A few Hunter 306 questions

[Arbee]

Hi,

I thought about posting these 306 questions separately but didn't want to spam the forum. We've had our boat for 2 years now and, between frequent Covid lockdowns here in Melbourne, we are totally in love with the boat. As a floating weekender and comfortable and manageable inshore/coastal cruiser it's a perfect fit for the two of us. Questions for the brains trust here:

Lee Helm. We have in-mast furling, and while it's a great convenience that we'd not give up, I have suspected that these fractional rigs that expect a big paunchy mainsail are perhaps not as well suited to the inevitable in-mast furling sail shape as mast head rigs. The lee helm is very "soft" and not a big issue, but I wondered if I'm missing some tricks to get more power from the main and balance the boat better. The headsail doesn't seem to be oversize and the tell tales on both sails set well, we just find the wheel position is off centre by about 15 degrees when sailing to windward. If I let go, the boat will gradually drift off.

Motor rev range (2GM20F) and hull speed. The throttle cable moves easily from forward idle to 2000rpm then stiffens up considerably. I can then push it hard which gets me to about 2800rpm and just over 5 knots across the ground (across the tide) with our 14 x 10 fixed 3 blade prop. Then the throttle cable hits another "wall" that I've not been game to push it through. The local marina mechanic has assured me that all is "fine" a couple of times, just as car mechanics seem to tell you just before something breaks, but I'm not convinced. So, a couple of questions here. First, is the throttle pressure normally "graded" at all, or has it simply worn itself into a groove where the previous owner liked motoring at less than 2,000 rpm. And second, if the 306 hull speed is around 6.9 knots, what rpm should I normally expect to use to achieve that (or do I have the wrong prop size)?

Waste Tank. On the past couple of occasions when emptying the tank, the indicator will only go down as far as about 20%. The marina assures me their pump is fine and I've not seen any pressure leaks in the fitting or hose. Do you have any particular cleaning ritual that you follow to keep the sensor and tank free of build up or paper debris. It doesn't get a heavy duty work out (that's what marina toilets are for!).

Thanks for any insights or wisdom you can provide!

Cheers, Robert

Charisma, 2004 Hunter 306
Melbourne, Australia

 

[jssailem]

Hello. Glad to hear you are enjoying your boat.

The LEE helm issue is one of sails verse hull shapes. Our selection of a boat for the type of sailing we want to do defines the hull shape. This is a compromise many boat owners do not consider. Some hull designs are more prone to unstability in water flow than others. Nothing you can do about that. We need to explore the sails. Lee helm happens when the fore sail exerts greater lateral force than the main. You have accepted some compromises in the shaping of your sails with the furlered main.

Balancing the sail's lateral forces would involve increasing the main (angle of attack or size) or decreasing the fore sail.

Here is a discussion about Center of Effort, CE

Here’s the definition according to Dave Acree* . “The Center of Effort (CE) is the geometric center where the wind pressure on the sails exerts its total heeling effect. The Center of Lateral Resistance (CLR) is the geometrical center of the yacht while in the water.” ​

​

So what does this all mean is layman’s terms? Basically, there are forces acting on a boat above the water; the wind flows on either side of the sail, causing lift. The lift force is countered by lateral resistance created by the keel. The balanced combination of the two forces causes a sailboat to move forward in a relatively straight line. If the sail is trimmed properly, for example: trimmed in over the centerline of the boat on a close-hauled course, the boat will feel balanced, exhibiting neutral helm.​

​

Using a simple single sail on a Laser, it helps to identify the ways the sail is altered to adjust the forces on the sail.

 

[jdrutten]

Hey Robert! Fellow 2004 306 owner here. We're in a similar position, although I've only had mine for slightly more than one season. I've only been sailing for slightly longer than that, having started out in a Force 5 dinghy two seasons ago. We're on the hard now for the season, but the countdown clock has started and I can't wait to get back on the water.

I'm way too much of a novice to comment on any weather/lee helm issues. I certainly remember not quite being able to balance my sail plan but attributed that to user error more than any particular design issue. I tended to keep my sails pretty small as the wind got stronger, and the wheel always felt pretty light, but I was certainly never able to just let go and keep sailing the same tack.

I've been able to get my 2gm20f beyond 3000 rpm, and I want to say at least 3200, maybe even 3400, but I can't remember exactly for certain. I don't know my prop configuration either. Even with 3000+ rpm, I don't remember being able to get much past 5.5 knots or so. I figured that was just the 2gm20f being a tad underpowered for the 306. It gets me in and out of the marina well enough, but I'd love to know how to optimize this combo to get a little closer to hull speed.

I spent most of last season struggling with the head and not being able to flush very well, or fully empty the tank. Then one day as I was washing the boat I noticed a little fuzz sticking out of the holding tank vent (aft starboard side) and proceeded to pull out a surprisingly large spider along with what I can only assume was a spider's nest. A sharp shriek and a few swipes of a pipe cleaner later, and I've been flushing with ease and pumping out clean like a champ. So you might want to check that the spiders haven't laid claim to your vent.

 

[jssailem]

Look at two hull designs of similar length boats

• one is quick to turn,
• the other plows straight
• One has a wide belly and carries it towards the stern
• the other s more symmetrical in shape yet the beam width is within .25ft of each other.

The hull design provides a clue to the ease of turning, or sailing a straight line. Also the distance from the keel to the rudder influences the affect of water flow under the boat, reflected in the handling of the rudder.

 

[Joe]

Most weather or lee helm issues can be solved through trim correction. So a good sail trim guide (Don Guillette's book, available in SBO store), should clear up these issues. Once you're satisfied you need more than that you may consider more complex solutions like rig adjustment, equipment mods and sail alteration.

Here are a few comments on trim adjustment for balancing the sail plan (especially important if you use an auto pilot). Essentially, if you have lee helm you'll want less power on the headsail and more on the main. Make the jib flatter and the main rounder... that simple enough for you? heh, heh. Move the jib lead back make the head sail flatter (de power) and then examine your mainsail's shape. Move the outhaul forward to increase draft depth. This adds power to main. You can also experiment with the sheet and traveler. Putting more tension on the mainsheet will add power to the sail by closing the leech. Laying back and looking up at the leech while this adjustment is made will reveal its effect. Once you feel the sail plan is balanced, you can adjust for apparent wind direction changes by playing the traveler or steering to the tell tales. Generally, we use the steering tell tales (the lowest set of headsail tells) when we are sailing close hauled, attempting to make progress upwind, and we make small traveler adjustments (playing it) to tweak the main's angle of attack when we want to maintain a particular course or react to sudden gusts.

Once you've experimented with all trim settings and feel there's nothing left in the bag, and that your sails themselves are not creating a weather or lee helm problem, then you can make some rig adjustments. Moving the center of effort aft can help with lee helm. That involves RAKING.... NOT the same as BENDING ....the mast. Raking is like leaning the mast forward or back and you use the shrouds to do that on fractional rigs. Anyhow... you need to go to any spar manufacturer's website, or simply google "mast tuning guide" and you will get a plethora of info.

Finally, your sails. I have literally no experience with roller furling mains and can offer you no insight there. All I can say is, keep researching and asking questions. Balancing the rig is your goal, go for it. Good luck, have fun.

 

[jssailem]

Got info from @Joe

Before you start to furl the main, remember you eased the outhaul to add power and tighten the outhaul up to allow a smooth furl. A bunched sail in the mast is no fun.

 

[Arbee]

I've been able to get my 2gm20f beyond 3000 rpm, and I want to say at least 3200, maybe even 3400, but I can't remember exactly for certain. I don't know my prop configuration either. Even with 3000+ rpm, I don't remember being able to get much past 5.5 knots or so. I figured that was just the 2gm20f being a tad underpowered for the 306. It gets me in and out of the marina well enough, but I'd love to know how to optimize this combo to get a little closer to hull speed.

I spent most of last season struggling with the head and not being able to flush very well, or fully empty the tank. Then one day as I was washing the boat I noticed a little fuzz sticking out of the holding tank vent (aft starboard side) and proceeded to pull out a surprisingly large spider along with what I can only assume was a spider's nest. A sharp shriek and a few swipes of a pipe cleaner later, and I've been flushing with ease and pumping out clean like a champ. So you might want to check that the spiders haven't laid claim to your vent.

Thanks for this info, and especially the tip about critters in the holding tank vent. I'd forgotten about that as a potential cause and we have plenty of potential spider suspects and moths trying to breed in unwanted places!

Cheers, Robert

 

[Arbee]

Thanks for the info @jssailem and @Joe, I may not have framed my question too clearly. I'm (painfully at times!) aware of the science of CofE and lee/weather helm, I was really interested to see if any other Hunter owners with in-mast furling had a similar lee helm experience. Looking at the owners' manual, it seems that the in-mast furling config has a slightly larger headsail area and slightly smaller main area, but the furling main shape has much less roach than the standard main. That added to my curiosity about other owners' experiences.

I will experiment with trim as you both suggest and see if I can correct it. I'll start here "Putting more tension on the mainsheet will add power to the sail by closing the leech". There is a certain pride in sailing a boat that tends to keep itself on course "no hands" . So far, the main furling has behaved itself nicely. Both sails seem to be quite new and in good shape and I had the 15 year old standing rigging replaced and tuned by a very well respected local pro when we bought the boat.

 

[jdrutten]

Just thought I’d drop a link to this other thread going on, initially talking about smoke but going on to talk about the 2gm20f rpm vs boat speed in the 326 (big brother to the 306). They mention prop adjustment among others.

Yanmar 2GM20F blew black smoke

Hi all - The Yanmar 2GM20F in my 2003 Hunter 326 may be unwell. In an attempt to sail 5 nm from my marina to another, for a haul out appointment, I was punching into 25kts and 2kt tide, and 1m waves (3'). Thumping along I couldn't get more than 2300 rpm and 2.5 - 3.5kts OTG. Looked around and...

forums.sailboatowners.com

 

[Arbee]

Thanks @jdrutten, that's a great thread and answered my question I think. Sounds like 5+ knots at 2,800rpm is about right and I should be pushing for a higher rev range for max hp. I'm keen to resolve this now as I've just replaced a totally clogged elbow that was making the problem worse. So it's better, but no cigar yet - I'd be happy with the ability to cruise at 6 knots.

 

[jssailem]

1. in-mast furling config has a slightly larger headsail area and
2. slightly smaller main area,
3. the furling main shape has much less roach than the standard main.

1 and 2 both impact your lee helm issue.

1 the furling space available to capture the defines the amount of sail possible in the main. Smaller overall size would be one way to manage the sail's furling ability.

A second element would be the Camber designed into the sail. A sail that is going to be furled has to be constructed with less camber than the one not furled. To our eye the sail would appear flatter.

How Camber is Built into a Sail ​

​

First, the sailmaker cuts the luff and foot of the sail in a curve. This is shown in the left hand diagram. When the boom and mast are straight, the extra material leaves a pocket in the sail. These pockets can be flattened by bending the mast or the boom. ​

Next, the sailmaker curves the edges of the panels, as shown in the right-hand digram. The picture above is exaggerated to show these curves. When sewn together the extra material forms pockets along the seams. These pockets are less responsive to flattening. ​

The sail designer determines how much curvature is desired for the luff, foot and each of the seams to optimize the sail shape and its response to the sail controls. ​

Camber Controls​

For this discussion, we’re using a fairly simple fractional rig, with no jib. The mast has one set of stays with swept spreaders. This boat’s controls include a mainsheet, vang, and outhaul.​

The third element Roach. While the swept back fractional rig design on your 306 could accommodate a larger roach on your sail, the space in the mast for a furled sail might not. The compromise of sail design (and thus sail control and function) is dependent on the systems you have on your boat.

A bendable mast with slab reefing can accommodate a larger main sail with shape features to enhance your speed and performance but sacrifice the convenience of a furling mainsail.

That said you may be able to find a sail loft that can design a higher performance mainsail that still will function in your furler. This of course will likely come at a greater price point.

Sail trim thoughts.

• Guidelines for Good Mainsail Shape
• Upwind Sail Trim Archives

 

[Arbee]

While the swept back fractional rig design on your 306 could accommodate a larger roach on your sail, the space in the mast for a furled sail might not. The compromise of sail design (and thus sail control and function) is dependent on the systems you have on your boat.

Thanks @jssailem, I believe this is the heart of the matter in this case due to the large roach of the standard non-furling Hunter main. Before I start shrinking my headsail I'll see what I can do to compensate for the compromised furling sail shape and try tightening the leech more to get some extra power back there.

 

[jssailem]

That sounds like a good idea. Just remember to release the trim tension when you begin to furl the main. Main sail furlers like the sail “just right” for optimum function.

 

[Crazy Dave Condon]

On in mast furling, the rake has been discussed but prebend should be limited to 1 degree. Otherwise, the furling mainsail will jam within the mast.