speed of boats

[rick stoehrer]

got to thinking in speaking about the "speed" of the romany surf below.

engine vs hull....

how many and how often are any of us actually paddling at or trying to exceed the theoretical speed of a hull?

the rough old school way to determine this is that you take the square root of the water line multiplied by 1.34. certainly there are other opinions on how to do this, some by racers whose opinion's i would value but bear with me....

so for a surf, that's 16 foot length less the overhang to determine waterline (lets "assume" an overhang of 30 inches to be conservative) and you get 13.5 feet - square root of that is 3.67 and then multiply THAT by 1.34 and you get 4.9 knots....or 5.6mph. and think too that as a group, you're making 3 knots, best.

so okay, my understanding is that the reason this is considered the theoretical speed limit is because after this speed, the bow wake created at the front of the boat by your progress is such that you'd have to paddle the boat up and over this wake to get on plane...and for the most part, we don't have the horsepower.

so anyways, i ask how often we see someone trying to paddle over their own bow wake to get up on plane? if they're just cruising right there and then when they really pour it on get hung up on it, then yup, it's an issue....BUT if you're paddling along and NOT even close to bumping into and trying to paddle over that bow wake....yeah, then it ain't the boat....it's the engine!

so i guess my question is this: how big a deal is it really? are we engines outperforming the hulls or is the whole "speed of the boat" thing really kinda overblown?

remember too, when we're surfin these things, we're sure going faster than 5 knots BUT we're getting all the power/propulsion we need from the sea....so then it isn't an issue. i'm talking about just plunking around and even day trips here. yes, i agree that if i was going to paddle for weeks on end, longer would be better as the cumulative effects of the difference would be huge. i'm talking about the paddles most us do - day paddles. maybe an overnighter...not huge mileage.

thoughts? opinion (and please if you start talking about mathematical equations for wetted hull surface and drag coefficients and other such things, my eyes glaze over and i stop paying attention)

[EEL]

thoughts? opinion (and please if you start talking about mathematical equations for wetted hull surface and drag coefficients and other such things, my eyes glaze over and i stop paying attention)

Hey, all that wetted hull/drag/etc. is great fun stuff when trapped away from the water. <g>

Beats me, I cannot paddle anything fast. However I have a few opinions based on wallowing about on the water from time to time. For the typical day paddle, it seems to me the important thing is the ease with which a boat can be paddled at a "normal" pace of say 3-4Kts. It seems some boats can be very easy to paddle at that speed, but are difficult to paddle say much above 4.5Kts. Looking at the drag numbers it seems boats that are really fast tend to be harder to paddle at "normal" speeds. That said, essentially all "normal" sea kayaks seem to require about the same effort when paddled at a "normal" pace. I have found the SOF to be extremely easy to paddle at a slightly higher "normal" pace even though it is hardly smooth and streamlined, but the techie curves suggest it would hit a very hard wall soon if pushed. Still, I don't notice much difference between the AA and the Force at a "normal pace, but obviously the Force is a much more efficient boat and can more easily be paddled at higher speeds. This summer I was with a group that did a crossing in the fog and they upped the pace to minimize the time at risk. So we covered about 1.5NM at a pace of @5 Kts. For me it was work, but not bad in the Force, but it would have been impossible in the AA. The other side of that coin is a small paddler may well be able to paddle a shorter/slower boat faster and/or with less effort than a longer/faster boat due to lower inherent drag at "normal" speeds even if the hull speed in theory is lower and the resistance of the shorter boat is higher at speeds which will not be reached anyway. And with that bit of techno babble I will stop.

Ed Lawson

[Nick Schade]

got to thinking in speaking about the "speed" of the romany surf below.

the rough old school way to determine this is that you take the square root of the water line multiplied by 1.34. certainly there are other opinions on how to do this, some by racers whose opinion's i would value but bear with me....

Just forget that old school method. It is meaningless with regards to how fast your boat can go. Long narrow boats like kayaks exceed their hull speed consistently. This equation tells you when the wavelength of your wake matches the waterline length of the boat. This is just a physical curiosity, not a speed limit.

If you want to know how fast you can go, get in the boat and paddle it. If you want to predict how fast you can go without actually paddling you can model the hull and determine a drag curve then do some testing to see how much power you can produce, but during that time you could be paddling.

[rick stoehrer]

Just forget that old school method. It is meaningless with regards to how fast your boat can go. Long narrow boats like kayaks exceed their hull speed consistently. This equation tells you when the wavelength of your wake matches the waterline length of the boat. This is just a physical curiosity, not a speed limit.

If you want to know how fast you can go, get in the boat and paddle it. If you want to predict how fast you can go without actually paddling you can model the hull and determine a drag curve then do some testing to see how much power you can produce, but during that time you could be paddling.

....duh, can't paddle while i'm at work! but i can think about it!

and that was a good response, my eyes didn't glaze over once.

my observation was more about some grousing over the "speed" of boats and attibuting the hull as being the limitation while in most instances i think it's the engine.

see you gents in about just about 2 weeks or so and you can explain it to me with diagrams and a slide rule over beer...that'll help...hope you're well.

[Michael_Crouse]

I'm not to sure about the hull speed theories, I agree with Nick on the just paddle it sentiment. I think unless you feel like you have more energy than your boat can handle you shouldn't worry about it. In other words if you have a big mo-honkin' bow wave in front of your boat, you still have some more ommffpp (highly technical term for enery reserve) then by all means go get a faster boat. That's assuming you want to go faster.

Some fast boats make me feel slow, no bow wave, no wake, and that feeling that it wants a much faster paddler than I.

[EEL]

I think unless you feel like you have more energy than your boat can handle you shouldn't worry about it.

I doubt many weekend warriors ever have that problem.

I have seen a powerful paddler trying to accelerate a Romany make the boat vertically oscillate with their strokes. I wondered at the time if that was a paddling technique issue or applying more thrust than the boat could "take" to move forward through the water so part of the applied power was wasted in a vertical component. Talk about tugboat bow wave, it all looked dramatic and fast. That is the bad thing about efficient hulls, they move through the water so cleanly you think you are going slow. As an example, look at the picture on Nick's site of the Mystery. Without a heart rate monitor and a way of measuring speed, you head can really deceive you about what is going on.

Ed Lawson

[Michael_Crouse]

The boat definetely make a difference but the question is at what speed? At the last GOMSKS I tried a Chatham 18, I was paddling next to a Viviane, we we're paddling at the same speed but the Chatham was leaving a large wake, the water behind the Viviane was flat.

Having said that we we're sprinting, not paddling at 3-4 mph. If we'd been going slower I doubt it would have made any difference.

[JohnHuth]

Hmmm.....I'll avoid quoting from my book "Fluid Dynamics for Physicists".

That formula is clearly a "rule of thumb" - there is no real speed limit, as far as I'm aware, it's just a question of overcoming forces. I think that the rule of thumb does have something to do with size of the wake versus boat length, but it's more of an issue of the speed where the forces holding you back start to climb exponentially with every additional fraction of a knot you pile on. That probably sets in around the speed that your rule of thumb gives you. I'll try to look up the relevant formulas and see if I can translate it into normal human-speak.

Just for grins, I paddled around with a GPS to get an idea of my speed and such. I think I topped out at about 7 mph in a flat sprint, but, I was a wreck after about 1 minute of that. That was in a Tempest 170, which isn't noted for anything, other than feeling a bit too roomy in the cockpit and having leaky hatches. I'm seriously toying with a major upgrade to a Cetus or somesuch.

[JohnHuth]

OK, I'm trying to figure out your comments, Rick. Do you have a reference for this?

I'm trying to see how this aligns with what I know about fluid mechanics.

There are two contributions to the forces that will limit the ultimate speed of a boat -

1.) drag caused by turbulence

2.) the waves caused by both the bow and the stern

It's the sum of these two that give you the overall force that you have to paddle against.

From your description, the formula sounds a lot like the figures of merit for the forces caused by waves - the velocity of the boat divided by the square root of the wet length of the vessel (times a constant).

Basically, when a vessel moves through water, the bow wave - and the stern wave create forces. The wave velocity is dictated by the velocity of the vessel - so there is a relationship between the wavelength of the bow and stern waves and the speed of the vessel. Greater than a certain velocity, there will be no waves generated, because the boat is always outrunning any distrubances it creates.

If you have a reference for this figure of merit you talk about, I'd like to look further into it. I had the opportunity to paddle on very quiet water the other day - I paddled backwards for quite some distance, and it gave me an opportunity to see how my bow wave and stern wave interact. Depending on the boat's velocity, the bow wave and the stern wave and act to create greater or lesser resistance - depending on whether the bow and stern waves constructively or destructively interfere. (this is known, but it was fun to actually see this in action)

[wilsoj2]

I doubt many weekend warriors ever have that problem.

I have seen a powerful paddler trying to accelerate a Romany make the boat vertically oscillate with their strokes. I wondered at the time if that was a paddling technique issue or applying more thrust than the boat could "take" to move forward through the water so part of the applied power was wasted in a vertical component. Talk about tugboat bow wave, it all looked dramatic and fast. That is the bad thing about efficient hulls, they move through the water so cleanly you think you are going slow.

Ed Lawson

A couple of weeks ago I was paddling my Romany alongside a guy in a QCC700. My bow wake was enormous and the boat was lurching with every stroke. The QCC bow wake was minimal and the paddler barely working. Had the same experience earlier this year paddling my Romany alongside an Epic Endurance 18.

Most times I paddle my Romany because it is great fun and plenty fast for most paddling. If I want to cover distance or knowingly paddling with fast folk, I paddle my Aquanaut. Sometimes the hull speed does make a difference.

[JohnHuth]

Do you have any place where I could find the statistics of the QCC, Endurance and Romany?

In general - there seems to be two important numbers - the ratio of the square root of the length of the hull to the wetted area of the hull is one of the determining factors, but there are funny bumps, deepending on the peculiarities of speed.

This article is more than you probably want to see - but if you're interested in the subject, maybe just check out the figures at the end - it talks about the number of wavelengths and planing.

http://www.sname.org/newsletter/Savitskyreport.pdf

[wilsoj2]

Sea Kayaker reviewed the Epic Endurance 18, so the stats are available on that boat. I have never seen any stats on the Romany. There maybe some on the QCC site for their boats.

For kayaks, it seems that up to about 4 knots, wetted surface maybe the significant determinant of drag, while at and above 4.5 knots waterline trumps wetted surface.

[Bob C]

Do you have any place where I could find the statistics of the QCC, Endurance and Romany?

In general - there seems to be two important numbers - the ratio of the square root of the length of the hull to the wetted area of the hull is one of the determining factors, but there are funny bumps, deepending on the peculiarities of speed.

This article is more than you probably want to see - but if you're interested in the subject, maybe just check out the figures at the end - it talks about the number of wavelengths and planing.

http://www.sname.org/newsletter/Savitskyreport.pdf

[Bob C]

It would be fun to head down the boathouse rowing tank with a quiver of kayaks and some "control" dead weights (volunteer paddlers) and plot the pull on a spring scale vs water (hull) speed for each kayak, just to get some raw data for different boats. It wouldn't be definitive because much depends on the engine as Rick stated and Greg Barton's recent time in the Blackburn Challenge proved.

But it would be a fun experiment!

[EEL]

It would be fun to head down the boathouse rowing tank with a quiver of kayaks and some "control" dead weights (volunteer paddlers) and plot the pull on a spring scale vs water (hull) speed for each kayak, just to get some raw data for different boats.

Unfortunately there is very little real empirical data out there concerning kayak hull resistances from tank testing. However, there are decent approximations by running hull modeling software.

The following link is very instructive, IMHO, even though it shows numbers for a collection of native Greenland boats. Notice that at the speed range most people paddle all the boats are basically the same in terms of resistance/energy required to achieve that speed. However, at higher speeds the some boats require much less energy to achieve those speeds. At the intermediate speeds some boats that take more energy at higher speeds are better than average. Interesting stuff especially if you have the book so you can see the plans for the boats.

I don't get the point about the engine makes the difference in kayak speed. You can make a pig fly if you attach an adequate rocket engine, but that does not say anything about how efficiently the pig flies.

Also, the stability curves are interesting. Some of these boats are undoubtedly tippy, but the curves are very impressive compared to modern, commercial boats. Combined with light weight and low volume, it suggests they could be heeled way, way over compared to most modern boats and still brought back easily.

Ed Lawson

[JohnHuth]

The following link is very instructive, IMHO, even though it shows numbers for a collection of native Greenland boats.

I missed the link - can you repost that?

It would be interesting to try the experiment with modern kayaks. I'd bet good money that many people would find that an informative study.

This also begins to merge into the "ballast" thread. Stability in roll and yaw are the two most interesting characteristics to me - and there isn't a lot of data published on hulls.

[EEL]

I missed the link - can you repost that?

Thats because I forgot to include it. Duh. Here it is:

http://personal.inet.fi/koti/tonivee/KOG/

BTW, you can download the hull modeling software which is free..it is called DelftShip... and the data for all these Greenalnd boats used to model them. You can even design your own and check out how various changes affect performance characteristics or input data derived from commercial boats and see what they are like and what changes might to do them.

Ed Lawson

[Bob C]

Unfortunately there is very little real empirical data out there concerning kayak hull resistances from tank testing. However, there are decent approximations by running hull modeling software.

The following link is very instructive, IMHO, even though it shows numbers for a collection of native Greenland boats. Notice that at the speed range most people paddle all the boats are basically the same in terms of resistance/energy required to achieve that speed. However, at higher speeds the some boats require much less energy to achieve those speeds. At the intermediate speeds some boats that take more energy at higher speeds are better than average. Interesting stuff especially if you have the book so you can see the plans for the boats.

I don't get the point about the engine makes the difference in kayak speed. You can make a pig fly if you attach an adequate rocket engine, but that does not say anything about how efficiently the pig flies.

Also, the stability curves are interesting. Some of these boats are undoubtedly tippy, but the curves are very impressive compared to modern, commercial boats. Combined with light weight and low volume, it suggests they could be heeled way, way over compared to most modern boats and still brought back easily.

Ed Lawson

[JohnHuth]

Ed -

That DelftShip program is way cool. I tried downloading some of the greenland models and it was fun. I'm not quite up to modifying them, but I think I have enough info on the Explorer to see if I can put a model in and see if it reproduces the righting moments and such.

On the thread - I was trying to figure out all about hull speeds and such. There's a good, simple book called "The Physics of Sailling" - obviously the "sailing" part isn't relevant, but it has a good synopsis of hull shape, bow waves and all that stuff.

At Bar Harbor, I was chatting with some folks about hull speeds, and they asked me at what speed do kayaks plane. I had to confess that I didn't know, but - isn't surfing basically planing? So, clearly you can get a kayak to plane - just need a good enough wave and be able to catch it.

Anyway, thanks for the pointer to that greenland kayak website.

John H.

PS - are SOF boats at all robust? I saw one that a guy in Dennis made, and the material looking almost like Tyvek. With the amount of gelcoat I lose in one season, I figured that boat would go to Davy Jones' locker in less than an hour of my mishandling.

[rcohn]

PS - are SOF boats at all robust? I saw one that a guy in Dennis made, and the material looking almost like Tyvek. With the amount of gelcoat I lose in one season, I figured that boat would go to Davy Jones' locker in less than an hour of my mishandling.

Many of them are quite robust, it depends on how the frame is built and what skin material and coating are used. There are a few videos on line of SOF abuse and a report on fabric testing here http://www.qajaqusa.org/newsletter/Masik_S...r2003_07034.pdf . Those tests used an 8 ounce nylon. A 12 ounce nylon with a good polyurethane coat is quite tough, Miriam has stood on the deck of my qajaq during a rescue with no ill effect. I believe the greatest risk is if a sharp object cuts the fabric.

Also note that folding kayaks such as Kelpper and feathercraft are skin-on-frames and their skins seem to hold up well. You can get Hyperlon coating that is reported to be very tough and Dyson sells a 26-ounce Nylon, double weave material. Therefore, a SOF can be as robust as you want it to be.

Ralph

[shewhorn]

Yes, I think the speed of a boat is important. I'm an idiot when it comes to physics so I won't even try that BUT... I've been using a heart rate monitor to train in various sports for over 7 years now and I can tell you that if I run my engine at a given speed, my Aquanaut is faster than my Cap 161. Is a theoretical max hull speed important? Not really, at least not to me. Am I concerned with how much speed I'll get out of a boat for a given amount of input (efficiency)? Depending upon the application I am. For an expedition boat a more efficient hull means that for a given cruising speed (and we'll assume that the group determines the cruising speed) I'll be less tired at the end of the day which means I'll also recover faster to be ready for the next day. I think it's safe to say that boats with a theoretical "maximum hull speed" (is there a better term to use since it's been pointed out that this relates to wavelength and wake and blah blah blah???) are also more efficient. Then again... I know a certain someone who paddled 340 pounds of human, food, gear and Pintail around Maine and it worked just fine.

So my second answer (after initially opening with saying that yes it is important) is:

Yes...

and

No

Depends on who you are, where you're going, what you're doing, maybe even what kind of mood you're in when the question is asked... etc.

[Nick Schade]

At Bar Harbor, I was chatting with some folks about hull speeds, and they asked me at what speed do kayaks plane. I had to confess that I didn't know, but - isn't surfing basically planing? So, clearly you can get a kayak to plane - just need a good enough wave and be able to catch it.

Surfing is not universally "planing", but sometimes it does seem to achieve that at times. A boat is considered to be planing when its center of gravity rises above its position when in displacement mode - relative to the water surface. I.E. when the boat lifts up higher out of the water.

At lower speeds of surfing the boat is just getting pushed along by the wave and is still in displacement mode. As the waves become faster it is possible that the boat will be pushed fast enough to lift up. I have clocked myself at up to 12 mph and the boat still appeared to be in displacement mode. I have not had my GPS going at times when I felt I was planing, but I expect it would be at speeds over 15 mph.

When the transition occurs depends on the boat design. Long narrow boats with fine, rounded ends will need to be going faster than a short, fat boat with a flat run at the stern does not need to go as fast. In other words sea kayaks are very poorly designed for planing, and it is probably that it is not possible to make some designs plane at any attainable speed.