JEM Watercraft

In another thread, the comment was made:

Earvin wrote:Gday Matt,

I have yet to build my first boat but this one is on my shopping list now If you ever get to design a full blown expedition sea kayak that will be on my list too

So let's kick that idea around. What the parameters for a sea kayak?

As a start. \ At least 16'

Low back deck

A rounded front deck to allow water to slide off when breaking over the bow.

Front cockpit depth [enough to fit a size 12 foot[ [just for comfort]

Front cockpit bulkhead positioned so with addition of a layer [or two] of mincel type foam, it can be used as a foot brace.

Foot operated rudder system

Position the front hatch at least 20 or more inches foward of the cockpit . This will allow a compass installation for those who would use magnets to secure the hatch. [I think 20" is the recommended distance. not sure]

Cockpit size make to enable use of standard size skirts.

You may want to consider a sail base. for one of those V type two pole sails.

Bald Cypress wrote:
Front cockpit depth [enough to fit a size 12 foot[ [just for comfort]

I see this question come up a lot in other kayak build forums and I've done my own research on.

But let me ask this: do you mean to say the front of the cockpit should be about 13" high? That would be measuring in the hull interior from the bottom of the hull to the underside of the deck right at the front of the cockpit opening.

What kind of shape? Like an Arctic Hawk or more like a QCC kayak? Rounded bottom? Hard chine?

Hi Matt

I am no expert in design and have little experience in sea kayaks but have done a lot of research into them recently. So having said that the things I would look for would be:

-decent size hatches to stow gear and room to carry at least enough supplies for a week.
-A day hatch would be convenient.
-there is some debate as to whether a retractable skeg, rudder or even none at all is preferable.
-Good decklines to store gear on top of the deck and grab onto if you go for an unplanned swim
-cockpit to have good knee/thigh bracing and not too big so you feel a part of the kayak rather than floating around inside it
-sail capability
-a foot pump would be handy
-width between 55 and 62cm
-length 5metres to 5.8metres
-reasonable towing points
-able to handle reasonably rough conditions
-quick!

Well there is some of my thoughts. Hope they are helpful Matt. Good luck.

jem wrote: But let me ask this: do you mean to say the front of the cockpit should be about 13" high? That would be measuring in the hull interior from the bottom of the hull to the underside of the deck right at the front of the cockpit opening.

On one of my "other" built boats, a 16 footer, listed as a "touring" kayak, hard chined, that accommodates a size 13 shoe. The dimension from bottom side of the deck to the hull at the front of the cockpit opening measures 12.75", dimension at the "deck beam" just beyond the front of the cockpit opening, 11.75".

Myself being only 5'7" tall, I would look for a overall length close to 17' (not much longer). Width 22-24".

Hard chined hull or multi chined hull? Dont know, my understanding is hard chined gives you more space (for packing) and stability, while multi give you speed but less space and a little less stability.

Agree with Bald Cypress about the cockpit coaming that would take a "standard" spray skirt, rounded front deck for shedding water.

Rudders, skegs, hatch size & location, sail mounts, compass mounts, day hatches, pumps, bulkhead locations, etc.... all seem to be builder options to me.

DM

Matt,

Are you thinking of a dedicated expedition sea kayak here or a more typically general purpose sea kayak?

You allready have the concept of a very fine GP sea kayak and I think it is well worth persuing to fruition. Most kayak paddlers I know are more interested in a boat capable in most waters and comfortable for up to 2 or 3 nights. Your concept boat would work very well in this regard.

Length - I think a "series" of boats would be the ideal. ie something around 15' for the smaller paddlers with proportionally bigger models of the same boat for the bigger guys or those who would like to take more gear.

Varying cock-pit options are also a very good idea. The Keyhole cockpit is becoming very popular here, for some very good reasons.

Rounded deck - something like your Okwata? I would rather see a simple peaked foredeck with a flatish rear deck. (ease of build and very functional)

I would rather see a hull with water-line length mazimised and more verticle shear stems as opposed to the long overpointed bows so common now. In my opinion, this achieves nothing in a paddle craft other than create the illusion of a fast boat.

Deck heights, again - perhaps a variety of themes for the same boat? High Volume & Low Volume.

I think your concept boat lends herself very very well to all of the above. As drawn, she would suit me, in my waters to a "T"

Likewise, Your magnificent Southwind, scaled down to around 16' X 24" with a standard cockpit would also suit. Not a 'traditional" sea kayak by any means but any who paddle such a boat would be surprised by just how capable it is.

Well I did have the concept one we discussed via "back-channel" in mind but I wanted to get other input.

Varying sizes and options take a long time to develop. With this thread I'm seeing if there's any commonality of sizes and options to start with first.

Rounded deck: I'll do a multi panel deck, but I won't do a rounded one. They are a pain to draw and build and limit what you can do. Plus if I do a rounded deck via plans, I'll have to send a large pattern sheet and that gets expensive.

When ever I ship the large patterns (8' x 36") over-seas, they end up getting lost 25% of the time and I have to send another copy. That eats up profit margin. I'm having this issue trying to get a set of Sabalo patterns over to Oz. I just sent the second set at no cost to the builder. Cost of plans reprint plus $28 in shipping.

I'll probably redraw the Sabalo and do away with the pattern option. I'll end up replacing the Okwata deck as well. Costs too much and hinders good service. I've never been satisfied with the Okwata. Just doesn't look right to me.

Matt,

Your Okwata with a peaked deck or multi panel deck would be very similar in size and profile to a Contour sea kayak made by Perception in New Zealand. I think a very similar boat is marketed under the name Carolina by Perception in the US and Europe.

These are one of the most popular and versatile smaller sea kayaks in Australia.

I think Okwata will yet prove a winner, particularly so, if you re-draw the decks so as to be not so intimidating. easier for the builder and cheaper for you to post - win win

I am told, somewhere between 16 and 17 feet is about the ideal length for a solo kayak re effort to propell verses resistance through the water. I would suggest compromise here, ie as long as you can get with just one panel splice per panel.

I would also suggest a minimum of 3 panels per side for the hull, that is one bottom panel and two side panels. Again this is a compromise. Two panels per side boats can look a bit slab sided to me and of necessity, create a very hard chined boat.

I think your concept, back channel boat, as she is drawn right now would appeal to many. Particularly the intermediate and recreational paddlers who like to venture into rougher waters sometimes.

Have a look at the huge variance of styles of sea kayaks around. I don't think there is one boat that will suit every or even most tastes.

This is where your boats differ to all other designers I have come across. You actually listen to what your builders want and then try to create something that will work for them.

Mate, you know that I have a couple of boats that I just have to build first but I believe in your back channel kayak. Such a boat will be a winner with recreational, open water paddlers here. I would encourage you to run with this design first - see what sort of feedback you get and modify or improve it if it needs it. I don't think it will need much refining, if at all.

I am so convinced of the merrit of this particular boat, -pretty much, as is, that I am very happy to run with it as a custom order. I have mentioned this before and the offer still stands mate. any time you feel so inclined, just say the word and the check will be in the mail.

Just to get all that are interested up to speed, below are some concept images of the kayak that's been discuss "offline".





The one shown here is only 14'6. I'd want to stretch that out.

There's a bunch of fine-tuning that needs to be done. I might sweep the bow up just a tad bit more to help punch over waves.

I also need to adjust how the panels interact. I looked at the contour lines (imagine if you sliced the hull in 1" layers and then looked at the outline of the layer from a top view... those are contour lines) and they showed where there would be some drag to slow the hull down. So I want to fix that up.

Now the big debate: Length. If I go with something that has only one splice per panel, longest I can get it would be around 15'6. Well short of the desired 16'6 - 17' range. But what Mick said about waterline rings true: Waterline and hull shape dictate speed. Not overall length.

Also: The goal is a hull that can be built from plans only. So we can't get too complex. The hull shown above is a intermediate to advanced design. I could kick around the idea of simplifying it a bit.

Thoughts?