Hull speed vs. wind speed

[elibobeli]

Thanks to all for the topic suggestions.  I will look forward to my research.

Bob,  "Milk from a turnip", being an impossibility correlates to trying to reach hull speed of 5 knots in 5 knots of wind or 10 knots."  If it is impossible then I don't need to try.  What I am trying to answer by you gentlemen's input is where does the impossible become possible, or what wind does it take to reach hull speed, in general, of course.  I'll try to always make for best speed with max enjoyment.  If I have enough wind, and can't reach hull speed, then it's me or the boat, not the wind.

Don't want to beat a dead horse, so I will leave it at that.  Winter's coming so I'll enjoy my remaining days to sail.

[Craig Weis]

Get out there and sail your boat. Try things...then! Suddenly you'll hit the sweet spot and off you go.

Put that vertical wrinkle alone the mast in the main sail and then just sheet in the boom, holding course, till the wrinkle shakes out. The looser the sail in this manner the faster she'll sail. skip.

[Bob23]

Allan:
  Yeah, I got the milk from a turnip thing...just having a bit of cabin-fever induced fun. By the way, what do you sail?
  Bob23

[Potcake boy]

Have been following this topic for a couple and could no longer jumping in, so here goes. The best description I've heard about performance was that your boat has limits imposed by hull/rig designand a host of other factors. Meaning that every boat is truly unique, the difference is the way in which they are sailed. In racing the object is to sail her to her optimum and commit as few technical errors as possible.

So I agree with both sides of this question : to always try to maximize performance vs sit back and relax we're moving. After all we all have our own reasons for sailing, which probably from time to time.

Eliboli - I believe this slight friction I sensed has arisen because you are bringing a horse to a donkey show. Most of the folks who own Compacs do so because of their performance character. These boats are designed for the sit back and relax kind of sailing, so most of the folks participating in this forum aren't inclined to be concerned about speed.

I accept that the Eclipse model appears to be a variance or departure from the traditional Hutchins design criteria so you may well be a different kind of customer for Compac, with more of an eye toward speed performance. By the way, the reincarnation of the CP16 as the Legend does offer some tantalizing possibilities. The three stay rig would allow a fully battened main with a square or near square top (a very high performance configuration). Add a high aspect fixed or retractable ballast keel and polish it up with a bow sprit to fly a flat asymmetrical. You could be talkin' some serious performance here. Wait a minute, aren't there already a bunch of boats already available that fit that description?

So my whole point is if you really want to get optimum performance, first read some of the plenty already written by the experts about sail trim, and practice on your own boat. That being said, the caveat is that the results of proper sail trim aren't as dramatic on "relax and enjoy" designs as it would be on a all out racing design. Good sail trim knowledge is always an asset but if you really wish to squeak out every bit of performance you might consider signing as crew for one of the local sail race boats like a J boat. You will be able to see clearly the effect of proper sail trim, and apply to your more relaxed outings on your own boat.

Not to diminish your question, but hull speed is not only difficult to predict (manufacturers probably can't tell you accurately in most cases) but almost irrelevant. If you always sail her to her potential at some point you will begin to understand and feel her best performance regardless of the true wind speed. I am old school and advocate that as a novice (we probably all are to some degree) you should develop your intuitive interpretation of sailing before you get distracted by all the high tech go fast gadgets.

If you are sitting around all winter and  looking for some way of relating to sailing from your den, and if you have read the sailing magazines from cover to cover, and there is no sailing on ESPN, and you've watched Waterworld 3 times in the last month, then I suppose tackling your question would be a worthy endeavor. You'll come out next spring eager to put your conclusions to the test.

Remember - "it's not the destination, it's the journey"

Ron

[mrb]

Hello elibobeli

To answere your original question No it does not take close to overpowering wind to reach hull speed.  Not even close.

If we go with the twice wind speed to reach hull speed that would be only 10 mph to 5 mph.  If that makes a person comfortable live with that and happy sailing.

Personally I am happy in a steady breeze of 5 mph up to 15 mph and if it is consistant 20 and slightly higher.  Don't like those high gusts on top of high wind though.

Happy sailing
mrb

[Paul]

Elibobeli and MrB:

MrB, I agree.  The CP-16 really feels her best between 5 and 15 wind speed.  Of course, depends on sail configuration etc., but I generally don't worry about "hull speed" as much as feeling she's in the groove and doing well.  What a great feeling!  I'd estimate that somewhere in that range, hull speed is achieved, but I haven't measured it.  Actually, I like the challenge of sailing her smartly in higher wind speeds.  I think my comfort level begins to wane around 20 to 25, but that's just me.    She can handle more than I can. 

Which leads me to the question of overpowering.  She can be overpowered in a wide variety of conditions.  Simply depends on the sails used and wind strength.  IMHO, another factor is the rudder.  The foil rudder allows for better performance.  Also consider that she'll round up when overpowered.  You'll know it when it happens.  Kinda scary at first, but upon contemplating the situation (after a few beers on the hard) you may conclude as most of us have that she's designed well and really can handle more than the sailor.  

Most of us who sail north of the tropics use the winter months to study sailing related things or do upgrades.  All can benefit from studying good seamanship.  I have found Chapman's as a good reference.  I have thoroughly enjoyed John Rousmenere's tome on the subject.  These can give details in the matter of sailing safely in a variety of conditions.  Happy winter reading.

[elibobeli]

For all, I am sailing an Eclipse.  Thanks to all.  I'll look for the groove, probably in the Spring, unless Fall throws me another nice Saturday.

I have learned a lot in a dozen times out and look forward to the next time.

[mrb]

Hi Folks

My  last quarter on subject of hull speed for what it's worth.  Hull speed is a factor of the hull, not size of sails or engine.  Sails and engine size of coarse will allow boat to reach hull speed but then for every fraction of increased speed will require greater and great power until boat sinks or comes apart.  The reason for sinking pull apart is that as speed increases the wave that hull creates as it moves through the water begins to stretch out farther and farther from the stern of boat. The stern will begin to squat and sink lower and lower until it is pulled under water or suction becomes so strong that back of boat pulls out.  Granted those to are the extreams and highly unlikely unless skipper has been drinking to many absinthes.

A salmon fisherman years ago had a nice Monterey style boat.  Thought boat was slow so re power with larger engine.  He would crank that engine open exceed hull speed until green water swept decks from bow to stern.  lots of fuel no more speed.
My Father and others tried to explain but he was happy. Don't know what Finlay happend to boat but sure that nobody who knew how he treated it bought it.

I personally like to sail boat to max when wind cooperates.  Other times sit back and enjoy what comes my way.

If speed was my goal I would by a semidisplacement or plaining hull and enjoy the speed.

To figure speed of  displacement hull divide speed by square root of water line. A ratio of 1.34 is upper end of speed.  Example speed 6knots divide by 4 ( 16 ft wl.)gives ratio of 1.5 no go.  Speed 5.5 divided by 4 = 1.37 Therefore I am happy when boat is puttering along in a good breeze at or near hull speed.  when I had Coronado 27 7 knots was about it and I was happy.

Have fun and thats my last word mrb

[pattyhazz]

Eli:
My experience with an Eclipse is about 2.5 - 3 times actual wind to reach hull speed as a rule of thumb.. I had much better performace with Genoa sheeted outside the shrouds then back to the jib cars on any point of sail other than close hauled. I also found that an Eclipse likes to sail flatter than most boats, max. heel about 15 degrees. I'd like to try a larger Genoa about 135 instead of the 115. I just guessing here, but maybe the factory feels safer with a 115 Genoa due to the fractional rig design with no backstay. Everything is a compromise if you factor the quick mastendr system versus the size of the sails. There is not much written regarding rig and sail tuning for an Eclipse, Maybe you could due the tests, mess around with the shrouds,forestay tension, mast rake, outhaul,downhaul, traveler position, boom vang tension, Jib cars, etc. in differant wind speeds. It would be real valuable info.
regards,
Rob, B.E. (boatyard engineer)

[Potcake boy]

Rob & Eli,
I have heard that the eclipse is a line up replacement for the 19. If that is so, then considering your statement (Rob) about keeping her within 15 degree heel, it does sound like my CP19.

Here is my take on sails for my boat, though the Eclipse may be a better windward performer than th CP19. For the most part I figure sailing close hauled will only be useful in fairly calm water to get a decent boat speed, otherwise I'll be easing off the wind to keep speed up. The 110 is really close to being as good as a genoa in most of these conditions, and I have a furler on the 110. Given that the shape is badly distorted when furling a genoa, I've decided to leave the 110. However, what I believe will be most of my windward sailing, close reaching, can be done by the use of a flat asymmetrical spinnaker. I chose a North G3 because it is flat enough to close reach, and is also suitable for downwind, and can be sailed dead downwind with a whisker pole. Now, I have limited experience with this combination so far, and will update the list when I have more specifics on how it is working out. This approach seemed to me to keep it simple, give some good performance, and avoid the sheeting problems sited with the wide based shrouds, and provide some improvement in offwind sailing.

To add to this however, it is important to note that I have just replaced my main with a flatter cut full batten sail that I got from Rolley Tasker. Now my main is an important part of sailing to windward, whereas before it was hopeless trying to close haul.

So most of the time I can sail with main and 110, set the spinnaker when appropriate, nice combination, and simple.

I would certainly invite your view of this approach.

Thanks,
Ron

[Potcake boy]

Oh yeah a P.S. to my last post on this topic. The lack of a backstay does invite the idea of a big roach full batten main - wow what power you'd have along with a code 0 or flat asymmetrical. The eclipse has a plumb bow and reverse transom for a optimized waterline, and a deep centerboard for good pointing ability. I had a Picnic cat for a while and loved the Mastender system, it is the difference between a boat being really a trailer sailor or not.

Ron

[curtisv]

If I knew what to expect from the boat, then I could work toward those expectations.

Thanks for the input.

Expect to have fun and work toward that expectation.

Just a suggestion.

Curtis

[curtisv]

So does anyone want to discuss Hull speed vs. wind speed?  It may help me being a better seaman.

OK.  Hull speed is the knee of a speed power curve above which it takes quite a bit more power to move just a bit faster.  Hull speed is mostly related to the properties of water and the tendency of a boat to move more quickly at speeds that don't have the stern overtake the bow wake.

That means that it doesn't take much at all to reach 50% of hull speed.  More wind to reach 80%.  Much more to reach 90%.  Quite favorable conditions to reach 100%.  And some unusually good conditions to exceed 100% though it can  be done (surfing will do it, for example, and surfing with a CP23 is darn good fun, regardless of what percentage of hull speed is attained).

Hull speed is estimated as 1.34 times LWL squared but that is only an estimate.  Actual hull speed depends on the hull shape (beamy vs narrow, depth of the hull, wetted surface) making it very hard to get an exact number.

So what does this have to do with wind speed.  Very little actually.  Most boats go fastest on a beam reach.  Some are a bit better a little to windward of a beam reach, some better on more of a broad reach.  Most are usually a bit slower on a run than a reach though I mentioned that surfing can give you a push to get you going a bit faster on a run.  Four foot waves will do nicely (QED).

How fast any boat can go if sailed well depends mostly on the point of sail and less on the wind speed.  Compacs don't sail all that well in light air but stand out as the wind picks up.  At some point reefing is needed to keep the boat "sailing on her lines".  Too much heel adds drag so reducing sail beyond some point makes her sail faster.  OTOH - keeping the sail up makes you go slower but burying the rail gives the kids a thrill so sometimes not going as fast is more fun.  At what point the greatest efficiency is achieved varies with each boat.  If on a given boat you can flatten sail effectively, it may be at a higher wind speed than if your sail controls (or worse and older baggy sail) limit your ability to flatten sail.

Waves also tend to slow a boat's progress.  Where there is wind there are waves.  The longer the fetch, and the longer the wind have been sustained, the bigger the waves.  So waves are also a factor.  A steady wind also makes it easier to achieve a better boat speed than a gusty or shifting wind.

It may be that you can go fastest on a reach in moderate conditions that come up suddenly but steady wind and yield fairly flat water and a steady wind.

You might be better off asking how to improve your boat speed for a given set of conditions which is along the lines of the answers you got.  For most CP owners with older CPs there are improvements to the boat that will help.  The Eclipse seems to be set up better out of the factory (for example, with a traveller) so best at this point to focus on basic sail trim first (sheeting), then sail twist (getting the whole sail flowing well top to bottom), then the right sail draft for conditions (flattening as wind picks up, increasing draft in lighter conditions).

The point of my earlier short post was that you'll probably enjoy sailing more if you focus first on just having fun and second on whether you are going as fast as you possible could.

Curtis

[Paul]

Curtis,

Well said. 

[tmolik]

here is a web site that might be interesting, a little removed from the topic, but close enough, try and see.

http://www.image-ination.com/sailcalc.html

tom