Heavy sailboats are slower and

[barnakiel]

Back to that nuclear aircraft carrier the limit is not just power plant / required hp. Much as it is the first limit these meet with.



It is also (although probably at much higher speed) its hull stability.


Displacement hulls are ultimately unstable at very high speeds.


For sailing yachts with classic keels this actually happens not too far from their hull speed.



b.

[Smokeys Kitchen]

Originally Posted by CarinaPDX

You don't understand the concept of hull speed. It is not a brick wall. If you looked at a graph of power versus speed for any displacement vessel you would notice a roughly linear increase of both, out to a point near "hull speed", where the power curves up (i.e. it takes more power for incremental speed increases). If you have massive sources of power from a nuclear reactor an aircraft carrier or submarine can be pushed to much higher speeds than the hull speed - it is just highly inefficient.

Greg

Thanks Greg - it is a learning point for me.

So if I understand correctly, it is a little like the recent anchoring thread and the holding curve shown, where the extra scope over 5:1 doesn't result in the same increase in holding power as scope below that does.

[CarinaPDX]

Originally Posted by Smokeys Kitchen

So if I understand correctly, it is a little like the recent anchoring thread and the holding curve shown, where the extra scope over 5:1 doesn't result in the same increase in holding power as scope below that does.

I didn't see that thread. Of course the more scope the harder it is to pull out the anchor; I just don't know the shape of that curve. But there is a difference in concept: somewhere around 6:1 the angle of a straight rode to the bottom is small enough that the flukes or palms angle downwards and so want to bury deeper, while with lower scope the angle is too high relative to the fluke angle that the anchor is pulled up. Shorter scope with chain may still have an adequate angle at the anchor due to the catenary, until there is enough load to straighten the chain to the point the angle is too high. Most of the time a yacht is not really pulling that hard so the anchor is not tested, but when the stinky stuff hits the fan having a low angle of the chain to bottom is critical. But this isn't an anchoring thread...

Here is one power/speed plot. I don't know the vessel but I would guess that hull speed is around 10-12 knots. Notice how much more power is needed above that point to achieve an extra knot.

https://image.slidesharecdn.com/basi...ance-7-728.jpg

Greg

[a64pilot]

There are Supercavitating torpedoes capable of speed in the hundreds of kts, and they have been around I believe for quite a long time, decades
https://en.m.wikipedia.org/wiki/Supercavitation

After the wall fell, we learned a lot about some Soviet weaponry that we didn’t know about, for example the US Airforce has always needed for the pilot to drive the aircraft’s armament datum line onto the target for a missile to get a lock and be launched, the Russians knew that a missile was much more maneuverable than an aircraft and took a lesson from helicopters and had the missile‘s line of sight be slaved to the pilots helmet so that if a pilot could see the opponent, he could get missile lock and fire without being pointed at them, they also developed and fielded a rearward firing missile, so one of our pilots would get on a Soviet aircrafts tail to shoot like has been done since WWI and he would quickly be shot in the face.
It’s incredibly difficult to make a rearward firing missile work, it first comes out with an apparent wind up its tail, the accelerates to zero apparent wind, then transitions to forward apparent wind, I assume it would have to steer by thrust vectoring?

The Japanese WWII torpedo would hit close to 50 kts I think and travel 24 miles? Even further if it was sent out at a slower speed, but I have no idea how you could guide much less target out to 24 miles without some kind of seeker, which I don’t think the Japanese had, so I’d guess it was a launch and pray weapon at those ranges?

[Adelie]

The Shkval supercavitating torpedo is more akin to a rocket than other torpedos. It uses a rocket that exhausts at the nose. In addition to thrust the gases cover the body of the weapon so drag is vastly reduced. Small fins stick out past the gases into the water flow for control I believe it is wire guided since the is almost no contact for sonar.

[Dockhead]

Originally Posted by a64pilot

I guess my point is that you can spend shed loads of money and stress and work for those two kts, or you can sit back and enjoy life.
I’m the type that trims their sails a little tighter than optimum, so that I don’t have to mess with them, some however are trimming every 15 min, and watching the tell tales the whole time, I sit back and read a book and relax.
If I wanted to go fast I would have stayed with power, and kept my job to pay the fuel bill.
I have gotten lazy and not so much in a hurry, so I give up 30 miles a day. I gain a relaxed way of life.
Of course I knowingly, intentionally sought a comfortable boat over a fast boat, and one I could buy and Retire.

To me, that extra 35 miles a day isn’t worth spending loads more money on, or lots of extra work.

I think most Mom and Pop cruising teams have adopted the thought process of we will get there, when we get there.

Whatever kind of sailing bring you joy, is the right kind for you -- of course.



But don't think those of us who sail more actively do it just for the speed or primarily for the speed. We do it primarily for the feeling of the boat tuned exactly right, all the airfoils just right and all drawing strong, the boat coming alive. As an aviator, you'll understand well that a tiny adjustment to the foil is sometimes all it takes for the airflow to suddenly stay attached and produce the full amount of potential lift. Sailing upwind, more speed means still more apparent wind, so the effect of good trimming is compounded as you climb up the increasing apparent wind. That is cool and THAT's why we trim every 15 minutes -- because it feels good, and because it's FUN. It's SAILING.


It's also fun because it's a PUZZLE. Sail trim is complicated; it's fun and deeply satisfying when you figure it out and get it right.


This works best with good sails (and rigging), and with a reasonably light boat which responds quickly when you get it right. This gets back to the OP's question. There's a really big difference when you get to a D/L of about 200. And although a lot of people have argued about it, the OP is essentially right -- there is a basic tradeoff between speed and especially responsiveness, and motion comfort, mitigated only with increasing size.


One key technique for this kind of sailing is working out target speeds for different conditions and points of sail. With enough practice you will know exactly how fast you should be going in any given situation (and race boats often have a printed table stuck to a bulkhead). Then you quickly know when you've got it right.


I had to smile when I read your post, as you were describing me to a t -- I single handed again yesterday across the Gulf of Finland, on a gorgeous sunny summer day, uncharacteristically warm for this time of year, light steady wind 8 to 10 knots most of the time, flat sea, on a close to beam reach. Keeping the boat moving well in such a light wind is a challenge, especially when you've reduced the sail area of your boat like I have -- having substituted a 95% blade for the normal 120% yankee. This makes mainsail trim absolutely critical. But my target speeds in such conditions (close to slightly broad reach, wind less than 12 knots) are two thirds to three quarters of the lesser of the true or apparent wind speed, and with a really steady wind and really flat sea the target speeds are absolutely reachable, so I was able to average about 7 knots over the 50 miles, but with such little force in the wind it took very active trimming to keep the sails drawing. I was walking up to the pulpit every not 15 minutes, but more like 5 or 10 minutes, to look up at the sails from there, coming back to make often tiny adjustments.


Little force in the wind matched by very little force needed to cut through the glassy smooth water, and what a feeling -- like just magically flying through the water, on lift rather than being blown by the brute force of a stronger wind. What a feeling.



Not your kind of sailing, but there are different ways to get joy from this sport. Only the OP knows what kind of sailing he likes to do; and this profoundly influences the optimum choice of boat, so he is asking the right questions.

[TJ D]

I'm baaack.



Dock, sounds like the Baltic is treating you well, as always.



Probably not surprisingly, I have a different view of weight and comfort. Our last boat was 43' long, steel, and weighed 20 tons.


Current boat, 55', 12 tons laden.



Guess which one is more comfortable in snotty weather? Guess which one is more stable, empirically?



Light boats, if designed well, are a pleasure to sail even in harder weather. Jenny almost never gets seasick with the quicker motion of the current boat, whereas the heavy wallow of the tank turned her green often.



Not to self promote, but Bill Lee did a nice writeup on our boat-it's in the technical details tab of the site below. Some of you may find his analysis of interest.

[Dockhead]

Originally Posted by TJ D

I'm baaack.



Dock, sounds like the Baltic is treating you well, as always.



Probably not surprisingly, I have a different view of weight and comfort. Our last boat was 43' long, steel, and weighed 20 tons.


Current boat, 55', 12 tons laden.



Guess which one is more comfortable in snotty weather? Guess which one is more stable, empirically?



Light boats, if designed well, are a pleasure to sail even in harder weather. Jenny almost never gets seasick with the quicker motion of the current boat, whereas the heavy wallow of the tank turned her green often.



Not to self promote, but Bill Lee did a nice writeup on our boat-it's in the technical details tab of the site below. Some of you may find his analysis of interest.

Hey, good to see you TJ.




What TJ writes here doesn't contradict necessarily what else has been written.


Remember TJ's (totally awesome) boat has a 55 foot waterline. As a boat gets bigger, it can be lighter and lighter without losing too much motion comfort.

[hpeer]

To the idea or concept that it depends upon the sailing you do is important. As we live aboard for 6 months and my Wife is prone to seasickness and we can’t afford/don’t want a cat then a very heavy displacement boat made a lot of sense. We are happy with the decision. Of course there are trade offs in sailing performance but we still get there, and then stay for a while. We are not the day sailor type.

If anything I’d say I’m surprised at how little penalty we pay for our tonage.

[Chotu]

Originally Posted by hpeer

To the idea or concept that it depends upon the sailing you do is important. As we live aboard for 6 months and my Wife is prone to seasickness and we can’t afford/don’t want a cat then a very heavy displacement boat made a lot of sense. We are happy with the decision. Of course there are trade offs in sailing performance but we still get there, and then stay for a while. We are not the day sailor type.

If anything I’d say I’m surprised at how little penalty we pay for our tonage.

This is true. The penalty really isn’t that bad for the extra weight. As much as I complain about not getting that extra couple knots out of a boat, being able to carry all of that water, fuel and food is really something.

[robmo]

Originally Posted by CSY Man

No, not correct.

Heavier monohull require more wind to make them go, whereas lighter boats can be faster in ligh air;. However, once the wind picks up, the heavier boat will greatly outpace the lighter boat and give a much better ride.

[avnbuff]

I had the occasion to own an O'Day 35, which as a brand name was for years considered 'slow'.. in fact called 'slowday' by one surveyor I know.

What I learned during the ownership was that Pearson Yachts had taken over production of the O'Day in the mid 80's and the 1988 model I had purchased wasn't true to the reputation of earlier boats like the 34, O'Day for example.

Heavy isn't necessary slow, the thought should be about drive VS drag. Sure the 'light' boats today are working to be fast... but that is working against some limits enforced by "mother nature" in the form of waterline and wetted surface in the hull.

Figure out what you want, I did. The '88 O'Day was far from slow and provided a comfortable cruise speed with the comfort of a 'bigger' boat.

The Aviation Buff

[Don Braymer]

I owned the 72 foot schooner Dirigo II. I kept adding sails, and kept going to the Long Beach California yacht club in order to declare the newer greater possible sailing footage in order to update my PHRF rating in order enter the Ensenada race yearly...

Finally, the possible square footage got up to 3300. One guy on the board says "I know those old boats, it is pretty hard to get her moving".

Another pretty old guy interjects "yea, but you only need to get her going once!"

All generalizations are false, as is your current example. It depends upon conditions, and there are at least 5:

wave height
wave period
relationship of wind vectors to above
current
tide

given that hull cleanliness is not poor

[Capn Bri]

Originally Posted by agpilot88

Question:


This is the way I understand it. The heavier the boat, the more stable and slower it is and the lighter the boat the quickler and less stable it is?


Correct?

Not necessarily. It depends on the seas. Lighter boats are more easily held back by big headseas whereas heavier boats, once they get their way on, will keep their heads down and "plow" the seas because they can retain their momentum better.

Most people don't know that the Westsail 32 --not what you could mistake for a light-weight boat-- won the Transpac Race ...TWICE. While lighter boats more oriented toward racing were being beat back by heavy headseas, the Westsail was like a freight train and just plowed through them.

At the same time, however, racing a Westsail (or any full-keel, heave cruiser) in lighter seas and low winds is sure to generate lots of excuses as to why that boat is STILL out there, days later, having only just rounded the second mark.

[mstrebe]

Originally Posted by agpilot88

Question:


This is the way I understand it. The heavier the boat, the more stable and slower it is and the lighter the boat the quickler and less stable it is?


Correct?


Of course take into consideration of the draft and the shape of the hull. Seems like price and weight corresponse with each other.


Lee

No, this isn't how it works.

Regarding price, the price of a new boat is the cube of the waterline length in feet times about $5 ($4-$15, but generally around $5). Boats increase in price by volume, not by weight. They then depreciate along a pretty standard depreciation curve down to about $0.50 per cube where they stop until they sink.

Regarding speed, monohull sailboats are generally limited to their hull speed. That's a maximum that they might be able to surf a little beyond but that's really it. Additional power beyond the hull speed just goes into more heeling. Two boats of the same length are generally going to have the same maximum speed, regardless of their weight.

The weight affects acceleration: Light boats speed up faster in the same air. But it conversely affects deceleration: Light boats also loose momentum faster than that heavy boats.

Light boats can be faster in light air with standard sails because they can get to higher speeds with less power, but that can be matched by a heavier boat's ability to hoist a larger sail.

regarding stability or sea-kindliness, that is much more about the hull shape, keel configuration, and rudder configuration than it is about weight for the most part. A full keel that keeps a boat straight in broaching waves is also a full keel that will roll a boat when parallel to a breaking wave that a modern fin keel can more easily surf with leeway.

Racers light light because acceleration and light-air performance wins races. Cruisers like heavy because inertia dampens movement and is more sea-kindly.