Fishing kayak

[ShagRock]

I am looking to build a small kayak or canoe for fishing lakes and close to shore ocean fishing. I like the idea of a sit-on style that has flotation to self right, car top, and easy for one person to carry. I see there are plenty of rotomolded fishing rigs, eg. Cobra Fish and Dive and those from Ocean Kayak and Viking. Has anyone an idea or info on whether such designs can be mimicked using wood frame, composites, or materials like nylon.

May your big jib draw!
Newfie

[rasorinc]

I used to have a neat picture of a fishing kayak but lost it. The design allowed you to stand up and cast. It was designed so that the aft part would split apart into 2 self contained pieces with flotation. When this was done it looked like a Y. When done fishing he pulled them together and latched them His seat was at the center forward of where the 3 pieces meet. It was unique and should not be to hard to design. Stan https://www.boatdesigns.com/products.asp?dept=185
https://www.boatdesigns.com/products.asp?dept=186 You can imagine cutting the aft end into 2 pieces seperate from the hull closed off with 1/4" ply and filled with flotation 4 hinges and a latch. Would not even add much weight. If done to the aft 1/3 of the hull it should give necessary stability.

[ShagRock]

That's a design I haven't seen before and certainly worth a look if I can track it down. I think I would prefer 'low weight' tech seat that swivels, has adjustable back, lock position, etc. Perhaps a 13' Loa with 32"+ beam would give adequate stability, but I am not experienced enough to evaluate speed and maneuverability. I looked at the Sabalo design by Jem which offers some build possibilities.

I also read threads by Ancient Kayaker especially his posts to Millionwords inquiry on kayak. I am working on a design for a slip-out outrigger that could be used for drift control when fishing or to employ if water gets rough (paraw/proa type things come to mind). I'v heard that 26oz nylon is 'quite tough' but maybe s&g plywood is the way to go - others here may have some 'seaworthy opinions' to offer on that. I also reviewed an Arch Davis penobscot skiff where the plywood is glued and screwed to stringers, which I think might be a good technique for kayak or canoe.

May your big jib Draw!
Bayman

[rasorinc]

I'm a wood boat builder so that is where my vote goes. If you do use 1/4" plywood get 4 ply. Doug Fir 1/4" is 3 ply. Meranti "Hygro-Tek" BS 1088 I think has 4 plys and in 1/4" should be the same price as DF. Okoume "Joubert" BS 1088 has 4 plys and is quite light but cost 70% more than the others. You probanly will use only 2 sheets and the weight is important to you then use Okoume Here is a site for plywood that gives you info and pricing. Their prices seem high to me.
http://marine-plywood.us/

Do you like inlay? http://www.boatdesign.net/gallery/showphoto.php/photo/4112

[ShagRock]

rasorinc
The stand-up kayak you referenced is at this link:
www.hammacher.com/publish/11098.asp[/url] - 38k -
It's $2000. I think I'll opt for building my own for a lot less. I'll take your advise and look into marine ply here 'up North'! I'll continue to work on creating some detachable ama for extra stability. I once jerry-rigged a sealed aluminum tube on a canoe for large lakes. It worked but the bamboo amas are much nicer. I'll check if bamboo tubes are available here.

Fishing in a sit-on should be reasonably comfortable (after watching guys fly fishing in pontoons and belly boats):p . That won't do for me because I like to explore around.
1) Any suggestions re light weight outrigger?
2) What is the general opinion on creating your own design versus buying build plans?

May your big jib Draw!
Bayman

[rasorinc]

I always buy professional plans for the hull. Then I do my thing after that. This way I know the hull design will do what I want the boat to do and that all factors have been incorporated in the design.
For a simple outrigger look at Stryene pipe. Unlike PVC it is very light and you could fiberglass it for more strength. It has a crush strength of several thousand pounds I believe. Most lumber yards carry it. Stan
I'm glad you found the Y plan--Thanks PS make sure stryene is compatable with epoxy..Styrofoam is.

[ancient kayaker]

rasorinc
... I'll take your advise and look into marine ply here 'up North'...

Any suggestions re light weight outrigger?
Bayman

Here's a Canadian site for ply and other stuff, it's in Toronto but you can probably find one close to home: http://www.noahsboatbuilding.com/noahs

I find outriggers just get in the way when paddling. An inflatable bag on the end of the paddle provide lots extra stability when not paddling and can be tucked away when not needed. Anything airtight will do but proper ones are sold as reboarding aids in paddling/camping stores. On my canoes I can lash the paddle to the thwart to free up my hands; you can probably add a strong loop to do the same, or just sit on it.

[Rick Willoughby]

I am looking to build a small kayak or canoe for fishing lakes and close to shore ocean fishing. I like the idea of a sit-on style that has flotation to self right, car top, and easy for one person to carry. I see there are plenty of rotomolded fishing rigs, eg. Cobra Fish and Dive and those from Ocean Kayak and Viking. Has anyone an idea or info on whether such designs can be mimicked using wood frame, composites, or materials like nylon.

May your big jib draw!
Newfie

I will go into promotion mode.

Slenderness and length equate to speed. You are on the right track with a sit-on outrigger type hull if you want performance.

I would always go for twin outriggers over a single because I prefer the security and less twitchy approach. It also gives the best performance at least in reasonably calm water because the outriggers can be set up to carry zero load most of the time. With a single outrigger you have to remain alert and be prepared to counter a roll away from the outrigger because you only rely on the tiny weight of the outrigger for righting moment away from the outrigger. You can pre-load the outrigger with initial roll but this adds a lot of extra drag.

The beauty of this approach is you can make a very simple build. This link is a ply boat easily built:
http://www.boatdesign.net/forums/attachments/boat-design/27961d1230635527-pedal-powered-boats-p3.jpg
It pushes along at 5kts without much effort.

The key to these hulls is to keep them light and quick to launch. Mine is a pure speed machine and I fold the outriggers up to make it easy to carry and transport on cartop:
http://www.boatdesign.net/forums/attachments/boat-design/27845d1230111804-pedal-powered-boats-pc240005.jpg
You can see one outrigger is folded above the seat for transport. Both fold up like this. A male of average fitness can punt this along at 6 to 7kts for long periods. The whole thing weighs 20kg so quite easy to throw on the shoulder if not a little awkward in a strong breeze.

You may have noticed both boats are pedal powered. Leaves the hands mostly free to do what you want- maybe trolling or having a snack or brown ale. Very relaxed way to spend a day on the water. It borders on being illegal it is so much fun.

Happy to explain more about these ideas if you have further interest.

Rick W

[ShagRock]

Ahoy Mates, I'm most thankful for your input!

Rasorinc - I agree re starting with a proven design, especially if I can obtain one for decent price. Is the pipe you are referring to 'expanded closed-cell ploystyrene'?

Ancient Kayaker - Thanks for info on marine ply. I'm close to BC so maybe prices are a little better - I'll keep you posted on that.

Rick - I'm not as young as I once was - but who is;) That's a lovely kayak you have. Do you mind me asking its loa? Comparing yours to the other model you referenced, is yours easier to tack with the amas placed aft to CG like that? you noted getting up to 7knts max. That's fast! Is there a way of figuring speed if loa is slightly reduced and beam slightly increased -something simple, like a rule of thumb for kayaks?

[ancient kayaker]

Rick: gotta agree with Newfie, looks great.
Newfie: thought you were out East with that moniker!

I put an ama together that looked very like Rick's, not quite as narrow, part of an ill-conceived plan to enthrall the missus with the joys of canoing. I'm not sure whether it was her weight or the ama's drag or the fact that I was the only one paddling but neither of us were impressed!

However, the canoe was probably the drag-contributing culprit; that narrow hull of Rick's should cut hull drag and the ama's provide the stability instead of the hull.

If you have full-time ama's and a super-narrow hull then two is the way to go. However, if the hull can be paddled without ama's then one float may be better for Newfie's purpose as it leaves an unobstructed side to fish from.

[Rick Willoughby]

.....
Rick - I'm not as young as I once was - but who is;) That's a lovely kayak you have. Do you mind me asking its loa? Comparing yours to the other model you referenced, is yours easier to tack with the amas placed aft to CG like that? you noted getting up to 7knts max. That's fast! Is there a way of figuring speed if loa is slightly reduced and beam slightly increased -something simple, like a rule of thumb for kayaks?

The Yelow boat is 7.2m - that is long. It overhangs the car by 1m either end. The white one is 5m.

The 6 to 7kts is not max speed. That is a sustainable level for a moderately fit individual. I have nudged 10kts for a few seconds and I am on the mature side of 55yo. I averaged 11kph (6kts) over a 404km river course in December running over 5 days with two long days over 90km each. That includes current assist, a lot of headwind, dodging logs and substantial turning as the river meanders.

There is very good software called Michlet/Godzilla that provides accurate hull drag data for different hull shapes. The basic input is design displacement and maximum length. The Godzilla component can optimise the shape to minimise the drag.

Hull speed, as defined, is the typical sustainable speed of a long slender hull using human power. This is determined as:
Speed in kts = 1.34 x (LWL ft)^0.5
So 16ft slender boat displacing say 100kg could be punted along at say 5.5kts for a long period. Going up to 25ft gives 6.7kts. These are close to what is possible.

Rick W

[ShagRock]

Yes AK, it was the Rock but I am left for the bigger rocks called the Rockies, when the fish ran out!:) :) The amas I rode on in the Philippines last year were really efficient. Most were of bamboo with spider arms and kind of just skimmed the surface under motor or sail.

Rick, thanks for the software tip and the details on your kayak. Regarding the speed factor for the 16' you referenced, what speed gain could be possible with the addition of a lateen sail? Is there a maximum limit for for this hull?

Also, does the choice of multi chine as opposed to hard chine make much difference in a kayak of 16' LOA variety - for lake use as opposed to racing or whitewater?

Newfie

[ancient kayaker]

A multi-chine hull is a closer approximation to a rounded hull than one with few planks and hard chines. Hard chines are more likely to cause turbulence and the hull would have more wetted area.

The given truth is soft chines are faster than hard chines, but I haven't paddled boats that are close enough in design to establish that. My own experience is, my hard chine home-built boat can leave my (longer) soft chine boat in its wake unless both paddlers are working hard, so it's a minor effect.

You're sailing question was directed at Rick, but my kayak sailing experience so far indicates that a small sail (12-15 sq ft) will easily push a kayak to sprint paddling speed in anything more than a gentle breeze on a reach or run. Upwind performance was so limited by the paddlers air resistance as to be non-existent an dis the only time I have felt the need for a larger sail.

I have read varying reports about lateen sail efficiency so I am going to try one this year to see for myself.

[Rick Willoughby]

.....

Rick, thanks for the software tip and the details on your kayak. Regarding the speed factor for the 16' you referenced, what speed gain could be possible with the addition of a lateen sail? Is there a maximum limit for for this hull?

Also, does the choice of multi chine as opposed to hard chine make much difference in a kayak of 16' LOA variety - for lake use as opposed to racing or whitewater?

Newfie

The speed figures I provided would be achieved with 120 to 150W. So the hull drag is around 50N on the 16' boat and around 35N on the 25' at their respective hull speed.

50N (11lbf) is not very much when you are considering a sail. If you can react the rolling moment and use a keel to reduce leeway then kayaks make fast sailing boats.

If you add a sail to pedal powered boat then you are adding weight and complexity. I certainly would not bother because I can already outperform most sailing dinghies and small cats. Once you start fiddling with sails you increase the set up time and the utility of the boat. Also my preferred days to be on the water are when it is very still. A sail is useless in these circumstances. I think sailing is its own end rather than a means to get to a fishing spot. I expect you will find you will become a sailor rather than a fisherman. Depends on what your objective is.

There is very little difference in performance between a hard chine and a rounded chine hull. You typically find that for a particular design speed you can optimise to a rounded chine hull if you are not length constrained. Once you are length constrained, as you are with a 16' boat, the slight reduction in beam with the hard chine reducing wave drag effectively offsets the tiny reduction in wetted area that can bee achieved with a rounded chine.

The 5m long white hull in the earlier photo is 300mm beam. If the boat had rounded chine you would have a beam more like 450mm for the same displacement.

Rick W

[ShagRock]

I have to admit I have only used paddles in the past and never used a Hobie peddle type. I didn't realize as noted by Rick that this could produce such speeds. Also, I can see Rick's point re the uselessness of a sail on a calm day. However, in my local you only need wait a bit for a weather change.
I suppose one could have both, but it does complicate things.

At this junction, I am looking at combining design features from a Philippine sailing canoe and a kayak like the 14' to 16' Arctic Tern. The hard chine type would be an easier build. As you note, there is not a big factorial difference between hard and soft chine in this size of boat (something which has been noted by the designer at Pygmy kayaks). However, I have read that the round hull will be better for tacking with a sail.

On the subject of sail, I would say AC that if you go to a larger sail, you need to best consult a sail expert; because too large will cause the outrigger to bury and drag on the leeward side. I also read somewhere that a cat ketch rig may be just as effective and easier to handle than a lateen - something I need to study more myself.

Before I forget, I want to follow up on Rasorinc's comments on plywood. Here, the options for 'marine ply' are limited in my locale: (1) Okoume but expensive, (2) 1/4" fir (Douglas not available) and it's seems a little heavy and bit rough, and (3) 4mm, 3 ply South American mahogany (Meranti not available either). With some stringers, I think the lighter weight mahogany is better choice, but I could certainly use some feedback on that.

Newfie

[Rick Willoughby]

I have to admit I have only used paddles in the past and never used a Hobie peddle type. ......
Newfie

In terms of performance the Hobie is quite poor compared with a hull like mine or Ian's. They are good for about half the speed of my hull. The flappers are not very efficient compared with a propeller. Data I have indicate they achieve about 35% efficiency in cruising mode and lift to 50% in a sprint although the latter does not achieve much because the hull drag kicks in once over 8kph.

The actual speed can be quite deceptive because most tend to relate big waves to high speed. I see waves as wasted energy. The attached photo shows a Hobie tandem competing in a 100m sprint. It averaged 10.2kph for the distance.

This video shows my boat with a late model engine fitted just looping the lake at 12kph:
http://www.boatdesign.net/forums/attachments/boat-design/26581d1225663272-pedal-powered-boats-jn_150.wmv
It takes a minute or two to download this clip - almost 5Mb.

The Hobies are durable and I believe reasonable value for money but they are slugs compared with most other paddled or pedalled boats apart from short sit-ons. Most people who buy them do not have experience in other boats and some get disappointed when they find they cannot keep pace with a small kayak.

Rick W

[ancient kayaker]

Rick: I see what you mean about (hobie) inefficiency, white water all over the place and a big wake with roostertail to boot! Big contrast with your boat's minimal wake. I had the same experience with my sailing kayak which is a Crittur, 9.3 ft long, BWL 30" and shaped like a sharpened bathtub. Under sail in a goodly breeze I had to keep my elbows tucked in or the bow wave would soak them, it was halfway up up to shoulder height. Almost as stable as a dock though. Molded hulls designs are compromises, not made for speed.

Not sure if I mentioned it in this thread, but I did not use an ama for the sailing kayak, I used a 1.5 sq ft Bruce foil on that, and it was very effective for cancelling heeling moment once I had the outrigger length and tilt angle right. Monster for leeway though.

[ShagRock]

Rick - that video was great and I certainly know of no way someone's going to catch you on a calm day like that!:) Is that a home-made propeller system? Also, I meant to ask earlier if styrene pipe can be bent to shape using heat?

Ak - Ive seen many types of sails on canoe/kayak. The lateen sail has traditionally been the choice for local fishermen in southeast Asia - easy to take down and out of the way while fishing. But I have seen balanced lug and other rigs used there as well.

I decided to build one with 4mm marine plywood and chine logs (stringers). I'm going to use dual amas designed to provide flotation to match displacement - but not sure yet how to calculate that? Since I will be using a sail rig, I plan to install the arms just ahead of the mast. There are so many different designs being used for the ama itself. I'm thinking of placing them more forward so as to give more fishing space for rod use at the center and rear of canoe. What defines acceptable placement of amas with respect to lift, buoyancy, drag etc?

Finally, what do you guys think of using a double-ended kayak paddle in an oarlock at the stern? Will it serve adequately as a rudder? I've found it's handy for turning the boat side to side or keeping it in line while drift fishing. I just leave it in the oarlock while attending the rod (like a traditional sculling oar:).

Newfie

[Rick Willoughby]

Rick - that video was great and I certainly know of no way someone's going to catch you on a calm day like that!:) Is that a home-made propeller system? Also, I meant to ask earlier if styrene pipe can be bent to shape using heat?

...

Most of it. The frame, seat, crankshaft, prop shaft and propeller are all home fabrications. The gearbox is an industrial item while the chainring, sprocket and chain are bicycle components.

I have never used styrene pipe. Polystyrene is a thrmoplastic so can be formed with heat but if it is expanded then it will take a while to heat soak to soften it.

Rick

[ancient kayaker]

Ak - Ive seen many types of sails on canoe/kayak. The lateen sail has traditionally been the choice for local fishermen in southeast Asia - easy to take down and out of the way while fishing. But I have seen balanced lug and other rigs used there as well.
Newfie

On a kayak even more than a larger craft it is important to be able to lower the sail rig quickly and easily from inside the boat if you are planning long trips. Another issue is keeping the CoE (center of effort) down to limit the heeling moment.

My first kayak sail was a square sail which rolled up over its spar and was hoisted with the paddle but was very small at 8 sq ft. The last sail I had was triangular and folded umbrella style in seconds but it was still small at 15 sq ft and short on performance. I am planning a 25 sq ft lateen on my next experimental effort but have not yet figured how to lower it easily and pack it away for paddling. That may be easier with amas however

Ak -
I decided to build one with 4mm marine plywood and chine logs (stringers).
Newfie

That is the construction I use for my simple lightweight canoes. Simple box shaped “3-plank” hulls like pirogues practically build themselves; you can glue the chine logs and inwales to the sheer planks before bending them over one or two molds; this makes the planks stronger and easier to handle and gives a good fitting joint which allows me to use Titebond III. You can glue the bottom directly to the sheer chine logs, then a sit-on-top kayak could have the deck added at this stage. My canoes are open 5-plankers; after bending the sheers as above I glue chine logs around the bottom plank, bend it over the mold(s) and plane bevels for the garboards; it is more difficult to get a good joint here so I use epoxy. For a more complex hull a proper jig with station and stem molds and stringers is indicated.

Ak -
I'm going to use dual amas designed to provide flotation to match displacement - but not sure yet how to calculate that? Since I will be using a sail rig, I plan to install the arms just ahead of the mast. There are so many different designs being used for the ama itself. I'm thinking of placing them more forward so as to give more fishing space for rod use at the center and rear of canoe. What defines acceptable placement of amas with respect to lift, buoyancy, drag etc?
Newfie

Design depends on the kind of performance you are aiming for, screaming along on one ama or more sedate progress. For the screaming mode one ama and its outrigger must support the entire weight and you might wish to hike out on a trapeze, net or platform. For sedate mode, think along the lines of:
ama displacement X outrigger length > wind pressure X sail area X CoE

Having the amas well forward is usual for a kayak to facilitate paddling as well as fishing. That drives sail CoE placement which again is usually well forward. This is not optimal for sailing as it usually puts the sail too far ahead of the CoG. Note that a lateen sail with its CoE somewhat aft of the amas may have more potential for a capsize: this is less of a problem for me as I use Bruce foils which are easier to retract than amas.

Ak -
Finally, what do you guys think of using a double-ended kayak paddle in an oarlock at the stern? Will it serve adequately as a rudder? I've found it's handy for turning the boat side to side or keeping it in line while drift fishing. I just leave it in the oarlock while attending the rod (like a traditional sculling oar:).

Newfie

In my experience using a paddle as a rudder is not effective and I tend to run out of arms even though I’m not fishing! It is difficult to turn the paddle to a sufficient angle to get enough steering effort especially at slow speed. A foot operated rudder worked better, unless you are planning on pedal power of course.

[ShagRock]

Rick - that's very creative work on your kayak with all the home-built parts!

AK wrote: I am planning a 25 sq ft lateen on my next experimental effort but have not yet figured how to lower it easily and pack it away for paddling. That may be easier with amas however
The akas do come in handy for this purpose. The favorite for many fishermen is the unstayed tacking crab claw, which comes down real easy when you're ready to fish and easy to set up again.

AK wroteMy canoes are open 5-plankers; after bending the sheers as above I glue chine logs around the bottom plank, bend it over the mold(s) and plane bevels for the garboards; it is more difficult to get a good joint here so I use epoxy. For a more complex hull a proper jig with station and stem molds and stringers is indicated.

I guess one way of getting a more rounded shape in a hull would be to rip strips from plywood sheets and then strip-plank on ribs? Do you see any disadvantages to this method?

AK wroteHaving the amas well forward is usual for a kayak to facilitate paddling as well as fishing. That drives sail CoE placement which again is usually well forward. This is not optimal for sailing as it usually puts the sail too far ahead of the CoG.
Another way to free up fishing space is to use a single aka (crossbeam). By the way, what do think of the placement of the outriggers in this picture re it's impact on sailing and stability? Also for theoretical discussion, what effect would 'tacking amas" (like skidoo skis that shift attitude with the 'humps and bumps' of uneven trails) potentially have on sailing capacity.
http://i374.photobucket.com/albums/oo187/Bayman_bucket/kayakoutriggers3.jpg

As you suggest AK, a foot operated rudder is practical and convenient,especially if you are fishing too.

Newfie

[ancient kayaker]

I guess one way of getting a more rounded shape in a hull would be to rip strips from plywood sheets and then strip-plank on ribs? Do you see any disadvantages to this method?
Newfie

For a rounded hull I’d prefer to use cedar strips which bend both ways. Ply objects to bending within it’s own plane. Unless the planks are very narrow they must be cut accurately as in the stitch-and-glue method or cut to fit by building over an accurate jig.

[ShagRock]

Ak - as you note, plywood is more difficult to 'twist' to fit, so I guess that's why it is more applicable to hard chine hulls. I was actually planning to use battens and install ribs first (more of an east coast method), in which case the narrow plywood strips should bend enough to tack to the ribs before gluing seams. However, since we're on this topic, you mentioned 5 plank method. If one was using 10 planks to 'approximate' a round hull (more smooth chine hull), would not the plywood planks bend to fit on stringers just as well as gluing them to chine logs and then bending them?

Since cedar is getting more expensive here and less quality, would western spruce be a reasonable alternative? I ask this because eastern spruce is widely used for round bilge hulls in small boats in Atlantic Canada?

By the way, the 'tacking amas' was bit of an offbeat question, but what do think theoretically?

[ancient kayaker]

Ak - as you note, plywood is more difficult to 'twist' to fit, so I guess that's why it is more applicable to hard chine hulls. I was actually planning to use battens and install ribs first (more of an east coast method), in which case the narrow plywood strips should bend enough to tack to the ribs before gluing seams. However, since we're on this topic, you mentioned 5 plank method. If one was using 10 planks to 'approximate' a round hull (more smooth chine hull), would not the plywood planks bend to fit on stringers just as well as gluing them to chine logs and then bending them?

Since cedar is getting more expensive here and less quality, would western spruce be a reasonable alternative? I ask this because eastern spruce is widely used for round bilge hulls in small boats in Atlantic Canada?

By the way, the 'tacking amas' was bit of an offbeat question, but what do think theoretically?

Ply is about 50% denser than cedar so for similar weight you might use 2/3 thickness, say 4 mm ply instead of 6 mm (1/4") cedar. Ply strips or planks must be very narrow to bend, you would need much more than 10, or planks must be cut accurately to the development. If you use a great many narrow strips with battens you will end up with a stripper with a ply skin, it’s not worth it, and it would be very difficult to build. Not sure about using spruce. Makes more sense to me to reduce number of planks. A bought design for stitching-and-gluing should have plank developments or you could download FreeShip which will provide plank developments.

I didn’t pick up on the tacking amas first time I read you post: it should do the same thing as an idea of mine-
http://www.boatdesign.net/forums/sailboats/articulated-sailboat-24598.html
-which would use Bruce foils instead of amas; for my design I plan to mount the outriggers and mast on a turntable; using a lateen sail theoretically results in the sail automatically taking the wind on the other surface when the turntable is rotated. It leaves the hull unrotated of course, but as the sail/mast/amas move along the new heading it should fall into line with the aid of a fixed skeg.

[ShagRock]

Well AK, that poses some some interesting issues. One would seem to be a force choice into either strip-plank with wood, or stitch and glue plywood. That's a decision I'll have to make. However, in some situations one could use a combination of both. I say this because some Pacific islanders actually employ both , even today, i.e. hollowing out a log to get the below waterline round raked hull and continuing with mortised ribs and plywood for the upper sections. If your planks are same width as 4mm plywood, then both can be used; especially if the thing is going to be painted.

Take your idea of a 'turntable' for masts and amas. I've never seen such a thing but it sounds innovative. Is this your own creative design? Are you going to build without an engineer's plan? Just curious;) Also, have you ever seen amas made out of a discarded foam-sandwiched surf board and would such a thing work?

Maybe I should be specific re the 'close to' rounded hull on a sailing canoe. If a beam measure at waterline was say 24" at midship and the depth of displacement below the water line was say 6" at the keel line, what number of plywood strakes would be "reasonable" to achieve said 'close to' round bottom, without pushing the plywood into 'fracture mode'?

Newfie

[ancient kayaker]

Certainly cedar-strip and stitch-and-glue with plywood are the most popular construction methods today, but you still have plywood plus chine logs. Hybrid construction is also a possibility which can give the boat rounded below underwater shape with the simplicity of ply from the waterline up; the interface between strip and ply may be a challenge. Do you need/want the rounded underwater shape that much? There is not a great deal of difference in performance as Rick noted in post #14, and I suspect it is more of an issue with monohull design where the stability has to come from beam and hull shape rather than the amas. Rick say his boat is a "pure speed machine" and it looks it, but his first picture showed a flat bottomed hull, very easy to build and you might not notice much difference in performance.

The 'turntable' for masts and foils is my own design, of course there's little new under the Sun so someone may have already tried it, but if so I haven't found any information on the attempt. Being an engineer, although long retired, I am incapable of building without a plan but it has to be tailored to fit the kayak so I will build it more or less around the boat. There's a bit of science in the thing but I try to get out of old habits these days.

I haven’t seen amas using bits from foam-sandwiched surf boards but I imagine it would work rather well. The hard part would be the joint with the outrigger.

It’s not the beam and draft that determine the number of bottom planks required so much as how ‘round’ you want it to be. Using cedar strips allows you to round off the corners between the strips to achieve a round hull. You can’t do that with ply or you may remove the outer veneer which is responsible for much of its strength. If the amount of thickness you are prepared to remove is T from a strip of width W on a hull of radius R then:

W = sqrt (8RT)

For a half-round hull bottom 24" beam, using 1/4" thick cedar strips and restricting thickness loss to 0.05" allows you to use 2" wide strips, but with 4 mm ply you should not take off more than 0.01" or 20% of veneer thickness so plank width is limited to 1", requiring 38 planks. Handling 38 ply planks 4 mm thick and 1" wide is going to be far more difficult than 19 cedar strips 1/4 x 2".

If cedar is costly, I know of no reason why a cheaper wood cannot be substituted provided it is reasonably light and straight-grained, fairly knot free or with small tight knots, glues well and is easy to work. The major cost in cedar strip construction is the milling of the strip edges, if you can do that yourself cost is reduced by an order of magnitude. That being said, I still think a simple rectangular-section hull will be adequate and easier, faster and cheaper to build, especially if the amas are made using the same construction method.

[ShagRock]

AK - I suspected you were an engineer and it shows in your well reasoned response - just excellent! Thanks so much for the math based analysis regarding wood, plywood and relation to build shape. AK wrote Hybrid construction is also a possibility which can give the boat rounded below underwater shape with the simplicity of ply from the waterline up; the interface between strip and ply may be a challenge.. Yes, and the key is simply faring the wood strip to match the plywood thickness.

AK wroteRick say his boat is a "pure speed machine" and it looks it, but his first picture showed a flat bottomed hull, very easy to build and you might not notice much difference in performance.
Perhaps Rick might comment on the capacity of his craft to sail. The Boracay paraw has quite the knife edge, deep V shape with a ratio of L:W of 20:1, but it will flop over without amas to support it - different type of race machine. But you do make an excellent point with respect to 'just how rounded' the lower hull needs to be. The amas allow one to have a more rounded hull, aka Hawaiian, Polynesian, and Micronesian sailing canoes. The other factor is depth, which can be referenced by drawing a circle and moving a ruler from the horizontal diameter downward and observing what happens to the shape at the bottom.

AK wroteYou can’t do that with ply or you may remove the outer veneer which is responsible for much of its strength.. Key point made!

AK wroteFor a half-round hull bottom 24" beam, using 1/4" thick cedar strips and restricting thickness loss to 0.05" allows you to use 2" wide strips, but with 4 mm ply you should not take off more than 0.01" or 20% of veneer thickness so plank width is limited to 1", requiring 38 planks. Handling 38 ply planks 4 mm thick and 1" wide is going to be far more difficult than 19 cedar strips 1/4 x 2". Stated like only an engineer can, and most helpful. This certainly opens up the third option you refer to as 'hybrid construction'!

I'll re-check the cedar option at a specialty cedar store as opposed to big box store, but I could use spruce anyway. The cedar could look good matched with South America mahogany plywood. I could also use the ply for decking. I'm hoping to have a 'track saw' by the time I start this project which should make stripping my own planks easier. I don't know if you or others have used one for boat building purposes?

The winds of indecision are starting to abate!
Newfie

[ancient kayaker]

I must admit I hadn't heard of a track saw. I'll pass on some tips that might help.

My method for cutting up a large sheet of thin ply is to use a 3-1/2" circular saw (the "precision saw" from Canadian Tire in my case). I lay the ply on a cutting table that is topped with a sheet of 1" insulating foam to protect the blade and the table.

I use a regular 7-1/4" circular saw for stripping planks, also on top of the cutting table, with a thin kerf finish quality blade (cost as much as the saw!) and a home made guide which extends at least a foot either end of the saw foot plate to ensure the start and end of the cut remain straight. I fit a ply plate under the foot plate of the saw and drop the blade through it while running to get a zero clearance slot.

I prefer a hand saw to a table saw for cutting long planks as the workshop has to be more than twice as long as the plank with a table saw, something I cannot always guarantee. A hand saw is not quite as accurate but I can easily keep thickness variations below 1/64" which is adequate for most purposes.

Good luck! Don't forget to post the pictures.

[ancient kayaker]

Newfie: I can't get those elegant boats of Rick's out of my mind! A hard chine "square" hull is much easier to build than a half-round bottomed hull. Here is my take on the construction of a compromise hull with quarter-round chines. It would be really easy to build, pretty and maybe just a hair faster than a square hull due to reduced turbulence.

Basically it just consists of cutting square and rectangular section strips off a plank of clean wood of a split resistant kind such as straight-grained poplar and gluing them to ply planks in the order shown in the figure. The chine would be of constant radius, and each stem foot would turn out with a rather nice elliptical profile and a sharp entry.