Glen-L Poweryak- efficient design- need bigger

Im Sure you guys are familiar with the Glen-l designs at boatdesigns.com
I have been thinking (poweryak) is the ideal design for me and my dog, but would like to scale it up about 33% and build it out of steel for economy. I dont want it to plane out, and I would rather power it with a 3-5 hp outboard on the stern, rather than the electric propulsion it has in the plans.
Would any of you guys be interested in doing a cad rendition of this to be plasma cut locally? Im thinking about a trip from kansas city to new orleans to visit friends, then back, so cruise efficiency is very important. I have built
two metal boats so far, and this is what my "ideal boat" has evolved into.
the thumbnail below is a few renderings that would possibly make for an enclosed cabin and reclining seat that converts into a lounging position for naps in coves.
I understand the nice thing to do is to actually buy a set of plans from Glen-l but how would I go about enlarging them? I have bought their plans for 'Tubby Tug'
and i plan to make that out of steel with an air cooled inboard, but lack the expertise to extract offsets to enlarge for the 'Mega Yak'- advice?

 

Scaling up all of the measurements by .33 will increase the displacement by 2.35 (I think). Any case, if you adjust the offsets it might be best to convert to centimeters first, and then times 1.33.
You might consider only respacing the station molds and leaving the other offsets alone. Your speed will be better and stability will be increased by 33%.
Other changes such as half-breadths and waterlines would require a complete redesign even if the material didn't change.
Building in steel might work better if all measurements (length, depth, beam) are increased, but that would reqiuire a complete in-depth analysis.
The increase of length alone is the simplest of all enlargements in terms of both design and building, so unless you're sold on steel, think about just using wood as specified.

Alan

 

Alan-
Thanks very much for the thoughts, I am very much sold on Steel being my material of choice, The price of 5052-h32 aluminum here in KCMO has doubled this last year, 4x10x .125= $188.00, steel (14ga.) is $67.00, and steel is a bit easier to weld considering my semi open workshop. (not using fluxcore) Also, I am a metal worker, NOT a woodworker (trust me)
How will stability be increased if the design is lengthened and not wider?
well, actually I really need more width, a 24" cockpit width is just not workable, on that note, even at 36" seems tight, and thats 50% wider- not 33%! Well, thats why I really NEED some help with a redesign. I would like to let my dog pass to the side of me, not have to pass over my shoulders...
I really want a MEGAYAK, Indestructible and beachable.

 

The Tubby Tug-

Well everyone knows and loves it- I want more weather protection, heres what I came up with.... dont hate me because Im beautiful!
The lower right model has a chopped top and an inside headroom of 38", just enough to not bump my head when sitting on a four inch mattress.
I am thinking I would stay with an outboard, already have one.....

 

What is the relative weight difference per square foot of hull material/framing, and how does the increased length/depth/beam carry that additional weight? The goal is for the waterline to remain at the same height.
If the design specifications include such figures as immersed volume and wetted surface, you're in luck, because you can analyze what woukd happen if you increased each value.
Ther first thing to do is to get the weight of steel per square ft at 14 ga., then the weight of plywood per the same area, etc. etc..
I figured displacement increase if all offsets were increased at approx 2.35 times original displacement (1.3 3x 1.33 x 1.33 = 2.35). If steel would increase displacement by a similar value, your 1.33 multiplyer will be right on target. That only gets you a 32 inch width. To go wider, you'd have to make changes in the multipliers. For example, you could maintain or increase length or depth and increase width, just so long as the three multipliers yield the same overall displacement increase.
So first see what would happen if the original unaltered boat were made of steel--- let's say it comes out to 2.1 times heavier. Now you can adjust beam increase and see how the other two dimensions need to (or can/should) be adjusted.
You would want to multiply all three and achieve that (e.g.) 2.1 times original displacement.

 

ok, Alan, you were on it with your 2.35 x's original displacement, but that is only with changing to steel, not with a size change., that would be 16 ga. steel, witch is still uber strong. So the original kayak weighed in at:
Length overall 16'-10"
Beam 37"
Hull Draft at 500 lbs 3 1/2"
Midship hull depth 14"
Hull weight (approx.) 110 lbs.
Cockpit size (approx.) 2' x 7'-6"
Average passengers 1 or 2
Hull type: Hard chine vee bottom hull developed for 1/4" sheet plywood planking assembled by the Stitch and Glue method.


I will also be deleting the weight of the batteries, so that could possibly make up for the difference in materials.

 

The 2.35 multiplier was what happened when you increased all of the dimensions by 1.33. The reason is that volume always increases faster than surface area.
If using the original (wood) materials, even increasing the thickness of the ply by 1.33 will not sink the boat into her new lines. That means that if the batteries exactly equal the additional steel weight, you will float high and will need to add ballast.
A lot of calculations have to be done. First, let's say you increase all dimensions--- you'll have a boat that must have 2.35 times the weight of the opriginal to sit in her waterlines.
Second, what WOULD exchanging wood for steel do to the original all-up weight, once an outboard was added and the batteries dispensed with?
Let's say the exchange WAS a wash.
Third, increase all dimensions by a factor of 1.33. The bigger boat will need to displace 2.35 the original displacement (the original displacement times 1.33 cubed), while the wetted surface will increase by only 1.77 (1.33 squared).
In other words, you might want to only increase length and beam dimensions and not height dimensions. Whatever you do, bear in mind that the worst thing you could do is to have to add sandbags just to get the boat to sit in her waterlines.

 

Length and slenderness equate to fuel economy. The tug would be a slug by comparison with the Glen-l. Do you have ambition to cover distance economically at reasonable speed? The tug will bog down around 4kts.

The scaled up Glen-l would likely do 6 or 7kts with less power than the tug.

Rick W

 

There is some free software called Delftship that enables you to do plate developments. It might be worth your while to learn how to use it. I can help you with the design and give you a starter hull optimised for your constraints.

I would not be prepared to do the complete design as you need to own any errors but I can point you in the right direction.

I once had a steel dinghy built and it was awful. Just too heavy to be useful but it was indestructible.

Rick W

 

Learning Delftship

newinertia,
I have written some beginner level lessons for Delftship that I email without cost, they assume you don't know anything about D'Ship and teach key stroke at a time.

Not very sophisticated, they're not very well written but I know for a fact many others have learned to move around in D'Ship a bit faster using these lessons than if they just hacked on their own.

I have shown them to Martijn von Engeland, Delftship's author/developer and he's approved them for use; in fact he edited the first lesson to his standard visual presentation.

No cost, just email mail me and I'll attach some returns. They are made by giving a text narrative with screen dumps inserted in the text to illustrate the steps. The step by step/keystroke for keystroke method may be too slow for experienced CAD users but these lessons could help you take advantage of Rick's extremely generous offer to nudge your progress back between the lines as you work.

iisco@acsalaska.net

cheers,
kmorin

 

A Christmas present. I have played around for a few minutes. I think it is smaller than you want but easy to scale by different factors in each axis.

Rick W

 

Thanks, Rick- you are right, I should look at this as an opportunity to learn, not to take the easy road- Delfship is on my list now- just got back from grandmas for x-mas and got to do things, but I really wish all you guys a Salty Christmas and a happy Festivus for the restofus!