About landing crafts

Another potential problem with a catamaran landing craft is they will generally have a greater draft than a monohull with a flat or shallow V bottom due to less waterplane area.

 

Yes, that all makes since. I would think the hulls would need to be rather fat as well as high, with the bridge deck as low as possible when loaded with its capacity and still have a fair bit of clearance (what ever that might be). A double folding ramp (making it twice as long) might help as well as ramps to extend the off loading and loading angle. Maybe a ramp like those on the U-Haul moving trucks that would lock down so they didn't bang all the time.

Just thinking it would be more efficient than moving a brick. Another issue for a trailerable boat would be the hulls, say being three feet wide which only gives you two and a half feet in the center (with part of the deck into the hulls could be wider) but how efficient would that be with the hulls so close?

Not much difference between 24 feet and 27 or 30, in length, if that makes a significant difference.

Seems like the flat LCs would put your teeth in your lap in any chop. Flat water might be good. And, more HP would be required to get out of the hole, I'd rather see a displacement hull with lower HP and better fuel efficiency that would allow you to keep your teeth in your mouth.

 

Agree than monohull would be better. If hull still needs to be wider than standard 102 inches, could make side hulls that fold up/down for trailering.

It seems like 26 feet is the cutoff point for varying regulations; check your local regs as well as national regs (e.g. - Coast Guard).

If it's heavy enough, it won't pound too badly at any sane speeds. I'd stick with flat-bottom for inland waters and/or rivers, and save the deadrise for offshore.

 

By displacement I was hoping for better mpg with a smaller power plant. OTH, I'd think anything below 10 K would require you to get up earlier and get going on your trip if you were to arrive before dark. I think making time to meet lock deadlines for example might be a big plus.

I was under the impression that pleasure boats didn't really bump into regulatory issues until they were in the 50/60 foot range.

Saving the deadrise for offshore? I'm not sure I can picture that flat bow in offshore conditions in a boat say, 26' long and even with 4' of leeboard. I know troops got sick in just a few miles on the Higgins boats.....but if it could head out safely, that might be a good option.

Would anyone want to leave the Keys for the Bahamas in a 26/28' LC, flat bottom and draw bridge bow? 20 or 25hp? (actually a smaller OB was hoped for)

And then I wondered too, if it would be possible to have a false bow, a pointy bow that would fit over the flat bow as a temporary bow, anything like a cow catcher on a locomotive to cut the wave?

I think if I ever had such a boat I'd have to name it "Wavewacker"!

 

In a small LC the cargo weight is likely to vastly increase displacement, to minimise changes in draft a high CB is useful.

The easiest hullform is a monohull with a decent overhang at the front to keep most of the draft off the beach. A flat bottom makes for an easy design and build – if you want a better hull, a wide flat form with some deadrise increasing forward (but still likely fairly low 10-15° or so) coming into a gentle point. The other major thing with a landing craft is that the bow needs to be as wide as what is to be loaded.

Major changes in draft between the loaded and unloaded cases give you more problems in service.

Ideally you only want a single hinged ramp. Double ramps are heavy and harder to extend - if they get too big you need rams or a winch which is more weight (and at the forward extreme).

In all likelihood, as a cat there are just two bricks to move. If you lose the airgap in the wetdeck it’s less of a cat and more of a monohull with an odd hull form (and increased wetted surface area).

Making a trailerable LC makes for a lot of additional problems.

LCs have a lot against them as the greatest of sea boats. If light/empty they can plane alright as they have plenty of lifting surface.

This is pretty much what commercial ferry uses but you'd just be adding weight for little real advantage in a small LC. A little wavebreaker on the bottom of the ram may slightly reduce impact pressures etc. Though if waves are hitting the bow-ramp then the deck is likely going to be awash - which may be causing bigger problems.

All this said it depends on what you are loading and how far you want to take it and in what conditions.

 

Thanks Drew, I hope I'm not stealing the OP's thread but it's on LCs I guess.
I'm sure others are getting good info as well.

I have a utility trailer that has a 5' ramp, angle with expanded steel floor and 4' wide and I don't have a problem with it. I can see if you had a 12' ramp, one guy might have a problem raising and lowering it.

I guess I could throw some thoughts out: A beam of 6' and 26' wl, say 28' overall, plywood stich and glue. 3' for the engine and aft are (not much) 14' cabin and 8' cargo area and the rest forward would be open to the bow. Self bailing cago open deck area and aft, the cabin would be tight with higher thresholds. 6' 6" headroom accomodations for two, 4 rarely (not counting anyone who would dare to ride up front. A canvas top could cover the cargo area as well. 42" leeboard I guess. A winch could be used for the ramp.

Cargo would be less than 800 pounds, a motorcycle, that would fit in a rail, with fixed supports and bolted steady, no rolling or movement of the cargo.
I would think the max capacity would be 2,000 lbs of cargo, provisions and personal gear. Porta pottie, shower, queen berth, small galley, helm and 2 seat dinning/saloon seating. 50 gal fuel, 25 gal water. 2 House batteries.

I'm thinking along the lines of a canal boat with the LC bow and more open deck forward.

Anything like that? Plans? Better ideas or tell me if I'm wasting everyone's time (lol)....a short term liveaboard, nicer than camping but a work boat...

 

My brother-in-law builds small 20 ft - 40 ft landing craft in Kodiak Alaska. They have even built an M-Ship high speed landing craft. You may get some ideas from the site:

http://www.emersonboats.com/home.html

 

Wavewacker,
my boat ( see post #12) is 21' 6" long, it is about 4' 6" wide at the chine, about 7' wide overall, lots of flare. If I remember right the sides are 30" from the chine up to the gunwale. The boat has a shallow vee section in the back that flattens out towards the front (just the opposite of most planing hulls) This keeps the draft shallow at the front and makes the transition into the ramp easier.

In big waves the ramp slams pretty hard. If you slow down the motion is not bad, but it does throw a bit of spray. In smaller waves the boat runs nice because it is riding on the vee section in the back. It is not built for offshore work, but can haul a 2000lb payload with no problem up and down the coast on nice days.

The boat is constructed from 1/2" ply with some regular lumber yard type 2x material for framing in the bottom. It is all held together with epoxy and taped seams. The outside and the sole are sheathed in fiberglass. The sole is one flat surface with no frames or stringers to get in your way, trip over, or catch crud. Having a flat floor in the boat is very nice. The ramp on the front is obviously nice for loading big stuff, but is also great for getting anything in and out. Much nicer than lifting gas cans, etc over the side.

C.O.
http://www.rudstrom.blogspot.com/

 

Drive-on, drive off (double-ended) can be an advantage in some situations.

 

We designed landing craft both mono and cat. With cat it works better as stable and fast platform, especially if one needs to carry a vehicle.

 

Cor, that's an interesting design, where did you get it? And what kind of power do you have?

Alik, where doyou have your designs?

Joe, those are really nice, that M-ship must be the tri-hull, little bigger than I was thinking....But it certainly shows the squared off bow above the conventional V.

Hey Mr. E, yes having a drive through would be nice, just ride through the saloon...lol. A bike jack rolls (the wheels fit in a track) and rotates in its own space/length. Otherwise, to load a large bike you need to roll on backwards with a winch pulling the bike up the ramp and into place.

Those Alaskan LCs looked to be carring some serious outboards, 200+ on one shown in the pic gallery. How could you get 10-15 knots at cruise with less than a 25 hp outboard?

To the OPs question, I would think that an LC could be made with any conventional hull form. The fact that something can be opened up at the bow (or above it) doesn't seem to be as critical as other requirements, weight, displacement, stability and efficiency. But which would be the most efficient with low power hauling less than 2000 pounds?

 

Wavewacker,
I designed the boat myself. It has worked very well for me, the only thing that I would change is to make it a little bit wider, ATVs have gotten bigger since I first built the boat and the ramp is a little narrow for some of the new machines. My boat is powered by a 90 hp Honda outboard. I can cruise around 25 mph with a typical (1000 lb) load. It is probably a little slower with a big load. If you are interested I could dig up more photos of the boat.

If you do not want to design the whole thing from scratch I think that you could use the plans from a regular (non landing craft) hull and modify them with a ramp in the front. Take a look at the Tolman Skiff.
http://www.alaska.net/~tolmanskiffs/
http://www.fishyfish.com/
That is a great hull shape and a simple construcion technique.

Of coarse you should remember that if you are going to spend a pile of money to build a boat it is a good idea to spend a small part of it on getting a profesional to design for you.

C.O.
http://www.rudstrom.blogspot.com/
http://whatsintheshop.blogspot.com/

 

Cor, thanks for the sights, they have some good looking boats. The M-ship is a little bigger than I had in mind, lol.

I would think that a cat that had the deck lowered would work as well, but that would need hydraulic rams or some really heavy duty winches and anchor points.

And, a narrow mono might need amas to stablize the boat (which could make for a cool tri ). I would not want my boat to flip over, but I'd really be unhappy if a wave took me over while loaded with some vehicle!

The great lakes, bays, the ICW and running around in the gulf, not seriously off shore, but out there, would define the harshest waters to be traveled I would think.

Do you all think that Bolger's Tennessee couldbe the boat to use, leaving more room forward (less cabin) and designing an opening above the WL for a ramp? The Tenessee is a sharpie cruising houseboat about 32' long and a 7' beam.

 

I'm sure somewhere in the Atkin catalog of design there is a very good LC.

 

Thanks for the lead, I will google it and see!