Boat Hull Design Question

If you design your boat with the shapes of a shoe box, you will get close to 100% use of the plates. but I'm sure you wouldn't want a boat like that.
You can increase the use of aluminum plates if you do not put lightening in the floors and longitudinal girders, but that would increase the weight a lot and you would be transporting useless material all your life and spending more fuel to transport it.
If you place sheets of the same thickness on the bottom, side and decks, you will be able to get a better use of the aluminum sheets but you will be, as before, transporting much more weight of material than necessary.
You should not design a boat based on the use of the plates. It's crazy.

 

@TANSL really hits the nail on the head here.

I am wondering why you would not build in marine foam. You won't gain much for weight reduction in a smaller craft, but the boat won't be heavy and it won't have yield problems and it won't be eaten by termites right?

As for material efficiency, I rip all my scraps bigger than one inch to the nearest inch and make them into internals on the vac table. My waste on a 10m powercat build has been about three trash bins of offcuts under an inch. And could have been less if I reripped down to 1/2". I use a raptor plastic stapler to keep the panels together before they are glassed.

Foam will be slower, but not by much. And you have to protect the wood station jigs from the termites. The transom foam would be say coosa bw.

Not sure on the availability of marine foams, glass, and your choice of resin there.

The speed and hp range of the vessels you are looking at work great in foam because foam gets very complicated when you go to really fast and high powered vessels.

Foam would also never corrode in seawater like aluminum.

 

Construction method with prefabricated sandwich panels https://www.boatdesign.net/threads/construction-method-with-prefabricated-sandwich-panels.64651/#post-891098

 

I live in Thailand on a waterway that is 2 km from the gulf of Thailand. My SOP is quite simple. A boat that can get me, my wife, and our two small children safely across the gulf of Thailand. Samut Sakhon to Pattaya a distance of 60 miles. People regularly make this trip on jet skis in about 2 or 3 hours.

What do I have going for me? I have access to cheap Thai labor. Thai's are great at hand plaster jobs and they are also good at autobody repair (from a visual perspective only - they love the thick bondo a bit too much) I could easily afford two auto body men to sand and finish a plug and mold.

I am open to foam core construction. The problem is there seems to be a lack of plans for this process. Most plans are for stitch @ glue boats or AL plate. Who has stock plans for a Panga like boat made with foam core? Most designers in foam core tend to be sail boats and catamarans.

Richard Woods has some nice plans, the smaller Skoota looks great, but I am again dealing with wood and there is just a lack of quality wood here in Thailand.

I even went down the rabbit hole of super long displacement boats, and am still open to that. Mooring is just not a problem as I am on the waterway.

 

These folk have plans available for an aluminium 22' power catamaran - they mention a minimum total power of 90 hp, so you could use 2 x 50 hp 2 stroke O/B motors?
Wildcat E-X-T Sport-boatdesign https://www.boatdesigns.com/Wildcat-E-X-T-Sport/products/30/

Here is another 22' power cat design - under 'Options' they note that "The standard material is our plywood cored epoxy sandwich. Foam sandwich specifications are available as an alternative."
https://boatbuildercentral.com/StudyPlans/CT22_STUDY.pdf?prod=CT22

While this cat is more like a pontoon boat. It can be used with a single engine, but the plans seem to only be for ply / epoxy. Lots of good general reference info here though.
https://www.boatbuildercentral.com/StudyPlans/PC22_STUDY.pdf

Re the above, what are the typical wind / sea conditions in the Gulf? If folk regularly cross the Gulf on jet-skis, I am thinking that it must be pretty calm most of the time?

 

Many years ago I lived on Guam and purchased a nice fiberglass 14 foot center console boat. Fine boat but that thing would pound you to death with very little chop. Better handling in rough water is a huge plus. I want to take the boat to the various off shore islands that Thailand has and the weather can be unpredictable. I think going a Catamaran direction might be a very good idea.

 

It would be easier to visualise if you show the three boats in plan view together.
For some reason the one in the middle looks the best for me.
You could try using the 'contour' command in Rhino to make stations, buttocks and waterlines.

 

I have asked if Mertens has foam plans. Almost any hull built in plywood can be built with foam. Sometimes the panel laminations must be done on a table in part or all first. It may not be as fast as aluminum to build, but you can build really good boats in foam and they are ftmp not sinkable done right.

 

Restricting yourself to a single 50hp engine is very limiting for an offshore vessel, if you go to 2 x 50 you could consider something like this Stormcat 17, the design seems OK (there are some pics around of actual boats, and they look up to the job to my eye). It would be no speed machine, but propped right the 2x50 would be OK, you get the benefit of a better riding boat, than a low/medium deadrise mono, something that is "gold" when you are taking women and children out on bumpy water. Plans and patterns seem ridiculously cheap, so you can't go too far wrong on that score. Plans for either ply or alloy.
BoatPlans.com

 

The OP appears to envisage some fairly long hops over open water, and I see he intends to have wife and children aboard, then I would consider those low-deadrise monos would be unsuitable. You can put up with a slamming boat over short distances, but over a long run everyone, especially mum and the kids, will rebel.

 

a fair comment for sure, what is the dr in a tolman or panga

 

dr ? Most makers of plate alloy trailer boats have settled on 17 degrees transom deadrise as being about the minimum to avoid complaints of a bone-jarring ride, lighter boats with less deadrise will reliably deliver a punishing ride into a chop. The 17 degrees works well enough because the plate boats are not that light, when you reduce weight and deadrise, there is a compounding effect, that is more or less unavoidable, that tends to less comfortable riding. A light boat needs modest deadrise to not be tender at rest. Deeper forefoots don't really help much, they just create problems with broaching. The cat of course its a different animal altogether, with its own set of pros and cons. But on balance, if you can afford twin motors, the better boat.

 

The panga is 13 iirc. Not sure on the Tolman. But both are certainly sea capable.

 

Sea capable, sea-kindly less so. Women on boats rarely tolerate discomfort. You probably need 20 degrees amidships to get a reasonable ride, and you won't get there with 50hp.