small shanty cat hull tips

hi everyone,

I want to build a small shanty boat for weekends but also longer river trips. Needs to be trailerable, so dimensions will be around 5mt long x 2mt wide ( 16"x7" ). Length is limited by my current trailer, but also a reasonable compromise to keep overall weight down.

I actually have already built kind of a prototype out of some hobie 16 hulls, which works great but is a little low on bouyancy (I am planning quite a light build, but have to add water, small kitchen, supplies, a more comfy bedding, and people... weight adds up). So I need to build or supply some hulls that will works, and I can use some help
* sailing cat hulls of this length are a little low on bouyancy, I could go with my current hulls but I am afraid they will run almost completely submerged, so not great;
* aluminium pontoon boat hulls are probably too expensive (I want to keep the budget as low as possible) and usually longer than I like - at least for used options;
* a custom plywood build has the advantage of total costomization, but a lot more work - also I'm undecided on which shape - is it better a square box or a rounded bottom? I mostly care for ease of assembly and final resilience.

any suggestions? I'm reading many tutorials and build logs, but nothing quite like what I have in mind.
thanks!

 

Welcome to the forum @aleph. It seems that a plywood hull could have advantages for you. Have you considered multi-chines hulls?

 

thanks!
you mean use multiple flat elements to approximate a rounded bottom? I have considered that, but maybe a simple U shape is kinda easy to make by bending thin plywood over U shaped bulkheads, or something like that... but maybe I am overestimating the flexybility of plywood.

 

I vote for square box with maybe a little rocker in the bottom.

 

Indeed, that's what I'm referring to.
You could also combine plywood for flat areas, or areas with little longitudinal curvature, and strip planking or veneers for areas with U-shaped sections.

 

so something like C right? Do you think the sides work better straight or slightly angled?

I thought that B whould also be easy to make with a thin plywood and good bending tecnique, am I wrong?

do you know if I can find plans for a shape like this? I found a bunch of plans for more complex shapes, but nothing for something as simple XD I would prefer to copy a tested design, expecially for the front and tail edges... maybe I can find some canoe plans...

 

Of course, I would completely rule out version "A."
I don't think there's much difference between versions "B" and "C" in terms of hydrodynamics or drag. However, it would require a sharp bow that cuts through the water well and doesn't produce large bow waves.
I think that, at this stage of the project, talking about rocker or similar issues doesn't make much sense.
Rather than using very thin plywood and requiring several layers, I would go for cold molding or strip planking. But that's your choice, depending on your preferences, tools, and skill level.

 

Your easiest, cheapest quick build or buy option would be a jonboat hull.
Catamaran build will be almost twice as expensive, and twice the work, and then the intricate problem of deck structure must be addressed.
Hobie cat and similar designs truly suck at weight carrying, will barely float a couple of people at rest, so don’t waste your time and money on that option.
Try to put together a weight estimate of everything that will be on the boat, including persons, hull weight, cabin and contents, motor and fuel, including everything and everything.
This will be a tremendous help in determining the suitability of a hull type.

 

We should wait to know what @aleph has in mind before telling him that his idea, which we don't know, is wrong.

 

Would a boat like the Ceecan 19 be too big for you?
It is a monohull, not a cat, with a beam of 6'10".
Ceecan 19 Plans https://duckworks.com/ceecan-19-plans/

Here is a shanty boat that is 16' x 6' -
Shanteuse Plans PDF https://duckworks.com/shanteuse-plans/

Shanteuse is a bigger version of Harmonica, which is 13' x 5' -
Harmonica Plans PDF https://duckworks.com/harmonica-plans/

Would the 20' Millie Hill designed by Sam Devlin be too big for you?
Millie Hill 20 Plans https://devlinboat.com/product/millie-hill-20-plans/

It is not a lot more effort to build something is boat shaped, rather than a rectangular box - and Sam's 17' Dipper would meet your requirements, as well being a lot more 'seaworthy' than a box (useful even on a river if it gets choppy in a strong breeze).
Dipper 17 https://devlinboat.com/dipper-17/

A 20' Water Lodge from Glen-L is probably a bit too big for you -
Waterlodge & Waterlodge Too https://www.glen-l.com/Water-Lodge/products/771/

A 16' Huck Finn catamaran might be suitable for what you have in mind?
Huck Finn https://www.glen-l.com/12-28-Huck-Finn-trailerable-pontoons/products/169/

Or an 18' garvey type house boat from Clark Craft?
Clark Craft - Boat Plans, Boat Supplies & Marine Epoxy https://www.clarkcraft.com/cgi-local/shop_responsive.pl?type=item&categ=010&item=943220565&cart_id=9c583f8221f652e9c33d0a9d2fadb14b

Or this little house boat from Selway Fisher - 16' x 6'5" -
Motor Boats up to 16' https://www.selway-fisher.com/Mcup16.htm

 

Texas Sled 18’. Check them out.

 

I thought of that, but I don't need to carry that much weight, so a cat/pontoon hull is probably better.

My estimate is around 500kg between hull, cabin, equipment, with a max of 1000kg fully loaded with more passengers, water tanks and supplies.
With a couple hulls 40cm wide and 500cm long I can carry a load of 500kg with a 12.5cm draft, 1000kg with 25cm draft.
Once I decide a layout, construction method and materials I'll make a more accurate estimate of hull weight (but I'll have to keep plenty of margin anyway for extra passengers and equipment).

Also, another couple advantages of cat layout I like:
* hulls can be split into multiple compartments and/or partially filled with closed cell foam to get some bouyancy reserve, in case of a hull breach or other incident;
* I can have an higher deck, and thus a dryier boat ( I intend to cross mostly protected waters, river and lagoon, but there is always the occasional wave from a speeding motorboat passing by to take in account... )

Btw another couple of thinks I would like for this project:
* I won't build solid walls, but only a wooden frame with clear sheet for rain protection and dark shades for nighttime; I like to be able to open all up and have a really open air experience and also it is cheap and lightweight
* I want to build a solar panel roof - solar panels are very cheap, weatherproof, and with an electric motor I can get unlimited cruise range in good weather. My hobie prototype can cruise at 6km on solar alone with a cheap trolling motor .

thanks for all the suggestions! the huck finn is very close to what I have in mind, I'll look into that!

 

btw this is my prototype

which I realize looks like a refugee camp on floats XD but works ok to test the concept

 

Some of your conepts are similar to my 33' motor-cat project.

 

another couple doubts:

1. the hull bottom should be reinforced for a trailerable boat (compared to a standard boat) since on the trailer the pressure (weight) is concentrated on a smaller surface (rollers) compared to when floating on water, or any hull thats good on water is usually sturdy enough for trailer loading?

2. when I join the hulls and assemble the deck, I could integrate the crossbeams and deck framing with the hulls (ie build everything as a single piece, with crossbeams that penetrate the hull skin and are joined within the hull frame), OR I can assemble the hulls as separate units and then join them with crossbeams placed on top of the hulls. The last approach allows easier maintenance/disassembly if I ever need to do that, but the first approach gives a lower weight for the same strength I think (since the beams are at the same time part of the hull frame and of the deck frame).

what do you think?