Sail Trim Question

LuzSD · Jun 7, 2011

I'm going to stab at this one, mainly because I saw another picture posted recently and wondered why no one asked the same question. Here is what I think the skipper of the boat I crew on would be asking me to do......
1. travel down about 2 inches
2. let the mainsheet out until it creates a bubble
3. then bring the mainsheet back up just until the top tail on the main flickers and the bubble is gone if possible
4. might need to travel back up a tad after all that is done.

That's all I have

Stu Jackson · Jun 7, 2011

Plus the open top of the jib seems to need the fairlead car moved forward.

"2 inches" on the traveler? I agree on down, but so specific...

cwkemp · Jun 7, 2011

I'd try taking a little twist out of the heads'l (move the car forward) unless my passengers were uncomfortable with a little more heel, but also, depending on the telltales, maybe the main could benefit from slightly more twist?

LuzSD · Jun 7, 2011

"2 inches" on the traveler? I agree on down, but so specific...[/quote]

Ha Ha, you don't know our skipper!!! I sometimes get 1/2 inch down please!!

mcrow33 · Jun 8, 2011

I agree that the traveler can be dropped, but the jib cars need to come back.

Todd Smith · Jun 8, 2011

The picture looks more like a close reach than close hauled.

It's hard to say without being able to see the tell tales, but either the main is under twisted and over trimmed or the jib is over twisted.

It also looks like the main is really flat, with a very deep draft jib. Ease the main outhaul/backstay to match those up.

I would put the jib on an outboard lead and trim in some. Ease the main trim some, probably with sheet to add some twist.

RichH · Jun 8, 2011

The pic shows a close reach (angle of the oncoming waves).

The foot of the genoa is somewhat overtrimmed and the head is overtwisted which causes the 'timing' of the genoa leech to no longer match the curve of the mainsail leech. In all probability only the middle panels of the genoa are flying with any semblance of 'aerodynamic' flow.

This is usually caused by easing of the jibsheet ... and not moving the fairlead car forward when that sheet was well eased out to correctly re-set the angle of attack across the WHOLE sail. If they were carefully watching the leech tell tales on the jib they would have probably seen this 'mistake' in trim. In all probability they had the fairlead cars set in proper position when the were beating ... but didnt re-set them to a more forward position when they 'cracked off' to close reach; not doing so will lead to all sorts of trim problems as seen in the pic - overtrimmed foot and twisted-off head and only the mid-sections of the sail having the tell tales flying correctly.

Rx: When the jib sheet goes 'out' (to adjust for more 'open' sailing angle), the fairlead car goes forward .... usually by an equal distance forward as the distance that the clew goes forward - the leech and head tell tales will tell you so. This is a good case for fairlead cars that are 'conveniently' adjustable from the cockpit.

If I were racing against this boat with a boat of near 'equal numbers', id crack off and give this boat a VERY 'loose cover', as I would soon be passing him by taking advantage of his poor trim. An other reason that Id 'crack off' would be the hope that he'd take the bait and follow me into an ever deeper reach and Id expect the mal-trim on his boat would get even worse. If I put a 'tight cover' on him he might tack, or harden up etc., and he might sooner discover the trim error.

Scott T-Bird · Jun 8, 2011

Perhaps, they have started by trimming the main sail first as they should with a fractional rig and haven't trimmed their genny yet. I think from the angle of the boom and the orientation of the leech that the mainsail is pretty good. I actually thought it might be good to move the traveler up and ease the sheet to give it a little more twist.

The genny looks over-twisted and not sheeted in (yet). Not sure about moving the fairlead up until sheeting in more. I'd start by sheeting in and then think about the fairlead.

steelcastle · Jun 14, 2011

Max speed

OK. All you experts. What I would like to know, is based on a 25' sloop with max hull speed of 6.5 knots....
At what wind speed, in general, should I expect achieve maximum boat speed for each position??? Running, broad reach, close hauled, etc.

Todd Smith · Jun 15, 2011

steel,

that's a really broad question. It depends a LOT on the boat design. On a Tartan 28 I sail a lot, ( which has a waterline close to 25' ) I would say 10-12 knots true wind close hauled. 16-18 knots true wind for running deep.

Joe · Jun 15, 2011

steelcastle said:
OK. All you experts. What I would like to know, is based on a 25' sloop with max hull speed of 6.5 knots....
At what wind speed, in general, should I expect achieve maximum boat speed for each position??? Running, broad reach, close hauled, etc.

Did you mean maximum theoretical hull speed? You don't want to open that can of worms. Especially when you're talking about a non-displacement hull centerboarder.

See if you can find a set of "polars" for your particular boat. That will give you the info you desire.

RichH · Jun 15, 2011

What everyone else states ... for 'dispacement' sailing 1.34 times the sq. root of the waterline length is the approx. maximum. If 'displacement' sailing then the 'theoretical' max. will be ~6.5 knots

However a Mac25 is a lightweight / centerboard boat that under the 'right' conditions can get up onto a plane and thus break free of the restricting generated bow/stern wave .... under these conditions it is possible to get upwards of perhaps 12-15 knots.

steelcastle · Jun 15, 2011

What? A Mac25 doing 12 knots? I have only been sailing for 6 months, on a desert lake at Phoenix, at that.
How would I double hull speed for each position?

OldCat · Jun 16, 2011

steelcastle said:
What? A Mac25 doing 12 knots? I have only been sailing for 6 months, on a desert lake at Phoenix, at that.
How would I double hull speed for each position?

I don't know either. The Mac carries water ballast, so it is not a "centerboard" boat like a laser/470/49'er/Rich's scow, etc.

However, I regularly exceed the 5.9 kt hull speed of my C22 on a flat water lake - no waves to surf, no currents - & I do it even when close hauled. So do many other C22 owners. No where near as fast as a U20/J22/J24, but still, we get over hull speed by 10-20%+. Hull speed may not apply as much to a light keel boat on flat water...

Or, we are planing, but the boat never seems to generate much of a wave, so I don't know. But hull speed is not a limitation that I have seen in my boat...

While 12 for a Mac sounds high to me - maybe with an asym? Maybe Mac owners could chime in. RichH is really good - who knows how fast he could get it going...

OC

Joe · Jun 16, 2011

First of all....... it's THEORETICAL Hull Speed. It's a mathematical model based on a boat's bow wave length that attempts to show the maximum speed a FULL DISPLACEMENT HULL can attain. A full displacement hull boat must push the water aside to make progress... as opposed to a planing hull boat, which can ride on top of the water. There are varying shapes of hulls that fall in between and are sometimes called "semi-displacement" hulls.

The theoretical hull speed formula(1.34 x square root of Waterline) was devised during the age of steam power to determine the most effecient size engine for a displacement hull vessel. Operators had to consider the cost, and weight, of the additional fuel required by higher horsepower engines compared to the performance increase. Going beyond the theoretical hull speed, or getting up on plane, required an exponential increase in power, thus the number was used to determine optimal engine size.

Now... how does this relate to modern sailboats? The simple answer is.. "it doesn't" but that's not completely correct. Full keel sailboats are, by and large, displacement hulls..... many popular heavy cruising boats fall into that category... but the modern sailboat's hull is far from full displacement and, therefore, not restricted by the "theoretical hull speed" formula.

The most practical use, today, of the theoretical hull speed formula is to determine the optimal auxiliary motor size for our sail boats...

But...... it doesn't really mean much when the sails are up, does it? Because many sailboats routinely exceed theoretical hull speed.

Oh, and just remember that you SOG (speed over ground, i.e. GPS) is not a measure of hull speed. STW (speed through the water) is the standard... measured with your speed log. (the spinning wheel)

FourPoints · Jun 17, 2011

I often manage to exceed my hull speed of 6.2kts (22ft waterline), most of the time it is on a beam reach, or on downwind tacks with the spinnaker up, but usually it is only by a few tenths of a know, however in just the right conditions I have hit speeds of over 8kts before (Exact STW not sure, there may have been as much as a half a kt of current going on there according to eldridge, but my paddle wheel was fouled at the time so i couldn't compare it with gps speed...)

That said, the hull speed calculation is a good general rule of thumb that determines the fastest the boat will be going in most circumstances (like when closehauled), and most of the time i can sail the boat right up to 6.1 or 6.2kts, and no amount of trim improvement will get me past that limit.

OldCat · Jun 17, 2011

FourPoints said:
That said, the hull speed calculation is a good general rule of thumb that determines the fastest the boat will be going in most circumstances (like when closehauled), and most of the time i can sail the boat right up to 6.1 or 6.2kts, and no amount of trim improvement will get me past that limit.

We have different boats - yours is heavier. Your cruising boat is also heavier than a light weight racing keel boat - perhaps a J80 would be a reasonable comparison for about the same length boat - and a J80 type of boat will blow past hull speed on all points of sail given enough wind. The price of nice cruising amenities is more limitations to having a chance at exceeding hull speed...

IMHO: "the boat" and "close hauled" don't limit my boat as much, and especially doesn't limit modern racing designs (U20, J80, etc). My FASTEST speed to date was CLOSE HAULED in the aftermath of a big gust - over 7kt (5.9 hull speed). Both sails were reefed at the time. My 12 year old hit 6.5 last Saturday:dance:. As I said above - I know C22 owners who have gotten higher speeds than I have...

FourPoints, You sail well, but gravity and the weight of those nice cruising amenities keep you limited closer to hull speed than the owners of lighter boats. If you sailed my boat on my lake on a day with a good westerly blowing - you would have no problem going over its 5.9 kt hull speed. No trouble at all...

OC

FourPoints · Jun 17, 2011

Lighter boats that are able to plane will definitely be able to more easily and more frequently exceed their hull speed, but that doesn't make the hull speed calculation any less true as a good "rule of thumb" calculation.

I have a good friend with a Catalina 25, which on paper is almost the same boat as my Hunter 27 (waterline is almost identical, displacement is almost identical, sail area @ 110% genoa is almost identical, he draws 6" more than me, but I think his keel is roughly the same length as mine below the hull) and I can sail circles around him most of the time (one night sail when we were both out in really light air, I actually did sail in a circle around him

, he wasn't impressed...)

Why is my boat so much faster than his? Sure some of it is probably the skipper :dance:, but the shape of my hull is different. My hull is very flat on the bottom, where his more round.

I have also had his boat up above 7kts many times, even close hauled, but it's usually because of unusual circumstances such as when double reefed in 25kt winds... In most average circumstances, he still never exceeds 6.1/6.2kts...

So Yes, given the right conditions our club cruiser / racers (like most Catalinas, Hunters, and Beneteau's, what the majority of people on this board have), will be limited to the hull speed when sailing in average conditions. Those with race hulls specifically designed to exceed thee average hull speed are clearly except from this discussion.

RichH · Jun 17, 2011

A clarification --- the 1.34 times sq. rt. of the waterline length doesnt calculate the speed of the BOAT, it calculates the speed of the bow/stern wave produced by the boat. The hull form vs. boat mass, etc. will determine if the boat can go faster than the bow/stern wave ... ie.: a boat that is planing or semi-planing.

1.34 (WLL)E2 is speed of the WAVES produced by the boat, not the boat.

Sail Trim Question

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