wave anatomy in relation to hull design

[aquafiend65]

hello everyone/anyone,
i recently asked for input on outrigger canoe hull design. this time i am looking for info on wave dynamics/structure. the reason i am asking is that i am approaching the design of my outrigger canoe with the intention of "fitting" in the trough. since waves have specific characteristics regarding their height, length, speed, frequency, etc( the conditions we paddle in are flat seas up to 4'-5' wind chop). i am thinking of creating the rocker of the boat based on the "average" wave specs( about 2.5' wind chop). in other words i hope to create a boat that fits into the trough, catches the waves energy and does not plow the bow into the wave in front. does this make sense? is this a good idea/approach? because an outrigger canoe relies on human power we want to harness the ocean/wave energy whenever possible. the most difficult aspect of designing the hull is the rocker. after that i am unsure of a planing bow or a displacement. at this point i am thinking of a fine entry planing bow that fuses into a wide flat stern. can anybody offer some advice? please?? thank you.-gary

[Not A Guest]

I would think the trough is the worse place to be but ...

[aquafiend65]

Originally Posted by Not A Guest

I would think the trough is the worse place to be but ...

thank you for pointing out the vagueness of my statement. i should clarify by explaining that we want to use the energy of the oncoming wave (traveling in the same direction in which we are paddling). the wave makes the trough. there is a "sweet spot" where the energy is concentrated and is most accessible(the "face"). there is also a nuetral spot(bottom dead center of the trough) and even what i will call a dead spot (the back ofthe wave as it passes by)where we actually slide back down the face as the wave passes. (we don't actually slide back but it feels that way) since the canoes are about 45' long and we have establishied by experience that the canoe bow tends to plow into the wave in front in 2-3' seas, i am hoping to take the wave profile of 2.5' waves and create a rocker that fits. we don't actually want to be "cradeled in the trough but to be riding on the "face" of the wave. (does any of this make sense?) at this poiont i am trying to find a wy to create a model of the wave profile. i think there is a formula. but if some one knows that this is a bad approach please let me know.

[gonzo]

Do you plan to paddle at wave speeds of over 10 knots or surf the waves. If surfing, look at surfboard design. It has straight buttocks with a hook.

[aquafiend65]

Originally Posted by gonzo

Do you plan to paddle at wave speeds of over 10 knots or surf the waves. Isurfing, look at surfboard design. It has straight buttocks with a hook.

yes and no. we are able to actually paddle at 7-9 knots. but when we "catch" a wave we can accelerate up to 15+ knots. as a surfer i have experience with surfboard shapes. the differance lies in the water conditions. when surfing with a surf board i am catching a wave that has hit the ocean floor and the energy is accelerating and being forced upwards. once the waves energy has been reshaped and extends beyond 90 degrees it falls upon itself or breaks. a surfboard has the advantage of the steeper surface and accelerated energy. that is why the surfboard has a flat planning bottom. the board is not trying to displace water, but merely stay on top of it. the conditions are different in the open ocean in that the waves do not bottom out. therefore we can only harness the waves energy so long as we can stay on it. the problem is two fold in that we also need to be able to move the boat with as little energy expended as possible when nnot surfing. of course the act of paddling an outrigger takes alot of effort anyways but the team that wins is the team that has the greatest stamina/strength. which is why it is so appealing/neccessary to catch the waves (it is a free ride, and faster one at that). let me say at this point that we have an excellent surfing canoe called the mirage designed and built by karel tresnak of outrigger connection. that canoe is king of the surf. but it was created for the hawaiian waters. here in southern california we have much calmer seas. more like that of the tahitians. thus we are leaning towards a design more like the tahitian canoes. the problem with those is that they don't surf as well. they have much less rocker and a much finer bow entry. they are also lighter. they have many good attributes that lend to a faster boat to move by human power. since we are creating a totally new class of canoe the specs are open and unlimited at this point. so we are coming to the table with just a few demands. 1. that it be faster than the tahitian canoes. 2. that it surf better in our conditions than the hawaiian canoe. 3. and that it be cost effective to build. 4. that it maintain the traditional hull, iako's, and ama assembly.(iako's are the "arms" that extend beyond the canoe and attach to the ama. the ama is the pontoon/float.) that is about it. the sky is the limit beyond that. the reason i am approaching it from the wave/trough perspective is to try to optimize the canoes surfing ability. but i am unsure if that is the way to go at it. (i really appreciate the feed back i am getting. it is helping me to think through these problems and clarify them in my mind)thanks. -gary

[aquafiend65]

Originally Posted by Not A Guest

I would think the trough is the worse place to be but ...

i am curios. why do you say the trough is the worse place to be?

[Not A Guest]

Originally Posted by aquafiend65

i am curios. why do you say the trough is the worse place to be?

1) location reguiring the greatest steering effort,

2) location producing the least stability, and

3) location requiring the greatest energy output during a sprint (assuming you have enough power to climb over the wave).

To do a design for specific conditons one has to know more about the crew: weight, number, and power output. And in any case designing for specific conditions implies designing away other conditions which means either lots of boats or lots of losses.

Remember the locals use boats for transportation and can wait for ideal conditions. Racers seldom have that ability.

(Short design philosophy deleted)

[tspeer]

If you're surfing, I suspect you're still interested in waves that are long compared to the size of the canoe. So work related to surfboards is still relevant - it's just that the range of wave slopes will be more restricted for your case.

The shape of the wave is the most visible characteristic, but the wave-induced currents may be more important. At the wave crest, the current is moving with the wave. In the trough, it is moving opposite to the wave direction. Half way down the wave face, the water is moving vertically and there's no net horizontal motion. So if you're sitting in the trough, you are paddling against the current.

Half way up the wave, the water both ahead and behind you is moving toward you. If the canoe is at an angle to the wave direction, there is an adverse current at the bow and a favorable current on the stern. The wave current is thus trying to turn the boat broadside to the the wave. You'll have the most trouble steering here. But the wave slope high, so the acceleration is maximized. So the sections of the canoe should be comparatively flat and full at the bow to prevent it from digging in and steering the boat in this condition. The full bow sections will also provide reserve buoyancy when meeting a wave.

Since the favorable current is at its maximum at the wave crest, it seems to me you want to ride as close to the crest as possible, but on the front side so that gravity help overcome the drag of the canoe.

Also, the front side is stable in that if you speed up you will encounter an increasing adverse current that will tend to slow you down and move you back toward the crest. If you slow down, you will move up onto the crest and get more of a favorable current. But once on the backside of the crest, if you get slowed down your favorable current will decrease, slowing you further, and dropping you back so you lose the wave.

See:

Letcher, John S., Jr., "Surfing: Motions of a Vessel Running in Large Waves", The Third CSYS, January, 1977. (http://wseweb.ew.usna.edu/nahl/csys/)

http://www1.tpgi.com.au/users/mpaine/thesis.html

[aquafiend65]

there are six athletes that are paddling, one of which is the steersman. the current canoes are 400 lbs. but we are plnning on the new class to be sub 250 lbs. as far as the power out i have no idea how to measure something like that. if you could explain why that was important i could probably figure out a way. i see what you are saying about designing for specific conditions. but we know, by experience, that it is usually calm and glassy in the morning when the women race and blowing 15-20 knots with 2-3' seas in the afternoon when the men race. we are hoping to design a boat that is conducive to our conditions here in southern cal. all, and i mean all, the existing outriggers we have are designed to work in hawaiian waters. i realize that we will never create a boat that is ideal for all conditions. but we hope to create something that works much better than a hawaiian canoe. how would you recomend i go about creating a canoe hull that surfs well but runs well on the flats too? we have the lines of the hawaiian canoe and the lines of a k-4 (flatwater 4 man sprint kayak) and we even have a tahitian canoe. the problem is we are not sure what hull characteristics cause what results. thanks tspeer for the info and leads. it was both helpful and educational.

[aquafiend65]

i should also mention that the waves are wind swells. i guess you could call them fetch waves in that they are locally derived. i am not sure of the fetch size or the wave speed. i was thinking of trying to establish an average from weather service reports. (i.e. buoy's, surf reports, etc.) also when we surf we may have a considerable amount of the boat's stern out of the water. does this reduced waterline matter?

[gonzo]

I just designed an outrigger sailing canoe. They will be built for use in Guam, so the looks are classical Marianas Islands. Your canoe, at 400 lbs, seems pretty heavy. 250 lbs is an easy target without exotic materials.

[aquafiend65]

the hawaiian and california outrigger governing body's require the 400 lbs. it was originally established to allow the traditional wood koa canoes to compete with the "new" fiberglass canoes (late 6o's). anyway we are looking into a vartm type process. i will do the original design and plug work. but the production will be out of my hands. i, personally, would like to see the hull be sub 200 lbs. but the powers that be want to over build to "insure" sea worthiness. i have built 22' one man outriggers at less than 20 lbs. and 14' paddleboards at 12 lbs. i still paddle the board 3 years later. but that was all carbon, epoxy, vacuum bag laminates. of course i would like to do that with this canoe or even prepregs but the canoes have to be in the range of $10-12,000.00 how did you go about designing your sailing canoe and what were the design specifications? what kinds of speeds does the boat see and how does it respond at those speeds? i know we will never reach your speeds but i am curios as to know how an outrigger hull behaves at higher speeds and how to possibly use the information to better design our canoe.

[aquafiend65]

hey tspeer,
thanks for the input. everyones advice is helping clarify my thoughts. as you and not-a-guest have pointed out the trough is a bad place to be. however when we paddle and surf in the open ocean it is in wind chop swells about 2-3'+. it seems like the swells are tighter and that the canoe bow is down in the trough and some times reaching toward the swell in front even when we are positioned on the waves face. do you think that it would be a good idea to try to figure out what that wave profile looks like and create the rocker to best fit? by best fit i mean to allow the canoe to sit on the face without digging/plowing the bow in the trough. also how might anyone suggest i be able to maintain my position on the wave face for as long as possible? one more thing tspeer, could you explain in greater detail what is happening when the boat wants to "round-up". i am not a great steersman but have had plenty of experience with the wave turning the canoe broadside. how can the water be moving in opposite directions on the wave?

[gonzo]

When the boat starts surfing, it goes faster than the wave. If the forefoot (where the bowstem and keel meet) digs in and slows the boat, the stern will keep going resulting in a broach.

[aquafiend65]

Originally Posted by gonzo

When the boat starts surfing, it goes faster than the wave. If the forefoot (where the bowstem and keel meet) digs in and slows the boat, the stern will keep going resulting in a broach.

what exactly is the bow stem??? and how do i determine the forefoot of a hull that has no keel??? that statement above is very helpful information in that i will try to create a "forefoot that will not dig in. the question is how to best go about it. at this point i am leaning towards a planing hull that has a fine entry with plenty of reserve boyancy above the water line. kind of like a big elongated wedge with rocker. of course i will soften the rails (transition from horizontal to vertical).