder without the waterline cutaway of the scimitar, I had to add lateral area to the leading edge of the keel to maintain the lead and balance. We added 300lb of cast lead boomerangs epoxy splodge-bolted into the nose of the fiberglass keel, and faired it to a Petersen foil section. Balance remained slightly positive weather helm and the boat was stiffened for Buzzards Bay souwesters. Won the '76 MORC season championship, the year before the J24.

[DeValency]

Good points by most posts here.

For both questions, the practical bottom line, considering you're not going to re-engineer the keel/skeg/rudder/mast is a proper sail trimming.

As frequently suggested by furling the main to the right balance - indeed easier with in mast/boom furlers and roll out more genny/staysail out - considering the conditions. If you minimize the weather helm, you actually gain speed and make your life (and the autopilot life) easier.